TWI871059B - Mixed solution of lithium metal oxide and manufacturing method thereof - Google Patents

Abstract

The mixed liquid of lithium metal oxide of the present invention contains two or more metals selected from the group consisting of niobium, tantalum, molybdenum, and tungsten, and is characterized by: the molar quantity of lithium in the mixed liquid of lithium metal oxides, per 1L, is designated as Li; the total molar quantity of two or more metals in the mixed solution of lithium metal oxides, per 1L, is designated as M; the molar ratio of Li/M is is 0.1 or more and 10 or less; and, the particle size (D50) of particles in the mixed solution of lithium metal oxide, obtained through dynamic light scattering method, is 100nm or less.

Description

Lithium metal oxide mixed solution and its production method

The present invention relates to a lithium metal oxide mixed solution and a manufacturing method thereof.

Lithium metal oxides formed by combining lithium with metal elements such as niobium, tantalum, molybdenum, and tungsten are used in nonlinear optical materials, piezoelectric elements, battery materials, etc. For example, Patent Document 1 discloses a composite active material particle that can reduce the battery resistance generated in a fully solid lithium ion battery. The lithium ion conductive oxide that covers at least a portion of the surface of the composite active material particle can be exemplified by: lithium niobate and lithium tantalum. [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 2018-125214

However, depending on the type of lithium metal oxide, the dispersibility or solubility in polar solvents, especially in water, is poor. For example, compared with lithium niobate, lithium tantalum has poor dispersibility or solubility in water, and has the characteristic of easily generating precipitates due to changes over time. Specifically, lithium tantalum produced using the lithium niobate production method disclosed in Patent Document 1 has low dispersibility in water, poor solubility in water, and poor storage stability.

In view of the above-mentioned problems, the present invention provides a lithium metal oxide mixed solution and its manufacturing method which has high dispersibility in polar solvents, especially in water, good solubility in water and excellent storage stability.

The lithium metal oxide mixed solution of the present invention is completed to solve the above-mentioned problem. The lithium metal oxide mixed solution contains two or more lithium metal oxide dispersions selected from the group consisting of niobium, tungsten, molybdenum, and tungsten. The characteristics are that the molar number of lithium contained in the lithium metal oxide mixed solution per 1L is set as Li (mol/L), the total molar number of two or more metals in the lithium metal oxide mixed solution per 1L is set as M (mol/L), the molar ratio Li/M is 0.1 or more and 10 or less, and the particle size (D50) of the particles in the lithium metal oxide mixed solution obtained by dynamic light scattering method is 100nm or less. The lithium metal oxide mixed solution of the present invention can be a lithium metal oxide mixed solution obtained by mixing two or more lithium metal oxide dispersions selected from lithium niobate dispersion, lithium tantalum dispersion, lithium molybdenum dispersion and lithium tungstate dispersion, and can be a lithium metal oxide mixed solution obtained by mixing three or four lithium metal oxide dispersions. In addition, at least one of the two or more lithium metal oxide dispersions selected from the group consisting of niobium, tantalum, molybdenum and tungsten can be a lithium niobate dispersion or a lithium tantalum dispersion.

Unless otherwise specified, the niobium, tantalum, molybdenum and tungsten mentioned in this specification include niobium oxide compounds, tantalum oxide compounds, molybdenum oxide compounds and tungsten oxide compounds.

The molar number of lithium in 1L of the lithium metal oxide mixed solution contained in the lithium metal oxide mixed solution of the present invention is set as Li (mol/L), and the total molar number of two or more metals in 1L of the lithium metal oxide mixed solution is set as M (mol/L). If the molar ratio Li/M is 0.1 to 10, the dispersibility, solubility and stability of the mixed solution in water are improved. In addition, the molar ratio Li/M is more preferably 0.2 to 6, more preferably 0.25 to 5, particularly preferably 0.4 to 4, and even more preferably 0.5 to 2.

Here, the total molar number "M" (mol/L) of two or more metals in 1L of the lithium metal oxide mixed solution of the present invention can be calculated as follows.

In the case where the lithium metal oxide mixed solution of the present invention is generated by mixing two lithium metal oxide dispersions, namely, a lithium niobate dispersion and a lithium tantalum dispersion, if the molar number of niobium per 1L of the lithium metal oxide mixed solution is set as "M1" (mol/L), and the molar number of tantalum per 1L of the lithium metal oxide mixed solution is set as "M2" (mol/L), then the total molar number "M" (mol/L) of metals contained in the lithium metal oxide mixed solution (1L) is "M=M1+M2" (mol/L). In addition, the lithium metal oxide dispersions selected as the two lithium metal oxide dispersions are not limited to the lithium niobate dispersion and the lithium tantalum dispersion.

Furthermore, when the lithium metal oxide mixed solution of the present invention is generated by mixing three lithium metal oxide dispersions, namely, lithium niobate dispersion, lithium tantalum dispersion and lithium molybdate dispersion, if the molar number of molybdenum in each 1L of the lithium metal oxide mixed solution is set as "M3" (mol/L), then the total molar number "M" (mol/L) of metals contained in the lithium metal oxide mixed solution (1L) is "M=M1+M2+M3" (mol/L). In addition, the lithium metal oxide dispersions selected as the three lithium metal oxide dispersions are not limited to lithium niobate dispersion, lithium tantalum dispersion and lithium molybdate dispersion.

Furthermore, when the lithium metal oxide mixed solution of the present invention is generated by mixing four lithium metal oxide dispersions, namely, lithium niobate dispersion, lithium tantalum dispersion, lithium molybdate dispersion and lithium tungstate dispersion, if the molar number of tungsten in 1L of the lithium metal oxide mixed solution is set as "M4" (mol/L), then the total molar number "M" (mol/L) of metals contained in the lithium metal oxide mixed solution (1L) is "M=M1+M2+M3+M4" (mol/L).

In addition, it is presumed that the lithium metal oxide in the lithium metal oxide mixed solution of the present invention exists in the mixed solution as ions in a state of ionic bonding between a metallic acid and lithium. Hydroxyl ions exist as anions in the lithium metal oxide mixed solution of the present invention, while halogenide ions such as fluoride ions and chloride ions are almost absent, and lithium is considered to exist as cations. Furthermore, for example, niobium is considered to exist as anions such as NbO ₃ ^- or polyoxometalate (polyacid) ions formed by bonding of a plurality of niobium atoms and oxygen atoms. Furthermore, tungsten is considered to exist as anions such as TaO ₃ ^- or polymetallic oxoacid ions (polyacid) formed by bonding of a plurality of tungsten atoms and oxygen atoms. Furthermore, molybdenum is considered to exist as anions such as MoO ₄ ^2- or polymetallic oxoacid ions (polyacid) formed by bonding of a plurality of molybdenum atoms and oxygen atoms. Furthermore, tungsten is considered to exist as anions such as (W ₂ O ₇ ) ^2- and (W ₁₂ O ₁₀ ) ^8- or polymetallic oxoacid ions (polyacid) formed by bonding of a plurality of tungsten atoms and oxygen atoms.

From the viewpoints of high dispersibility, stability with little change over time, reactivity when reacting or compounding with other substances, and film uniformity when forming a film, the particle size (D50) of the particles in the lithium metal oxide mixed solution of the present invention obtained by dynamic light scattering is preferably 100 nm or less. Examples of the particles in the lithium metal oxide mixed solution of the present invention include lithium niobate, lithium tantalum, lithium molybdenum, lithium tungstate, lithium ions, niobium ions, tungsten ions, niobium acid ions, tungsten acid ions, molybdenum acid ions, tungsten acid ions, and the like. Furthermore, the particle size (D50) is preferably a smaller particle size, more preferably 80 nm or less, more preferably 50 nm or less, particularly preferably 30 nm or less, particularly preferably 20 nm or less, further particularly preferably 10 nm or less, and even more particularly preferably 5 nm or less. Furthermore, in this specification, unless otherwise specified, "particle size (D50)" includes both "initial particle size D50" of particles in the lithium metal oxide mixed solution of the present invention adjusted to a liquid temperature of 25°C immediately after production, and "time-dependent particle size D50" of particles in the lithium metal oxide mixed solution after standing in a thermostat set at room temperature of 25°C for one month from the date of production of the lithium metal oxide mixed solution of the present invention. Furthermore, it is estimated that if the temporal variation range of the "initial particle size D50" and the "temporal particle size D50" in the "particle size (D50)" of the particles in the lithium metal oxide mixed solution of the present invention is small, then the temporal variation range of the "temporal particle size D50" in the particle size (D50) of the particles in the lithium metal oxide mixed solution after being left to stand for more than one month from the date of production of the lithium metal oxide mixed solution of the present invention is also small. In this way, the particle size (D50) of the particles in the lithium metal oxide mixed solution of the present invention is measured using a dynamic light scattering method, and the liquid in a state where the particle size (D50) is 100 nm or less is regarded as the "lithium metal oxide mixed solution" of the present invention.

Here, the dynamic light scattering method is a method of irradiating a solution such as a suspension solution with light such as laser light, measuring the light scattering intensity from a group of particles performing Brownian motion, and obtaining the particle size and distribution from the time variation of the intensity. Specifically, the particle size distribution evaluation method is implemented using an azimuthal potential/particle size/molecular weight measurement system (manufactured by Otsuka Electronics Co., Ltd.: ELSZ-2000) in accordance with JIS Z 8828:2019 "Particle size analysis-dynamic light scattering method". In addition, before the measurement, in order to remove dust and the like in the solution to be measured, the solution is filtered with a filter with a pore size of 1μm, and an ultrasonic treatment is performed at 28kHz for 3 minutes using an ultrasonic cleaner (manufactured by AS ONE: VS-100III). In addition, the particle size (D50) refers to the median diameter (D50), which is the particle size representing 50% cumulative value of the cumulative distribution curve.

In addition, the lithium metal oxide mixed solution of the present invention contains two or more lithium metal oxide dispersions selected from the group consisting of niobium, tantalum, molybdenum, and tungsten, and is characterized in that the molar number of lithium contained in the lithium metal oxide mixed solution per 1L is set as Li, the total molar number of two or more metals in the lithium metal oxide mixed solution per 1L is set as M, the molar ratio Li/M is greater than 0.1 and less than 10, and the maximum value of the transmittance in the wavelength range of 400nm~760nm is greater than 65%. Here, since the lithium metal oxide mixed solution of the present invention includes two or more lithium metal oxide dispersions selected from the group consisting of niobium, tantalum, molybdenum, and tungsten and the molar ratio Li/M as described above, detailed description is omitted.

From the viewpoint of high dispersion and excellent uniformity of the components in the liquid, the maximum value of the transmittance of the lithium metal oxide mixed solution of the present invention in the wavelength range of 400nm to 760nm is preferably 65% or more. The maximum value of the transmittance in the wavelength range of 400nm to 760nm is more preferably 75% or more, more preferably 80% or more, particularly preferably 85% or more, even more preferably 90% or more, and even more preferably 95% or more. The maximum value of the transmittance in the wavelength range of 400nm to 760nm may also be 100%.

Furthermore, the transmittance of the lithium metal oxide mixed solution of the present invention in any one or more wavelengths of 400nm, 600nm, and 750nm is preferably 65% or more, more preferably 70% or more, more preferably 80% or more, particularly preferably 90% or more, and most preferably 100%. The transmittance in any one or more wavelengths of 400nm, 600nm, and 750nm can be 70% or more, 72% or more, 74% or more, 76% or more, 78% or more, 80% or more, 90% or more, 95% or more, 97% or more, 98% or more, 99% or more, or 100% or more.

Furthermore, the transmittance of the lithium metal oxide mixed solution of the present invention in the wavelength range of 400nm to 760nm is preferably 65% or more, more preferably 70% or more, even more preferably 80% or more, particularly preferably 90% or more, and most preferably 100%. The transmittance in the wavelength range of 400nm to 760nm can be 70% or more, 72% or more, 74% or more, 76% or more, 78% or more, 80% or more, 90% or more, 95% or more, 97% or more, 98% or more, 99% or more, or 100% or more.

In addition, due to measurement errors, the measured value of the above transmittance may be greater than 100%, but the theoretical upper limit is 100%, so when the measured value is greater than 100%, it is regarded as 100%. In addition, in this specification, unless otherwise specified, "transmittance" includes both the "initial transmittance" of the lithium metal oxide mixed solution of the present invention adjusted to a liquid temperature of 25°C just after production, and the "transmittance over time" of the lithium metal oxide mixed solution after being left in a thermostat set at room temperature of 25°C for one month from the date of production of the lithium metal oxide mixed solution of the present invention. Furthermore, it is inferred that if the temporal variation range of the "initial transmittance" and the "temporal transmittance" in the "transmittance" of the lithium metal oxide mixed solution of the present invention is smaller, then the temporal variation range of the "temporal transmittance" in the transmittance of the lithium metal oxide mixed solution after being left to stand for more than one month from the date of production of the lithium metal oxide mixed solution of the present invention will also be smaller.

Here, the above transmittance is measured for the lithium metal oxide mixed solution of the present invention using a spectrometer according to the following transmittance measurement conditions.

=Transmittance measurement conditions= ･Measurement device: UV/visible/near-infrared spectrometer UH4150 (manufactured by Hitachi High-Tech Science Corporation) ･Measurement mode: Wavelength scan ･Data mode: %T (transmission) ･Measurement wavelength range: 200nm~2000nm ･Scanning speed: 600nm/min ･Sampling interval: 2nm

In addition, the "dispersion liquid" and "mixed liquid" in the present invention are not limited to the solute dispersed or mixed in the solvent in the form of a single molecule, but also include aggregates of multiple molecules attracted by intermolecular interactions, such as (1) polymer molecules, (2) solvated molecules, (3) molecular clusters, (4) colloids, etc. dispersed in a solvent.

In addition, the lithium metal oxide mixed solution of the present invention is characterized in that it further contains ammonia. As described in detail in the method for producing the lithium metal oxide mixed solution of the present invention described later, in the process, two or more lithium metal oxide dispersions are generated by a reverse neutralization method of adding an acidic metal acid solution to ammonia water, and then the lithium metal oxide mixed solution of the present invention is generated by mixing the two or more lithium metal oxide dispersions. Therefore, it is considered that ammonia containing ammonium ions substituted with lithium ions exists as cations in the mixed solution.

The method for measuring the ammonia content in the mixed solution can be listed as follows: adding sodium hydroxide to the mixed solution and separating the ammonia by distillation, and quantitatively measuring the ammonia content by an ion meter; quantitatively measuring the _N2 component in the vaporized sample by a thermal conductivity analyzer; Kjeldahl method, gas chromatography (GC), ion chromatography, gas chromatography-mass spectrometry (GC-MS), etc. The method of quantitatively measuring by an ion meter is particularly preferred.

The ammonia content of ammonia containing ammonium ions contained in the lithium metal oxide mixed solution of the present invention is preferably 0.001 mass % to 25 mass %, more preferably 0.003 mass % to 15 mass %. The ammonia content may be 0.1 mass % to 10 mass %, 0.5 mass % to 10 mass %, or 1 mass % to 8 mass %.

Furthermore, the lithium metal oxide mixed solution of the present invention is characterized in that it further contains hydrogen peroxide and/or organic nitride.

When the lithium metal oxide mixed solution of the present invention includes a lithium tantalum dispersion, in the method for producing the lithium tantalum dispersion described later, a tantalum compound aqueous solution can be generated by adding hydrogen peroxide to a tantalum fluoride aqueous solution and mixing them, so the lithium metal oxide mixed solution of the present invention may also contain hydrogen peroxide. On the other hand, when the lithium metal oxide mixed solution of the present invention includes a lithium niobate dispersion, if hydrogen peroxide is included, there is a concern that a part of the soluble niobium acid forms an unstable peroxide complex. For example, when the lithium metal oxide mixed solution of the present invention includes a lithium tantalum dispersion and a lithium niobate dispersion, it is preferred that the content of hydrogen peroxide in the lithium metal oxide mixed solution of the present invention is less.

The method for detecting hydrogen peroxide in the lithium metal oxide mixed solution of the present invention can be used, for example, to confirm the content of hydrogen peroxide in the mixed solution by measuring the relative intensity of the absorbance of the standard solution containing hydrogen peroxide using the standard addition method. Specifically, it is found that the wavelength region in which the absorbance change accompanied by the formation of peroxide complex is observed from the ultraviolet-visible absorption spectra of each of the standard solution containing a known content, for example, 1 mass % hydrogen peroxide and the standard solution without hydrogen peroxide added, if the difference in absorbance between the standard solution without hydrogen peroxide added and the sample with unknown hydrogen peroxide content in the wavelength region is less than 1%, it can be confirmed that the sample with unknown hydrogen peroxide content does not substantially contain hydrogen peroxide. When hydrogen peroxide is contained in the solution, hydrogen peroxide reacts with the metal polyacid to form a peroxide complex. Therefore, as described above, by confirming the difference in absorbance of the standard solution without hydrogen peroxide added, it can be confirmed that the mixed solution does not contain hydrogen peroxide. In addition, in addition to the above-mentioned standard addition method, there are also the following methods: using, for example, a commercially available hydrogen peroxide measurement kit, adding a reagent that reacts with hydrogen peroxide to form a color, and measuring its color; or adding a reagent that reacts with hydrogen peroxide to form a fluorescence, and measuring its luminescence, to qualitatively and quantitatively analyze the hydrogen peroxide in the mixed solution.

It is speculated that the organic nitride in the lithium metal oxide mixed solution of the present invention exists in the mixed solution as ions in a state of ionic bonding with the metal acid.

Here, as the organic nitride, there can be listed aliphatic amines, aromatic amines, amino alcohols, amino acids, polyamines, quaternary ammonium, guanidine compounds, and azole compounds.

Examples of the aliphatic amine include methylamine, dimethylamine, trimethylamine, ethylamine, methylethylamine, diethylamine, triethylamine, methyldiethylamine, dimethylethylamine, n-propylamine, di-n-propylamine, tri-n-propylamine, isopropylamine, diisopropylamine, triisopropylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, isobutylamine, diisobutylamine, triisobutylamine, tert-butylamine, n-pentylamine, n-hexylamine, cyclohexylamine, and piperidine.

As aromatic amines, for example, aniline, phenylenediamine, diamine toluene, etc. can be mentioned. Furthermore, as amino alcohols, for example, methanolamine, ethanolamine, propanolamine, butanolamine, pentanolamine, dimethanolamine, diethanolamine, trimethanolamine, methylmethanolamine, methylethanolamine, methylpropanolamine, methylbutanolamine, ethylmethanolamine, ethylethanolamine, ethylpropanolamine, dimethylmethanolamine, dimethylethanolamine, dimethylpropanolamine, methyldimethanolamine, methyldiethanolamine, diethylmethanolamine, hydroxymethylaminomethane, bis(2-hydroxyethyl)aminophenyl(hydroxymethyl)methane, and aminophenol, etc. can be mentioned. Again, as amino acids, for example, alanine, arginine, aspartic acid, EDTA, etc. can be mentioned. Furthermore, as polyamines, for example, polyamines, polyetheramines, etc. can be mentioned.

Examples of the quaternary ammonium include alkyl imidazolium, pyridinium, pyrrolidinium, tetraoxane ammonium, etc. Specific examples of the alkyl imidazolium include 1-methyl-3-methyl imidazolium, 1-ethyl-3-methyl imidazolium, 1-propyl-3-methyl imidazolium, 1-butyl-3-methyl imidazolium, 1-hexyl-3-methyl imidazolium, 1-methyl-2,3-dimethyl imidazolium, 1-ethyl-2,3-dimethyl imidazolium, 1-propyl-2,3-dimethyl imidazolium, 1-butyl-2,3-dimethyl imidazolium, etc. Specific examples of pyridinium and pyrrolidinium include N-butyl-pyridinium, N-ethyl-3-methyl-pyridinium, N-butyl-3-methyl-pyridinium, N-hexyl-4-(dimethylamino)-pyridinium, N-methyl-1-methylpyrrolidinium, N-butyl-1-methylpyrrolidinium, etc. Specific examples of tetraoxammonium include tetramethylammonium, tetraethylammonium, tetrabutylammonium, and ethyl-dimethyl- ^{propylammonium} . In addition, as anions that form salts with the above-mentioned cations, OH- ^, Cl- ^, Br- ^, I- ^, _BF4- , _HSO4- , ^etc. can be cited.

Examples of the guanidine compound include guanidine, diphenylguanidine, and xyleneguanidine. Examples of the azole compound include imidazole compounds and triazole compounds. Here, specific examples of the imidazole compound include imidazole, 2-methylimidazole, and 2-ethyl-4-methylimidazole. Examples of the triazole compound include 1,2,4-triazole, 1,2,4-triazole-3-carboxylic acid methyl ester, and 1,2,3-benzotriazole.

Here, the organic nitrogen compound is preferably an aliphatic amine because of its high volatility and low toxicity. Specifically, an aliphatic amine having 1 to 4 carbon atoms is more preferred, and an aliphatic amine having 1 to 2 carbon atoms is particularly preferred. Examples thereof include methylamine and dimethylamine.

Furthermore, if the organic nitride is quaternary ammonium, it is preferred because it has high solubility and can suppress high crystallization and high solubility. For example, tetraoxammonium salts are preferred, tetraoxammonium hydroxide salts are more preferred, tetramethylammonium hydroxide and tetraethylammonium are particularly preferred, and tetramethylammonium hydroxide (TMAH) is particularly preferred.

Furthermore, the organic nitride may be a mixture of two or more selected from aliphatic amines, aromatic amines, amino alcohols, amino acids, polyamines, quaternary ammonium, guanidine compounds, and azole compounds instead of one selected from aliphatic amines, aromatic amines, amino alcohols, amino acids, polyamines, quaternary ammonium, guanidine compounds, and azole compounds. For example, a mixture of aliphatic amines and quaternary ammonium is preferred because the amount added can be reduced to avoid an increase in toxicity and the solubility can be increased.

Specifically, examples include: a mixture of two organic nitrides such as methylamine and tetramethylammonium hydroxide (TMAH), dimethylamine and tetramethylammonium hydroxide (TMAH), and methylamine and dimethylamine; and a mixture of three organic nitrides such as methylamine, dimethylamine, and tetramethylammonium hydroxide (TMAH).

In addition, the method for measuring the content of the organic nitride in the tantalum compound dispersion of the present invention can be listed as follows: gas chromatography (GC), liquid chromatography (LC), mass spectrometry (MS), gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), etc. It is particularly preferred to measure by liquid chromatography (LC) or liquid chromatography-mass spectrometry (LC-MS).

As mentioned above, the organic nitride contained in the lithium metal oxide mixed solution of the present invention is preferably an aliphatic amine such as methylamine, dimethylamine, ethylamine, trimethylamine, or a mixture thereof, or a quaternary ammonium compound such as tetramethylammonium hydroxide (TMAH) or tetraethylammonium hydroxide (TEAH).

Furthermore, the lithium metal oxide mixed solution of the present invention is characterized in that the solvent of the lithium metal oxide mixed solution is water. Since the lithium metal oxide mixed solution of the present invention has high dispersibility in polar solvents, especially in water, and good solubility in water, pure water can be used as the solvent. An organic solvent can also be used as the solvent. Examples of organic solvents include alcohol solvents, ketone solvents, ether solvents, ester solvents, aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, etc., and solvents obtained by mixing these organic solvents with pure water can also be used. Furthermore, alcohol solvents include alcohols with carbon numbers of 5 or less (methanol, ethanol, n-propanol, isopropanol, butanol, ethylene glycol, propylene glycol), acetone, high boiling point solvents, etc. The above solvents are preferably miscible with water. Furthermore, the lithium metal oxide mixed solution of the present invention may contain one or more solvents in any proportion within the range that does not hinder stability.

Examples of high boiling point solvents include polyol solvents and glycol solvents. Examples of polyol solvents include glycerol (boiling point: 290°C), 1,6-hexanediol (boiling point: 250°C), 1,7-heptanediol (boiling point: 259°C), etc. Examples of glycol solvents include ethylene glycol (boiling point: 197.3°C), propylene glycol (boiling point: 188.2°C), diethylene glycol (boiling point: 244.3°C), triethylene glycol (boiling point: 287.4°C), oligoethylene glycol (boiling point: 287°C~460°C), polyethylene glycol (PEG) (boiling point: above 460°C), polyethylene glycol (PEG)-polypropylene glycol (PPG) copolymer (boiling point: above 460°C). ), diethylene glycol monohexyl ether (boiling point: 260°C), polyoxyalkylene monoalkyl ether (boiling point: 260°C or more), polyoxyethylene sorbitan monolaurate (boiling point: 321°C or more), other anionic fluorine-based surfactants (boiling point: 180°C or more), amphoteric fluorine-based surfactants (boiling point: 180°C or more), nonionic fluorine-based surfactants (boiling point: 180°C or more), amine oxides (boiling point: 180°C or more), etc. The above boiling points are boiling points at 1 atmosphere.

Furthermore, the solvent of the lithium metal oxide mixed solution of the present invention may also contain a binder such as a resin component. If the solvent of the lithium metal oxide mixed solution of the present invention contains a binder such as a resin component, the film-forming property of the lithium metal oxide film formed using the lithium metal oxide mixed solution of the present invention can be improved. Here, the resin component used as the binder can be, for example, acrylic resin, polyurethane, epoxy resin, polystyrene, polycarbonate, glycol resin, cellulose resin, and mixed resins and copolymer resins thereof.

Furthermore, the lithium metal oxide mixed solution of the present invention is characterized in that, when the lithium metal oxide mixed solution is set to 100 mass %, the metal element content of the selected lithium metal oxide dispersion is, when the lithium metal oxide mixed solution is set to 100 mass %, the niobium content is 20 mass % or less in terms of Nb conversion, the tungsten content is 12 mass % or less in terms of Ta conversion, the molybdenum content is 23 mass % or less in terms of Mo conversion, and the tungsten content is 22 mass % or less in terms of W conversion.

When the selected lithium metal oxide dispersion is a lithium niobate dispersion, the niobium content is preferably 20% by mass or less in terms of Nb conversion from the viewpoint of both practicality and stability of the lithium metal oxide mixed solution. Furthermore, the niobium content is more preferably 0.001% by mass to 20% by mass in terms of Nb conversion, more preferably 0.01% by mass to 15% by mass, particularly preferably 0.1% by mass to 10% by mass, more preferably 0.1% by mass to 5% by mass, and even more preferably 1% by mass to 5% by mass. Furthermore, the niobium content in the lithium metal oxide mixed solution of the present invention may also be 3% by mass to 20% by mass in terms of Nb conversion.

When the selected lithium metal oxide dispersion is a lithium tantalum dispersion, the tantalum content is preferably 12% by mass or less in terms of Ta conversion from the viewpoint of improving dispersibility and solubility in solvents, especially water. Furthermore, the tantalum content is more preferably 0.001% by mass to 12% by mass, more preferably 0.01% by mass to 10% by mass, particularly preferably 0.1% by mass to 8% by mass, more preferably 0.1% by mass to 5% by mass, and even more preferably 1% by mass to 5% by mass. Furthermore, the tantalum content in the lithium metal oxide mixed solution of the present invention may also be 1% by mass to 12% by mass in terms of Ta conversion.

When the selected lithium metal oxide dispersion is a lithium molybdate dispersion, the molybdenum content is preferably 22 mass % or less in terms of Mo conversion from the viewpoint of improving dispersibility and solubility in a solvent, especially in water. Furthermore, the molybdenum content is more preferably 0.001 mass % to 22 mass % in terms of Mo conversion, more preferably 0.01 mass % to 20 mass %, particularly preferably 0.01 mass % to 15 mass %, more particularly preferably 0.1 mass % to 10 mass %, further particularly preferably 0.1 mass % to 5 mass %, and even more particularly preferably 1 mass % to 5 mass %.

When the selected lithium metal oxide dispersion is a lithium tungstate dispersion, the tungsten content is preferably 23% by mass or less in terms of W conversion from the viewpoint of improving dispersibility and solubility in a solvent, especially in water. Furthermore, the tungsten content is more preferably 0.001% by mass to 23% by mass, more preferably 0.01% by mass to 20% by mass, particularly preferably 0.01% by mass to 15% by mass, more particularly preferably 0.1% by mass to 10% by mass, still more particularly preferably 0.1% by mass to 5% by mass, and still more particularly preferably 1% by mass to 5% by mass.

Here, the contents of niobium, tungsten, molybdenum, tungsten and lithium in the lithium metal oxide mixed solution of the present invention are measured and calculated by appropriately diluting the mixed solution with dilute hydrochloric acid as needed, using inductively coupled plasma atomic emission spectroscopy (ICP-AES) (manufactured by Agilent Technologies: AG-5110) in accordance with JIS K0116:2014 to obtain the Nb mass fraction converted to Nb, the Ta mass fraction converted to Ta, the Mo mass fraction converted to Mo, the W mass fraction converted to W and the Li mass fraction converted to Li. By specifying the mass fractions of niobium, niobium, molybdenum, tungsten and lithium in the lithium metal oxide mixed solution of the present invention, the total mass fraction (H) of two or more metals selected from the group consisting of lithium (Li), niobium (Nb), niobium (Ta), molybdenum (Mo) and tungsten (W) in the lithium metal oxide mixed solution contained in the lithium metal oxide mixed solution of the present invention can be specified.

The molar ratio of niobium and tantalum, and niobium, tungsten and molybdenum in the lithium metal oxide mixed solution of the present invention is preferably 0.001-0.999. The molar ratio Nb+Ta/Nb+Ta+Mo+W is more preferably 0.01-0.999, more preferably 0.1-0.999, particularly preferably 0.25-0.999, more particularly preferably 0.5-0.999, still more particularly preferably 0.75-0.999, and particularly preferably 0.8-0.999, 0.9-0.999.

In addition, in the lithium metal oxide mixed solution of the present invention, when the lithium metal oxide mixed solution is set to 100 mass %, the total content of niobium, tungsten, molybdenum and tungsten in the lithium metal oxide mixed solution is 0.001 mass % or more and 50 mass % or less in terms of metal conversion. In the lithium metal oxide mixed solution of the present invention, from the viewpoint of forming a good lithium metal oxide film, when the lithium metal oxide mixed solution is set to 100 mass %, the total content of the niobium content, the tungsten content, the molybdenum content, the molybdenum content, and the tungsten content calculated using the above-mentioned inductively coupled plasma atomic emission spectrometry (AG-5110 manufactured by Agilent Technologies, Inc.) is preferably 0.001 mass % or more and 50 mass % or less in terms of metal conversion, that is, Nb conversion, Ta conversion, Mo conversion, and W conversion. Moreover, when the lithium metal oxide mixed solution is set to 100 mass %, the total content is more preferably 0.1 mass % or more, more preferably 1 mass % or more, and particularly preferably 3 mass % or more in terms of metal conversion. On the other hand, when the lithium metal oxide mixed solution is set to 100 mass %, the total content is preferably less than 40 mass %, more preferably less than 30 mass %, and particularly preferably less than 20 mass %.

Furthermore, the lithium metal oxide mixed solution of the present invention is characterized in that the pH of the lithium metal oxide mixed solution is greater than 8. From the viewpoint that the polyacid ions contained in the mixed solution are stable, the pH of the lithium metal oxide mixed solution of the present invention is preferably greater than 8. Furthermore, the pH of the lithium metal oxide mixed solution of the present invention is more preferably greater than 9, further preferably greater than 10, and particularly preferably greater than 10.5. Furthermore, the pH of the lithium metal oxide mixed solution of the present invention may be greater than 11 and less than 14, or may be greater than 12 and less than 14, or may be greater than 13 and less than 14. Furthermore, from the viewpoint that the inclusion of an organic acid in the lithium metal oxide mixed solution of the present invention will lower the pH, it is also preferable that the organic acid is not contained. In addition, in this specification, unless otherwise specified, "pH" includes both the "initial pH" of the lithium metal oxide mixed solution of the present invention adjusted to a liquid temperature of 25°C immediately after production, and the "time-dependent pH" of the lithium metal oxide mixed solution after standing for one month from the date of production of the lithium metal oxide mixed solution of the present invention in a thermostat set at room temperature of 25°C. In addition, it is inferred that if the temporal variation range of the "initial pH" and "time-dependent pH" in the "pH" of the lithium metal oxide mixed solution of the present invention is smaller, the temporal variation range of the "time-dependent pH" in the pH of the lithium metal oxide mixed solution after standing for more than one month from the date of production of the lithium metal oxide mixed solution of the present invention is also smaller.

Here, the pH of the lithium metal oxide mixed solution of the present invention is measured by immersing the electrode (HORIBA: Standard ToupH electrode 9615S-10D) of a pH meter (HORIBA: Glass electrode type hydrogen ion concentration indicator D-51) in the lithium metal oxide mixed solution of the present invention and confirming that the liquid temperature is stable at 25°C.

In addition, the lithium metal oxide mixed solution of the present invention may also contain compounds of Na, Mg, Al, Si, K, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Sn, Sr, Zr, Hf, Ba, La, Y, etc. as additives. Here, the compound may be, for example, oxides, metal acid alkali metal salts, metal acid alkali earth metal salts, chlorides, metal acid alkoxides, polymetallic oxoacid salts, etc. In addition, when the total molar number (mol) of each element as an additive is set as X, the molar ratio X/M of the total molar number (X) of each element as an additive to the total molar number (M) of niobium, tantalum, tungsten and tungsten is preferably 0.0002 to 0.8. Furthermore, the molar ratio X/M may be 0.01-0.5, 0.1-0.4, or 0.2-0.3. Furthermore, since the lithium metal oxide mixed solution of the present invention is a uniform solution, even if the compounds are in a suspended state, it is expected that the uniformity and reactivity (reactivity rate) can be improved. Furthermore, if the compounds are dissolved in the lithium metal oxide mixed solution of the present invention to form a uniform solution, the composite element can be in a state with the best reactivity.

Furthermore, the lithium metal oxide mixed solution of the present invention may also contain components other than components derived from niobium or niobium acid, tantalum or tantalum acid, molybdenum or molybdenum acid, tungsten or tungsten acid, components derived from ammonia, hydrogen peroxide and organic nitrides (referred to as "other components") within the range that does not hinder its effect. Examples of other components include: Na, Mg, Al, Si, K, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Sn, Sr, Zr, Hf, Ba, La, Y, etc. However, it is not limited to this. When the lithium metal oxide mixed solution of the present invention is set to 100% by mass, the content of other components is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. In addition, the lithium metal oxide mixed solution of the present invention is assumed to contain unintentionally added inevitable impurities. The content of the inevitable impurities is preferably 0.01 mass % or less.

The lithium metal oxide film of the present invention is characterized in that it contains salts of lithium metal oxide in the lithium metal oxide mixed solution of the present invention. The lithium metal oxide film of the present invention includes: a dried film obtained by applying the lithium metal oxide mixed solution of the present invention on the surface of a substrate and then vacuum drying; and a sintered film obtained by sintering the obtained dried film. In addition, the lithium metal oxide film of the present invention also includes lithium metal oxide films with different physical properties such as crystal structures generated by vacuum drying or sintering the lithium metal oxide mixed solution of the present invention. In addition, the method for manufacturing the lithium metal oxide film of the present invention is described below.

The lithium metal oxide mixed solution of the present invention is characterized in that it is used to coat the positive electrode for lithium ion secondary batteries. In addition to the results of the stability test of the mixed solution after standing at room temperature (25°C) for 1 month by visual observation and the dynamic light scattering method to measure the particle size (D50) of the particles in the mixed solution over time, the results of the film forming test of coating the mixed solution on a glass substrate as a substitute for the collector plate of the positive electrode for lithium ion secondary batteries and observing the coating state under an optical microscope show that the lithium metal oxide mixed solution of the present invention is suitable for coating the positive electrode for lithium ion secondary batteries or for coating the positive electrode material.

The positive electrode active material for lithium ion secondary battery of the present invention is characterized in that its surface is coated with the salt of lithium metal oxide contained in the lithium metal oxide mixed solution of the present invention. By observing the surface of the particles of the positive electrode active material for lithium ion secondary battery coated with the lithium metal oxide mixed solution of the present invention using a scanning electron microscope, it can be confirmed that the surface of the positive electrode active material is coated with the salt of lithium metal oxide. Furthermore, the coating amount of the salt of lithium metal oxide coating the surface of the positive electrode active material for lithium ion secondary battery of the present invention can be calculated by the following method: dissolving the positive electrode active material for lithium ion secondary battery in an appropriate amount of hydrofluoric acid, using inductively coupled plasma atomic emission spectrometry (AG-5110 manufactured by Agilent Technologies) in accordance with JIS K0116: 2014, measuring the mass fraction content of niobium, tungsten, molybdenum and tungsten of the salt of lithium metal oxide coating the particle surface of the positive electrode active material. Specifically, it is calculated as (the sum of the mass of niobium, tungsten, molybdenum and tungsten/the positive electrode active material coated on the surface) × 100. The amount of lithium metal oxide salt coating the surface of the positive electrode active material for the lithium ion secondary battery of the present invention can be expressed as a mass fraction content. The mass fraction content is preferably 0.001% to 5%. The mass fraction content can be 0.01% to 3%, or 0.1% to 1%.

The lithium ion secondary battery of the present invention is characterized in that it has a positive electrode coated with the positive electrode active material for lithium ion secondary batteries of the present invention. As described above, the positive electrode active material coated with the lithium metal oxide mixed solution of the present invention is suitable for coating the surface of the positive electrode for lithium ion secondary batteries. Therefore, by coating the positive electrode active material coated with the lithium metal oxide mixed solution of the present invention on the positive electrode surface, the performance of the lithium ion secondary battery can be improved.

The lithium metal oxide powder of the present invention is characterized in that it contains lithium metal oxide particles contained in the lithium metal oxide mixed solution of the present invention. The lithium metal oxide powder of the present invention includes: a dry powder obtained by vacuum drying the lithium metal oxide mixed solution of the present invention; and a calcined powder obtained by calcining the obtained dry powder. In addition, the lithium metal oxide powder of the present invention also includes lithium metal oxide powders with different physical properties such as crystal structures produced by vacuum drying or calcining the lithium metal oxide mixed solution of the present invention. In addition, the method for producing the lithium metal oxide powder of the present invention is described below.

The following is a description of the method for producing the lithium metal oxide mixed solution of the present invention.

The method for producing a lithium metal oxide mixed solution of the present invention is characterized in that it comprises the step of mixing two or more lithium metal oxide dispersions selected from the group consisting of niobium, tantalum, molybdenum, and tungsten. The two or more lithium metal oxide dispersions selected from the group consisting of niobium, tantalum, molybdenum, and tungsten generated by the methods for producing lithium metal oxide dispersions described below are weighed in a predetermined ratio, mixed, and stirred for 5 minutes to obtain the lithium metal oxide mixed solution of the present invention.

Furthermore, the method for producing a lithium metal oxide mixed solution of the present invention is characterized in that the lithium metal oxide dispersion is prepared by adding an acidic aqueous solution containing a metal selected from the group consisting of niobium, tungsten and tungsten to an alkaline aqueous solution to generate a precipitate slurry containing the metal, and by mixing the precipitate slurry, lithium hydroxide and pure water to generate the lithium metal oxide dispersion.

Here, the method for producing the lithium niobate dispersion among the lithium metal oxide dispersions used in the method for producing the lithium metal oxide mixed solution of the present invention is described below.

The method for preparing a lithium niobate dispersion comprises the following steps: a step of generating an acidic niobium solution containing niobium; a step of obtaining a precipitate slurry containing niobium by a reverse neutralization method of adding the acidic niobium solution to aqueous ammonia; and a step of obtaining a lithium niobate dispersion by stirring a mixture of the precipitate slurry containing niobium, lithium hydroxide and pure water while maintaining the mixture at 20°C to 100°C.

In the step of generating an acidic niobium solution containing niobium, the acidic niobium solution refers to an acidic niobium solution containing fluoride ions, which is obtained by dissolving niobium in an acidic solution containing hydrofluoric acid and performing solvent extraction.

Here, the acidic niobium solution containing fluoride ions, such as an aqueous niobium fluoride solution, is preferably adjusted to contain 1 to 100 g/L of niobium in terms of Nb ₂ O ₅ by adding water (e.g., pure water). At this time, if the niobium concentration is 1 g/L or more in terms of Nb ₂ O ₅ , it is preferably a niobium acid compound hydrate that is easily soluble in water. In consideration of productivity, it is more preferably 10 g/L or more, and even more preferably 20 g/L or more. On the other hand, if the niobium concentration is 100 g/ _{L or less in terms of Nb2O5 ,} it is preferably a niobium acid compound hydrate that is easily soluble in water. In order to synthesize a niobium acid compound hydrate that is easily and more reliably soluble in water, it is more preferably 90 g/L or less, more preferably 80 g/L or less, and particularly preferably 70 g/L or less. In addition, from the viewpoint of completely dissolving niobium or niobium oxide, the pH of the niobium fluoride aqueous solution is preferably 2 or less, and more preferably 1 or less.

Next, in the step of obtaining a niobium-containing precipitate slurry by a reverse neutralization method of adding the acidic niobium solution to aqueous ammonia (hereinafter referred to as the reverse neutralization step), it is preferred that the niobium-containing precipitate slurry be obtained by adding the acidic niobium solution containing fluoride ions to aqueous ammonia having a predetermined content, i.e., by a reverse neutralization method.

The ammonia content of the ammonia water used for reverse neutralization is preferably 10% to 30% by mass. If the ammonia content is 10% by mass, niobium is not easily incompletely dissolved, and niobium or niobium acid can be completely dissolved in water. On the other hand, if the ammonia content is less than 30% by mass, it is close to a saturated aqueous solution of ammonia, so it is better.

From the above viewpoints, the ammonia content of the ammonia water is preferably 10 mass % or more, more preferably 15 mass % or more, further preferably 20 mass % or more, and particularly preferably 25 mass % or more. On the other hand, the ammonia content is preferably 30 mass % or less, more preferably 29 mass % or less, and further preferably 28 mass % or less.

In the reverse neutralization step, the amount of the aqueous niobium fluoride solution added to the aqueous ammonia is preferably 95 to 500 in a molar ratio of NH ₃ /Nb ₂ O ₅ , more preferably 100 to 450, and even more preferably 110 to 400. Furthermore, the amount of the aqueous niobium fluoride solution added to the aqueous ammonia is preferably 3.0 to 3.0 in a molar ratio of NH ₃ /HF, more preferably 4.0 to 5.0, from the viewpoint of generating a niobium acid compound soluble in amine or dilute aqueous ammonia. On the other hand, from the viewpoint of reducing costs, the molar ratio of NH ₃ /HF is preferably 100 to 100, more preferably 50 to 50, and even more preferably 40 to 40.

In the reverse neutralization step, the time taken to add the niobium fluoride aqueous solution to the ammonia water is preferably within 1 minute, more preferably within 30 seconds, and even more preferably within 10 seconds. That is, the niobium fluoride aqueous solution is not added slowly over time, but is added to the ammonia water as quickly as possible, such as by adding it all at once, to allow the neutralization reaction to proceed. In addition, in the reverse neutralization step, the acidic niobium fluoride aqueous solution is added to the alkaline ammonia water, so the neutralization reaction can proceed while maintaining a high pH. In addition, the niobium fluoride aqueous solution and the ammonia water can be used directly at room temperature.

Furthermore, the method for producing a lithium niobate dispersion includes the step of removing fluoride ions from a niobium-containing precipitate obtained by a reverse neutralization method to obtain a niobium-containing precipitate from which fluoride ions have been removed. Fluorine compounds such as ammonium fluoride exist as impurities in the niobium-containing precipitate obtained by the reverse neutralization method, and it is preferred to remove them.

The removal method of fluorine compounds is arbitrary, for example, the following methods can be adopted: reverse osmosis filtration using ammonia water or pure water, ultrafiltration, microfiltration and other membrane filtration methods, centrifugal separation, and other known methods. In addition, when removing fluoride ions from the niobium-containing precipitate slurry, it is not necessary to specially adjust the temperature, and it can be carried out at room temperature.

Specifically, the niobium-containing precipitate slurry obtained by the reverse neutralization method is decanted using a centrifuge and repeatedly washed until the amount of free fluoride ions is less than 100 mg/L, thereby obtaining a niobium-containing precipitate from which fluoride ions have been removed.

The cleaning liquid used to remove fluoride ions is preferably ammonia water. Specifically, ammonia water with a mass% or less of 5.0% is preferred, ammonia water with a mass% or less of 4.0% is more preferred, ammonia water with a mass% or less of 3.0% is more preferred, and ammonia water with a mass% or less of 2.5% is particularly preferred. If ammonia water with a mass% or less of 5.0% is used, ammonia containing ammonium ions is appropriate relative to fluoride ions, and unnecessary cost can be avoided.

The niobium-containing precipitate from which fluoride ions have been removed is diluted with pure water or the like to obtain a niobium-containing precipitate slurry from which fluoride ions have been removed. The niobium content of the niobium-containing precipitate slurry is determined by collecting a portion of the slurry, drying it at 110°C for 24 hours, and then calcining it at 1,000°C for 4 hours to generate Nb ₂ O ₅ . The weight of the Nb ₂ O ₅ generated in this way is measured, and the niobium content of the slurry can be calculated from the weight.

Then, the mixture of the niobium-containing precipitate slurry from which fluoride ions have been removed and lithium hydroxide monohydrate is stirred while being kept at 50° C. to 100° C., thereby obtaining a lithium niobate dispersion.

Specifically, the obtained niobium-containing precipitate slurry is mixed with lithium hydroxide monohydrate in such a manner that the niobium content of the final mixture is 0.001 mass % to 20 mass % in terms of Nb and the molar ratio of lithium to niobium Li/Nb is 0.8 to 2.0, thereby obtaining a translucent white slurry. While stirring the translucent white slurry, the liquid temperature is maintained at 50°C to 100°C (e.g., 70°C) for 1 hour to 24 hours, thereby obtaining a colorless and transparent lithium niobate dispersion. Furthermore, the obtained lithium niobate dispersion may be cooled to room temperature. In addition, in order to remove the ammonia component contained in the obtained lithium niobate dispersion, the following concentration adjustment step may be performed. In the concentration adjustment step, the evaporated solvent (pure water, etc.) is added at, for example, 60°C to 90°C, and the mixture is heated and stirred for 1 hour to 100 hours, and then cooled to room temperature. Alternatively, the mixture is heated and stirred for 1 hour to 100 hours at 60°C to 90°C, and then cooled to room temperature. Thereafter, a solvent (pure water, etc.) is added to replenish the evaporated solvent (pure water, etc.). The amount of the solvent added is adjusted so that the niobium content of the lithium niobate dispersion after the removal of the ammonia component is consistent with the niobium content of the lithium niobate dispersion before the removal of the ammonia component.

In addition, pure water or an alkaline aqueous solution, such as aqueous ammonia, may be added to the mixture of the niobium-containing precipitate slurry and lithium hydroxide monohydrate and mixed. The ammonia content of the aqueous ammonia added to the mixture may be any content. For example, it may be 0.1 mass % to 30 mass %, or 10 mass % to 25 mass %.

From the viewpoint of stability, the pH of the lithium niobate dispersion obtained by the above production method is preferably 9 or more. Furthermore, the pH of the lithium niobate dispersion is more preferably 10 or more, further preferably 10.5 or more, and particularly preferably 11 or more.

Furthermore, the method for producing a lithium tantalum dispersion among the lithium metal oxide dispersions used in the method for producing a lithium metal oxide mixed solution of the present invention is described below.

The preparation method of the lithium tantalum dispersion comprises: a reaction step of adding hydrogen peroxide to a tantalum fluoride aqueous solution to generate a tantalum compound aqueous solution; a reverse neutralization step of adding the tantalum compound aqueous solution to an alkaline aqueous solution to generate a tantalum-containing precipitate; and a step of stirring a mixture of the generated tantalum-containing precipitate, lithium hydroxide and pure water while maintaining the mixture at 20°C to 100°C to obtain the lithium tantalum dispersion.

First, the tantalum fluoride aqueous solution can be prepared by reacting tantalum, tantalum oxide or tantalum hydroxide with fluoric acid (HF) such as hydrofluoric acid aqueous solution to form tantalum fluoride (H ₂ TaF ₇ ), and then dissolving the tantalum fluoride in water.

Here, the acidic tantalum solution containing fluoride ions, such as an aqueous tantalum fluoride solution, is preferably adjusted to contain 1 to 100 g/L of tantalum in terms of Ta ₂ O ₅ by adding water (e.g., pure water). At this time, if the tantalum concentration is 1 g/L or more in terms of Ta ₂ O ₅ , it is preferably a tantalum acid compound hydrate that is easily soluble in water. In consideration of productivity, it is more preferably 10 g/L or more, and even more preferably 20 g/L or more. On the other hand, if the tantalum concentration is 100 g/ _L or less in terms of _Ta2O5 , it is preferably a tantalum acid compound hydrate that is easily soluble in water. In order to more reliably synthesize a tantalum acid compound hydrate that is easily soluble in water, it is more preferably 90 g/L or less, more preferably 80 g/L or less, and particularly preferably 70 g/L or less. In addition, from the viewpoint of completely dissolving tantalum or tantalum oxide, the pH of the tantalum fluoride aqueous solution is preferably 2 or less, and more preferably 1 or less.

Next, in the reaction step of adding hydrogen peroxide to the tantalum fluoride aqueous solution to generate the tantalum compound aqueous solution, the hydrogen peroxide aqueous solution is added to the tantalum fluoride aqueous solution and mixed to obtain the tantalum compound aqueous solution. In addition, it is estimated that at least a portion of the obtained tantalum compound aqueous solution forms a peroxide complex.

Here, the hydrogen peroxide content of the hydrogen peroxide solution added to the tantalum fluoride aqueous solution is preferably 0.5 mass % to 35 mass %. In addition, the hydrogen peroxide is preferably added so that the molar ratio of hydrogen peroxide to tantalum H ₂ O ₂ /Ta is 0.6 to 1.5. Since hydrogen peroxide may decompose during mixing, it is more preferably 0.7 to 1.2.

In the reverse neutralization step of adding the obtained aqueous solution of the tantalum compound to an alkaline aqueous solution to generate a precipitate containing tantalum acid, the aqueous solution of the tantalum compound is added to an alkaline aqueous solution, such as ammonia water, i.e., a reverse neutralization method, to obtain a precipitate containing tantalum. Then, by removing fluoride ions from the obtained precipitate containing tantalum, a precipitate containing tantalum from which fluoride ions have been removed is obtained.

The ammonia content of the ammonia water used for reverse neutralization is preferably 10% to 30% by mass. If the ammonia content is 10% by mass, tantalum is not easily dissolved incompletely, and tantalum or tantalum acid can be completely dissolved in water. On the other hand, if the ammonia content is less than 30% by mass, it is close to a saturated aqueous solution of ammonia, so it is better.

From the above viewpoints, the ammonia content of the ammonia water is preferably 10 mass % or more, more preferably 15 mass % or more, further preferably 20 mass % or more, and particularly preferably 25 mass % or more. On the other hand, the ammonia content is preferably 30 mass % or less, more preferably 29 mass % or less, and further preferably 28 mass % or less.

In the reverse neutralization step, the amount of the tantalum fluoride aqueous solution added to the ammonia water is preferably 95 to 500 in the molar ratio of NH ₃ /Ta, more preferably 100 to 450, and even more preferably 110 to 400. Furthermore, the amount of the tantalum fluoride aqueous solution added to the ammonia water is preferably 3.0 to 3.0 in the molar ratio of NH ₃ /HF, more preferably 4.0 to 5.0, from the viewpoint of generating a tantalum acid compound soluble in amine or dilute ammonia water. On the other hand, from the viewpoint of reducing costs, the molar ratio of NH ₃ /HF is preferably 100 to 100, more preferably 50 to 100, and even more preferably 40 to 100.

In the reverse neutralization step, the time taken for the tantalum fluoride aqueous solution to be added to the ammonia water is preferably within 10 minutes, more preferably within 8 minutes, and even more preferably within 5 minutes. That is, the tantalum fluoride aqueous solution is not added slowly over time, but is preferably added to the ammonia water in a short time as possible, such as by adding it all at once, so that it undergoes a neutralization reaction. In addition, in the reverse neutralization step, the acidic tantalum fluoride aqueous solution is added to the alkaline ammonia water, so that it can undergo a neutralization reaction while maintaining a high pH. In addition, the tantalum fluoride aqueous solution and the ammonia water can be used directly at room temperature.

Then, in the reverse neutralization step, fluoride ions are removed from the precipitated slurry containing tantalum obtained by the reverse neutralization method, thereby obtaining a precipitate containing tantalum from which fluoride ions are removed. Fluorine compounds such as ammonium fluoride exist as impurities in the precipitated slurry containing tantalum obtained by the reverse neutralization method, and it is preferred to remove them.

The removal method of fluorine compounds is arbitrary, for example, the following methods can be adopted: reverse osmosis filtration using ammonia water or pure water, ultrafiltration, microfiltration and other membrane filtration methods, centrifugal separation, and other known methods. In addition, when removing fluoride ions from a precipitated slurry containing tantalum, it is not necessary to specifically adjust the temperature, and it can be carried out at room temperature.

Specifically, the precipitate containing tantalum obtained by the reverse neutralization method is decanted using a centrifuge and repeatedly washed until the amount of free fluoride ions is less than 100 mg/L, thereby obtaining a precipitate containing tantalum from which fluoride ions have been removed. In addition, by repeatedly performing this washing, the hydrogen peroxide added in the reaction step is also removed.

The cleaning liquid used to remove fluoride ions is preferably ammonia water. Specifically, it is preferably 1 mass % to 35 mass % ammonia water. If it is the ammonia water, ammonia containing ammonium ions is appropriate relative to fluoride ions to avoid unnecessary cost increase.

The precipitate containing fluoride ions removed from the above reaction step and the reverse neutralization step is diluted with pure water or the like to obtain a precipitate slurry containing fluoride ions removed from the precipitate. Then, a mixture of the precipitate slurry containing fluoride ions removed from the precipitate, lithium hydroxide monohydrate of lithium hydroxide and pure water is stirred while being kept at 5°C to 100°C for 0.1 hour to 72 hours to obtain a lithium tantalum dispersion.

Specifically, the obtained tantalum-containing precipitate slurry, lithium hydroxide monohydrate and pure water are mixed and stirred so that the tantalum content of the final mixture is 0.001 mass % to 12 mass % in terms of Ta and the molar ratio of lithium to tantalum (Li/Ta) is 0.8 to 1.5, thereby obtaining a lithium tantalum dispersion. In addition, in order to remove the ammonia component contained in the obtained lithium tantalum dispersion, the following concentration adjustment step can also be performed. In the concentration adjustment step, while adding the evaporated part of the solvent (pure water, etc.) at, for example, 60°C to 90°C, the mixture is heated and stirred for 1 hour to 100 hours, and then cooled to room temperature. Or, heat and stir at 60℃~90℃ for 1 hour~100 hours, and then cool to room temperature. Then, add solvent (pure water, etc.) to replenish the evaporated solvent (pure water, etc.). The amount of solvent added is adjusted so that the tantalum content of the lithium tantalum dispersion after removing the ammonia component is consistent with the tantalum content of the lithium tantalum dispersion before removing the ammonia component.

The following is a description of a method for producing a lithium tungstate dispersion among the lithium metal oxide dispersions used in the method for producing a lithium metal oxide mixed solution of the present invention.

The method for preparing a lithium tungstate dispersion comprises the steps of stirring a mixture of ammonium secondary tungstate, lithium hydroxide and pure water while maintaining the mixture at 20°C to 100°C to obtain a lithium tungstate dispersion.

A mixture of ammonium secondary tungstate, lithium hydroxide monohydrate and pure water is stirred while being kept at 15°C to 100°C for 5 minutes to 1 hour to obtain a lithium tungstate dispersion. In addition, in order to remove the ammonia component contained in the obtained lithium tungstate dispersion, the following concentration adjustment step can also be performed. In the concentration adjustment step, while adding the evaporated solvent (pure water, etc.) at, for example, 60°C to 90°C, the mixture is heated and stirred for 1 hour to 100 hours, and then cooled to room temperature. Alternatively, the mixture is heated and stirred at 60°C to 90°C for 1 hour to 100 hours, and then cooled to room temperature. Afterwards, a solvent (pure water, etc.) is added to replenish the evaporated solvent (pure water, etc.). The amount of the solvent added is adjusted so that the tungsten content of the lithium tungstate dispersion after the removal of the ammonia component is the same as the tungsten content of the lithium tungstate dispersion before the removal of the ammonia component.

As another example of a method for producing a lithium tungstate dispersion, there can be cited a method comprising the following steps: a step of adding an acidic tungsten aqueous solution containing 1 to 100 g/L of tungsten in terms of WO ₃ to a 10 to 30 mass % ammonia aqueous solution to produce a tungsten-containing precipitate; a step of slurrying the tungsten-containing precipitate to obtain a tungsten-containing precipitate slurry, and adding an organic nitride thereto to produce a tungstate dispersion; and a step of adding lithium hydroxide and pure water to the tungstate dispersion to produce a lithium tungstate dispersion.

Specifically, in the step of adding an acidic tungsten aqueous solution containing 1-100 g/L of tungsten in terms of WO ₃ to a 10-30 mass % ammonia aqueous solution to generate a tungsten-containing precipitate, the acidic tungsten aqueous solution refers to an aqueous tungsten sulfate solution obtained by solvent extraction with a solution obtained by dissolving tungsten in an acidic aqueous solution containing sulfuric acid.

Here, the aqueous solution of tungsten sulfate is preferably adjusted to contain 1 to 100 g/L of tungsten in terms of WO ₃ by adding water (e.g., pure water). At this time, if the tungsten concentration is 1 g/L or more in terms of WO ₃ , it is preferably a tungsten acid compound hydrate that is easily soluble in water. In consideration of productivity, it is more preferably 10 g/L or more, and more preferably 20 g/L or more. On the other hand, if the tungsten concentration is 100 g/L or less in terms of WO ₃ , it is preferably a tungsten acid compound hydrate that is easily soluble in water. In order to synthesize a tungsten acid compound hydrate that is easily and more reliably soluble in water, it is more preferably 90 g/L or less, more preferably 80 g/L or less, and particularly preferably 70 g/L or less. Furthermore, from the viewpoint of completely dissolving tungsten or tungsten oxide, the pH of the aqueous solution of tungsten sulfate is preferably 2 or less, more preferably 1 or less.

When adding the aqueous tungsten sulfate solution to the aqueous ammonia solution, in the so-called reverse neutralization method, preferably, the aqueous tungsten sulfate solution is added to a 10% to 30% by mass ammonia solution, i.e., the reverse neutralization method, to obtain a slurry of a tungsten acid compound hydrate, i.e., a slurry of a tungsten-containing precipitate.

The ammonia content of the ammonia solution used for reverse neutralization is preferably 10 mass% to 30 mass%. If the ammonia content is 10 mass%, tungsten is not easily incompletely dissolved, and tungsten or tungsten oxide can be completely dissolved in water. On the other hand, if the ammonia content is less than 30 mass%, it is close to a saturated aqueous solution of ammonia, so it is better.

From the above viewpoints, the ammonia content of the aqueous ammonia solution is preferably 10 mass % or more, more preferably 15 mass % or more, further preferably 20 mass % or more, and particularly preferably 25 mass % or more. On the other hand, the ammonia content is preferably 30 mass % or less, more preferably 29 mass % or less, and further preferably 28 mass % or less.

In the reverse neutralization, the amount of the aqueous tungsten sulfate solution added to the ammonia water is preferably 0.1 or more and 300 or less in the molar ratio of NH ₃ /WO ₃ , more preferably 5 or more and 200 or less. Furthermore, the aqueous tungsten sulfate solution added to the ammonia water is preferably 3.0 or more, more preferably 10.0 or more, and even more preferably 20.0 or more in the molar ratio of NH ₃ /SO ₄ ^2- , from the viewpoint of generating a tungstate compound soluble in amine or dilute ammonia water. On the other hand, from the viewpoint of reducing the cost, the molar ratio of NH ₃ /SO ₄ ^2- is preferably 200 or less, more preferably 150 or less, and even more preferably 100 or less.

In the reverse neutralization, the time taken for the tungsten sulfate aqueous solution to be added to the ammonia water is preferably within 1 minute, more preferably within 30 seconds, and even more preferably within 10 seconds. That is, instead of slowly adding the tungsten sulfate aqueous solution, it is suitable to add it to the ammonia water as soon as possible, such as by putting it in all at once, so as to make it undergo a neutralization reaction. In the reverse neutralization, the acidic tungsten sulfate aqueous solution is added to the alkaline ammonia water, so that it can undergo a neutralization reaction while maintaining a high pH. In addition, the tungsten sulfate aqueous solution and the ammonia water can be used directly at room temperature.

Then, the sulfur component is removed from the slurry of the tungsten-containing precipitate obtained by the reverse neutralization method to generate a tungsten-containing precipitate from which the sulfur component is removed. The slurry of the tungsten-containing precipitate obtained by the reverse neutralization method contains sulfur components such as sulfuric acid ions and hydrogen sulfate ions that remain without reacting with tungsten or tungsten oxide as impurities, so it is preferred to remove them.

The sulfur component can be removed by any method, for example, reverse osmosis filtration using ammonia water or pure water, ultrafiltration, microfiltration, or other membrane filtration methods, centrifugal separation, or other known methods. In addition, when removing the sulfur component from the slurry of the tungsten-containing precipitate, it is not necessary to adjust the temperature in particular, and it can be carried out at room temperature.

Specifically, the tungsten-containing precipitate obtained by the reverse neutralization method was decanted using a centrifuge and repeatedly washed until the conductivity of the tungsten-containing precipitate was 500 μS/cm or less, thereby obtaining a tungsten-containing precipitate from which the sulfur component was removed. The conductivity was obtained by adjusting the liquid temperature of the tungsten-containing precipitate to 25°C, immersing the measuring part of a conductivity meter (AS ONE: ASCON2) in the supernatant of the precipitate slurry, and reading the value of the conductivity after the value of the conductivity stabilized.

The cleaning liquid used to remove the sulfur component is preferably ammonia water. Specifically, ammonia water with a mass% or less of 5.0% is preferred, ammonia water with a mass% or less of 4.0% is more preferred, ammonia water with a mass% or less of 3.0% is more preferred, and ammonia water with a mass% or less of 2.5% is particularly preferred. If ammonia water with a mass% or less of 5.0% is used, the ammonia containing ammonium ions is appropriate relative to the sulfur component, and unnecessary cost increase can be avoided.

Next, in the step of making the tungsten-containing precipitate into a slurry to obtain a tungsten-containing precipitate slurry, and adding an organic nitride thereto to generate a tungsten acid dispersion, as described above, the tungsten-containing precipitate slurry is prepared by diluting the tungsten-containing precipitate from which the sulfur component has been removed with pure water or the like to form a slurry. In addition, the tungsten content of the tungsten-containing precipitate slurry from which the sulfur component has been removed is obtained by collecting a portion of the slurry, drying it at 110°C for 24 hours, and then calcining it at 1,000°C for 4 hours to generate WO ₃ . The weight of the WO ₃ generated in this manner is measured, and the tungsten content of the slurry can be calculated from the weight.

Then, the organic nitride is mixed with the tungsten-containing precipitate slurry from which the sulfur component has been removed, thereby obtaining a tungsten acid dispersion.

Specifically, the obtained tungsten-containing precipitate slurry is added with an organic nitride and mixed with pure water in such a manner that the tungsten content of the final mixture becomes 0.1 mass % to 40 mass % in terms of WO ₃ , and the mixture is stirred while the liquid temperature is maintained at room temperature (25° C.) for 1 hour, thereby obtaining a colorless and transparent tungsten acid dispersion.

The organic nitride mixed with the tungsten-containing sedimentation slurry is preferably an aliphatic amine and/or quaternary ammonium.

Here, from the viewpoint of solubility, the aliphatic amine is preferably mixed so that the aliphatic amine content in the tungsten-containing sedimentation slurry is 40 mass % or less, more preferably 0.1 mass % to 30 mass %, further preferably 0.5 mass % to 20 mass %, particularly preferably 1 mass % to 10 mass %. In addition, the aliphatic amine is more preferably methylamine, dimethylamine, ethylamine, trimethylamine, or a mixture thereof.

On the other hand, from the viewpoint of solubility, the quaternary ammonium is preferably mixed in such a manner that the content of the quaternary ammonium in the tungsten-containing sedimentation slurry is 40 mass % or less, more preferably 0.1 mass % or more and 30 mass % or less, further preferably 0.5 mass % or more and 20 mass % or less, and particularly preferably 1 mass % or more and 10 mass % or less. In addition, the quaternary ammonium is more preferably tetramethylammonium hydroxide (TMAH) or tetraethylammonium hydroxide (TEAH).

Furthermore, the organic nitride mixed with the tungsten-containing sedimentation slurry may not be any one of aliphatic amines and quaternary ammonium, but may be a mixture of two or more organic nitrides. For example, two or more organic nitrides such as methylamine and tetramethylammonium hydroxide (TMAH), dimethylamine and tetramethylammonium hydroxide (TMAH), methylamine and dimethylamine may be mixed; three or more organic nitrides such as methylamine, dimethylamine and tetramethylammonium hydroxide (TMAH) may be mixed. The organic nitrides may be appropriately changed depending on the application.

The tungstate dispersion, lithium hydroxide monohydrate and pure water produced in this manner are weighed so that the molar ratio Li/W of lithium to tungsten in the final mixture is 0.2 or more and 20 or less, and the mixture is kept at 10° C. to 100° C. for 1 minute to 3 days while being stirred, thereby obtaining a lithium tungstate dispersion.

Specifically, a tungsten acid dispersion, lithium hydroxide monohydrate and pure water are mixed and stirred so that the tungsten content of the final mixture is 0.001 mass % to 23 mass % in terms of W and the molar ratio of lithium to tungsten Li/W is 0.001 to 5, thereby obtaining a lithium tungstate dispersion. In addition, in order to remove the ammonia component contained in the obtained lithium tungstate dispersion, the following concentration adjustment step can also be performed. In the concentration adjustment step, while adding the evaporated solvent (pure water, etc.) at, for example, 60°C to 90°C, the mixture is heated and stirred for 1 hour to 100 hours, and then cooled to room temperature. Or, heat and stir at 60℃~90℃ for 1 hour~100 hours, and then cool to room temperature. Then, add solvent (pure water, etc.) to replenish the evaporated solvent (pure water, etc.). The amount of solvent added is adjusted so that the tungsten content of the lithium tungstate dispersion after removing the ammonia component is consistent with the tungsten content of the lithium tungstate dispersion before removing the ammonia component.

Furthermore, the lithium molybdate dispersion in each lithium metal oxide dispersion used in the method for producing a lithium metal oxide mixed solution of the present invention may be a lithium molybdate dispersion obtained by dissolving commercially available lithium molybdate in pure water.

Specifically, lithium molybdate and pure water are mixed so that the molybdenum content of the final mixture is 0.001 mass % or more and 22 mass % or less in terms of Mo and the molar ratio of lithium to molybdenum Li/Mo is 0.001 or more and 5 or less, and the mixture is stirred while the liquid temperature is maintained at 25° C. for 1 hour to obtain a lithium molybdate dispersion. In addition, lithium hydroxide may be added when lithium molybdate and pure water are mixed. Furthermore, in order to remove the ammonia component contained in the obtained lithium molybdate dispersion, the following concentration adjustment step may be performed. In the concentration adjustment step, the evaporated solvent (pure water, etc.) is added at, for example, 60°C to 90°C, and the mixture is heated and stirred for 1 hour to 100 hours, and then cooled to room temperature. Alternatively, the mixture is heated and stirred at 60°C to 90°C for 1 hour to 100 hours, and then cooled to room temperature. Thereafter, a solvent (pure water, etc.) is added to replenish the evaporated solvent (pure water, etc.). The amount of the solvent added is adjusted so that the molybdenum content of the lithium molybdate dispersion after the removal of the ammonia component is consistent with the molybdenum content of the lithium molybdate dispersion before the removal of the ammonia component.

Two or more lithium metal oxide dispersions among the lithium niobate dispersion, lithium tantalum dispersion, lithium molybdate dispersion and lithium tungstate dispersion generated by the above-mentioned production method are weighed in a predetermined ratio, mixed, and stirred at 15° C. to 100° C. for 1 minute to 1 hour to obtain the lithium metal oxide mixed solution of the present invention.

The method for producing a lithium metal oxide film of the present invention is characterized in that the lithium metal oxide mixed solution of the present invention is applied to a substrate and then dried and/or sintered. The lithium metal oxide mixed solution of the present invention used in the method for producing a lithium metal oxide film of the present invention may also be generated by the method for producing a lithium metal oxide mixed solution of the present invention.

Among the lithium metal oxide films, the manufacturing method of the lithium metal oxide dry film includes: a coating step, coating a lithium metal oxide mixed solution on the surface of a substrate; and a film drying step, drying the lithium metal oxide mixed solution coated on the surface of the substrate to obtain a dry film.

Specifically, the lithium metal oxide mixed solution obtained by the method for producing the lithium metal oxide mixed solution of the present invention is filtered through a filter with a pore size of 0.22 μm as required, and then dripped onto the surface of the substrate using a syringe, and then applied by spin coating (700 rpm, 10 seconds; then 1500 rpm, 15 seconds). Then, it is dried at 110° C. for 30 minutes to form a lithium metal oxide dry film on the surface of the substrate.

Among lithium metal oxide films, a method for manufacturing a lithium metal oxide sintered film includes: a coating step, coating a lithium metal oxide mixed solution on a substrate surface; a film drying step, drying the lithium metal oxide mixed solution coated on the substrate surface to obtain a dry film; and a film sintering step, sintering the dry film in the atmosphere at a sintering temperature of 300°C to 1,200°C and a sintering time of 1 hour to 12 hours to obtain a sintered film.

Specifically, as described above, a lithium metal oxide mixed liquid is applied to the surface of a substrate and dried, and the substrate on which a lithium metal oxide dry film is formed is placed in a static furnace and fired at a firing temperature of 300°C to 1,200°C for a firing time of 1 hour to 12 hours in the atmosphere, thereby forming a lithium metal oxide fired film on the surface of the substrate.

The method for producing lithium metal oxide powder of the present invention is characterized in that the lithium metal oxide mixed solution of the present invention is dried and/or calcined. The lithium metal oxide mixed solution of the present invention used in the method for producing lithium metal oxide powder of the present invention may also be produced by the method for producing lithium metal oxide mixed solution of the present invention.

Among the lithium metal oxide powders, a method for producing a lithium metal oxide dry powder is to place a lithium metal oxide mixed solution obtained by the method for producing a lithium metal oxide mixed solution of the present invention in a static furnace and perform vacuum drying at a heating temperature of about 60°C to 200°C for 1 hour to 72 hours, thereby evaporating the water in the lithium metal oxide mixed solution of the present invention, and obtaining a lithium metal oxide dry powder containing crystal particles of a lithium metal oxide salt contained in the lithium metal oxide mixed solution of the present invention.

On the other hand, the method for producing the lithium metal oxide sintered powder is as described above, wherein the lithium metal oxide mixed solution of the present invention is vacuum dried to obtain the lithium metal oxide dry powder, which is placed in a static furnace and sintered under atmosphere at a sintering temperature of 300°C to 1,200°C for a sintering time of 1 hour to 72 hours to obtain the lithium metal oxide sintered powder.

Furthermore, the lithium metal oxide dry powder and the calcined powder obtained by pulverizing the above-mentioned lithium metal oxide can also be used as lithium metal oxide powder. Moreover, regardless of whether or not the above-mentioned lithium metal oxide dry powder and the calcined powder are pulverized, the part below the sieve (the fine particle side) obtained by classifying the above-mentioned lithium metal oxide dry powder and the calcined powder by a sieve or the like can be used as lithium metal oxide powder. The part above the sieve (the coarse particle side) can also be pulverized again and classified before use. Furthermore, a vibrating sieve can be used for pulverization and classification at the same time, and iron balls coated with nylon or fluororesin are put into the vibrating sieve as a pulverization medium. By performing classification and pulverization at the same time in this way, even excessive lithium metal oxide powder can be removed. Specifically, when using a sieve for classification, it is preferred to use a pore size of 150μm-1,000μm. If the particle size is 150 μm-1,000 μm, the portion above the sieve will not be excessive and does not need to be repeatedly crushed. Also, the portion below the sieve that needs to be crushed again does not need to be classified.

The lithium metal oxide powder obtained in this way is mixed with water or an organic solvent as a dispersion medium, and wet-pulverized using a medium such as beads, thereby obtaining a lithium metal oxide powder dispersion. Here, the organic solvent used as the dispersion medium can be, for example, alcohols, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, ethers, and mixed solvents thereof. Furthermore, in order to improve the film-forming properties of the lithium metal oxide film using the lithium metal oxide powder dispersion, a binder such as a resin component can also be added. The resin component used as a binder can be, for example, acrylic resin, polyurethane, epoxy resin, polystyrene, polycarbonate, glycol resin, cellulose resin, and mixed resins and copolymer resins thereof.

Furthermore, the following describes a method for producing a positive electrode active material for a lithium ion secondary battery coated with the lithium metal oxide mixed solution of the present invention.

The method for producing a positive electrode active material for a lithium ion secondary battery coated with the lithium metal oxide mixed solution of the present invention comprises: mixing the lithium metal oxide mixed solution of the present invention, a positive electrode active material and an aqueous lithium hydroxide solution added as required to generate a positive electrode active material slurry for a battery containing lithium metal oxide; and drying the positive electrode active material slurry for a battery containing lithium metal oxide.

First, a positive electrode active material for a battery, such as LiMn ₂ O ₄ (Merck: spinel type, particle size <0.5 μm) is added to the lithium metal oxide mixed solution of the present invention after diluting the lithium metal oxide mixed solution with pure water to obtain a slurry containing lithium metal oxide. Then, the slurry containing lithium metal oxide is dripped into a lithium hydroxide aqueous solution while being stirred and maintained at 90°C for 10 minutes to generate a positive electrode active material slurry containing lithium metal oxide for a battery.

As the positive _electrode active material for _the battery, in addition to the above-mentioned _{LiMn2O4 ,} LiCoO2, _LiNiO2 , _LiFeO2 , _Li2MnO3 , _{LiFePO4 , LiCoPO4 , LiNiPO4 , LiMnPO4} , _{LiNi0.5Mn1.5O4} , _{LiMn1 / 3Co1} /3Ni1/3O2, LiCo0.2Ni0.4Mn0.4O2 _{, lithium} molybdate, _{LiMnO4 , LiNi0.8Co0.15Al0.05O2} , _LiMnO2 and _the like _{can be used} .

Next, the positive electrode active material slurry containing lithium metal oxide is dried in an atmospheric drying furnace for 15 hours while maintaining the temperature in the furnace at 110°C, thereby producing a positive electrode active material for a lithium ion secondary battery coated with lithium metal oxide.

Although the lithium metal oxide mixed solution of the present invention is used in the positive electrode active material for lithium ion secondary battery coated with the above-mentioned lithium metal oxide mixed solution, dry powder obtained by drying the lithium metal oxide mixed solution of the present invention, or calcined powder obtained by drying and calcining the lithium metal oxide mixed solution of the present invention and dispersing it in a dispersion medium may also be used.

In addition, although the above-mentioned method for manufacturing a positive electrode active material for lithium-ion secondary batteries involves adding a positive electrode active material for a battery, it may be appropriately changed depending on the application. For example, a dispersant, a pH adjuster, a colorant, a thickener, a wetting agent, a binder resin, etc. may also be added.

Thus, by coating the surface of the positive electrode active material particles for lithium ion secondary batteries with the lithium metal oxide mixed solution of the present invention, the interface resistance between the positive electrode of the lithium ion secondary battery and the electrolyte of the positive electrode active material particles of the secondary battery can be reduced.

In addition, in this manual, when "X~Y" (X and Y are arbitrary numbers) is expressed, unless otherwise specified, it includes the meaning of "above X and below Y", and also includes the meaning of "preferably greater than X" or "preferably less than Y". In addition, when "above X" (X is an arbitrary number) or "below Y" (Y is an arbitrary number) is expressed, it also includes the meaning of "preferably greater than X" or "preferably less than Y".

The lithium metal oxide mixed solution of the present invention has high dispersibility in polar solvents, especially in water, good solubility in water, and excellent storage stability.

The lithium metal oxide mixed solution of the embodiment of the present invention is further described by the following examples. However, the following examples are not intended to limit the present invention.

The lithium niobate dispersion, lithium tantalum dispersion, lithium molybdenum dispersion and lithium tungstate dispersion used in the following examples are produced by the above-mentioned methods for producing the lithium metal oxide dispersions.

The physical properties of each lithium metal oxide dispersion produced by the above-mentioned method for producing each lithium metal oxide dispersion are as follows.

The niobium content in the lithium niobate dispersion is 0.60 mol/L when converted to Nb, the lithium content is 0.62 mol/L, and the density is 1069 g/L. The niobium content in the lithium tantalum dispersion is 0.24 mol/L when converted to Ta, the lithium content is 0.23 mol/L, and the density is 1048 g/L. The molybdenum content in the lithium molybdenum dispersion is 0.29 mol/L when converted to Mo, the lithium content is 0.58 mol/L, and the density is 1035 g/L. The tungsten content in the lithium tungstate dispersion is 0.22 mol/L when converted to W, the lithium content is 0.43 mol/L, and the density is 1042 g/L.

(Example 1) 6.39 g of lithium niobate dispersion and 1.72 g of lithium tirbate dispersion were weighed and placed in a polypropylene container so that the molar ratio of niobium in the lithium niobate dispersion was 0.9:0.1. Then, 22.38 g of pure water was added to the polypropylene container so that the total content of niobium and tirbium in the final mixed solution was 0.133 mol/L, and the mixture was mixed and stirred for 5 minutes to obtain the lithium metal oxide mixed solution of Example 1.

In 30.49 g of the lithium metal oxide mixed solution of Example 1, the niobium content in the lithium metal oxide mixed solution calculated as Nb was 1.097 mass % (0.334 g, 0.120 mol/L), the tantalum content in the lithium metal oxide mixed solution calculated as Ta was 0.237 mass % (0.072 g, 0.013 mol/L), and the total content of niobium and tantalum in metal conversion was 1.334 mass % (0.407 g, 0.133 mol/L). In addition, the lithium content in the lithium metal oxide mixed solution calculated as Li was 0.091 mass % (0.091 g, 0.133 mol/L). Then, the lithium metal oxide mixed solution of Example 1 has a molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution of 0.9. Moreover, the molar ratio Ta/M of tantalum (Ta) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution is 0.1. Furthermore, the molar ratio Li/M of lithium (Li) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution is 1.0.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 1 was 11.6, and the pH after time was 11.5.

(Example 2) In Example 2, 3.55 g of lithium niobate dispersion and 8.58 g of lithium tidate dispersion were weighed and placed in a polypropylene container so that the molar ratio of niobium in the lithium niobate dispersion and the molar ratio of tibidium in the lithium tibidium dispersion was 0.5:0.5. Then, 18.5 g of pure water was added to the polypropylene container so that the total content of niobium and tibidium in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 2.

In 30.63 g of the lithium metal oxide mixed solution of Example 2, the niobium content in the lithium metal oxide mixed solution calculated as Nb was 0.607 mass % (0.186 g, 0.067 mol/L), the tantalum content in the lithium metal oxide mixed solution calculated as Ta was 1.182 mass % (0.362 g, 0.067 mol/L), and the total content of niobium and tantalum in metal conversion was 1.788 mass % (0.548 g, 0.133 mol/L). In addition, the lithium content in the lithium metal oxide mixed solution calculated as Li was 0.091 mass % (0.091 g, 0.133 mol/L). Then, the lithium metal oxide mixed solution of Example 2 has a molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution of 0.5. Also, a molar ratio Ta/M of tantalum (Ta) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution is 0.5. Furthermore, a molar ratio Li/M of lithium (Li) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution is 1.0.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 2 was 12.1, and the pH after time was 12.2.

(Example 3) In Example 3, 0.71 g of lithium niobate dispersion and 15.44 g of lithium tantalum dispersion were weighed and placed in a polypropylene container so that the molar ratio of niobium in the lithium niobate dispersion to the molar ratio of tantalum in the lithium tantalum dispersion was 0.1:0.9. Then, 14.61 g of pure water was added to the polypropylene container so that the total content of niobium and tantalum in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 3.

In 30.76 g of the lithium metal oxide mixed solution of Example 3, the niobium content in the lithium metal oxide mixed solution calculated as Nb was 0.121 mass % (0.037 g, 0.013 mol/L), the tantalum content in the lithium metal oxide mixed solution calculated as Ta was 2.118 mass % (0.651 g, 0.120 mol/L), and the total content of niobium and tantalum in metal conversion was 2.239 mass % (0.689 g, 0.133 mol/L). In addition, the lithium content in the lithium metal oxide mixed solution calculated as Li was 0.090 mass % (0.028 g, 0.133 mol/L). Then, the lithium metal oxide mixed solution of Example 3 has a molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution of 0.1. Moreover, the molar ratio Ta/M of tantalum (Ta) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution is 0.9. Furthermore, the molar ratio Li/M of lithium (Li) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution is 1.0.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 3 was 12.3, and the pH after time was 12.3.

(Example 4) In Example 4, 6.39 g of lithium niobate dispersion and 1.42 g of lithium molybdate dispersion were weighed and placed in a polypropylene container so that the molar ratio of niobium in the lithium niobate dispersion to molybdenum in the lithium molybdate dispersion was 0.9:0.1. Then, 22.65 g of pure water was added to the polypropylene container so that the total content of niobium and molybdenum in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 4.

In 30.46 g of the lithium metal oxide mixed solution of Example 4, the content of niobium in the lithium metal oxide mixed solution converted to Nb was 1.098 mass % (0.334 g, 0.120 mol/L), the content of molybdenum in the lithium metal oxide mixed solution converted to Mo was 0.126 mass % (0.038 g, 0.013 mol/L), and the total content of niobium and molybdenum in metal conversion was 1.224 mass % (0.373 g, 0.133 mol/L). In addition, the content of lithium in the lithium metal oxide mixed solution converted to Li was 0.100 mass % (0.031 g, 0.147 mol/L). Then, the molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium and molybdenum in the lithium metal oxide mixed solution contained in Example 4 is 0.9. In addition, the molar ratio Mo/M of molybdenum (Mo) to the total content (M) of niobium and molybdenum in the lithium metal oxide mixed solution is 0.1. Furthermore, the molar ratio Li/M of lithium (Li) to the total content (M) of niobium and molybdenum in the lithium metal oxide mixed solution is 1.10.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 4 was 11.2, and the pH after time was 11.3.

(Example 5) In Example 5, 6.39 g of lithium niobate dispersion and 1.87 g of lithium tungstate dispersion were weighed and placed in a polypropylene container so that the molar ratio of niobium in the lithium niobate dispersion and tungsten in the lithium tungstate dispersion was 0.9:0.1. Then, 22.23 g of pure water was added to the polypropylene container so that the total content of niobium and tungsten in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 5.

In 30.49 g of the lithium metal oxide mixed solution of Example 5, the niobium content in the lithium metal oxide mixed solution calculated as Nb was 1.097 mass % (0.334 g, 0.120 mol/L), the tungsten content in the lithium metal oxide mixed solution calculated as W was 0.241 mass % (0.074 g, 0.013 mol/L), and the total content of niobium and tungsten in metal conversion was 1.338 mass % (0.408 g, 0.133 mol/L). In addition, the lithium content in the lithium metal oxide mixed solution calculated as Li was 0.100 mass % (0.031 g, 0.147 mol/L). Then, the molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium and tungsten in the lithium metal oxide mixed solution of Example 5 is 0.9. In addition, the molar ratio W/M of tungsten (W) to the total content (M) of niobium and tungsten in the lithium metal oxide mixed solution is 0.1. Furthermore, the molar ratio Li/M of lithium (Li) to the total content (M) of niobium and tungsten in the lithium metal oxide mixed solution is 1.10.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 5 was 11.3, and the pH after time was 11.2.

(Example 6) In Example 6, 15.44 g of lithium tantalum dispersion and 1.42 g of lithium molybdenum dispersion were weighed and placed in a polypropylene container so that the molar ratio of tantalum in the lithium tantalum dispersion to molybdenum in the lithium molybdenum dispersion was 0.9:0.1. Then, 13.9 g of pure water was added to the polypropylene container so that the total content of tantalum and molybdenum in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 6.

In 30.76 g of the lithium metal oxide mixed solution of Example 6, the content of tantalum calculated as Ta in the lithium metal oxide mixed solution was 2.118 mass % (0.651 g, 0.120 mol/L), the content of molybdenum calculated as Mo was 0.125 mass % (0.038 g, 0.013 mol/L), and the total content of tantalum and molybdenum was 2.242 mass % (0.690 g, 0.133 mol/L) in terms of metal conversion. In addition, the content of lithium calculated as Li in the lithium metal oxide mixed solution was 0.099 mass % (0.031 g, 0.147 mol/L). Then, the lithium metal oxide mixed solution of Example 6 has a molar ratio Ta/M of tantalum (Ta) to the total content (M) of tantalum and molybdenum in the lithium metal oxide mixed solution of 0.9. Moreover, the molar ratio Mo/M of molybdenum (Mo) to the total content (M) of tantalum and molybdenum in the lithium metal oxide mixed solution is 0.1. Furthermore, the molar ratio Li/M of lithium (Li) to the total content (M) of tantalum and molybdenum in the lithium metal oxide mixed solution is 1.10.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 6 was 12.0, and the pH after time was 12.0.

(Example 7) In Example 7, 15.44 g of lithium tantalum dispersion and 1.87 g of lithium tantalum dispersion were weighed and placed in a polypropylene container so that the molar ratio of tantalum in the lithium tantalum dispersion to the molar ratio of tungsten in the lithium tungstate dispersion was 0.9:0.1. Then, 13.48 g of pure water was added to the polypropylene container so that the total content of tantalum and tungsten in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 7.

In 30.79 g of the lithium metal oxide mixed solution of Example 7, the content of tungsten in the lithium metal oxide mixed solution calculated as Ta was 2.116 mass % (0.651 g, 0.120 mol/L), the content of tungsten in the lithium metal oxide mixed solution calculated as W was 0.239 mass % (0.074 g, 0.013 mol/L), and the total content of tungsten and tungsten in metal conversion was 2.355 mass % (0.725 g, 0.133 mol/L). In addition, the content of lithium in the lithium metal oxide mixed solution calculated as Li was 0.099 mass % (0.031 g, 0.147 mol/L). Then, the molar ratio Ta/M of tungsten (Ta) to the total content (M) of tungsten and tungsten in the lithium metal oxide mixed solution of Example 7 is 0.9. In addition, the molar ratio W/M of tungsten (W) to the total content (M) of tungsten and tungsten in the lithium metal oxide mixed solution is 0.1. Furthermore, the molar ratio Li/M of lithium (Li) to the total content (M) of tungsten and tungsten in the lithium metal oxide mixed solution is 1.10.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 7 was 12.0, and the pH after time was 12.0.

(Example 8) In Example 8, 3.55 g of lithium niobate dispersion, 6.86 g of lithium niobate dispersion and 1.42 g of lithium molybdenum dispersion were weighed and placed in a polypropylene container so that the molar ratio of niobium in the lithium niobate dispersion, the molar ratio of tantalum in the lithium tantalum dispersion and the molar ratio of molybdenum in the lithium molybdenum dispersion was 0.5:0.4:0.1. Then, 18.76 g of pure water was added to the polypropylene container so that the total content of niobium, tantalum and molybdenum in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 8.

In 30.60 g of the lithium metal oxide mixed solution of Example 8, the niobium content in the lithium metal oxide mixed solution is 0.607 mass% (0.186 g, 0.067 mol/L) in terms of Nb, the tantalum content in the lithium metal oxide mixed solution is 0.946 mass% (0.290 g, 0.053 mol/L) in terms of Ta, the molybdenum content in the lithium metal oxide mixed solution is 0.125 mass% (0.038 g, 0.013 mol/L), and the total content of niobium, tantalum and molybdenum in terms of metal conversion is 1.679 mass% (0.514 g, 0.133 mol/L). In addition, the lithium content in the lithium metal oxide mixed solution is 0.100 mass% (0.031 g, 0.147 mol/L) in terms of Li. Then, the lithium metal oxide mixed solution of Example 8 has a molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium, tantalum and molybdenum in the lithium metal oxide mixed solution of 0.5. Moreover, the molar ratio Ta/M of tantalum (Ta) to the total content (M) of niobium, tantalum and molybdenum in the lithium metal oxide mixed solution is 0.4. Furthermore, the molar ratio Mo/M of molybdenum (Mo) to the total content (M) of niobium, tantalum and molybdenum in the lithium metal oxide mixed solution is 0.1. Furthermore, the molar ratio Li/M of lithium (Li) to the total content (M) of niobium, tantalum and molybdenum in the lithium metal oxide mixed solution is 1.10.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 8 was 11.7, and the pH after time was 11.8.

(Example 9) In Example 9, 3.55 g of lithium niobate dispersion, 6.86 g of lithium niobate dispersion and 1.87 g of lithium tungstate dispersion were weighed and placed in a polypropylene container so that the molar ratio of niobium in the lithium niobate dispersion, the molar ratio of tungsten in the lithium tungstate dispersion was 0.5:0.4:0.1. Then, 18.34 g of pure water was added to the polypropylene container so that the total content of niobium, tungsten and tungsten in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 9.

In 30.62 g of the lithium metal oxide mixed solution of Example 9, the niobium content in the lithium metal oxide mixed solution is 0.607 mass% (0.186 g, 0.067 mol/L) in terms of Nb, the tungsten content in terms of Ta is 0.945 mass% (0.290 g, 0.053 mol/L), the tungsten content in terms of W is 0.240 mass% (0.074 g, 0.013 mol/L), and the total content of niobium, tungsten and tungsten is 1.792 mass% (0.549 g, 0.133 mol/L) in terms of metal conversion. In addition, the lithium content in the lithium metal oxide mixed solution is 0.100 mass% (0.031 g, 0.147 mol/L) in terms of Li. Then, the lithium metal oxide mixed solution of Example 9 includes a molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium, tungsten and tungsten in the lithium metal oxide mixed solution of 0.5. Moreover, a molar ratio Ta/M of tungsten (Ta) to the total content (M) of niobium, tungsten and tungsten in the lithium metal oxide mixed solution is 0.4. Furthermore, a molar ratio W/M of tungsten (W) to the total content (M) of niobium, tungsten and tungsten in the lithium metal oxide mixed solution is 0.1. Furthermore, a molar ratio Li/M of lithium (Li) to the total content (M) of niobium, tungsten and tungsten in the lithium metal oxide mixed solution is 1.10.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 9 was 11.6, and the pH after time was 11.5.

(Example 10) In Example 10, 2.84 g (0.4 mol) of lithium niobate dispersion, 6.86 g (0.4 mol) of lithium niobate dispersion, 1.42 g (0.1 mol) of lithium molybdate dispersion and 1.87 g (0.1 mol) of lithium tungstate dispersion were weighed and placed in a polypropylene container so that the molar ratio of niobium in lithium niobate dispersion, molar ratio of tungsten in lithium tungstate dispersion was 0.4:0.4:0.1:0.1. Then, 17.63 g of pure water was added to the polypropylene container so that the total content of niobium, tantalum, molybdenum and tungsten in the final mixed solution became 0.133 mol/L. Otherwise, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 10.

In 30.62 g of the lithium metal oxide mixed solution of Example 10, the niobium content in the lithium metal oxide mixed solution converted by Nb was 0.485 mass % (0.149 g, 0.053 mol/L), the tantalum content converted by Ta was 0.945 mass % (0.290 g, 0.053 mol/L), the molybdenum content converted by Mo was 0.125 mass % (0.038 g, 0.013 mol/L), the tungsten content converted by W was 0.240 mass % (0.074 g, 0.013 mol/L), and the total content of niobium, tantalum, molybdenum and tungsten was 1.796 mass % (0.550 g, 0.133 mol/L) when converted by metal. In addition, the lithium content calculated as Li in the lithium metal oxide mixed solution is 0.109 mass % (0.033 g, 0.160 mol/L). Then, the molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium, tungsten, molybdenum and tungsten contained in the lithium metal oxide mixed solution of Example 10 is 0.4. In addition, the molar ratio Ta/M of tungsten (Ta) to the total content (M) of niobium, tungsten, molybdenum and tungsten in the lithium metal oxide mixed solution is 0.4. Furthermore, the molar ratio Mo/M of molybdenum (Mo) to the total content (M) of niobium, tungsten, molybdenum and tungsten in the lithium metal oxide mixed solution is 0.1. The molar ratio W/M of tungsten (W) to the total content (M) of niobium, tungsten, molybdenum and tungsten in the lithium metal oxide mixed solution is 0.1. Furthermore, the molar ratio Li/M of lithium (Li) to the total content (M) of niobium, tungsten, molybdenum and tungsten in the lithium metal oxide mixed solution is 1.20.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 10 was 11.6, and the pH after time was 11.6.

(Example 11) In Example 11, 0.36 g of lithium niobate dispersion and 0.86 g of lithium tidate dispersion were weighed and placed in a polypropylene container so that the molar ratio of niobium in the lithium niobate dispersion and the molar ratio of tibidium in the lithium tibidium dispersion was 0.5:0.5. Then, 28.85 g of pure water was added to the polypropylene container so that the total content of niobium and tibidium in the final mixed solution was 0.013 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 11.

In 30.06 g of the lithium metal oxide mixed solution of Example 11, the niobium content in the lithium metal oxide mixed solution calculated as Nb was 0.062 mass % (0.019 g, 0.007 mol/L), the tantalum content in the lithium metal oxide mixed solution calculated as Ta was 0.120 mass % (0.036 g, 0.007 mol/L), and the total content of niobium and tantalum in metal conversion was 0.182 mass % (0.055 g, 0.013 mol/L). In addition, the lithium content in the lithium metal oxide mixed solution calculated as Li was 0.009 mass % (0.003 g, 0.013 mol/L). Then, the lithium metal oxide mixed solution of Example 11 has a molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution of 0.5. Also, a molar ratio Ta/M of tantalum (Ta) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution is 0.5. Furthermore, a molar ratio Li/M of lithium (Li) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution is 1.0.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 11 was 11.1, and the pH after time was 11.0.

(Example 12) In Example 12, 3.55 g of lithium niobate dispersion and 7.09 g of lithium molybdate dispersion were weighed and placed in a polypropylene container so that the molar ratio of niobium in the lithium niobate dispersion and molybdenum in the lithium molybdate dispersion was 0.5:0.5. Then, 19.82 g of pure water was added to the polypropylene container so that the total content of niobium and molybdenum in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 12.

In 30.47 g of the lithium metal oxide mixed solution of Example 12, the content of niobium in the lithium metal oxide mixed solution converted to Nb was 0.610 mass % (0.186 g, 0.067 mol/L), the content of molybdenum in the lithium metal oxide mixed solution converted to Mo was 0.630 mass % (0.192 g, 0.067 mol/L), and the total content of niobium and molybdenum in metal conversion was 1.240 mass % (0.378 g, 0.133 mol/L). In addition, the content of lithium in the lithium metal oxide mixed solution converted to Li was 0.137 mass % (0.042 g, 0.200 mol/L). Then, the lithium metal oxide mixed solution of Example 12 has a molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium and molybdenum in the lithium metal oxide mixed solution of 0.5. Also, the molar ratio Mo/M of molybdenum (Mo) to the total content (M) of niobium and molybdenum in the lithium metal oxide mixed solution is 0.5. Furthermore, the molar ratio Li/M of lithium (Li) to the total content (M) of niobium and molybdenum in the lithium metal oxide mixed solution is 1.50.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 12 was 10.5, and the pH after time was 10.5.

(Example 13) In Example 13, 8.58 g of lithium tantalum dispersion and 7.09 g of lithium molybdenum dispersion were weighed and placed in a polypropylene container so that the molar ratio of tantalum in the lithium tantalum dispersion to molybdenum in the lithium molybdenum dispersion was 0.5:0.5. Then, 14.96 g of pure water was added to the polypropylene container so that the total content of tantalum and molybdenum in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 13.

In 30.64 g of the lithium metal oxide mixed solution of Example 13, the content of tantalum calculated as Ta in the lithium metal oxide mixed solution was 1.181 mass % (0.362 g, 0.067 mol/L), the content of molybdenum calculated as Mo was 0.626 mass % (0.192 g, 0.067 mol/L), and the total content of tantalum and molybdenum was 1.808 mass % (0.378 g, 0.133 mol/L) in terms of metal conversion. In addition, the content of lithium calculated as Li in the lithium metal oxide mixed solution was 0.137 mass % (0.042 g, 0.200 mol/L). Then, the lithium metal oxide mixed solution of Example 13 has a molar ratio Ta/M of tantalum (Ta) to the total content (M) of tantalum and molybdenum in the lithium metal oxide mixed solution of 0.5. Also, the molar ratio Mo/M of molybdenum (Mo) to the total content (M) of tantalum and molybdenum in the lithium metal oxide mixed solution is 0.5. Furthermore, the molar ratio Li/M of lithium (Li) to the total content (M) of tantalum and molybdenum in the lithium metal oxide mixed solution is 1.50.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 13 was 11.2, and the pH after time was 11.2.

(Example 14) In Example 14, 0.71 g of lithium niobate dispersion and 12.77 g of lithium molybdate dispersion were weighed and placed in a polypropylene container so that the molar ratio of niobium in the lithium niobate dispersion to molybdenum in the lithium molybdate dispersion was 0.1:0.9. Then, 17.00 g of pure water was added to the polypropylene container so that the total content of niobium and molybdenum in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 14.

In 30.48 g of the lithium metal oxide mixed solution of Example 14, the content of niobium in the lithium metal oxide mixed solution converted to Nb was 0.122 mass % (0.037 g, 0.013 mol/L), the content of molybdenum in the lithium metal oxide mixed solution converted to Mo was 1.133 mass % (0.345 g, 0.120 mol/L), and the total content of niobium and molybdenum in metal conversion was 1.255 mass % (0.383 g, 0.133 mol/L). In addition, the content of lithium in the lithium metal oxide mixed solution converted to Li was 0.173 mass % (0.053 g, 0.253 mol/L). Then, the molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium and molybdenum in the lithium metal oxide mixed solution contained in Example 14 is 0.1. In addition, the molar ratio Mo/M of molybdenum (Mo) to the total content (M) of niobium and molybdenum in the lithium metal oxide mixed solution is 0.9. Furthermore, the molar ratio Li/M of lithium (Li) to the total content (M) of niobium and molybdenum in the lithium metal oxide mixed solution is 1.90.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 14 was 9.8, and the pH after time was 9.6.

(Example 15) In Example 15, 1.72 g of lithium tantalum dispersion and 12.77 g of lithium molybdenum dispersion were weighed and placed in a polypropylene container so that the molar ratio of tantalum in the lithium tantalum dispersion to molybdenum in the lithium molybdenum dispersion was 0.1:0.9. Then, 16.03 g of pure water was added to the polypropylene container so that the total content of tantalum and molybdenum in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Example 15.

In 30.51 g of the lithium metal oxide mixed solution of Example 15, the content of tantalum calculated as Ta in the lithium metal oxide mixed solution was 0.237 mass % (0.072 g, 0.013 mol/L), the content of molybdenum calculated as Mo was 1.132 mass % (0.345 g, 0.120 mol/L), and the total content of tantalum and molybdenum was 1.369 mass % (0.418 g, 0.133 mol/L) in terms of metal conversion. In addition, the content of lithium calculated as Li in the lithium metal oxide mixed solution was 0.173 mass % (0.053 g, 0.253 mol/L). Then, the lithium metal oxide mixed solution of Example 15 has a molar ratio Ta/M of tantalum (Ta) to the total content (M) of tantalum and molybdenum in the lithium metal oxide mixed solution of 0.1. Moreover, the molar ratio Mo/M of molybdenum (Mo) to the total content (M) of tantalum and molybdenum in the lithium metal oxide mixed solution is 0.9. Furthermore, the molar ratio Li/M of lithium (Li) to the total content (M) of tantalum and molybdenum in the lithium metal oxide mixed solution is 1.90.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Example 15 was 10.4, and the pH after time was 10.3.

(Comparative Example 1) In Comparative Example 1, 0.3 g of lithium niobate powder (manufactured by High Purity Chemical Research Institute Co., Ltd.) and 0.47 g of lithium tantalum powder (manufactured by High Purity Chemical Research Institute Co., Ltd.) were weighed and placed in a polypropylene container so that the molar ratio of niobium in the lithium niobate powder to the molar ratio of tantalum in the lithium tantalum powder was 0.5:0.5. Then, 29.9 g of pure water was added to the polypropylene container so that the total content of niobium and tantalum in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Comparative Example 1. In addition, the lithium niobate powder and the lithium tantalum powder are not dissolved, and the state of the powders can be visually confirmed in the lithium metal oxide mixed solution.

In 30.67 g of the lithium metal oxide mixed solution of Comparative Example 1, the niobium content in the lithium metal oxide mixed solution calculated as Nb is 0.606 mass % (0.186 g, 0.067 mol/L), the tantalum content in the lithium metal oxide mixed solution calculated as Ta is 1.180 mass % (0.362 g, 0.067 mol/L), and the total content of niobium and tantalum in metal conversion is 1.786 mass % (0.548 g, 0.133 mol/L). In addition, the lithium content in the lithium metal oxide mixed solution calculated as Li is 0.091 mass % (0.028 g, 0.133 mol/L). Then, the lithium metal oxide mixed solution of Comparative Example 1 includes a molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution of 0.5. In addition, a molar ratio Ta/M of tantalum (Ta) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution is 0.5. Furthermore, a molar ratio Li/M of lithium (Li) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution is 1.0.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Comparative Example 1 was 10.0, and the pH after time was 10.0.

(Comparative Example 2) In Comparative Example 2, 3.55 g of lithium niobate dispersion and 0.47 g of lithium niobate powder (manufactured by High Purity Chemical Research Institute Co., Ltd.) were weighed and placed in a polypropylene container so that the molar ratio of niobium in the lithium niobate dispersion and the molar ratio of tantalum in the lithium tantalum dispersion was 0.5:0.5. Then, 26.45 g of pure water was added to the polypropylene container so that the total content of niobium and tantalum in the final mixed solution was 0.133 mol/L. Except for this, the same manufacturing method as in Example 1 was implemented to obtain the lithium metal oxide mixed solution of Comparative Example 2.

In 30.47 g of the lithium metal oxide mixed solution of Comparative Example 2, the niobium content in the lithium metal oxide mixed solution calculated as Nb is 0.610 mass % (0.186 g, 0.067 mol/L), the tantalum content in the lithium metal oxide mixed solution calculated as Ta is 1.188 mass % (0.362 g, 0.067 mol/L), and the total content of niobium and tantalum in metal conversion is 1.797 mass % (0.548 g, 0.133 mol/L). In addition, the lithium content in the lithium metal oxide mixed solution calculated as Li is 0.091 mass % (0.028 g, 0.133 mol/L). Then, the lithium metal oxide mixed solution of Comparative Example 2 includes a molar ratio Nb/M of niobium (Nb) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution of 0.5. In addition, a molar ratio Ta/M of tantalum (Ta) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution is 0.5. Furthermore, a molar ratio Li/M of lithium (Li) to the total content (M) of niobium and tantalum in the lithium metal oxide mixed solution is 1.0.

Furthermore, the initial pH of the lithium metal oxide mixed solution in Comparative Example 2 was 11.0, and the pH after time was 11.0.

Then, the following physical properties were measured for the lithium metal oxide mixed solutions of Examples 1 to 15 and Comparative Examples 1 to 2. The measured physical property values and the measuring methods of the physical property values are shown below, and the measurement results of the lithium metal oxide mixed solutions of Examples 1 to 15 and Comparative Examples 1 to 2 are shown in FIG. 1 and FIG. 2.

<Elemental analysis> The sample was appropriately diluted with dilute hydrochloric acid as required, and the Nb mass fraction converted to Nb, the Ta mass fraction converted to Ta, the Mo mass fraction converted to Mo, the W mass fraction converted to W, or the Li mass fraction converted to Li was measured using inductively coupled plasma atomic emission spectrometry (AG-5110, manufactured by Agilent Technologies) in accordance with JIS K0116:2014.

<pH measurement> The electrode (HORIBA: Standard ToupH electrode 9615S-10D) of the pH meter (HORIBA: Glass electrode type hydrogen ion concentration indicator D-51) was immersed in the lithium metal oxide mixed solution of Examples 1 to 15 and Comparative Examples 1 to 2, and the pH was measured after confirming that the liquid temperature was stable at 25°C. The "initial pH" in Figure 2 indicates the pH measured just after the formation. The "time-dependent pH" in Figure 2 indicates the pH measured after standing at room temperature of 25°C for 1 month.

<Transmittance measurement> 3 ml of the lithium metal oxide mixed solution of Examples 1 to 15 and Comparative Examples 1 to 2 was placed in a synthetic quartz cell with an optical diameter of 5 mm. The transmittance of the lithium metal oxide mixed solution of Examples 1 to 15 and Comparative Examples 1 to 2 was measured with a spectrometer according to the above transmittance measurement conditions. The transmittance was measured for the lithium metal oxide mixed solution just after it was generated and for the lithium metal oxide mixed solution after it was left at room temperature of 25°C for 1 month. Then, if the transmittance of wavelength 400nm, 600nm, 750nm is 75% or more, the evaluation is "○○ (VERY GOOD)", if the transmittance of wavelength 400nm, 600nm, 750nm is 65% or more and less than 75%, the evaluation is "○ (GOOD)", if the transmittance of wavelength 400nm is less than 65%, the evaluation is "× (BAD)". The "initial transmittance" in Figure 2 indicates the transmittance of wavelength 400nm, 600nm, 750nm measured just after generation. In addition, the "transmittance over time" in Figure 2 indicates the transmittance of wavelength 400nm, 600nm, 750nm measured after standing at room temperature 25°C for 1 month from the date of generation.

<Dynamic light scattering method> The evaluation of particle size distribution is performed by dynamic light scattering method in accordance with JIS Z 8828:2019 using an azimuthal potential/particle size/molecular weight measurement system (manufactured by Otsuka Electronics Co., Ltd.: ELSZ-2000). Before the measurement, the mixed solution to be measured is filtered with a filter with a pore size of 1 μm in order to remove dust and the like in the mixed solution. Furthermore, an ultrasonic cleaning machine (manufactured by AS ONE: VS-100III) is used to perform ultrasonic treatment at 28 kHz for 3 minutes, and ultrasonic dispersion treatment is performed. Then, after the mixed solution is stirred, the mixed solution is taken out and placed in a measuring tank for measurement. Furthermore, D50 represents the particle size that reaches 50% by volume fraction. The "initial particle size D50 (nm)" in Figure 2 refers to the particle size (D50) of the particles in the lithium metal oxide mixed solution just after it is generated. In addition, the "time-dependent particle size D50 (nm)" in Figure 2 refers to the particle size (D50) of the particles in the lithium metal oxide dispersion after being left at room temperature of 25°C for 1 month.

Then, the measured "initial particle size D50 (nm)" and "time-dependent particle size D50 (nm)" are evaluated according to the evaluation criteria "○○ (VERY GOOD)", "○ (GOOD)" or "× (BAD)". The evaluation criteria "○○ (VERY GOOD)" means that "D50 < 20nm" is satisfied. The evaluation criteria "○ (GOOD)" means that "20nm ≤ D50 ≤ 100nm" is satisfied. The evaluation criteria "× (BAD)" means that "100nm < D50" is satisfied. In addition, the above-mentioned filtration is performed when measuring the "initial particle size D50 (nm)", but it is not performed when measuring the "time-dependent particle size D50 (nm)", and only ultrasonic treatment is performed.

<Time stability test> The test was conducted in the following manner: the lithium metal oxide mixed solution of Examples 1 to 15 and Comparative Examples 1 to 2 was left at room temperature of 25°C for 1 month, and then visually observed for white precipitation or gelation. If neither white precipitation nor gelation was observed, it was considered to have time stability and was evaluated as "○", and if either white precipitation or gelation was observed, it was considered to have no time stability and was evaluated as "×". Here, the determination of gelation was that each tantalum acid compound dispersion was placed in a plastic container, and when the container was inverted, the dispersion that did not fall quickly was determined to be gelled. In addition, the above-mentioned dynamic light scattering method was used to measure the particle size D50 of the particles in the lithium metal oxide mixed solution of Examples 1 to 15 and Comparative Examples 1 to 2 after standing for one month.

<Film-forming property test> The appearance of the coating formed on the surface of the glass substrate of the substitute for the collector plate was evaluated by observation under an optical microscope. The lithium metal oxide mixed solution of Examples 1 to 15 and Comparative Examples 1 to 2 was filtered through a filter with a pore size of 0.22 μm and degreased with a neutral detergent using a syringe, then dropped onto a 25 mm × 25 mm glass substrate that had been dried and applied by spin coating (700 rpm, 10 seconds; then 1500 rpm, 15 seconds). Then, the coating was formed on the glass substrate by drying at 110°C for 30 seconds. The glass substrate was observed with an optical microscope (magnification: 40 times) in the central 10mm×10mm area of the formed coating. If no bubbles, uneven coating, or cracks were observed, the film forming property was considered to be excellent and evaluated as "○ (GOOD)". If any of these was observed, the film forming property was considered to be poor and evaluated as "× (BAD)".

As shown in FIG. 1 and FIG. 2 , the lithium metal oxide mixed solution of Examples 1 to 15 has high dispersibility in water and excellent solubility, if the molar number of lithium contained in the lithium metal oxide mixed solution is set as Li, the total molar number of two or more metals is set as M, the molar ratio Li/M is greater than or equal to 0.1 and less than or equal to 10, and the particle size (D50) of the particles in the lithium metal oxide mixed solution obtained by dynamic light scattering is less than 100 nm.

In the lithium metal oxide mixed solution of Examples 1 to 15, if the selected lithium metal oxide dispersion is a lithium niobate dispersion, the niobium content is 0.001 mass % to 20 mass % in terms of Nb conversion; if it is a lithium tantalum dispersion, the tantalum content is 0.001 mass % to 12 mass % in terms of Ta conversion; if it is a lithium molybdenum dispersion, the molybdenum content is 0.001 mass % to 12 mass % in terms of M conversion. When the content of tungsten is 0.001 mass % to 22 mass % in terms of W conversion, and when it is a lithium tungstate dispersion, the content of tungsten is 0.001 mass % to 23 mass % in terms of W conversion, which is preferred from the viewpoint of both the practicality and stability of the lithium metal oxide mixed solution, and also from the viewpoint of improving the dispersibility and solubility in polar solvents, especially in water.

The lithium metal oxide mixed solutions of Examples 1 to 15 are dispersion solutions with high dispersibility if the total content of niobium, tungsten, molybdenum and tungsten in the lithium metal oxide mixed solution is 0.001 mass % or more and 50 mass % or less in terms of metal.

If the pH of the lithium metal oxide mixed solution of Examples 1 to 15 is 8 or above, the stability over time is excellent.

The lithium metal oxide mixed solutions of Examples 1 to 15 have no significant difference in the time-dependent particle size D50 of the particles in the lithium metal oxide mixed solutions compared to the initial particle size D50 even after one month, and the time-dependent stability is excellent.

The lithium metal oxide films formed by the lithium metal oxide mixed solutions of Examples 1 to 15 were observed under an optical microscope. The results showed that there were no coarse particles in the films, and no bubbles, uneven coating, or cracks were observed. The films had excellent film-forming properties.

In addition to the configurations of each invention or implementation form, the invention disclosed in this specification also includes, within the scope of application: those that are formed by changing some of the configurations to other configurations disclosed in this specification and specifying them; or those that are formed by adding other configurations disclosed in this specification to these configurations and specifying them; or those that are formed by deleting some of the configurations and specifying them within the scope of obtaining some effects. [Industrial Applicability]

The lithium metal oxide mixed solution of the present invention has high dispersibility in polar solvents, especially in water, and has good solubility in water and excellent storage stability, so it is suitable as a material for coating the positive electrode active material of lithium ion secondary batteries. In addition, the lithium metal oxide mixed solution of the present invention has excellent storage stability and can suppress the occurrence rate of defective products caused by precipitates generated due to changes over time, so waste can be reduced and the energy cost of waste treatment can also be reduced. Furthermore, the lithium metal oxide mixed solution of the present invention also has good film-forming properties, so in the coated positive electrode active material of the lithium ion secondary battery, waste can also be reduced and the occurrence rate of defective products can be suppressed. As a result of these perspectives, sustainable management and efficiency advantages of natural resources, as well as decarbonization (carbon neutrality) can be achieved.

without.

FIG1 is a table showing the physical property values of the lithium metal oxide mixed solution of Examples 1 to 15 and Comparative Examples 1 and 2 of the present invention. FIG2 is a table showing the measurement results of the lithium metal oxide mixed solution of Examples 1 to 15 and Comparative Examples 1 and 2 of the present invention.

Claims (20)

A lithium metal oxide mixed solution, the lithium metal oxide mixed solution containing two or more lithium metal oxide dispersions selected from the group consisting of niobium, tungsten, molybdenum, and tungsten, characterized in that the molar number of lithium contained in the lithium metal oxide mixed solution per 1L is set as Li, the total molar number of the two or more metals in the lithium metal oxide mixed solution per 1L is set as M, the molar ratio Li/M is not less than 0.1 and not more than 10, and the particle size (D50) of the particles in the lithium metal oxide mixed solution obtained by a dynamic light scattering method is not more than 100nm. A lithium metal oxide mixed solution, the lithium metal oxide mixed solution contains two or more lithium metal oxide dispersions selected from the group consisting of niobium, tantalum, molybdenum, and tungsten, characterized in that: the molar number of lithium contained in the lithium metal oxide mixed solution per 1L is set as Li, the total molar number of two or more metals in the lithium metal oxide mixed solution per 1L is set as M, the molar ratio Li/M is greater than 0.1 and less than 10, and the maximum value of the transmittance in the wavelength range of 400nm~760nm is greater than 65%. The lithium metal oxide mixed solution as described in claim 1 or 2 further contains ammonia. The lithium metal oxide mixed solution as described in claim 1 or 2 further contains hydrogen peroxide and/or an organic nitride. The lithium metal oxide mixed solution as described in claim 4, wherein the organic nitride is an aliphatic amine of methylamine, dimethylamine, ethylamine, trimethylamine, or a mixture thereof, or a quaternary ammonium compound of tetramethylammonium hydroxide (TMAH) or tetraethylammonium hydroxide (TEAH). The lithium metal oxide mixed solution as described in claim 1 or 2, wherein the solvent of the lithium metal oxide mixed solution is water. A lithium metal oxide mixed solution as described in claim 1 or 2, wherein the metal element content of the selected lithium metal oxide dispersion is, when the lithium metal oxide mixed solution is set to 100 mass %, the niobium content is 20 mass % or less when converted to Nb, the tantalum content is 12 mass % or less when converted to Ta, the molybdenum content is 23 mass % or less when converted to Mo, and the tungsten content is 22 mass % or less when converted to W. The lithium metal oxide mixed solution as described in claim 1 or 2, wherein the total content of niobium, tantalum, molybdenum and tungsten in the lithium metal oxide mixed solution is 0.001 mass % or more and 50 mass % or less in terms of metal conversion when the lithium metal oxide mixed solution is set to 100 mass %. The lithium metal oxide mixed solution as described in claim 1 or 2, wherein the pH of the lithium metal oxide mixed solution is greater than 8. A lithium metal oxide film, characterized by containing a lithium metal oxide salt in the lithium metal oxide mixed solution as described in claim 1 or 2. The lithium metal oxide mixed solution as described in claim 1 or 2 is used for coating a positive electrode for a lithium ion secondary battery. A positive electrode active material for a lithium ion secondary battery is characterized in that its surface is coated with a salt of lithium metal oxide contained in the lithium metal oxide mixed solution as described in claim 1 or 2. A lithium ion secondary battery is characterized by having a positive electrode coated with the positive electrode active material as described in claim 12. A lithium metal oxide powder is characterized by containing lithium metal oxide particles contained in the lithium metal oxide mixed solution as described in claim 1 or 2. A method for preparing a lithium metal oxide mixed solution is characterized by comprising the step of mixing two or more lithium metal oxide dispersions selected from the group consisting of niobium, tungsten, molybdenum and tungsten. A method for producing a lithium metal oxide mixed solution as described in claim 15, wherein the lithium metal oxide dispersion is produced by adding an acidic aqueous solution containing a metal selected from the group consisting of niobium, tungsten and tungsten to an alkaline aqueous solution to generate a precipitate slurry containing the metal, and by mixing the precipitate slurry, lithium hydroxide and pure water to produce the lithium metal oxide dispersion. A method for manufacturing a lithium metal oxide film is characterized in that the lithium metal oxide mixed solution as described in claim 1 or 2 is applied to a substrate and then dried and/or fired. A method for producing a lithium metal oxide film is characterized in that a lithium metal oxide mixed solution produced by the method for producing a lithium metal oxide mixed solution as described in claim 15 or 16 is applied to a substrate and then dried and/or fired. A method for producing lithium metal oxide powder, characterized in that the lithium metal oxide mixed solution as described in claim 1 or 2 is dried and/or sintered. A method for producing lithium metal oxide powder, characterized in that a lithium metal oxide mixed solution produced by the method for producing a lithium metal oxide mixed solution as described in claim 15 or 16 is dried and/or sintered.