JP2024042658A - Method for producing oxo-acid metal salt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an oxo-acid metal salt having high degree of freedom in material design and excellent mass productivity.

SOLUTION: A method for producing an oxo-acid metal salt includes a step of making an oxo-acid salt react with an alkali-free metal salt in a solvent containing water and/or alcohol to obtain a precipitate, and recovering the obtained precipitate by solid-liquid separation, and a step of heat-treating the recovered precipitate at a temperature of 50°C or higher and 1600°C or lower to obtain a heat-treated product. The oxo-acid salt is either one or both of an oxo-acid alkali metal salt and an oxo-acid ammonium salt. The metal element contained in the alkali-free metal salt is at least one kind selected from the group consisting of a typical element, a transition element, and a rare earth element. The final pKa of the conjugate acid of the anion of the alkali-free metal salt is 7.0 or less. The reaction is carried out at a temperature of 0°C or higher and less than 100°C under a pressure of 0.8 atm or more and 1.2 atm or less.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a method for producing an oxoacid metal salt.

The oxoacid metal salt is a metal salt containing as a constituent ion an ion generated from an oxoacid, and typically includes a phosphate metal salt. Oxoacid metal salts are used in a wide variety of fields including batteries, piezoelectric devices, and fluorescent devices. Furthermore, it has been proposed in the past to synthesize oxoacid metal salts by methods such as hydrothermal synthesis, high-temperature solid-phase synthesis, or sol-gel method.

For example, Non-Patent Document 1 summarizes the manufacturing methods of _LiMnPO4- based positive electrode materials for lithium ion batteries, and introduces the sol-gel method, solid phase method, hydrothermal synthesis method, spray pyrolysis method, and polyol synthesis method. (Non-patent Document 1, pages 21-38). Non-Patent Document 2 discloses ion exchange of Na in NASICON type superionic conductor Na ₃ Zr ₂ Si ₂ PO ₁₂ with respect to the synthesis of high performance solid electrolyte Li ₃ Zr ₂ Si ₂ PO ₁₂ ( (Summary of Non-Patent Document 2).

Non-Patent Document 3 discloses that gallium orthophosphate (GaPO ₄ ) single crystal is hydrothermally synthesized and that GaPO ₄ single crystal is a promising material exhibiting piezoelectric properties (Summary of Non-Patent Document 3 , p. 275, left column). Non-Patent Document 4 describes that LaPO ₄ doped with Ce ³⁺ or Tb ³⁺ is synthesized by a method combining a sol-gel method and an electrospinning method, and that LaPO ₄ :Ce ³⁺ , Tb ³⁺ fluorescent material exhibits high light intensity. is disclosed (Summary of Non-Patent Document 4).

Furthermore, Patent Document 1 discloses a solution synthesis method in which a large amount of water-soluble Li salt and phosphoric acid are added to a water-soluble metal salt as a method for producing LiMPO ₄ (M=Mn, Fe, Co, Ni). There is.

Patent No. 5245084

T.A. Wani, et al., Journal of Energy Storage, 44 (2021) 103307 L. Zhu, et al., Science Advances, 8, eabj7698 (2022) 18 March 2022 S. Hirano et al., Bulletin of the Chemical Society of Japan, 62, 275-278 (1989) Z. Hou, et al., Journal of Solid State Chemistry, 182 (2009), 698-708

As described above, although the development of oxoacid metal salts is progressing in various fields, all materials are manufactured using expensive and complicated methods such as hydrothermal synthesis and high-temperature synthesis. Therefore, synthesis and homogeneous reaction may be difficult, resulting in poor material design.

For example, the sol-gel method disclosed in Non-Patent Document 1 requires the use of expensive raw materials such as alkoxide raw materials, and is inferior in mass productivity. In the alkali metal ion exchange method from Na to Li proposed in Non-Patent Document 2, it is necessary to prepare an Na-type solid electrolyte in advance and use an excess of Li salt. Furthermore, there are problems in that the process time is long and mass productivity is poor. In the solid-phase method, the raw material must be fired at a high temperature, so the resulting material tends to become coarse grained. In addition, there is a problem that the reaction tends to be non-uniform, and by-products are likely to be produced in the reaction of replacing multiple metal elements. The hydrothermal method requires the use of expensive and complicated equipment such as an autoclave, and is inferior in mass productivity. Furthermore, the manufacturing method disclosed in Patent Document 1 uses excessive raw materials, which poses a problem in terms of cost. As described above, with conventional methods, it has been difficult to achieve both material designability and mass production.

The present inventors conducted extensive studies in view of such conventional problems. As a result, by utilizing the acid-base reaction caused by the difference between the acid dissociation constant of the conjugate acid and the acid dissociation constant of the oxoacid of the anion of the alkali-free metal salt, a method with a high degree of freedom in material design and excellent mass production. We found that oxoacid metal salts can be obtained by

The present invention was completed based on such knowledge, and an object of the present invention is to provide a method for producing an oxoacid metal salt, which has a high degree of freedom in material design and is excellent in mass productivity.

The present invention encompasses the following aspects (1) to (6). In this specification, the expression "to" includes both ends of the expression. In other words, "X to Y" is synonymous with "X or more and Y or less."

(1) A method for producing an oxoacid metal salt, comprising:
A step of reacting an oxoacid salt and an alkali-free metal salt in a solvent containing water and/or alcohol to obtain a precipitate, and recovering the obtained precipitate by solid-liquid separation, and the recovered precipitate. A step of heat-treating at a temperature of 50°C or more and 1600°C or less to obtain a heat-treated product,
The oxo acid salt is either or both of an oxo acid alkali metal salt and an oxo acid ammonium salt,
The metal element contained in the alkali-free metal salt is at least one selected from the group consisting of typical elements, transition elements, and rare earth elements,
The alkali-free metal salt has a final pKa of the conjugate acid of its anion of 7.0 or less,
A method in which the reaction is carried out at a temperature of 0°C or more and less than 100°C under a pressure of 0.8 atm or more and 1.2 atm or less.

(2) The oxoacid salt has a hydrogen number x of 0 or more and 2 or less, and the alkali-free metal salt is at least one selected from the group consisting of nitrates, halides, sulfates, and carboxylates. The method of (1) above.

(3) The method of (2) above, wherein the heat treatment is performed in an argon (Ar) and/or hydrogen (H ₂ ) gas atmosphere, thereby reducing the precipitate.

(4) The method of (2) above, wherein the oxoacid salt has a hydrogen number x greater than 0, and the heat treatment is performed to dehydrate the precipitate.

(5) The method of (2) above, wherein the oxoacid salt has a hydrogen number x greater than 0, and the heat treatment is performed in an oxidizing gas atmosphere, thereby oxidizing the precipitate.

(6) The oxoacid metal salt may be a dielectric material, a luminescent material, a solid electrolyte material, an optical material, a magnetic material, an electrically conductive material, a semiconductor material, an electrically insulating material, a thermoelectric conversion material, a structural material, a heat-resistant material, The method according to any one of (1) to (5) above, wherein the material is at least one selected from the group consisting of biomaterials and catalysts.

According to the present invention, a method for producing an oxoacid metal salt is provided, which has a high degree of freedom in material design and is excellent in mass productivity.

1 shows XRD profiles of oxoacid metal salts (Examples 1 and 2). The XRD profiles of oxoacid metal salts are shown (Examples 3 and 4). The XRD profiles of oxoacid metal salts are shown (Examples 5 and 6). The XRD profiles of oxoacid metal salts are shown (Examples 7 and 8). The XRD profiles of oxoacid metal salts are shown (Examples 9 and 10). The XRD profiles of oxoacid metal salts are shown (Examples 11 and 12). The XRD profiles of oxoacid metal salts are shown (Examples 13 and 14). The XRD profiles of oxoacid metal salts are shown (Examples 15 to 17). 1 shows XRD profiles of oxoacid metal salts (Examples 18 and 19). The XRD profile of oxoacid metal salt is shown (Example 20). The XRD profiles of oxoacid metal salts are shown (Examples 21 and 22). The XRD profile of oxoacid metal salt is shown (Example 23). The PL spectrum of oxoacid metal salt is shown (Example 4). 1 shows PL spectra of oxoacid metal salts (Examples 5 and 6).

A specific embodiment of the present invention (hereinafter referred to as "this embodiment") will be described. Note that the present invention is not limited to the following embodiments, and various changes can be made without departing from the gist of the present invention.

<<1. Manufacturing method of oxoacid metal salt >>
This embodiment is directed to a method for producing an oxoacid metal salt. Oxoacid metal salts are salts composed of ions (anions) and metal ions (cations) generated from oxoacids. Further, an oxoacid is a compound in which oxygen is bonded to a central atom and a hydrogen atom is bonded to all or part of the oxygen atom, and this hydrogen atom is dissociated as a proton (H ⁺ ) to form an oxoanion. Oxoacids that form an anion consisting of a metal element and oxygen, such as titanic acid, zirconic acid, aluminic acid, germanic acid, and nickelic acid, are also classified as oxoacids.

Oxoacid metal salts are used in a wide variety of fields including batteries, piezoelectric devices, and fluorescent devices. For example, Li _1+x Al _x Zr _2-x (PO ₄ ) ₃ (0≦x≦1), Li _1+x Al _x Ti _2-x (PO ₄ ) ₃ (0≦x≦1), Li _1+x Al _x Ge _{2 -x} (PO ₄ ) ₃ (0≦x≦1) and 2[Li _1+x Ti ₂ Si _x P _3-x O ₁₂ ]・AlPO ₄ (0≦x≦1) have high ionic conductivity and are solid Used as an electrolyte material. Further, Ga _1-x M _x PO ₄ (M is Al, Fe, and/or Mn, 0≦x≦0.5) is known as a piezoelectric material. Furthermore, LaPO ₄ , LaPO ₄ :Ce, Tb, LiSrPO ₄ :Eu, Li(Sr,Mg)PO ₄ :Eu, NaMgPO ₄ :Eu, (Nd _1-x Gd _x ) _1/3 Zr ₂ (PO ₄ ) ₃ (0≦x≦1), (Sr, Ba, Ca) ₁₀ (PO ₄ ) ₆ Cl ₁₂ :Eu is known as a fluorescent material.

The use of the oxoacid metal salt targeted by this embodiment is not particularly limited. Examples of oxoacid metal salts include dielectric materials, luminescent materials, solid electrolyte materials, optical materials, magnetic materials, electrically conductive materials, semiconductor materials, electrically insulating materials, thermoelectric conversion materials, structural materials, heat-resistant materials, and biomaterials. At least one selected from the group consisting of , and a catalyst is exemplified. Further, the oxoacid metal salt may be a material other than the positive electrode active material.

The production method of this embodiment involves reacting an oxoacid salt and an alkali-free metal salt in a solvent containing water and/or alcohol to obtain a precipitate, and recovering the obtained precipitate by solid-liquid separation. (reaction recovery step), and a step (heat treatment step) of heat-treating the collected precipitate at a temperature of 50° C. or higher and 1600° C. or lower to obtain a heat-treated product. Each step will be explained in detail below.

<Reaction recovery process>
In the reaction recovery step, the oxoacid salt and the alkali-free metal salt are reacted in a solvent. Here, the oxoacid salt is either one or both of an oxoacid alkali metal salt and an oxoacid ammonium salt. That is, it is an oxoacid salt of an alkali metal and/or ammonium (hereinafter collectively referred to as "A"). The alkali-free metal salt is a salt containing a metal other than an alkali metal, or a compound or complex thereof (hereinafter referred to as "B component"). This reaction is an acid-base reaction due to the difference between the acid dissociation constant of the conjugate acid of the anion of the alkali-free metal salt and the acid dissociation constant of the oxoacid. During the reaction, an exchange occurs between the alkali metal ion or ammonium ion (A ⁺ ) contained in the oxoacid salt and the ion (B ⁿ⁺ ) of the B component contained in the alkali-free metal salt. As a result, a precipitate containing the oxoacid metal salt of the B component or its hydrate is formed.

For example, when the oxoacid salt is a phosphate of alkali metal A (A _3-x H _x PO ₄ ), phosphate (A _3-x H _x PO ₄ ) and a salt of n-valent metal B (B ⁿ⁺ - salt) in a solvent at a molar ratio of 1:y, the metal phosphate salt (A _3-x-ny B _y H _x PO ₄ ) is mixed as shown in the following formula (1). At the same time, a salt of alkali metal A (A ⁺ -salt) is produced as a by-product.

On the right side of the above formula (1), the metal phosphate (A _3-x-ny B _y H _x PO ₄ ) is poorly soluble and therefore forms a precipitate in the solvent. On the other hand, the by-product (A ⁺ -salt) is easily soluble and is therefore dissolved in the solvent. Therefore, by recovering the precipitate from the solvent by solid-liquid separation in the subsequent recovery step, the precipitate metal phosphate (A _3-x-ny B _y H _x PO ₄ ) or its hydrate can be obtained. Can be done. In addition, in the product actually obtained, the amounts of the component elements may deviate from the chemical formula. For example, the amount of oxygen (O) may be deficient from the value in the chemical formula. This embodiment also includes cases where the component element amounts deviate from the values in the chemical formula.

The oxo acid salt is a raw material for the oxo acid that constitutes the desired oxo acid metal salt. The oxo acid contained in the oxo acid salt may be selected depending on the type of oxo acid metal salt to be produced. The oxoacid may be an inorganic acid or an organic acid. It may also be a metal oxoacid such as titanic acid, zirconic acid, aluminic acid, germanic acid, and/or nickelic acid. Examples of oxoacids include phosphoric acid, silicic acid, boric acid, sulfuric acid, carbonic acid, carboxylic acid, nitric acid, and metal acids, among which phosphoric acid, silicic acid, boric acid, sulfuric acid, aluminic acid, and titanic acid At least one selected from the group consisting of , zirconic acid, germanic acid, vanadic acid, molybdic acid, tungstic acid, and complex acids thereof is preferred. Further, the oxo acid salt is either or both of an oxo acid alkali metal salt and an oxo acid ammonium salt. When the oxo acid salt is an oxo acid alkali metal salt, the alkali metal is preferably at least one selected from the group consisting of lithium (Li), sodium (Na), and potassium (K); and sodium (Na), or both are particularly preferred. In particular, when the purpose is to synthesize an oxoacid metal salt containing an alkali metal, the alkali metal may be selected.

The oxoacid salt may be hydrogen-free. Alternatively, it may be a hydrogen salt containing hydrogen. Preferably, the number of hydrogen atoms in the oxoacid salt is 0 or more and 2 or less. If the number of hydrogen atoms is excessively large, the amounts of alkali metal and ammonia (A) will decrease, making it difficult for the exchange reaction with component B to occur during the reaction. The number of hydrogens may be 0 or more and 1 or less, and may be zero (0).

The amount of the oxoacid salt to be blended is not particularly limited as long as the desired final product (oxoacid metal salt) can be obtained. However, if the amount is too small, it may be difficult to obtain the desired final product. Moreover, if the blending amount is excessively large, there will be a large amount of surplus raw materials, which may lead to an increase in costs. The blending amount of the oxo acid salt is preferably 0.7 times or more and 1.3 times or less, and 0.8 times or more and 1.2 times or less, relative to the amount (equivalent) required to obtain the oxo acid metal salt. is more preferable, and even more preferably 0.9 times or more and 1.1 times or less.

The alkali-free metal salt is a raw material for the metal constituting the desired oxoacid metal salt. The metal element contained in the alkali-free metal salt is at least one selected from the group consisting of typical elements other than alkali metals, transition elements, and rare earth elements. Here, typical elements are elements of Groups 1, 2, and 12 to 18 of the periodic table. A transition element is an element that exists between Group 3 elements and Group 12 elements in the periodic table. Rare earth elements are a general term for elements that make up the group consisting of scandium (Sc) with atomic number 21, yttrium (Y) with atomic number 39, and lanthanum (La) with atomic number 57 to lutetium (Lu) with atomic number 71. be. Examples of metal elements include magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), and niobium (Nb). , tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn) , aluminum (Al), gallium (Ga), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), cadmium (Cd), indium (In), tin (Sn), rhenium (Re) , osmium (Os), iridium (Ir), platinum (Pt), gold (Au), thallium (Tl), lead (Pb), bismuth (Bi), polonium (Po), lanthanum (La), cerium (Ce) , praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er) , thulium (Tm), ytterbium (Yb), and lutetium (Lu). The alkali-free metal salt may also contain components other than metals, such as metalloid elements. Specifically, it may contain boron (B), silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), and/or tellurium (Te).

In this embodiment, the alkali-free metal salt is limited to a final pKa of the conjugate acid of its anion of 7.0 or less. Here, pKa is the negative common logarithm (-log ₁₀ Ka) of the acid dissociation constant (Ka) in an aqueous solution at room temperature (25° C.). Further, the final pKa is the acid dissociation constant at the final stage of ionization (maximum dissociation stage) of the conjugate acid of the anion. That is, when ionization occurs in only one step, it is the acid dissociation constant in that ionization step. In addition, when ionization occurs in multiple stages, it is the acid dissociation constant at the final ionization stage (maximum dissociation stage). For example, when the conjugate acid of the anion has only pK1, this corresponds to the final pKa. On the other hand, when the conjugate acid of the anion has pK1, pK2, and pK3, pK3 corresponds to the final pKa.

By reacting under conditions where the final pKa is 7.0 or less, component A ions (alkali metal ions and/or ammonium ions; A + ) contained in the oxoacid salt and component B ions (alkali metal ions and/or ammonium ions; A ⁺ ) contained in the alkali-free metal salt B ⁿ⁺ ) exchange takes place, thereby making it possible to obtain an oxoacid metal salt with a desired composition. For example, when the oxoacid is phosphoric acid, the second pKa of phosphoric acid is 7.2. Therefore, if the final pKa of the conjugate acid of the anion of the alkali-free metal salt is 7.0 or less, this anion will easily form a salt with the two alkali metals A of A ₃ PO ₄ . Therefore, the exchange reaction between the alkali metal A and B components is likely to occur. On the other hand, if the final pKa is more than 7.0, it becomes difficult to form a salt of the anion and the alkali metal A. The final pKa is not particularly limited as long as it is 7.0 or less.

The alkali-free metal salt may be an inorganic salt or an organic salt as long as the final pKa is 7.0 or less. The specific metal salt is preferably at least one selected from the group consisting of nitrates, halides, sulfates, and carboxylates. Examples of halides include chloride, fluoride, bromide, iodide, and/or astatinide. When an alkali metal or ammonium remains in the oxoacid metal salt, the final pKa is preferably 2 or more and 7 or less, more preferably 2 or more and 5 or less. When no alkali metal or ammonium salt remains in the oxoacid metal salt, the ratio is preferably 5 or less, more preferably 2 or less, and even more preferably 0 or less. If the final pKa is too small, the reaction may occur too quickly and by-products may be generated. Note that the pKa of various compounds are summarized in Table 1 below. Furthermore, even if the pKa is excessively small, the production of by-products can be suppressed by controlling the reaction rate by dropping or the like.

The amount of the alkali-free metal salt blended is not particularly limited as long as the desired final product (oxo acid metal salt) can be obtained. However, if the amount is too small, it may be difficult to obtain the desired final product. Moreover, if the blending amount is excessively large, there will be a large amount of surplus raw materials, which may lead to an increase in costs. The blending amount of the alkali-free metal salt is preferably 0.7 times or more and 1.3 times or less, and 0.8 times or more and 1.2 times the amount (equivalent) required to obtain the oxoacid metal salt. It is more preferably 0.9 times or more and 1.1 times or less.

The reaction is carried out in a solvent containing water and/or alcohol. The solvent may be water, alcohol, or a mixed solvent of water and alcohol. When the solvent is alcohol, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and/or ethylene glycol are preferred.

As long as the desired oxoacid metal salt can be obtained, the reaction method of the oxoacid salt and the alkali-free metal salt is not limited. However, preferably the solvent containing the oxoacid salt and the solvent containing the alkali-free metal salt are prepared separately, and the latter (the solvent containing the alkali-free metal salt) is added dropwise to the former (the solvent containing the oxoacid salt). . Since excessively rapid progress of the reaction is suppressed, a uniform reaction product can be obtained. Further, the solvent may be stirred to promote a uniform reaction, or bubbling may be performed using an inert gas such as argon (Ar) to prevent oxidation of the metal.

The reaction is carried out at a temperature in the range of 0° C. or more and less than 100° C. under a pressure of 0.8 atm or more and 1.2 atm or less. According to the production method of this embodiment, it is possible to carry out the reaction at room temperature and near normal pressure without using expensive and complicated equipment such as an autoclave that is required in hydrothermal synthesis. Therefore, the desired oxoacid metal salt can be obtained with good mass productivity. The pressure is preferably 0.9 atm or more and 1.1 atm or less, more preferably 0.95 atm or more and 1.05 atm or less. Furthermore, if the reaction temperature is too low, the required reaction time becomes longer, and there is a possibility that the cycle time becomes longer. On the other hand, if the reaction temperature is too high, the reaction may proceed rapidly, making it difficult to control the production of the oxoacid metal salt having the desired composition. The reaction temperature is preferably 5°C or higher and 80°C or lower, more preferably 10°C or higher and 60°C or lower.

Next, the precipitate obtained by the reaction of the oxoacid salt with the non-alkali-containing metal salt is recovered from the solvent by solid-liquid separation. This allows the precipitate consisting of the oxoacid metal salt or its hydrate to be separated and recovered from the solvent and by-products. The precipitate can be recovered by solid-liquid separation techniques such as filtration and centrifugation. In order to more reliably remove the by-products, the recovered precipitate may be washed. Examples of washing techniques include pouring water and/or alcohol onto the recovered precipitate, or dispersing the recovered precipitate in water and/or alcohol and then recovering it again.

<Heat treatment process>
In the heat treatment step, the obtained precipitate is heat-treated to obtain a heat-treated product (oxoacid metal salt). Heat treatment improves the crystallinity of the precipitate. Further, when the precipitate is hydrated, dehydration of the precipitate can be promoted.

The heat treatment temperature is limited to 50°C or higher and 1600°C or lower. If the temperature is too low, crystallization and dehydration may become insufficient. On the other hand, if the temperature is excessively high, grain growth of the finally obtained heat-treated product (oxoacid metal salt) may progress and the properties may deteriorate. The heat treatment temperature is preferably 100°C or more and 1000°C or less, more preferably 200°C or more and 800°C or less, and even more preferably 300°C or more and 700°C or less. The heat treatment time is preferably 1 hour or more and 100 hours or less, more preferably 2 hours or more and 50 hours or less, and even more preferably 3 hours or more and 20 hours or less.

Reduction of the precipitate is possible by heat treatment in a controlled atmosphere. Specifically, the heat treatment can be performed in an argon (Ar) and/or hydrogen (H ₂ ) gas atmosphere, thereby reducing the precipitate. By reducing the precipitate, some of the oxygen is removed from it. For example, when a precipitate is composed of a phosphate compound (A _3-ny B _y PO ₄ ) of alkali metals A and B, if this precipitate is heat-treated at 900°C in an argon (Ar) gas atmosphere, the following (2) ), the B component is reduced and oxygen (O ₂ ) is eliminated.

Further, when the precipitate is a hydrogen salt, the precipitate can be dehydrated. Specifically, when the hydrogen number x of the oxoacid salt is more than 0, heat treatment can be performed to dehydrate the precipitate. For example, when the precipitate is a hydrogen phosphate compound of alkali metal A and component B (A _3-x-ny B _y H _x PO ₄ ), if this precipitate is heat-treated at 900°C, the following formula (3) is obtained. As shown in , hydrogen contained in the compound reacts with a portion of oxygen to become water (H ₂ O) and is eliminated, thereby forming a metal phosphate salt (A _3-x-ny B _y PO _{4- x/2} ) can be obtained.

More specifically, when the alkali metal A is lithium (Li) and the B component is zirconyl (ZrO), the precipitate lithium zirconyl hydrogen phosphate (Li(ZrO) ₂ H ₄ (PO ₄ ) ₃ ), as shown in equation (4) below, the hydrogen contained in hydrogen phosphate reacts with the oxygen in zirconyl to become water (H ₂ O) and desorb, and as a result, lithium phosphate Zirconium (LiZr ₂ (PO ₄ ) ₃ ) is produced. This lithium zirconium phosphate is a NASICON type metal phosphate and is useful as a solid electrolyte.

Furthermore, the precipitate can be oxidized by performing heat treatment under a predetermined atmosphere. Specifically, when the hydrogen number x of the oxoacid alkali metal salt is more than 0, the heat treatment can be performed in an oxidizing gas atmosphere, thereby oxidizing the precipitate. Oxygen (O ₂ ), high oxygen (O ₂ ) partial pressure gas, and/or air may be used as the oxidizing gas. For example, when the precipitate is a hydrogen phosphate compound (A _3-x-ny B _y H _x PO ₄ ) of alkali metals A and B, the precipitate is heat-treated at 900°C in an oxygen (O ₂ ) atmosphere. Then, as shown in the following equation (5), hydrogen and oxygen react to become water (H ₂ O) and are eliminated. As a result, a metal phosphate salt in which part or all of component B is oxidized is obtained.

<Post-processing process>
If necessary, the heat-treated product may be subjected to post-treatments such as crushing and classification. The crushing may be performed using a known crusher such as an attritor or a ball mill. Further, the classification may be performed using a known classifier such as a sieve classifier or an air classifier.

In this way, an oxoacid metal salt can be obtained. According to the manufacturing method of the present embodiment, the oxo-acid metal salt is synthesized by a solution method under conditions near normal temperature and normal pressure, so the oxo-acid metal salt can be obtained by a method with excellent mass productivity. Furthermore, by using a plurality of metal salts, element substitution can be easily performed. Furthermore, since reduction, dehydration, and oxidation during heat treatment can be performed by compositional design and atmosphere control, it has the advantage of excellent material designability.

The present invention will be explained in more detail using the following examples. However, the present invention is not limited to the following examples.

(1) Preparation of oxoacid metal salt [Example 1]
While stirring the Na ₃ PO ₄ aqueous solution, a Ga(NO ₃ ) ₃ aqueous solution in an amount of 1 equivalent to Na ₃ PO ₄ was added dropwise, and the mixture was stirred overnight at room temperature. This produced a precipitate consisting of GaPO ₄ or its hydrate. The obtained precipitate was collected by filtration, washed with water and dried, and the dried powder was heat-treated at 900° C. for 6 hours in an argon (Ar) atmosphere to obtain GaPO ₄ as a heat-treated product.

[Example 2]
Instead of the Ga(NO ₃ ) ₃ aqueous solution, a mixed aqueous solution of 0.5 equivalent of Ga(NO ₃ ) ₃ and 0.5 equivalent of Al(NO ₃ ) ₃ with respect to Na ₃ PO ₄ was used. Other than that, the same operation as in Example 1 was performed to obtain Al _0.5 Ga _0.5 PO ₄ .

[Example 3]
Instead of the Ga(NO ₃ ) ₃ aqueous solution, an La(NO ₃ ) ₃ aqueous solution having an amount of 1 equivalent to Na ₃ PO ₄ was used. Other than that, LaPO ₄ was obtained by performing the same operation as in Example 1.

[Example 4]
Instead of the Ga(NO ₃ ) _{3 aqueous} solution, 0.65 equivalents of La( _{NO 3} ) ₃ , 0.20 equivalents of Ce(NO ₃ ) ₃ , 0.15 equivalents of Tb(NO ₃ ) A mixed aqueous solution of ₃ was used. Other than that, the same operation as in Example 1 was performed to obtain La _0.65 Ce _0.2 Tb _0.15 PO ₄ (green fluorescence).

[Example 5]
While stirring the LiOH aqueous solution, a 1/3 equivalent amount of H ₃ PO ₄ aqueous solution with respect to LiOH was added dropwise, and the mixture was stirred at room temperature for 1 hour. This produced a precipitate of Li ₃ PO ₄ . Furthermore, a mixed aqueous solution of 0.98 equivalents of Sr(OAc) ₂ , 0.01 equivalents of Eu(OAc) ₃ , and 0.01 equivalents of Mg(OAc) ₂ was added to the first stage product Li ₃ PO ₄ . The mixture was added dropwise with stirring, and the mixture was further stirred at room temperature overnight. The obtained precipitate was collected by filtration, washed with water and dried, and the dried powder was heat-treated at 900°C for 6 hours in an argon (Ar) atmosphere to obtain LiSr _0.98 Eu _0.01 Mg _0.01 PO ₄ (Eu ²⁺ ) was obtained (blue fluorescence). Note that "Ac" is an abbreviation for acetyl group.

[Example 6]
Heat treatment was carried out under the conditions of 900° C. for 6 hours in an air atmosphere, and otherwise the same operation as in Example 5 was carried out to obtain LiSr _0.98 Eu _0.01 Mg _0.01 PO ₄ (Eu ³⁺ ) (red fluorescence).

[Example 7]
While stirring the H ₃ PO ₄ aqueous solution, a LiOH aqueous solution in an amount of 1.67 equivalents relative to H ₃ PO ₄ was added dropwise, and the mixture was stirred at room temperature for 1 hour. This produced a precipitate of Li _1.67 H _1.33 PO ₄ . Furthermore, an aqueous solution of ZrO(NO ₃ ) ₂ in an amount of 0.67 equivalent to the first-stage product Li _1.67 H _1.33 PO ₄ was added dropwise, and the mixture was further stirred at room temperature overnight. This produced a precipitate. The obtained precipitate was estimated to be a phosphate compound having a composition of Li(ZrO) ₂ H ₄ (PO ₄ ) ₃ or a hydrate thereof. After collecting the precipitate by filtration, it was washed with water and dried, and the dried powder was heat-treated at 900° C. for 6 hours in an argon (Ar) atmosphere to obtain LiZr ₂ (PO ₄ ) ₃ .

[Example 8]
While stirring the H ₃ PO ₄ aqueous solution, a LiOH aqueous solution in an amount of 2 equivalents to H ₃ PO ₄ was added dropwise, and the mixture was stirred at room temperature for 1 hour. This produced a precipitate of Li ₂ HPO ₄ . 0.5 equivalents of ZrO(NO ₃ ) ₂ aqueous solution was added dropwise to the first-stage product Li ₂ HPO ₄ , and after stirring at room temperature for 4 hours, 0.17 equivalents of Al(NO ₃ ) ₃ aqueous solution was added dropwise. and stirred at room temperature overnight. The obtained precipitate was collected by filtration, washed with water and dried, and the dried powder was heat-treated at 900°C for 6 hours in an argon (Ar) atmosphere to obtain Li _1.5 Al _0.5 Zr _1.5 ( _PO4 ) ₃ was obtained.

[Example 9]
While stirring the LiOCH ₃ methanol solution, 0.5 equivalent of Ti(OEt) ₄ relative to LiOCH ₃ was added, and after stirring at room temperature for 1 hour, a large excess of water was added and the mixture was stirred at 50° C. for 4 hours. After returning the temperature to room temperature, an aqueous solution of La(NO ₃ ) ₃ in an amount of 0.55 equivalent to Ti(OEt) ₄ was added dropwise, and the mixture was stirred at room temperature overnight. The obtained precipitate was collected by centrifugation, washed with water and dried, and the dried powder was heat-treated at 1100° C. for 12 hours in an air atmosphere to obtain La _0.55 Li _0.35 TiO ₃ . Note that "Et" is an abbreviation for ethyl group.

[Example 10]
A LiOH aqueous solution in an amount of 4 equivalents to K ₂ TiO(C ₂ O ₄ ) ₂ was added dropwise to the K ₂ TiO(C ₂ O ₄ ) ₂ aqueous solution with stirring, and the mixture was stirred at room temperature for 3 hours. Furthermore, an aqueous solution of La(NO ₃ ) ₃ in an amount of 0.55 equivalent to K ₂ TiO(C ₂ O ₄ ) ₂ was added dropwise, and the mixture was stirred overnight at room temperature. The obtained precipitate was collected by centrifugation, washed with water and dried, and the dried powder was heat-treated at 1100° C. for 12 hours in an air atmosphere to obtain La _0.55 Li _0.35 TiO ₃ .

[Example 11]
A methanol solution of Si( _OCH3 ) ₄ was stirred with 2 equivalents of _LiOCH3 methanol solution relative to Si( _OCH3 ) ₄ , and stirred at room temperature for 1 hour, and then a large excess of water was added and stirred at 50°C for 4 _hours . After returning to room temperature, a mixed aqueous solution of 0.98 equivalents of ZrO( _NO3 ) ₂ and 0.02 equivalents of Eu( _NO3 ) ₃ relative to Si(OCH3) ₄ was dropped and stirred at room temperature overnight. The resulting precipitate was collected by centrifugation, washed with water and dried, and the dried powder was subjected to heat treatment at 1100°C for 9 hours in an air atmosphere to obtain _{Zr0.98Eu0.02SiO4} . ( _{Red fluorescence} )

[Example 12]
An aqueous LiOH solution in an amount of 2 equivalents to H ₂ SiO ₃ was added to a suspension of H ₂ SiO ₃ with stirring, and the mixture was stirred at 50° C. for 3 hours. After the temperature was returned to room temperature, a mixed aqueous solution of 0.98 equivalents of SrCl ₂ and 0.02 equivalents of Eu(NO ₃ ) ₃ relative to H ₂ SiO ₃ was added dropwise, and the mixture was stirred at room temperature overnight. The obtained precipitate was collected by centrifugation, washed with water and dried, and the dried powder was heat-treated at 900° C. for 9 hours in an air atmosphere to obtain Sr _0.98 Eu _0.02 SiO ₃ . (red fluorescence)

[Example 13]
An aqueous LiOH solution in an amount of 2 equivalents to H ₂ SiO ₃ was added to a suspension of H ₂ SiO ₃ with stirring, and the mixture was stirred at 50° C. for 3 hours. After the temperature was returned to room temperature, an aqueous solution of Al(NO ₃ ) ₃ in an amount of 0.5 equivalent to H ₂ SiO ₃ was added dropwise, and the mixture was stirred at room temperature overnight. The obtained precipitate was collected by centrifugation, washed with water and dried, and the dried powder was heat-treated at 900° C. for 9 hours in an air atmosphere to obtain LiAlSi ₂ O ₆ .

[Example 14]
An aqueous LiOH solution in an amount of 4 equivalents to H ₂ SiO ₃ was added to a suspension of H ₂ SiO ₃ with stirring, and the mixture was stirred at 50° C. for 3 hours. After the temperature was returned to room temperature, an aqueous solution of Al(NO ₃ ) ₃ in an amount of 1 equivalent to H ₂ SiO ₃ was added dropwise, and the mixture was stirred at room temperature overnight. The obtained precipitate was collected by centrifugation, washed with methanol and dried, and the dried powder was heat-treated at 900° C. for 9 hours in an air atmosphere to obtain LiAlSiO ₄ .

[Example 15]
An aqueous LiOH solution in an amount of 2 equivalents to GeO ₂ was added to the GeO ₂ suspension water with stirring, and the mixture was stirred at room temperature for 4 hours. Furthermore, 1 equivalent of SrCl ₂ aqueous solution with respect to GeO ₂ was added dropwise, and the mixture was stirred at room temperature overnight. The obtained precipitate was collected by centrifugation, washed with water and dried, and the dried powder was heat-treated at 900° C. for 9 hours in an air atmosphere to obtain SrGeO ₃ .

[Example 16]
SrGeO ₃ was obtained in the same manner as in Example 15 using a NaOH aqueous solution instead of the LiOH aqueous solution.

[Example 17]
An aqueous LiOH solution of 4 equivalents to GeO ₂ was added to the GeO ₂ suspension water with stirring, and the mixture was stirred at room temperature for 4 hours. Furthermore, an aqueous solution of Al(NO ₃ ) ₃ in an amount of 1 equivalent to GeO ₂ was added dropwise, and the mixture was stirred at room temperature overnight. The obtained precipitate was collected by centrifugation, washed with methanol and dried, and the dried powder was heat-treated at 900° C. for 9 hours in an air atmosphere to obtain LiAlGeO ₄ .

[Example 18]
An aqueous LiOH solution in an amount of 2 equivalents to WO ₃ was added to the WO ₃ suspension with stirring, and the mixture was stirred at room temperature for 1 hour. Furthermore, an aqueous solution of Al(NO ₃ ) ₃ in an amount of 0.67 equivalent to WO ₃ was added dropwise, and the mixture was stirred overnight at room temperature. The obtained precipitate was collected by centrifugation, washed with methanol and dried, and the dried powder was heat-treated at 900° C. for 9 hours in an air atmosphere to obtain Al ₂ (WO ₄ ) ₃ .

[Example 19]
An aqueous LiOH solution in an amount of 2 equivalents to V ₂ O ₅ was added to the V ₂ O ₅ suspension water with stirring, and the mixture was stirred at room temperature for 1 hour. Further, an aqueous solution of ZrO(NO ₃ ) ₂ in an amount of 0.5 equivalent to V ₂ O ₅ was added dropwise, and the mixture was stirred overnight at room temperature. The obtained precipitate was collected by centrifugation, washed with water and dried, and the dried powder was heat-treated at 600° C. for 9 hours in an air atmosphere to obtain ZrV ₂ O ₇ .

[Example 20]
A 4-equivalent LiOH solution relative to _GeO2 was added to the GeO2 suspension while stirring, and the mixture was stirred at room temperature for 1 hour. A 2-equivalent Zn(OAc) ₂ solution relative to _GeO2 was then added dropwise _, and the mixture was stirred at room temperature overnight. The resulting precipitate was collected by centrifugation, washed with water, and dried. The dried powder was then heat-treated at 1100°C for 9 hours in an air atmosphere to obtain _{Zn2GeO4 .}

[Example 21]
While stirring the (NH ₄ ) ₃ PO ₄ aqueous solution, a Zr(SO ₄ ) ₂ aqueous solution in an amount of 2/3 equivalent to (NH ₄ ) ₃ PO ₄ was added dropwise, and the mixture was stirred at room temperature for 3 hours. The precipitate was collected by centrifugation and further washed three times with ion-exchanged water. By dispersing this in water, adding dropwise an aqueous LiOH solution of 1/3 equivalent to (NH ₄ ) ₃ PO ₄ and stirring overnight at room temperature, LiZr ₂ (PO ₄ ) ₃ or its hydrate was dissolved. A precipitate was formed. The obtained precipitate was collected by centrifugation, further washed with ion-exchanged water three times and dried, and the dried powder was heat-treated in air at 900° C. for 6 hours to obtain LiZr ₂ (PO ₄ ) ₃ . Ta.

[Example 22]
LiZr ₂ (PO ₄ ) ₃ was obtained in the same manner as in Example 21 except that the heat treatment temperature was changed from 900° C. to 600° C.

[Example 23]
A mixed aqueous solution of 1 equivalent of Na ₂ SiO ₃ and 1/2 equivalent of Na ₃ PO ₄ with respect to Zr(SO ₄ ) ₂ was added dropwise to the Zr(SO ₄ ) ₂ aqueous solution, and the mixture was stirred at room temperature for 3 hours. Furthermore, 1 equivalent of a NaOH aqueous solution was added dropwise to Zr(SO ₄ ) ₂ and stirred overnight at room temperature. The obtained precipitate was collected by centrifugation, further washed three times with ion-exchanged water and dried, and 3/2 equivalent of Na ₂ CO ₃ was added to the dried powder and Zr(SO ₄ ) ₂ in a mortar. After mixing, heat treatment was performed at 1200° C. for 6 hours in air to obtain Na ₃ Zr ₂ Si ₂ PO ₁₂ .

(2) Evaluations The samples (heat-treated products) obtained in Examples 1 to 23 were subjected to various evaluations as shown below.

<XRD>
The obtained sample (heat-treated product) was analyzed by X-ray diffraction (XRD) to examine the generated phase. XRD measurement was performed under the following conditions.

-X-ray diffraction device: Rigaku SmartLab II
- Source: Cu kα1
-Tube voltage: 40kV
-Tube current: 30mA
-Scan speed: 2°/min -Scan range: 5° to 90°

<PL measurement>
Absolute PL quantum yield measurement was performed on a part of the obtained sample (heat-treated product) by photoluminescence (PL) method, and the emission characteristics were investigated. PL analysis was conducted under the following conditions.

-Analyzer: Hamamatsu Photonics Co., Ltd. Absolute PL quantum yield device C9920-02
-Excitation wavelength: 250nm to 800nm

(3) Evaluation results The XRD profiles obtained for the samples of Examples 1 to 23 are shown in FIGS. 1 to 12. Also shown in the figure is a reference profile determined based on crystallographic data of the target compound or its neighboring compounds. The crystallographic data included in the Inorganic Crystal Structure Database (ICSD) and the Open Access Crystal Structure Database (COD) were used.

As shown in Figures 1-12, the XRD profiles of all samples were comparable to the reference profile. From this, it was confirmed that the target compounds (oxoacid metal salts) were synthesized in Examples 1 to 23.

The PL spectra obtained for the samples of Examples 4 to 6 are shown in FIGS. 13 and 14. In the figure, the wavelength of the excitation light is also shown.

The sample of Example 4 emitted light when irradiated with ultraviolet light with a wavelength of 275 nm, and the emitted light was green light with a wavelength of 540 nm as the center. The sample of Example 5 emitted light when irradiated with ultraviolet light with a wavelength of 360 nm, and the emitted light was blue light with a wavelength of 440 nm as its center. The sample of Example 6 was emitted by ultraviolet radiation at a wavelength of 395 nm, and the emitted light was red light centered at a wavelength of 620 nm. From these results, it was confirmed that the oxoacid metal salts obtained in Examples 4 to 6 exhibited fluorescent properties.

Note that although the target compounds of Examples 5 and 6 are the same, their fluorescence characteristics (wavelengths of emitted light) are different. This is considered to reflect the difference in the heat treatment atmosphere. That is, in Example 5, since the heat treatment was performed in an argon (Ar) atmosphere, it is considered that europium (Eu) in the sample was reduced to a +2-valent state. On the other hand, in Example 6, since the heat treatment was performed in an air atmosphere, it is presumed that Eu maintains the +3 valence state.

From the above results, it can be seen that the present embodiment provides a method for producing an oxoacid metal salt, which has a high degree of freedom in material design and is excellent in mass productivity.

Claims (6)

A method for producing an oxoacid metal salt, the method comprising:
A step of reacting an oxoacid salt and an alkali-free metal salt in a solvent containing water and/or alcohol to obtain a precipitate, and recovering the obtained precipitate by solid-liquid separation, and the recovered precipitate. A step of heat-treating the object at a temperature of 50° C. or higher and 1600° C. or lower to obtain a heat-treated object,
The oxo acid salt is either or both of an oxo acid alkali metal salt and an oxo acid ammonium salt,
The metal element contained in the alkali-free metal salt is at least one selected from the group consisting of typical elements, transition elements, and rare earth elements,
The alkali-free metal salt has a final pKa of the conjugate acid of its anion of 7.0 or less,
A method in which the reaction is carried out at a temperature of 0°C or more and less than 100°C under a pressure of 0.8 atm or more and 1.2 atm or less. The oxoacid salt has a hydrogen number x of 0 or more and 2 or less, and the alkali-free metal salt is at least one selected from the group consisting of nitrates, halides, sulfates, and carboxylates. The method according to claim 1. 3. The method according to claim 2, wherein the heat treatment is performed under an argon (Ar) and/or hydrogen ( _H2 ) gas atmosphere, thereby reducing the precipitate. The method according to claim 2, wherein the oxoacid salt has a hydrogen number x greater than 0, and the heat treatment is performed to dehydrate the precipitate. The method according to claim 2, wherein the oxoacid salt has a hydrogen number x greater than 0, and the heat treatment is performed in an oxidizing gas atmosphere, thereby oxidizing the precipitate. The oxoacid metal salt can be used as a dielectric material, a luminescent material, a solid electrolyte material, an optical material, a magnetic material, an electrically conductive material, a semiconductor material, an electrically insulating material, a thermoelectric conversion material, a structural material, a heat-resistant material, a biological material, The method according to claim 1 or 2, wherein the method is at least one selected from the group consisting of

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