Niobic acid compound dispersion and method for producing same

Abstract

A niobic acid compound dispersion according to the present invention contains: niobium; at least one element X selected from the group consisting of alkali metal elements and alkaline earth metal elements; and a phosphorus compound and / or a chlorine compound. The niobic acid compound dispersion has a particle diameter (D50) of at most 1000 nm as obtained by a dynamic light scattering method. An other niobic acid compound dispersion according to the present invention contains: niobium; at least one element X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements; and a phosphorus compound and / or a chlorine compound. The niobic acid compound dispersion has a maximum value of at least 70%T for transmittance in the wavelength range of 400-760 nm.

Description

Niobic acid compound dispersion and method for producing same

[0001] The present invention relates to a niobic acid compound dispersion and a method for producing the same.

[0002] Lithium niobate, a niobate compound, is used in the form of a single crystal as a nonlinear optical material, a piezoelectric material, and a battery material. For example, lithium niobate is cited as a lithium ion conductive oxide that coats at least a portion of the surface of composite active material particles that can reduce the battery resistance generated in all-solid-state lithium-ion batteries. Patent Document 1 also discloses a piezoelectric sensor in which a piezoelectric film layer containing lithium niobate powder is formed on a substrate layer of the piezoelectric sensor. In Patent Document 1, the piezoelectric film layer is formed by spray-coating a mixture of lithium niobate powder and a sol-gel solution, followed by sintering.

[0003] JP 2023-63187 A

[0004] However, when spray-coating a mixture of lithium niobate powder and a sol-gel solution, if the lithium niobate powder has low dispersibility or solubility in the solvent, it is difficult to form a uniform piezoelectric film layer. Furthermore, if the mixture of lithium niobate powder and a solvent has poor storage stability, the spray-coating process becomes complicated. Therefore, in addition to high dispersibility and solubility in the solvent, excellent storage stability is required.

[0005] In view of the above problems, the present invention provides a niobic acid compound dispersion liquid that has high dispersibility in polar solvents, particularly water, good solubility in water, and excellent storage stability, and a method for producing the same.

[0006] The niobic acid compound dispersion of the present invention, which has been made to solve the above problems, is a niobic acid compound dispersion containing niobium, which contains one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, and a phosphorus compound and / or a chlorine compound, and is characterized in that the particle diameter (D50) of particles in the niobic acid compound dispersion measured by dynamic light scattering (D50) is 1000 nm or less. The niobic acid compound dispersion of the present invention contains niobium, one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, and a phosphorus compound and / or a chlorine compound, and it is preferable that the particle diameter (D50) of particles in the niobic acid compound dispersion measured by dynamic light scattering (D50) is 1000 nm or less, in terms of improving dispersibility and solubility in polar solvents, particularly water.

[0007] The niobium compound dispersion of the present invention contains niobium. Niobium is present in the niobium compound dispersion of the present invention as an oxide, for example, NbO ３ － or polyoxometalate (polyacid) ions in which multiple niobium atoms are bonded to oxygen atoms.

[0008] The niobic acid compound dispersion of the present invention contains one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements. That is, it is presumed that niobic acid in the niobic acid compound dispersion of the present invention is present in the dispersion as ions in an ionic bond with ions of one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements. In the niobic acid compound dispersion of the present invention, hydroxide ions are present as anions, while halide ions such as fluoride ions and chloride ions are hardly present, and alkali metal elements and alkaline earth metal elements are presumed to be present as cations, and therefore niobium is NbO ３ － It is believed that the niobium atoms exist as anions such as the above or as polyoxometalate (polyacid) ions in which multiple niobium atoms are bonded to oxygen atoms.

[0009] Furthermore, the element X preferably contains Li. Furthermore, the element X is not limited to only one alkali metal element, Li, but is preferably two alkali metal elements, Li and Na or K, or three alkali metal elements, Li, Na, and K. Furthermore, the element X may be one alkali metal element, Na or K, or two alkali metal elements, Na and K.

[0010] The niobic acid compound dispersion of the present invention contains a phosphorus compound. In addition, in the niobic acid compound dispersion of the present invention, the phosphorus compound may contain one or more compounds selected from inorganic phosphorus compounds, organic phosphorus compounds, and salts thereof.

[0011] Examples of inorganic phosphorus compounds include inorganic phosphoric acids, particularly phosphoric acids, phosphonic acids, and phosphinic acids. Specific examples of phosphoric acids include phosphoric acid (CAS No.: 7664-38-2), condensed phosphoric acid, pyrophosphoric acid (CAS No.: 2466-09-3), and polyphosphoric acid (CAS No.: 8071-16-1). Specific examples of phosphonic acids include phosphorous acid (CAS No.: 13598-36-2) and hypophosphorous acid (CAS No.: 6303-21-5). Specific examples of phosphinic acids include phosphinic acid (CAS No.: 6303-21-5).

[0012] Examples of organic phosphorus compounds include phosphate esters, organic phosphites, organic phosphonic acids, and organic phosphines. Specific examples of the organic phosphorus compound include methyl phosphate (CAS number: 52932-95-3), ethyl phosphate (CAS number: 37203-76-2), butyl phosphate (CAS number: 107-66-4), phenyl phosphate (CAS number: 701-64-4), dimethyl phosphate (CAS number: 813-78-5), diethyl phosphate (CAS number: 598-02-7), dibutyl phosphate (CAS number: 107-66-4), diphenyl phosphate (CAS number: 838-85-7), trimethyl phosphate (CAS number: 512-56-1), triethyl phosphate (CAS number: 78-40-0), tributyl phosphate (CAS number: 126-73-8), and triphenyl phosphate (CAS number: 115-86-6).

[0013] In addition, examples of organic phosphite ester acids and organic phosphonate esters include methylphosphonic acid (CAS number: 993-13-5), ethylphosphonic acid (CAS number: 6779-09-5), butylphosphonic acid (CAS number: 3321-64-0), phenylphosphonic acid (CAS number: 1571-33-1), dimethyl phosphite (dimethyl phosphonate) (CAS number: 868-85-9), diethyl phosphite (diethyl phosphonate) (CAS number : 762-04-9), dibutyl phosphite (dibutyl phosphonate) (CAS No.: 1809-19-4), diphenyl phosphite (diphenyl phosphonate) (CAS No.: 4712-55-4), trimethyl phosphite (CAS No.: 121-45-9), triethyl phosphite (CAS No.: 122-52-1), tributyl phosphite (CAS No.: 102-85-2), and triphenyl phosphite (CAS No.: 101-02-0).

[0014] Examples of the salts of inorganic phosphorus compounds and / or organic phosphorus compounds include ammonium salts of inorganic phosphorus compounds and / or organic phosphorus compounds, salts with organic nitrogen compounds, alkali metal salts, and alkaline earth metal salts.

[0015] An example of the organic phosphinic acids is triphenylphosphine (CAS number: 603-35-0).

[0016] Inorganic ammonium phosphate salts, salts with organic nitrogen compounds, alkali metal salts, and alkaline earth metal salts include ammonium phosphate, monoammonium phosphate (CAS No.: 7722-76-1), diammonium phosphate (CAS No.: 7783-28-0), sodium metaphosphate (CAS No.: 10361-03-2), potassium metaphosphate (CAS No.: 7790-53-6), and sodium hexametaphosphate (CAS No.: 10124-56-8). Examples of the polyphosphate include potassium hexametaphosphate, sodium pyrophosphate (CAS No.: 7722-88-5), potassium pyrophosphate (CAS No.: 7320-34-5), sodium polyphosphate (CAS No.: 68915-31-1), potassium polyphosphate, sodium tripolyphosphate (CAS No.: 7758-29-4), potassium tripolyphosphate (CAS No.: 13845-36-8), sodium ultrapolyphosphate, and potassium ultrapolyphosphate.

[0017] Furthermore, in the niobic acid compound dispersion of the present invention, the phosphorus compound preferably contains one or more selected from phosphoric acid (CAS No.: 7664-38-2), condensed phosphoric acid, pyrophosphoric acid (CAS No.: 2466-09-3), polyphosphoric acid (CAS No.: 8071-16-1), phosphorous acid (CAS No.: 13598-36-2), hypophosphorous acid (CAS No.: 6303-21-5), ammonium phosphate, monoammonium phosphate (CAS No.: 7722-76-1), diammonium phosphate (CAS No.: 7783-28-0), ammonium pyrophosphate, and ammonium polyphosphate. When the phosphorus compound is phosphoric acid or a salt of phosphoric acid, this is more preferable when adjusting a solution to a pH closer to neutral. On the other hand, when the phosphorus compound is condensed phosphoric acid, or when the condensed phosphoric acid is pyrophosphoric acid, polyphosphoric acid, or a salt of condensed phosphoric acid, this is more preferable when adjusting a solution to a high pH.

[0018] In this specification, "phosphoric acid" refers to orthophosphoric acid and does not include other phosphoric acids such as pyrophosphoric acid, polyphosphoric acid, and phosphorous acid. The phosphorus compound may form a compound with an alkali metal element or an alkaline earth metal element. For example, when the phosphorus compound contains a hydroxyl group (P-OH group), the phosphorus compound has a structure in which some or all of the hydrogen atoms in the hydroxyl group are substituted with an alkali metal element or an alkaline earth metal element.

[0019] The niobic acid compound dispersion of the present invention further contains a chlorine compound.

[0020] Examples of chlorine compounds include hydrochloric acid (CAS number: 7647-01-0), hypochlorous acid (CAS number: 7790-92-3), chlorous acid (CAS number: 13898-47-0), chloric acid (CAS number: 7790-93-4), and perchloric acid (CAS number: 7601-90-3).

[0021] The chlorine compound may also be a salt of the above-mentioned chlorine compound, such as an ammonium salt, an amine salt, a quaternary ammonium salt, or a lithium salt, with ammonium salts and lithium salts being preferred. Specific examples include ammonium chloride (CAS No.: 12125-02-9), ammonium perchlorate (CAS No.: 7790-98-9), lithium chloride (CAS No.: 7447-41-8), lithium perchlorate (CAS No.: 7791-03-9), methylamine hydrochloride (CAS No.: 593-51-1), and dimethylamine hydrochloride (CAS No.: 506-59-2).

[0022] In addition, when a chlorine compound is contained in the niobic acid compound dispersion of the present invention, corrosion of the substrate or elution of the substrate may occur depending on the material or type of the substrate to which the niobic acid compound dispersion of the present invention is applied, it is preferable that the chlorine compound is not contained. For example, when the niobic acid compound dispersion of the present invention is used for coating a positive electrode or a positive electrode material for a lithium ion secondary battery described later, it is preferable that the chlorine compound is not contained.

[0023] Furthermore, when the particle diameter (D50) of the particles in the niobic acid compound dispersion liquid measured by dynamic light scattering is 1000nm or less, it is highly dispersible, has little change over time, is stable, and is preferable in terms of the reactivity when reacting with other substances or compounding, and the film uniformity when forming a film.In addition, this particle diameter (D50) is preferably smaller, more preferably 800nm ​​or less, more preferably 600nm or less, particularly preferably 500nm or less, more particularly preferably 300nm or less, more particularly preferably 200nm or less, particularly preferably 100nm or less, more preferably 50nm or less, more particularly preferably 30nm or less, more particularly preferably 20nm or less, even more particularly preferably 10nm or less, particularly preferably 8nm or less, more particularly preferably 6nm or less, more particularly preferably 4nm or less, even more particularly preferably 2nm or less, even more particularly preferably 1nm or less, particularly preferably 1nm or less, more particularly preferably 0.6nm or less, and most preferably more than 0. In this way, a liquid in which the particle diameter (D50) of the particles in the niobic acid compound dispersion of the present invention is 1000 nm or less as a result of measurement using a dynamic light scattering method is defined as the "niobic acid compound dispersion" of the present invention.

[0024] Here, dynamic light scattering is a method in which a solution such as a suspension is irradiated with light such as laser light, and the light scattering intensity from a group of particles undergoing Brownian motion is measured, and particle size and distribution are determined from the temporal fluctuation of that intensity. Specifically, the particle size distribution is evaluated using a zeta potential, particle size, and 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." Just before measurement, the solution to be measured is filtered through a filter with a 1 μm pore size to remove dust and other particles. The particle size (D50) refers to the median diameter (D50), which is the particle size that represents the 50% integrated value of the integrated distribution curve. Furthermore, in this specification, unless otherwise specified, the term "particle diameter (D50)" includes both an "initial particle diameter D50" which indicates the particle diameter (D50) of particles in the niobic acid compound dispersion of the present invention adjusted to a liquid temperature of 25°C immediately after production, and an "aged particle diameter D50" which indicates the particle diameter (D50) of particles in the niobic acid compound dispersion of the present invention after it has been left to stand for one month from the day the niobic acid compound dispersion of the present invention was produced in an incubator set at room temperature of 25°C.

[0025] The niobic acid compound dispersion of the present invention is a niobium-containing niobic acid compound dispersion, characterized in that it contains one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, and a phosphorus compound and / or a chlorine compound, and has a maximum transmittance of 70% T or more in a wavelength region of 400 nm to 760 nm. Here, the niobium, the one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, and the phosphorus compound and / or chlorine compound in the niobic acid compound dispersion of the present invention are as described above, and therefore detailed description thereof will be omitted.

[0026] The niobic acid compound dispersion of the present invention preferably has a maximum transmittance in the wavelength region of 400 nm to 760 nm of 70% T or more, because this provides high dispersibility and excellent uniformity of the components in the liquid. The maximum transmittance in the wavelength region of 400 nm to 760 nm is more preferably 72% T or more, even more preferably 74% T or more, particularly preferably 76% T or more, even more particularly preferably 78% T or more, even more particularly preferably 80% T or more, even more particularly preferably 85% T or more, even more preferably 90% T or more, even more preferably 95% T or more, even more particularly preferably 97% T or more, especially preferably 98% T or more, even more especially preferably 99% T or more, and most preferably 100% T.

[0027] Furthermore, the niobic acid compound dispersion of the present invention may have a transmittance of 70% T or more at any one wavelength of 400 nm, 600 nm, or 750 nm. The transmittance at any one wavelength of 400 nm, 600 nm, or 750 nm, or at any two or more wavelengths, may be 72% T or more, 74% T or more, 76% T or more, 78% T or more, 80% T or more, 85% T or more, 90% T or more, 95% T or more, 97% T or more, 98% T or more, 99% T or more, or 100% T or more.

[0028] Furthermore, the niobate compound dispersion of the present invention may have a minimum transmittance in a wavelength region of 400 nm to 760 nm of 70% T or more. The minimum transmittance in the wavelength region of 400 nm to 760 nm may be 72% T or more, 74% T or more, 76% T or more, 78% T or more, 80% T or more, 85% T or more, 90% T or more, 95% T or more, 97% T or more, 98% T or more, 99% T or more, or 100% T or more.

[0029] Although the measured value of the transmittance may exceed 100%T due to measurement error or the like, since the theoretical upper limit is 100%T, when the measured value exceeds 100%T, it is considered to be 100%T. Thus, a liquid in which the maximum value of the transmittance in the wavelength region of 400 nm to 760 nm of the niobic acid compound dispersion of the present invention is 70%T or more is defined as the "niobic acid compound dispersion" of the present invention. Furthermore, unless otherwise specified, in this specification, "transmittance" includes both "initial transmittance" which indicates the transmittance of the niobic acid compound dispersion of the present invention adjusted to a liquid temperature of 25°C immediately after production, and "temporary transmittance" which indicates the transmittance of the niobic acid compound dispersion of the present invention after being left to stand for one month from the day the niobic acid compound dispersion of the present invention was produced in an incubator set at room temperature of 25°C.

[0030] Here, the above-mentioned transmittance can be determined by measuring the ultraviolet-visible absorption spectrum (UV-Vis absorption spectrum) of the niobic acid compound dispersion of the present invention in accordance with JIS K 0115, 2004 "General rules for absorptiometric analysis methods" under the following transmittance measurement conditions.

[0031] =Transmittance measurement conditions= Measuring device: Ultraviolet-visible-near-infrared spectrophotometer UH4150 (manufactured by Hitachi High-Tech Science Corporation) Measurement mode: Wavelength scan Data mode: %T (transmittance) Measurement wavelength range: 200 nm to 2000 nm Scan speed: 600 nm / min Sampling interval: 2 nm

[0032] In the present invention, the term "dispersion" is not limited to a dispersion in which a solute is dispersed or mixed in a solvent in a monomolecular state, but also includes aggregates in which a plurality of molecules are attracted to each other by intermolecular interactions, such as (1) polymer molecules, (2) solvated molecules, (3) molecular clusters, and (4) colloidal particles dispersed in a solvent.

[0033] The niobic acid compound dispersion of the present invention may further contain ammonia and / or an organic nitrogen compound. The niobic acid compound dispersion of the present invention may also contain an ionized alkaline aqueous solution, such as ammonia or an organic nitrogen compound. The contents of ammonia and the organic nitrogen compound in the niobic acid compound dispersion of the present invention are preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 1% by mass or less, respectively, when the niobic acid compound dispersion of the present invention is taken as 100% by mass.

[0034] As will be explained in detail in the production method of the niobate compound dispersion of the present invention below, in the production process, a niobic acid-containing precipitate, such as a hydrous ammonium niobate cake, which is a precipitate slurry containing niobium, is produced by a reverse neutralization method in which an acidic niobium complex aqueous solution is added to an alkaline aqueous solution, for example, ammonia water, and then the niobate compound dispersion of the present invention is produced. Therefore, it is believed that ammonia contains ammonium ions and exists in the dispersion as cations. Furthermore, in the production process, a neutralized aqueous niobium compound solution is produced by mixing the niobic acid-containing precipitate obtained through the reverse neutralization method in which ammonia is added to ammonia water with an organic nitrogen compound, and therefore the organic nitrogen compound is believed to exist in the dispersion as cations.

[0035] The method for measuring the ammonia content in the dispersion liquid is to add sodium hydroxide to the dispersion liquid, distill and separate the ammonia, and then quantify the ammonia content using an ion meter; ２ Examples of methods for quantifying the ammonia content include a method using a thermal conductivity meter, the Kjeldahl method, gas chromatography (GC), ion chromatography, and gas chromatography mass spectrometry (GC-MS). In particular, a method for quantifying the ammonia content using an ion meter is preferred.

[0036] Examples of organic nitrogen compounds include aliphatic amines, aromatic amines, amino alcohols, amino acids, polyamines, quaternary ammonium compounds, guanidine compounds, and azole compounds.

[0037] Examples of aliphatic amines include methylamine, dimethylamine, trimethylamine, ethylamine, methylethylamine, diethylamine, triethylamine, methyldiethylamine, dimethylethylamine, n-propylamine, di-n-propylamine, tri-n-propylamine, iso-propylamine, di-iso-propylamine, tri-iso-propylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, iso-butylamine, di-iso-butylamine, tri-iso-butylamine, tert-butylamine, n-pentaamine, n-hexylamine, cyclohexylamine, and piperidine.

[0038] Examples of aromatic amines include aniline, phenylenediamine, and diaminotoluene. Furthermore, examples of amino alcohols include methanolamine, ethanolamine, propanolamine, butanolamine, pentanolamine, dimethanolamine, diethanolamine, trimethanolamine, methylmethanolamine, methylethanolamine, methylpropanolamine, methylbutanolamine, ethylmethanolamine, ethylethanolamine, ethylpropanolamine, dimethylmethanolamine, dimethylethanolamine, dimethylpropanolamine, methyldimethanolamine, methyldiethanolamine, diethylmethanolamine, trishydroxymethylaminomethane, bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane, and aminophenol. Furthermore, examples of amino acids include alanine, arginine, aspartic acid, and EDTA. Furthermore, examples of polyamines include polyamines and polyetheramines.

[0039] Examples of quaternary ammonium include alkylimidazolium, pyridinium, pyrrolidium, tetraalkylammonium, etc. Specific examples of alkylimidazolium include 1-methyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-propyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-methyl-2,3-dimethylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-propyl-2,3-dimethylimidazolium, and 1-butyl-2,3-dimethylimidazolium. Specific examples of pyridinium and pyrrolidium include N-butyl-pyridinium, N-ethyl-3-methyl-pyridinium, N-butyl-3-methyl-pyridinium, N-hexyl-4-(dimethylamino)-pyridinium, N-methyl-1-methylpyrrolidinium, and N-butyl-1-methylpyrrolidinium. Specific examples of tetraalkylammonium include tetramethylammonium, tetraethylammonium, tetrabutylammonium, and ethyl-dimethyl-propylammonium. Examples of anions that form salts with the above-mentioned cations include OH, － , Cl － ,Br － , I － , B.F. ４ － , HSO ４ － Examples include:

[0040] Examples of guanidine compounds include guanidine, diphenylguanidine, and ditolylguanidine. Examples of azole compounds include imidazole compounds and triazole compounds. Specific examples of imidazole compounds include imidazole, 2-methylimidazole, and 2-ethyl-4-methylimidazole. Specific examples of triazole compounds include 1,2,4-triazole, 1,2,4-triazole-3-methylcarboxylate, and 1,2,3-benzotriazole.

[0041] Here, the organic nitrogen compound is preferably an aliphatic amine because it has high volatility and low toxicity. Specifically, an aliphatic amine having 1 to 4 carbon atoms is more preferable, and an aliphatic amine having 1 to 2 carbon atoms is particularly preferable. Examples include methylamine and dimethylamine.

[0042] Furthermore, the organic nitrogen compound is preferably a quaternary ammonium, which not only has high solubility but also has high crystallization suppression and high solation suppression. For example, tetraalkylammonium salts are preferred, tetraalkylammonium hydroxide salts are more preferred, tetramethylammonium hydroxide and tetraethylammonium are particularly preferred, and tetramethylammonium hydroxide (TMAH) is also particularly preferred.

[0043] Furthermore, the organic nitrogen compound may be a mixture of two or more compounds selected from aliphatic amines, aromatic amines, amino alcohols, amino acids, polyamines, quaternary ammonium compounds, guanidine compounds, and azole compounds, rather than a single compound. For example, a mixture of two compounds, an aliphatic amine and a quaternary ammonium compound, is preferred because it can increase solubility while limiting the amount added so as not to increase toxicity.

[0044] Specific examples include mixtures of two organic nitrogen compounds such as methylamine and tetramethylammonium hydroxide (TMAH), dimethylamine and tetramethylammonium hydroxide (TMAH), and methylamine and dimethylamine, and mixtures of three organic nitrogen compounds such as methylamine, dimethylamine, and tetramethylammonium hydroxide (TMAH).

[0045] The content of the organic nitrogen compound present in the niobic acid compound dispersion of the present invention can be measured by gas chromatography (GC), liquid chromatography (LC), mass spectrometry (MS), gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), etc. When a low-volatility organic nitrogen compound is contained, it is preferable to measure the content of the organic nitrogen compound by liquid chromatography (LC) or liquid chromatography-mass spectrometry (LC-MS).

[0046] The niobium content in the niobate compound dispersion of the present invention is preferably 0.01% by mass or more and 30% by mass or less in terms of Nb atoms. The niobium content in the niobate compound dispersion of the present invention is preferably 0.01% by mass or more and 30% by mass or less in terms of Nb atoms, in terms of both practicality and stability of the niobate compound dispersion, more preferably 0.5% by mass or more and 25% by mass or less in terms of Nb atoms, even more preferably 1% by mass or more and 20% by mass or less in terms of Nb atoms, particularly preferably 1% by mass or more and 15% by mass or less in terms of Nb atoms, even more particularly preferably 3% by mass or more and 10% by mass or less in terms of Nb atoms, and even more particularly preferably 5% by mass or more and 10% by mass or less in terms of Nb atoms.

[0047] Here, the niobium content in the niobium compound dispersion is calculated by appropriately diluting the dispersion with dilute hydrochloric acid as needed, and measuring Nb mass% in terms of Nb atoms using high-frequency inductively coupled plasma atomic emission spectroscopy (ICP atomic emission spectroscopy (AG-5110 manufactured by Agilent Technologies)) in accordance with JIS K0116:2014. Furthermore, when the niobic acid in the niobic acid compound dispersion of the present invention is ionically bonded to an alkali metal or alkaline earth metal, for example, a lithium niobate salt ionically bonded to lithium ions, the lithium content may be calculated by measuring Li mass% in terms of Li atoms, similarly to the niobium content. By specifying the niobium content and lithium content in the niobium compound dispersion of the present invention, the molar ratio Li / Nb of lithium (Li) to niobium (Nb) of the lithium niobate contained in the niobate compound dispersion of the present invention can be specified. The content of each element X of one or more elements X selected from the group consisting of alkali metal elements other than lithium and / or alkaline earth metal elements can be calculated by measuring X mass % of each element in terms of element X atoms, similarly to the niobium content.

[0048] The niobic acid compound dispersion of the present invention is characterized in that the phosphorus content in the niobic acid compound dispersion is 0.01% by mass or more and 10% by mass or less in terms of P atoms. When the phosphorus content in the niobic acid compound dispersion of the present invention is 0.01% by mass or more and 10% by mass or less in terms of P atoms, it is preferable in terms of improving dispersibility and solubility in polar solvents, particularly water. Furthermore, it is more preferable that it is 0.1% by mass or more and 5% by mass or less in terms of P atoms, even more preferable that it is 0.1% by mass or more and 2% by mass or less in terms of P atoms, particularly preferable that it is 0.1% by mass or more and 1% by mass or less in terms of P atoms, and even more particularly preferable that it is 0.1% by mass or more and 0.4% by mass or less in terms of P atoms.

[0049] The phosphorus content in the niobate compound dispersion of the present invention is calculated by diluting the dispersion appropriately with dilute hydrochloric acid as needed, and measuring the P mass% in terms of P atoms using ICP emission spectrometry (AG-5110 manufactured by Agilent Technologies) in accordance with JIS K0116:2014.

[0050] The phosphorus content in the niobic acid compound dispersion of the present invention is preferably analyzed by the above-mentioned ICP emission spectrometry. ３１ It can also be determined by measuring P-NMR spectrum. Specifically, the phosphorus content in the niobic acid compound dispersion of the present invention can be determined by the following procedure using a nuclear magnetic resonance spectrometer (AVANCE NEO 600 manufactured by Bruker). A measurement sample is prepared by mixing 70 μL of the niobic acid compound dispersion of the present invention with 650 μL of a phosphonoacetic acid heavy water solution prepared by dissolving 10 g / L of phosphonoacetic acid in heavy water. The prepared measurement sample is subjected to the following ３１ According to the P-NMR spectrum measurement conditions, ３１ The P-NMR spectrum is measured.

[0051] = ３１P-NMR spectrum measurement conditions = Magnetic field: 14.1 T (1H 600 MHz) Spectrometer: AVANCE NEO 600 manufactured by Bruker Measurement and data processing software: TopSpin manufactured by Bruker NMR probe: Solvent probe (Type: PA BBO 600S3 BBF-H-D-05 Z SP) Solvent: Heavy water Internal sample for chemical shift value and phosphorus amount: Phosphonoacetic acid Chemical shift value reference: The apex of the central peak of the triplet peak of phosphonoacetic acid is set to 14.96 ppm. Spectral center (O1 value - SR value (chemical shift value)): 0.00 ppm Radio frequency pulse intensity: The intensity is set so that 14 μs results in a 90-degree pulse with respect to the peak at the irradiation center. Radio frequency pulse width: 14 μs Measurement interval: 80 μs (DW = 40 μs on the software) Number of measurement points: 32,768 points (TD = 65,536 on the software) Number of spectrum points (SI on the software): 65,536 points

[0052] As mentioned above ３１ By performing a Fourier transform on the FID data measured under the P-NMR spectrum measurement conditions without using a window function, ３１ P-NMR spectrum was obtained. ３１ The peak areas of the P-NMR spectrum can be calculated using the Integrate function of the measurement and data processing software described above, and the contents of phosphonoacetic acid and each phosphate ion can be calculated from the peak areas. For example, in the case of the diphosphate raw material, the peak area is 6.5 ppm (PO ４ -1.7 ppm (presumed to be derived from the chemical shift value of P ２ O ７ (presumed origin) and ３１ In the phosphoric acid raw material, a peak of 6.2 ppm (PO ４ (presumed origin) ３１ The P peak is observed. The chemical shifts vary depending on the pH of the sample, so calculations should be made taking this into consideration.

[0053] Furthermore, the niobic acid compound dispersion of the present invention preferably has a chlorine content of 0.0% by mass or more and 2.0% by mass or less in terms of Cl atoms. The chlorine content of the niobic acid compound dispersion of the present invention is preferably 0.0% by mass or more and 2.0% by mass or less in terms of Cl atoms, from the viewpoint of corrosion concerns of the substrate. Furthermore, the chlorine content is more preferably 0.001% by mass or more and 2.0% by mass or less in terms of Cl atoms, even more preferably 0.001% by mass or more and 0.5% by mass or less in terms of Cl atoms, particularly preferably 0.001% by mass or more and 0.2% by mass or less in terms of Cl atoms, and even more particularly preferably 0.001% by mass or more and 0.1% by mass or less in terms of Cl atoms.

[0054] The chlorine content in the niobic acid compound dispersion of the present invention is calculated by diluting the dispersion appropriately with dilute hydrochloric acid as needed, and measuring the Cl mass % in terms of Cl atoms using ICP optical emission spectrometry (AG-5110 manufactured by Agilent Technologies) in accordance with JIS K0116: 2014. In this case, the chlorine content in the niobic acid compound dispersion of the present invention can be determined by subtracting the chlorine content derived from the dilute hydrochloric acid used for dilution.

[0055] Furthermore, in the niobic acid compound dispersion of the present invention, the total content of the phosphorus content calculated as P atoms and the chlorine content calculated as Cl atoms in the niobic acid compound dispersion is preferably 0.01% by mass or more and 10% by mass or less. When the total content in the niobic acid compound dispersion of the present invention is 0.01% by mass or more and 10% by mass or less, this is preferred in terms of improving dispersibility and solubility in polar solvents, particularly water. Furthermore, the total content is more preferably 0.01% by mass or more and 5% by mass or less, even more preferably 0.05% by mass or more and 2% by mass or less, and particularly preferably 0.05% by mass or more and 1% by mass or less.

[0056] The niobic acid compound dispersion of the present invention is characterized in that the molar ratio M / Nb of the total amount (M) of the element X to niobium (Nb) in the niobic acid compound dispersion is 0.01 or more and 10 or less. When the molar ratio M / Nb of the total amount (M) of the element X to niobium (Nb) in the niobic acid compound dispersion of the present invention is 0.01 or more and 10 or less, it is preferable in terms of improving dispersibility and solubility in water, and is more preferably 0.1 or more and 10 or less, even more preferably 1 or more and 9 or less, and particularly preferably 1 or more and 7 or less. The molar ratio M / Nb of the total amount (M) of the element X to niobium (Nb) in the niobic acid compound dispersion of the present invention may be 0.1 or more and 9 or less, or may be 0.1 or more and 7 or less.

[0057] The niobic acid compound dispersion of the present invention is characterized in that the element X in the niobic acid compound dispersion is Li, and the molar ratio Li / Nb of lithium (Li) to niobium (Nb) is 0.01 or more and 10 or less. When the element X in the niobic acid compound dispersion of the present invention is Li, and the molar ratio Li / Nb of lithium (Li) to niobium (Nb) is 0.01 or more and 10 or less, it is preferable in terms of improving dispersibility and solubility in water, and it is more preferable that it is 1 or more and 9 or less, and even more preferable that it is 1 or more and 7 or less. Note that when the element X in the niobic acid compound dispersion of the present invention is Li, the molar ratio Li / Nb of lithium (Li) to niobium (Nb) may be 0.1 or more and 9 or less, or may be 0.1 or more and 7 or less.

[0058] The niobic acid compound dispersion of the present invention is characterized in that the molar ratio M / (P+Cl) of the total amount (M) of the element X to the total amount (P+Cl) of the phosphorus compounds and / or chlorine compounds in the niobic acid compound dispersion is 0.01 or more and 10 or less. When the molar ratio M / (P+Cl) of the total amount (M) of the element X to the total amount (P+Cl) of the phosphorus compounds and / or chlorine compounds in the niobic acid compound dispersion of the present invention is 0.01 or more and 10 or less, it is preferable from the viewpoint of improving dispersibility and solubility in water, it is more preferable to be 0.05 or more and 8 or less, even more preferable to be 0.05 or more and 7 or less, particularly preferable to be 0.07 or more and 5 or less, more particularly preferable to be 0.1 or more and 4 or less, even more particularly preferable to be 0.1 or more and 3 or less, still particularly preferable to be 0.1 or more and 2 or less, and even more particularly preferable to be 0.4 or more and 1.9 or less. In this specification, unless otherwise specified, the total amount of phosphorus compounds and / or chlorine compounds (P+Cl) is the sum of the value (P) calculated in terms of P atoms and the value (Cl) calculated in terms of Cl atoms. When the niobate compound dispersion of the present invention is used for coating a positive electrode for a lithium ion secondary battery, or a positive electrode material, as described below, it is preferable that Cl=0.

[0059] Furthermore, in the niobic acid compound dispersion of the present invention, it is more preferable that the molar ratio M / P of the total amount (M) of the element X to the total amount (P) of the phosphorus compounds in the niobic acid compound dispersion is 0.01 or more and 5 or less. If the molar ratio M / P of the total amount (M) of the element X to the total amount (P) of the phosphorus compounds in the niobic acid compound dispersion of the present invention is 0.01 or more and 5 or less, it is preferable from the viewpoint of improving dispersibility and solubility in water, it is more preferable that it is 0.01 or more and 2 or less, even more preferable that it is 0.05 or more and 2 or less, and particularly preferable that it is 0.1 or more and 1.95 or less.

[0060] The niobic acid compound dispersion of the present invention is characterized in that the element X in the niobic acid compound dispersion is Li, and the molar ratio Li / (P+Cl) of lithium (Li) to the total amount (P+Cl) of the phosphorus compound and / or chlorine compound is 0.01 or more and 10 or less. When the element X in the niobic acid compound dispersion of the present invention is Li, and the molar ratio Li / (P+Cl) of lithium (Li) to the total amount (P+Cl) of the phosphorus compound and / or chlorine compound is 0.01 or more and 10 or less, it is preferable in terms of improving dispersibility and solubility in water, it is more preferable to be 0.05 or more and 8 or less, even more preferable to be 0.05 or more and 7 or less, particularly preferable to be 0.07 or more and 5 or less, more particularly preferable to be 0.1 or more and 4 or less, even more particularly preferable to be 0.1 or more and 3 or less, still particularly preferable to be 0.1 or more and 2 or less, and even more particularly preferable to be 0.4 or more and 1.9 or less.

[0061] Furthermore, in the niobic acid compound dispersion of the present invention, it is more preferable that the element X in the niobic acid compound dispersion is Li, and the molar ratio Li / P of lithium (Li) to the total amount (P) of the phosphorus compounds is 0.01 or more and 5 or less. If the element X in the niobic acid compound dispersion of the present invention is Li, and the molar ratio Li / P of lithium (Li) to the total amount (P) of the phosphorus compounds is 0.01 or more and 5 or less, it is preferable from the viewpoint of improving dispersibility and solubility in water, it is more preferable that it is 0.01 or more and 2 or less, even more preferable that it is 0.05 or more and 2 or less, and particularly preferable that it is 0.1 or more and 1.95 or less.

[0062] The niobic acid compound dispersion of the present invention is characterized in that the molar ratio Nb / (P+Cl) of niobium (Nb) to the total amount (P+Cl) of the phosphorus compound and / or chlorine compound in the niobic acid compound dispersion of the present invention is 0.01 or more and 10 or less. If the molar ratio Nb / (P+Cl) of niobium (Nb) to the total amount (P+Cl) of the phosphorus compound and / or chlorine compound in the niobic acid compound dispersion of the present invention is 0.01 or more and 10 or less, it is preferable from the viewpoint of improving dispersibility and solubility in water, and is more preferably 0.1 or more and 5 or less, even more preferably 0.1 or more and 1 or less, and particularly preferably 0.1 or more and 0.4 or less.

[0063] Furthermore, in the niobic acid compound dispersion of the present invention, the molar ratio Nb / P of niobium (Nb) in the niobic acid compound dispersion to the total amount (P) of the phosphorus compounds is more preferably 0.01 or more and 10 or less. If the molar ratio Nb / P of niobium (Nb) in the niobic acid compound dispersion of the present invention to the total amount (P) of the phosphorus compounds is 0.01 or more and 10 or less, it is preferable from the viewpoint of improving dispersibility and solubility in water, more preferably 0.05 or more and 5 or less, even more preferably 0.1 or more and 3 or less, and particularly preferably 0.1 or more and 1.95 or less.

[0064] The niobic acid compound dispersion of the present invention is also characterized as being an aqueous dispersion. The niobic acid compound in the niobic acid compound dispersion of the present invention has high dispersibility in water and good solubility in water, allowing pure water to be used as the solvent. Organic solvents may also be used. Examples of organic solvents include alcohol solvents, ketone solvents, ether solvents, ester solvents, aromatic hydrocarbon solvents, and aliphatic hydrocarbon solvents, and mixtures of these organic solvents with pure water may also be used. Examples of alcohol solvents include alcohols having 5 or fewer carbon atoms (methanol, ethanol, n-propanol, isopropyl alcohol, butanol, ethylene glycol, and propylene glycol), high-boiling point solvents, and acetone. It is preferable that the above-mentioned solvents are compatible with water. The niobic acid compound dispersion of the present invention can contain one or more solvents in any proportion, as long as stability is not impaired.

[0065] Examples of high-boiling point solvents include polyhydric alcohol solvents and glycol solvents, such as glycerin (boiling point: 290°C), 1,6-hexanediol (boiling point: 250°C), and 1,7-heptanediol (boiling point: 259°C). Examples of glycol-based 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 to 460°C), polyethylene glycol (PEG) (boiling point: 460°C or higher), polyethylene glycol (PEG)-polypropylene glycol (PPG) copolymer (boiling point: 460°C or higher), diethylene glycol monohexyl ether (boiling point: 260°C), polyoxyalkylene monoalkyl ether (boiling point: 260°C or higher), polyoxyethylene sorbitan monolaurate (boiling point: 321°C or higher), other anionic fluorine-based surfactants (boiling point: 180°C or higher), amphoteric fluorine-based surfactants (boiling point: 180°C or higher), nonionic fluorine-based surfactants (boiling point: 180°C or higher), and amine oxides (boiling point: 180°C or higher). The boiling points mentioned above are those at 1 atmosphere.

[0066] The niobic acid compound dispersion of the present invention is characterized in that the pH of the niobic acid compound dispersion is 2 or more and 11 or less. A pH of 2 or more and 11 or less of the niobic acid compound dispersion of the present invention is preferred in that the polyacid ions contained in the dispersion are stable. Depending on the application, the niobic acid compound dispersion of the present invention may be an acidic niobic acid compound dispersion, a neutral niobic acid compound dispersion, or a basic niobic acid compound dispersion. Unless otherwise specified, in this specification, "pH" refers to both the "initial pH," which is the pH of the niobic acid compound dispersion of the present invention adjusted to a liquid temperature of 25°C immediately after production, and the "aged pH," which is the pH of the niobic acid compound dispersion of the present invention after being left to stand for one month from the day the niobic acid compound dispersion of the present invention was produced in an incubator set at room temperature of 25°C.

[0067] When an acidic niobic acid compound dispersion is preferred, the pH of the niobic acid compound dispersion of the present invention is preferably less than 7, and preferably from 2 to less than 7. When a neutral niobic acid compound dispersion is preferred, the pH of the niobic acid compound dispersion of the present invention is preferably from 6 to 8, and more preferably 7. When a basic niobic acid compound dispersion is preferred, the pH of the niobic acid compound dispersion of the present invention is preferably 7 or more, more preferably 8 or more, even more preferably 9 or more, and particularly preferably 10 or more. On the other hand, the pH is preferably 11 or less. Furthermore, the pH may be 11 or more, or may be 12 or more. Note that, if an organic acid is contained in the niobic acid compound dispersion of the present invention, the pH will fluctuate and the components in the niobic acid compound dispersion of the present invention may interact with the organic acid, so it is preferable that no organic acid is contained.

[0068] Here, the pH of the niobic acid compound dispersion of the present invention is measured by immersing an electrode (manufactured by HORIBA: Standard ToupH electrode 9615S-10D) of a pH meter (manufactured by HORIBA: Glass electrode type hydrogen ion concentration indicator D-51) in the niobic acid compound dispersion of the present invention, and after confirming that the liquid temperature has stabilized at 25°C.

[0069] The niobic acid compound dispersion of the present invention may contain, as an additive, an element or compound thereof that does not constitute the niobic acid compound contained in the niobic acid compound dispersion of the present invention. Examples of such additives include elements or compounds such as Al, Si, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ge, Zr, Ta, Mo, Sn, La, and W. Examples of the compound include oxides, alkali metal salts of metal acids, alkaline earth metal salts of metal acids, chlorides, metal alkoxides, and polyoxometalates. Furthermore, the content of the additives in the niobate compound dispersion of the present invention is such that, when the total number of moles of each additive element is Z, the molar ratio Z / Nb of the total number of moles of each additive element (Z) to niobium (Nb) may be 0.001 to 75, 0.002 to 50, 0.01 to 40, 0.2 to 30, 0.5 to 25, 0.8 to 1.5, 0.8 to 1.3, 0.9 to 1.2, or 0.9 to 1.1. The content of each element corresponding to the additive is calculated by measuring the mass% of each element in atomic terms, similar to the niobium content described above. Furthermore, since the niobate compound dispersion of the present invention is a uniform dispersion, improved uniformity and improved reactivity (reaction rate) are expected even when these compounds are in a suspended state. Furthermore, if these compounds are dissolved in the niobic acid compound dispersion of the present invention to form a uniform dispersion, the composite element can be made to have the most favorable reactivity.

[0070] Furthermore, the niobic acid compound dispersion of the present invention may contain components other than the components derived from niobium or niobic acid, ammonia, organic nitrogen compounds, and element X (hereinafter referred to as "other components"), provided that the effects of the dispersion are not impaired. Examples of other components include Al, Si, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ge, Zr, Ta, Mo, Sn, La, and W. However, the other components are not limited to these. When the niobic acid compound dispersion of the present invention is taken as 100% by mass, the content of the 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. The content of each element corresponding to the other components is calculated by measuring the mass% of each element in atomic terms, similar to the niobium content described above. It should be noted that the niobic acid compound dispersion of the present invention is expected to contain unavoidable impurities, although this is not intended. The content of the unavoidable impurities is preferably 0.01% by mass or less.

[0071] The niobic acid compound powder of the present invention is characterized by containing the niobic acid compound in the niobic acid compound dispersion of the present invention described above. The niobic acid compound powder of the present invention includes a dried powder obtained by drying the niobic acid compound dispersion of the present invention, for example, by vacuum drying, and a fired powder obtained by firing the resulting dried powder. The niobic acid compound powder of the present invention also includes niobic acid compound powders with different physical properties, such as crystalline structure, produced by vacuum drying or firing the niobic acid compound dispersion of the present invention, and may have an amorphous structure, a single crystal structure, or a polycrystalline structure. The method for producing the niobic acid compound powder of the present invention will be described later.

[0072] The niobic acid compound film of the present invention is characterized by containing the niobic acid compound in the niobic acid compound dispersion liquid of the present invention described above. The niobic acid compound film of the present invention includes a dried film obtained by applying the niobic acid compound dispersion liquid of the present invention to the surface of a substrate and then drying, for example, vacuum drying, and a fired film obtained by firing the resulting dried film. The niobic acid compound film of the present invention also includes niobic acid compound films with different physical properties, such as crystal structure, produced by vacuum drying or firing the niobic acid compound dispersion liquid of the present invention, and may have an amorphous structure, a single crystal structure, or a polycrystalline structure. Since the niobium compound, which is the raw material for the niobic acid compound film of the present invention, has high chemical resistance, coating the surface of the substrate with the niobic acid compound film of the present invention can improve the high-temperature properties (e.g., protection from thermal degradation of the substrate) and chemical resistance of the substrate. The method for producing the niobic acid compound film of the present invention will be described later.

[0073] The coating agent of the present invention is characterized by containing the above-mentioned niobic acid compound dispersion of the present invention. The coating agent of the present invention contains the niobic acid compound dispersion of the present invention, which has high dispersibility in water, good solubility in water, and excellent storage stability.

[0074] The coating agent of the present invention is characterized by containing the above-mentioned niobic acid compound powder of the present invention. The coating agent of the present invention contains the niobic acid compound powder of the present invention, which has high dispersibility in water, good solubility in water, and excellent storage stability.

[0075] The niobic acid compound dispersion of the present invention is characterized in that it is used for coating a positive electrode or a positive electrode material for a lithium ion secondary battery. The niobic acid compound dispersion of the present invention can also be used for coating a positive electrode or a positive electrode material for a lithium ion secondary battery.

[0076] The positive electrode active material for a lithium ion secondary battery of the present invention is characterized in that the surface thereof is coated with the niobic acid compound contained in the niobic acid compound dispersion of the present invention. ２ O４ (Merck: spinel type, particle size <0.5 μm), LiCoO ２ , LiNiO ２ , LiFeO ２ , Li ２ MnO ３ , LiFePO ４ , LiCoPO ４ , LiNiPO ４ , LiMnPO ４ , LiNi ０．５ Mn １．５ O ４ , LiMn １／３ Co １／３ Ni １／３ O ２ , LiCo ０．２ Ni ０．４ Mn ０．４ O ２ , lithium molybdate, LiMnO ４ , LiNi ０．８ Co ０．１５ Al ０．０５ O ２ , LiMnO ２ etc. can be used

[0077] The lithium ion secondary battery of the present invention is characterized by having a positive electrode the surface of which is coated with the above-mentioned positive electrode active material for lithium ion secondary batteries of the present invention.

[0078] The method for producing the above-mentioned niobic acid compound dispersion of the present invention will be described below.

[0079] The method for producing a niobium acid compound dispersion of the present invention may include a reaction step of producing a niobium fluoride aqueous solution, a neutralization reaction step of adding the niobium fluoride aqueous solution to an alkaline aqueous solution containing one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements to produce a neutralized niobium compound aqueous solution, and a mixing step of mixing the neutralized niobium compound aqueous solution with a phosphorus compound or a phosphorus compound solution and / or a chlorine compound or a chlorine compound solution.

[0080] First, the niobium fluoride aqueous solution is prepared by reacting niobium, niobium oxide, or niobium hydroxide with hydrofluoric acid (HF), such as an aqueous solution of hydrofluoric acid, to obtain niobium fluoride (H ２ NbF ７ ) and dissolving it in water to prepare the product.

[0081] Here, the niobium fluoride aqueous solution is prepared by adding water (e.g., pure water) to convert niobium into Nb ２ O ５ It is preferable to adjust the niobium content to 1 to 100 g / L in terms of Nb ２ O ５ When the niobium content is 1 g / L or more in terms of Nb, a niobium compound hydrate that is easily soluble in water is obtained, and when productivity is taken into consideration, the niobium content is more preferably 10 g / L or more, and even more preferably 20 g / L or more. ２ O ５ A concentration of 100 g / L or less in terms of conversion is preferable because it results in a niobic acid compound hydrate that is easily soluble in water, and in order to more reliably synthesize a niobic acid compound hydrate that is easily soluble in water, a concentration of 90 g / L or less is more preferable, a concentration of 80 g / L or less is even more preferable, and a concentration of 70 g / L or less is particularly preferable. Note that the pH of the niobium fluoride aqueous solution is preferably 2 or less, more preferably 1 or less, from the viewpoint of completely dissolving niobium or niobium oxide.

[0082] The neutralization reaction step of adding the obtained niobium fluoride aqueous solution to an alkaline aqueous solution containing one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements to produce a neutralized niobium compound aqueous solution is as follows.

[0083] In the neutralization reaction step, the obtained niobium fluoride aqueous solution is first added to ammonia water, i.e., a reverse neutralization method is used to obtain a niobium-containing precipitate slurry. Then, fluoride ions are removed from the obtained niobium-containing precipitate slurry to obtain a niobium-containing precipitate from which fluoride ions have been removed.

[0084] The ammonia content of the ammonia water used for reverse neutralization is preferably 10% by mass to 30% by mass. When the ammonia content is 10% by mass, niobium is less likely to remain undissolved, and niobium or niobic acid can be completely dissolved in water. On the other hand, when the ammonia content is 30% by mass or less, it is preferably close to a saturated aqueous solution of ammonia.

[0085] From this viewpoint, the ammonia content of the ammonia water is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and particularly preferably 25% by mass, while the ammonia content is preferably 30% by mass or less, more preferably 29% by mass or less, and even more preferably 28% by mass or less.

[0086] The amount of niobium fluoride aqueous solution added to the ammonia water is NH ３ / Nb ２ O ５ The molar ratio of NH to NH is preferably 95 or more and 500 or less, more preferably 100 or more and 450 or less, and even more preferably 110 or more and 400 or less. In addition, the amount of niobium fluoride aqueous solution added to ammonia water is adjusted to NH ３ The molar ratio of NH to HF is preferably 3.0 or more, more preferably 4.0 or more, and even more preferably 5.0 or more. ３ The molar ratio of HF to HCl is preferably 100 or less, more preferably 50 or more, and even more preferably 40 or more.

[0087] The time for adding 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, rather than gradually adding the niobium fluoride aqueous solution over time, it is preferable to add it to the ammonia water in as short a time as possible, for example, by adding it all at once, and carry out the neutralization reaction. 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 be carried out while maintaining a high pH. The niobium fluoride aqueous solution and the ammonia water can be used at room temperature.

[0088] Then, fluoride ions are removed from the niobium-containing precipitate slurry obtained by the reverse neutralization method, thereby obtaining a niobium-containing precipitate from which fluoride ions have been removed. Since fluorine compounds such as ammonium fluoride are present as impurities in the niobium-containing precipitate slurry obtained by the reverse neutralization method, it is preferable to remove these.

[0089] Any method for removing fluorine compounds can be used, and examples of such methods include reverse osmosis filtration using aqueous ammonia or pure water, filtration using a membrane such as ultrafiltration or microfiltration, centrifugation, and other known methods. When removing fluoride ions from a niobium-containing precipitate slurry, temperature control is not particularly required, and the removal may be carried out at room temperature.

[0090] Specifically, the niobium-containing precipitate slurry obtained by the reverse neutralization method is decanted using a centrifuge, and washing is repeated until the amount of liberated fluoride ions becomes 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluoride ions have been removed.

[0091] The cleaning solution used to remove fluoride ions is preferably ammonia water. Specifically, ammonia water of 5.0 mass % or less is preferred, ammonia water of 4.0 mass % or less is more preferred, ammonia water of 3.0 mass % or less is even more preferred, and ammonia water of 2.5 mass % is particularly preferred. When the ammonia water is 5.0 mass % or less, ammonia containing ammonium ions is suitable for fluoride ions, and unnecessary cost increases can be avoided.

[0092] The niobium-containing precipitate thus obtained, from which fluoride ions have been removed, is diluted with pure water or the like to obtain a precipitate slurry containing niobium from which fluoride ions have been removed. The niobium content of the niobium-containing precipitate slurry can be 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 obtain a Nb ２ O ５ The Nb produced in this way ２ O ５ The weight of the slurry is measured, and the niobium content of the slurry can be calculated from the weight.

[0093] Next, in the neutralization reaction step, the produced fluoride ions are removed to obtain a niobium-containing precipitate slurry.The niobium-containing precipitate slurry from which the fluoride ions have been removed, a hydroxide of element X (e.g., lithium hydroxide monohydrate), and pure water are mixed together and stirred at 20°C to 100°C for 0.1 to 72 hours to obtain a neutralized aqueous solution of a niobium compound.

[0094] The mixing step of mixing the obtained aqueous neutralized solution of a niobium compound with a phosphorus compound or a phosphorus compound solution and / or a chlorine compound or a chlorine compound solution is as follows.

[0095] In the mixing step, a phosphorus compound or a phosphorus compound solution and / or a chlorine compound or a chlorine compound solution is added to the obtained neutralized aqueous solution of a niobium compound, and the mixture is mixed at room temperature for 0.1 to 2 hours, thereby obtaining the niobic acid compound dispersion of the present invention.

[0096] Here, the phosphorus compound preferably contains at least one selected from inorganic phosphorus compounds, organic phosphorus compounds, and salts thereof.

[0097] Furthermore, it is preferable that the phosphorus compound contains at least one selected from condensed phosphoric acid, pyrophosphoric acid (CAS No.: 2466-09-3), polyphosphoric acid (CAS No.: 8071-16-1), phosphorous acid (CAS No.: 13598-36-2), hypophosphorous acid (CAS No.: 6303-21-5), ammonium phosphate, monoammonium phosphate (CAS No.: 7722-76-1), diammonium phosphate (CAS No.: 7783-28-0), ammonium pyrophosphate, and ammonium polyphosphate.

[0098] Alternatively, the niobate compound dispersion of the present invention may be a phosphorus compound solution obtained by adding pure water to the above-mentioned phosphorus compound and adjusting the concentration so that the phosphorus content in terms of P atoms in the niobate compound dispersion of the present invention is 0.01 mass % or more and 10 mass % or less.

[0099] Examples of chlorine compounds include hydrochloric acid (CAS number: 7647-01-0), hypochlorous acid (CAS number: 7790-92-3), chlorous acid (CAS number: 13898-47-0), chloric acid (CAS number: 7790-93-4), and perchloric acid (CAS number: 7601-90-3).

[0100] The chlorine compound may also be a salt of the above-mentioned chlorine compound, such as an ammonium salt, an amine salt, a quaternary ammonium salt, or a lithium salt, with ammonium salts and lithium salts being preferred. Specific examples include ammonium chloride (CAS No.: 12125-02-9), ammonium perchlorate (CAS No.: 7790-98-9), lithium chloride (CAS No.: 7447-41-8), lithium perchlorate (CAS No.: 7791-03-9), methylamine hydrochloride (CAS No.: 593-51-1), and dimethylamine hydrochloride (CAS No.: 506-59-2).

[0101] Alternatively, the niobic acid compound dispersion of the present invention may be a chlorine compound solution obtained by adding pure water to the above-mentioned chlorine compound and adjusting the concentration so that the chlorine content in terms of Cl atoms in the niobic acid compound dispersion of the present invention is 0.0 mass % or more and 2.0 mass % or less.

[0102] In the method for producing a niobic acid compound dispersion of the present invention, the mixing step may involve mixing the phosphorus compound, or the phosphorus compound solution and / or the chlorine compound, or the chlorine compound solution with the element X in advance to produce a phosphorus compound mixed solution and / or a chlorine compound mixed solution, with the niobium compound neutralized aqueous solution. In the mixing step in the method for producing a niobic acid compound dispersion of the present invention, before adding the phosphorus compound, or the phosphorus compound solution and / or the chlorine compound, or the chlorine compound solution to the niobium compound neutralized aqueous solution, the phosphorus compound, or the phosphorus compound solution and / or the chlorine compound, or the chlorine compound solution may be mixed in advance with one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements to form a phosphorus compound mixed solution and / or a chlorine compound mixed solution.

[0103] The one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements to be premixed with the phosphorus compound or phosphorus compound solution and / or chlorine compound or chlorine compound solution include, for example, lithium hydroxide monohydrate.

[0104] Furthermore, in order to remove the ammonia component contained in the obtained niobic acid compound dispersion of the present invention, the following concentration adjustment step may be carried out. In the concentration adjustment step, for example, 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 niobium content of the niobium compound dispersion of the present invention after the ammonia component has been removed matches the niobium content of the niobium compound dispersion of the present invention before the ammonia component has been removed.

[0105] Specifically, the niobium compound dispersion of the present invention is obtained by mixing and stirring the obtained aqueous solution of a neutralized niobium compound with a phosphorus compound or a phosphorus compound solution and / or a chlorine compound or a chlorine compound solution so that the niobium content of the final mixture is 0.01% by mass or more and 30% by mass or less in terms of Nb atoms. The composition ratio of each component in the niobate compound dispersion of the present invention obtained in this manner is preferably as follows:

[0106] When the element X contained in the niobate compound dispersion of the present invention is lithium, the molar ratio Li / (P+Cl) of lithium (Li) to the total amount of phosphorus compounds and / or chlorine compounds (P+Cl) is preferably 0.01 or more and 10 or less in terms of improving dispersibility and solubility in water, more preferably 0.05 or more and 8 or less, even more preferably 0.05 or more and 7 or less, particularly preferably 0.07 or more and 5 or less, more particularly preferably 0.1 or more and 4 or less, even more particularly preferably 0.1 or more and 3 or less, still particularly preferably 0.1 or more and 2 or less, and even more particularly preferably 0.4 or more and 1.9 or less. Even when the element X contained in the niobate compound dispersion of the present invention is an element X selected from alkali metal elements and / or alkaline earth metal elements other than lithium, the molar ratio M / (P+Cl) of the total amount of element X (M) to the total amount of phosphorus compounds and / or chlorine compounds (P+Cl) is preferably 0.01 or more and 10 or less in terms of improving dispersibility and solubility in water, more preferably 0.05 or more and 8 or less, even more preferably 0.05 or more and 7 or less, particularly preferably 0.07 or more and 5 or less, more particularly preferably 0.1 or more and 4 or less, even more particularly preferably 0.1 or more and 3 or less, still particularly preferably 0.1 or more and 2 or less, and even more particularly preferably 0.4 or more and 1.9 or less. Note that this also includes cases where the element X is a plurality of elements, including lithium and other alkali metal elements and / or alkaline earth metal elements, and a plurality of elements selected from alkali metal elements and / or alkaline earth metals other than lithium.

[0107] When the element X contained in the niobate compound dispersion of the present invention is lithium, the molar ratio Li / P of lithium (Li) to the total amount of phosphorus compounds (P) is preferably 0.01 or more and 10 or less in terms of improving dispersibility and solubility in water, more preferably 0.05 or more and 8 or less, even more preferably 0.05 or more and 7 or less, particularly preferably 0.07 or more and 5 or less, more particularly preferably 0.1 or more and 4 or less, even more particularly preferably 0.1 or more and 3 or less, also particularly preferably 0.1 or more and 2 or less, and even more particularly preferably 0.4 or more and 1.9 or less. Even when the element X contained in the niobate compound dispersion of the present invention is an element X selected from alkali metal elements and / or alkaline earth metal elements other than lithium, the molar ratio M / P of the total amount of element X (M) to the total amount of phosphorus compounds (P) is preferably 0.01 or more and 10 or less in terms of improving dispersibility and solubility in water, more preferably 0.05 or more and 8 or less, even more preferably 0.05 or more and 7 or less, particularly preferably 0.07 or more and 5 or less, more particularly preferably 0.1 or more and 4 or less, even more particularly preferably 0.1 or more and 3 or less, still particularly preferably 0.1 or more and 2 or less, and even more particularly preferably 0.4 or more and 1.9 or less.

[0108] Furthermore, the molar ratio Nb / (P+Cl) of niobium (Nb) contained in the niobic acid compound dispersion of the present invention to the total amount (P+Cl) of phosphorus compounds and / or chlorine compounds is preferably 0.01 or more and 10 or less, from the viewpoint of improving dispersibility and solubility in water, more preferably 0.1 or more and 5 or less, even more preferably 0.1 or more and 1 or less, and particularly preferably 0.1 or more and 0.4 or less.

[0109] Furthermore, the molar ratio Nb / P of niobium (Nb) contained in the niobic acid compound dispersion of the present invention to the total amount (P) of phosphorus compounds is preferably 0.01 or more and 10 or less, in terms of improving dispersibility and solubility in water, more preferably 0.1 or more and 5 or less, even more preferably 0.1 or more and 1 or less, and particularly preferably 0.1 or more and 0.4 or less.

[0110] Furthermore, when the element X contained in the niobate compound dispersion of the present invention is lithium, the molar ratio Li / Nb of lithium (Li) to niobium (Nb) is preferably 0.01 or more and 10 or less, from the viewpoint of improving dispersibility and solubility in water, more preferably 1 or more and 9 or less, and even more preferably 1 or more and 7 or less. When the element X contained in the niobate compound dispersion of the present invention is an element X selected from alkali metal elements and / or alkaline earth metal elements other than lithium, the molar ratio M / Nb of the total amount of element X (M) to niobium (Nb) is also preferably 0.01 or more and 10 or less, from the viewpoint of improving dispersibility and solubility in water, more preferably 0.1 or more and 10 or less, even more preferably 1 or more and 9 or less, and particularly preferably 1 or more and 7 or less. Note that this also includes cases where the element X is a plurality of elements, such as lithium and other alkali metal elements and / or alkaline earth metal elements, and cases where the element X is a plurality of elements selected from alkali metal elements and / or alkaline earth metals other than lithium.

[0111] Another example of the method for producing a niobium acid compound dispersion of the present invention may include a reaction step of producing a niobium fluoride aqueous solution, a neutralization reaction step of adding the niobium fluoride aqueous solution to an alkaline aqueous solution containing an organic nitrogen compound to produce a neutralized niobium compound aqueous solution, and a mixing step of adding a phosphorus compound mixed solution and / or a chlorine compound mixed solution produced by mixing a phosphorus compound, or a phosphorus compound solution and / or a chlorine compound, or a chlorine compound solution with one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, to the neutralized niobium compound aqueous solution and mixing.

[0112] Here, in another example of the method for producing a niobium compound dispersion of the present invention, the steps up to obtaining a niobium-containing precipitate slurry from which fluoride ions have been removed are the same as those in the method for producing a niobium compound dispersion of the present invention described above, and therefore detailed explanations thereof will be omitted.

[0113] In the same manner as in the above-described method for producing a niobium acid compound dispersion of the present invention, the obtained niobium-containing precipitate slurry from which fluoride ions have been removed, an organic nitrogen compound, and pure water are mixed together, and the mixture is maintained at 5°C to 90°C for 0.1 to 48 hours with stirring, to obtain a neutralized aqueous solution of a niobium compound.

[0114] The organic nitrogen compound to be mixed with the niobium-containing precipitation slurry is preferably an aliphatic amine, an aromatic amine, an amino alcohol, an amino acid, a polyamine, a quaternary ammonium, a guanidine compound, or an azole compound, as described above, and more preferably an aliphatic amine and / or a quaternary ammonium compound.

[0115] From the viewpoint of solubility, the aliphatic amine is preferably mixed so that the aliphatic amine content in the niobium-containing precipitation slurry is 40% by mass or less, more preferably 20% by mass or less. From the same viewpoint, the aliphatic amine is preferably mixed so that the aliphatic amine content in the niobium-containing precipitation slurry is 0.1% by mass or more, more preferably 1% by mass or more, and may be 5% by mass or more, or may be 10% by mass or more. The aliphatic amine is more preferably methylamine or dimethylamine.

[0116] From the viewpoint of solubility, the quaternary ammonium compound is preferably mixed so that the content of the quaternary ammonium compound in the niobium-containing precipitation slurry is 40% by mass or less, more preferably 20% by mass or less. From the same viewpoint, the quaternary ammonium compound is preferably mixed so that the content of the quaternary ammonium compound in the niobium-containing precipitation slurry is 0.1% by mass or more, more preferably 1% by mass or more, and may be 5% by mass or more, or may be 10% by mass or more. The quaternary ammonium compound is more preferably tetramethylammonium hydroxide (TMAH) or tetraethylammonium hydroxide (TEAH).

[0117] In the mixing step in another example of the method for producing a niobic acid compound dispersion of the present invention, a phosphorus compound mixed solution and / or a chlorine compound mixed solution produced by mixing a phosphorus compound, or a phosphorus compound solution and / or a chlorine compound, or a chlorine compound solution with one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, is added to the obtained neutralized aqueous solution of niobium compound, and mixed.

[0118] The phosphorus compound mixed solution is produced by previously mixing a phosphorus compound or a phosphorus compound solution with one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements.

[0119] Here, the phosphorus compound preferably contains at least one selected from inorganic phosphorus compounds, organic phosphorus compounds, and salts thereof.

[0120] Furthermore, it is preferable that the phosphorus compound contains one or more compounds selected from phosphoric acid (CAS No.: 7664-38-2), condensed phosphoric acid, pyrophosphoric acid (CAS No.: 2466-09-3), polyphosphoric acid (CAS No.: 8071-16-1), phosphorous acid (CAS No.: 13598-36-2), hypophosphorous acid (CAS No.: 6303-21-5), ammonium phosphate, monoammonium phosphate (CAS No.: 7722-76-1), diammonium phosphate (CAS No.: 7783-28-0), ammonium pyrophosphate, and ammonium polyphosphate.

[0121] Alternatively, the niobate compound dispersion of the present invention may be a phosphorus compound solution obtained by adding pure water to the above-mentioned phosphorus compound and adjusting the concentration so that the phosphorus content in terms of P atoms in the niobate compound dispersion of the present invention is 0.01 mass % or more and 10 mass % or less.

[0122] The chlorine compound mixed solution is produced by pre-mixing a chlorine compound or a chlorine compound solution with one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements.

[0123] Examples of chlorine compounds include hydrochloric acid (CAS number: 7647-01-0), hypochlorous acid (CAS number: 7790-92-3), chlorous acid (CAS number: 13898-47-0), chloric acid (CAS number: 7790-93-4), and perchloric acid (CAS number: 7601-90-3).

[0124] The chlorine compound may also be a salt of the above-mentioned chlorine compound, such as an ammonium salt, an amine salt, a quaternary ammonium salt, or a lithium salt, with ammonium salts and lithium salts being preferred. Specific examples include ammonium chloride (CAS No.: 12125-02-9), ammonium perchlorate (CAS No.: 7790-98-9), lithium chloride (CAS No.: 7447-41-8), lithium perchlorate (CAS No.: 7791-03-9), methylamine hydrochloride (CAS No.: 593-51-1), and dimethylamine hydrochloride (CAS No.: 506-59-2).

[0125] Alternatively, the niobic acid compound dispersion of the present invention may be a chlorine compound solution obtained by adding pure water to the above-mentioned chlorine compound and adjusting the concentration so that the chlorine content in terms of Cl atoms in the niobic acid compound dispersion of the present invention is 0.0 mass % or more and 2.0 mass % or less.

[0126] Furthermore, examples of the one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements that are premixed with the phosphorus compound or phosphorus compound solution and / or chlorine compound or chlorine compound solution include lithium hydroxide monohydrate.

[0127] The order of adding the niobium compound neutralized aqueous solution, the phosphorus compound or phosphorus compound solution and / or the chlorine compound or chlorine compound solution, one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, pure water, etc., which are mixed in the mixing step of the method for producing a niobic acid compound dispersion of the present invention, is not limited to the order described above and can be changed as appropriate.

[0128] A method for producing a niobic acid compound powder containing a niobic acid compound in a niobic acid compound dispersion of the present invention will be described below.

[0129] Among the niobic acid compound powders, a method for producing a dry powder of a niobic acid compound involves placing the niobic acid compound dispersion obtained by the above-mentioned method for producing a niobic acid compound dispersion of the present invention in a static furnace and drying, for example, vacuum drying, for 1 hour to 72 hours at a heating temperature of about 60°C to 200°C, thereby evaporating the water content of the niobic acid compound dispersion of the present invention and producing a dry powder of the niobic acid compound containing crystal particles of the niobic acid compound contained in the niobic acid compound dispersion of the present invention.

[0130] On the other hand, the method for producing the calcined powder of the niobic acid compound includes vacuum-drying the niobic acid compound dispersion of the present invention as described above, placing the obtained dry powder of the niobic acid compound in a static furnace, and calcining it in the atmosphere at a calcination temperature of 300°C or higher and 1,200°C or lower for a calcination time of 1 hour or higher and 72 hours or lower, thereby obtaining the calcined powder of the niobic acid compound.

[0131] The niobic acid compound powder may be obtained by pulverizing the dried powder and calcined powder of the niobic acid compound described above. Furthermore, regardless of whether or not the powder is pulverized, the undersized particles (fine particles) obtained by classifying the dried powder and calcined powder of the niobic acid compound described above using a sieve or the like may be used as the niobic acid compound powder. The oversized particles (coarse particles) may be re-pulverized and classified for use. It is also possible to combine pulverization and classification using a vibrating sieve containing nylon- or fluororesin-coated iron balls or the like as a grinding medium. By combining classification and pulverization in this way, even if excessively large niobic acid compound powder is present, it is possible to remove it. Specifically, when classifying using a sieve, it is preferable to use one with a mesh size of 150 μm to 1,000 μm. When the particle size is 150 μm to 1,000 μm, the proportion of oversized particles does not become too high, so that repeated re-pulverization is not required, and the niobic acid compound powder that requires re-pulverization is not classified as undersized particles.

[0132] The niobic acid compound powder thus obtained can be mixed with water or an organic solvent as a dispersion medium and wet-pulverized using media such as beads to obtain a niobic acid compound powder dispersion. Examples of organic solvents used as dispersion media include alcohols, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, ethers, and mixtures thereof. Furthermore, to improve the film-forming properties of a niobic acid compound film using the niobic acid compound powder dispersion, a binder such as a resin component may be added. Examples of resin components used as binders include acrylic resins, polyurethanes, epoxy resins, polystyrene, polycarbonates, glycol-based resins, cellulose-based resins, and mixtures and copolymer resins thereof.

[0133] Furthermore, a method for producing a niobate compound film containing a niobate compound in the niobate compound dispersion of the present invention will be described below.

[0134] Among niobic acid compound films, a method for producing a niobic acid compound dry film includes a coating step of coating a niobic acid compound dispersion onto the surface of a substrate, and a film drying step of drying the niobic acid compound dispersion coated on the surface of the substrate to obtain a dry film.

[0135] Specifically, the niobic acid compound dispersion obtained by the above-described method for producing a niobic acid compound dispersion of the present invention is dropped onto the surface of a substrate using a syringe while, if necessary, filtering it through a filter with a pore size of 1 μm, for example, and applied by spin coating (700 rpm, 10 seconds, then 1500 rpm, 30 seconds). Next, the resulting mixture is dried at 110° C. for 30 minutes to form a dry niobic acid compound film on the surface of the substrate.

[0136] Of the niobic acid compound films, the method for producing a fired niobic acid compound film includes a coating step of coating a niobic acid compound dispersion onto the surface of a substrate, a film drying step of drying the niobic acid compound dispersion coated on the surface of the substrate in the atmosphere or under vacuum to obtain a dried film, and a film firing step of firing the dried film in the atmosphere at a firing temperature of 300°C or higher and 1,200°C or lower for a firing time of 1 hour or higher and 12 hours or lower to obtain a fired film.

[0137] Specifically, as described above, the niobic acid compound dispersion is applied to the surface of a substrate, and the substrate having a niobic acid compound dry film formed thereon by drying is placed in a static furnace and fired in the atmosphere at a firing temperature of 300°C or higher and 1,200°C or lower for a firing time of 1 hour or higher and 12 hours or lower, thereby forming a niobic acid compound fired film on the surface of the substrate.

[0138] Furthermore, a method for producing a positive electrode active material for a lithium ion secondary battery coated with a niobic acid compound contained in the niobic acid compound dispersion of the present invention will be described below.

[0139] The method includes a step of mixing the niobic acid compound dispersion of the present invention, a positive electrode active material, and, if necessary, an aqueous lithium hydroxide solution to produce a positive electrode active material slurry for a battery containing a niobic acid compound, and a step of drying the positive electrode active material slurry for a battery containing the niobic acid compound.

[0140] First, the niobic acid compound dispersion of the present invention is diluted with pure water, and a positive electrode active material for a battery, for example, LiMn ２ O ４ (Merck: spinel type, particle size <0.5 μm) is added to obtain a slurry containing a niobic acid compound. Then, while stirring the slurry containing the niobic acid compound, an aqueous solution of lithium hydroxide is added dropwise, and the mixture is maintained at 90° C. for 10 minutes, thereby producing a slurry of a positive electrode active material for a battery containing the niobic acid compound.

[0141] Next, the battery positive electrode active material slurry containing the niobic acid compound is dried in an atmospheric drying furnace for 15 hours while maintaining the furnace temperature at 110°C, thereby producing a positive electrode active material for a lithium ion secondary battery coated with a niobic acid compound.

[0142] In this specification, when "X to Y" (X and Y are any numbers) is expressed, unless otherwise specified, it means "X or more and Y or less", and also means "preferably larger than X" or "preferably smaller than Y". Furthermore, when "X or more" (X is any number) or "Y or less" (Y is any number), it also means "preferably larger than X" or "preferably smaller than Y".

[0143] The niobic acid compound dispersion of the present invention has high dispersibility in polar solvents, particularly water, good solubility in water, and excellent storage stability. Furthermore, the method for producing a niobic acid compound dispersion of the present invention can produce a niobic acid compound dispersion that has high dispersibility in polar solvents, particularly water, good solubility in water, and excellent storage stability.

[0144] 1 is a table listing the physical property values ​​of niobic acid compound dispersions according to Examples 1 to 10 of the present invention and Comparative Examples 1 to 3. 2 is a table listing the measurement results of niobic acid compound dispersions according to Examples 1 to 10 of the present invention and Comparative Examples 1 to 3.

[0145] The niobate compound dispersion liquid according to the embodiment of the present invention will be further described below with reference to the following examples, although the present invention is not limited to these examples.

[0146] Example 1 0.3 g of pyrophosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: diphosphoric acid (containing phosphoric acid), CAS number: 2466-09-3) and 28.5 g of pure water were placed in a polypropylene container, and 0.84 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0147] Here, the 5 mass % lithium hydroxide monohydrate aqueous solution is LiOH·H ２ It was obtained by mixing 15 g of 0 with 285 g of pure water.

[0148] Then, 2.93 g of a neutralized aqueous solution of a niobium compound, which will be described later, was added to the phosphorus compound mixed solution, and the mixture was stirred for 30 minutes to obtain a niobic acid compound dispersion liquid according to Example 1.

[0149] The neutralized aqueous solution of a niobium compound according to Example 1 was obtained as follows.

[0150] 100 g of niobium pentoxide was dissolved in 200 g of 55% aqueous hydrofluoric acid solution, and 830 mL of pure water was added to obtain a niobium fluoride aqueous solution containing 100 g / L of niobium calculated as NbO (NbO = 8.85 wt%). 200 mL of this niobium fluoride aqueous solution was added to 1 L of aqueous ammonia (NH concentration 25 wt%) over a period of less than 1 minute (NH / NbO molar ratio = 176.9, NH / HF molar ratio = 12.1) to obtain a reaction solution (pH 11). This reaction solution was a slurry of niobium acid compound hydrate, in other words, a slurry of niobium-containing precipitate.

[0151] The reaction solution was then decanted using a centrifuge and washed until the amount of liberated fluoride ions was 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which the fluoride ions had been removed. At this time, aqueous ammonia was used as the washing liquid.

[0152] Furthermore, the niobium-containing precipitate from which the fluoride ions had been removed was diluted with pure water to obtain a slurry. A portion of this slurry was dried at 110°C for 24 hours and then calcined at 1,000°C for 4 hours to produce NbO, and the weight of the NbO contained in the slurry was calculated. ２ O ５ The content was calculated.

[0153] The niobium-containing precipitate slurry diluted with pure water, 5 mass % lithium hydroxide, and pure water were mixed to obtain a translucent slurry mixture. This mixture was stirred and maintained at a liquid temperature of 50°C to 100°C, for example, 70°C, for 1 hour to obtain a neutralized aqueous solution of a niobium compound according to Example 1. The niobium content in the neutralized aqueous solution of a niobium compound according to Example 1 was 2.86 mass %, and the lithium content was 0.23 mass %.

[0154] Example 2 In Example 2, 0.29 g of pyrophosphoric acid and 26.85 g of pure water were placed in a polypropylene container, and 2.85 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0155] Then, 3.02 g of the niobium compound neutralized aqueous solution used in Example 1 was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a niobic acid compound dispersion liquid according to Example 2.

[0156] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 2 were the same as those used in Example 1.

[0157] Example 3 In Example 3, 0.29 g of pyrophosphoric acid and 25.51 g of pure water were placed in a polypropylene container, and 4.22 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0158] Then, 2.96 g of the niobium compound neutralized aqueous solution used in Example 1 was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a niobic acid compound dispersion liquid according to Example 3.

[0159] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 3 were the same as those used in Example 1.

[0160] Example 4 In Example 4, 0.40 g of phosphoric acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., product name: phosphoric acid, CAS number: 7664-38-2) and 28.7 g of pure water were placed in a polypropylene container, and 0.85 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the obtained aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0161] Then, 3.02 g of the niobium compound neutralized aqueous solution used in Example 1 was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a niobic acid compound dispersion liquid according to Example 4.

[0162] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 4 was the same as that used in Example 1.

[0163] Example 5 In Example 5, 0.38 g of phosphoric acid and 26.7 g of pure water were placed in a polypropylene container, and 2.89 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0164] Then, 2.97 g of the niobium compound neutralized aqueous solution used in Example 1 was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a niobic acid compound dispersion liquid according to Example 5.

[0165] The phosphoric acid used in Example 5 was the same as that used in Example 4, and the 5 mass % aqueous solution of lithium hydroxide monohydrate was the same as that used in Example 1.

[0166] Example 6 In Example 6, 0.41 g of phosphoric acid and 25.39 g of pure water were placed in a polypropylene container, and 4.28 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0167] Then, 3.01 g of the niobium compound neutralized aqueous solution used in Example 1 was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a niobic acid compound dispersion liquid according to Example 6.

[0168] The phosphoric acid used in Example 6 was the same as that used in Example 4, and the 5 mass % aqueous solution of lithium hydroxide monohydrate was the same as that used in Example 1.

[0169] Example 7 In Example 7, 3.44 g of 1 mol / L hydrochloric acid and 24.01 g of pure water were placed in a polypropylene container, and 4.24 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the obtained aqueous solution of chlorine compounds to obtain a mixed solution of chlorine compounds.

[0170] Then, 3.27 g of the niobium compound neutralized aqueous solution used in Example 1 was added to the chlorine compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a niobic acid compound dispersion liquid according to Example 7.

[0171] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 7 was the same as that used in Example 1.

[0172] Example 8 In Example 8, 0.28 g of phosphonic acid and 27.06 g of pure water were placed in a polypropylene container, and 4.27 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the obtained aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0173] Then, 3.29 g of the niobium compound neutralized aqueous solution used in Example 1 was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a niobic acid compound dispersion liquid according to Example 8.

[0174] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 8 was the same as that used in Example 1.

[0175] Example 9 In Example 9, 0.75 g of 30 mass% phosphinic acid and 26.74 g of pure water were placed in a polypropylene container, and 4.22 g of 5 mass% lithium hydroxide monohydrate aqueous solution was added to the obtained phosphorus compound aqueous solution to obtain a phosphorus compound mixed solution.

[0176] Then, 3.29 g of the niobium compound neutralized aqueous solution used in Example 1 was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a niobic acid compound dispersion liquid according to Example 9.

[0177] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 9 was the same as that used in Example 1.

[0178] (Example 10) In Example 10, a polypropylene container was filled with 80% by mass of P ２ O ５ 0.29 g of polyphosphoric acid and 27.15 g of pure water were added, and 4.23 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0179] Then, 3.29 g of the niobium compound neutralized aqueous solution used in Example 1 was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a niobic acid compound dispersion liquid according to Example 10.

[0180] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 10 was the same as that used in Example 1.

[0181] Comparative Example 1 In Comparative Example 1, 0.3 g of pyrophosphoric acid and 25.42 g of pure water were placed in a polypropylene container, and 4.21 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0182] Then, 0.16 g of lithium niobate powder (manufactured by Kojundo Chemical Laboratory Co., Ltd.) was added to the phosphorus compound mixed solution, and the mixture was stirred for 30 minutes to obtain a niobate compound dispersion liquid according to Comparative Example 1.

[0183] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Comparative Example 1 were the same as those used in Example 1.

[0184] Comparative Example 2 In Comparative Example 2, 3.33 g of 10 mass % sulfuric acid and 24.13 g of pure water were placed in a polypropylene container, and 4.25 g of 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the obtained aqueous sulfur compound solution to obtain a sulfur compound mixed solution.

[0185] Then, 3.28 g of the niobium compound neutralized aqueous solution used in Example 1 was added to the sulfur compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a niobic acid compound dispersion liquid according to Comparative Example 2.

[0186] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Comparative Example 2 was the same as that used in Example 1.

[0187] Comparative Example 3 In Comparative Example 3, 7.64 g of a 5 mass % lithium hydroxide monohydrate aqueous solution and 5.98 g of the niobium compound neutralized aqueous solution used in Example 1 were added to 21.32 g of pure water placed in a polypropylene container, and the mixture was stirred and mixed for 30 minutes to obtain a niobate compound dispersion liquid according to Comparative Example 3.

[0188] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Comparative Example 3 was the same as that used in Example 1.

[0189] The following physical properties were measured for the niobic acid compound dispersions according to Examples 1 to 10 and Comparative Examples 1 to 3. The measured physical properties and the methods for measuring the physical properties are shown below, and the physical properties and measurement results for the niobic acid compound dispersions according to Examples 1 to 10 and Comparative Examples 1 to 3 are shown in Figures 1 and 2.

[0190] <Elemental Analysis> If necessary, the sample was appropriately diluted with dilute hydrochloric acid, and for the niobic acid compound dispersions according to Examples 1 to 10 and Comparative Examples 1 to 3, Nb mass % in terms of Nb atoms, P mass % in terms of P atoms, Li mass % in terms of Li atoms, Cl mass % in terms of Cl atoms, and S mass % in terms of S atoms were measured using an ICP optical emission spectrometry (AG-5110 manufactured by Agilent Technologies) in accordance with JIS K0116:2014.

[0191] <pH Measurement> The pH of the niobic acid compound dispersions according to Examples 1 to 10 and Comparative Examples 1 to 3 was measured using an electrode (HORIBA: Standard ToupH electrode 9615S-10D) of a pH meter (HORIBA: Glass electrode type hydrogen ion concentration indicator D-51) after confirming that the liquid temperature had stabilized at 25°C. The "initial pH" in FIG. 2 refers to the pH of the niobic acid compound dispersions whose liquid temperature was adjusted to 25°C immediately after production. The "pH over time" in FIG. 2 refers to the pH of the niobic acid compound dispersions according to Examples 1 to 10 and Comparative Examples 1 to 3 after they were allowed to stand for one month from the day of production in an incubator set at room temperature of 25°C.

[0192] <Dynamic Light Scattering Method> Particle size distribution was evaluated by dynamic light scattering in accordance with JIS Z 8828:2019 using a zeta potential, particle size, and molecular weight measurement system (ELSZ-2000, manufactured by Otsuka Electronics Co., Ltd.). Furthermore, immediately before measurement, the niobic acid compound dispersions of Examples 1 to 10, which were the measurement targets, were filtered through a filter with a 1 μm pore size to remove dust and other particles. Furthermore, D50 indicates the particle diameter at which the volume fraction reaches 50%. In FIG. 2, "initial particle diameter D50 (nm)" refers to the particle diameter (D50) of particles in the niobic acid compound dispersion immediately after production. Furthermore, "aged particle diameter D50 (nm)" in FIG. 2 refers to the particle diameter (D50) of particles in the niobic acid compound dispersions of Examples 1 to 10 and Comparative Examples 1 to 3 after they were left standing in an incubator set at room temperature of 25°C for one month from the day of production. In addition, in the niobic acid compound dispersions according to Comparative Examples 1 to 3, precipitates were visible, so the particle diameter (D50) was not measured.

[0193] <Transmittance Measurement> 3 ml of the niobic acid compound dispersions according to Examples 1 to 10 and Comparative Examples 1 to 3 were placed in a synthetic quartz cell with an optical path length of 5 mm, and the transmittance in the wavelength region of 400 nm to 760 nm (specifically, the transmittance at wavelengths of 400 nm, 600 nm, and 750 nm) of the niobic acid compound dispersions according to Examples 1 to 10 and Comparative Examples 1 to 3 was measured using a spectrophotometer under the transmittance measurement conditions described above. The "initial transmittance" in FIG. 1 refers to the transmittance of the niobic acid compound dispersions adjusted to a liquid temperature of 25°C immediately after production. Furthermore, the "temporary transmittance" in FIG. 1 refers to the transmittance of the niobic acid compound dispersions according to Examples 1 to 10 and Comparative Examples 1 to 3 after they were left in an incubator set at room temperature of 25°C for one month from the day of production.

[0194] <Film Formability Test> The appearance of the coating film formed on the surface of a glass substrate, which was a substitute for a current collector plate, was evaluated by observation with an optical microscope. First, the niobic acid compound dispersions according to Examples 1 to 10 and Comparative Examples 1 to 3 were allowed to stand for one month from the day of production in an incubator set at room temperature (25°C). Next, the niobic acid compound dispersions according to Examples 1 to 10 and Comparative Examples 1 to 3 after standing for one month were dropped onto a 50 mm x 50 mm glass substrate that had been degreased and washed with acetone using a syringe while being filtered through a 0.22 μm pore size filter, and then dried, and coated by spin coating (700 rpm, 10 seconds, followed by 1500 rpm, 15 seconds). The coated area was then allowed to dry naturally, forming a coating film on the glass substrate. The glass substrate was observed with an optical microscope (magnification: 40x) in a central 15 mm x 15 mm area of ​​the formed coating film. If no particles were present and a film was formed, the substrate was evaluated as having excellent film-forming properties and was rated as "Good (◯)," and if particles were observed, the substrate was evaluated as having poor film-forming properties and was rated as "Bad (×)."

[0195] < ３１ P-NMR Spectroscopic Measurement> The phosphorus content in the niobic acid compound dispersion liquid according to Examples 3 and 6 was measured by ３１The P-NMR spectrum was used for calculation. Specifically, 70 μL of the niobic acid compound dispersions according to Examples 3 and 6 were mixed with 650 μL of a phosphonoacetic acid heavy water solution in which 10 g / L of phosphonoacetic acid was dissolved in heavy water to prepare a measurement sample. The prepared measurement sample was subjected to the above-mentioned ３１ By performing a Fourier transform on the FID data measured under the P-NMR spectrum measurement conditions without using a window function, ３１ P-NMR spectrum was obtained. ３１ For the P-NMR spectrum, the peak areas were calculated using the Integrate function of the above-mentioned measurement and data processing software, and the contents of phosphonoacetic acid and each phosphate ion in the niobic acid compound dispersion liquids according to Examples 3 and 6 were calculated from the peak areas.

[0196] As shown in FIGS. 1 and 2 , the niobate compound dispersions according to Examples 1 to 10 contained niobium and one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, and a phosphorus compound and / or a chlorine compound. When the particle diameter (D50) of the particles in the niobate compound dispersions measured by dynamic light scattering method was 1000 nm or less, the dispersions had high dispersibility in a dispersion medium and excellent solubility.

[0197] The niobic acid compound dispersions according to Examples 1 to 10 contained niobium, one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, and a phosphorus compound and / or a chlorine compound, and when the maximum value of the transmittance in the wavelength region of 400 nm to 760 nm was 70% T or more, the dispersions had high dispersibility in the dispersion medium and excellent solubility.

[0198] The niobium compound dispersions according to Examples 1 to 10 had excellent stability over time when the niobium content in the niobium compound dispersions according to Examples 1 to 10 was 0.01 mass % or more and 30 mass % or less in terms of Nb atoms.

[0199] The niobic acid compound dispersions according to Examples 1 to 10 had excellent stability over time when the phosphorus content in the niobic acid compound dispersions according to Examples 1 to 10 was 0.01 mass % or more and 10 mass % or less in terms of P atoms.

[0200] The niobic acid compound dispersions according to Examples 1 to 10 showed excellent stability over time, with the particle diameter (D50) over time not significantly different from the initial particle diameter (D50) even after one month had passed. Note that the niobic acid compound dispersion according to Comparative Example 1 showed precipitates.

[0201] The niobic acid compound dispersions according to Examples 1 to 10 exhibited improved stability during long-term storage when the molar ratio M / Nb of the total amount (M) of one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements to niobium (Nb) was 0.01 or more and 10 or less. Furthermore, the niobic acid compound dispersions according to Examples 1 to 6 exhibited improved stability during long-term storage when the element X was Li and the molar ratio Li / Nb of lithium (Li) to niobium (Nb) was 0.01 or more and 10 or less.

[0202] The niobic acid compound dispersions according to Examples 1 to 10 exhibited improved stability during long-term storage when the molar ratio M / (P+Cl) of the total amount (M) of one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements to the total amount (P+Cl) of phosphorus compounds and / or chlorine compounds was 0.01 or more and 10 or less. Furthermore, the niobic acid compound dispersions according to Examples 1 to 10 exhibited improved stability during long-term storage when the molar ratio Li / (P+Cl) of lithium (Li) to the total amount (P+Cl) of phosphorus compounds and / or chlorine compounds when the element X was Li was 0.01 or more and 10 or less. Note that in the niobic acid compound dispersion according to Comparative Example 2 in the item "Li / (P+Cl)" in FIG. 1 , the value is the molar ratio "Li / (P+S)", and "S" is the value calculated in terms of S atoms.

[0203] The niobic acid compound dispersions according to Examples 1 to 10 had improved stability during long-term storage when the molar ratio Nb / (P+Cl) of niobium (Nb) to the total amount (P+Cl) of phosphorus compounds and / or chlorine compounds was 0.01 or more and 10 or less. In the niobic acid compound dispersion according to Comparative Example 2 in the item "Nb / (P+Cl)" in Fig. 1, this is the value of the molar ratio "Nb / (P+S)", and "S" is a value calculated in terms of S atoms.

[0204] The niobic acid compound dispersions according to Examples 1 to 10 had excellent stability over time when the pH of the dispersions was 2 or more and 11 or less.

[0205] The niobic acid compound films formed from the niobic acid compound dispersions according to Examples 1 to 10 were observed with an optical microscope to find that no coarse particles were present in the coating films, and the coating films had excellent film-forming properties.

[0206] ３１ The P-NMR spectrum measurement results are as follows: ４ The ion concentration was 4.0 mg / mL (42 mmol / L), P ２ O ７ The ion concentration was 1.9 mg / mL (11 mmol / L), which was converted into a molar concentration of phosphorus in the niobic acid compound dispersion of 64 mmol / L, and the weight of phosphorus in the niobic acid compound dispersion of 2.0 g / L. ４ The ion concentration was 7.4 mg / mL (78 mmol / L), which was converted into a molar concentration of phosphorus in the niobic acid compound dispersion of 78 mmol / L, and the weight of phosphorus in the niobic acid compound dispersion of 2.4 g / L.

[0207] The inventions disclosed in this specification include, in addition to the configurations of each invention and embodiment, those specified by changing these partial configurations to other configurations disclosed in this specification, to the extent applicable, or those specified by adding other configurations disclosed in this specification to these configurations, or those specified as higher-level concepts specified by deleting these partial configurations to the extent that partial effects can be obtained.

[0208] ​The niobic acid compound dispersion according to the present invention has high dispersibility in polar solvents, particularly water, good solubility in water, and excellent storage stability. Furthermore, the niobic acid compound dispersion according to the present invention has excellent storage stability, which reduces the rate of defective products caused by sediment formation over time, thereby reducing waste and energy costs for waste disposal. These advantages contribute to the sustainable management and efficient use of natural resources, as well as the achievement of decarbonization (carbon neutrality).

Claims

1. A niobium-containing niobate compound dispersion liquid, comprising: one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements; and a phosphorus compound and / or a chlorine compound, wherein the particle diameter (D50) of particles in the niobate compound dispersion liquid measured by dynamic light scattering method is 1000 nm or less.

2. A niobium-containing niobate compound dispersion liquid, comprising one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, and a phosphorus compound and / or a chlorine compound, and wherein the maximum transmittance in the wavelength region of 400 nm to 760 nm is 70% T or more.

3. The niobate compound dispersion according to claim 1 or 2, characterized in that the element X contains Li.

4. The niobate compound dispersion according to claim 1 or 2, characterized in that the phosphorus compound contains one or more compounds selected from inorganic phosphorus compounds, organic phosphorus compounds, and salts thereof.

5. The niobate compound dispersion liquid according to claim 3, characterized in that the phosphorus compound contains one or more compounds selected from the group consisting of condensed phosphoric acid, pyrophosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, ammonium phosphate, primary ammonium phosphate, secondary ammonium phosphate, ammonium pyrophosphate, and ammonium polyphosphate.

6. The niobic acid compound dispersion according to claim 1 or 2, further comprising ammonia and / or an organic nitrogen compound.

7. A niobium compound dispersion according to claim 1 or 2, characterized in that the niobium content in the niobium compound dispersion is 0.01% by mass or more and 30% by mass or less in terms of Nb atoms.

8. A niobate compound dispersion according to claim 1 or 2, characterized in that the phosphorus content in the niobate compound dispersion is 0.01% by mass or more and 10% by mass or less in terms of P atoms.

9. The niobate compound dispersion liquid according to claim 1 or 2, characterized in that the molar ratio M / Nb of the total amount (M) of the element X to niobium (Nb) in the niobate compound dispersion liquid is 0.01 or more and 10 or less.

10. The niobate compound dispersion liquid according to claim 1 or 2, characterized in that the element X in the niobate compound dispersion liquid is Li, and the molar ratio Li / Nb of lithium (Li) to niobium (Nb) is 0.01 or more and 10 or less.

11. The niobate compound dispersion liquid according to claim 1 or 2, characterized in that the molar ratio M / (P+Cl) of the total amount (M) of the element X in the niobate compound dispersion liquid to the total amount (P+Cl) of the phosphorus compound and / or the chlorine compound is 0.01 or more and 10 or less.

12. The niobate compound dispersion liquid according to claim 1 or 2, characterized in that the element X in the niobate compound dispersion liquid is Li, and the molar ratio Li / (P+Cl) of lithium (Li) to the total amount (P+Cl) of the phosphorus compound and / or the chlorine compound is 0.01 or more and 10 or less.

13. A niobate compound dispersion liquid according to claim 1 or 2, characterized in that the molar ratio Nb / (P+Cl) of niobium (Nb) in the niobate compound dispersion liquid to the total amount (P+Cl) of the phosphorus compound and / or the chlorine compound is 0.01 or more and 10 or less.

14. The niobic acid compound dispersion according to claim 1 or 2, characterized in that the niobic acid compound dispersion is an aqueous dispersion.

15. A niobate compound dispersion according to claim 1 or 2, characterized in that the particle diameter (D50) of particles in the niobate compound dispersion measured by dynamic light scattering is 100 nm or less.

16. The niobic acid compound dispersion according to claim 1 or 2, characterized in that the pH of the niobic acid compound dispersion is 2 or more and 11 or less.

17. A niobic acid compound powder comprising the niobic acid compound in the niobic acid compound dispersion liquid according to claim 1 or 2.

18. A niobate compound film comprising a niobate compound in the niobate compound dispersion liquid according to claim 1 or 2.

19. A coating agent comprising the niobic acid compound dispersion liquid according to claim 1 or 2.

20. A coating agent comprising the niobic acid compound powder according to claim 17.

21. The niobate compound dispersion according to claim 1 or 2, which is used for a positive electrode of a lithium ion secondary battery or for coating a positive electrode material.

22. A positive electrode active material for a lithium ion secondary battery, the surface of which is coated with a niobic acid compound contained in the niobic acid compound dispersion liquid according to claim 1 or 2.

23. A lithium ion secondary battery having a positive electrode the surface of which is coated with the positive electrode active material for lithium ion secondary batteries as defined in claim 22.