Tantalic acid compound dispersion and method for producing same

Abstract

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

Description

Tantalic acid compound dispersion and method for producing same

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

[0002] Tantalum acid compounds are used as materials for optoelectronics, catalysts, and the like. Patent Document 1 discloses tantalum oxide sol as a tantalum acid compound that is composed of uniform particles and can be stored for long periods of time and used as a coating agent for the surfaces of various components. Tantalum acid compounds, particularly lithium tantalate, have excellent optical, nonlinear, and electro-optical properties and are used in piezoelectric elements, nonlinear optical materials, battery materials, and the like. For example, lithium tantalate is cited as a lithium ion conductive oxide that coats at least a portion of the surface of composite active material particles that can reduce the battery resistance generated in all-solid-state lithium-ion batteries.

[0003] Japanese Patent Application Publication No. 8-143315

[0004] However, the tantalum oxide sol disclosed in Patent Document 1 contains an organic component, such as oxalic acid, which is difficult to volatilize, and this organic component can hinder the formation of a uniform film and, when used as an additive for a catalyst, can inhibit the catalytic action. Furthermore, compared with lithium niobate, lithium tantalate has poor dispersibility and solubility in water, is prone to precipitate over time, and does not have excellent storage stability.

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

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

[0007] The tantalic acid compound dispersion of the present invention contains tantalum. Tantalum is contained in the tantalic acid compound dispersion of the present invention as an oxide, for example, TaO ３ － or polyoxometalate (polyacid) ions in which multiple tantalum atoms are bonded to oxygen atoms.

[0008] The tantalic 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 tantalic acid in the tantalic 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 tantalic acid compound dispersion of the present invention, hydroxide ions are present as anions, while halide ions such as fluoride ions and chloride ions are hardly present, and alkali metal elements and alkaline earth metal elements are presumed to be present as cations, and therefore tantalum is TaO ３ － These tantalum atoms are thought to exist as anions such as those shown below, or as polyoxometalate (polyacid) ions in which multiple tantalum atoms are bonded to oxygen atoms.

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

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

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

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

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

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

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

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

[0017] Furthermore, in the tantalic acid compound dispersion of the present invention, the phosphorus compound preferably contains one or more selected from phosphoric acid (CAS No.: 7664-38-2), condensed phosphoric acid, pyrophosphoric acid (CAS No.: 2466-09-3), polyphosphoric acid (CAS No.: 8071-16-1), phosphorous acid (CAS No.: 13598-36-2), hypophosphorous acid (CAS No.: 6303-21-5), ammonium phosphate, monoammonium phosphate (CAS No.: 7722-76-1), diammonium phosphate (CAS No.: 7783-28-0), ammonium pyrophosphate, and ammonium polyphosphate. Phosphorus compounds and salts of phosphoric acid are preferred for adjusting solutions with a pH closer to neutral. Conversely, condensed phosphoric acid compounds, such as pyrophosphoric acid, polyphosphoric acid, and salts of condensed phosphoric acid, are preferred for adjusting solutions with a high pH.

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

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

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

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

[0022] In addition, if the inclusion of a chlorine compound in the tantalic acid compound dispersion of the present invention causes concern about corrosion or elution of the substrate depending on the material or type of the substrate to which the tantalic acid compound dispersion of the present invention is applied, it is preferable that the tantalic acid compound not be contained. For example, when the tantalic acid compound dispersion of the present invention is used for coating a positive electrode or positive electrode material for a lithium ion secondary battery described below, it is preferable that the tantalic acid compound not be contained.

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

[0024] Here, dynamic light scattering is a method in which a solution such as a suspension is irradiated with light such as laser light, and the light scattering intensity from a group of particles undergoing Brownian motion is measured, and particle size and distribution are determined from the temporal fluctuation of that intensity. Specifically, the particle size distribution is evaluated using a zeta potential, particle size, and molecular weight measurement system (manufactured by Otsuka Electronics Co., Ltd.: ELSZ-2000) in accordance with JIS Z 8828:2019 "Particle size analysis - dynamic light scattering." Just before measurement, the solution to be measured is filtered through a filter with a 1 μm pore size to remove dust and other particles. The particle size (D50) refers to the median diameter (D50), which is the particle size that represents the 50% integrated value of the integrated distribution curve. Furthermore, in this specification, unless otherwise specified, the term "particle diameter (D50)" includes both the "initial particle diameter D50" which indicates the particle diameter (D50) of particles in the tantalic acid compound dispersion of the present invention adjusted to a liquid temperature of 25°C immediately after production, and the "aged particle diameter D50" which indicates the particle diameter (D50) of particles in the tantalic acid compound dispersion of the present invention after it has been left to stand for one month from the day the tantalic acid compound dispersion of the present invention was produced in an incubator set at room temperature of 25°C.

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

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

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

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

[0029] Although the measured value of the transmittance may exceed 100%T due to measurement error or the like, since 100%T is the theoretical upper limit, when the measured value exceeds 100%T, it is considered to be 100%T. Thus, a liquid in which the maximum value of the transmittance in the wavelength region of 400 nm to 760 nm of the tantalic acid compound dispersion of the present invention is 70%T or more is defined as the "tantalic acid compound dispersion" of the present invention. Furthermore, unless otherwise specified, in this specification, "transmittance" includes both "initial transmittance," which indicates the transmittance of the tantalic acid compound dispersion of the present invention adjusted to a liquid temperature of 25°C immediately after production, and "temporary transmittance," which indicates the transmittance of the tantalic 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 tantalic acid compound dispersion of the present invention in accordance with JIS K 0115, 2004 "General rules for absorptiometric analysis methods" under the following transmittance measurement conditions:

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

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

[0033] The tantalic acid compound dispersion of the present invention may further contain hydrogen peroxide, since the tantalic acid compound dispersion of the present invention can produce an aqueous tantalum compound solution by adding hydrogen peroxide to an aqueous tantalum fluoride solution and mixing them in the method for producing a tantalic acid compound dispersion described below.

[0034] The method for detecting hydrogen peroxide in a tantalum acid compound dispersion of the present invention can be performed, for example, by using the standard addition method to measure the relative absorbance intensity with respect to a standard solution of hydrogen peroxide, thereby confirming the hydrogen peroxide content in the dispersion. Specifically, the wavelength region in which a change in absorbance associated with peroxo complex formation is observed is identified from the UV-visible absorption spectra of a standard solution containing a known amount of hydrogen peroxide, e.g., 1% by mass, and a standard solution containing no added hydrogen peroxide. If the difference in absorbance between the standard solution containing no added hydrogen peroxide and a sample with an unknown hydrogen peroxide content in that wavelength region is less than 1%, it can be confirmed that the sample with an unknown hydrogen peroxide content does not substantially contain hydrogen peroxide. If hydrogen peroxide is present in the dispersion, hydrogen peroxide reacts with a tantalum polyacid to form a peroxo complex. Therefore, the absence of hydrogen peroxide in the dispersion can be confirmed by determining the difference in absorbance with the standard solution containing no added hydrogen peroxide, as described above. In addition to the above-mentioned standard addition method, qualitative and quantitative analysis of hydrogen peroxide in the dispersion may be performed by, for example, using a commercially available hydrogen peroxide measurement kit, adding a reagent that undergoes a color reaction with hydrogen peroxide to the dispersion and measuring the color development, or by adding a reagent that undergoes a fluorescent reaction with hydrogen peroxide to the dispersion and measuring the luminescence.

[0035] The tantalic acid compound dispersion of the present invention may further contain ammonia and / or an organic nitrogen compound. The tantalic acid compound dispersion of the present invention may also contain an ionized alkaline aqueous solution, such as ammonia or an organic nitrogen compound. The contents of ammonia and organic nitrogen compounds in the tantalic acid compound dispersion of the present invention are preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 1% by mass or less, respectively, when the tantalic acid compound dispersion of the present invention is taken as 100% by mass.

[0036] As will be explained in detail in the production method of the tantalic acid compound dispersion of the present invention below, in the production process, a tantalic acid-containing precipitate, e.g., a hydrous ammonium tantalate cake, which is a precipitate slurry containing tantalum, is produced by a reverse neutralization method in which an acidic tantalum complex aqueous solution is added to an alkaline aqueous solution, for example, ammonia water, and then the tantalic acid compound dispersion of the present invention is produced, and therefore it is believed that ammonia contains ammonium ions and exists in the dispersion as cations. Furthermore, in the production process, a tantalic acid-containing precipitate obtained through the reverse neutralization method in which ammonia is added to ammonia water is mixed with an organic nitrogen compound to produce a neutralized tantalum compound aqueous solution, and therefore it is believed that the organic nitrogen compound exists in the dispersion as cations.

[0037] The method for measuring the ammonia content in the dispersion liquid is to add sodium hydroxide to the dispersion liquid, distill and separate the ammonia, and then quantify the ammonia content using an ion meter; ２ Examples of methods 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.

[0038] Examples of organic nitrogen compounds include aliphatic amines, aromatic amines, amino alcohols, amino acids, polyamines, quaternary ammonium compounds, guanidine compounds, and azole compounds.

[0039] Examples of aliphatic amines include methylamine, dimethylamine, trimethylamine, ethylamine, methylethylamine, diethylamine, triethylamine, methyldiethylamine, dimethylethylamine, n-propylamine, di-n-propylamine, tri-n-propylamine, iso-propylamine, di-iso-propylamine, tri-iso-propylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, iso-butylamine, di-iso-butylamine, tri-iso-butylamine, tert-butylamine, n-pentaamine, n-hexylamine, cyclohexylamine, and piperidine.

[0040] Examples of aromatic amines include aniline, phenylenediamine, and diaminotoluene. Furthermore, examples of amino alcohols include methanolamine, ethanolamine, propanolamine, butanolamine, pentanolamine, dimethanolamine, diethanolamine, trimethanolamine, methylmethanolamine, methylethanolamine, methylpropanolamine, methylbutanolamine, ethylmethanolamine, ethylethanolamine, ethylpropanolamine, dimethylmethanolamine, dimethylethanolamine, dimethylpropanolamine, methyldimethanolamine, methyldiethanolamine, diethylmethanolamine, trishydroxymethylaminomethane, bis(2-hydroxyethyl)aminotris(hydroxymethyl)methane, and aminophenol. Furthermore, examples of amino acids include alanine, arginine, aspartic acid, and EDTA. Furthermore, examples of polyamines include polyamines and polyetheramines.

[0041] Examples of quaternary ammonium include alkylimidazolium, pyridinium, pyrrolidium, tetraalkylammonium, etc. Specific examples of alkylimidazolium include 1-methyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium, 1-propyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-methyl-2,3-dimethylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-propyl-2,3-dimethylimidazolium, and 1-butyl-2,3-dimethylimidazolium. Specific examples of pyridinium and pyrrolidium include N-butyl-pyridinium, N-ethyl-3-methyl-pyridinium, N-butyl-3-methyl-pyridinium, N-hexyl-4-(dimethylamino)-pyridinium, N-methyl-1-methylpyrrolidinium, and N-butyl-1-methylpyrrolidinium. Specific examples of tetraalkylammonium include tetramethylammonium, tetraethylammonium, tetrabutylammonium, and ethyl-dimethyl-propylammonium. Examples of anions that form salts with the above-mentioned cations include OH, － , Cl － ,Br － , I － , B.F. ４ － , HSO ４ － Examples include:

[0042] Examples of guanidine compounds include guanidine, diphenylguanidine, and ditolylguanidine. Examples of azole compounds include imidazole compounds and triazole compounds. Specific examples of imidazole compounds include imidazole, 2-methylimidazole, and 2-ethyl-4-methylimidazole. Specific examples of triazole compounds include 1,2,4-triazole, 1,2,4-triazole-3-methylcarboxylate, and 1,2,3-benzotriazole.

[0043] Here, the organic nitrogen compound is preferably an aliphatic amine because it has high volatility and low toxicity. Specifically, an aliphatic amine having 1 to 4 carbon atoms is more preferable, and an aliphatic amine having 1 to 2 carbon atoms is particularly preferable. Examples include methylamine and dimethylamine.

[0044] Furthermore, the organic nitrogen compound is preferably a quaternary ammonium, which not only has high solubility but also has high crystallization suppression and high solation suppression. For example, tetraalkylammonium salts are preferred, tetraalkylammonium hydroxide salts are more preferred, tetramethylammonium hydroxide and tetraethylammonium are particularly preferred, and tetramethylammonium hydroxide (TMAH) is also particularly preferred.

[0045] Furthermore, the organic nitrogen compound may be a mixture of two or more compounds selected from aliphatic amines, aromatic amines, amino alcohols, amino acids, polyamines, quaternary ammonium compounds, guanidine compounds, and azole compounds, rather than a single compound. For example, a mixture of two compounds, an aliphatic amine and a quaternary ammonium compound, is preferred because it can increase solubility while limiting the amount added so as not to increase toxicity.

[0046] Specific examples include mixtures of two organic nitrogen compounds such as methylamine and tetramethylammonium hydroxide (TMAH), dimethylamine and tetramethylammonium hydroxide (TMAH), and methylamine and dimethylamine, and mixtures of three organic nitrogen compounds such as methylamine, dimethylamine, and tetramethylammonium hydroxide (TMAH).

[0047] The content of the organic nitrogen compound present in the tantalic acid compound dispersion of the present invention can be measured by gas chromatography (GC), liquid chromatography (LC), mass spectrometry (MS), gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), etc. When a low-volatility organic nitrogen compound is contained, it is preferable to measure the content of the organic nitrogen compound by liquid chromatography (LC) or liquid chromatography-mass spectrometry (LC-MS).

[0048] The tantalum content of the tantalic acid compound dispersion of the present invention is preferably 0.01% by mass or more and 30% by mass or less in terms of Ta atoms, in order to achieve both practicality and stability of the tantalic acid compound dispersion, more preferably 0.5% by mass or more and 25% by mass or less in terms of Ta atoms, even more preferably 1% by mass or more and 20% by mass or less in terms of Ta atoms, particularly preferably 1% by mass or more and 15% by mass or less in terms of Ta atoms, even more particularly preferably 3% by mass or more and 10% by mass or less in terms of Ta atoms, and even more particularly preferably 5% by mass or more and 10% by mass or less in terms of Ta atoms.

[0049] Here, the tantalum content in the tantalum acid compound dispersion is calculated by appropriately diluting the dispersion with dilute hydrochloric acid as needed, and measuring the Ta mass % in terms of Ta atoms using high-frequency inductively coupled plasma atomic emission spectroscopy (ICP atomic emission spectroscopy (AG-5110 manufactured by Agilent Technologies)) in accordance with JIS K0116:2014. Furthermore, when the tantalic acid in the tantalic acid compound dispersion of the present invention is ionically bonded to an alkali metal or alkaline earth metal, for example, a lithium tantalate salt ionically bonded to lithium ions, the lithium content may be calculated by measuring the Li mass % in terms of Li atoms, similarly to the tantalum content. By specifying the tantalum content and the lithium content in the tantalum acid compound dispersion of the present invention, the molar ratio Li / Ta of lithium (Li) to tantalum (Ta) in the lithium tantalate contained in the tantalic acid compound dispersion of the present invention can be specified. The content of each element X of one or more elements X selected from the group consisting of alkali metal elements other than lithium and / or alkaline earth metal elements can be calculated by measuring X mass % of each element in terms of element X atoms, in the same manner as the tantalum content.

[0050] The tantalic acid compound dispersion of the present invention is characterized in that the phosphorus content in the tantalic acid compound dispersion is 0.01% by mass or more and 10% by mass or less in terms of P atoms. A phosphorus content of 0.01% by mass or more and 10% by mass or less in terms of P atoms is preferred in terms of improving dispersibility and solubility in polar solvents, particularly water. Furthermore, a phosphorus content of 0.01% by mass or more and 5% by mass or less in terms of P atoms is more preferred, a content of 0.05% by mass or more and 2% by mass or less in terms of P atoms is even more preferred, and a content of 0.05% by mass or more and 1% by mass or less in terms of P atoms is particularly preferred.

[0051] The phosphorus content in the tantalic acid compound dispersion of the present invention is calculated by diluting the dispersion appropriately with dilute hydrochloric acid as needed, and measuring the P mass % in terms of P atoms using ICP optical emission spectrometry (AG-5110 manufactured by Agilent Technologies) in accordance with JIS K0116:2014.

[0052] The phosphorus content in the tantalic acid compound dispersion of the present invention is preferably analyzed by the above-mentioned ICP emission spectrometry. ３１ It can also be determined by measuring P-NMR spectrum. Specifically, the phosphorus content in the tantalic acid compound dispersion of the present invention can be determined by the following procedure using a nuclear magnetic resonance spectrometer (AVANCE NEO 600 manufactured by Bruker). A measurement sample is prepared by mixing 70 μL of the tantalic acid compound dispersion of the present invention with 650 μL of a phosphonoacetic acid heavy water solution prepared by dissolving 10 g / L of phosphonoacetic acid in heavy water. The prepared measurement sample is subjected to the following measurement. ３１ According to the P-NMR spectrum measurement conditions, ３１ The P-NMR spectrum is measured.

[0053] = ３１P-NMR spectrum measurement conditions = Magnetic field: 14.1 T (1H 600 MHz) Spectrometer: AVANCE NEO 600 manufactured by Bruker Measurement and data processing software: TopSpin manufactured by Bruker NMR probe: Solvent probe (Type: PA BBO 600S3 BBF-H-D-05 Z SP) Solvent: Heavy water Internal sample for chemical shift value and phosphorus amount: Phosphonoacetic acid Chemical shift value reference: The apex of the central peak of the triplet peak of phosphonoacetic acid is set to 14.96 ppm. Spectral center (O1 value - SR value (chemical shift value)): 0.00 ppm Radio frequency pulse intensity: The intensity is set so that 14 μs results in a 90-degree pulse with respect to the peak at the irradiation center. Radio frequency pulse width: 14 μs Measurement interval: 80 μs (DW = 40 μs on the software) Number of measurement points: 32,768 points (TD = 65,536 on the software) Number of spectrum points (SI on the software): 65,536 points

[0054] As mentioned above ３１ By performing a Fourier transform on the FID data measured under the P-NMR spectrum measurement conditions without using a window function, ３１ P-NMR spectrum was obtained. ３１ The peak areas of the P-NMR spectrum can be calculated using the Integrate function of the measurement and data processing software described above, and the contents of phosphonoacetic acid and each phosphate ion can be calculated from the peak areas. For example, in the case of the diphosphate raw material, the peak area is 6.5 ppm (PO ４ -1.7 ppm (presumed to be derived from the chemical shift value of P ２ O ７ (presumed origin) and ３１ In the phosphoric acid raw material, a peak of 6.2 ppm (PO ４ (presumed origin) ３１ The P peak is observed. The chemical shifts vary depending on the pH of the sample, so calculations should be made taking this into consideration.

[0055] Furthermore, the tantalic acid compound dispersion of the present invention preferably has a chlorine content of 0.0% by mass or more and 2.0% by mass or less in terms of Cl atoms. The chlorine content of the tantalic acid compound dispersion of the present invention is preferably 0.0% by mass or more and 2.0% by mass or less in terms of Cl atoms, from the viewpoint of corrosion concerns of the substrate. Furthermore, the chlorine content is more preferably 0.001% by mass or more and 2.0% by mass or less in terms of Cl atoms, even more preferably 0.001% by mass or more and 0.5% by mass or less in terms of Cl atoms, particularly preferably 0.001% by mass or more and 0.2% by mass or less in terms of Cl atoms, and even more particularly preferably 0.001% by mass or more and 0.1% by mass or less in terms of Cl atoms.

[0056] The chlorine content in the tantalic acid compound dispersion of the present invention is calculated by diluting the dispersion appropriately with dilute hydrochloric acid as needed, and measuring the Cl mass % in terms of Cl atoms using ICP optical emission spectrometry (AG-5110 manufactured by Agilent Technologies) in accordance with JIS K0116: 2014. In this case, the chlorine content in the tantalic acid compound dispersion of the present invention can be determined by subtracting the chlorine content derived from the dilute hydrochloric acid used for dilution.

[0057] Furthermore, the tantalic acid compound dispersion of the present invention preferably has a total content of the phosphorus content calculated as P atoms and the chlorine content calculated as Cl atoms in the tantalic acid compound dispersion of 0.01% by mass to 10% by mass. This total content in the tantalic acid compound dispersion of the present invention is preferably 0.01% by mass to 10% by mass, since this improves dispersibility and solubility in polar solvents, particularly water. Furthermore, this total content is more preferably 0.01% by mass to 5% by mass, even more preferably 0.05% by mass to 2% by mass, and particularly preferably 0.05% by mass to 1% by mass.

[0058] The tantalic acid compound dispersion of the present invention is also characterized in that the molar ratio M / Ta of the total amount (M) of element X to tantalum (Ta) in the tantalic acid compound dispersion of the present invention is 0.01 or more and 10 or less. In terms of improving dispersibility and solubility in water, the molar ratio M / Ta of the total amount (M) of element X to tantalum (Ta) in the tantalic acid compound dispersion of the present invention is preferably 0.01 or more and 10 or less, more preferably 0.05 or more and 9 or less, even more preferably 0.1 or more and 8 or less, and particularly preferably 1 or more and 7 or less. The molar ratio M / Ta of the total amount (M) of element X to tantalum (Ta) in the tantalic acid compound dispersion of the present invention may be 0.1 or more and 9 or less, or may be 0.1 or more and 7 or less.

[0059] The tantalic acid compound dispersion of the present invention is characterized in that the element X in the tantalic acid compound dispersion is Li, and the molar ratio Li / Ta of lithium (Li) to tantalum (Ta) is 0.01 or more and 10 or less. When the element X in the tantalic acid compound dispersion of the present invention is Li, and the molar ratio Li / Ta of lithium (Li) to tantalum (Ta) is 0.01 or more and 10 or less, it is preferable in terms of improving dispersibility and solubility in water, and it is more preferable that it is 0.05 or more and 9 or less, even more preferable that it is 0.1 or more and 8 or less, and particularly preferable that it is 1 or more and 7 or less. When the element X in the tantalic acid compound dispersion of the present invention is Li, the molar ratio Li / Ta of lithium (Li) to tantalum (Ta) may be 0.1 or more and 9 or less, or may be 0.1 or more and 7 or less.

[0060] The tantalic acid compound dispersion of the present invention is characterized in that the molar ratio M / (P+Cl) of the total amount of element X (M) to the total amount of phosphorus compounds and / or chlorine compounds (P+Cl) in the tantalic acid compound dispersion is 0.01 or more and 5 or less. In terms of improving dispersibility and solubility in water, the molar ratio M / (P+Cl) of the total amount of element X (M) to the total amount of phosphorus compounds and / or chlorine compounds (P+Cl) in the tantalic acid compound dispersion of the present invention is preferably 0.01 or more and 5 or less, 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. In this specification, unless otherwise specified, the total amount of phosphorus compounds and / or chlorine compounds (P+Cl) is the sum of the value (P) calculated in terms of P atoms and the value (Cl) calculated in terms of Cl atoms. Furthermore, when the tantalic 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 that the total amount of phosphorus compounds and / or chlorine compounds (P+Cl) be 0.

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

[0062] The tantalic acid compound dispersion of the present invention is characterized in that the element X in the tantalic acid compound dispersion is Li, and the molar ratio Li / (P+Cl) of lithium (Li) to the total amount (P+Cl) of the phosphorus compound and / or chlorine compound is 0.01 or more and 5 or less. If the element X in the tantalic acid compound dispersion of the present invention is Li, and the molar ratio Li / (P+Cl) of lithium (Li) to the total amount (P+Cl) of the phosphorus compound and / or chlorine compound is 0.01 or more and 5 or less, it is preferable in terms of improving dispersibility and solubility in water, and is 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.

[0063] Furthermore, in the tantalic acid compound dispersion of the present invention, it is more preferable that the element X in the tantalic acid compound dispersion is Li, and the molar ratio Li / P of lithium (Li) to the total amount (P) of the phosphorus compounds is 0.01 or more and 5 or less. If the element X in the tantalic acid compound dispersion of the present invention is Li, and the molar ratio Li / P of lithium (Li) to the total amount (P) of the phosphorus compounds is 0.01 or more and 5 or less, it is preferable in terms of improving dispersibility and solubility in water, and it is more preferable that it is 0.01 or more and 2 or less, even more preferable that it is 0.05 or more and 2 or less, and particularly preferable that it is 0.1 or more and 1.95 or less.

[0064] The tantalic acid compound dispersion of the present invention is characterized in that the molar ratio Ta / (P+Cl) of tantalum (Ta) to the total amount (P+Cl) of the phosphorus compound and / or chlorine compound in the tantalic acid compound dispersion of the present invention is 0.01 or more and 10 or less. If the molar ratio Ta / (P+Cl) of tantalum (Ta) to the total amount (P+Cl) of the phosphorus compound and / or chlorine compound in the tantalic acid compound dispersion of the present invention is 0.01 or more and 10 or less, it is preferable from the viewpoint of improving dispersibility and solubility in water, and is more preferably 0.05 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.

[0065] Furthermore, in the tantalic acid compound dispersion of the present invention, the molar ratio Ta / P of tantalum (Ta) to the total amount (P) of the phosphorus compounds in the tantalic acid compound dispersion is more preferably from 0.01 to 10. If the molar ratio Ta / P of tantalum (Ta) to the total amount (P) of the phosphorus compounds in the tantalic acid compound dispersion of the present invention is from 0.01 to 10, this is preferred in terms of improving dispersibility and solubility in water, more preferably from 0.05 to 5, even more preferably from 0.1 to 3, and particularly preferably from 0.1 to 1.95.

[0066] The tantalic acid compound dispersion of the present invention is also characterized as being an aqueous dispersion. Because the tantalic acid compound in the tantalic acid compound dispersion of the present invention has high dispersibility in water and good solubility in water, pure water can be used as the solvent. Organic solvents may also be used. Examples of organic solvents include alcohol solvents, ketone solvents, ether solvents, ester solvents, aromatic hydrocarbon solvents, and aliphatic hydrocarbon solvents, and mixtures of these organic solvents with pure water may also be used. Examples of alcohol solvents include alcohols having 5 or fewer carbon atoms (methanol, ethanol, n-propanol, isopropyl alcohol, butanol, ethylene glycol, and propylene glycol), high-boiling point solvents, and acetone. The above-mentioned solvents are preferably compatible with water. The tantalic acid compound dispersion of the present invention may contain one or more solvents in any proportion, as long as stability is not impaired.

[0067] Examples of high-boiling point solvents include polyhydric alcohol solvents and glycol solvents, such as glycerin (boiling point: 290°C), 1,6-hexanediol (boiling point: 250°C), and 1,7-heptanediol (boiling point: 259°C). Examples of glycol-based solvents include ethylene glycol (boiling point: 197.3°C), propylene glycol (boiling point: 188.2°C), diethylene glycol (boiling point: 244.3°C), triethylene glycol (boiling point: 287.4°C), oligoethylene glycol (boiling point: 287°C to 460°C), polyethylene glycol (PEG) (boiling point: 460°C or higher), polyethylene glycol (PEG)-polypropylene glycol (PPG) copolymer (boiling point: 460°C or higher), diethylene glycol monohexyl ether (boiling point: 260°C), polyoxyalkylene monoalkyl ether (boiling point: 260°C or higher), polyoxyethylene sorbitan monolaurate (boiling point: 321°C or higher), other anionic fluorine-based surfactants (boiling point: 180°C or higher), amphoteric fluorine-based surfactants (boiling point: 180°C or higher), nonionic fluorine-based surfactants (boiling point: 180°C or higher), and amine oxides (boiling point: 180°C or higher). The boiling points mentioned above are those at 1 atmosphere.

[0068] The tantalic acid compound dispersion of the present invention is characterized in that the pH of the tantalic acid compound dispersion is from 2 to 11. A pH of from 2 to 11 is preferred for the tantalic acid compound dispersion of the present invention, as it stabilizes the polyacid ions contained in the dispersion. Depending on the application, the tantalic acid compound dispersion of the present invention may be an acidic tantalic acid compound dispersion, a neutral tantalic acid compound dispersion, or a basic tantalic acid compound dispersion. Unless otherwise specified, in this specification, "pH" refers to both the "initial pH," which is the pH of the tantalic acid compound dispersion of the present invention adjusted to a liquid temperature of 25°C immediately after production, and the "chronic pH," which is the pH of the tantalic 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.

[0069] When an acidic tantalic acid compound dispersion is preferred, the pH of the tantalic acid compound dispersion of the present invention is preferably less than 7, and preferably from 2 to less than 7. When a neutral tantalic acid compound dispersion is preferred, the pH of the tantalic acid compound dispersion of the present invention is preferably from 6 to 8, and more preferably 7. When a basic tantalic acid compound dispersion is preferred, the pH of the tantalic acid compound dispersion of the present invention is preferably 7 or more, more preferably 8 or more, even more preferably 9 or more, and particularly preferably 10 or more. On the other hand, the pH is preferably 11 or less. Furthermore, the pH may be 11 or more, or may be 12 or more. Note that, if an organic acid is contained in the tantalic acid compound dispersion of the present invention, it will fluctuate the pH and may cause interactions between the components in the tantalic acid compound dispersion of the present invention and the organic acid, so it is preferable that no organic acid is contained.

[0070] Here, the pH of the tantalic acid compound dispersion of the present invention is measured by immersing an electrode (manufactured by HORIBA: Standard ToupH electrode 9615S-10D) of a pH meter (manufactured by HORIBA: Glass electrode type hydrogen ion concentration indicator D-51) in the tantalic acid compound dispersion of the present invention, and after confirming that the liquid temperature has stabilized at 25°C.

[0071] The tantalic acid compound dispersion of the present invention may also contain, as an additive, an element or compound thereof that does not constitute the tantalic acid compound contained in the tantalic acid compound dispersion of the present invention. Examples of such additives include elements or compounds such as Al, Si, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Sn, La, and W. Examples of the compound include oxides, alkali metal salts of metal acids, alkaline earth metal salts of metal acids, chlorides, metal alkoxides, and polyoxometalates. Furthermore, the content of additives in the tantalic acid compound dispersion of the present invention is such that, when the total number of moles of each additive element is Z, the molar ratio Z / Ta of the total number of moles of each additive element (Z) to tantalum (Ta) 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 atomic weight, similar to the tantalum content described above. Furthermore, because the tantalic acid compound dispersion of the present invention is a uniform dispersion, improved uniformity and improved reactivity (reaction rate) are expected even when these compounds are in a suspended state. Furthermore, if these compounds are dissolved in the tantalic acid compound dispersion of the present invention to form a uniform dispersion, the composite element can be made to have the most favorable reactivity.

[0072] Furthermore, the tantalic acid compound dispersion of the present invention may contain components other than the components derived from tantalum or tantalic acid, ammonia, organic nitrogen compounds, and element X (hereinafter referred to as "other components"), provided that the effects of the dispersion are not impaired. Examples of other components include Al, Si, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Ge, Zr, Nb, Mo, Sn, La, and W. However, the other components are not limited to these. When the tantalic acid compound dispersion of the present invention is taken as 100% by mass, the content of the other components is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. The content of each element corresponding to the other components is calculated by measuring the mass% of each element in atomic terms, similar to the tantalum content described above. It is anticipated that the tantalic acid compound dispersion of the present invention may contain unavoidable impurities, although this is not intended. The content of the unavoidable impurities is preferably 0.01% by mass or less.

[0073] The tantalic acid compound powder of the present invention is characterized by containing the tantalic acid compound in the tantalic acid compound dispersion of the present invention described above. The tantalic acid compound powder of the present invention includes a dried powder obtained by drying the tantalic acid compound dispersion of the present invention, for example, by vacuum drying, and a fired powder obtained by firing the resulting dried powder. The tantalic acid compound powder of the present invention also includes tantalic acid compound powders with different physical properties, such as crystalline structure, produced by vacuum drying or firing the tantalic acid compound dispersion of the present invention, and may have an amorphous structure, a single crystal structure, or a polycrystalline structure. The method for producing the tantalic acid compound powder of the present invention will be described later.

[0074] The tantalic acid compound film of the present invention is characterized by containing the tantalic acid compound in the tantalic acid compound dispersion of the present invention described above. The tantalic acid compound film of the present invention includes a dried film obtained by applying the tantalic acid compound dispersion of the present invention to the surface of a substrate and then drying, for example, by vacuum drying, and a fired film obtained by firing the resulting dried film. The tantalic acid compound film of the present invention also includes tantalic acid compound films with different physical properties, such as crystalline structure, produced by vacuum drying or firing the tantalic acid compound dispersion of the present invention, and may have an amorphous structure, a single crystal structure, or a polycrystalline structure. The tantalum compound, which is the raw material for the tantalic acid compound film of the present invention, has high chemical resistance. Therefore, coating the surface of a substrate with the tantalic acid compound film of the present invention can improve the high-temperature properties (e.g., protection from thermal degradation of the substrate) and chemical resistance of the substrate. The method for producing the tantalic acid compound film of the present invention will be described later.

[0075] The coating agent of the present invention is characterized by containing the above-mentioned tantalic acid compound dispersion of the present invention. The coating agent of the present invention contains the tantalic acid compound dispersion of the present invention, which has high dispersibility in water, good solubility in water, and excellent storage stability.

[0076] The coating agent of the present invention is characterized by containing the above-mentioned tantalic acid compound powder of the present invention, which has high dispersibility in water, good solubility in water, and excellent storage stability.

[0077] The tantalic acid compound dispersion of the present invention is characterized in that it is used for coating a positive electrode or a positive electrode material for a lithium ion secondary battery. The tantalic acid compound dispersion of the present invention can also be used for coating a positive electrode or a positive electrode material for a lithium ion secondary battery.

[0078] The positive electrode active material for a lithium ion secondary battery of the present invention is characterized in that its surface is coated with the tantalic acid compound contained in the tantalic acid compound dispersion of the present invention.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

[0079] The lithium ion secondary battery of the present invention is characterized by having a positive electrode the surface of which is coated with the above-mentioned positive electrode active material for lithium ion secondary batteries of the present invention.

[0080] The method for producing the above-mentioned tantalic acid compound dispersion of the present invention will be described below.

[0081] The method for producing a tantalum acid compound dispersion of the present invention may include a reaction step of adding hydrogen peroxide to an aqueous tantalum fluoride solution to produce an aqueous tantalum compound solution; a neutralization reaction step of adding the aqueous tantalum compound 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 tantalum compound solution; and a mixing step of mixing the neutralized tantalum compound solution with a phosphorus compound or a phosphorus compound solution and / or a chlorine compound or a chlorine compound solution.

[0082] First, the tantalum fluoride aqueous solution is prepared by reacting tantalum, tantalum oxide, or tantalum hydroxide with hydrofluoric acid (HF), such as a hydrofluoric acid aqueous solution, to produce tantalum fluoride (H ２ TaF ７ ) and dissolving it in water to prepare the product.

[0083] Here, an acidic tantalum solution containing fluoride ions, for example, a tantalum fluoride aqueous solution, is prepared by adding water (for example, pure water) to convert tantalum into Ta. ２ O ５ It is preferable to adjust the tantalum content to 1 to 100 g / L in terms of Ta. ２ O ５ When the tantalum content is 1 g / L or more in terms of Ta, the resulting tantalic acid compound hydrate is easily soluble in water, and when productivity is taken into consideration, the tantalum content is more preferably 10 g / L or more, and even more preferably 20 g / L or more. ２ O ５ A concentration of 100 g / L or less in terms of conversion is preferred because it results in a tantalic acid compound hydrate that is easily soluble in water, and in order to more reliably synthesize a tantalic acid compound hydrate that is easily soluble in water, a concentration of 90 g / L or less is more preferred, a concentration of 80 g / L or less is even more preferred, and a concentration of 70 g / L or less is particularly preferred. Note that the pH of the tantalum fluoride aqueous solution is preferably 2 or less, more preferably 1 or less, from the viewpoint of completely dissolving tantalum or tantalum oxide.

[0084] Next, in the reaction step of adding hydrogen peroxide to the tantalum fluoride aqueous solution to produce a tantalum compound aqueous solution, the hydrogen peroxide solution is added to the tantalum fluoride aqueous solution and mixed to obtain a tantalum compound aqueous solution. It is presumed that at least a portion of the obtained tantalum compound aqueous solution forms a peroxo complex.

[0085] Here, the hydrogen peroxide content of the hydrogen peroxide solution added to the tantalum fluoride aqueous solution is preferably 0.5% by mass to 35% by mass. ２ O ２It is preferable to add hydrogen peroxide so that / Ta is 0.6 or more and 1.5 or less, and since there is a possibility that hydrogen peroxide may decompose during mixing, it is more preferable that it is 0.7 or more and 1.2 or less.

[0086] The neutralization reaction step in which the obtained aqueous tantalum compound 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 aqueous tantalum compound solution is as follows.

[0087] In the neutralization reaction step, the obtained aqueous tantalum compound solution is first added to aqueous ammonia, i.e., a reverse neutralization method is used to obtain a precipitate slurry containing tantalum. Fluoride ions are then removed from the obtained precipitate slurry containing tantalum, thereby obtaining a tantalum-containing precipitate from which fluoride ions have been removed.

[0088] 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, tantalum is less likely to remain undissolved, and tantalum or tantalic acid can be completely dissolved in water. On the other hand, when the ammonia content is 30% by mass or less, the ammonia content is close to a saturated aqueous solution of ammonia, which is preferable.

[0089] 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 or more, 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.

[0090] The amount of tantalum fluoride aqueous solution added to the ammonia water is NH ３ The molar ratio of NH 3 to Ta is preferably 95 or more and 500 or less, more preferably 100 or more and 450 or less, and even more preferably 110 or more and 400 or less. In addition, the amount of tantalum fluoride aqueous solution added to the ammonia water is set to NH 3 from the viewpoint of generating tantalic acid compounds that are soluble in amines or diluted ammonia water. ３The molar ratio of NH to HF is preferably 3.0 or more, more preferably 4.0 or more, and even more preferably 5.0 or more. ３ The molar ratio of HF to HCl is preferably 100 or less, more preferably 50 or less, and even more preferably 40 or less.

[0091] The time for adding the tantalum fluoride aqueous solution to the ammonia water is preferably within 10 minutes, more preferably within 8 minutes, and even more preferably within 5 minutes. That is, rather than gradually adding the tantalum fluoride aqueous solution over time, it is preferable to add it to the ammonia water in as short a time as possible, for example, by adding it all at once, and carry out the neutralization reaction. In addition, since the acidic tantalum fluoride aqueous solution is added to the alkaline ammonia water, the neutralization reaction can be carried out while maintaining a high pH. Note that the tantalum fluoride aqueous solution and the ammonia water can be used at room temperature.

[0092] Then, by removing fluoride ions from the tantalum-containing precipitate slurry obtained by the reverse neutralization method, a tantalum-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 tantalum-containing precipitate slurry obtained by the reverse neutralization method, it is preferable to remove these.

[0093] Any method for removing fluorine compounds can be used, and examples of methods that can be used include reverse osmosis filtration using aqueous ammonia or pure water, filtration using a membrane such as ultrafiltration or microfiltration, centrifugation, and other known methods. When removing fluoride ions from a tantalum-containing precipitate slurry, temperature control is not particularly required, and the removal can be carried out at room temperature.

[0094] Specifically, the tantalum-containing precipitate slurry obtained by the reverse neutralization method is decanted using a centrifuge and repeatedly washed until the amount of liberated fluoride ions becomes 100 mg / L or less, thereby obtaining a tantalum-containing precipitate from which fluoride ions have been removed. Note that by repeating this washing, the hydrogen peroxide added in the reaction step is also removed.

[0095] The cleaning solution used to remove fluoride ions is preferably ammonia water. Specifically, ammonia water having a concentration of 1 mass % to 35 mass % is preferred. With such ammonia water, ammonia is suitable for fluoride ions, and unnecessary cost increases can be avoided.

[0096] Next, in the neutralization reaction step, the tantalum-containing precipitate from which the produced fluoride ions have been removed is diluted with pure water or the like to obtain a tantalum-containing precipitate slurry from which the fluoride ions have been removed.The tantalum-containing precipitate slurry from which the fluoride ions have been removed, a hydroxide of element X, for example, lithium hydroxide monohydrate, and pure water are mixed together and maintained at 5°C to 100°C for 0.1 to 72 hours with stirring to obtain a neutralized aqueous tantalum compound solution.

[0097] The mixing step of mixing the obtained neutralized aqueous solution of a tantalum compound with a phosphorus compound or a phosphorus compound solution and / or a chlorine compound or a chlorine compound solution is as follows.

[0098] In the mixing step, a phosphorus compound or a phosphorus compound solution and / or a chlorine compound or a chlorine compound solution is added to the obtained neutralized aqueous solution of a tantalum compound, and the mixture is mixed at room temperature for 0.1 to 2 hours, thereby obtaining a tantalic acid compound dispersion of the present invention.

[0099] Here, the phosphorus compound preferably contains at least one selected from inorganic phosphorus compounds, organic phosphorus compounds, and salts thereof.

[0100] Furthermore, it is preferable that the phosphorus compound contains one or more compounds selected from phosphoric acid (CAS No.: 7664-38-2), condensed phosphoric acid, pyrophosphoric acid (CAS No.: 2466-09-3), polyphosphoric acid (CAS No.: 8071-16-1), phosphorous acid (CAS No.: 13598-36-2), hypophosphorous acid (CAS No.: 6303-21-5), ammonium phosphate, monoammonium phosphate (CAS No.: 7722-76-1), diammonium phosphate (CAS No.: 7783-28-0), ammonium pyrophosphate, and ammonium polyphosphate.

[0101] Alternatively, the tantalic acid compound dispersion of the present invention may be a phosphorus compound solution obtained by adding pure water to the above-mentioned phosphorus compound and adjusting the concentration so that the phosphorus content in terms of P atoms in the tantalic acid compound dispersion of the present invention is 0.01 mass % or more and 10 mass % or less.

[0102] 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).

[0103] The chlorine compound may also be a salt of the above-mentioned chlorine compound, such as an ammonium salt, an amine salt, a quaternary ammonium salt, or a lithium salt, with ammonium salts and lithium salts being preferred. Specific examples include ammonium chloride (CAS No.: 12125-02-9), ammonium perchlorate (CAS No.: 7790-98-9), lithium chloride (CAS No.: 7447-41-8), lithium perchlorate (CAS No.: 7791-03-9), methylamine hydrochloride (CAS No.: 593-51-1), and dimethylamine hydrochloride (CAS No.: 506-59-2).

[0104] Alternatively, the tantalic acid compound dispersion of the present invention may be a chlorine compound solution obtained by adding pure water to the above-mentioned chlorine compound and adjusting the concentration so that the chlorine content in terms of Cl atoms in the tantalic acid compound dispersion of the present invention is 0.0 mass % or more and 2.0 mass % or less.

[0105] In the method for producing a tantalum acid compound dispersion of the present invention, the mixing step may involve mixing the phosphorus compound, 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 tantalum compound neutralization aqueous solution. In the mixing step in the method for producing a tantalum acid compound dispersion of the present invention, before adding the phosphorus compound, the phosphorus compound solution, and / or the chlorine compound, or the chlorine compound solution to the tantalum compound neutralization aqueous solution, the phosphorus compound, the phosphorus compound solution, and / or the chlorine compound, or the chlorine compound solution may be mixed in advance with one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements to form a phosphorus compound mixed solution and / or a chlorine compound mixed solution.

[0106] The one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements to be premixed with the phosphorus compound or phosphorus compound solution and / or chlorine compound or chlorine compound solution include, for example, lithium hydroxide monohydrate.

[0107] Furthermore, the following concentration adjustment step may be carried out to remove ammonia components contained in the obtained tantalic acid compound dispersion of the present invention. 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 (e.g., pure water) is added to replenish the evaporated solvent (e.g., pure water). The amount of solvent added is adjusted so that the tantalum content of the tantalic acid compound dispersion of the present invention after the ammonia component has been removed is equal to the tantalum content of the tantalic acid compound dispersion of the present invention before the ammonia component has been removed.

[0108] Specifically, the tantalum acid compound dispersion of the present invention is obtained by mixing and stirring the obtained neutralized aqueous solution of tantalum compound with a phosphorus compound or a phosphorus compound solution and / or a chlorine compound or a chlorine compound solution so that the tantalum content of the final mixture is 0.01% by mass or more and 30% by mass or less in terms of Ta atom. The composition ratio of each component in the tantalum acid compound dispersion of the present invention thus obtained is preferably as follows:

[0109] When the element X contained in the tantalic acid compound dispersion of the present invention is lithium, the molar ratio Li / (P+Cl) of lithium (Li) to the total amount of phosphorus compounds and / or chlorine compounds (P+Cl) is preferably 0.01 to 5 in terms of improving dispersibility and solubility in water, more preferably 0.01 to 2, even more preferably 0.05 to 2, and particularly preferably 0.1 to 1.95. When the element X contained in the tantalic acid compound dispersion of the present invention is an element X selected from alkali metal elements and / or alkaline earth metal elements other than lithium, the molar ratio M / (P+Cl) of the total amount of element X (M) to the total amount of phosphorus compounds and / or chlorine compounds (P+Cl) is also preferably 0.01 to 5 in terms of improving dispersibility and solubility in water, more preferably 0.01 to 2, even more preferably 0.05 to 2, and particularly preferably 0.1 to 1.95. The element X may be a combination of lithium and other alkali metal elements and / or alkaline earth metal elements, or may be a combination of alkali metal elements other than lithium and / or alkaline earth metal elements.

[0110] Furthermore, when the element X contained in the tantalic acid compound dispersion of the present invention is lithium, the molar ratio Li / P of lithium (Li) to the total amount of phosphorus compounds (P) is preferably from 0.01 to 5 in terms of improving dispersibility and solubility in water, more preferably from 0.01 to 2, even more preferably from 0.05 to 2, and particularly preferably from 0.1 to 1.95. When the element X contained in the tantalic acid compound dispersion of the present invention is an element X selected from alkali metal elements and / or alkaline earth metal elements other than lithium, the molar ratio M / P of the total amount of element X (M) to the total amount of phosphorus compounds (P) is also preferably from 0.01 to 5 in terms of improving dispersibility and solubility in water, more preferably from 0.01 to 2, even more preferably from 0.05 to 2, and particularly preferably from 0.1 to 1.95.

[0111] Furthermore, the molar ratio Ta / (P+Cl) of tantalum (Ta) to the total amount (P+Cl) of phosphorus compounds and / or chlorine compounds contained in the tantalic acid compound dispersion of the present invention is preferably 0.01 or more and 10 or less, from the viewpoint of improving dispersibility and solubility in water, more preferably 0.05 or more and 5 or less, even more preferably 0.1 or more and 3 or less, and particularly preferably 0.1 or more and 1.95 or less.

[0112] Furthermore, the molar ratio Ta / P of tantalum (Ta) to the total amount (P) of phosphorus compounds contained in the tantalic acid compound dispersion of the present invention is preferably 0.01 or more and 10 or less, from the viewpoint of improving dispersibility and solubility in water, more preferably 0.05 or more and 5 or less, even more preferably 0.1 or more and 3 or less, and particularly preferably 0.1 or more and 1.95 or less.

[0113] Furthermore, when the element X contained in the tantalic acid compound dispersion of the present invention is lithium, the molar ratio Li / Ta of lithium (Li) to tantalum (Ta) is preferably 0.01 to 10 in terms of improving dispersibility and solubility in water, more preferably 0.05 to 9, even more preferably 0.1 to 8, and particularly preferably 1 to 7. When the element X contained in the tantalic acid compound dispersion of the present invention is an element X selected from alkali metal elements and / or alkaline earth metal elements other than lithium, the molar ratio M / Ta of the total amount (M) of element X to tantalum (Ta) is also preferably 0.01 to 10 in terms of improving dispersibility and solubility in water, more preferably 0.05 to 9, even more preferably 0.1 to 8, and particularly preferably 1 to 7. Note that this also includes cases where the element X is a combination of multiple elements, such as lithium and another alkali metal element and / or an alkaline earth metal element, and multiple elements selected from alkali metal elements and / or alkaline earth metals other than lithium.

[0114] Another example of the method for producing a tantalum acid compound dispersion of the present invention may include a reaction step of adding hydrogen peroxide to an aqueous tantalum fluoride solution to produce a tantalum compound aqueous solution; a neutralization reaction step of adding the tantalum compound aqueous solution to an alkaline aqueous solution containing an organic nitrogen compound to produce a neutralized tantalum 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 tantalum compound aqueous solution and mixing them.

[0115] Here, in this other example of the method for producing a tantalum acid compound dispersion of the present invention, the steps up to obtaining a tantalum-containing precipitate slurry from which fluoride ions have been removed are the same as those in the method for producing a tantalum acid compound dispersion of the present invention described above, and therefore detailed explanations thereof will be omitted.

[0116] In the same manner as in the above-described method for producing a tantalum acid compound dispersion of the present invention, the resulting tantalum-containing precipitate slurry from which fluoride ions have been removed, an organic nitrogen compound, and pure water are mixed together, and the resulting mixture is maintained at 5°C to 90°C for 0.1 to 48 hours with stirring, to obtain a neutralized aqueous tantalum compound solution.

[0117] As described above, the organic nitrogen compound to be mixed with the tantalum-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, and is particularly preferably an aliphatic amine and / or a quaternary ammonium compound.

[0118] From the viewpoint of solubility, the aliphatic amine is preferably mixed so that the aliphatic amine content in the tantalum-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 tantalum-containing precipitation slurry is 0.1 mass% or more, more preferably 1 mass% or more, and may be 5 mass% or more, or even 10 mass% or more. The aliphatic amine is more preferably methylamine or dimethylamine.

[0119] Furthermore, from the viewpoint of solubility, the quaternary ammonium compound is preferably mixed so that the content of the quaternary ammonium compound in the tantalum-containing precipitation slurry is 40% by mass or less, more preferably 20% by mass or less. From the same viewpoint, the quaternary ammonium compound is preferably mixed so that the content of the quaternary ammonium compound in the tantalum-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 even 10% by mass or more. The quaternary ammonium compound is more preferably tetramethylammonium hydroxide (TMAH) or tetraethylammonium hydroxide (TEAH).

[0120] In the mixing step in another example of the method for producing a tantalic acid compound dispersion of the present invention, a phosphorus compound mixed solution and / or a chlorine compound mixed solution produced by mixing a phosphorus compound, or a phosphorus compound solution and / or a chlorine compound, or a chlorine compound solution with one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, is added to the obtained neutralized aqueous tantalum compound solution, and then mixed.

[0121] The phosphorus compound mixed solution is produced by previously mixing a phosphorus compound or a phosphorus compound solution with one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements.

[0122] Here, the phosphorus compound preferably contains at least one selected from inorganic phosphorus compounds, organic phosphorus compounds, and salts thereof.

[0123] Furthermore, it is preferable that the phosphorus compound contains one or more compounds selected from phosphoric acid (CAS No.: 7664-38-2), condensed phosphoric acid, pyrophosphoric acid (CAS No.: 2466-09-3), polyphosphoric acid (CAS No.: 8071-16-1), phosphorous acid (CAS No.: 13598-36-2), hypophosphorous acid (CAS No.: 6303-21-5), ammonium phosphate, monoammonium phosphate (CAS No.: 7722-76-1), diammonium phosphate (CAS No.: 7783-28-0), ammonium pyrophosphate, and ammonium polyphosphate.

[0124] Alternatively, the tantalic acid compound dispersion of the present invention may be a phosphorus compound solution obtained by adding pure water to the above-mentioned phosphorus compound and adjusting the concentration so that the phosphorus content in terms of P atoms in the tantalic acid compound dispersion of the present invention is 0.01 mass % or more and 10 mass % or less.

[0125] The chlorine compound mixed solution is produced by pre-mixing a chlorine compound or a chlorine compound solution with one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements.

[0126] 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).

[0127] The chlorine compound may also be a salt of the above-mentioned chlorine compound, such as an ammonium salt, an amine salt, a quaternary ammonium salt, or a lithium salt, with ammonium salts and lithium salts being preferred. Specific examples include ammonium chloride (CAS No.: 12125-02-9), ammonium perchlorate (CAS No.: 7790-98-9), lithium chloride (CAS No.: 7447-41-8), lithium perchlorate (CAS No.: 7791-03-9), methylamine hydrochloride (CAS No.: 593-51-1), and dimethylamine hydrochloride (CAS No.: 506-59-2).

[0128] Alternatively, the tantalic acid compound dispersion of the present invention may be a chlorine compound solution obtained by adding pure water to the above-mentioned chlorine compound and adjusting the concentration so that the chlorine content in terms of Cl atoms in the tantalic acid compound dispersion of the present invention is 0.0 mass % or more and 2.0 mass % or less.

[0129] The one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, which are mixed in advance with the phosphorus compound or phosphorus compound solution and / or chlorine compound or chlorine compound solution, include, for example, lithium hydroxide monohydrate.

[0130] The order of adding the tantalum compound neutralized aqueous solution, the phosphorus compound or phosphorus compound solution and / or the chlorine compound or chlorine compound solution, one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, pure water, etc., which are mixed in the mixing step of the method for producing a tantalic acid compound dispersion of the present invention, is not limited to the order described above and can be changed as appropriate.

[0131] The method for producing the tantalic acid compound powder containing the tantalic acid compound in the tantalic acid compound dispersion of the present invention will be described below.

[0132] Among the tantalic acid compound powders, a method for producing a dry powder of a tantalic acid compound involves placing the tantalic acid compound dispersion obtained by the above-mentioned method for producing a tantalic acid compound dispersion of the present invention in a static furnace and drying, for example vacuum drying, for 1 hour to 72 hours at a heating temperature of about 60°C to 200°C, thereby evaporating the water content of the tantalic acid compound dispersion of the present invention and producing a dry powder of the tantalic acid compound containing crystal particles of the tantalic acid compound contained in the tantalic acid compound dispersion of the present invention.

[0133] On the other hand, a method for producing a calcined powder of a tantalic acid compound includes vacuum-drying the tantalic acid compound dispersion of the present invention as described above, placing the obtained dry powder of the tantalic acid compound in a static furnace, and calcining it in the atmosphere at a calcination temperature of 300°C or higher and 1,200°C or lower for a calcination time of 1 hour or higher and 72 hours or lower, thereby obtaining a calcined powder of the tantalic acid compound.

[0134] The tantalic acid compound powder may be prepared by pulverizing the dry powder and calcined powder of the tantalic acid compound described above. Furthermore, regardless of whether or not the powder is pulverized, the undersized particles (fine particles) obtained by classifying the dry powder and calcined powder of the tantalic acid compound described above using a sieve or the like may be used as the tantalic acid compound powder. The oversized particles (coarse particles) may be re-pulverized and classified for use. It is also possible to combine pulverization and classification using a vibrating sieve containing nylon- or fluororesin-coated iron balls or the like as a grinding medium. By combining classification and pulverization in this way, even if excessively large tantalic acid compound powder particles are present, they can be removed. Specifically, when classifying using a sieve, it is preferable to use one with a mesh size of 150 μm to 1,000 μm. When the particle size is 150 μm to 1,000 μm, the proportion of oversized particles will not be too high, so that repeated re-pulverization will not be required, and the tantalic acid compound powder that needs to be re-pulverized will not be classified as undersized particles.

[0135] The tantalic acid compound powder thus obtained can be mixed with water or an organic solvent as a dispersion medium and wet-pulverized using media such as beads to obtain a tantalic acid compound powder dispersion. Examples of organic solvents used as dispersion media include alcohols, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, ethers, and mixtures thereof. Furthermore, a binder such as a resin component may be added to improve the film-forming properties of a tantalic acid compound film using the tantalic acid compound powder dispersion. Examples of resin components used as binders include acrylic resins, polyurethanes, epoxy resins, polystyrene, polycarbonates, glycol-based resins, cellulose-based resins, and mixtures and copolymer resins thereof.

[0136] Furthermore, a method for producing a tantalic acid compound film containing a tantalic acid compound in the tantalic acid compound dispersion of the present invention will be described below.

[0137] Among the tantalic acid compound films, a method for producing a tantalic acid compound dried film includes a coating step of coating a tantalic acid compound dispersion onto the surface of a substrate, and a film drying step of drying the tantalic acid compound dispersion coated on the surface of the substrate to obtain a dry film.

[0138] Specifically, the tantalic acid compound dispersion obtained by the above-described method for producing a tantalic acid compound dispersion of the present invention is dropped onto the surface of a substrate using a syringe while, if necessary, filtering it through a filter with a pore size of 1 μm, for example, and then applied by spin coating (700 rpm, 10 seconds, followed by 1500 rpm, 30 seconds). Next, the resulting mixture is dried at 110° C. for 30 minutes to form a dry tantalic acid compound film on the surface of the substrate.

[0139] Among the tantalic acid compound films, the method for producing a calcined tantalic acid compound film includes a coating step of coating a tantalic acid compound dispersion onto the surface of a substrate, a film drying step of drying the tantalic acid compound dispersion coated on the surface of the substrate in the atmosphere or under vacuum to obtain a dried film, and a film calcination step of calcining the dried film in the atmosphere at a temperature of 300°C or higher and 1,200°C or lower for a calcination time of 1 hour or higher and 12 hours or lower to obtain a calcined film.

[0140] Specifically, as described above, the tantalic acid compound dispersion is applied to the surface of a substrate, and the substrate on which a tantalic acid compound dry film is formed by drying is placed in a static furnace and baked in the atmosphere at a baking temperature of 300°C or higher and 1,200°C or lower for a baking time of 1 hour or higher and 12 hours or lower, thereby forming a tantalic acid compound baked film on the surface of the substrate.

[0141] Furthermore, a method for producing a positive electrode active material for a lithium ion secondary battery coated with a tantalic acid compound contained in the tantalic acid compound dispersion of the present invention will be described below.

[0142] The method includes a step of mixing the tantalic 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 the tantalic acid compound, and a step of drying the positive electrode active material slurry for a battery containing the tantalic acid compound.

[0143] First, the tantalic 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 tantalic acid compound. Then, while stirring the slurry containing the tantalic acid compound, an aqueous solution of lithium hydroxide is added dropwise, and the mixture is maintained at 90° C. for 10 minutes, thereby producing a slurry of a positive electrode active material for a battery containing the tantalic acid compound.

[0144] Next, the battery positive electrode active material slurry containing the tantalic acid compound is dried in an atmospheric drying furnace for 15 hours while the furnace temperature is maintained at 110°C, thereby producing a positive electrode active material for a lithium ion secondary battery coated with the tantalic acid compound.

[0145] In this specification, when "X to Y" (X and Y are any numbers) is expressed, unless otherwise specified, it means "X or more and Y or less", and also means "preferably larger than X" or "preferably smaller than Y". Furthermore, when "X or more" (X is any number) or "Y or less" (Y is any number), it also means "preferably larger than X" or "preferably smaller than Y".

[0146] The tantalic acid compound dispersion of the present invention has high dispersibility in polar solvents, particularly water, good solubility in water, and excellent storage stability. Furthermore, the method for producing a tantalic acid compound dispersion of the present invention can produce a tantalic acid compound dispersion that has high dispersibility in polar solvents, particularly water, good solubility in water, and excellent storage stability.

[0147] 1 is a table listing the physical property values ​​of the tantalic acid compound dispersions according to Examples 1 to 22 of the present invention and Comparative Examples 1 to 3. 2 is a table listing the measurement results of the tantalic acid compound dispersions according to Examples 1 to 22 of the present invention and Comparative Examples 1 to 3.

[0148] The tantalic acid 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.

[0149] Example 1 0.315 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 28.81 g of pure water were placed in a polypropylene container, and 0.87 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the obtained aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0150] Here, the 5 mass % lithium hydroxide monohydrate aqueous solution is LiOH·H ２ It was obtained by mixing 15 g of 0 with 285 g of pure water.

[0151] Then, 4.96 g of a neutralized aqueous solution of a tantalum compound, which will be described later, was added to the phosphorus compound mixed solution, and the mixture was stirred for 30 minutes to obtain a tantalic acid compound dispersion liquid according to Example 1.

[0152] The neutralized aqueous solution of tantalum compound according to Example 1 was obtained as follows.

[0153] First, 137.9 g of tantalum hydroxide (Ta ２ O ５ A tantalum fluoride aqueous solution (Ta 66 mass%) was dissolved in 120 g of a 55 mass% hydrofluoric acid aqueous solution, and 849 mL of pure water was added to the solution. ２ O ５ A content of 8.2% by mass was obtained.

[0154] 1,000 g of this tantalum fluoride aqueous solution was mixed with 36.1 g of hydrogen peroxide (H ２ O ２ Content 35 mass%) was added (H ２ O ２ The mixture was stirred for 5 minutes (molar ratio of tantalum to tantalum = 1.0), to obtain an aqueous solution of a tantalum compound.

[0155] 1,036.1 g of this tantalum compound aqueous solution was added to ammonia water (NH ３ (NH ３ / Ta molar ratio = 245, NH ３ A reaction solution (pH 11) was obtained (mole ratio of HCl / HF=30.6). This reaction solution was a slurry of a tantalic acid compound hydrate, in other words, a slurry of a tantalum-containing precipitate.

[0156] The reaction solution was then decanted using a centrifuge and washed until the amount of liberated fluoride ions was 100 mg / L or less, yielding a tantalum-containing precipitate from which the fluoride ions had been removed, using aqueous ammonia as the washing liquid.

[0157] The tantalum-containing precipitate from which the fluoride ions had been removed was diluted with pure water to obtain a tantalum-containing precipitate slurry. A portion of this tantalum-containing precipitate slurry was dried at 110°C for 24 hours and then fired at 1,000°C for 4 hours to obtain Ta. ２ O ５ and from the weight thereof, the Ta contained in the tantalum-containing precipitation slurry is calculated. ２ O ５ The content was calculated.

[0158] Then, pure water adjusted to a temperature of 70°C to 80°C, the tantalum-containing precipitate slurry diluted with pure water, and a 5 mass% aqueous solution of lithium hydroxide monohydrate were mixed to obtain the neutralized aqueous solution of a tantalum compound according to Example 1. The tantalum content in the neutralized aqueous solution of a tantalum compound according to Example 1 was 4.06 mass%, and the lithium content was 0.14 mass%.

[0159] Example 2 In Example 2, 0.318 g of pyrophosphoric acid and 26.85 g of pure water were placed in a polypropylene container, and 2.84 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0160] Then, 4.96 g of the tantalum 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 tantalic acid compound dispersion liquid according to Example 2.

[0161] 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.

[0162] Example 3 In Example 3, 0.307 g of pyrophosphoric acid and 25.57 g of pure water were placed in a polypropylene container, and 4.29 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0163] Then, 4.95 g of the tantalum 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 tantalic acid compound dispersion liquid according to Example 3.

[0164] 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.

[0165] Example 4 In Example 4, 0.58 g of pyrophosphoric acid and 15.96 g of pure water were placed in a polypropylene container, and 8.5 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the obtained aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0166] Then, 9.93 g of the tantalum 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 tantalic acid compound dispersion liquid according to Example 4.

[0167] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 4 were the same as those used in Example 1.

[0168] Example 5 In Example 5, 0.92 g of pyrophosphoric acid and 6.4 g of pure water were placed in a polypropylene container, and 12.71 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0169] Then, 14.83 g of the tantalum 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 tantalic acid compound dispersion liquid according to Example 5.

[0170] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 5 were the same as those used in Example 1.

[0171] Example 6 In Example 6, 0.142 g of pyrophosphoric acid and 26.76 g of pure water were placed in a polypropylene container, and 1.42 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0172] Then, 6.66 g of the tantalum 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 tantalic acid compound dispersion liquid according to Example 6.

[0173] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 6 were the same as those used in Example 1.

[0174] Example 7 In Example 7, 0.081 g of pyrophosphoric acid and 27.11 g of pure water were placed in a polypropylene container, and 0.25 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0175] Then, 7.43 g of the tantalum 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 tantalic acid compound dispersion liquid according to Example 7.

[0176] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 7 were the same as those used in Example 1.

[0177] Example 8 In Example 8, 0.39 g of phosphoric acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., product name: phosphoric acid, CAS number: 7664-38-2) and 25.33 g of pure water were placed in a polypropylene container, and 4.24 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the obtained aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0178] Then, 4.97 g of the tantalum 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 tantalic acid compound dispersion liquid according to Example 7.

[0179] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 8 was the same as that used in Example 1.

[0180] Example 9 In Example 9, 4.25 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate and 25.42 g of pure water were added to 4.93 g of the neutralized aqueous solution of tantalum compounds used in Example 1 contained in a polypropylene container, thereby obtaining a mixed aqueous solution of tantalum compounds according to Example 9.

[0181] Then, 0.29 g of pyrophosphoric acid was added to the tantalum compound mixed aqueous solution of Example 9, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a tantalic acid compound dispersion of Example 9.

[0182] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 9 were the same as those used in Example 1.

[0183] Example 10 In Example 10, 4.25 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate and 25.46 g of pure water were placed in a polypropylene container, and 4.94 g of the tantalum compound neutralized aqueous solution used in Example 1 was added to obtain a tantalum compound mixed aqueous solution according to Example 10.

[0184] Then, 0.31 g of pyrophosphoric acid was added to the tantalum compound mixed aqueous solution of Example 10, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a tantalic acid compound dispersion of Example 10.

[0185] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 10 were the same as those used in Example 1.

[0186] Example 11 In Example 11, 4.23 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate and 25.47 g of pure water were placed in a polypropylene container, and 0.29 g of pyrophosphoric acid was added to obtain a phosphorus compound mixed solution according to Example 11.

[0187] Then, 5.00 g of the tantalum compound neutralized aqueous solution used in Example 1 was added to the phosphorus compound mixed solution of Example 11, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a tantalic acid compound dispersion of Example 11.

[0188] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 11 were the same as those used in Example 1.

[0189] Example 12 In Example 12, 25.57 g of pure water, 4.94 g of the tantalum compound neutralized aqueous solution used in Example 1, and 4.23 g of a 5 mass % lithium hydroxide monohydrate aqueous solution were added to 0.32 g of pyrophosphoric acid placed in a polypropylene container, and the mixture was stirred and mixed for 30 minutes to obtain a tantalic acid compound dispersion according to Example 12.

[0190] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 12 were the same as those used in Example 1.

[0191] Example 13 In Example 13, 25.43 g of pure water, 0.3 g of pyrophosphoric acid, and 4.24 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate were added to 4.93 g of the neutralized aqueous solution of the tantalum compound used in Example 1 placed in a polypropylene container, and the mixture was stirred and mixed for 30 minutes to obtain a tantalic acid compound dispersion according to Example 13.

[0192] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 13 were the same as those used in Example 1.

[0193] Example 14 In Example 14, 0.15 g of pyrophosphoric acid and 27.18 g of pure water were placed in a polypropylene container, and 0.13 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the obtained aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0194] Then, 7.53 g of the tantalum 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 tantalic acid compound dispersion liquid according to Example 14.

[0195] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 14 were the same as those used in Example 1.

[0196] Example 15 In Example 15, 0.19 g of phosphoric acid and 27.35 g of pure water were placed in a polypropylene container, and 0.13 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the obtained aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0197] Then, 7.34 g of the tantalum 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 tantalic acid compound dispersion liquid according to Example 15.

[0198] The phosphoric acid used in Example 15 was the same as that used in Example 8, and the 5 mass % aqueous solution of lithium hydroxide monohydrate was the same as that used in Example 1.

[0199] Example 16 In Example 16, 0.18 g of phosphoric acid and 26.71 g of pure water were placed in a polypropylene container, and 1.17 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the obtained aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0200] Then, 6.96 g of the tantalum 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 tantalic acid compound dispersion liquid according to Example 16.

[0201] The phosphoric acid used in Example 16 was the same as that used in Example 8, and the 5 mass % aqueous solution of lithium hydroxide monohydrate was the same as that used in Example 1.

[0202] Example 17 In Example 17, 0.19 g of pyrophosphoric acid and 14.79 g of pure water were placed in a polypropylene container, and 7.53 g of the neutralized aqueous solution of tantalum compound used in Example 1 and 8.92 g of an aqueous solution of tantalic acid were added to the resulting aqueous solution of phosphorus compound. The mixture was stirred and mixed for 30 minutes to obtain a tantalic acid compound dispersion according to Example 17.

[0203] The aqueous tantalic acid solution used in Example 17 was obtained as follows.

[0204] First, 137.9 g of tantalum hydroxide (Ta ２ O ５ A tantalum fluoride aqueous solution (Ta 66 mass%) was dissolved in 120 g of a 55 mass% hydrofluoric acid aqueous solution, and 849 mL of pure water was added to the solution. ２ O ５ A content of 8.2% by mass was obtained.

[0205] 1,000 g of this tantalum fluoride aqueous solution was mixed with 28.9 g of hydrogen peroxide (H ２ O ２ Content 35 mass%) was added (H ２ O ２ The mixture was stirred for 5 minutes (molar ratio of tantalum to tantalum = 0.8), to obtain an aqueous solution of a tantalum compound.

[0206] 1,028.9 g of this tantalum compound aqueous solution was added to ammonia water (NH ３(NH ３ / Ta molar ratio = 245, NH ３ A reaction solution (pH 11) was obtained (mole ratio of HCl / HF=30.6). This reaction solution was a slurry of a tantalic acid compound hydrate, in other words, a slurry of a tantalum-containing precipitate.

[0207] The reaction solution was then decanted using a centrifuge and washed until the amount of liberated fluoride ions was 100 mg / L or less, yielding a tantalum-containing precipitate from which the fluoride ions had been removed, using aqueous ammonia as the washing liquid.

[0208] Furthermore, the tantalum-containing precipitate from which the fluoride ions had been removed was diluted with pure water to obtain a tantalum-containing precipitate slurry.

[0209] Then, the tantalum-containing precipitate slurry diluted with pure water, 5 mass % dimethylamine, and pure water were mixed to obtain a tantalic acid aqueous solution according to Example 17.

[0210] The pyrophosphate used in Example 17 was the same as that used in Example 1.

[0211] Example 18 In Example 18, 3.37 g of 1 mol / L hydrochloric acid and 22.71 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 obtained aqueous solution of chlorine compounds to obtain a mixed solution of chlorine compounds.

[0212] Then, 4.65 g of the tantalum compound neutralized aqueous solution was added to the chlorine compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a tantalic acid compound dispersion liquid according to Example 18.

[0213] The neutralized aqueous solution of a tantalum compound used in Example 18 was obtained in the same manner as the neutralized aqueous solution of a tantalum compound in Example 1, except that the concentrations were adjusted so that the tantalum content was 3.89% by mass and the lithium content was 0.15% by mass.

[0214] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 18 was the same as that used in Example 1.

[0215] Example 19 In Example 19, 0.28 g of phosphonic acid and 25.65 g of pure water were placed in a polypropylene container, and 4.3 g of a 5 mass% aqueous solution of lithium hydroxide monohydrate was added to the obtained aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0216] Then, 4.8 g of the tantalum compound neutralized aqueous solution used in Example 18 was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a tantalic acid compound dispersion liquid according to Example 19.

[0217] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 19 was the same as that used in Example 1.

[0218] Example 20 In Example 20, 0.74 g of 30 mass% phosphinic acid and 25.3 g of pure water were placed in a polypropylene container, and 4.22 g of 5 mass% lithium hydroxide monohydrate aqueous solution was added to the obtained phosphorus compound aqueous solution to obtain a phosphorus compound mixed solution.

[0219] Then, 4.69 g of the tantalum compound neutralized aqueous solution used in Example 18 was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a tantalic acid compound dispersion liquid according to Example 20.

[0220] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 20 was the same as that used in Example 1.

[0221] (Example 21) In Example 21, a polypropylene container was filled with 80% by mass of P ２ O ５ 0.3 g of polyphosphoric acid and 25.72 g of pure water were added, and 4.26 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0222] Then, 4.73 g of the tantalum compound neutralized aqueous solution used in Example 18 was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a tantalic acid compound dispersion liquid according to Example 21.

[0223] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 21 was the same as that used in Example 1.

[0224] Example 22 In Example 22, 0.62 g of triethyl phosphate and 25.52 g of pure water were placed in a polypropylene container, and 4.23 g of a 5 mass% aqueous solution of lithium hydroxide monohydrate was added to the obtained aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0225] Then, 4.68 g of the tantalum compound neutralized aqueous solution used in Example 18 was added to the phosphorus compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a tantalic acid compound dispersion liquid according to Example 22.

[0226] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Example 22 was the same as that used in Example 1.

[0227] Comparative Example 1 In Comparative Example 1, 0.3 g of pyrophosphoric acid and 25.56 g of pure water were placed in a polypropylene container, and 4.23 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate was added to the resulting aqueous solution of phosphorus compounds to obtain a mixed solution of phosphorus compounds.

[0228] Then, 0.26 g of lithium tantalate 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 tantalate compound dispersion liquid according to Comparative Example 1.

[0229] The pyrophosphoric acid and the 5 mass % aqueous solution of lithium hydroxide monohydrate used in Comparative Example 1 were the same as those used in Example 1.

[0230] Comparative Example 2 In Comparative Example 2, 3.3 g of 10% by mass sulfuric acid and 25.52 g of pure water were placed in a polypropylene container, and 4.24 g of 5% by mass lithium hydroxide monohydrate aqueous solution was added to the obtained sulfur compound aqueous solution to obtain a sulfur compound mixed solution.

[0231] Then, 4.69 g of the tantalum compound neutralized aqueous solution used in Example 18 was added to the sulfur compound mixed solution, and the mixture was stirred and mixed for 30 minutes, thereby obtaining a tantalic acid compound dispersion liquid according to Comparative Example 2.

[0232] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Comparative Example 2 was the same as that used in Example 1.

[0233] Comparative Example 3 In Comparative Example 3, 6.58 g of a 5 mass % aqueous solution of lithium hydroxide monohydrate and 4.68 g of the tantalum compound neutralized aqueous solution used in Example 18 were added to 25.52 g of pure water placed in a polypropylene container, and the mixture was stirred and mixed for 30 minutes to obtain a tantalic acid compound dispersion according to Comparative Example 3.

[0234] The 5 mass % aqueous solution of lithium hydroxide monohydrate used in Comparative Example 3 was the same as that used in Example 1.

[0235] The following physical properties were measured for the tantalic acid compound dispersions of Examples 1 to 22 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 tantalic acid compound dispersions of Examples 1 to 22 and Comparative Examples 1 to 3 are shown in Figures 1 and 2.

[0236] <Elemental Analysis> If necessary, the sample was appropriately diluted with dilute hydrochloric acid, and for the tantalic acid compound dispersions according to Examples 1 to 22 and Comparative Examples 1 to 3, Ta mass % in terms of Ta atoms, P mass % in terms of P atoms, Li mass % in terms of Li atoms, Cl mass % in terms of Cl atoms, and S mass % in terms of S atoms were measured using ICP optical emission spectrometry (AG-5110 manufactured by Agilent Technologies) in accordance with JIS K0116:2014.

[0237] <pH Measurement> The pH of the tantalic acid compound dispersions of Examples 1 to 22 and Comparative Examples 1 to 3 was measured using an electrode (HORIBA: Standard ToupH electrode 9615S-10D) of a pH meter (HORIBA: Glass electrode type hydrogen ion concentration indicator D-51) after confirming that the liquid temperature had stabilized at 25°C. The "initial pH" in FIG. 2 refers to the pH of the tantalic 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 tantalic acid compound dispersions of Examples 1 to 22 and Comparative Examples 1 to 3 after they were allowed to stand for one month from the day of production in an incubator set at room temperature of 25°C.

[0238] <Dynamic Light Scattering Method> Particle size distribution was evaluated by dynamic light scattering in accordance with JIS Z 8828:2019 using a zeta potential, particle size, and molecular weight measurement system (ELSZ-2000, manufactured by Otsuka Electronics Co., Ltd.). Immediately before measurement, the tantalic acid compound dispersions of Examples 1 to 22 and Comparative Examples 1 to 3 were filtered through a 1 μm pore size filter to remove dust and other particles. Furthermore, D50 indicates the particle size at which the volume fraction reaches 50%. In Figure 2, "initial particle size D50 (nm)" refers to the particle size (D50) of particles in the tantalic acid compound dispersions immediately after production. In Figure 2, "aged particle size D50 (nm)" refers to the particle size (D50) of particles in the tantalic acid compound dispersions of Examples 1 to 22 and Comparative Examples 1 to 3 after they were left standing in an incubator set at room temperature of 25°C for one month from the date of production. In addition, since precipitates were visible in the tantalic acid compound dispersion liquid according to Comparative Example 1, the particle diameter (D50) was not measured.

[0239] <Transmittance Measurement> 3 ml of the tantalic acid compound dispersions according to Examples 1 to 22 and Comparative Examples 1 to 3 were placed in a synthetic quartz cell with an optical path length of 5 mm, and the transmittance in the wavelength range of 400 nm to 760 nm (specifically, the transmittance at wavelengths of 400 nm, 600 nm, and 750 nm) of the tantalic acid compound dispersions according to Examples 1 to 22 and Comparative Examples 1 to 3 was measured using a spectrophotometer under the transmittance measurement conditions described above. The "initial transmittance" in Figure 2 refers to the transmittance of the tantalic acid compound dispersions adjusted to a liquid temperature of 25°C immediately after production. Furthermore, the "temporary transmittance" in Figure 2 refers to the transmittance of the tantalic acid compound dispersions according to Examples 1 to 22 and Comparative Examples 1 to 3 after they were left in an incubator set at room temperature of 25°C for one month from the day of production.

[0240] <Film Formability Test> The appearance of the coating film formed on the surface of a glass substrate, which served as a substitute for a current collector plate, was evaluated by observation with an optical microscope. First, the tantalic acid compound dispersions of Examples 1 to 22 and Comparative Examples 1 to 3 were allowed to stand for one month from the day of production in an incubator set at room temperature (25°C). Next, the tantalic acid compound dispersions of Examples 1 to 22 and Comparative Examples 1 to 3 after standing for one month were dropped onto a 50 mm x 50 mm glass substrate that had been degreased and washed with acetone using a syringe while being filtered through a 0.22 μm pore size filter, and then dried. The resulting glass substrate was then coated by spin coating (700 rpm, 10 seconds, followed by 1500 rpm, 15 seconds). The coated area was then dried at 110°C for 30 minutes in a static oven, forming a coating film on the glass substrate. The glass substrate was observed with an optical microscope (magnification: 40x) in a central 15 mm x 15 mm area of ​​the formed coating film. If no particles were present and a film was formed, the substrate was evaluated as having excellent film-forming properties and was rated as "Good (◯)," and if particles were observed, the substrate was evaluated as having poor film-forming properties and was rated as "Bad (×)."

[0241] As shown in FIGS. 1 and 2 , the tantalic acid compound dispersions according to Examples 1 to 22 contained tantalum, 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 tantalic acid compound dispersions measured by dynamic light scattering method was 1000 nm or less, the dispersions had high dispersibility in a dispersion medium and excellent solubility.

[0242] The tantalic acid compound dispersions according to Examples 1 to 22 contained tantalum, one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, and a phosphorus compound and / or a chlorine compound, and when the maximum value of the transmittance in the wavelength region of 400 nm to 760 nm was 70% T or more, the dispersions had high dispersibility in the dispersion medium and excellent solubility.

[0243] The tantalic acid compound dispersions according to Examples 1 to 22 had excellent stability over time when the tantalum content in the tantalic acid compound dispersions according to Examples 1 to 22 was 0.01% by mass or more and 30% by mass or less in terms of Ta atoms.

[0244] The tantalic acid compound dispersions according to Examples 1 to 22 had excellent stability over time when the phosphorus content in the tantalic acid compound dispersions according to Examples 1 to 22 was 0.01% by mass or more and 10% by mass or less in terms of P atoms.

[0245] The tantalic acid compound dispersions of Examples 1 to 22 showed excellent stability over time, with the particle diameter (D50) after one month not significantly different from the initial particle diameter (D50). However, the tantalic acid compound dispersions of Comparative Examples 1 to 3 showed precipitates.

[0246] The tantalic acid compound dispersions according to Examples 1 to 22 exhibited improved stability during long-term storage when the molar ratio M / Ta 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 tantalum (Ta) was 0.01 or more and 10 or less. Furthermore, when the element X is Li, the tantalic acid compound dispersions according to Examples 1 to 22 exhibited improved stability during long-term storage when the molar ratio Li / Ta between lithium (Li) and tantalum (Ta) was 0.01 or more and 10 or less.

[0247] The tantalic acid compound dispersions of Examples 1 to 22 exhibited improved stability during long-term storage when the molar ratio M / (P+Cl) of the total amount (M) of one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements to the total amount (P+Cl) of phosphorus compounds and / or chlorine compounds was 0.01 or more and 5 or less. Furthermore, the tantalic acid compound dispersions of Examples 1 to 22 exhibited improved stability during long-term storage when the molar ratio Li / (P+Cl) of lithium (Li) to the total amount (P+Cl) of phosphorus compounds and / or chlorine compounds was 0.01 or more and 5 or less, when the element X was Li. Note that for the tantalic acid compound dispersion of 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.

[0248] The tantalic acid compound dispersions according to Examples 1 to 22 had improved stability during long-term storage when the molar ratio Ta / (P+Cl) of tantalum (Ta) to the total amount (P+Cl) of phosphorus compounds and / or chlorine compounds was 0.01 or more and 10 or less. Note that in the tantalic acid compound dispersion according to Comparative Example 2 in the item "Ta / (P+Cl)" in Fig. 1, this is the value of the molar ratio "Ta / (P+S)", and "S" is a value calculated in terms of S atoms.

[0249] The tantalic acid compound dispersions according to Examples 1 to 22 were excellent in stability over time when the pH of the dispersions was 2 or more and 11 or less.

[0250] The tantalic acid compound films formed from the tantalic acid compound dispersions according to Examples 1 to 22 were observed with an optical microscope to show that no coarse particles were present in the coating films, and the coating films had excellent film-forming properties.

[0251] The inventions disclosed in this specification include, in addition to the configurations of each invention and embodiment, those specified by changing these partial configurations to other configurations disclosed in this specification, to the extent applicable, or those specified by adding other configurations disclosed in this specification to these configurations, or those specified as higher-level concepts specified by deleting these partial configurations to the extent that partial effects can be obtained.

[0252] The tantalic acid compound dispersion according to the present invention has high dispersibility in polar solvents, particularly water, good solubility in water, and excellent storage stability. Furthermore, the excellent storage stability of the tantalic acid compound dispersion according to the present invention reduces the rate of defective products caused by sedimentation over time, thereby reducing waste and energy costs for waste disposal. These advantages contribute to the sustainable management and efficient use of natural resources, as well as the achievement of decarbonization (carbon neutrality).

Claims

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

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

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

4. The tantalic acid compound dispersion according to claim 1 or 2, characterized in that the phosphorus compound contains at least one type selected from the group consisting of inorganic phosphorus compounds, organic phosphorus compounds, and salts thereof.

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

6. The tantalic acid compound dispersion according to claim 1 or 2, further comprising hydrogen peroxide.

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

8. The tantalic acid compound dispersion liquid according to claim 1 or 2, characterized in that the tantalum content in the tantalic acid compound dispersion liquid is 0.01% by mass or more and 30% by mass or less in terms of Ta atoms.

9. The tantalic acid compound dispersion liquid according to claim 1 or 2, characterized in that the phosphorus content in the tantalic acid compound dispersion liquid is 0.01% by mass or more and 10% by mass or less in terms of P atoms.

10. The tantalic acid compound dispersion liquid according to claim 1 or 2, wherein the molar ratio M / Ta of the total amount (M) of the element X to tantalum (Ta) in the tantalic acid compound dispersion liquid is 0.01 or more and 10 or less.

11. The tantalic acid compound dispersion liquid according to claim 1 or 2, wherein the element X in the tantalic acid compound dispersion liquid is Li, and the molar ratio Li / Ta of lithium (Li) to tantalum (Ta) is 0.01 or more and 10 or less.

12. The tantalic acid compound dispersion liquid according to claim 1 or 2, wherein the molar ratio M / (P+Cl) of the total amount (M) of the element X to the total amount (P+Cl) of the phosphorus compound and / or the chlorine compound in the tantalic acid compound dispersion liquid is 0.01 or more and 5 or less.

13. The tantalic acid compound dispersion liquid according to claim 1 or 2, wherein the element X in the tantalic acid compound dispersion liquid is Li, and the molar ratio Li / (P+Cl) of lithium (Li) to the total amount (P+Cl) of the phosphorus compound and / or the chlorine compound is 0.01 or more and 5 or less.

14. The tantalic acid compound dispersion liquid according to claim 1 or 2, characterized in that the molar ratio Ta / (P+Cl) of tantalum (Ta) in the tantalic acid compound dispersion liquid to the total amount (P+Cl) of the phosphorus compound and / or the chlorine compound is 0.01 or more and 10 or less.

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

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

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

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

19. A tantalic acid compound film comprising the tantalic acid compound in the tantalic acid compound dispersion liquid according to claim 1 or 2.

20. A coating agent comprising the tantalic acid compound dispersion according to claim 1 or 2.

21. A coating agent comprising the tantalic acid compound powder according to claim 17.

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

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

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