JP7144907B2 - Method for producing lithium germanium phosphate - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing lithium germanium phosphate useful as a solid electrolyte.

As one method for improving the safety of lithium secondary batteries, a method using an oxide-based solid electrolyte that has a wide operating temperature range and is stable in the air is being studied.

As oxide-based solid electrolytes, for example, garnet-type oxides, NASICON-type oxides, perovskite-type oxides, and the like have been investigated.

Phosphate-based oxides having a NASICON structure are stable in the atmosphere. In particular, lithium aluminum germanium phosphate (LAGP), in which part of germanium in lithium germanium phosphate is replaced with Al element, is lithium. Due to its high ionic conductivity, it is one of the materials attracting attention as a solid electrolyte (see Patent Documents 1 to 3, for example).

As a method for producing LAGP, for example, lithium carbonate, germanium dioxide, aluminum oxide and ammonium phosphate are mixed, and the mixture is baked in the air to obtain LAGP by a solid phase reaction (for example, Patent Documents 1 to 3 ) is disclosed. Further, in Patent Document 4 below, GeO ₂ is used as a germanium source, GeO ₂ is dissolved in water with ammonia or the like, and the solution is made to contain a water-soluble Li source, an Al source and a P source. A method of removing the solvent from the raw material mixture, then heat-treating to obtain amorphous LAGP, and then calcining to crystallize the LAGP is disclosed.

JP 2019-149298 A, claim 1, paragraphs 0019 to 0020 JP 2013-157195 A, claim 1, paragraph 0042 JP-A-2009-140911, claim 6, paragraph 0044 JP 2019-46559 A, claim 1

However, in the solid-phase methods of Patent Documents 1 to 3, it is difficult to obtain a raw material mixture in which the germanium source and the phosphorus source are uniformly mixed. There is a problem that it is difficult to obtain an advantage. In addition, the method of Patent Document 4 is not industrially advantageous because the process is likely to be complicated and the problem of disposal of waste liquid and waste gas is likely to occur.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing lithium germanium phosphate which is industrially advantageous and which can obtain single-phase lithium germanium phosphate according to X-ray diffraction.

In view of the above-mentioned circumstances, the present inventors have made intensive studies, and as a result, using phosphorous acid as a P source, a raw material mixture in which a Li source, an M source, a Ge source, and a P source are dissolved or dispersed in a solvent A single-phase lithium germanium phosphate can be easily obtained in terms of X-ray diffraction by preparing a liquid, then heat-treating the raw material mixed liquid, and calcining the resulting reaction precursor. In addition, in the production of lithium germanium phosphate, when phosphoric acid is used as the P source, rapid volumetric expansion occurs during firing. A single-phase lithium germanium phosphate can be obtained by a mild firing reaction without significant volume expansion. Furthermore, according to a particularly preferred embodiment of the present invention, it was found that the strong adhesion of lithium germanium phosphate to the crucible after firing can be suppressed and recovery is facilitated, depending on the firing conditions. reached completion.

That is, the present invention (1) is represented by the following general formula (1):
Li1 _{+ xMxGe2 -x (} PO4) ₃ (1)
(In the formula, 0.0 < x ≤ 1.0, and M is one or more selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In and Co. Indicates a valent or trivalent metal element.)
A method for producing lithium germanium phosphate having a NASICON structure represented by
A first step of preparing a raw material mixture in which a Li source, an M source, a Ge source, and a P source are dissolved or dispersed in a solvent; A second step of removing at least part of the reaction precursor to prepare a reaction precursor, and a third step of firing the reaction precursor,
the P source is phosphorous acid;
A method for producing lithium germanium phosphate is provided.

The present invention (2) also provides the method for producing lithium germanium phosphate of (1), wherein the Ge source is germanium dioxide.

Further, in the present invention (3), a slurry containing germanium dioxide, an organic acid, and a solvent is heated to perform a dissolving step of obtaining a germanium dioxide solution, and then the germanium dioxide solution is , the Li source, the M source and the P source are mixed to prepare the raw material mixture to prepare the raw material mixture, thereby performing the first step. It provides.

The present invention (4) also provides the method for producing lithium germanium phosphate of (3), wherein the organic acid is a carboxylic acid.

Further, according to the present invention (5), the lithium germanium phosphate according to any one of (1) to (4), wherein at least the reaction precursor is fired at 600 to 1000° C. in the third step. It is intended to provide a manufacturing method of.

Further, in the present invention (6), in the third step, the reaction precursor is pre-fired at 350 to 550°C, and then main-fired at 600 to 1000°C. A method for producing lithium germanium phosphate according to any one of features (1) to (4) is provided.

In addition, the present invention (7) is the phosphorus according to any one of (1) to (6), wherein M in the general formula (1) is Al, and the M source is an Al source. A method for producing lithium germanium acid is provided.

The present invention (8) also provides the method for producing lithium germanium phosphate of (7), wherein the Al source is alumina.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the lithium germanium phosphate which can obtain the single-phase lithium germanium phosphate by X-ray-diffraction by an industrially advantageous method can be provided.

4 is a photograph showing the state of the calcined product after calcining in the third step of Example 1 and Comparative Example 1. FIG. 1 is an X-ray diffraction diagram of calcined products of Example 1 and Comparative Example 1. FIG. 1 is an X-ray diffraction diagram of LAGP obtained in Example 1 and Comparative Example 1. FIG. FIG. 10 is an X-ray diffraction diagram of calcined products of Example 4 and Comparative Example 2; SEM photograph of LAGP obtained in Example 5. FIG.

The present invention will be described below based on its preferred embodiments.
The method for producing lithium germanium phosphate of the present invention comprises the following general formula (1):
Li1 _{+ xMxGe2 -x (} PO4) ₃ (1)
(In the formula, 0.0 < x ≤ 1.0, and M is one or more selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In and Co. Indicates a valent or trivalent metal element.)
A method for producing lithium germanium phosphate having a NASICON structure represented by
A first step of preparing a raw material mixture in which a Li source, an M source, a Ge source, and a P source are dissolved or dispersed in a solvent; A second step of removing at least part of the reaction precursor to prepare a reaction precursor, and a third step of firing the reaction precursor,
the P source is phosphorous acid;
A method for producing lithium germanium phosphate characterized by

The lithium germanium phosphate obtained by the method for producing lithium germanium phosphate of the present invention has the following general formula (1):
Li1 _{+ xMxGe2 -x (} PO4) ₃ (1)
(In the formula, 0.0 < x ≤ 1.0, and M is one or more selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In and Co. Indicates a valent or trivalent metal element.)
Lithium germanium phosphate having a NASICON structure represented by

x in the general formula (1) satisfies 0.0<x≤1.0, preferably 0.1≤x≤0.5, and particularly preferably 0.2≤x≤0.4. M in the general formula (1) is, for example, a metal element contained for the purpose of improving performance such as lithium ion conductivity. M is a divalent or trivalent metal element and represents one or more metal elements selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In and Co, Al is particularly preferred.

In the first step of the method for producing lithium germanium phosphate of the present invention, a Li source, an M source, a Ge source and a P source are mixed with a solvent and stirred to obtain a Li source, an M source, a Ge source and a P source. , dissolving or dispersing in a solvent to prepare a raw material mixture. In the first step, the method of dissolving or dispersing the Li source, the M source, the Ge source and the P source in the solvent by mixing and stirring is not particularly limited.

Examples of the Li source for the first step include lithium hydroxide, lithium carbonate, lithium oxide, and lithium organic oxide. Of these, lithium hydroxide can be dissolved in an aqueous solvent, and , is preferable from the viewpoint of industrial availability.

Examples of the M source related to the first step include oxides, hydroxides, carbonates, organic acid salts, nitrates, phosphates, etc. containing the M element. In particular, when the M element is Al, the Al source is alumina (Al ₂ O ₃ ), which is easily available industrially, has excellent reactivity, and has little concern about residual impurities. preferred from

The Ge source for the first step includes, for example, germanium sulfate, germanium chloride, germanium nitrate, potassium germanate, germanium dioxide, etc. Germanium dioxide is particularly industrially easy to obtain, excellent in reactivity, and , there is little concern about residual impurities.

The P source for the first step is phosphorous acid. Phosphorous acid is not particularly limited as long as it is industrially available. The phosphorous acid may be an aqueous solution.

In addition, although the production history of the Li source, M source, Ge source, and P source does not matter, it is preferable that the impurity content is as low as possible in order to produce high-purity lithium germanium phosphate. In addition, among the Li source, M source, and Ge source, those that are insoluble in the solvent preferably have an average particle size of 10 μm or less, as determined by laser diffraction, in order to increase the reactivity of the reaction precursor. ~5 μm is particularly preferred.

The solvent in the first step may be a water solvent or a mixed solvent of water and a hydrophilic organic solvent. The hydrophilic organic solvent is not particularly limited as long as it is inert to the raw material, and examples thereof include alcohols such as ethanol, propanol and butanol, and methyl ethyl ketone. In the case of a mixed solvent of water and hydrophilic organic solvent, the mixing ratio of water and hydrophilic organic solvent is appropriately selected.

The phosphorous acid concentration in the raw material mixture is 1.4 to 1.8 mol/L, preferably 1.5 to 1.7 mol/L, in terms of P atoms. Further, by adjusting the contents of the Li source, M source and Ge source in the raw material mixture so that the composition of the general formula (1) is obtained, Li atoms in the Li source, M atoms in the M source, It is preferable to appropriately adjust the molar ratio of Ge atoms in the Ge source and P atoms in the P source.

In the raw material mixture, the Li source, M source, Ge source and P source are dissolved or dispersed in the solvent. The raw material mixture may be in the form of a slurry or a solution in which each raw material is dissolved in a solvent.

When the raw material mixture is in the form of a slurry, the concentration of solids in the raw material mixture is preferably 30 to 70% by mass, particularly preferably 40 to 60% by mass. Since the concentration of the solid content in the raw material mixed liquid is within the above range, the reaction efficiency is increased and the viscosity of the slurry is not excessively increased.

In the method for producing lithium germanium phosphate of the present invention, when germanium dioxide is used as the Ge source, in the first step, germanium dioxide is dissolved in an aqueous solvent or an aqueous solvent, and a solution in which the Ge source is dissolved in the solvent is prepared. Use is particularly preferred from the viewpoint of obtaining a reaction precursor with even better reactivity.

As a method of using a solution in which a Ge source is dissolved in an aqueous solvent in the first step, germanium dioxide is dissolved in an aqueous solvent or an aqueous solvent to obtain a solution of germanium dioxide. A method of performing the first step by mixing an aqueous solution with a Li source, an M source, and a P source to prepare a raw material mixed solution is exemplified.

As a method of dissolving germanium dioxide in a water solvent, there is a method using ammonia water (Japanese Patent Application Laid-Open No. 2019-46559), but there is a problem of waste water and waste gas treatment. On the other hand, since the organic acid is removed as _CO2 gas from the reaction system by the calcination in the third step, which will be described later, in the dissolution step, the method of using an organic acid to dissolve germanium dioxide in an aqueous solvent or an aqueous solvent is preferred. In the method for producing lithium germanium phosphate of the present invention, using a solution obtained by dissolving germanium dioxide obtained in the dissolution step in an aqueous solvent or an aqueous solvent makes it difficult to cause the problem of waste water or waste gas treatment, and furthermore, The use of a solution in which the Ge source is dissolved in a water solvent is particularly preferable from the viewpoint of obtaining a reaction precursor in which the reactivity of the Ge source is further enhanced.

In the first step, as a method of using a solution in which the Ge source is dissolved in an aqueous solvent or an aqueous solvent, a slurry containing germanium dioxide, an organic acid, and a solvent is heated to obtain a solution of germanium dioxide. A method of performing the first step by performing a dissolving step to obtain and then mixing a Li source, an M source and a P source with a solution of germanium dioxide to prepare a raw material mixed solution.

Examples of organic acids involved in the dissolution step include monocarboxylic acids such as formic acid, acetic acid, glycolic acid, lactic acid, and gluconic acid; dicarboxylic acids such as oxalic acid, maleic acid, malonic acid, malic acid, tartaric acid, and succinic acid; Examples thereof include carboxylic acids having 3 groups such as citric acid, and these may be used singly or in combination of two or more. Among these, oxalic acid is highly soluble in water solvents, has a high ability to dissolve germanium dioxide, and is easily decomposed by firing in the third step described later, and is easy to remove from the reaction system. is preferred.

The amount of the organic acid to be added is 4 to 8, preferably 5 to 7 in terms of the molar ratio of C atoms in the organic acid to germanium dioxide (C/GeO ₂ ). It is preferable from an economical point of view.

The solvent used in the dissolving step may be a water solvent or a mixed solvent of water and a hydrophilic organic solvent (also referred to as an aqueous solvent). The hydrophilic organic solvent is not particularly limited as long as it is inert to the raw material, and examples thereof include alcohols such as ethanol, propanol and butanol, and methyl ethyl ketone. In the case of an aqueous solvent (a mixed solvent of water and a hydrophilic organic solvent), the mixing ratio of water and hydrophilic organic solvent is appropriately selected.

The amount of germanium dioxide added in the dissolution step is 10 to 40 parts by mass, preferably 20 to 30 parts by mass, per 100 parts by mass of the solvent, from the viewpoint of reaction efficiency and preventing an increase in viscosity of the slurry. preferable.

The heating temperature in the dissolution step is preferably 40 to 90° C., preferably 50 to 80° C., from the viewpoint of increasing the dissolution rate. In addition, the heating time in the dissolving step is not critical in the dissolving step, but it is preferably 1 hour or more, particularly preferably 1 to 3 hours. It is preferable in that a dissolved solution can be obtained.

In the first step according to the method for producing lithium germanium phosphate of the present invention, when the dissolving step is performed, after the dissolving step is performed, the "solution in which germanium dioxide is dissolved in an aqueous solvent or an aqueous solvent A raw material mixed solution can be prepared by adding predetermined amounts of Li source, M source and P source to ", and stirring the mixture.

The temperature at which the Li source, the M source and the P source are added to the solution of germanium dioxide obtained in the dissolving step in an aqueous solvent or aqueous solvent is not particularly limited, and may be room temperature. In addition, in the dissolution step, the Li source, M source and P source may be added while the temperature of the solution is maintained as it is without cooling, or until the temperature of the heat treatment in the second step described later is reached. The Li source, M source and P source may be added after the temperature of the solution is raised or during the temperature raising process.

The second step is a step of heat-treating the raw material mixture obtained in the first step to remove at least part of the solvent in the raw material mixture to prepare a reaction precursor.

In the second step, the raw material mixture obtained in the first step is heat-treated to remove at least part of the solvent in the raw material mixture to obtain a pasty reaction precursor. In the present invention, the term "paste" refers to a viscous state. Therefore, in the present invention, it is not necessary to remove all the solvent in the reaction precursor in the second step. Generally, if the solvent content in the reaction precursor is 30% by mass or less, preferably 20% by mass or less, a pasty reaction precursor with satisfactory physical properties can be obtained.

The heating temperature in the heat treatment according to the second step is not particularly limited as long as it is a temperature that can remove the solvent, but it is usually 100 to 150 ° C., preferably 110 to 140 ° C. It is effective to remove the water solvent. It is preferable from the viewpoint of The heating time in the heat treatment in the second step is not particularly limited, and may be performed until the raw material mixture becomes a paste. Although it varies depending on the raw material concentration of the raw material mixture and the heating temperature in the heat treatment, for example, when the raw material concentration of the raw material mixture is 40 to 60% by mass and the heating temperature in the heat treatment is 120 to 130 ° C., heating The time is 1 hour or more, preferably 1 to 4 hours, in that a pasty reaction precursor having satisfactory physical properties can be obtained.

The third step is a step of calcining the reaction precursor obtained in the second step to obtain lithium germanium phosphate.

In the third step, firing at least the reaction precursor at 600 to 1000° C., preferably 650 to 850° C. makes it easier to obtain the single-phase lithium germanium phosphate represented by the general formula (1). is preferred. The reason for this is that if the firing temperature is lower than the above temperature, the synthesis of lithium germanium phosphate represented by the general formula (1) tends to be insufficient, and if the above temperature is exceeded, the general formula ( This is because the particles of lithium germanium phosphate represented by 1) tend to grow, making it difficult to obtain fine particles.

In the third step, the firing time for firing the reaction precursor is not particularly limited, and the firing is performed for a time sufficient to form the lithium germanium phosphate represented by the general formula (1) in terms of X-ray diffraction. . In the third step, in many cases, the time for calcining the reaction precursor at 600 to 1000° C., preferably 650 to 850° C., is 3 hours or more, preferably 3 to 10 hours. A fired product with various physical properties can be obtained. Moreover, in the third step, the firing atmosphere for firing the reaction precursor is not particularly limited, and may be an inert gas atmosphere, a vacuum atmosphere, an oxidizing gas atmosphere, or the atmosphere.

In the third step, firing may be performed once, or may be performed multiple times as desired. Alternatively, in the third step, for the purpose of uniforming the powder characteristics, the material that has been fired once may be pulverized and then fired again.

In addition, in the method for producing lithium germanium phosphate of the present invention, lithium germanium phosphate may adhere to the crucible during firing in the third step, making it difficult to recover the desired product. In the method for producing lithium germanium phosphate of the present invention, in the third step, the reaction precursor is fired at a low temperature and then at a high temperature to prevent lithium germanium phosphate from adhering to the crucible during firing. This is industrially advantageous because it suppresses the formation of the desired lithium germanium phosphate and allows the target lithium germanium phosphate to be easily recovered from the crucible or the like.

As such a third step, the reaction precursor is calcined at 350 to 550 ° C., and then subjected to main calcination at 600 to 1000 ° C. A third step (hereinafter referred to as the third step Also described as the first form of.).

The firing temperature of the calcination in the first form of the third step is 350 to 550° C., preferably 400 to 550° C., particularly preferably 450 to 550° C., so that the paste-like reaction precursor can be solidified. Moreover, it is preferable from the viewpoint of maintaining releasability without firmly adhering to the container. In addition, the calcination time of calcination in the first form of the third step is not particularly limited, and it is 3 hours or more, preferably 3 to 10 hours, to obtain a calcination product with satisfactory physical properties. It is preferable in that it can be done. The calcination atmosphere of the calcination in the first form of the third step is not particularly limited, and may be an inert gas atmosphere, a vacuum atmosphere, an oxidizing gas atmosphere, or the atmosphere.

In the calcination in the first form of the third step, the reaction of the compound contained in the calcined product is complicated and unknown, but at least when the calcined product is analyzed by X-ray diffraction, some kind of crystalline substance Diffraction peaks are observed. The crystal substance detected by X-ray diffraction analysis varies depending on the calcination temperature, but in the first mode of the third step, when calcination is performed in a preferable calcination temperature range, the general formula ( In addition to the lithium germanium phosphate represented by 1), crystals such as GeP ₂ O ₇ and lithium-M-phosphorus composite oxides (eg, LiMP ₂ O ₇ etc.) are contained.

After calcining, the product is cooled to room temperature, and the obtained calcined product is pulverized or crushed to homogenize each component. It is preferable in that it is easy to be broken.

There are no particular restrictions on the methods of pulverization and crushing, and conventional methods can be used. The pulverization treatment and crushing treatment may be dry or wet. Examples of wet pulverizers include ball mills and bead mills. Examples of dry pulverizing devices include known pulverizing or pulverizing devices such as jet mills, pin mills, roll mills, ball mills and bead mills. Further, at the laboratory level, pulverization or pulverization using a household mixer, mortar, or the like is sufficient.

Next, in the first form of the third step, main firing is performed after temporary firing. In the main firing according to the first form of the third step, the temporarily fired product is main fired at 600 to 1000 ° C., preferably at 650 to 850 ° C. Single-phase phosphoric acid represented by the general formula (1) It is preferable in that it becomes easy to obtain germanium lithium. The reason for this is that if the firing temperature in the main firing is lower than the above range, the synthesis of the lithium germanium phosphate represented by the general formula (1) tends to be insufficient, and if it exceeds the above range, This is because the particles of the lithium germanium phosphate represented by the general formula (1) tend to grow, making it difficult to obtain fine particles.

In addition, the firing time of the main firing in the first form of the third step is not particularly limited, and it is necessary to sufficiently perform until the single-phase lithium germanium phosphate represented by the general formula (1) is obtained. . In the main firing in the first form of the third step, in many cases, the temperature is 600 to 1000° C., preferably 650 to 850° C., and the firing time is 3 hours or more, preferably 3 to 10 hours. The firing atmosphere for the main firing in the first form of the third step is not particularly limited, and may be any of an inert gas atmosphere, a vacuum atmosphere, an oxidizing gas atmosphere, and the air.

In the first form of the third step, calcination and main calcination may be performed once, or may be performed multiple times as desired. Alternatively, in the first form of the third step, for the purpose of uniforming the powder characteristics, the material that has been calcined once may be pulverized and then calcined again.

In the third step, after sintering, the product is appropriately cooled, and pulverized, pulverized, classified, etc., as necessary, to obtain the target lithium germanium phosphate represented by the general formula (1).

One feature of the method for producing lithium germanium phosphate of the present invention is that phosphorous acid is used as the P source. When phosphoric acid is used as the P source, phosphoric acid is easily dehydrated and condensed by heating, and the dehydration condensation occurs preferentially over the reaction with each raw material. By heat-treating the reaction precursor at, for example, 210° C. or 500° C., a substantially amorphous one can be obtained (see FIGS. 2 and 4). On the other hand, when a reaction precursor prepared using phosphorous acid as a P source is heat-treated at, for example, 210° C. or 500° C., diffraction peaks of crystals are observed (see FIGS. 2 and 4). The present inventors have found that when phosphorous acid is used as the P source, the formation reaction of lithium germanium phosphate represented by the general formula (1) proceeds preferentially over the dehydration condensation between phosphorus. I think it's because

Furthermore, when phosphorous acid is used as the P source, the volume expansion of the heat-treated product is suppressed when the reaction precursor is heat-treated, compared to when phosphoric acid is used as the P source. This is because when phosphoric acid is used as the P source, the dehydration reaction proceeds by heat treatment and polyphosphoric acid, which is a viscous liquid, is generated. is confined in the highly viscous liquid of polyphosphoric acid, resulting in a foamed state and rapid volume expansion.

The lithium germanium phosphate represented by the general formula (1) obtained by the method for producing lithium germanium phosphate of the present invention is single-phase in X-ray diffraction. Furthermore, the lithium germanium phosphate represented by the general formula (1) obtained by the method for producing lithium germanium phosphate of the present invention has an average particle size of preferably 0.5 to 10 μm, particularly preferably 0.5 to 10 μm, as determined by a laser diffraction method. is 1 to 5 μm, and the BET specific surface area is preferably 1 to 15 m ² /g, particularly preferably 2 to 10 m ² /g, from the viewpoint of excellent powder properties and easy handling.

Lithium germanium phosphate obtained by the method for producing lithium germanium phosphate of the present invention is suitably used as a solid electrolyte, positive electrode, or negative electrode material for secondary batteries.

EXAMPLES The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples.
<Preparation of Al source>
Alumina was wet pulverized by a ball mill to prepare an alumina slurry used in Examples.
The prepared alumina slurry had a solid content concentration of 8% by mass, and an average particle size of the solid content determined by a laser diffraction method was 1.3 μm.

<Preparation of Li _1.3 Al _0.3 Ge _1.7 (PO ₄ ) ₃ (hereinafter referred to as “LAGP”) having a NASICON structure>
(Example 1)
<First step>
100 g of pure water was put into a 500 ml beaker lined with Teflon (registered trademark), and 30 g of germanium dioxide (GeO ₂ ) was added and stirred.
Then, 104.15 g of oxalic acid dihydrate was added while stirring, and heated to 60°C with a heater. 60 minutes after heating, the germanium dioxide dissolved to form a clear solution.
To this clear solution maintained at 60° C. was then added sequentially 32.1 g of the alumina slurry prepared above, 39.85 g of phosphorous acid and 8.84 g of lithium hydroxide monohydrate.
<Second step>
After the raw materials were added, heating was continued by increasing the output of the heater, and the mixture was concentrated until the liquid temperature reached 120° C. to obtain 175 g of a paste-like reaction precursor. It took 3 hours for the liquid temperature to reach 120°C. The content of the solvent in the paste-like reaction precursor was measured by the loss-on-drying method and found to be 13% by mass.
<Third step>
A heat-resistant container was charged with 10 g of the obtained paste-like reaction precursor, and calcined in an electric furnace in an air atmosphere at 210° C. for 4 hours.
After the calcination, the product was naturally cooled to room temperature and the calcined product was collected. No volumetric expansion was observed in the calcined product (see FIG. 1). In addition, the calcined product could be easily recovered by inverting the heat-resistant container and scraping it out with a scoop.
Next, the collected calcined product was pulverized in a mortar to obtain a pulverized product. FIG. 2 shows an X-ray diffraction diagram of the obtained pulverized product. It was confirmed that the calcined product contained crystalline substances.
Next, 5 g of the pulverized product thus obtained was placed in an alumina crucible and fired in an air atmosphere at 800° C. for 4 hours to obtain a fired product. After the main firing, since the whole adhesion to the alumina crucible was observed, the main fired product was scraped off with a spatula to collect the entire amount of the main fired product, and then pulverized with a mortar to obtain the main fired product.
As a result of X-ray diffraction analysis of the obtained sintered product, the presence of a different phase such as GeP ₂ O ₇ was not confirmed, and it was confirmed to be a single-phase LAGP (see FIG. 3).

(Example 2)
A main fired product was obtained in the same manner as in Example 1, except that the temperature of the temporary firing in the third step was set to 250°C.
No volume expansion was observed in the calcined product. After calcination, the calcined product was easily collected by inverting the heat-resistant container and scraping it out with a scoop.
In addition, after the main firing, since the entire sticking to the alumina crucible was observed, the whole amount of the main fired product was recovered by scraping off with a spatula, and the main fired product was obtained by pulverizing with a mortar.
As a result of X-ray diffraction analysis of the obtained main fired product, the presence of a different phase such as GeP ₂ O ₇ was not confirmed, and it was confirmed to be a single-phase LAGP.

(Example 3)
A main fired product was obtained in the same manner as in Example 1, except that the temperature of the temporary firing in the third step was set to 400°C.
No volume expansion was observed in the calcined product. After calcination, the calcined product was easily collected by inverting the heat-resistant container and scraping it out with a scoop.
In addition, after the main firing, partial adhesion to the alumina crucible was observed, so the entire amount of the main fired product was recovered by scraping off the adhered portion with a spatula, and the main fired product was pulverized with a mortar to obtain the main fired product.
As a result of X-ray diffraction analysis of the obtained main fired product, the presence of a different phase such as GeP ₂ O ₇ was not confirmed, and it was confirmed to be a single-phase LAGP.

(Example 4)
A main fired product was obtained in the same manner as in Example 1, except that the temperature of the temporary firing in the third step was set to 500°C.
After calcination, the calcined product could be easily collected by turning over the heat-resistant container.
No volume expansion was observed in the calcined product. Further, the collected calcined product was pulverized in a mortar to obtain a pulverized product. FIG. 4 shows an X-ray diffraction diagram of the obtained pulverized product. In the calcined product, diffraction peaks of GeP ₂ O ₇ and LiAlP ₂ O ₇ were confirmed in addition to LATP as crystalline products.
In addition, the recovery after the main calcination could easily recover the entire content by inverting the alumina crucible and scraping it out with a scoop. Then, the product was pulverized in a mortar to obtain a main fired product.
As a result of X-ray diffraction analysis of the obtained main fired product, the presence of a different phase such as GeP ₂ O ₇ was not confirmed, and it was confirmed to be a single-phase LAGP.

(Example 5)
A main fired product was obtained in the same manner as in Example 1 except that the temperature of the temporary firing in the third step was set to 500°C and the temperature of the main firing was set to 700°C.
No volume expansion was observed in the calcined product. After calcination, the calcined product was easily collected by inverting the heat-resistant container and scraping it out with a scoop.
In addition, the content after main firing could be easily recovered by inverting the alumina crucible. Then, the product was pulverized in a mortar to obtain a main fired product.
As a result of X-ray diffraction analysis of the obtained main fired product, the presence of a different phase such as GeP ₂ O ₇ was not confirmed, and it was confirmed to be a single-phase LAGP.

(Comparative example 1)
<First step>
100 g of pure water was put into a 500 ml beaker lined with Teflon (registered trademark), and 30 g of germanium dioxide (GeO ₂ ) was added and stirred.
Then, 104.15 g of oxalic acid dihydrate was added while stirring, and heated to 60°C with a heater. 60 minutes after heating, the germanium dioxide dissolved to form a clear solution.
To this clear solution was then added sequentially 32.1 g of the alumina slurry prepared above, 65.45 g of 85% phosphoric acid and 8.84 g of lithium hydroxide monohydrate.
<Second step>
After the raw materials were added, the heater output was increased to continue heating, and the mixture was concentrated until the liquid temperature reached 120° C. to obtain 200 g of a paste-like reaction precursor. It took 3 hours for the liquid temperature to reach 120°C. The content of the solvent in the paste-like reaction precursor was measured by the loss-on-drying method and found to be 17% by mass.
<Third step>
A heat-resistant container was charged with 10 g of the obtained paste-like reaction precursor, and calcined in an electric furnace in an air atmosphere at 210° C. for 4 hours.
After the calcination, the product was naturally cooled to room temperature and the calcined product was collected. In addition, volumetric expansion was observed in the calcined product (see FIG. 1). The calcined products could be easily recovered by inverting the heat-resistant container.
Next, the recovered calcined product was pulverized in a mortar to obtain a pulverized product. FIG. 2 shows the X-ray diffraction diagram of the obtained pulverized product. The calcined product was amorphous.
Next, 5 g of the pulverized product thus obtained was placed in an alumina crucible and fired in an air atmosphere at 800° C. for 4 hours to obtain a fired product.
In addition, the entire amount of the content could be easily recovered after the main firing by turning over the alumina crucible. Then, the product was pulverized in a mortar to obtain a main fired product.
As a result of X-ray diffraction analysis of the obtained main fired product, diffraction peaks of GeP ₂ O ₇ were confirmed in addition to LAGP (see FIG. 3).

(Comparative example 2)
A main fired product was obtained in the same manner as in Comparative Example 1, except that the temporary firing temperature was changed to 500°C.
After the calcination, the product was naturally cooled to room temperature and the calcined product was recovered. In addition, volume expansion was seen in the calcined product. The calcined products could be easily recovered by inverting the heat-resistant container.
Next, the recovered calcined product was pulverized in a mortar to obtain a pulverized product. FIG. 4 shows the X-ray diffraction diagram of the obtained pulverized product. The calcined product was almost amorphous.
Next, 5 g of the pulverized product thus obtained was placed in an alumina crucible and fired in an air atmosphere at 800° C. for 4 hours to obtain a fired product.
In addition, the entire amount of the content could be easily recovered after the main firing by turning over the alumina crucible. Then, the product was pulverized in a mortar to obtain a main fired product.
As a result of X-ray diffraction analysis of the obtained main sintered product, diffraction peaks of GeP ₂ O ₇ were confirmed in addition to LAGP.

<Physical property evaluation>
For the LAGP obtained in Examples 4 and 5, the average particle size and BET specific surface area after jet mill pulverization were measured.
Incidentally, the average particle size was determined as follows.
Moreover, the SEM photograph of LAGP obtained in Example 5 is shown in FIG.
(Measurement of average particle size)
The D50 value in the particle size distribution measured by a particle size distribution analyzer (Microtrack Bell MT3300) using water as a dispersion medium was defined as the average particle size.

Claims (8)

The following general formula (1):
Li1 _{+ xMxGe2 -x (} PO4) ₃ (1)
(In the formula, 0.0 < x ≤ 1.0, and M is one or more selected from Al, Ga, Sc, Y, La, Fe, Cr, Ni, Mn, In and Co. Indicates a valent or trivalent metal element.)
A method for producing lithium germanium phosphate having a NASICON structure represented by
A first step of preparing a raw material mixture in which a Li source, an M source, a Ge source, and a P source are dissolved or dispersed in a solvent; A second step of removing at least part of the reaction precursor to prepare a reaction precursor, and a third step of firing the reaction precursor,
The P source is phosphorous acid, and the raw material mixture in the first step is prepared by dissolving at least the Ge source in a water solvent or a mixed solvent of water and a hydrophilic organic solvent using an organic acid . be liquid,
A method for producing lithium germanium phosphate, characterized by: 2. The method for producing lithium germanium phosphate according to claim 1, wherein said Ge source is germanium dioxide. A slurry containing germanium dioxide, an organic acid, and a solvent is heated to perform a dissolving step of obtaining a germanium dioxide solution, and then the germanium dioxide solution is added with the Li source, the M source and 3. The method for producing lithium germanium phosphate according to claim 2, wherein the first step is performed by mixing the P source to prepare the raw material mixture. 4. The method for producing lithium germanium phosphate according to claim 3, wherein the organic acid is a carboxylic acid. The method for producing lithium germanium phosphate according to any one of claims 1 to 4, wherein at least the reaction precursor is fired at 600 to 1000°C in the third step. 5. Any one of claims 1 to 4, wherein in the third step, the reaction precursor is pre-fired at 350 to 550° C., and then main-fired at 600 to 1000° C. 1. The method for producing lithium germanium phosphate according to claim 1. The method for producing lithium germanium phosphate according to any one of claims 1 to 6, wherein M in the general formula (1) is Al, and the M source is an Al source. 8. The method for producing lithium germanium phosphate according to claim 7, wherein said Al source is alumina.

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