JP6278727B2 - Method for producing coprecipitate and method for producing lithium-containing composite oxide - Google Patents

Description

The present invention relates to a method for producing a coprecipitate used for producing a positive electrode active material of a lithium ion secondary battery, and a method for producing a lithium-containing composite oxide using the coprecipitate obtained by this production method.

  A positive electrode active material made of a lithium-containing composite oxide containing lithium and a transition metal is used for the positive electrode of the lithium ion secondary battery. As a method for producing the lithium-containing composite oxide, a method is known in which a lithium compound and a compound containing a transition metal (hereinafter abbreviated as a transition metal-containing compound) are mixed and fired. (For example, Non-Patent Documents 1 and 2).

  The lithium-containing composite oxide includes a plurality of transition metals, and the transition metal-containing compound also includes a plurality of transition metals. As such transition metal-containing compounds containing a plurality of transition metals, coprecipitates obtained by coprecipitation are widely used.

  When the lithium-containing composite oxide is produced by the above-described method, the diameter (hereinafter abbreviated as particle size) and the particle size distribution (hereinafter collectively referred to as powder characteristics) of the lithium-containing composite oxide are the same as those of the coprecipitate. Influenced by powder characteristics.

  In recent years, improvement of battery characteristics of lithium ion secondary batteries has been demanded, and as one of the improvements, control of powder characteristics of lithium-containing composite oxides has attracted attention. Therefore, the importance of the powder control is increasing also in the coprecipitate.

  Conventionally, methods for controlling the powder characteristics of coprecipitates mainly containing hydroxides containing transition metals have been studied (for example, Patent Documents 1 and 2). However, for coprecipitates mainly containing carbonate compounds containing transition metals, methods for controlling powder properties have not been sufficiently studied. Moreover, since the reaction mechanism of a hydroxide and a carbonate compound is different, the method for controlling the powder characteristics of the hydroxide cannot be applied to the production of a carbonate compound.

JP 2008-147068 A JP 2012-256435 A

J. et al. Power Sources 177 (2008) 177 Makio Naito et al. “Powder Technology for Pioneering the Future of Battery” published by Nikkan Kogyo Shimbun 2010

  The present invention has been made in view of the above problems, and is a method for producing a coprecipitate that is used for producing a lithium-containing composite oxide and mainly contains a carbonate compound containing a transition metal. An object of the present invention is to provide a production method capable of controlling the powder characteristics of a product.

  In the production of a coprecipitate, the inventors have obtained the above problem by obtaining a coprecipitate containing a carbonate compound by reacting a transition metal ion and a carbonate ion in a mixed solution containing an ionic surfactant. As a result, the present invention has been completed.

The method for producing a coprecipitate of the present invention (hereinafter referred to as the present production method) is a method for producing a coprecipitate containing two or more transition metals,
Supply water, ionic surfactant, aqueous solution (A) and aqueous solution (B) to the reaction vessel, mix,
In a mixed solution containing an ionic surfactant, the pH of the mixed solution is maintained at a predetermined pH of 7 to 9, and carbonate ions and two or more transition metal ions are reacted.
Aqueous solution (A): An aqueous solution containing metal ions of two or more transition metals selected from the group consisting of Ni, Co and Mn.
Aqueous solution (B): An aqueous solution containing carbonate ions.

  According to this production method, the particle size distribution of the obtained coprecipitate can be narrowed. Therefore, the particle size distribution of the lithium-containing composite oxide obtained by mixing and calcining the coprecipitate and the lithium compound can be narrowed.

It is a schematic flowchart of the process of manufacturing the coprecipitate of this manufacturing method. It is a schematic flowchart of the process of manufacturing a coprecipitate using an initial stage solution in this manufacturing method. It is a schematic flowchart of the process of using an initial solution in this manufacturing method, supplying an ionic surfactant to an initial solution and a liquid mixture, and manufacturing a coprecipitate.

  This production method is a method for producing a coprecipitate containing two or more transition metals.

In this production method, water, an ionic surfactant, an aqueous solution (A) and an aqueous solution (B) are supplied to the reaction vessel and mixed. Thereby, in the liquid mixture containing an ionic surfactant, carbonate ions and two or more kinds of transition metal ions are reacted and coprecipitated to obtain a coprecipitate containing two or more kinds of transition metals.
The aqueous solution (A) is an aqueous solution containing metal ions of two or more transition metals selected from the group consisting of Ni, Co, and Mn. The aqueous solution (B) is an aqueous solution containing carbonate ions.

  In this production method, the co-precipitate is obtained by co-precipitation while maintaining the pH of the mixed solution at a predetermined pH in the range of 7 to 9. Since the mixed solution is carried out in the above pH range, the obtained coprecipitate contains one kind of carbonic acid compound containing two or more kinds of transition metals and two or more kinds of carbonic acid compounds containing one or more kinds of transition metals. It is.

  This production method includes an ionic surfactant in the mixed solution. Therefore, the coprecipitate obtained in this reaction tank can suppress the generation of particles that are extremely larger than the average particle diameter (referred to as coarse particles). Coarse particles are considered to be produced by agglomeration of coprecipitates in the mixed solution. As a result of intensive studies by the inventors, it has been found that aggregation of coprecipitates can be suppressed by making an ionic surfactant present in the mixed solution. As a result, it was found that the production of coarse particles can be suppressed by carrying out this production method.

  In addition, although the action of the ionic surfactant is not clear, as an example of the action, the ionic surfactant partially covers the surface of the coprecipitate in the mixed liquid, and the surface of the coprecipitate is charged. Can be mentioned. When the surface of the coprecipitate is charged, the coprecipitate is repelled in the mixed solution, and aggregation of the coprecipitate is considered to be suppressed.

  In this production method, as shown in FIG. 1, the order of supplying the ionic surfactant, the aqueous solution (A), the aqueous solution (B) and water is not limited. These may be supplied simultaneously to the reaction tank or may be supplied separately. In addition, you may supply components other than above to the reaction tank in the range which does not interfere with coprecipitation reaction.

In this production method, as shown in FIGS. 2 and 3, it is preferable to supply the aqueous solution (A) and the aqueous solution (B) to a reaction vessel containing water and an ionic surfactant. By containing an ionic surfactant in the reaction tank in advance, aggregation of the coprecipitate at the initial stage of the reaction can be efficiently suppressed. As long as the ionic surfactant is contained in the initial solution, the ionic surfactant may not be supplied during the reaction (FIG. 2), or the ionic surfactant may be further supplied during the reaction (FIG. 3).
In this specification, before supplying aqueous solution (A) and aqueous solution (B), the solution previously contained in the reaction tank is called initial solution.

  In this production method, at least the aqueous solution (A) and the aqueous solution (B) are supplied to the reaction vessel and the mixture solution is extracted from the reaction vessel so that the volume of the mixed solution in the reaction vessel becomes substantially constant. Is preferred. Thereby, since aqueous solution (A) and aqueous solution (B) can be continuously supplied to a reaction tank, a coprecipitate can be produced in large quantities irrespective of the volume of a reaction tank.

  When the volume of the liquid mixture in the reaction tank is substantially constant, as shown in FIGS. 1 and 3, an ionic surfactant or the like is supplied to the reaction tank in accordance with the supply of the aqueous solution (A) and the aqueous solution (B). May be. Thereby, it can prevent that the density | concentration of the ionic surfactant in a reaction tank becomes low.

  In this production method, the volume of the liquid mixture in the reaction tank is almost constant means that the volume of the liquid mixture in the reaction tank is maintained within a range of 70 to 130% of the set value. . The fluctuation of the volume means a value after the volume of the mixed liquid in the reaction tank reaches a set value. The variation of the volume of the mixed solution is preferably in the range of 80 to 120%, more preferably in the range of 85 to 115% with respect to the set value. It can be confirmed that the change in the volume of the mixed liquid is within a predetermined range by observing the height of the liquid level of the mixed liquid in the reaction tank and observing the fluctuation in the liquid level with respect to the set value. The change in the volume of the mixed solution in the reaction tank is described above by adjusting the total amount of various solutions added to the reaction tank per unit time and the amount of the solution withdrawn from the reaction tank per unit time. It can be maintained within a predetermined range.

  When the aqueous solution (A) and the aqueous solution (B) are supplied and the reaction proceeds, a coprecipitate is contained in the mixed solution, and the mixed solution becomes a suspension. As a method of extracting the mixed solution from the reaction tank, a method of extracting the suspension (hereinafter referred to as an overflow method) and a method of extracting a solution (hereinafter referred to as a supernatant) through which the suspension is passed through a filter cloth or the like ( Hereinafter referred to as a concentration method).

  In the overflow method, the coprecipitate stays in the reaction tank for a predetermined time, and is then extracted. While the coprecipitate stays in the reaction vessel, the coprecipitate grows and when it is extracted, the particle growth stops. The time during which each coprecipitate stays in the reaction tank is almost constant regardless of the time (reaction time) that has elapsed since the supply of the aqueous solution (A) and the aqueous solution (B).

  On the other hand, in the overflow method, the concentration of the coprecipitate in the mixed liquid (hereinafter referred to as solid content concentration) is low. Therefore, nucleation of coprecipitates and particle growth occur alternately, and particle growth is faster. As a result, the overflow method tends to have a wide particle size distribution.

  In the case of the overflow method, it is preferable that the concentration of the ionic surfactant in the mixed solution is maintained almost constant. That is, even when the initial solution contains an ionic surfactant, the ionic surfactant is supplied in accordance with the supply of the aqueous solution (A) and the aqueous solution (B) as shown in FIGS. Is preferred.

  In the concentration method, only the supernatant liquid is extracted, so that the coprecipitate stays in the reaction tank until the reaction is completed. Therefore, the time for which the coprecipitate stays in the reaction vessel varies depending on the reaction time. That is, the residence time of the coprecipitate generated at the beginning of the reaction is long, and the residence time of the coprecipitate generated at the end of the reaction is short. Therefore, in the concentration method, the particle size of the coprecipitate can be distributed due to the difference in residence time, and the distribution tends to be wider.

  In the concentration method, since the solid content concentration in the mixed solution in the reaction tank is high, the speed at which each coprecipitate grows is slow. For this reason, when coprecipitates staying in the reaction tank for a long time aggregate together, coarse particles are likely to be generated.

  In the case of the concentration method, in order to suppress the generation of coarse particles, it is preferable to suppress the coprecipitation of coprecipitates generated at the initial stage of the reaction due to the action of the ionic surfactant. Therefore, it is preferable that the initial solution contains an ionic surfactant as shown in FIGS.

  When the initial solution contains an ionic surfactant, the concentration of the ionic surfactant contained in the initial solution is preferably 0.01 to 1% with respect to the total mass of the initial solution. If it exists in this range, aggregation of a coprecipitate can be suppressed. As a result, the particle size distribution of the coprecipitate can be narrowed. The concentration of the ionic surfactant in the initial solution is more preferably 0.05 to 0.5%, and particularly preferably 0.1 to 0.25%.

  The initial solution may contain other components described later in addition to the ionic surfactant as long as the effects of the present invention are not hindered. The total concentration of the other components is preferably 0 to 20%, more preferably 0 to 10%, and particularly preferably 0 to 1% with respect to the total mass of the initial solution.

  In this manufacturing method, the temperature of the mixed solution is preferably 20 to 70 ° C, and more preferably 30 to 50 ° C. By carrying out the reaction in this temperature range, a coprecipitate having a desired composition can be efficiently precipitated. When the temperature of the liquid mixture in the reaction vessel is lowered, by-product sodium sulfate or the like may precipitate, and a coprecipitate having a desired composition may not be obtained. By covering the reaction vessel with a heater or the like and heating as necessary, the temperature of the mixed solution in the reaction vessel can be made constant at the above-described temperature.

  In this production method, the pH of the mixed solution is maintained at a predetermined pH in the range of 7 to 9 on the basis of the liquid temperature of 25 ° C. When the pH of the mixed solution is within this range, a coprecipitate having a desired composition can be obtained. Further, by maintaining the pH at a predetermined value, the reaction rate of the reaction (or the rate of particle growth) can be kept constant, and variations in the composition and particle size between coprecipitates can be reduced. In addition, pH of a liquid mixture can be controlled by adjusting the supply amount of aqueous solution (B).

  In this manufacturing method, when supplying aqueous solution (A) and aqueous solution (B), it is preferable to stir the initial solution and liquid mixture in a reaction tank. By stirring, the concentration of transition metal (M) ions and carbonate ions can be made uniform throughout the reaction vessel. Thereby, the reaction proceeds uniformly and the particle size distribution can be narrowed. As a stirring apparatus, a three-one motor etc. are mentioned, for example. Examples of the stirring blade include a stirring blade such as an anchor type, a propeller type, and a paddle type.

  This production method is preferably performed in an inert gas atmosphere. Since the coprecipitate obtained by this production method is easily oxidized, the oxidation of the coprecipitate can be prevented by carrying out in an inert gas atmosphere. Examples of the inert gas include argon gas or nitrogen gas.

  The reaction rate of the coprecipitation reaction can be controlled by controlling the amount (supply rate) of supplying the aqueous solution (A) and the aqueous solution (B) per unit time to the reaction tank. The supply rate is preferably 0.2 to 7.5 g / (min · L) independently. When the supply rate is within this range, most of the metal ions of the transition metal supplied to the reaction vessel can be involved in the reaction, and the production efficiency can be increased.

  The supply rates of the aqueous solution (A) and the aqueous solution (B) may be equal to or different from each other as long as they are within the above range. As described above, the aqueous solution (B) also functions to adjust the pH of the mixed solution in the reaction vessel. Therefore, it is preferable that the supply rate is adjusted independently for each of the aqueous solutions (A) and (B).

  The speed at which the solution is extracted from the reaction vessel is not particularly limited. As described above, it is preferable to adjust according to the speed at which the solution is supplied to the reaction vessel so that the volume of the solution in the reaction vessel is substantially constant.

  Below, the ionic surfactant, aqueous solution (A), and aqueous solution (B) used for this manufacturing method are demonstrated.

(Ionic surfactant)
In this production method, examples of the ionic surfactant include an anionic surfactant, a cationic surfactant, and an amphoteric surfactant. The ionic surfactant includes a monomolecular surfactant and a polymeric surfactant.

  As the ionic surfactant, an anionic surfactant is more preferable because it has an excellent effect of suppressing coprecipitation aggregation. An anionic surfactant having a carboxylic acid group is more preferred because of excellent dispersibility of the coprecipitate and less foaming during the reaction. From the viewpoint of excellent dispersibility of the coprecipitate, a polymeric anionic surfactant is particularly preferred.

  Examples of the cationic surfactant include alkyl pyridinium salts, alkyl imidazole types, and alkyl amino acid types.

Examples of the monomolecular anionic surfactant include the following.
Anionic surfactants having a carboxylic acid group such as citric acid, octanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid, perfluorononanoic acid, N-lauroyl sarcosine, cocoyl glutamic acid, and alkali salts thereof .
1-hexanesulfonic acid, 1-octanesulfonic acid, 1-decanesulfonic acid, 1-dodecanesulfonic acid, perfluorobutanesulfonic acid, linear alkylbenzenesulfonic acid having 4 to 18 carbon atoms, toluenesulfonic acid, cumene Sulfonic acid, octylbenzene sulfonic acid, naphthalene sulfonic acid, naphthalene disulfonic acid, naphthalene trisulfonic acid, butyl naphthalene sulfonic acid and the like and alkali salts thereof.
Lauryl sulfate, myristyl sulfate, polyoxyethylene alkylphenol sulfonic acid having an alkyl group having 4 to 18 carbon atoms, and alkali salts thereof.
Alkyl phosphoric acid having an alkyl group having 4 to 18 carbon atoms, polyoxyethylene alkyl ether phosphoric acid having an alkyl group having 4 to 18 carbon atoms, polyoxyethylene alkylphenyl ether phosphoric acid having an alkyl group having 4 to 18 carbon atoms Etc. and their alkali salts.
Examples of the polymeric anionic surfactant include anionic group-containing polymers. The molecular weight of the polymeric anionic surfactant is preferably 1000 to 20000, and more preferably 2000 to 10,000.
As monomer components used in the anionic group-containing polymer, acrylic acid, methacrylic acid, maleic acid, maleic anhydride, itaconic acid, maleic acid half ester, itaconic acid half ester and other carboxyl group-containing monomers, styrene sulfonic acid, Examples include sulfone group-containing monomers such as allyl sulfonic acid, methallyl sulfonic acid, and 2-acrylamido-2-methylpropane sulfonic acid, phosphoric acid group-containing monomers such as acid phosphooxyethyl (meth) acrylate, and alkali salts thereof. .

  The anionic group-containing polymer is preferably polyacrylic acid or an anionic group-containing copolymer using two or more of the above monomer components. The anionic group-containing copolymer is more preferably a copolymer using two kinds selected from the monomer components described above. As the anionic group-containing polymer, polyacrylic acid or a copolymer made of acrylic acid and maleic acid is particularly preferred because of its particularly excellent ability to suppress coprecipitation aggregation.

(Aqueous solution (A))
The coprecipitate obtained by this production method is used for production of a positive electrode active material for a lithium ion secondary battery. Therefore, the coprecipitate preferably contains a transition metal contained in the positive electrode active material. Such transition metals include Ni, Co and Mn. Moreover, W, Zr, Mo, Mg, Ca, Sr, Ba, and Al are mentioned preferably as metal elements (M) other than Ni, Co, and Mn contained in the coprecipitate.

  The aqueous solution (A) is an aqueous solution containing metal ions of two or more transition metals selected from the group consisting of Ni, Co and Mn. The aqueous solution (A) more preferably contains at least one of Ni ions or Co ions and Mn ions. As described above, the aqueous solution (A) may contain ions of the metal element (M).

The molar ratio of Ni, Co and Mn contained in the aqueous solution (A) is appropriately adjusted according to the composition of the positive electrode active material produced using this coprecipitate. In this production method, since the obtained positive electrode active material exhibits a high discharge capacity, the molar ratio of Ni, Co and Mn contained in the aqueous solution (A) is based on the total amount (X) of these three components. The following relationship is preferably satisfied.
Ni / X = 0.1 to 0.7, Co / X = 0 to 0.4, Mn / X = 0.2 to 0.8
In order to produce a lithium-containing composite oxide used for a positive electrode active material having a high initial discharge capacity and initial discharge voltage of a lithium ion secondary battery, the molar ratio of Ni, Co and Mn contained in the aqueous solution (A) satisfies the following conditions: It is preferable to satisfy.
Ni / X = 0.35 to 0.6, Co / X = 0 to 0.13, Mn / X = 0.33 to 0.65
Further, Mn / X is preferably 0.34 to 0.5 for the same reason as described above.

When the metal element (M) is contained in the aqueous solution (A), the content of the metal element (M) satisfies the following relationship in terms of molar ratio with respect to the total amount (X) of Ni, Co and Mn. preferable.
M / X = 0 to 0.05
In order to produce a lithium-containing composite oxide used for a positive electrode active material having a high initial discharge capacity and initial discharge voltage of a lithium ion secondary battery, M / X is more preferably 0.001 to 0.05. 0.001 to 0.02 is more preferable.

  The aqueous solution (A) is preferably prepared by dissolving a metal salt (1) containing Ni, Co or Mn in water. Examples of the metal salt (1) include sulfates and nitrates, and sulfates are preferred from the viewpoint of solubility in water.

  Suitable Ni sulfate, Co sulfate and Mn sulfate dissolved in the aqueous solution (A) include manganese (II) sulfate pentahydrate, manganese sulfate (II) ammonium hexahydrate, sulfuric acid Nickel (II) hexahydrate, nickel sulfate (II) heptahydrate, nickel (II) ammonium sulfate hexahydrate, cobalt sulfate (II) heptahydrate, cobalt sulfate (II) ammonium -Hexahydrate etc. are mentioned.

  The concentration of the aqueous solution (A) is preferably 0.1 to 3 mol / kg in terms of the total amount of the metal salt (1) to be dissolved. When the metal salt (1) is a sulfate, if the concentration of the aqueous solution (A) is within this range, the sulfate (1) can be sufficiently dissolved in water, and the solution concentration is not too thin. Coprecipitate can be produced. If the solution concentration is low, a large amount of solvent water may be used, which may reduce productivity. The concentration of the sulfate is more preferably 0.5 to 2.5 mol / kg from the viewpoint of stably growing the coprecipitate while maintaining productivity.

  The aqueous solution (A) may be adjusted as an aqueous solution containing all of the supplied metal ions, or the aqueous solution may be adjusted for each supplied metal ion. When adjusting aqueous solution for every component, the average density | concentration of each aqueous solution should just be in the said range. Moreover, when adjusting aqueous solution for every component, you may supply separately to a reaction tank simultaneously, and you may supply aqueous solution after mixing aqueous solution.

  When adjusting aqueous solution for every component and setting it as aqueous solution (A), a density | concentration is adjusted between aqueous solution so that the metal component contained in a coprecipitate may become a desired composition. On the other hand, when it is set as the aqueous solution (A) which consists of all the components, content of Ni, Co, and Mn in each aqueous solution is adjusted so that the metal component contained in a coprecipitate may become a desired composition.

  When the aqueous solution (A) contains ions of the metal element (M), in addition to the metal salts (1) of Ni, Co and Mn, the metal salt (2) containing the metal element (M) is also dissolved and the aqueous solution (A) Is preferably adjusted. Examples of the metal salt (2) include sulfates and nitrates. From the viewpoint of solubility in water, the metal salt (2) is preferably a sulfate of the metal element (M). Specific examples of the metal element (M) sulfate include W sulfate, Zr sulfate, Mo sulfate, Mg sulfate, Ca sulfate, Sr sulfate, Ba sulfate, Examples include Al sulfate.

  The aqueous solution (A) may contain other components described later for the purpose of adjusting the solubility of these ions in addition to the above-described transition metal ions and metal element (M) ions.

(Aqueous solution (B))
In this production method, the aqueous solution (B) contains carbonate ions. In this production method, the aqueous solution (B) functions to adjust the pH of the mixed solution. The aqueous solution (B) may contain other components described later in addition to the carbonate ion source.

  The aqueous solution (B) is preferably prepared by dissolving a carbonate or hydrogen carbonate containing an alkali metal (hereinafter referred to as a carbonate ion source). If this aqueous solution (B) is supplied to the reaction vessel, the pH of the mixed solution can be maintained at 7-9. As the alkali metal, Na or K is preferable. Such carbonate or bicarbonate is preferably at least one selected from the group consisting of sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate. From the viewpoint of ease of handling, sodium carbonate or potassium carbonate is more preferable.

  The concentration of carbonate ions dissolved in the aqueous solution (B) is preferably 0.1 to 2 mol / kg. Within this range, the carbonate ion source can be sufficiently dissolved in water, and the coprecipitation reaction can proceed efficiently. The concentration is more preferably 0.5 to 2 mol / kg.

  When a plurality of components are contained as a carbonate ion source, an aqueous solution may be prepared for each component to obtain an aqueous solution (B), or an aqueous solution (B) composed of all components. When adjusting aqueous solution for every component, the average concentration of each aqueous solution should just be in the said range. Moreover, when adjusting aqueous solution for every component, you may supply separately to a liquid mixture.

(Other ingredients)
Examples of other components that may be contained in the aqueous solution (A), the aqueous solution (B), or the initial solution include water-soluble alcohols. Examples of the water-soluble alcohol include 1 to 3 alcohols. Examples of the monovalent alcohol include methanol, ethanol, 1-propanol, 2-propanol and the like. Examples of the divalent alcohol include alcohol ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, polyethylene glycol, and butanediol. Examples of the trivalent alcohol include glycerin and the like.

  The total concentration of the other components is preferably 0 to 20%, more preferably 0 to 10%, and 0 to 1% based on the total mass of each of the aqueous solution (A), the aqueous solution (B), and the initial solution. Further preferred. If the total concentration of the other components is 20% or less, it is excellent in terms of environment, handling properties, and manufacturing costs. From the viewpoint of production cost, it is particularly preferable not to include other components.

  In this production method, in addition to the ionic surfactant, the aqueous solution (A), and the aqueous solution (B), for example, an aqueous solution containing ammonia or an ammonium salt may be supplied. An aqueous solution containing ammonia or an ammonium salt may have an effect of adjusting the pH of the mixed solution and adjusting the solubility of transition metal ions and metal (M) ions in the mixed solution. Examples of the ammonium salt include ammonium chloride, ammonium sulfate, and ammonium nitrate.

  The reaction ends when the supply of the aqueous solution (A) and the aqueous solution (B) to the reaction vessel is stopped. After completion of the reaction, the coprecipitate can be separated from the mixed solution by a known method. Examples of the separation method include filtration or centrifugation. Filtration can be performed using a pressure filter, a vacuum filter or the like. Centrifugation can be performed using a centrifugal classifier, a filter press, a screw press, a rotary dehydrator or the like.

  It is preferable to wash and dry the separated coprecipitate. By washing the coprecipitate, impurity ions adsorbed on the surface of the coprecipitate can be removed. Examples of the coprecipitate washing method include a method of repeating pressure filtration and dispersion in distilled water.

  The drying temperature when drying the coprecipitate is preferably 60 to 200 ° C. If the drying temperature is within this range, the obtained coprecipitate can be dried in a short time, and oxidation of carbonate during drying can be suppressed. The drying temperature is more preferably 80 to 130 ° C. The drying time is preferably 1 to 300 hours, and more preferably 5 to 120 hours.

The average particle size of the coprecipitate obtained by the present production method _{(D 50)} is, 1～12Myuemu is preferred. If the average particle diameter is in this range, it is preferable because it is easy to handle. The D ₅₀ of the coprecipitate is more preferably 2 to 10 μm, further preferably 3 to 8 μm.

In the present specification, D ₅₀ of the coprecipitate refers to a particle diameter at which the cumulative volume is 50% in a cumulative curve obtained by obtaining a particle size distribution on a volume basis and setting the total volume to 100%. The volume-based particle size distribution can be calculated from a frequency distribution and a cumulative volume distribution curve measured using a laser diffraction / scattering particle size distribution measuring apparatus. The particle diameter is measured by dispersing the particles in an aqueous medium.

According to this production method, the generation of coarse particles can be suppressed. This can be confirmed by calculating the ratio (D ₉₉ / D ₁₀ ) of D ₉₉ and D ₁₀ of the coprecipitate obtained. D ₉₉ and D ₁₀ are particle sizes at which the cumulative volume becomes 99% and 10%, respectively, in the cumulative volume distribution curve obtained by measurement in the same manner as D ₅₀ . The D ₉₉ / D ₁₀ of the coprecipitate is preferably 4.5 or less, more preferably 3.8 or less, and particularly preferably 3.5 or less.

(composition)
The coprecipitate obtained by this production method preferably contains at least one of Ni or Co and Mn. The contents of Ni, Co, and Mn with respect to the total amount of the metal element (X) in the coprecipitate preferably satisfy the following conditions in terms of molar ratio.
Ni / X = 0.1 to 0.7, Co / X = 0 to 0.4, Mn / X = 0.2 to 0.8
In order to produce a lithium-containing composite oxide used for a positive electrode active material having a high initial discharge capacity and initial discharge voltage of a lithium ion secondary battery, Ni, Co, and Mn with respect to the total amount of metal element (X) in the coprecipitate The content of is preferably in the following molar ratio.
Ni / X = 0.35 to 0.6, Co / X = 0 to 0.13, Mn / X = 0.33 to 0.65
Mn / X is preferably 0.34 to 0.5 for the same reason as described above.

The coprecipitate may contain a metal element (M). Examples of the metal element (M) include the same metals as those contained in the aqueous solution (A). When the coprecipitate contains the metal element (M), the content of the metal element (M) with respect to the total amount of the metal element (X) contained in the coprecipitate preferably satisfies the following condition in terms of molar ratio.
M / X = 0 to 0.05
In order to produce a lithium-containing composite oxide used for a positive electrode active material having a high initial discharge capacity and initial discharge voltage of a lithium ion secondary battery, the metal element (M ) Is a total amount, and the molar ratio (M / X) is more preferably 0.001 to 0.05, and further preferably 0.001 to 0.02.

  The coprecipitate obtained by this production method is suitable as a raw material for producing a lithium-containing composite oxide suitable for a positive electrode active material of a lithium ion secondary battery.

  The lithium-containing composite oxide is preferably obtained by mixing a coprecipitate obtained by the present production method and a lithium compound and baking the mixture.

  As the lithium compound, lithium hydroxide, lithium nitrate, lithium carbonate or a mixture thereof is preferable. From the viewpoint of production efficiency, lithium hydroxide, lithium carbonate, or a mixture thereof is more preferable.

  The coprecipitate and the lithium compound can be mixed using, for example, a mixer. If the mixing is insufficient, the ratio of the total amount of lithium and transition metal may vary between the particles of the positive electrode active material after firing. As a mixer, a shaker mixer, a Laedige mixer, a Julia mixer, a V blender, or the like can be used.

  The firing is preferably performed in an oxygen atmosphere at a firing temperature of 800 to 1000 ° C. Under an oxygen atmosphere, the coprecipitate can be efficiently made into a lithium-containing composite oxide by firing, and the coprecipitate of the unoxidized reaction can be reduced. When the firing temperature is within this range, a lithium-containing composite oxide having a uniform crystal structure within the particles can be obtained. The firing temperature is more preferably 800 to 950 ° C.

The average particle size (D ₅₀ ) of the lithium-containing composite oxide is preferably 3 to 7 μm. D ₅₀ of the lithium-containing composite oxide is more preferably 4 to 7 μm, and further preferably 5 to 6 μm. D ₅₀ is a value measured by a coprecipitate the same way.

Lithium-containing composite _oxide, the ratio of _{D 99} and _{D 10 (D 99 / D 10} ) is. 5 or less is preferable, 3.8 or less is more preferable, and 3.5 or less is particularly preferable. D ₉₉ and _{D 10} represent _{respectively the particle diameters} obtained by measuring in the same manner as _{D 99} and _{D 10} of the coprecipitate.

A lithium ion secondary battery having a lithium-containing composite oxide in which D ₅₀ and D ₉₉ / D ₁₀ satisfy the above conditions is excellent in reliability.

The specific surface area of the lithium-containing composite oxide is preferably 0.4 to ²⁰ m ² / g. If the specific surface area of the lithium-containing composite oxide is within this range, the discharge capacity is high and a dense positive electrode layer can be formed. The specific surface area is a value measured by the same method as that for the carbonic acid compound. The specific surface area of the lithium-containing composite oxide is more preferably 3 to 10 m ² / g.

The tap density of the lithium-containing composite oxide is preferably 1.0 / cm ³ or more. If the tap density is high, the amount of the lithium-containing composite oxide that can be filled in the unit volume can be increased, and a lithium ion secondary battery having a high capacity and a high energy density can be obtained.

  The lithium-containing composite oxide is preferably a compound represented by the following formula (1). The following formula (1) is a composition in a state where Li is not taken in and out from a compound such as charge / discharge and activation treatment. The activation treatment refers to an electrochemical reaction in which a potential is applied to the lithium-containing composite oxide, or a treatment in which lithium oxide, lithium, or both are removed from the lithium-containing composite oxide by chemical reaction by immersion in a strong acid. .

The lithium-containing composite oxide is preferably a compound represented by the following formula (1).
_{Li x Ni a Co b Mn c} M d O 2 ··· (1)
In formula (1), 1.1 ≦ x ≦ 1.7, 0.1 ≦ a ≦ 0.7, 0 ≦ b ≦ 0.4, 0.2 ≦ c ≦ 0.8, 0 ≦ d ≦ 0. 05, and a + b + c + d = 1. M is one or more metals selected from the group consisting of W, Zr, Mo, Mg, Ca, Sr, Ba and Al.

  The present invention will be specifically described with reference to examples. The present invention is not construed as being limited to the following examples. Examples 1 to 4 are examples of the present invention, and examples 5 and 6 are comparative examples.

(Example 1)
Nickel (II) sulfate hexahydrate (305 g, 1.16 mol), cobalt sulfate (II) heptahydrate (72 g, 0.26 mol) and manganese sulfate (II) pentahydrate (383 g) , 1.59 mol) was dissolved in distilled water to prepare 2 kg of an aqueous solution (A) having a transition metal ion concentration of 1.5 mol / kg in the aqueous solution.

  Sodium carbonate (0.92 kg, 8.7 mol) was dissolved in 4.88 kg of distilled water to prepare 5.8 kg of an aqueous solution (B) having a carbonate ion concentration of 1.5 mol / kg in the aqueous solution.

  An anionic surfactant (trade name: Polity A550, manufactured by Lion Co., Ltd.) consisting of a copolymer of distilled water, acrylic acid and maleic acid is mixed, and the concentration of the anionic surfactant with respect to the total mass of the initial solution is 1%. The initial solution was prepared.

  1.9 L of the initial solution was added to a glass reaction vessel with a baffle and heated to 30 ° C. with a mantle heater. Next, while stirring the initial solution with a paddle type stirring blade, the aqueous solution (A) and the aqueous solution (B) are continuously supplied to the reaction vessel, mixed, and mixed with carbonate ions and two or more transition metal ions. To give a coprecipitate.

  The aqueous solution (A) was supplied at a rate of 5.0 g / min, and the aqueous solution (B) was supplied so that the pH of the mixed solution was maintained at 8. At this time, the supernatant liquid of the mixed liquid was extracted from the reaction vessel through a filter cloth so that the volume of the mixed liquid became substantially constant.

  After completion of the reaction, the coprecipitate was separated from the mixed solution containing the coprecipitate in the reaction tank by pressure filtration. The operation of dispersing the separated coprecipitate in distilled water and performing pressure filtration was repeated to wash the coprecipitate. Washing was completed when the electrical conductivity of the filtrate of pressure filtration reached 20 mS / m. The coprecipitate after washing was dried at 120 ° C. for 15 hours.

  The compositional analysis of the elements contained in the coprecipitate after drying was performed. The composition analysis was performed using an inductively coupled plasma emission spectrometer (manufactured by SII Nanotechnology, apparatus name: SPS3100H). Ni, Co, and Mn with respect to the total amount of the metal element (X) contained in the coprecipitate were Ni / X = 0.39, Co / X = 0.09, and Mn / X = 0.52 in molar ratios. It was.

The particle size (D ₉₉ , D ₅₀ , and D ₁₀ ) of the coprecipitate was measured. The particle size was measured using a dispersion in which the coprecipitate was added to water and dispersed using ultrasonic waves. Measurement was performed using a laser diffraction / scattering particle size distribution measuring apparatus (manufactured by Nikkiso Co., Ltd., apparatus name: MT-3300EX) to obtain a frequency distribution and a cumulative volume distribution curve. The results are shown in Table 1.

(Example 2)
A coprecipitate was obtained in the same manner as in Example 1 except that the concentration of the anionic surfactant relative to the total mass of the initial solution was 0.1%. About the obtained coprecipitate, the composition analysis and the particle diameter were measured in the same manner as in Example 1. The composition of the coprecipitate was the same as in Example 1. Table 1 shows the particle diameter results.

(Example 3)
A coprecipitate was obtained in the same manner as in Example 1 except that the concentration of the anionic surfactant relative to the total mass of the initial solution was 0.01%. About the obtained coprecipitate, the composition analysis and the particle diameter were measured in the same manner as in Example 1. The composition of the coprecipitate was the same as in Example 1. Table 1 shows the particle diameter results.

(Example 4)
Coprecipitation was carried out in the same manner as in Example 1 except that sodium citrate was used as the anionic surfactant contained in the initial solution, and the concentration of the anionic surfactant with respect to the total mass of the initial solution was adjusted to 1%. I got a thing. About the obtained coprecipitate, the composition analysis and the particle diameter were measured in the same manner as in Example 1. The composition of the coprecipitate was the same as in Example 1. Table 1 shows the particle diameter results.

(Example 5)
A coprecipitate was obtained in the same manner as in Example 1 except that the initial solution did not contain an ionic surfactant. About the obtained coprecipitate, the composition analysis and the particle diameter were measured in the same manner as in Example 1. The composition of the coprecipitate was the same as in Example 1. Table 1 shows the particle diameter results.

(Example 6)
The initial solution contains a nonionic surfactant (manufactured by Nissin Chemical Industry Co., Ltd., trade name: Surfynol) and is adjusted so that the concentration of the nonionic surfactant with respect to the total mass of the initial solution is 1%. Obtained a coprecipitate in the same manner as in Example 1. About the obtained coprecipitate, the composition analysis and the particle diameter were measured in the same manner as in Example 1. The composition of the coprecipitate was the same as in Example 1. The results are shown in Table 1.

As shown in Table 1, coprecipitates of Examples 1 to 4 obtained in this manufacturing _method, a small _{D 50, D} 99 _{/ D 10} is small. That is, it is possible to achieve particle size control and suppression of generation of coarse particles.

On the other hand, Example 5 which does not contain an ionic surfactant and Example 6 which contains a nonionic surfactant in the initial solution have both large D ₅₀ and D ₉₉ / D ₁₀ . This indicates that excessive growth of coprecipitate and coarse particles of coprecipitate are generated in the coprecipitation reaction.

  From the above, by reacting carbonate ions and two or more transition metal ions in a mixed solution containing an ionic surfactant, excessive coagulation of the coprecipitate is suppressed, and the powder characteristics of the coprecipitate Can be controlled.

  The coprecipitate obtained by the production method of the present invention can be suitably used for production of a positive electrode active material for a lithium ion secondary battery. Since the particle size and particle size distribution of the coprecipitate can be controlled, the particle size and particle size distribution of the positive electrode active material obtained using this coprecipitate can be controlled within an appropriate range.

Claims (7)

A method for producing a coprecipitate containing two or more transition metals, wherein an aqueous solution (A), an aqueous solution (B), an ionic surfactant and water are supplied to a reaction vessel, mixed, and the pH of the mixed solution Is kept in the range of 7-9, and at least the aqueous solution (A) is added to the reaction vessel so that the volume of the mixed solution in the reaction vessel becomes substantially constant by reacting two or more kinds of transition metal ions and carbonate ions. and simultaneously supplying the aqueous solution (B), coprecipitate method for producing and performing step to exit vent liquid mixture to overflow from the reaction vessel.
Aqueous solution (A): An aqueous solution containing metal ions of two or more transition metals selected from the group consisting of Ni, Co and Mn.
Aqueous solution (B): An aqueous solution containing carbonate ions.   A method comprising: supplying water and an ionic surfactant to a reaction tank to form an initial solution, and supplying at least the aqueous solution (A) and the aqueous solution (B) to the initial solution while maintaining a pH in a range of 7 to 9. The method for producing a coprecipitate according to 1.   The method for producing a coprecipitate according to claim 2, wherein the concentration of the ionic surfactant in the initial solution is 0.01 to 1% with respect to the total mass of the initial solution.   The coprecipitate according to any one of claims 1 to 3, wherein the supply rates of the aqueous solution (A) and the aqueous solution (B) are each independently 0.2 to 7.5 g / (min · L). Manufacturing method. The method for producing a coprecipitate according to any one of claims 1 to 4 , wherein the ionic surfactant is an anionic surfactant. The coprecipitate according to any one of claims 1 to 5 , wherein the molar ratio of Ni, Co and Mn contained in the aqueous solution (A) satisfies the following relationship with respect to the total amount (X) of these three components. Manufacturing method.
Ni / X = 0.1 to 0.7, Co / X = 0 to 0.4, Mn / X = 0.2 to 0.8 The aqueous solution (B) is an aqueous solution containing at least one selected from the group consisting of sodium carbonate, potassium carbonate, sodium hydrogen carbonate and potassium hydrogen carbonate. The coprecipitate according to any one of claims 1 to 6 Production method.

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