Niobic acid compound dispersion and method for producing the same

Abstract

To provide a niobic acid compound dispersion with excellent water dispersibility, solubility, and storage stability, and a method for producing the same.SOLUTION: 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, wherein the niobic acid compound dispersion has a particle diameter (D50) of at most 1000 nm as determined by the dynamic light scattering method. Alternatively, 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 / or alkaline earth metal elements; and a phosphorus compound and / or a chlorine compound, wherein the niobic acid compound dispersion has a maximum value of at least 70%T for transmittance in the wavelength range of 400-760 nm.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Lithium niobate, a niobic acid compound, is used as a single crystal for nonlinear optical materials, piezoelectric materials, and battery materials. For example, in composite active material particles capable of reducing the battery resistance generated in all-solid-state lithium ion batteries, lithium niobate is cited as a lithium ion conductive oxide that covers at least a part of the surface of the composite active material particles. 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 spraying a mixture of lithium niobate powder and a sol-gel solution and then sintering the mixture. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-63187 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the mixture of lithium niobate powder and sol-gel solution is spray-coated, if the lithium niobate powder has low dispersibility or solubility in the solvent, it is difficult to form a uniform piezoelectric film layer. Also, if the mixture of lithium niobate powder and the solvent has poor storage stability, the spray-coating operation 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 niobate 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. [Means for solving the problem]

[0006] The niobate compound dispersion of the present invention, which has been made to solve the above problems, is a niobium-containing niobate compound dispersion, 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 niobate compound dispersion measured by dynamic light scattering method is 1000 nm or less. The niobium 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 the particle diameter (D50) of particles in the niobium compound dispersion measured by dynamic light scattering method is 1000 nm or less, which is preferable 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 the niobic acid in the niobic acid compound dispersion of the present invention is present in the dispersion as ions in an ionic state 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 it is considered that alkali metal elements and alkaline earth metal elements are present as cations, and therefore niobium is NbO 3 - These ions are thought to exist as anions such as those shown below, or as polyoxometalate (polyacid) ions in which multiple niobium atoms are bonded to oxygen atoms.

[0009] Furthermore, the element X preferably contains Li. Moreover, 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, the niobic acid compound dispersion of the present invention may contain one or more phosphorus 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 number: 7664-38-2), condensed phosphoric acid, pyrophosphoric acid (CAS number: 2466-09-3), and polyphosphoric acid (CAS number: 8071-16-1).In addition, examples of phosphonic acids include phosphorous acid (CAS number: 13598-36-2) and hypophosphorous acid (CAS number: 6303-21-5).In addition, examples of phosphinic acids include phosphinic acid (CAS number: 6303-21-5).

[0012] In addition, examples of the organic phosphorus compound 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, organic phosphite acids and organic phosphonates 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 number: 1809-19-4), diphenyl phosphite (diphenyl phosphonate) (CAS number: 4712-55-4), trimethyl phosphite (CAS number: 121-45-9), triethyl phosphite (CAS number: 122-52-1), tributyl phosphite (CAS number: 102-85-2), and triphenyl phosphite (CAS number: 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] Examples of inorganic ammonium phosphate salts, salts with organic nitrogen compounds, alkali metal salts, and alkaline earth metal salts include ammonium phosphate, monoammonium phosphate (CAS number: 7722-76-1), diammonium phosphate (CAS number: 7783-28-0), sodium metaphosphate (CAS number: 10361-03-2), potassium metaphosphate (CAS number: 7790-53-6), sodium hexametaphosphate (CAS number: 10124-56-8), potassium hexametaphosphate, sodium pyrophosphate (CAS number: 7722-88-5), potassium pyrophosphate (CAS number: 7320-34-5), sodium polyphosphate (CAS number: 68915-31-1), potassium polyphosphate, sodium tripolyphosphate (CAS number: 7758-29-4), potassium tripolyphosphate (CAS number: 13845-36-8), sodium ultrapolyphosphate, and potassium ultrapolyphosphate.

[0017] In addition, in the niobium acid compound dispersion of the present invention, the phosphorus compound preferably contains one or more selected from phosphoric acid (CAS number: 7664-38-2), condensed phosphoric acid, pyrophosphoric acid (CAS number: 2466-09-3), polyphosphoric acid (CAS number: 8071-16-1), phosphorous acid (CAS number: 13598-36-2), hypophosphorous acid (CAS number: 6303-21-5), ammonium phosphate, primary ammonium phosphate (CAS number: 7722-76-1), secondary ammonium phosphate (CAS number: 7783-28-0), ammonium pyrophosphate, and ammonium polyphosphate. A phosphoric acid salt is more preferable when adjusting a solution to a pH closer to neutral, whereas a phosphorus compound that is a condensed phosphoric acid, or a salt of a condensed phosphoric acid such as pyrophosphoric acid, polyphosphoric acid, or a condensed phosphoric acid 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 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), it 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 be a salt of the above-mentioned chlorine compound, for example, ammonium salt, amine salt, quaternary ammonium salt, lithium salt, and preferably ammonium salt or lithium salt.Specific examples include ammonium chloride (CAS number: 12125-02-9), ammonium perchlorate (CAS number: 7790-98-9), lithium chloride (CAS number: 7447-41-8), lithium perchlorate (CAS number: 7791-03-9), methylamine hydrochloride (CAS number: 593-51-1), and dimethylamine hydrochloride (CAS number: 506-59-2).

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

[0023] Furthermore, when the particle diameter (D50) of the particles in the niobic acid compound dispersion liquid by dynamic light scattering method is 1000nm or less, it is preferred in terms of high dispersibility, little change over time, stability, reactivity when reacting with other substances or compounding, and film uniformity when forming a film.Furthermore, the particle diameter (D50) is preferably smaller, more preferably 800nm ​​or less, even more preferably 600nm or less, particularly preferably 500nm or less, more particularly preferably 300nm or less, even more particularly preferably 200nm or less, even more particularly preferably 100nm or less, more preferably 50nm or less, even more preferably 30nm or less, even more preferably 20nm or less, even more preferably 10nm or less, especially more preferably 8nm or less, even more particularly preferably 6nm or less, even more particularly preferably 4nm or less, even more particularly preferably 2nm or less, even more particularly preferably 1nm or less, even 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, the dynamic light scattering method is a method in which a solution such as a suspension is irradiated with light such as a laser beam to measure the light scattering intensity from a group of particles undergoing Brownian motion, and the particle size and distribution are obtained from the temporal variation of the intensity. Specifically, the particle size distribution is evaluated in accordance with JIS Z 8828:2019 "Particle Size Analysis - Dynamic Light Scattering Method" using a Zeta Potential, Particle Size, and Molecular Weight Measurement System (Otsuka Electronics Co., Ltd.: ELSZ-2000). In addition, the solution to be measured is filtered through a filter with a pore size of 1 μm to remove dust and other particles in the solution just before the measurement. The particle size (D50) refers to the median diameter (D50), which is the particle size that indicates the 50% cumulative value of the cumulative distribution curve. Furthermore, in this specification, unless otherwise specified, "particle diameter (D50)" includes both "initial particle diameter D50" indicating 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 "time-dependent particle diameter D50" indicating the particle diameter (D50) of particles in 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.

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

[0026] The niobic acid compound dispersion of the present invention is preferably such that the maximum transmittance in the wavelength region of 400nm to 760nm is 70%T or more, since the degree of dispersion is high and the uniformity of the liquid components is excellent. The maximum transmittance in the wavelength region of 400nm to 760nm is more preferably 72%T or more, even more preferably 74%T or more, particularly preferably 76%T or more, 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, even more particularly preferably 98%T or more, even more particularly preferably 99%T or more, and most preferably 100%T.

[0027] In addition, the niobic acid compound dispersion of the present invention may have a transmittance of 70%T or more at any one of wavelengths 400nm, 600nm, and 750nm, or at two or more wavelengths. The transmittance at any one of wavelengths 400nm, 600nm, and 750nm, or at 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] In addition, due to measurement errors, the measured value of the transmittance may exceed 100%T, but since the theoretical upper limit is 100%T, when the measured value exceeds 100%T, it is considered to be 100%T. In this way, the 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 the "niobic acid compound dispersion" of the present invention. Furthermore, in this specification, unless otherwise specified, "transmittance" includes both "initial transmittance" indicating 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" indicating the transmittance of the niobic acid compound dispersion of the present invention after being left to stand for one month from the day of production 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 niobate compound dispersion of the present invention in accordance with the following transmittance measurement conditions in accordance with JIS K 0115, 2004 "General rules for spectrophotometric analysis methods".

[0031] =Transmittance measurement conditions= Measurement equipment: UV-Vis-NIR spectrophotometer UH4150 (manufactured by Hitachi High-Tech Science Corporation) Measurement mode: Wavelength scan Data mode: %T (transparent) Measurement wavelength range: 200nm~2000nm Scan speed: 600nm / min Sampling interval: 2nm

[0032] In the present invention, the "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 an aggregate 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 contain an ionized alkaline aqueous solution, such as ammonia or an organic nitrogen compound. The content of ammonia or an organic nitrogen compound in the niobic acid compound dispersion of the present invention is preferably 10% by mass or less, more preferably 5% by mass or less, further preferably 3% by mass or less, and particularly preferably 1% by mass or less, when the niobic acid compound dispersion of the present invention is taken as 100% by mass.

[0034] As will be described in detail in the manufacturing method of the niobic acid compound dispersion of the present invention later, in the manufacturing process, a reverse neutralization method is used to add an acidic niobium complex aqueous solution to an alkaline aqueous solution, for example, ammonia water, to generate a niobic acid-containing precipitate, which is a precipitation slurry containing niobium, for example, a cake containing hydrated ammonium niobate, and then the niobic acid compound dispersion of the present invention is generated, so it is considered that ammonia contains ammonium ions and exists in the dispersion as cations. In addition, in the manufacturing process, a reverse neutralization method is used to add ammonia water, and the niobic acid-containing precipitate obtained is mixed with an organic nitrogen compound to generate a niobium compound neutralized aqueous solution, so it is considered that the organic nitrogen compound exists in the dispersion as cations.

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

[0036] Examples of the 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, isopropylamine, diisopropylamine, triisopropylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, isobutylamine, diisobutylamine, triisobutylamine, tert-butylamine, n-pentamine, n-hexylamine, cyclohexylamine, piperidine, and the like.

[0038] Examples of aromatic amines include aniline, phenylenediamine, and diaminotoluene. 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. Examples of amino acids include alanine, arginine, aspartic acid, and EDTA. 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, 1-butyl-2,3-dimethylimidazolium, etc. 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 - etc.

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

[0041] Here, the organic nitrogen compound is preferably an aliphatic amine because it is highly volatile and has 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 of the organic nitrogen compound include methylamine and dimethylamine.

[0042] In addition, the organic nitrogen compound is preferably a quaternary ammonium, since it has high solubility and high crystallization inhibition and high sol formation inhibition. 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 selected from aliphatic amines, aromatic amines, amino alcohols, amino acids, polyamines, quaternary ammonium, guanidine compounds, and azole compounds, rather than one selected from them. For example, a mixture of two types of compounds, an aliphatic amine and a quaternary ammonium compound, is preferable in that the amount of the compound added is reduced so as not to increase toxicity, while the solubility can be increased.

[0044] Specifically, examples of such mixtures 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 method for measuring the content of the organic nitrogen compound present in the niobate compound dispersion of the present invention includes 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 0.01% by mass or more and 30% by mass or less in terms of Nb atoms. The niobium content in the niobium 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 achieving both practicality and stability of the niobium 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 diluting the dispersion appropriately with dilute hydrochloric acid as necessary, and measuring Nb mass% in terms of Nb atoms in accordance with JIS K0116:2014 using high-frequency inductively coupled plasma optical emission spectroscopy (ICP optical emission spectroscopy (manufactured by Agilent Technologies: AG-5110)). In addition, when the niobic acid in the niobic acid compound dispersion of the present invention is ionically bonded with an alkali metal or an alkaline earth metal, for example, a lithium niobate salt ionically bonded with a lithium ion, the lithium content may be calculated by measuring Li mass% in terms of Li atoms in the same manner as 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) and 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 the mass % of each element X in terms of element X atom, in the same manner as the niobium content.

[0048] The niobate compound dispersion of the present invention is 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. The phosphorus content in the niobate compound dispersion of the present invention is preferably 0.01% by mass or more and 10% by mass or less in terms of P atom, since it improves dispersibility and solubility in polar solvents, especially water.More preferably, the phosphorus content is 0.1% by mass or more and 5% by mass or less in terms of P atom, even more preferably, the phosphorus content is 0.1% by mass or more and 2% by mass or less in terms of P atom, particularly preferably, the phosphorus content is 0.1% by mass or more and 1% by mass or less in terms of P atom, and even more particularly preferably, the phosphorus content is 0.1% by mass or more and 0.4% by mass or less in terms of P atom.

[0049] The phosphorus content in the niobium acid compound dispersion of the present invention is calculated by diluting the dispersion appropriately with dilute hydrochloric acid as necessary, 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 niobate compound dispersion of the present invention is preferably analyzed by the above-mentioned ICP emission spectrometry. 31 It can also be determined by measuring the 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 apparatus (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 in which 10 g / L of phosphonoacetic acid is dissolved in heavy water. The prepared measurement sample is subjected to the following measurement. 31 According to the P-NMR spectrum measurement conditions, 31 Measure the P-NMR spectrum.

[0051] = 31 P-NMR spectrum measurement conditions: ·Magnetic field: 14.1 T (1H 600Mhz) Spectrometer: Bruker AVANCE NEO 600 Measurement and data processing software: Bruker, TopSpin NMR probe: Solvent probe (Type: PA BBO 600S3 BBF-HD-05 Z SP) Solvent: Deuterium oxide Chemical shift values ​​and phosphorus content of internal sample: phosphonoacetic acid Chemical shift value standard: 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 at which a 14μs pulse is at 90 degrees to the peak at the center of irradiation. Radio frequency pulse width: 14μs Measurement interval: 80μs (DW=40μs on the software) Number of measurement points: 32768 points (TD=65536 on the software) Number of spectrum points (SI on the software): 65536 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 The P-NMR spectrum was obtained. 31 The peak areas of the P-NMR spectrum can be calculated using the Integrate function of the above-mentioned measurement and data processing software, and the contents of phosphonoacetic acid and each phosphate ion can be calculated from the peak areas. For example, the diphosphate raw material has a concentration of 6.5 ppm (PO 4 Origin of the nucleus) and -1.7 ppm (P 2 O 7 (presumed origin) and 31 P peak is observed. In phosphoric acid raw material, 6.2 ppm (PO 4 (presumed origin) 31 The P peak is observed. The chemical shifts of each peak are affected by factors such as the pH of the sample, so calculations must be made taking this into account.

[0053] In addition, 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 in the niobate 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 atom conversion from the viewpoint of corrosion of the substrate.Moreover, it is more preferably 0.001% by mass or more and 2.0% by mass or less in terms of Cl atom conversion, further preferably 0.001% by mass or more and 0.5% by mass or less in terms of Cl atom conversion, particularly preferably 0.001% by mass or more and 0.2% by mass or less in terms of Cl atom conversion, and more particularly preferably 0.001% by mass or more and 0.1% by mass or less in terms of Cl atom conversion.

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

[0055] Furthermore, in the niobate 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 niobate compound dispersion is preferably 0.01% by mass or more and 10% by mass or less. The total content in the niobic acid compound dispersion of the present invention is preferably 0.01% by mass or more and 10% by mass or less, since dispersibility and solubility in polar solvents, particularly water, are improved.The total content is more preferably 0.01% by mass or more and 5% by mass or less, further 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 niobate 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 niobate compound dispersion is 0.01 or more and 10 or less. The molar ratio M / Nb of the total amount (M) of the element X to niobium (Nb) in the niobate compound dispersion of the present invention 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 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 niobate 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] In addition, the niobate compound dispersion of the present invention is characterized in that the element X in the niobate 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. In the niobate compound dispersion of the present invention, the element X is Li, and the molar ratio Li / Nb of lithium (Li) to niobium (Nb) is preferably 0.01 or more and 10 or less in terms 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. In addition, in the niobate compound dispersion of the present invention, the element X is Li, and the molar ratio Li / Nb of lithium (Li) to niobium (Nb) may be 0.1 or more and 9 or less, or 0.1 or more and 7 or less.

[0058] The niobate 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 in the niobate compound dispersion to the total amount (P+Cl) of the phosphorus compound and / or the chlorine compound in the niobate compound dispersion is 0.01 or more and 10 or less. The molar ratio M / (P+Cl) of the total amount (M) of the element X in the niobic acid compound dispersion of the present invention to the total amount (P+Cl) of the phosphorus compound and / or the chlorine compound 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. In this specification, unless otherwise specified, the total amount (P+Cl) of the phosphorus compound and / or the chlorine compound is the sum of the value (P) calculated in terms of P atom and the value (Cl) calculated in terms of Cl atom. In addition, when the niobate compound dispersion of the present invention is used for a positive electrode for a lithium ion secondary battery described later, or for coating a positive electrode material, it is preferable that the total amount of phosphorus compounds and / or chlorine compounds (P+Cl) is Cl=0.

[0059] Furthermore, in the niobate 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 compound in the niobate compound dispersion is 0.01 or more and 5 or less. The molar ratio M / P of the total amount (M) of the element X to the total amount (P) of the phosphorus compound in the niobate compound dispersion of the present invention is preferably 0.01 or more and 5 or less in terms of improving dispersibility and solubility in water, more preferably 0.01 or more and 2 or less, even more preferably 0.05 or more and 2 or less, and particularly preferably 0.1 or more and 1.95 or less.

[0060] In addition, the niobate compound dispersion of the present invention is characterized in that the element X in the niobate 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 the chlorine compound is 0.01 or more and 10 or less. In the niobate compound dispersion of the present invention, the element X 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 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.

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

[0062] The niobium acid compound dispersion of the present invention is characterized in that the molar ratio Nb / (P+Cl) of niobium (Nb) in the niobium acid compound dispersion to the total amount (P+Cl) of the phosphorus compound and / or the chlorine compound is 0.01 or more and 10 or less. The molar ratio Nb / (P+Cl) of niobium (Nb) to the total amount (P+Cl) of the phosphorus compound and / or the chlorine compound in the niobate compound dispersion of the present invention 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.

[0063] Furthermore, in the niobate compound dispersion of the present invention, the molar ratio Nb / P of niobium (Nb) in the niobate compound dispersion to the total amount (P) of the phosphorus compound is more preferably 0.01 or more and 10 or less. The molar ratio Nb / P of niobium (Nb) to the total amount (P) of the phosphorus compound in the niobate compound dispersion of the present invention 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 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 characterized in that it is 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, so pure water can be used as the solvent. An organic solvent may be used as the solvent. Examples of the organic solvent include alcohol solvents, ketone solvents, ether solvents, ester solvents, aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, etc., and the solvent may be a mixture of these organic solvents and pure water. Examples of the alcohol solvent include alcohols having 5 or less carbon atoms (methanol, ethanol, n-propanol, isopropyl alcohol, butanol, ethylene glycol, propylene glycol), high boiling point solvents, acetone, etc. It is preferable that the above-mentioned solvents and water are compatible with each other. The niobic acid compound dispersion of the present invention can contain one or more solvents at any ratio within a range that does not impair stability.

[0065] Examples of high boiling point solvents include polyhydric alcohol solvents and glycol solvents. Examples of polyhydric alcohol solvents include glycerin (boiling point: 290°C), 1,6-hexanediol (boiling point: 250°C), and 1,7-heptanediol (boiling point: 259°C). Examples of glycol solvents include ethylene glycol (boiling point: 197.3°C), propylene glycol (boiling point: 188.2°C), diethylene glycol (boiling point: 244.3°C), triethylene glycol (boiling point: 287.4°C), oligoethylene glycol (boiling point: 287°C 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 fluorosurfactants (boiling point: 180°C or higher), amphoteric fluorosurfactants (boiling point: 180°C or higher), nonionic fluorosurfactants (boiling point: 180°C or higher), amine oxides (boiling point: 180°C or higher), etc. The above boiling points are those at 1 atmospheric pressure.

[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. The pH of the niobic acid compound dispersion of the present invention is preferably 2 or more and 11 or less in terms of stabilizing the polyacid ions contained in the dispersion. In addition, 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, depending on the application. In this specification, unless otherwise specified, "pH" refers to both "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 "pH over time", 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 more preferably pH 2 or more and 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 6 or more and 8 or less, and more preferably pH 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 pH 8 or more, even more preferably pH 9 or more, and particularly preferably pH 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. In addition, when an organic acid is contained in the niobic acid compound dispersion of the present invention, the pH is changed, and the components in the niobic acid compound dispersion of the present invention and the organic acid may interact with each other, 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 (HORIBA: Standard ToupH electrode 9615S-10D) of a pH meter (HORIBA: Glass electrode type hydrogen ion concentration indicator D-51) in the niobic acid compound dispersion of the present invention, and confirming that the liquid temperature has stabilized at 25°C.

[0069] The niobic acid compound dispersion of the present invention may contain an element or a compound thereof that does not constitute the niobic acid compound contained in the niobic acid compound dispersion of the present invention as an additive. Examples of the additive 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. In addition, the content of the additive in the niobic acid compound dispersion of the present invention is, when the total molar content of each element as an additive is Z, the molar ratio Z / Nb of the total molar content (Z) of each element as an additive 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 terms of each element atom, similarly to the above-mentioned niobium content. Furthermore, since the niobic acid compound dispersion of the present invention is a uniform dispersion, even if these compounds are in a suspended state, improvement in uniformity and improvement in reactivity (reaction rate) are expected. In addition, if these compounds are dissolved in the niobic acid compound dispersion of the present invention and become a uniform dispersion, the composite element can be in the most reactive state.

[0070] Furthermore, the niobic acid compound dispersion of the present invention may contain components (referred to as "other components") other than the components derived from niobium or niobic acid, ammonia, organic nitrogen compounds, and the components derived from element X, within a range that does not impair the action and effect of the niobic acid compound dispersion. Examples of the 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 mass%, the content of the other components is preferably 5 mass% or less, more preferably 4 mass% or less, and even more preferably 3 mass% or less. The content of each element corresponding to the other components is calculated by measuring the mass% of each element in terms of each element atom, similarly to the above-mentioned niobium content. It is assumed that the niobic acid compound dispersion of the present invention contains unavoidable impurities, not intentionally. The content of the unavoidable impurities is preferably 0.01 mass% or less.

[0071] The niobic acid compound powder of the present invention is characterized by containing the niobic acid compound in the above-mentioned niobic acid compound dispersion of the present invention. The niobic acid compound powder of the present invention includes a dried powder obtained by drying, for example, vacuum drying, the niobic acid compound dispersion of the present invention, and a fired powder obtained by firing the obtained dried powder. The niobic acid compound powder of the present invention also includes niobic acid compound powders having different physical properties such as crystal structure, which are generated by vacuum drying or firing the niobic acid compound dispersion of the present invention, and may be 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 a niobic acid compound in the above-mentioned niobic acid compound dispersion of the present invention. The niobic acid compound film of the present invention includes a dried film obtained by applying the niobic acid compound dispersion 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 obtained dried film. The niobic acid compound film of the present invention also includes a niobic acid compound film having different physical properties such as a crystal structure, which is generated by vacuum drying or firing the niobic acid compound dispersion of the present invention, and may be an amorphous structure, a single crystal structure, or a polycrystalline structure. Since the niobium compound, which is the raw material of the niobic acid compound film of the present invention, has high chemical resistance, the high temperature characteristics (for example, protection from deterioration of the substrate due to heat, etc.) and chemical resistance of the substrate can be improved by covering the surface of the substrate with the niobic acid compound film of the present invention. 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 niobate compound dispersion of the present invention. The coating agent of the present invention contains the niobate 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 niobate compound dispersion of the present invention is characterized in that it is used for a positive electrode of a lithium ion secondary battery or for coating a positive electrode material. The niobic acid compound dispersion of the present invention can also be used for coating the positive electrode or positive electrode material for lithium ion secondary batteries.

[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 above-mentioned niobic acid compound dispersion of the present invention. Here, the positive electrode active material for lithium ion secondary batteries is specifically LiMn 2 O 4 (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 in that it has 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 niobate 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 aqueous solution of a niobium compound, and a mixing step of mixing the neutralized aqueous solution of the niobium compound with a phosphorus compound or a phosphorus compound solution and / or a chlorine compound or a chlorine compound solution.

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

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

[0082] The neutralization reaction step in which the obtained niobium fluoride aqueous solution is added 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 preferable because it is 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 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 further preferably 110 or more and 400 or less. In addition, the amount of the niobium fluoride aqueous solution added to the ammonia water is set to NH 3 The molar ratio of NH / 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 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, it is preferable to add the niobium fluoride aqueous solution to the ammonia water in as short a time as possible, for example, all at once, rather than gradually adding the niobium fluoride aqueous solution over a long period of time, and to carry out the neutralization reaction. In the reverse neutralization step, the acidic niobium fluoride aqueous solution is added to the alkaline ammonia water, so that 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, and a niobium-containing precipitate from which fluoride ions have been removed can be obtained. 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 can be used to remove the fluorine compounds, and examples of such methods include filtration using a membrane such as reverse osmosis filtration, ultrafiltration, and microfiltration using aqueous ammonia or pure water, centrifugation, and other known methods. When removing fluoride ions from the niobium-containing precipitate slurry, temperature control is not particularly required, and the removal may be performed 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 the 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 preferable, ammonia water of 4.0 mass% or less is more preferable, ammonia water of 3.0 mass% or less is even more preferable, and ammonia water of 2.5 mass% is particularly preferable. When the ammonia water is 5.0 mass% or less, ammonia containing ammonium ions is suitable for fluoride ions, and unnecessary cost increase can be avoided.

[0092] The niobium-containing precipitate thus obtained, from which the fluoride ions have been removed, is diluted with pure water or the like to obtain a precipitate slurry containing niobium from which the fluoride ions have been removed. The niobium content of the precipitate slurry containing niobium can be determined by taking a portion of the slurry, drying it at 110°C for 24 hours, and then firing it at 1,000°C for 4 hours to obtain the Nb 2 O 5 The resulting Nb 2 O 5 The weight of the slurry can be measured, and the niobium content of the slurry can be calculated from the weight.

[0093] Next, in the neutralization reaction step, a niobium-containing precipitate slurry is obtained from which the generated fluoride ions are removed. The niobium-containing precipitate slurry from which the fluoride ions are removed, a hydroxide of element X, for example 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 the niobium compound, and the mixture is mixed at room temperature for 0.1 to 2 hours to obtain the niobate compound dispersion of the present invention.

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

[0097] Furthermore, it is preferable that the phosphorus compound contains one or more selected from condensed phosphoric acid, pyrophosphoric acid (CAS number: 2466-09-3), polyphosphoric acid (CAS number: 8071-16-1), phosphorous acid (CAS number: 13598-36-2), hypophosphorous acid (CAS number: 6303-21-5), ammonium phosphate, monoammonium phosphate (CAS number: 7722-76-1), diammonium phosphate (CAS number: 7783-28-0), ammonium pyrophosphate, and ammonium polyphosphate.

[0098] The phosphorus compound solution may also be one in which pure water is added to the above-mentioned phosphorus compound and the concentration is adjusted so that the phosphorus content in the niobate compound dispersion of the present invention is 0.01 mass % or more and 10 mass % or less in terms of P atoms.

[0099] Here, 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 be a salt of the above-mentioned chlorine compound, for example, ammonium salt, amine salt, quaternary ammonium salt, lithium salt, and preferably ammonium salt or lithium salt.Specific examples include ammonium chloride (CAS number: 12125-02-9), ammonium perchlorate (CAS number: 7790-98-9), lithium chloride (CAS number: 7447-41-8), lithium perchlorate (CAS number: 7791-03-9), methylamine hydrochloride (CAS number: 593-51-1), and dimethylamine hydrochloride (CAS number: 506-59-2).

[0101] The niobium acid compound dispersion of the present invention may also 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 the niobium acid compound dispersion of the present invention is 0.0 mass % or more and 2.0 mass % or less in terms of Cl atoms.

[0102] In the method for producing a niobium acid compound dispersion of the present invention, the mixing step may be a step of 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 niobium acid compound dispersion of the present invention, before the phosphorus compound, or the phosphorus compound solution and / or the chlorine compound, or the chlorine compound solution is added to the niobium compound neutralization aqueous solution, the phosphorus compound, or the phosphorus compound solution and / or the chlorine compound, or the chlorine compound solution may be pre-mixed 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] One or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, which are premixed with the phosphorus compound or the phosphorus compound solution and / or the chlorine compound or the chlorine compound solution, include, for example, lithium hydroxide monohydrate.

[0104] In addition, in order to remove ammonia components contained in the obtained niobium 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 acid compound dispersion of the present invention after the ammonia components have been removed is equal to the niobium content of the niobium acid compound dispersion of the present invention before the ammonia components have been removed.

[0105] Specifically, the niobium compound dispersion of the present invention is obtained by mixing and stirring the obtained niobium compound neutralized aqueous solution 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 niobium compound dispersion of the present invention thus obtained 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 (P+Cl) of phosphorus compounds and / or chlorine compounds 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 other than lithium and / or alkaline earth metal elements, the molar ratio M / (P+Cl) of the total amount (M) of element X to the total amount (P+Cl) of phosphorus compounds and / or chlorine compounds 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. The element X includes a case where it is a plurality of elements of lithium and other alkali metal elements and / or alkaline earth metal elements, and a case where it is a plurality of elements selected from alkali metal elements other than lithium and / or alkaline earth metals.

[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 (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 0.05 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 other than lithium and / or alkaline earth metal elements, the molar ratio M / P of the total amount (M) of the element X to the total amount (P) of the phosphorus compound 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.

[0108] Furthermore, the molar ratio Nb / (P+Cl) of niobium (Nb) contained in the niobium 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 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.

[0109] Furthermore, the molar ratio Nb / P of niobium (Nb) contained in the niobium 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] In addition, when the element X contained in the niobium acid compound dispersion of the present invention is lithium, the molar ratio Li / Nb of lithium (Li) and niobium (Nb) is preferably 0.01 to 10 in terms of improving dispersibility and solubility in water, more preferably 1 to 9, and even more preferably 1 to 7. In the case where the element X contained in the niobium acid compound dispersion of the present invention is an element X selected from alkali metal elements other than lithium and / or alkaline earth metal elements, the molar ratio M / Nb of the total amount (M) of element X and niobium (Nb) is preferably 0.01 to 10 in terms of improving dispersibility and solubility in water, more preferably 0.1 to 10, even more preferably 1 to 9, and particularly preferably 1 to 7. Note that the element X includes a case where it is a plurality of elements of lithium and other alkali metal elements and / or alkaline earth metal elements, and a case where it is a plurality of elements selected from alkali metal elements other than lithium and / or alkaline earth metals.

[0111] As another example of the method for producing a niobium acid compound dispersion of the present invention, the method 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 aqueous solution of the niobium compound, and mixing them.

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

[0113] In the same manner as in the above-mentioned 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 stirred and maintained at 5°C to 90°C for 0.1 to 48 hours, 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 mass% or less, more preferably 20 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 mass% or more, more preferably 1 mass% or more, and may be 5 mass% or more, or may be 10 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, and 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 embodiment 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 niobium compound neutralized aqueous solution, and mixed.

[0118] The phosphorus compound mixed solution is generated 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 may contain 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 selected from phosphoric acid (CAS number: 7664-38-2), condensed phosphoric acid, pyrophosphoric acid (CAS number: 2466-09-3), polyphosphoric acid (CAS number: 8071-16-1), phosphorous acid (CAS number: 13598-36-2), hypophosphorous acid (CAS number: 6303-21-5), ammonium phosphate, monoammonium phosphate (CAS number: 7722-76-1), diammonium phosphate (CAS number: 7783-28-0), ammonium pyrophosphate, and ammonium polyphosphate.

[0121] The phosphorus compound solution may also be one in which pure water is added to the above-mentioned phosphorus compound and the concentration is adjusted so that the phosphorus content in the niobate compound dispersion of the present invention is 0.01 mass % or more and 10 mass % or less in terms of P atoms.

[0122] The mixed solution of chlorine compounds is produced by previously 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] Here, 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 be a salt of the above-mentioned chlorine compound, for example, ammonium salt, amine salt, quaternary ammonium salt, lithium salt, and preferably ammonium salt or lithium salt.Specific examples include ammonium chloride (CAS number: 12125-02-9), ammonium perchlorate (CAS number: 7790-98-9), lithium chloride (CAS number: 7447-41-8), lithium perchlorate (CAS number: 7791-03-9), methylamine hydrochloride (CAS number: 593-51-1), and dimethylamine hydrochloride (CAS number: 506-59-2).

[0125] The niobium acid compound dispersion of the present invention may also 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 the niobium acid compound dispersion of the present invention is 0.0 mass % or more and 2.0 mass % or less in terms of Cl atoms.

[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 the phosphorus compound solution and / or the chlorine compound or the 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, the one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, the pure water, etc., which are mixed in the mixing step of the method for producing a niobium acid compound dispersion of the present invention, is not limited to the above-mentioned order 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 is to place 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 dry, for example vacuum dry, at a heating temperature of about 60°C to 200°C for 1 hour to 72 hours, thereby evaporating water from the niobic acid compound dispersion of the present invention, and to obtain 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 niobate compound includes vacuum drying the niobate compound dispersion liquid of the present invention as described above, placing the obtained dry powder of the niobate compound in a static furnace, and calcining it in the atmosphere at a calcination temperature of 300°C or more and 1,200°C or less for a calcination time of 1 hour or more and 72 hours or less, thereby obtaining the calcined powder of the niobate compound.

[0131] The above-mentioned dried powder and sintered powder of the niobic acid compound may be pulverized and used as the niobic acid compound powder. Regardless of whether or not the niobic acid compound is pulverized, the undersieve (fine grain side) obtained by classifying the above-mentioned dried powder and sintered powder of the niobic acid compound using a sieve or the like may be used as the niobic acid compound powder. The oversieve (coarse grain side) may be pulverized again and classified for use. It is also possible to combine pulverization and classification using a vibrating sieve into which iron balls coated with nylon or fluororesin are charged as pulverizing media. By combining classification and pulverization in this way, even if there is a niobic acid compound powder that is too large, it is possible to remove it. Specifically, when classifying using a sieve, it is preferable to use one with an opening of 150 μm to 1,000 μm. When the particle size is 150 μm to 1,000 μm, the proportion of oversized particles is not too high, so that re-pulverization is not required repeatedly, and the niobate compound powder that requires re-pulverization is not classified as undersized particles.

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

[0133] Further, 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] Of the 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 a surface of a substrate, and a film drying step of drying the niobic acid compound dispersion coated onto the surface of the substrate to obtain a dry film.

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

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

[0137] Specifically, as described above, the niobate compound dispersion is applied to the surface of a substrate, and the substrate on which a niobate compound dry film is formed by drying is placed in a static furnace and fired in air at a firing temperature of 300°C or more and 1,200°C or less for a firing time of 1 hour or more and 12 hours or less, thereby forming a niobate compound fired film on the surface of the substrate.

[0138] Further, 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 lithium hydroxide solution is dropped and the mixture is kept at 90° C. for 10 minutes to produce 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 niobate 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 the niobate compound.

[0142] In this specification, when "X to Y" (X and Y are any numbers) is expressed, unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as "preferably greater than X" or "preferably smaller than Y". In addition, when "X or more" (X is any number) or "Y or less" (Y is any number), it also includes the meaning of "preferably greater than X" or "preferably less than Y". Effect of the Invention

[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. The method for producing the 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. [Brief description of the drawings]

[0144] [Figure 1] 1 is a table showing physical property values ​​of niobate compound dispersions according to Examples 1 to 10 of the present invention and Comparative Examples 1 to 3. [Diagram 2] 1 is a table showing the measurement results of niobate compound dispersions according to Examples 1 to 10 of the present invention and Comparative Examples 1 to 3. BEST MODE FOR CARRYING OUT THEINVENTION

[0145] The niobate compound dispersion 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 phosphorus compound solution to obtain a mixed solution of phosphorus compounds.

[0147] Here, the 5% by mass lithium hydroxide monohydrate aqueous solution is LiOH H 2 It was obtained by mixing 15 g of O 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 and mixed for 30 minutes, thereby obtaining a niobate 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] Niobium pentoxide (100 g) was dissolved in 200 g of 55% hydrofluoric acid solution and 830 mL of pure water was added to convert it to Nb 2 O 5 Contains 100g / L (Nb 2 O 5 = 8.85 mass % niobium fluoride aqueous solution was obtained. 200 mL of this niobium fluoride aqueous solution was dissolved in ammonia water (NH 3 (NH 3 / Nb 2 O 5 Molar ratio = 176.9, NH 3 / HF molar ratio = 12.1), a reaction liquid (pH 11) was obtained. This reaction liquid was a slurry of a niobic acid compound hydrate, in other words, a slurry of a niobium-containing precipitate.

[0151] Next, the reaction solution was decanted using a centrifuge and washed until the amount of liberated fluoride ions was 100 mg / L or less, to obtain a niobium-containing precipitate from which the fluoride ions had been removed. At this time, ammonia water 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 obtain Nb 2 O 5 The weight of Nb in the slurry was calculated. 2 O 5 The content was calculated.

[0153] Then, the niobium-containing precipitate slurry diluted with pure water, 5 mass% lithium hydroxide, and pure water were mixed to obtain a translucent slurry mixture. The mixture was stirred and held for 1 hour at a liquid temperature of 50°C to 100°C, for example 70°C, 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 phosphorus compound solution to obtain a mixed phosphorus compound solution.

[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 niobate 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 phosphorus compound solution to obtain a mixed phosphorus compound solution.

[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 niobate 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 resulting aqueous phosphorus compound solution to obtain a mixed phosphorus compound solution.

[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 niobate compound dispersion liquid according to Example 4.

[0162] The 5 mass % lithium hydroxide monohydrate aqueous solution 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 phosphorus compound solution to obtain a mixed phosphorus compound solution.

[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 niobate 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 % lithium hydroxide monohydrate aqueous solution 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 phosphorus compound solution to obtain a mixed phosphorus compound solution.

[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 niobate 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 % lithium hydroxide monohydrate aqueous solution 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 resulting 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 niobate compound dispersion liquid according to Example 7.

[0171] The 5 mass % lithium hydroxide monohydrate aqueous solution 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 resulting aqueous phosphorus compound solution to obtain a mixed phosphorus compound solution.

[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 niobate compound dispersion liquid according to Example 8.

[0174] The 5 mass % lithium hydroxide monohydrate aqueous solution 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 resulting aqueous phosphorus compound solution to obtain a mixed phosphorus compound 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 niobate compound dispersion liquid according to Example 9.

[0177] The 5 mass % lithium hydroxide monohydrate aqueous solution 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 phosphorus compound solution to obtain a mixed phosphorus compound solution.

[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 niobate compound dispersion liquid according to Example 10.

[0180] The 5 mass % lithium hydroxide monohydrate aqueous solution 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 phosphorus compound solution to obtain a mixed phosphorus compound solution.

[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 % lithium hydroxide monohydrate aqueous solution 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 % lithium hydroxide monohydrate aqueous solution was added to the obtained sulfur compound aqueous 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 niobate compound dispersion liquid according to Comparative Example 2.

[0186] The 5 mass % lithium hydroxide monohydrate aqueous solution used in Comparative Example 2 was the same as that 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 % lithium hydroxide monohydrate aqueous solution used in Comparative Example 3 was the same as that 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 the Nb mass % calculated as Nb atoms, the P mass % calculated as P atoms, the Li mass % calculated as Li atoms, the Cl mass % calculated as Cl atoms, and the S mass % calculated as S atoms were measured for the niobate compound dispersions of Examples 1 to 10 and Comparative Examples 1 to 3 using ICP optical emission spectrometry (AG-5110 manufactured by Agilent Technologies) in accordance with JIS K0116:2014. was measured.

[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 was 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 leaving them to stand for one month from the day of production in an incubator set at room temperature of 25°C.

[0192] Dynamic Light Scattering The particle size distribution was evaluated by a dynamic light scattering method according to JIS Z 8828:2019 using a zeta potential, particle size, and molecular weight measurement system (ELSZ-2000 manufactured by Otsuka Electronics Co., Ltd.). In addition, immediately before the measurement, in order to remove dust and the like from the niobic acid compound dispersion liquid according to Examples 1 to 10, which is the measurement target, the dispersion liquid was filtered through a filter with a pore size of 1 μm. Furthermore, D50 indicates the particle diameter that reaches 50% in terms of volume fraction. "Initial particle diameter D50 (nm)" in FIG. 2 refers to the particle diameter (D50) of the particles in the niobic acid compound dispersion liquid immediately after it is generated. In addition, "particle diameter over time D50 (nm)" in FIG. 2 refers to the particle diameter (D50) of the particles in the niobic acid compound dispersion liquid after it is left standing for one month from the day of generation of the niobic acid compound dispersion liquid according to Examples 1 to 10 and Comparative Examples 1 to 3 in an incubator set at room temperature of 25°C. In addition, in the niobate compound dispersions according to Comparative Examples 1 to 3, since precipitates were visually observed, 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 transmittances of the niobic acid compound dispersions according to Examples 1 to 10 and Comparative Examples 1 to 3 in the wavelength region of 400 nm to 760 nm (specifically, the transmittances at wavelengths of 400 nm, 600 nm, and 750 nm) were measured using a spectrophotometer according to 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. The "temporary transmittance" in FIG. 1 refers to the transmittance of the niobic acid compound dispersions after leaving the niobic acid compound dispersions according to Examples 1 to 10 and Comparative Examples 1 to 3 in an incubator set at room temperature of 25° C. for one month from the day of production.

[0194] <Film-forming test> The appearance of the coating film formed on the surface of the glass substrate, which is a substitute for the current collector, was evaluated by observing it with an optical microscope. First, the niobic acid compound dispersion liquids according to Examples 1 to 10 and Comparative Examples 1 to 3 were left to stand for one month from the day of production of the niobic acid compound dispersion liquids according to Examples 1 to 10 and Comparative Examples 1 to 3 in an incubator set at room temperature 25°C. Next, the niobic acid compound dispersion liquids according to Examples 1 to 10 and Comparative Example 1 after standing for one month were dropped onto a 50 mm x 50 mm glass substrate that had been degreased and washed with acetone and then dried using a syringe while being filtered with a filter having a pore size of 0.22 μm, and then coated by spin coating (700 rpm, 10 seconds, then 1500 rpm, 15 seconds). Then, the coated area was naturally dried to form 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. Those on which no particles were present and a film was formed were evaluated as having excellent film-forming properties and were rated as "○ (GOOD)", and those on which particles were observed were evaluated as having poor film-forming properties and were rated as "× (BAD)".

[0195] < 31 P-NMR spectrum measurement The phosphorus content in the niobic acid compound dispersion liquid according to Examples 3 and 6 is 31 The P-NMR spectrum was used for calculation. Specifically, 70 μL of the niobate compound dispersion according to Examples 3 and 6 were mixed with 650 μL of a phosphonoacetic acid deuterium oxide solution in which 10 g / L of phosphonoacetic acid was dissolved in deuterium oxide 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 The peak areas of the P-NMR spectra 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 dispersions of 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 contain niobium, and have 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 in the dispersions is 1000 nm or less, the dispersions have high dispersibility in a dispersion medium and excellent solubility.

[0197] The niobate 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 had a maximum transmittance of 70%T or more in a wavelength region of 400 nm to 760 nm, and thus 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% by mass or more and 30% by 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% by mass or more and 10% by mass or less in terms of P atoms.

[0200] The niobic acid compound dispersions according to Examples 1 to 10 showed no significant difference in the particle size over time (D50) compared to the initial particle size (D50) even after one month had passed, and were excellent in stability over time. Note that the niobic acid compound dispersion according to Comparative Example 1 showed precipitation.

[0201] The niobic acid compound dispersions according to Examples 1 to 10 had improved stability during long-term storage when the molar ratio M / Nb between 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 and niobium (Nb) was 0.01 or more and 10 or less. Furthermore, the niobic acid compound dispersions according to Examples 1 to 6, when the element X is Li, had improved stability during long-term storage when the molar ratio Li / Nb between lithium (Li) and niobium (Nb) was 0.01 or more and 10 or less.

[0202] The niobic acid compound dispersions according to Examples 1 to 10 have 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 is 0.01 or more and 10 or less. Furthermore, the niobic acid compound dispersions according to Examples 1 to 10 have 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 is 0.01 or more and 10 or less, when the element X is Li. 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 a 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)" of Fig. 1, the value is the molar ratio "Nb / (P+S)", and "S" is the 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 of Examples 1 to 10 were observed with an optical microscope to show that the coating films formed from each niobic acid compound dispersion contained no coarse particles and had excellent film-forming properties.

[0206] 31 The results of P-NMR spectrum measurement are as follows: PO in the niobate compound dispersion liquid of Example 3 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 concentration 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 was converted into a weight concentration 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 or embodiment, those that are specified by changing these partial configurations to other configurations disclosed in this specification, to the extent applicable, or those that are specified by adding other configurations disclosed in this specification to these configurations, or those that are specified as higher-level concepts by deleting these partial configurations to the extent that partial action and effects are obtained. [Industrial Applicability]

[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. In addition, the niobic acid compound dispersion according to the present invention has excellent storage stability, and the occurrence rate of defective products due to precipitation caused by changes over time can be suppressed, so that waste can be reduced and the energy cost for waste disposal can be reduced. These points lead to the achievement of sustainable management and efficient benefits of natural resources, as well as decarbonization (carbon neutrality).

Claims

1. A niobium-containing niobate compound dispersion, One or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements; a phosphorus compound and / or a chlorine compound; Contains A niobic acid compound dispersion, characterized in that the particle diameter (D50) of particles in the niobic acid compound dispersion by dynamic light scattering method is 1000 nm or less.

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

3. 3. The niobate compound dispersion according to claim 1, wherein the element X contains Li.

4. 3. The niobate compound dispersion according to claim 1, wherein the phosphorus compound contains at least one selected from the group consisting of 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 selected from 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. 3. The niobate compound dispersion according to claim 1, further comprising ammonia and / or an organic nitrogen compound.

7. 3. The niobium compound dispersion according to claim 1, wherein the niobium content in the niobate compound dispersion is 0.01% by mass or more and 30% by mass or less in terms of Nb atoms.

8. 3. The niobate compound dispersion according to claim 1, wherein 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 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 is 0.01 or more and 10 or less.

10. 3. The niobate compound dispersion according to claim 1, wherein the element X in the niobate 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.

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

12. 3. The niobate compound dispersion according to claim 1, wherein the element X in the niobate 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 the chlorine compound is 0.01 or more and 10 or less.

13. The niobium compound dispersion according to claim 1 or 2, characterized in that the molar ratio Nb / (P+Cl) of niobium (Nb) in the niobium compound dispersion 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. 3. The niobic acid compound dispersion according to claim 1, wherein the niobic acid compound dispersion is an aqueous dispersion.

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

16. 3. The niobic acid compound dispersion according to claim 1, wherein 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. 3. The niobate compound dispersion according to claim 1, which is used for a positive electrode of a lithium ion secondary battery or for coating a positive electrode material.

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

23. A lithium ion secondary battery comprising a positive electrode having a surface coated with the positive electrode active material for lithium ion secondary batteries according to claim 22.

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