Tantalic acid compound dispersion

Abstract

The present invention provides a tantalic acid compound dispersion containing tantalum. The tantalic acid compound dispersion contains an organic acid and one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements. The tantalic acid compound dispersion has a D50 (on a volume integration basis) of 100 nm or less as measured by a dynamic light scattering.

Description

Tantalic acid compound dispersion

[0001] The present invention relates to a tantalic acid compound dispersion.

[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 is a sol solution, and therefore does not produce a uniform film, which may hinder the catalytic action when used as an additive for a catalyst. Furthermore, lithium tantalate has poor dispersibility and solubility in water compared to lithium niobate, 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 having excellent storage stability.

[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 an organic acid, and is characterized in that D50 (volume integrated basis) measured by dynamic light scattering is 100 nm or less. 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 an organic acid, and is characterized in that D50 (volume integrated basis) measured by dynamic light scattering is 100 nm or less, which is preferable in terms of excellent storage stability.

[0007] The tantalum acid compound dispersion of the present invention contains tantalum. The tantalum is considered to be present as an oxide in the tantalum acid compound dispersion of the present invention. Specifically, tantalum is TaO ３－ , Ta ６ O １９ ２－ These tantalum compounds are thought to exist as anions such as those listed above, polyoxometalate (polyacid) ions in which multiple tantalum atoms are bonded to oxygen atoms, or peroxo complexes in which hydrogen peroxide is coordinated.

[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. It is believed that the tantalic acid compound dispersion of the present invention contains hydroxide ions as anions, but is almost free of halide ions such as fluoride ions and chloride ions, and that the alkali metal elements and alkaline earth metal elements are present as cations.

[0009] Furthermore, the element X preferably contains lithium. Furthermore, the element X is not limited to only one alkali metal element, i.e., lithium, but is preferably two alkali metal elements, i.e., lithium and sodium, or lithium and potassium, or three alkali metal elements, i.e., lithium, sodium, and potassium. Furthermore, the element X may be one alkali metal element, i.e., sodium or potassium, or two alkali metal elements, i.e., sodium and potassium.

[0010] The tantalic acid compound dispersion of the present invention also contains an organic acid.

[0011] Examples of organic acids include carboxylic acids. Examples of carboxylic acids include saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, and carboxylic acid derivatives. Examples of saturated fatty acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, and stearic acid. Examples of unsaturated fatty acids include oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, and sorbic acid. Examples of hydroxy acids include lactic acid, malic acid, citric acid, tartaric acid, glycolic acid, hydroxybutyric acid, and glyceric acid. Examples of aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, gallic acid, mellitic acid, and cinnamic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, and maleic acid. Examples of tricarboxylic acids include aconic acid. Examples of oxocarboxylic acids include pyruvic acid and oxaloacetic acid. Examples of carboxylic acid derivatives include amino acids and nitrocarboxylic acids. Examples of amino acids include alanine, arginine, and aspartic acid. Other examples of carboxylic acids include ethylenediaminetetraacetic acid. The organic acid may be an alkali metal salt or alkaline earth metal salt. For example, sodium ethylenediaminetetraacetate or disodium ethylenediaminetetraacetate may be used.

[0012] Furthermore, in the tantalic acid compound dispersion of the present invention, the organic acid preferably contains one or more selected from carboxylic acids, saturated fatty acids, hydroxy acids, citric acid, tartaric acid, lactic acid, acetic acid, and salts thereof. Nitrogen-free organic acids are preferred, such as carboxylic acids, saturated fatty acids, and hydroxy acids, and more preferably contain one or more selected from citric acid, tartaric acid, lactic acid, malic acid, acetic acid, and salts thereof. Organic acids also include various isomers (structural isomers, optical isomers, etc.) of the above-mentioned compounds. Furthermore, the organic acid may be one or more of the above-mentioned compounds.

[0013] Furthermore, when the D50 (volume integrated basis) measured by dynamic light scattering is 100 nm or less, it is highly dispersible, has little change over time, is stable, and is preferable from the viewpoint of reactivity when reacting with other substances or compounding, and film uniformity during film formation.Furthermore, the D50 is preferably smaller, more preferably 50 nm or less, even more preferably 30 nm or less, particularly preferably 20 nm or less, more particularly preferably 10 nm or less, even particularly preferably 8 nm or less, particularly preferably 6 nm or less, even more preferably 4 nm or less, even more preferably 2 nm or less, even more preferably 1 nm or less, even more preferably 0.6 nm or less, and most preferably more than 0.In this way, a liquid having a D50 of 100 nm or less as measured by dynamic light scattering is defined as the "tantalic acid compound dispersion" of the present invention.

[0014] 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 fluctuations in this intensity. Specifically, 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. D50 refers to the median diameter (D50), which is the particle size that represents the 50% integrated value of the integrated distribution curve. Furthermore, unless otherwise specified, in this specification, "D50" includes both "initial particle diameter D50," which refers to the D50 of the tantalic acid compound dispersion of the present invention adjusted to a liquid temperature of 25°C immediately after production, and "aged particle diameter D50," which refers to the D50 of the tantalic acid compound dispersion of the present invention after it has been left to stand for one month from the day of production in an incubator set at room temperature of 25°C. Furthermore, it is not possible to clearly observe whether the tantalic acid compound in the tantalic acid compound dispersion of the present invention is dissolved in the solvent or exists as particles in the solvent. Therefore, the numerical value described as "particle diameter" in this specification means "the value measured as the particle diameter."

[0015] The tantalic acid compound dispersion of the present invention is a tantalic acid compound dispersion containing tantalum, characterized in that it contains one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, and an organic acid, and has a maximum transmittance in the wavelength region of 400 nm to 760 nm of 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 organic acid in the tantalic acid compound dispersion of the present invention are as described above, detailed description thereof will be omitted.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] Although the measured value of the transmittance may exceed 100%T due to measurement error or the like, since the theoretical upper limit is 100%, when the measured value exceeds 100%T, it is considered to be 100%T. Thus, a liquid in which the maximum transmittance of the tantalic acid compound dispersion of the present invention in the wavelength region of 400 nm to 760 nm is 70%T or greater is considered to be the "tantalic acid compound dispersion" of the present invention. Furthermore, in this specification, unless otherwise specified, the term "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.

[0020] 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:

[0021] =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

[0022] 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.

[0023] The tantalic acid compound dispersion of the present invention may further contain hydrogen peroxide, since in the method for producing a tantalic acid compound dispersion described below, a complexation reaction of tantalum is promoted by mixing and stirring a tantalum halide and hydrogen peroxide.

[0024] 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, for example, 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, for example, a tantalum polyacid to form a peroxo complex. Therefore, the absence of hydrogen peroxide in the dispersion can be confirmed by checking 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.

[0025] 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.

[0026] As will be explained in detail later in the method for producing the tantalum acid compound dispersion of the present invention, a tantalum halide and hydrogen peroxide are mixed and stirred, and the resulting mixture is reacted with an alkaline compound such as ammonia and / or an organic nitrogen compound to produce a precipitate, and therefore the tantalum acid compound dispersion of the present invention contains ammonia and / or an organic nitrogen compound.

[0027] 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.

[0028] Examples of organic nitrogen compounds include aliphatic amines, aromatic amines, amino alcohols, amino acids, polyamines, quaternary ammonium compounds, guanidine compounds, and azole compounds.

[0029] 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.

[0030] 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.

[0031] 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:

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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).

[0037] 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).

[0038] The tantalic acid compound dispersion of the present invention may further contain a phosphorus compound and / or a chlorine compound.

[0039] Here, the phosphorus compound preferably contains at least one selected from inorganic phosphorus compounds, organic phosphorus compounds, and salts thereof.

[0040] 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).

[0041] 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).

[0042] 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).

[0043] 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.

[0044] An example of the organic phosphinic acids is triphenylphosphine (CAS number: 603-35-0).

[0045] 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.

[0046] 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, or 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.

[0047] 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.

[0048] Examples of chlorine compounds include hydrochloric acid (CAS No.: 7647-01-0), hypochlorous acid (CAS No.: 7790-92-3), chlorous acid (CAS No.: 13898-47-0), chloric acid (CAS No.: 7790-93-4), and perchloric acid (CAS No.: 7601-90-3).

[0049] Furthermore, the chlorine compound may 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, and preferably an ammonium salt or a lithium salt. 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).

[0050] 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.

[0051] 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.

[0052] 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 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.

[0053] The tantalic acid compound dispersion of the present invention is characterized in that the organic acid content in the tantalic acid compound dispersion is 0.01% by mass or more and 30% by mass or less. The organic acid content in the tantalic acid compound dispersion of the present invention is preferably 0.01% by mass or more and 30% by mass or less, since the solution state has excellent stability over time. The organic acid content is more preferably 3% by mass or more and 38% by mass or less, and even more preferably 5% by mass or more and 35% by mass or less. Typically, the organic acid content may be 6% by mass or more, 7% by mass or more, 8% by mass or more, 9% by mass or more, 10% by mass or more, or 11% by mass or more. On the other hand, the organic acid content may be 33% by mass or less, 30% by mass or less, 27% by mass or less, or 25% by mass or less. When the tantalic acid compound dispersion of the present invention contains two or more organic acids, the organic acid content is the total content of the two or more organic acids contained.

[0054] The method for measuring the organic acid content in the tantalic acid compound dispersion of the present invention includes the steps of: １ Examples of the method include H-NMR, gas chromatography (GC), liquid chromatography (LC), mass spectrometry (MS), gas chromatography-mass spectrometry (GC-MS), and liquid chromatography-mass spectrometry (LC-MS). Of these, measurement of the organic acid content by liquid chromatography (LC) or liquid chromatography-mass spectrometry (LC-MS) is preferred.

[0055] １ The method for measuring the organic acid content in the tantalic acid compound dispersion of the present invention by H-NMR spectroscopy is as follows. Specifically, the organic acid 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 a sample solution, 70 μL of a DSS-d6 heavy water solution prepared by dissolving sodium 3-(trimethylsilyl)-1-propane-1,1,2,2,3,3-d6-sulfonate (hereinafter referred to as DSS-d6) in heavy water, and 560 μL of heavy water. The prepared measurement sample is subjected to the following measurement. １ According to the H-NMR spectrum measurement conditions, １ The H-NMR spectrum is measured. ​

[0056] = １ H-NMR spectrum measurement conditions = Magnetic field: 14.1 T (1H 600MHz) 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 organic acid amount: DSS-d6 Chemical shift value reference: The apex of the peak of DSS-d6 is set to 0.00 ppm. Spectral center (O1 value - SR value (chemical shift value)): 6 ppm or more and 6.4 ppm or less Radio frequency pulse intensity: The intensity is such that 15 μs results in a 90-degree pulse with respect to the peak of the irradiation center. Radio frequency pulse width: 15 μs Measurement interval: 84 μs (DW = 42 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 or more １ H-NMR spectrum measurement conditions １ The H-NMR spectrum is referred to as the “uncorrected spectrum.”

[0057] The calculation method for the integral value is as described above. １ The FID data measured under the H-NMR spectrum measurement conditions is Fourier transformed using a window function with a full width at half maximum of 0.3 Hz, and the baseline correction described below is performed. １ The H-NMR spectrum was obtained. １ A calculated spectrum is obtained from the H-NMR spectrum using the fitting method described below, and the range of the X-axis including the peak for which the integral value of the calculated spectrum is to be calculated is defined as the "integration range," and the sum of the spectral intensities at all points in the integration range is defined as the "integration value of the target sample." If there are multiple peaks for which the integral values ​​are to be calculated for one target sample, multiple integration ranges may be used.

[0058] The baseline correction method is wider than the integral range, and the X-axis range where the Y-axis values ​​on both sides of a certain X-axis range are close to 0 and the spectrum appears horizontal to the naked eye up to 0.1 ppm inside from both ends of that range is called the "baseline range." The number of baseline ranges is the same as the integral range. Point A is the point on the X-axis and Y-axis where the X-axis value of the uncorrected spectrum is closest to the value obtained by subtracting 0.01 ppm from the maximum value of the baseline range to the point closest to the maximum value of the baseline range, respectively, and Point B is the point on the X-axis and Y-axis where the X-axis value of the uncorrected spectrum is closest to the value obtained by adding 0.01 ppm to the minimum value of the baseline range, respectively. The straight line connecting Point A and Point B is called the "baseline." At each point from the minimum value to the maximum value of the baseline range where the X-axis values ​​are the minimum to maximum, the curve obtained by subtracting the Y-axis values ​​of the uncorrected spectrum from the Y-axis values ​​of the baseline is called the "measured spectrum."

[0059] The method for calculating the integral value from the measured spectrum is to take the sum of the Y-axis values ​​of all points on the measured spectrum from the point closest to the minimum value of the integral range to the point closest to the maximum value, and use this as the integral value within that integral range.

[0060] When it is difficult to apply the above-mentioned method of finding an integral value from an actually measured spectrum due to reasons such as overlapping of multiple peaks, the integral value can be found by performing fitting as follows.

[0061] The range in which the Y-axis values ​​appear to be the values ​​of only the peak for which the integral value is to be calculated, with no other peaks overlapping, is referred to as the "RMSD range." This RMSD range is included in the integral range. Furthermore, if another peak for which the integral value is not to be calculated overlaps within a single integral range, multiple RMSD ranges may be set for that integral range to avoid the peak for which the integral value is not to be calculated. The RMSD ranges for peaks for which the same integral value is to be calculated are included in the same integral range belonging to the peak for which the integral value is to be calculated. Furthermore, overlapping ranges between RMSD ranges are not included. Furthermore, the maximum value of the ratio of the RMSD to the sum of the Y-axis values ​​from the point closest to the minimum to the maximum value of the allowable X-axis value in the integral range is referred to as the "RMSD reference value." The curve represented by the sum of two pseudo-Voigt functions expressed by Equation (1), described below, is referred to as the "calculated spectrum." The root mean square error (hereinafter referred to as RMSD) is calculated for each of four variables (eight variables in total): the chemical shift values ​​of the peak centers of the two pseudo-Voigt functions, the scaling constant, the full width at half maximum, and the ratio of the Lorentzian function, at all points in the entire RMSD range, and the calculated spectrum is fitted using the Excel Solver function so that the ratio of the RMSD to the sum of the Y-axis values ​​from the point closest to the minimum value to the point closest to the maximum value of the integral range is equal to or less than the RMSD reference value.

[0062]

[0063] In the above formula (1), x is １ is the X-axis value (chemical shift value) of the H NMR spectrum, x0 is the chemical shift value of the peak top, S is a scaling coefficient for adjusting the Y-axis value of the peak to the actual measurement, η is the peak area ratio of the Lorentz function (first term) in the range of −∞ (minus infinity) to +∞ (plus infinity), Δ is the full width at half maximum of the peak, π is the constant of the circumference of a circle, ln is a natural logarithm function, and exp is a natural exponential function.

[0064] The above-mentioned "pseudo-Voigt function" is based on "6. Profile functions and pattern decomposition methods" in "Special feature: New developments in powder diffraction methods" in Journal of the Crystallographic Society of Japan, 34, 86 (1992).

[0065] In calculating the peak integral value of DSS-d6, the point C is the point on the X-axis and the Y-axis where the values ​​on the X-axis and the Y-axis are the averages of the values ​​on the X-axis and the Y-axis from the point closest to 0.04 ppm to the point closest to 0.05 ppm on the uncorrected spectrum, respectively, and the point D is the point on the X-axis and the Y-axis where the values ​​on the X-axis and the Y-axis are the averages of the values ​​on the X-axis and the Y-axis from the point closest to −0.05 ppm to the point closest to −0.04 ppm on the uncorrected spectrum, respectively. The line connecting points C and D is referred to as the "DSS-d6 baseline." At each point on the X-axis where the values ​​on the X-axis are chemical shift values ​​from −0.05 ppm to 0.05 ppm, the curve obtained by subtracting the values ​​on the Y-axis of the baseline from the values ​​on the Y-axis of the uncorrected spectrum is referred to as the "measured spectrum of DSS-d6." The sum of the Y-axis values ​​of all points in the measured spectrum of the reference reagent whose X-axis chemical shift values ​​are between −0.05 ppm and 0.05 ppm is called the “integral value of DSS-d6.”

[0066] The weight concentration of the target sample can be calculated from the concentration of DSS-d6 and the amount added to the measurement sample, the molecular weight of DSS-d6 and the number of hydrogen atoms per molecule, the molecular weight of the target sample and the number of hydrogen atoms assigned to the peak obtained by calculating the integral value per molecule of the target sample, the integral value of the standard reagent, the integral value of the target sample, the volume of the target sample added to the measurement sample, and the specific gravity of the target sample.

[0067] Here, a method for determining the amount of lactic acid contained in the Ta lactate aqueous solution, which is the raw material in the examples described later, will be described below.

[0068] DSS-d6, which is used to determine the amount of lactic acid contained in a Ta lactate aqueous solution, is dissolved in heavy water to a concentration of 10 g / L. Two types of lactic acid exist in the Ta lactate aqueous solution: "lactic acid contained in a tantalum complex" and "free lactic acid" that is not contained in a tantalum complex.

[0069] First, a method for determining the amount of lactic acid contained in a tantalum complex will be described below.

[0070] The integral value of lactic acid contained in the tantalum complex is defined as follows: baseline range: 4.55 ppm to 8 ppm; integral range: 4.55 ppm to 6.55 ppm; RMSD range 1: 5.14 ppm to 6.55 ppm; RMSD range 2: 4.95 ppm to 5.00 ppm; RMSD range 3: 4.55 ppm to 4.58 ppm; and RMSD reference value: 0.002%, and the sum of the spectral intensities obtained using the above-described method is defined as the "integral value of lactic acid contained in the tantalum complex."

[0071] The weight concentration of lactic acid contained in the tantalum complex in the Ta lactate dispersion was calculated using the lactic acid contained in the tantalum complex as the target sample. The weight concentration of lactic acid contained in the tantalum complex in the Ta lactate dispersion was calculated to be 16.7% by mass based on the concentration of the DSS-d6 heavy water solution (10 g / L), the volume of the DSS-d6 heavy water solution in the measurement sample (70 μL), the molecular weight of DSS-d6 (224.35), the number of hydrogen atoms per molecule of DSS-d6 (9), the molecular weight of lactic acid (90.08), the integral value of the target sample, the integral value of the reference reagent, the volume of the tantalum acid compound dispersion in the measurement sample (70 μL), and the specific gravity of the tantalum acid compound dispersion (1.3274).

[0072] Next, a method for determining the amount of free lactic acid will be described below.

[0073] Free lactic acid is used as the target sample. 4.85 ppm to 4.93 ppm is defined as baseline range 1 for free lactic acid, 4.31 ppm to 4.4 ppm is defined as baseline range 2 for free lactic acid, and 4.05 ppm to 4.28 ppm is defined as baseline range 3 for free lactic acid. 4.85 ppm to 4.93 ppm is defined as integral range 1 for free lactic acid, 4.31 ppm to 4.4 ppm is defined as integral range 2 for free lactic acid, and 4.05 ppm to 4.28 ppm is defined as integral range 3 for free lactic acid. The sum of the three integral values ​​calculated from the measured spectrum obtained from baseline range 1 and integration range 1, the measured spectrum obtained from baseline range 2 and integration range 2, and the measured spectrum obtained from baseline range 3 and integration range 3 is defined as the "integral value of free lactic acid."

[0074] The weight concentration of free lactic acid in the Ta lactate dispersion was calculated to be 12.2% by mass from the concentration of the DSS-d6 heavy water solution (10 g / L), the volume of the DSS-d6 heavy water solution in the measurement sample (70 μL), the molecular weight of DSS-d6 (224.35), the number of hydrogen atoms in one molecule of DSS-d6 (9), the molecular weight of lactic acid (90.08), the integral value of the target sample, the integral value of the reference reagent, the volume of the tantalic acid compound dispersion in the measurement sample (70 μL), and the specific gravity of the tantalic acid compound dispersion (1.3274).

[0075] The amount of lactic acid in the tantalum lactate aqueous solution is 28.9 mass % when the lactic acid content of the tantalum complex is 16.7 mass % and the free lactic acid content is 12.2 mass %.

[0076] 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.

[0077] 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.

[0078] The tantalic acid compound dispersion of the present invention is also characterized in that the molar ratio x / Ta of the total amount (x) of element X to tantalum (Ta) in the tantalic acid compound dispersion of the present invention is 0.001 or more and 50 or less. In terms of improving dispersibility and solubility in water, the molar ratio x / Ta of the total amount (x) of element X to tantalum (Ta) in the tantalic acid compound dispersion of the present invention is preferably 0.001 or more and 50 or less, more preferably 0.001 or more and 40 or less, even more preferably 0.01 or more and 35 or less, and particularly preferably 0.5 or more and 35 or less. The molar ratio x / Ta of the total amount (x) of element X to tantalum (Ta) in the tantalic acid compound dispersion of the present invention may be 0.01 or more and 40 or less, or may be 0.5 or more and 40 or less.

[0079] The tantalic acid compound dispersion of the present invention is characterized in that the element X in the tantalic acid compound dispersion is lithium, and the molar ratio Li / Ta of the lithium (Li) to the tantalum (Ta) is 0.001 or more and 50 or less. When the element X in the tantalic acid compound dispersion of the present invention is lithium, and the molar ratio Li / Ta of the lithium (Li) to the tantalum (Ta) is 0.001 or more and 50 or less, it is preferable in terms of improving dispersibility and solubility in water, and it is more preferable that it is 0.001 or more and 40 or less, even more preferable that it is 0.01 or more and 35 or less, and particularly preferable that it is 0.5 or more and 35 or less. When the element X in the tantalic acid compound dispersion of the present invention is lithium, the molar ratio Li / Ta of the lithium (Li) to the tantalum (Ta) may be 0.01 or more and 40 or less, or may be 0.5 or more and 40 or less.

[0080] Furthermore, in the tantalic acid compound dispersion of the present invention, when the element X in the tantalic acid compound dispersion is lithium and does not contain a phosphorus compound, if the molar ratio Li / Ta of the lithium (Li) to the tantalum (Ta) is 0.2 or more and 2.0 or less, a film formed using the tantalic acid compound dispersion of the present invention will have a composition of LiTaO ３ or LiTaO ３The molar ratio Li / Ta is more preferably 0.8 or more and 1.2 or less, further preferably 0.98 or more and 1.02 or less, and most preferably Li / Ta=1.

[0081] The tantalic acid compound dispersion of the present invention is characterized in that the molar ratio Ta / A of the tantalum (Ta) to the total amount (A) of the organic acid in the tantalic acid compound dispersion is 0.001 or more and 10 or less.

[0082] The molar ratio Ta / A of the tantalum (Ta) to the total amount (A) of the organic acid in the tantalic acid compound dispersion of the present invention is preferably 0.001 or more and 10 or less, since this provides excellent stability over time in the solution state. Furthermore, the molar ratio (Ta / A) is more preferably 0.001 or more and 4.9 or less, even more preferably 0.01 or more and 3.0 or less, particularly preferably 0.01 or more and 2.0 or less, more particularly preferably 0.01 or more and 1.5 or less, and even more particularly preferably 0.01 or more and 1.0 or less. Typically, the molar ratio (Ta / A) may be 0.001 or more, 0.01 or more, or 0.1 or more. Meanwhile, the molar ratio (Ta / A) may be 4 or less, 3 or less, 2 or less, 1.5 or less, or 1 or less.

[0083] Here, "A" in the molar ratio (Ta / A) represents the organic acid content (mol) in the tantalic acid compound dispersion of the present invention, while "Ta" in the molar ratio (Ta / A) represents the tantalum content (mol) in terms of Ta atoms in the tantalic acid compound dispersion of the present invention.

[0084] The tantalic acid compound dispersion of the present invention is characterized in that the molar ratio (x + Ta) / A of the sum of the element X (x) and the tantalum (Ta) to the total amount (A) of the organic acid in the tantalic acid compound dispersion is 0.001 or more and 10 or less. It is preferable that the molar ratio (x + Ta) / A of the sum of the element X (x) and the tantalum (Ta) to the total amount (A) of the organic acid in the tantalic acid compound dispersion of the present invention is 0.001 or more and 10 or less, since the solution state has excellent stability over time. The molar ratio (x + Ta) / A is more preferably 0.001 or more and 4.9 or less, even more preferably 0.01 or more and 3 or less, particularly preferably 0.01 or more and 2 or less, even more particularly preferably 0.01 or more and 1.5 or less, and even more particularly preferably 0.01 or more and 1 or less. Typically, the molar ratio (x+Ta) / A may be 0.001 or more, 0.01 or more, or 0.1 or more, while the molar ratio (x+Ta) / A may be 4 or less, 3 or less, 2 or less, 1.5 or less, or 1 or less.

[0085] Here, "A" in the molar ratio (x + Ta) / A represents the organic acid content (mol) in the tantalic acid compound dispersion of the present invention, while "x + Ta" represents the sum of the content (mol) of element X in terms of X atoms and the content (mol) of tantalum in terms of Ta atoms in the tantalic acid compound dispersion of the present invention.

[0086] The tantalic acid compound dispersion of the present invention is characterized in that the element X in the tantalic acid compound dispersion is lithium, and the molar ratio (Li + Ta) / A of the sum of the lithium (Li) and the tantalum (Ta) to the total amount (A) of the organic acid is 0.001 or more and 10 or less. It is preferable that the element X in the tantalic acid compound dispersion of the present invention is lithium, and the molar ratio (Li + Ta) / A of the sum of the lithium (Li) and the tantalum (Ta) to the total amount (A) of the organic acid is 0.001 or more and 10 or less, because the solution state has excellent stability over time. The molar ratio (Li + Ta) / A is more preferably 0.001 or more and 4.9 or less, even more preferably 0.01 or more and 3 or less, particularly preferably 0.01 or more and 2 or less, even more particularly preferably 0.01 or more and 1.5 or less, and even more particularly preferably 0.01 or more and 1 or less. Typically, the molar ratio (Li+Ta) / A may be 0.001 or more, 0.01 or more, or 0.1 or more, while the molar ratio (Li+Ta) / A may be 4 or less, 3 or less, 2 or less, 1.5 or less, or 1 or less.

[0087] Here, "A" in the molar ratio (Li + Ta) / A represents the organic acid content (mol) in the tantalic acid compound dispersion of the present invention, while "Li + Ta" represents the sum of the lithium content (mol) in terms of Li atoms and the tantalum content (mol) in terms of Ta atoms in the tantalic acid compound dispersion of the present invention.

[0088] The tantalic acid compound dispersion of the present invention is characterized in that the molar ratio x / P of the total amount (x) of the element X to the total amount (P) of the phosphorus compounds in the tantalic acid compound dispersion is 0.001 or more and 10 or less. It is preferable that the molar ratio x / P of the total amount (x) of the element X to the total amount (P) of the phosphorus compounds in the tantalic acid compound dispersion of the present invention is 0.001 or more and 10 or less, since this provides excellent stability over time in the solution state. The molar ratio x / P is more preferably 0.001 or more and 4.9 or less, even more preferably 0.01 or more and 3 or less, particularly preferably 0.01 or more and 2 or less, even more particularly preferably 0.01 or more and 1.5 or less, and even more particularly preferably 0.01 or more and 1 or less. Typically, the molar ratio x / P may be 0.001 or more, 0.01 or more, or 0.1 or more. On the other hand, the molar ratio x / P may be 4 or less, 3 or less, 2 or less, 1.5 or less, or 1 or less.

[0089] Here, "P" in the molar ratio x / P represents the phosphorus content (mol) in the tantalic acid compound dispersion of the present invention, while "x" represents the content (mol) of element X in the tantalic acid compound dispersion of the present invention in terms of X atoms.

[0090] The tantalic acid compound dispersion of the present invention is characterized in that the element X in the tantalic acid compound dispersion is lithium, and the molar ratio Li / P of the lithium (Li) to the total amount (P) of the phosphorus compounds is 0.001 or more and 10 or less. In the tantalic acid compound dispersion of the present invention, the element X in the tantalic acid compound dispersion is lithium, and the molar ratio Li / (P+A) of the lithium (Li) to the total amount (P) of the phosphorus compounds is 0.001 or more and 10 or less, which is preferable in terms of excellent stability over time in the solution state. The molar ratio Li / P is more preferably 0.001 or more and 4.9 or less, even more preferably 0.01 or more and 3 or less, particularly preferably 0.01 or more and 2 or less, even more particularly preferably 0.01 or more and 1.5 or less, and even more particularly preferably 0.01 or more and 1 or less. Typically, the molar ratio Li / P may be 0.001 or more, 0.01 or more, or 0.1 or more. On the other hand, the molar ratio Li / P may be 4 or less, 3 or less, 2 or less, 1.5 or less, or 1 or less.

[0091] Here, "P" in the molar ratio Li / P indicates the phosphorus content (mol) in the tantalic acid compound dispersion of the present invention, while "Li" indicates the lithium content (mol) in terms of Li atoms in the tantalic acid compound dispersion of the present invention.

[0092] The tantalic acid compound dispersion of the present invention is characterized in that the molar ratio Ta / P of the tantalum (Ta) to the total amount (P) of the phosphorus compounds in the tantalic acid compound dispersion is 0.001 or more and 10 or less. A molar ratio Ta / P of the tantalum (Ta) to the total amount (P) of the phosphorus compounds in the tantalic acid compound dispersion of the present invention of 0.001 or more and 10 or less is preferable in terms of excellent stability over time of the solution state. Furthermore, the molar ratio Ta / P is more preferably 0.001 or more and 4.9 or less, even more preferably 0.01 or more and 3 or less, particularly preferably 0.01 or more and 2 or less, even more particularly preferably 0.01 or more and 1.5 or less, and even more particularly preferably 0.01 or more and 1 or less. Typically, the molar ratio Ta / P may be 0.001 or more, 0.01 or more, or 0.1 or more. On the other hand, the molar ratio Ta / P may be 4 or less, 3 or less, 2 or less, 1.5 or less, or 1 or less.

[0093] Here, "P" in the molar ratio Ta / P indicates the phosphorus content (mol) in the tantalic acid compound dispersion of the present invention, while "Ta" indicates the tantalum content (mol) in terms of Ta atoms in the tantalic acid compound dispersion of the present invention.

[0094] The tantalic acid compound dispersion of the present invention is characterized in that the molar ratio x / (P+A) of the total amount of element X (x) to the sum of the total amount of phosphorus compounds (P) and the total amount of organic acids (A) in the tantalic acid compound dispersion is 0.001 or more and 10 or less. It is preferable that the molar ratio x / (P+A) of the total amount of element X (x) to the sum of the total amount of phosphorus compounds (P) and the total amount of organic acids (A) in the tantalic acid compound dispersion of the present invention is 0.001 or more and 10 or less, because the solution state has excellent stability over time. The molar ratio x / (P+A) is more preferably 0.001 or more and 4.9 or less, even more preferably 0.01 or more and 3 or less, particularly preferably 0.01 or more and 2 or less, even more particularly preferably 0.01 or more and 1.5 or less, and even more particularly preferably 0.01 or more and 1 or less. Typically, the molar ratio x / (P+A) may be 0.001 or more, 0.01 or more, or 0.1 or more, while the molar ratio x / (P+A) may be 4 or less, 3 or less, 2 or less, 1.5 or less, or 1 or less.

[0095] Here, "P+A" in the molar ratio x / (P+A) represents the sum of the phosphorus content (mol) and the organic acid content (mol) in the tantalic acid compound dispersion of the present invention, while "x" represents the content (mol) of element X in the tantalic acid compound dispersion of the present invention in terms of X atoms.

[0096] The tantalic acid compound dispersion of the present invention is characterized in that the element X in the tantalic acid compound dispersion is lithium, and the molar ratio Li / (P+A) of the lithium (Li) to the sum of the total amount of the phosphorus compounds (P) and the total amount of the organic acids (A) is 0.001 or more and 10 or less. It is preferable that the element X in the tantalic acid compound dispersion of the present invention is lithium, and the molar ratio Li / (P+A) of the lithium (Li) to the sum of the total amount of the phosphorus compounds (P) and the total amount of the organic acids (A) is 0.001 or more and 10 or less, in terms of excellent stability over time in the solution state. The molar ratio Li / (P+A) is more preferably 0.001 or more and 4.9 or less, even more preferably 0.01 or more and 3 or less, particularly preferably 0.01 or more and 2 or less, even more particularly preferably 0.01 or more and 1.5 or less, and even more particularly preferably 0.01 or more and 1 or less. Typically, the molar ratio Li / (P+A) may be 0.001 or more, 0.01 or more, or 0.1 or more, while the molar ratio Li / (P+A) may be 4 or less, 3 or less, 2 or less, 1.5 or less, or 1 or less.

[0097] Here, "P+A" in the molar ratio Li / (P+A) represents the sum of the phosphorus content (mol) and the organic acid content (mol) in the tantalic acid compound dispersion of the present invention, while "Li" represents the lithium content (mol) in terms of Li atoms in the tantalic acid compound dispersion of the present invention.

[0098] The tantalic acid compound dispersion of the present invention is characterized in that the molar ratio Ta / (P+A) of the tantalum (Ta) to the sum of the total amount of the phosphorus compounds (P) and the total amount of the organic acids (A) in the tantalic acid compound dispersion is 0.001 or more and 10 or less. It is preferable that the molar ratio Ta / (P+A) of the tantalum (Ta) to the sum of the total amount of the phosphorus compounds (P) and the total amount of the organic acids (A) in the tantalic acid compound dispersion of the present invention is 0.001 or more and 10 or less, since this provides excellent stability over time in the solution state. The molar ratio Ta / (P+A) is more preferably 0.001 or more and 4.9 or less, even more preferably 0.01 or more and 3 or less, particularly preferably 0.01 or more and 2 or less, even more particularly preferably 0.01 or more and 1.5 or less, and even more particularly preferably 0.01 or more and 1 or less. Typically, the molar ratio Ta / (P+A) may be 0.001 or more, 0.01 or more, or 0.1 or more, while the molar ratio Ta / (P+A) may be 4 or less, 3 or less, 2 or less, 1.5 or less, or 1 or less.

[0099] Here, "P+A" in the molar ratio Ta / (P+A) represents the sum of the phosphorus content (mol) and the organic acid content (mol) in the tantalic acid compound dispersion of the present invention, while "Ta" represents the tantalum content (mol) in terms of Ta atoms in the tantalic acid compound dispersion of the present invention.

[0100] The tantalic acid compound dispersion of the present invention is characterized in that the molar ratio (x+Ta) / (P+A) of the sum of the total amount of the element X (x) and the tantalum (Ta) to the sum of the total amount of the phosphorus compounds (P) and the total amount of the organic acids (A) in the tantalic acid compound dispersion is 0.001 or more and 10 or less. When the molar ratio (x+Ta) / (P+A) of the sum of the total amount of the element X (x) and the tantalum (Ta) to the sum of the total amount of the phosphorus compounds (P) and the total amount of the organic acids (A) in the tantalic acid compound dispersion of the present invention is 0.001 or more and 10 or less, this is preferred in terms of excellent stability over time in the solution state. Furthermore, the molar ratio (x + Ta) / (P + A) is more preferably 0.001 or more and 4.9 or less, even more preferably 0.01 or more and 3 or less, particularly preferably 0.01 or more and 2 or less, more particularly preferably 0.01 or more and 1.5 or less, and even more particularly preferably 0.01 or more and 1 or less. Typically, the molar ratio (x + Ta) / (P + A) may be 0.001 or more, 0.01 or more, or 0.1 or more. On the other hand, the molar ratio (x + Ta) / (P + A) may be 4 or less, 3 or less, 2 or less, 1.5 or less, or 1 or less.

[0101] Here, "P+A" in the molar ratio (x+Ta) / (P+A) represents the sum of the phosphorus content (mol) and the organic acid content (mol) in the tantalic acid compound dispersion of the present invention, while "x+Ta" represents the sum of the content (mol) of element X in terms of X atoms and the content (mol) of tantalum in terms of Ta atoms in the tantalic acid compound dispersion of the present invention.

[0102] The tantalic acid compound dispersion of the present invention is characterized in that the element X in the tantalic acid compound dispersion is lithium, and the molar ratio (Li + Ta) / (P + A) of the sum of the lithium (Li) and the tantalum (Ta) to the sum of the total amount of the phosphorus compounds (P) and the total amount of the organic acids (A) is 0.001 or more and 10 or less. When the element X in the tantalic acid compound dispersion of the present invention is lithium, and the molar ratio (Li + Ta) / (P + A) of the sum of the lithium (Li) and the tantalum (Ta) to the sum of the total amount of the phosphorus compounds (P) and the total amount of the organic acids (A) is 0.001 or more and 10 or less, this is preferred in terms of excellent stability over time in the solution state. Furthermore, the molar ratio (Li + Ta) / (P + A) is more preferably 0.001 or more and 4.9 or less, even more preferably 0.01 or more and 3 or less, particularly preferably 0.01 or more and 2 or less, more particularly preferably 0.01 or more and 1.5 or less, and even more particularly preferably 0.01 or more and 1 or less. Typically, the molar ratio (Li + Ta) / (P + A) may be 0.001 or more, 0.01 or more, or 0.1 or more. On the other hand, the molar ratio (Li + Ta) / (P + A) may be 4 or less, 3 or less, 2 or less, 1.5 or less, or 1 or less.

[0103] Here, "P+A" in the molar ratio (Li+Ta) / (P+A) represents the sum of the phosphorus content (mol) and the organic acid content (mol) in the tantalic acid compound dispersion of the present invention, while "Li+Ta" represents the sum of the lithium content (mol) in terms of Li atoms and the tantalum content (mol) in terms of Ta atoms in the tantalic acid compound dispersion of the present invention.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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, more preferably 6 or less, even more preferably 5 or less, particularly preferably 4 or less, and even more particularly preferably 3 or less. On the other hand, a pH of 2 or more is preferred. Furthermore, when a neutral tantalic acid compound dispersion is preferred, the pH of the tantalic acid compound dispersion of the present invention is preferably 6 or more and 8 or less, and more preferably 7. Furthermore, 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, a pH of 11 or less is preferred.

[0108] 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.

[0109] 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, V, Mn, Fe, Co, Ni, Cu, Zn, Ge, and Sn. Examples of such compounds include oxides, alkali metal salts of metal acids, alkaline earth metal salts of metal acids, chlorides, alkoxides of metal acids, and polyoxometalates. Furthermore, the content of additives in the tantalic acid compound dispersion of the present invention, where Z is the total number of moles of each additive element, is the molar ratio Z / Ta of the total number of moles of each additive element (Z) to the tantalum content (Ta). The content of each additive element is calculated by measuring the mass % of each element in atomic terms, 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.

[0110] 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, V, Mn, Fe, Co, Ni, Cu, Zn, Ge, and Sn, but are not limited thereto. When the tantalic acid compound dispersion of the present invention is taken as 100% by mass, the content of other components is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. 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 unavoidable impurities is preferably 0.01% by mass or less.

[0111] 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.

[0112] 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. Because the metal compounds used as raw materials for the tantalic acid compound film of the present invention have high chemical resistance, 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.

[0113] 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.

[0114] The positive electrode active material for a lithium ion secondary battery of the present invention is characterized in that the surface thereof is coated with a tantalic acid compound derived from the above-mentioned 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 Co１／３ Ni １／３ O ２ , LiCo ０．２ Ni ０．４ Mn ０．４ O ２ , LiMnO ４ , LiNi ０．８ Co ０．１５ Al ０．０５ O ２ , LiMnO ２ etc. can be used

[0115] 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.

[0116] The method for producing the above-mentioned tantalic acid compound dispersion of the present invention will be described below.

[0117] The method is characterized by comprising the steps of: mixing and stirring a tantalum halide and hydrogen peroxide to obtain a mixture; reacting the mixture with an alkaline compound and recovering the resulting precipitate by solid-liquid separation; washing the recovered precipitate with the alkaline compound; adding pure water and an organic acid to the washed precipitate to dissolve it; and mixing the precipitate dissolved by adding the organic acid with one or more elements X selected from the group consisting of alkali metals and / or alkaline earth metals.

[0118] First, a tantalum halide and hydrogen peroxide are mixed and stirred to obtain a mixture. Specifically, the mixture is obtained by adding hydrogen peroxide to the tantalum halide placed in a stirring vessel and mixing and stirring for 1 minute to 5 hours, preferably 5 minutes to 1 hour, and more preferably 5 minutes to 30 minutes. Heating is not required, and the mixture can be carried out at room temperature (25°C).

[0119] In the mixture thus obtained, tantalum reacts with hydrogen peroxide, a complexation reaction proceeds, and the tantalum exists as a hydroxide of tantalum, i.e., tantalum hydroxide.

[0120] The halide is preferably a fluoride and / or chloride of tantalum, and more preferably a fluoride of tantalum.

[0121] For example, tantalum fluoride is obtained by adding water (e.g., 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 converted concentration of 100 g / L or less is preferable because it results in a tantalic acid compound hydrate that is highly soluble in water. In order to more reliably synthesize a tantalic acid compound hydrate that is highly soluble in water, a concentration of 90 g / L or less is more preferable, a concentration of 80 g / L or less is even more preferable, and a concentration of 70 g / L or less is particularly preferable.

[0122] The hydrogen peroxide content in the mixture is preferably more than 0% by mass and not more than 10% by mass, more preferably 0.001% by mass or more and not more than 5% by mass, even more preferably 0.01% by mass or more and not more than 1% by mass, and particularly preferably 0.1% by mass or more and not more than 0.8% by mass. Typically, the hydrogen peroxide content may be 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, or 0.5% by mass or more. On the other hand, the hydrogen peroxide content may be 8% by mass or less, 6% by mass or less, 4% by mass or less, or 2% by mass or less.

[0123] The hydrogen peroxide (H ２ O ２ ) content is the molar ratio (H ２ O ２ / Ta). ２ O ２ / Ta) is preferably more than 0.5 and not more than 1.5, more preferably 0.7 or more and 1.3 or less, and even more preferably 0.8 or more and 1.2 or less. Typically, the molar ratio (H ２ O ２ / Ta) may be 0.65 or more, 0.7 or more, or 0.75 or more. ２ O ２ / Ta) may be 1.3 or less, 1.2 or less, or 1.1 or less.

[0124] Here, the molar ratio (H ２ O ２ / Ta) in "H ２ O ２ " indicates the hydrogen peroxide content (mol) in the mixture. Meanwhile, the molar ratio (H ２ O ２ / Ta) indicates the content (mol) of tantalum in the mixture in terms of Ta atoms.

[0125] Next, the resulting mixture is reacted with an alkaline compound, and the resulting precipitate is subjected to solid-liquid separation and recovered. Specifically, the alkaline compound is added to the resulting mixture at a rate of, for example, 1000 mL / min to obtain a white precipitate. The white precipitate is then placed in a centrifuge tube and centrifuged at 4500 rpm for 20 minutes, after which the supernatant is discarded and only the white precipitate is recovered.

[0126] The precipitate recovered in this manner is a precipitate of complexed tantalum resulting from the reaction of the complexed tantalum with the alkaline compound. Specifically, the precipitate is a precipitate of complexed tantalum hydroxide.

[0127] The alkaline compound used to react with the complexed tantalum is preferably one or more compounds selected from ammonia and organic nitrogen compounds. Examples of organic nitrogen compounds include amine compounds, quaternary ammonium compounds, guanidine compounds, and azole compounds. An amine compound or a quaternary ammonium compound is preferred, and methylamine, dimethylamine, tetramethylammonium hydroxide (TMAH), or tetraethylammonium hydroxide (TEAH) is more preferred. The alkaline compound may also be an alkaline solution in which the alkaline compound is dissolved. The alkaline solution is preferably an alkaline aqueous solution, particularly aqueous ammonia.

[0128] The content of the alkaline compound used to react with the complexed tantalum is preferably more than 0% by mass and less than 50% by mass, and more preferably 0.01% by mass or more and 15% by mass or less. From the viewpoints of reactivity and dispersibility, a higher content of the alkaline compound is desirable. Typically, the content of the alkaline compound may be 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, 5% by mass or more, 8% by mass or more, or 10% by mass or more. On the other hand, the content of the alkaline compound may be 30% by mass or less, 25% by mass or less, 20% by mass or less, or 10% by mass or less.

[0129] When the alkaline compound used to react with the complexed tantalum is ammonia water, the ammonia content is preferably more than 0% by mass and less than 50% by mass, and more preferably 0.01% by mass or more and 15% by mass or less. From the viewpoint of reactivity and dispersibility, a higher ammonia content is desirable. Typically, the ammonia content may be 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, 5% by mass or more, 8% by mass or more, or 10% by mass or more. On the other hand, the ammonia content may be 30% by mass or less, 25% by mass or less, 20% by mass or less, or 10% by mass or less.

[0130] The recovered precipitate is then washed with an alkaline compound. Specifically, the alkaline compound is added to the precipitate, the mixture is mixed, and the mixture is placed in a centrifuge tube again and centrifuged at 4,500 rpm for 20 minutes. The supernatant is then discarded, and only the precipitate is recovered.

[0131] By repeating this series of operations multiple times (for example, three times), it is possible to remove excess alkaline compounds and hydrogen peroxide contained in the precipitate, as well as excess fluorine and halogen elements such as chlorine.

[0132] Removing excess alkaline compounds from the precipitate makes it easier to use in terms of safety and workability. Also, removing excess hydrogen peroxide from the precipitate can suppress changes in the precipitate due to the evaporation of hydrogen peroxide, making it easier to use in terms of safety and compliance with regulations.

[0133] The alkaline compound used to wash the recovered precipitate is preferably one or more compounds selected from ammonia and organic nitrogen compounds. Examples of organic nitrogen compounds include amine compounds, quaternary ammonium compounds, guanidine compounds, and azole compounds. An amine compound or a quaternary ammonium compound is preferred, and methylamine, dimethylamine, ethylamine, diethylamine, tetramethylammonium hydroxide (TMAH), or tetraethylammonium hydroxide (TEAH) is more preferred. The alkaline compound may also be an alkaline solution in which the alkaline compound is dissolved. The alkaline solution is preferably an alkaline aqueous solution, particularly ammonia water.

[0134] The alkaline compound content used to wash the recovered precipitate is preferably more than 0% by mass and less than 50% by mass, and more preferably 0.01% by mass or more and 4% by mass or less. From the viewpoints of reactivity and dispersibility, a higher alkaline compound content is desirable. Typically, the alkaline compound content may be 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, 5% by mass or more, 8% by mass or more, or 10% by mass or more. On the other hand, the alkaline compound content may be 30% by mass or less, 25% by mass or less, 20% by mass or less, or 10% by mass or less.

[0135] When the alkaline compound used to wash the recovered precipitate is ammonia water, the ammonia content is preferably more than 0% by mass and less than 50% by mass, and more preferably 0.01% by mass or more and 4% by mass or less. From the viewpoint of reactivity and dispersibility, a higher ammonia content is desirable. Typically, the ammonia content may be 0.1% by mass or more, 0.5% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, 5% by mass or more, 8% by mass or more, or 10% by mass or more. On the other hand, the ammonia content may be 30% by mass or less, 25% by mass or less, 20% by mass or less, or 10% by mass or less.

[0136] The washed precipitate is dissolved by adding pure water and an organic acid. Specifically, the washed precipitate is dissolved by adding pure water and an organic acid, and then the precipitate is dissolved by, for example, ultrasonic treatment or a shaker.

[0137] The organic acid added to the washed precipitate may include carboxylic acids. Examples of carboxylic acids include saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, and carboxylic acid derivatives. Examples of saturated fatty acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, and stearic acid. Examples of unsaturated fatty acids include oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, and sorbic acid. Examples of hydroxy acids include lactic acid, malic acid, citric acid, tartaric acid, glycolic acid, hydroxybutyric acid, and glyceric acid. Examples of aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, gallic acid, mellitic acid, and cinnamic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, and maleic acid. Examples of tricarboxylic acids include aconic acid. Examples of oxocarboxylic acids include pyruvic acid and oxaloacetic acid. Examples of carboxylic acid derivatives include amino acids and nitrocarboxylic acids. Examples of amino acids include alanine, arginine, and aspartic acid. Other examples of carboxylic acids include ethylenediaminetetraacetic acid. The organic acid may be an alkali metal salt or alkaline earth metal salt of the organic acid. For example, sodium ethylenediaminetetraacetate or disodium ethylenediaminetetraacetate may be used. In particular, organic acids that do not contain nitrogen atoms are preferred, such as carboxylic acids, saturated fatty acids, and hydroxy acids, and it is more preferred to include one or more selected from citric acid, tartaric acid, lactic acid, malic acid, acetic acid, and salts thereof.

[0138] The content of the organic acid added to the washed precipitate is preferably more than 0% by mass and less than 100% by mass, more preferably 1% by mass or more and 40% by mass or less, and preferably 5% by mass or more and 30% by mass or less. Typically, the content of the organic acid may be 0.1% by mass or more, 0.5% by mass or more, 2% by mass or more, 5% by mass or more, 8% by mass or more, or 10% by mass or more. On the other hand, the content of the organic acid may be 45% by mass or less, 35% by mass or less, 25% by mass or less, 20% by mass or less, or 10% by mass or less. Here, when the organic acid added is a mixture of two or more organic acids, the content of the organic acid is the total content of the two or more organic acids added.

[0139] The content of the organic acid added to the washed precipitate can be expressed by the molar ratio (A / Ta). It is preferable to add the organic acid so that the molar ratio (A / Ta) is greater than 0 and less than 50. From the viewpoint of the stability and cost reduction of the tantalic acid compound dispersion of the present invention, the molar ratio is more preferably 0.001 to 10, even more preferably 0.01 to 9, and particularly preferably 0.01 to 6. Typically, the molar ratio (A / Ta) may be 0.005 or greater, 0.5 or greater, 1 or greater, 2 or greater, 3 or greater, or 5 or greater. On the other hand, the molar ratio (A / Ta) may be 20 or less, 5 or less, 4 or less, 3 or less, 2 or less, 1 or less, 0.8 or less, or 0.5 or less.

[0140] Here, "A" in the molar ratio (A / Ta) represents the content of organic acid in the tantalic acid compound dispersion of the present invention. When two or more organic acids are contained, the content (mol) of organic acid is the total content (mol) of these two or more organic acids. Meanwhile, "Ta" in the molar ratio (A / Ta) represents the content (mol) of tantalum in terms of Ta atoms in the tantalic acid compound dispersion of the present invention.

[0141] The precipitate dissolved by adding the organic acid is then mixed with one or more elements X selected from the group consisting of alkali metals and / or alkaline earth metals, thereby obtaining the tantalic acid compound dispersion of the present invention.

[0142] The type of compound of element X, i.e., alkali metal or alkaline earth metal, is not limited, but hydroxides, oxides, carbonates, hydrochlorides, sulfates, nitrates, and phosphates are preferred in terms of maintaining high dispersibility, and hydroxides are more preferred, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, and calcium hydroxide.

[0143] When the element X is lithium, a lithium compound dispersion obtained by dissolving a commercially available lithium compound in pure water may be mixed with the precipitate dissolved by adding the organic acid. Examples of the lithium compound include lithium hydroxide, lithium carbonate, lithium acetate, trilithium citrate, and lithium lactate.

[0144] In addition to the above-mentioned pure water and organic acids, the following organic solvents can be used as the solvent to be added to the washed precipitate. Examples of organic solvents include alcohol solvents, ketone solvents, ether solvents, ester solvents, aromatic hydrocarbon solvents, and aliphatic hydrocarbon solvents, and the solvent may be a mixture of these organic solvents and pure water. Examples of alcohol solvents include alcohols having 5 or less carbon atoms (methanol, ethanol, n-propanol, isopropyl alcohol, butanol, ethylene glycol, and propylene glycol), acetone, and high-boiling point solvents. It is preferable that the above-mentioned solvents and water are compatible with each other.

[0145] 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.

[0146] In addition to the solvent added to the washed precipitate, a resin may be added. The resin may be a polyolefin compound, a polyvinyl compound, or the like. The resin added to the solvent may be an anionic water-soluble resin and / or a nonionic water-soluble resin.

[0147] Here, the cationic water-soluble resin is a resin that has a positive charge in the polymer in water at pH = 7, and has any functional group such as an amino group, an imino group, a tertiary amine group, a quaternary ammonium group, a hydrazino group, an azole group, an alkylated azole group, an imidazole group, or an imidazolium group. The anionic water-soluble resin is a resin that has a negative charge in the polymer in water at pH = 7, and has any functional group such as a carboxyl group, a sulfonic acid group, a sulfate ester group, or a phosphate ester group. The nonionic water-soluble resin is a resin that does not fall under the category of the above-mentioned cationic water-soluble resin or anionic water-soluble resin, and has any functional group such as a hydroxyl group, an ether group, or an amide group in the polymer.

[0148] Furthermore, these resins may contain one or more water-soluble homopolymers selected from the group consisting of acrylic polymers, urethane polymers, styrene polymers, olefin polymers, amide polymers, siloxane polymers, epoxy polymers, vinyl chloride polymers, and vinyl acetate polymers, and / or water-soluble copolymers consisting of two or more of these polymers. In particular, it is preferable for the resins to contain one or more water-soluble homopolymers of acrylic polymers, styrene polymers, and olefin polymers, and / or water-soluble copolymers consisting of two or more of these polymers.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] 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.

[0154] Furthermore, a method for producing a tantalic acid compound film containing the tantalic acid compound in the tantalic acid compound dispersion of the present invention will be described below.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] Furthermore, a method for producing a positive electrode active material for a lithium ion secondary battery coated with a tantalic acid compound derived from the tantalic acid compound dispersion of the present invention will be described below.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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".

[0164] The tantalic acid compound dispersion of the present invention has excellent storage stability.

[0165] 1 is a table listing the compositions of tantalic acid compound dispersions according to Examples 1 to 11 of the present invention and Comparative Example 1. 2 is a table listing the composition ratios of tantalic acid compound dispersions according to Examples 1 to 11 of the present invention and Comparative Example 1. 3 is a table listing the measurement results of tantalic acid compound dispersions according to Examples 1 to 11 of the present invention and Comparative Example 1.

[0166] 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.

[0167] Example 1 0.41 g of an 85% aqueous solution of phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 12.29 g of a 5 mass % aqueous solution of lithium DL-lactate, 1.20 g of an aqueous solution of tantalum lactate, and 21.10 g of pure water were placed in a polypropylene container and mixed, thereby obtaining 35 g of a tantalic acid compound dispersion liquid according to Example 1.

[0168] A 5 mass % aqueous solution of lithium DL-lactate was obtained by mixing 25 g of lithium DL-lactate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) with 475 g of pure water for 1 hour.

[0169] Furthermore, an aqueous solution of tantalum lactate was obtained as follows.

[0170] In a 5L beaker, add Ta ２ O ５ TaF equivalent to 80.0 g / L (0.24 mol in terms of Ta atoms) ５ After 658 mL of the aqueous solution was added, 20.8 g (0.21 mol) of 35% by mass hydrogen peroxide solution was added, and the mixture was stirred at room temperature for 10 minutes using a stirrer tip to obtain a mixture.

[0171] To the resulting mixture, approximately 490 g (7.2 mol) of 25% by mass aqueous ammonia was added to obtain a white precipitate. The resulting white precipitate was placed in a centrifuge tube and centrifuged at 4,500 rpm for 20 minutes. The supernatant was discarded, and only the white precipitate was collected.

[0172] Approximately 250 g of 5% by mass aqueous ammonia was added to the recovered white precipitate, mixed, and then centrifuged again at 4,500 rpm for 20 minutes, the supernatant was discarded, and only the white precipitate was recovered. This series of operations was repeated three times.

[0173] Then, pure water was added to the white precipitate washed with 5% ammonia water, and the total weight of the white precipitate and pure water was adjusted to 167 g. 69.5 g (0.77 mol) of lactic acid was then added and dissolved using ultrasound. The mixture was then vacuum dried at 80°C for 12 hours to remove excess ammonia and lactic acid. The resulting dried powder was then added with 20% Ta. ２ O ５ Pure water was added to form a dispersion, and 250 g of an aqueous tantalum lactate solution (Ta ２ O ５ : 19.587% by mass, lactic acid: 28.9% by mass.

[0174] Example 2 0.3 g of an 85% aqueous solution of phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 24.98 g of a 5 mass % aqueous solution of lithium DL-lactate, 0.88 g of an aqueous solution of tantalum lactate, and 8.84 g of pure water were placed in a polypropylene container and mixed, thereby obtaining 35 g of a tantalic acid compound dispersion according to Example 2.

[0175] The 5 mass % aqueous solution of lithium DL-lactate and the aqueous solution of tantalum lactate used in Example 2 were the same as those used in Example 1, and therefore detailed description thereof will be omitted.

[0176] Example 3 0.2 g of an 85% aqueous solution of phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 33.31 g of a 5 mass % aqueous solution of lithium DL-lactate, 0.59 g of an aqueous solution of tantalum lactate, and 0.90 g of pure water were placed in a polypropylene container and mixed, thereby obtaining 35 g of a tantalic acid compound dispersion liquid according to Example 3.

[0177] The 5 mass % aqueous solution of lithium DL-lactate and the aqueous solution of tantalum lactate used in Example 3 were the same as those in Example 1, and therefore detailed description thereof will be omitted.

[0178] Example 4 0.41 g of an 85% aqueous solution of phosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 6.02 g of a 10% by mass aqueous solution of trilithium citrate tetrahydrate, 1.20 g of an aqueous solution of tantalum lactate, and 27.37 g of pure water were placed in a polypropylene container and mixed, thereby obtaining 35 g of a tantalic acid compound dispersion liquid according to Example 4.

[0179] Here, the 10 mass % aqueous solution of trilithium citrate tetrahydrate was obtained by mixing 50 g of trilithium citrate tetrahydrate and 450 g of pure water for 1 hour.

[0180] The tantalum lactate aqueous solution used in Example 4 was the same as that used in Example 1, and therefore a detailed description thereof will be omitted.

[0181] Example 5 0.6 g of a 5 mass % aqueous solution of lithium DL-lactate, 3.52 g of an aqueous solution of tantalum lactate, and 45.88 g of pure water were placed in a polypropylene container and mixed to obtain 50 g of a tantalic acid compound dispersion according to Example 5.

[0182] The 5 mass % aqueous solution of lithium DL-lactate and the aqueous solution of tantalum lactate used in Example 5 were the same as those in Example 1, and therefore detailed description thereof will be omitted.

[0183] Example 6 6.0 g of a 5 mass % aqueous solution of lithium DL-lactate, 3.52 g of an aqueous solution of tantalum lactate, and 40.48 g of pure water were placed in a polypropylene container and mixed, thereby obtaining 50 g of a tantalic acid compound dispersion liquid according to Example 6.

[0184] The 5 mass % aqueous solution of lithium DL-lactate and the aqueous solution of tantalum lactate used in Example 6 were the same as those in Example 1, and therefore detailed explanations thereof will be omitted.

[0185] Example 7 45.0 g of a 5 mass % aqueous solution of lithium DL-lactate, 2.64 g of an aqueous solution of tantalum lactate, and 2.36 g of pure water were placed in a polypropylene container and mixed to obtain 50 g of a tantalic acid compound dispersion according to Example 7.

[0186] The 5 mass % aqueous solution of lithium DL-lactate and the aqueous solution of tantalum lactate used in Example 7 were the same as those in Example 1, and therefore detailed explanations thereof will be omitted.

[0187] Example 8 0.3 g of a 5 mass % aqueous solution of lithium DL-lactate, 0.18 g of an aqueous solution of tantalum lactate, and 49.52 g of pure water were placed in a polypropylene container and mixed to obtain 50 g of a tantalic acid compound dispersion according to Example 8.

[0188] The 5 mass % aqueous solution of lithium DL-lactate and the aqueous solution of tantalum lactate used in Example 8 were the same as those in Example 1, and therefore detailed explanations thereof will be omitted.

[0189] Example 9 30.0 g of a 5 mass% aqueous solution of lithium DL-lactate, 17.62 g of an aqueous solution of tantalum lactate, and 2.38 g of pure water were placed in a polypropylene container and mixed to obtain 50 g of a tantalic acid compound dispersion according to Example 9.

[0190] The 5 mass % aqueous solution of lithium DL-lactate and the aqueous solution of tantalum lactate used in Example 9 were the same as those used in Example 1, and therefore detailed description thereof will be omitted.

[0191] Example 10 3.00 g of a 10 mass% aqueous solution of trilithium citrate tetrahydrate, 3.60 g of an aqueous solution of tantalum lactate, and 43.40 g of pure water were placed in a polypropylene container and mixed to obtain 50 g of a tantalic acid compound dispersion according to Example 10.

[0192] The tantalum lactate aqueous solution used in Example 10 is the same as that used in Example 1, and therefore a detailed description thereof will be omitted. The 10 mass % trilithium citrate tetrahydrate aqueous solution used in Example 10 is the same as that used in Example 4, and therefore a detailed description thereof will be omitted.

[0193] Example 11: 5% by mass of LiOH·H was added to a polypropylene container. ２ 2.60 g of the O aqueous solution, 3.49 g of the tantalum lactate aqueous solution, and 43.91 g of pure water were mixed together to obtain 50 g of a tantalic acid compound dispersion according to Example 11.

[0194] Here, 5 mass% LiOH·H ２ The O solution is LiOH·H ２ This was obtained by mixing 25 g of O with 475 g of pure water for 1 hour.

[0195] The tantalum lactate aqueous solution used in Example 11 was the same as that used in Example 1, and therefore a detailed description thereof will be omitted.

[0196] Comparative Example 1 6.00 g of a 5 mass % aqueous solution of lithium DL-lactate, 0.69 g of tantalum oxide powder (manufactured by Mitsui Mining & Smelting Co., Ltd., purity 99.9%), and 43.31 g of pure water were placed in a polypropylene container and mixed, thereby obtaining 50 g of a tantalic acid compound dispersion according to Comparative Example 1.

[0197] The 5 mass % aqueous solution of lithium DL-lactate used in Comparative Example 1 was the same as that used in Example 1, and therefore a detailed description thereof will be omitted.

[0198] The following physical properties were measured for the tantalic acid compound dispersions of Examples 1 to 11 and Comparative Example 1. The measured physical properties and the methods for measuring the physical properties are shown below, and the compositions of the tantalic acid compound dispersions of Examples 1 to 11 and Comparative Example 1 are shown in Figure 1, the composition ratios of the tantalic acid compound dispersions of Examples 1 to 11 and Comparative Example 1 are shown in Figure 2, and the measurement results of the tantalic acid compound dispersions of Examples 1 to 11 and Comparative Example 1 are shown in Figure 3.

[0199] <Elemental Analysis> The sample was appropriately diluted with dilute hydrochloric acid as needed, and the Ta mass % in terms of Ta atoms and the Li mass % in terms of Li atoms were measured for the tantalic acid compound dispersions according to Examples 1 to 11 and Comparative Example 1 using an ICP optical emission spectrometry (AG-5110 manufactured by Agilent Technologies) in accordance with JIS K0116:2014.

[0200] <pH Measurement> The pH of the tantalic acid compound dispersions of Examples 1 to 11 and Comparative Example 1 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. 3 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. 3 refers to the pH of the tantalic acid compound dispersions of Examples 1 to 11 and Comparative Example 1 after they were allowed to stand for one month from the day of production in an incubator set at room temperature of 25°C.

[0201] <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.). Just before measurement, the tantalic acid compound dispersions of Examples 1 to 11 were filtered through a filter with a 1-μm pore size to remove dust and other particles. Furthermore, D50 indicates the particle size at which the volume fraction reaches 50%. In FIG. 3 , "initial particle diameter D50 (nm)" refers to the D50 of the tantalic acid compound dispersion immediately after production. In FIG. 3 , "time-dependent particle diameter D50 (nm)" refers to the D50 of the tantalic acid compound dispersions of Examples 1 to 11 and Comparative Example 1 after they were left standing for one month from the day of production in an incubator set at room temperature of 25°C. Furthermore, for the tantalic acid compound dispersion of Comparative Example 1, because a precipitate was visible in the dispersion immediately after production, measurements of the initial particle diameter D50 (nm) and the aged particle diameter D50 (nm) were not performed. The above-mentioned filtering was performed when measuring the "initial particle diameter D50 (nm)," but not when measuring the "aged particle diameter D50 (nm)." Only ultrasonic treatment was performed. Furthermore, it was not possible to clearly observe whether the tantalic acid compounds in the tantalic acid compound dispersions of Examples 1 to 11 were dissolved in the solvent or present as particles in the solvent. Therefore, the numerical values ​​shown as "initial particle diameter D50 (nm)" and "aged particle diameter D50 (nm)" in Figure 3 refer to "values ​​measured as particle diameters."

[0202] <Transmittance Measurement> 3 ml of the tantalic acid compound dispersions according to Examples 1 to 11 and Comparative Example 1 were placed in a synthetic quartz cell with an optical path length of 5 mm, and the transmittances of the metals according to Examples 1 to 11 and Comparative Example 1 in the wavelength region of 400 nm to 760 nm (specifically, the transmittances at wavelengths of 400 nm, 600 nm, and 750 nm) were measured using a spectrophotometer under the transmittance measurement conditions described above. The "initial transmittance" in Figure 3 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 3 refers to the transmittance of the tantalic acid compound dispersions according to Examples 1 to 11 and Comparative Example 1 after they were left in an incubator set at room temperature of 25°C for one month from the day of production.

[0203] < １ H-NMR> Measurement samples were prepared by mixing 70 μL of the tantalic acid compound dispersions according to Examples 1 to 11 and Comparative Example 1, 70 μL of a DSS-d6 heavy water solution prepared by dissolving sodium 3-(trimethylsilyl)-1-propane-1,1,2,2,3,3-d6-sulfonate (hereinafter referred to as DSS-d6) in heavy water at a concentration of 10 g / L, and 560 μL of heavy water. The prepared measurement samples were analyzed by the above-mentioned method. １ According to the H-NMR spectrum measurement conditions, １ The H-NMR spectrum was measured. １ The organic acid contents in the tantalic acid compound dispersions of Examples 1 to 11 and Comparative Example 1 were determined from the H-NMR spectra.

[0204] <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 11 and Comparative Example 1 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 11 and Comparative Example 1 after standing for one month were dropped onto a 50 mm x 50 mm glass substrate that had been degreased and washed with acetone using a syringe while being filtered through a 0.22 μm pore size filter, and then dried. The coating was applied by spin coating (700 rpm, 10 seconds, followed by 1500 rpm, 15 seconds). The coated area was then allowed to dry naturally, forming a coating film on the glass substrate. The glass substrate was observed with an optical microscope (magnification: 40x) in a central 15 mm x 15 mm area of ​​the formed coating film. If no particles were present and a film was formed, the substrate was evaluated as having excellent film-forming properties and was rated as "○ (GOOD)," and if particles were observed, the substrate was evaluated as having poor film-forming properties and was rated as "× (BAD)."

[0205] As shown in FIGS. 1 and 2 , the tantalic acid compound dispersions according to Examples 1 to 11 were tantalum-containing tantalic acid compound dispersions containing one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, and an organic acid. When the D50 (volume integrated basis) measured by dynamic light scattering was 100 nm or less, the dispersions had excellent storage stability.

[0206] The tantalic acid compound dispersions according to Examples 1 to 11 were tantalum-containing tantalic acid compound dispersions containing one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements, and an organic acid. 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 excellent storage stability.

[0207] The tantalum content of the tantalic acid compound dispersions according to Examples 1 to 11 was 0.01% by mass or more and 30% by mass or less in terms of Ta atoms, and the tantalic acid compound dispersions according to Examples 1 to 11 had excellent stability over time.

[0208] The tantalic acid compound dispersions according to Examples 1 to 11 had excellent stability over time when the organic acid content in the tantalic acid compound dispersions according to Examples 1 to 11 was 0.01% by mass or more and 30% by mass or less.

[0209] The tantalic acid compound dispersions according to Examples 1 to 11 had excellent stability over time in the solution state when the phosphorus content was 0.01% by mass or more and 10% by mass or less in terms of P atoms.

[0210] As shown in FIG. 3, the tantalic acid compound dispersions according to Examples 1 to 11 had excellent stability over time when the pH of the dispersions was 2 or more and 11 or less.

[0211] 2 , the tantalic acid compound dispersions according to Examples 1 to 11 exhibited improved stability during long-term storage when the molar ratio x / Ta of the total amount (x) of one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements to the tantalum content (Ta) in the tantalic acid compound dispersions was 0.001 or more and 50 or less. Furthermore, when the element X was Li, the tantalic acid compound dispersions according to Examples 1 to 11 exhibited improved stability during long-term storage when the molar ratio Li / Ta of the lithium (Li) to the tantalum content (Ta) in the tantalic acid compound dispersions was 0.001 or more and 50 or less.

[0212] The tantalic acid compound dispersions according to Examples 1 to 11 exhibited improved stability over time in the solution state when the molar ratio Ta / A of tantalum (Ta) to the total amount (A) of organic acids in the tantalic acid compound dispersions was 0.001 or more and 10 or less. Furthermore, the tantalic acid compound dispersions according to Examples 1 to 11 exhibited improved stability over time in the solution state when the molar ratio (x+Ta) / A of the sum of the total amount (x) of one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements and the tantalum (Ta) to the total amount (A) of organic acids in the tantalic acid compound dispersions was 0.001 or more and 10 or less. Furthermore, in the tantalic acid compound dispersions according to Examples 1 to 11, when the element X was lithium and the molar ratio (Li+Ta) / A of the sum of lithium (Li) and tantalum (Ta) in the tantalic acid compound dispersion to the total amount (A) of organic acids was 0.001 or more and 10 or less, the temporal stability of the solution state was improved.

[0213] The tantalic acid compound dispersions according to Examples 1 to 11 exhibited improved stability over time in the solution state when the molar ratio x / (P+A) of the total amount (x) 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 to the sum of the total amount (P) of the phosphorus compounds and the total amount (A) of the organic acids was 0.001 or more and 10 or less. Furthermore, the tantalic acid compound dispersions according to Examples 1 to 11 exhibited improved stability over time in the solution state when the element X was lithium and the molar ratio Li / (P+A) of lithium (Li) in the tantalic acid compound dispersion to the sum of the total amount (P) of the phosphorus compounds and the total amount (A) of the organic acids was 0.001 or more and 10 or less.

[0214] The tantalic acid compound dispersions according to Examples 1 to 11 exhibited improved stability over time in the solution state when the molar ratio Ta / (P+A) of tantalum (Ta) to the sum of the total amount of phosphorus compounds (P) and the total amount of organic acids (A) in the tantalic acid compound dispersions was 0.001 or more and 10 or less. Furthermore, the tantalic acid compound dispersions according to Examples 1 to 11 exhibited improved stability over time in the solution state when the molar ratio (x+Ta) / (P+A) of the sum of the total amount of element X (x) and the tantalum (Ta) to the sum of the total amount of phosphorus compounds (P) and the total amount of organic acids (A) in the tantalic acid compound dispersions was 0.001 or more and 10 or less. Furthermore, in the tantalic acid compound dispersions according to Examples 1 to 11, when the element X was lithium and the molar ratio (Li+Ta) / (P+A) of the sum of lithium (Li) and tantalum (Ta) in the tantalic acid compound dispersion to the sum of the total amount of phosphorus compounds (P) and the total amount of organic acids (A) in the tantalic acid compound dispersion was 0.001 or more and 10 or less, the temporal stability of the solution state was improved.

[0215] 3, the tantalic acid compound dispersions of Examples 1 to 11 showed excellent stability over time, with the particle size (D50) after one month not significantly different from the initial particle size (D50). Note that the tantalic acid compound dispersion of Comparative Example 1 showed precipitates.

[0216] The tantalic acid compound films formed from the tantalic acid compound dispersions according to Examples 1 to 11 were observed with an optical microscope, and as a result, no coarse particles were present in the coating films, and the coating films had excellent film-forming properties.

[0217] 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.

[0218] The tantalic acid compound dispersion according to the present invention has excellent storage stability. Furthermore, because the tantalic acid compound dispersion according to the present invention has excellent storage stability and can suppress the rate of defective products caused by sedimentation due to changes over time, it is possible to reduce waste and the energy costs involved in waste disposal. These points lead to the sustainable management and efficient benefits of natural resources, as well as the achievement of decarbonization (carbon neutrality).

Claims

1. A tantalum-containing tantalic acid compound dispersion liquid, comprising: one or more elements X selected from the group consisting of alkali metal elements and / or alkaline earth metal elements; and an organic acid; wherein the D50 (volume integrated basis) measured by dynamic light scattering is 100 nm or less.

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

3. The tantalic acid compound dispersion liquid according to claim 1 or 2, wherein the element X contains lithium.

4. The tantalic acid compound dispersion liquid according to claim 1 or 2, characterized in that the organic acid contains one or more selected from the group consisting of carboxylic acids, saturated fatty acids, hydroxy acids, lactic acid, citric acid, acetic acid, and salts thereof.

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

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

7. The tantalic acid compound dispersion according to claim 1 or 2, further comprising a phosphorus compound and / or a chlorine compound.

8. The tantalic acid compound dispersion according to claim 7, wherein the phosphorus compound contains at least one compound selected from the group consisting of inorganic phosphorus compounds, organic phosphorus compounds, and salts thereof.

9. The tantalic acid compound dispersion liquid according to claim 8, characterized in that the phosphorus compound contains one or more compounds selected from the group consisting of phosphoric acid, pyrophosphoric acid, polyphosphoric acid, phosphorous acid, hypophosphorous acid, ammonium phosphate, monoammonium phosphate, diammonium phosphate, ammonium pyrophosphate, and ammonium polyphosphate.

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

11. The tantalic acid compound dispersion according to claim 1 or 2, characterized in that the organic acid content in the tantalic acid compound dispersion is 0.01% by mass or more and 30% by mass or less.

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

13. 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.

14. The tantalic acid compound dispersion according to claim 7, wherein 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.

15. The tantalic acid compound dispersion liquid according to claim 1 or 2, wherein the molar ratio x / Ta of the total amount (x) of the element X to the tantalum (Ta) in the tantalic acid compound dispersion liquid is 0.001 or more and 50 or less.

16. The tantalic acid compound dispersion liquid according to claim 1 or 2, wherein the element X in the tantalic acid compound dispersion liquid is lithium, and the molar ratio Li / Ta of the lithium (Li) to the tantalum (Ta) is 0.001 or more and 50 or less.

17. The tantalic acid compound dispersion liquid according to claim 1 or 2, wherein the molar ratio Ta / A of the tantalum (Ta) to the total amount (A) of the organic acid in the tantalic acid compound dispersion liquid is 0.001 or more and 10 or less.

18. The tantalic acid compound dispersion liquid according to claim 1 or 2, wherein the molar ratio (x+Ta) / A of the sum of the total amount (x) of the element X and the sum of the tantalum (Ta) in the tantalic acid compound dispersion liquid to the total amount (A) of the organic acid is 0.001 or more and 10 or less.

19. The tantalic acid compound dispersion liquid according to claim 1 or 2, wherein the element X in the tantalic acid compound dispersion liquid is lithium, and the molar ratio (Li + Ta) / A of the sum of the lithium (Li) and the tantalum (Ta) to the total amount (A) of the organic acid is 0.001 or more and 10 or less.

20. The tantalic acid compound dispersion liquid according to claim 7, wherein the molar ratio x / (P+A) of the total amount (x) of the element X to the sum of the total amount (P) of the phosphorus compounds and the total amount (A) of the organic acids in the tantalic acid compound dispersion liquid is 0.001 or more and 10 or less.

21. The tantalic acid compound dispersion liquid according to claim 7, wherein the element X in the tantalic acid compound dispersion liquid is lithium, and the molar ratio Li / (P+A) of the lithium (Li) to the sum of the total amount of the phosphorus compound (P) and the total amount of the organic acid (A) is 0.001 or more and 10 or less.

22. The tantalic acid compound dispersion liquid according to claim 7, wherein the molar ratio Ta / (P+A) of the tantalum (Ta) to the sum of the total amount of the phosphorus compound (P) and the total amount of the organic acid (A) in the tantalic acid compound dispersion liquid is 0.001 or more and 10 or less.

23. The tantalic acid compound dispersion liquid according to claim 1 or 2, wherein the molar ratio (x+Ta) / (P+A) of the sum of the total amount of the element X (x) and the tantalum (Ta) to the sum of the total amount of the phosphorus compounds (P) and the total amount of the organic acids (A) in the tantalic acid compound dispersion liquid is 0.001 or more and 10 or less.

24. The tantalic acid compound dispersion liquid according to claim 1 or 2, wherein the element X in the tantalic acid compound dispersion liquid is lithium, and the molar ratio (Li + Ta) / (P + A) of the sum of the lithium (Li) and the tantalum (Ta) to the sum of the total amount of the phosphorus compounds (P) and the total amount of the organic acids (A) is 0.001 or more and 10 or less.

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

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

27. The tantalic acid compound dispersion according to claim 1 or 2, characterized in that it is used for coating a positive electrode or positive electrode material for a lithium ion secondary battery.

28. A positive electrode active material for a lithium ion secondary battery, characterized in that the surface is coated with a tantalic acid compound derived from the tantalic acid compound dispersion liquid described in claim 1 or 2.

29. A lithium ion secondary battery characterized by 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 28.

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