JP7652593B2 - Amorphous solid electrolyte precursor powder and method for producing the same, and method for producing a solid electrolyte having a NASICON crystal structure - Google Patents

Description

This invention relates to an amorphous solid electrolyte precursor powder and a method for producing the same, as well as a method for producing a solid electrolyte having a NASICON crystal structure.

As a solid electrolyte for an all-solid-state battery, a solid electrolyte having a NASICON crystal structure is known to have high ionic conductivity. One known solid electrolyte having a NASICON crystal structure is, for example, a solid electrolyte (sometimes referred to as "LAGP" in the present invention) made of a composite oxide containing lithium, aluminum, germanium, phosphorus, and oxygen and represented by the general formula Li1 _{+xAlxGe2 - x} ( _PO4 ) ₃ (x is in the range of 0<x≦1).

For example, as in Patent Documents 1 and 2, it is known that a solid electrolyte coating is formed on the particle surface of an electrode active material in order to increase the ionic conductivity of the electrode layer of an all-solid-state battery. Patent Documents 1 and 2 describe a method of efficiently forming a solid electrolyte coating on the particle surface of an electrode active material by mixing the electrode active material and LAGP in an amorphous state and baking the mixture to crystallize the amorphous LAGP and develop ionic conductivity, thereby forming an electrode layer of an all-solid-state battery with high ionic conductivity, and an amorphous precursor powder of a solid electrolyte that is crystallized to have a NASICON type crystal structure is known.

JP 2018-37341 A JP 2019-50083 A

However, in order to improve the output of all-solid-state batteries, further improvement in ionic conductivity is desired. According to the studies of the present inventors, even LAGP crystallized by firing amorphous LAGP produced by the methods described in Patent Documents 1 and 2 has low ionic conductivity. There is a demand for an amorphous precursor powder that can be crystallized to become a solid electrolyte with a NASICON type crystal structure that exhibits higher ionic conductivity.

The present invention was made under the above circumstances, and the problem it aims to solve is to provide an amorphous solid electrolyte precursor powder and a method for producing the same, which can be crystallized to obtain a solid electrolyte with a NASICON crystal structure that exhibits high ionic conductivity, as well as a method for producing a solid electrolyte with a NASICON crystal structure.

As a result of conducting research to solve the above problems, the inventors discovered that by adding a predetermined amount of nitrogen to an amorphous solid electrolyte precursor powder containing predetermined amounts of lithium, aluminum, germanium, phosphorus, and oxygen, the amorphous solid electrolyte precursor powder exhibits high ionic conductivity when crystallized.

That is, the first invention for solving the above-mentioned problems is:
Lithium is 1% by mass or more and 4% by mass or less,
Aluminum: 0.5% by mass or more and 6% by mass or less;
germanium, 15% by mass or more and 35% by mass or less;
Phosphorus: 10% by mass or more and 30% by mass or less;
Contains nitrogen in an amount of 0.05% by mass or more and 3% by mass or less,
The remainder is oxygen, resulting in an amorphous solid electrolyte precursor powder.
The second invention is
The amorphous solid electrolyte precursor powder is the amorphous solid electrolyte precursor powder according to the first aspect of the present invention, which contains 2.5 mass % or less of nitrogen.
The third invention is
The amorphous solid electrolyte precursor powder is the amorphous solid electrolyte precursor powder according to the first or second invention, which contains 0.1 mass % or more of nitrogen.
The fourth invention is
The amorphous solid electrolyte precursor powder according to any one of the first to third aspects of the present invention contains 1.5 mass % or less of nitrogen and 23.5 mass % or more of germanium.
The fifth invention is
The amorphous solid electrolyte precursor powder according to any one of the first to fourth aspects of the present invention contains the nitrogen in the form of nitrous acid.
The sixth invention is
The amorphous solid electrolyte precursor powder according to any one of the first to fifth aspects of the present invention, further containing one or more elements selected from the group consisting of titanium, zirconium, and silicon in a total amount of 5 mass% or less.
The seventh invention is
1. A method for producing an amorphous solid electrolyte precursor powder comprising lithium, aluminum, germanium, phosphorus, nitrogen, and oxygen, the method comprising the steps of: 1% by mass or more and 4% by mass or less of lithium; 0.5% by mass or more and 6% by mass or less of aluminum; 15% by mass or more and 35% by mass or less of germanium; 10% by mass or more and 30% by mass or less of phosphorus; 0.05% by mass or more and 3% by mass or less of nitrogen; and the remainder being oxygen,
A step of adjusting the pH of a liquid containing lithium, aluminum, germanium, phosphorus, and ammonia to 2 or more and less than 4.5 to obtain a pH-adjusted slurry;
spray drying the pH adjusted slurry to obtain a dry powder;
and calcining the dried powder at 300° C. or more and 500° C. or less.
The eighth invention is
A seventh aspect of the present invention provides a method for producing an amorphous solid electrolyte precursor powder, wherein the molar ratio of nitric acid to ammonia (NO ₃ /NH ₃ ) in the pH-adjusted slurry is 1.0 or more and 3.0 or less.
The ninth invention is
The method for producing an amorphous solid electrolyte precursor powder according to the seventh or eighth invention includes further adding one or more elements selected from the group consisting of titanium, zirconium, and silicon to the liquid containing lithium, aluminum, germanium, phosphorus, and ammonia, so that the amorphous solid electrolyte precursor powder contains one or more elements selected from the group consisting of titanium, zirconium, and silicon in a total amount of 5 mass% or less.
The tenth invention is
A method for producing a solid electrolyte having a NASICON-type crystal structure, comprising a step of calcining the amorphous solid electrolyte precursor powder according to any one of the first to sixth aspects at a temperature higher than 500°C.

According to the present invention, it is possible to provide an amorphous solid electrolyte precursor powder containing lithium, aluminum, germanium, phosphorus, nitrogen, and oxygen, which is a precursor of a solid electrolyte having a NASICON crystal structure that exhibits high ionic conductivity when sintered and crystallized, a method for producing the amorphous solid electrolyte precursor powder, and a method for producing a solid electrolyte having a NASICON crystal structure.

1 is an XRD spectrum of an amorphous solid electrolyte precursor powder according to Example 1. 1 is a Raman spectrum of an amorphous solid electrolyte precursor powder according to Example 1. 1 is a SEM photograph of amorphous solid electrolyte precursor powders according to Example 1 and Comparative Examples 1 and 2.

The amorphous solid electrolyte precursor powder according to the present invention is an amorphous powder, but when calcined and crystallized, a solid electrolyte having a NASICON crystal structure exhibiting high ionic conductivity can be obtained, and the powder is a precursor of a solid electrolyte having a NASICON crystal structure.
The solid electrolyte obtained by crystallizing the amorphous solid electrolyte precursor powder according to the present invention may be any other than those having the general formula Li1 _{+ xAlxGe2 -x} ( _PO4 ) ₃ (x in the range of 0<x≦1) that can be identified by JCPDS Card No. 01-080-1922, as long as it has LAGP as the main phase, or may be a mixed phase having LAGP as the main phase and other oxides as subphases. Here, the fact that LAGP is the main phase in the obtained solid electrolyte can be confirmed by confirming that the maximum peak obtained when the solid electrolyte is subjected to XRD measurement is LAGP.

The following describes the embodiments of the invention in the following order: 1. The effect and content ratio of each constituent element in the amorphous solid electrolyte precursor powder, 2. The properties of the amorphous solid electrolyte precursor powder, 3. The method for producing the amorphous solid electrolyte precursor powder, and the method for producing a solid electrolyte having a NASICON crystal structure.

1. Effects and Contents of Each Constituent Element in Amorphous Solid Electrolyte Precursor Powder The amorphous solid electrolyte precursor powder according to the present invention contains lithium, aluminum, germanium, phosphorus, and nitrogen as constituent elements, and optionally contains other elements, with the remainder being oxygen. Hereinafter, the effects and contents of each constituent element will be described in the following order: (1) lithium, (2) aluminum, (3) germanium, (4) phosphorus, (5) nitrogen, (6) other elements, (7) oxygen, and (8) impurities.

(1) Lithium The amorphous solid electrolyte precursor powder of the present invention contains lithium in an amount of 1% by mass or more and 4% by mass or less. If the lithium content is 1% by mass or more and 4% by mass or less, when the amorphous solid electrolyte precursor powder is crystallized, it becomes a solid electrolyte with a NASICON type crystal structure having high ion conductivity, and lithium ion conductivity is ensured. The lithium content is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and even more preferably 1.8% by mass or more, while it is preferably 4.0% by mass or less, preferably 3.5% by mass or less, and even more preferably 3.3% by mass or less.

(2) Aluminum The amorphous solid electrolyte precursor powder of the present invention contains aluminum in an amount of 0.5% by mass or more and 6% by mass or less. By containing aluminum in an amount of 0.5% by mass or more and 6% by mass or less, when the amorphous solid electrolyte precursor powder is crystallized, a solid electrolyte having a NASICON crystal structure is obtained. The aluminum content is preferably 1.0% by mass or more, more preferably 2.0% by mass or more. On the other hand, it is preferably 5.5% by mass or less, more preferably 5.0% by mass or less.

(3) Germanium The amorphous solid electrolyte precursor powder of the present invention contains germanium in an amount of 15% by mass or more and 35% by mass or less. If the germanium content is 15% by mass or more, it can form glass and become amorphous. On the other hand, if the germanium content is 35% by mass or less, when the amorphous solid electrolyte precursor powder is crystallized, it becomes a solid electrolyte with a NASICON type crystal structure. The germanium content is preferably 20% by mass or more, more preferably 22% by mass or more, and most preferably 23.5% by mass or more, so that when the amorphous solid electrolyte precursor powder is crystallized, a solid electrolyte with a higher ion conductivity can be obtained. On the other hand, it is preferably 33% by mass or less, more preferably 30% by mass or less.

(4) Phosphorus The amorphous solid electrolyte precursor powder of the present invention contains phosphorus in an amount of 10% by mass or more and 30% by mass or less. In this case, glass can be formed to make it amorphous. On the other hand, when crystallized, the amorphous solid electrolyte precursor powder becomes a NASICON type crystal structure. The phosphorus content is preferably 15% by mass or more, more preferably 20% by mass or more. On the other hand, it is preferably 28% by mass or less, more preferably 25% by mass or less.

(5) Nitrogen The amorphous solid electrolyte precursor powder according to the present invention contains nitrogen in an amount of 0.05% by mass or more and 3% by mass or less. When the amorphous solid electrolyte precursor powder is sintered and crystallized by containing nitrogen in an amount of 0.05% by mass or more and 3% by mass or less, it is presumed that the nitrogen acts as a sintering promoter, the grain boundaries of the crystals are reduced, the ion conduction resistance is reduced, and the ion conductivity of the solid electrolyte obtained by crystallization is improved. From the viewpoint of improving the ion conductivity of the solid electrolyte obtained by crystallization, the nitrogen content is more preferably 0.1% by mass or more, and even more preferably 0.15% by mass or more. On the other hand, from the viewpoint of improving the ion conductivity of the solid electrolyte obtained by crystallization, the nitrogen content is preferably 2.5% by mass or less, and preferably 1.5% by mass or less.

In the present invention, the nitrogen content of the amorphous solid electrolyte precursor powder can be calculated from the results of quantitative analysis of the nitrogen amount of the amorphous solid electrolyte precursor powder using a nitrogen analyzer (an apparatus for heating and decomposing a sample in an inert gas atmosphere, extracting the nitrogen contained in the sample as nitrogen gas, and quantitatively analyzing it). The nitrogen contained in the amorphous solid electrolyte precursor powder is preferably in the form of nitrous acid. In this specification, "nitrogen in the form of nitrous acid" is identified by measuring the Raman spectrum of the amorphous solid electrolyte precursor powder and detecting a peak due to the symmetric stretching of nitrous acid at around 1285 cm ^-1 ±5. When the nitrogen contained in the amorphous solid electrolyte precursor powder is in the form of nitrous acid, it is considered that the contained nitrous acid is mainly present as lithium nitrite. Since lithium nitrite has a decomposition temperature of 600°C or higher, it remains without being decomposed during drying and firing when producing an amorphous solid electrolyte precursor powder, and it is believed that the effect of containing nitrogen is exerted in subsequent processes, resulting in a solid electrolyte with a NASICON type crystal structure that exhibits high ionic conductivity.

(6) Other elements The amorphous solid electrolyte precursor powder according to the present invention may contain, in addition to the above-mentioned lithium, aluminum, germanium, phosphorus, nitrogen and oxygen, one or more elements selected from the group consisting of titanium, zirconium and silicon in a total amount of 5 mass% or less, so long as the amorphous solid electrolyte precursor powder according to the present invention has a NASICON-type crystal structure when crystallized. The total amount of the one or more elements selected from the group consisting of titanium, zirconium and silicon may be 0.1 mass% or more.

(7) Oxygen The oxygen content in the amorphous solid electrolyte precursor powder according to the present invention can be calculated by (100% by mass - total mass% of each constituent element other than oxygen). The oxygen content in the amorphous solid electrolyte precursor powder is preferably 40% by mass or more and 55% by mass or less.

(8) Impurities The amorphous solid electrolyte precursor powder according to the present invention may contain elements other than lithium, aluminum, germanium, phosphorus, nitrogen, oxygen, titanium, zirconium and silicon as impurity elements within a range that does not impair the effects of the present invention. The total amount of the impurity elements is preferably 5% by mass or less, more preferably 1% by mass or less.

2. Properties of the amorphous solid electrolyte precursor powder The properties of the amorphous solid electrolyte precursor powder according to the present invention will be described in the following order: (1) particle size, and (2) a method for confirming that the powder is amorphous.

(1) Particle Size The particle size of the amorphous solid electrolyte precursor powder according to the present invention is not particularly limited, but it is preferable that the volume-based particle size distribution of the amorphous solid electrolyte precursor powder is measured using a laser diffraction/scattering type particle size distribution measurement device, and the volume-based cumulative 50% particle size (D50) obtained by the measurement is 1 μm to 30 μm.
When a solid electrolyte having a NASICON type crystal structure described later is used as the solid electrolyte of an all-solid-state battery, the D50 of the amorphous solid electrolyte precursor powder, which is the precursor, is preferably 1 μm to 5 μm.

(2) A method for confirming that the material is amorphous;
The amorphous solid electrolyte precursor powder according to the present invention can be confirmed to be amorphous by observing a halo in the region of 2θ: 15° to 40° by powder X-ray diffraction (XRD) measurement. The "halo" is a gentle undulation of X-ray intensity, which is observed as a broad rise in an X-ray chart. If the half-width of the halo is 2θ: 2° or more, the powder is amorphous.

3. Method for producing amorphous solid electrolyte precursor powder, and method for producing solid electrolyte having NASICON crystal structure First, a method for producing an amorphous solid electrolyte precursor powder according to the present invention will be described. Then, a method for producing a solid electrolyte having a NASICON crystal structure using the produced amorphous solid electrolyte precursor powder as a precursor will be described.

The amorphous solid electrolyte precursor powder according to the present invention can be obtained by mixing aqueous solutions of raw materials containing the respective constituent elements to obtain a liquid mixture, adjusting the pH of the obtained liquid mixture, spray-drying the pH-adjusted slurry to obtain a dry powder, and calcining the dry powder.
As described below, the liquid mixture may be in the form of a slurry in which the salts of the constituent elements are dispersed, or in the form of a solution in which the salts of the constituent elements are dissolved.

The method for producing an amorphous solid electrolyte precursor powder according to the present invention and the method for producing a solid electrolyte having a NASICON crystal structure are described below in the following order: (1) preparation of raw material aqueous solution, (2) mixing, (3) pH adjustment, (4) spray drying, (5) calcination, (6) particle size adjustment, and (7) production of a solid electrolyte having a NASICON crystal structure.

(1) Preparation of raw material aqueous solution Raw materials containing lithium, aluminum, germanium, phosphorus, and optionally titanium, zirconia, and silicon, which are the constituent elements of the amorphous solid electrolyte precursor powder according to the present invention, are each completely dissolved in water to prepare an aqueous solution. The raw materials containing each constituent element are preferably nitrates, since this makes it easier for nitrogen to remain in the amorphous solid electrolyte precursor powder.

(2) Mixing This is a step of mixing the raw material aqueous solutions prepared in the above "(1) Preparation of raw material aqueous solutions" according to the composition of the target solid electrolyte precursor powder.
As a result of this mixing, a slurry containing the constituent elements of the solid electrolyte may be obtained by so-called coprecipitation, or a mixed solution may be obtained.

For example, when an acidic aqueous solution in which lithium nitrate, aluminum nitrate nonahydrate, and ammonium dihydrogen phosphate are dissolved is added to an alkaline aqueous solution of germanium dissolved in ammonia, the solution immediately becomes cloudy, and a slurry containing lithium, aluminum, germanium, phosphorus, and ammonia can be obtained by coprecipitation. In this mixing step, there is no need to particularly consider the liquid temperature, and it may or may not be heated. It is believed that the slurry contains constituent elements precipitated as hydroxides and constituent elements present as ions.
On the other hand, when the constituent elements of the amorphous solid electrolyte precursor powder are completely dissolved in the water as the solvent, a transparent mixed solution is formed instead of a slurry. In this case, a slurry is generated by coprecipitation in the next step "(3) pH adjustment."
In the present invention, the term "liquid" may be used as a concept including both the transparent mixed solution and the slurry produced by the coprecipitation.

(3) pH Adjustment This is a process for adjusting the pH of the liquid mixture to 2 or more and less than 4.5 by adding nitric acid to the liquid mixture, which is the mixed slurry or mixed solution containing lithium, aluminum, germanium, phosphorus and ammonia obtained in the above "(2) Mixing", or by increasing the ratio of the amount of nitrate in the raw material. As a result, even in the case of the mixed solution, a slurry is generated by coprecipitation, so that a pH-adjusted slurry having a pH of 2 or more and less than 4.5 can be obtained whether it is from the mixed slurry or the mixed solution.
In "(2) Mixing" or "(3) pH Adjustment", a supersaturated state in which the ion concentration product of the constituent elements is higher than the solubility product is achieved, and a slurry is generated by a coprecipitation method, because improving the uniformity of the constituent elements is essential for obtaining a solid electrolyte having a NASICON crystal structure.

The present inventors speculate that nitrogen is contained in the amorphous solid electrolyte precursor powder by adding nitric acid in this step and adjusting the pH of the mixed slurry to 2 or more and less than 4.5 as described below. The mixed slurry obtained in the above "(2) mixing" is considered to contain nitrate salts and ammonium salts. The present inventors believe that by adding nitric acid to the mixed slurry obtained in the above "(2) mixing" and adjusting the pH of the mixed slurry to 2 or more and less than 4.5, the amount of lithium nitrate, which has a high decomposition temperature, among nitrates such as lithium nitrate, ammonium nitrate, and aluminum nitrate contained in the pH-adjusted slurry is increased.
It is believed that the lithium nitrate contained in the pH-adjusted slurry generates lithium nitrite by heating in "(5) sintering" described below. As a result, it is presumed that nitrogen in the form of nitrite remains in the amorphous solid electrolyte precursor powder, and nitrogen is contained in the amorphous solid electrolyte precursor powder.

From this viewpoint, the pH of the pH-adjusted slurry is preferably 4.4 or less, and more preferably 4.3 or less. On the other hand, the pH of the pH-adjusted slurry is preferably 2.3 or more, and more preferably 2.6 or more.

The molar ratio of nitric acid to ammonia (NO ₃ /NH ₃ ) in the pH-adjusted slurry is preferably set to 1.0 or more and 3.0 or less.
Here, the number of moles of nitric acid and ammonia in the pH-adjusted slurry means the total number of moles of nitric acid molecules and ammonium molecules added until the pH-adjusted slurry is prepared. In the pH range of 2 or more and less than 4.5, each molecule is considered to exist in the form of nitrate ion and ammonium ion in the aqueous solution.

By adjusting the molar ratio of ammonia to nitric acid in the slurry in this manner, as described above, it is considered that the amount of lithium nitrate in the slurry increases, and nitrogen in the form of nitrous acid can be contained in the amorphous solid electrolyte precursor powder, which is preferable. From this viewpoint, it is more preferable that the molar ratio of nitric acid to ammonia ( _NO3 / _NH3 ) in the pH-adjusted slurry is 1.0 or more and 2.0 or less.

(4) spray drying;
This is a step in which the pH-adjusted slurry having a pH of 2 or more and less than 4.5 obtained in the above "(3) pH adjustment" is spray-dried using a spray dryer or the like to evaporate the water in the pH-adjusted slurry and obtain a dry powder. By spray-drying the slurry obtained through "(3) pH adjustment", the constituent elements present as ions in the slurry can be rapidly precipitated in a short period of time, reducing the non-uniformity of precipitation caused by the difference in solubility between the constituent elements, resulting in a dry powder with a uniform composition. Furthermore, the generation of germanium dioxide is suppressed, and a preferable amorphous solid electrolyte precursor powder can be obtained.

According to the inventor's preliminary tests, when a slurry adjusted to a pH of 2 or more and less than 4.5 was dried by evaporating to dryness using a hot plate or the like, rather than by spray drying, germanium dioxide was produced in the "(5) sintering" step described below, and a germanium dioxide peak was observed in the 2θ: 15° to 40° region in powder X-ray diffraction (XRD) measurements, making it impossible to obtain an amorphous solid electrolyte conductor oxide powder.

The drying temperature may be appropriately set so that no moisture remains in the resulting dry powder. However, since the dry powder is thought to contain nitrates and ammonium salts, similar to the slurry after pH adjustment, it is preferable that the inlet temperature of the spray dryer, which is a spray dryer, is 150 to 250°C and the hot air outlet temperature is 60 to 120°C.
This is because, if the inlet temperature is 150° C. or higher, a sufficient drying rate can be obtained and the situation in which the dried powder is likely to remain in the drying tower of the spray dryer can be avoided, and, if it is 250° C. or lower, the situation in which the components in the slurry are thermally decomposed and the desired dried powder cannot be obtained can be avoided. Also, if the hot air outlet temperature is 60° C. or higher, preferably 80° C. or higher, the moisture content in the dried powder can be sufficiently reduced, and, if it is 120° C. or lower, preferably 110° C. or lower, the situation in which segregation of germanium dioxide occurs can be avoided.

(5) Calcination This is a process in which the dried powder obtained in the above "(4) spray drying" is calcined and vitrified to obtain an amorphous solid electrolyte precursor powder. Specifically, the dried powder is placed in a container made of alumina or the like, and heated from room temperature to 300°C to 500°C at a heating rate of 0.1 to 20°C/min in an air atmosphere to obtain an amorphous solid electrolyte precursor powder. By calcining at 300°C to 500°C, the ammonium salt with a low decomposition temperature contained in the dried powder is removed, but the lithium nitrate contained in the dried powder becomes lithium nitrite, and nitrogen in the form of nitrite remains in the amorphous solid electrolyte precursor powder, and it is believed that nitrogen is contained in the amorphous solid electrolyte precursor powder according to the present invention.

(6) Particle Size Adjustment In the later-described "(7) Production of a solid electrolyte having a NASICON-type crystal structure", when the solid electrolyte obtained by crystallizing the amorphous solid electrolyte precursor powder is formed into a sheet, the particle size of the amorphous solid electrolyte precursor powder may be appropriately adjusted as necessary according to the target sheet thickness. Although a known method can be used for adjusting the particle size, wet grinding using a bead mill or the like is preferable. When wet grinding is performed, solid-liquid separation is performed after the wet grinding process, and the recovered amorphous solid electrolyte precursor powder after wet grinding is dried. The particle size of the amorphous solid electrolyte precursor powder obtained by drying is preferably 1 μm to 5 μm in terms of the cumulative 50% particle size (D ₅₀ ) on a volume basis determined by laser diffraction scattering particle size distribution measurement.

As a solvent for wet grinding, an organic solvent is preferable from the viewpoint of preventing lithium in the amorphous solid electrolyte precursor powder from ion-exchanging with protons, thereby reducing the ionic conductivity of the solid electrolyte, and specifically, IPA is preferable. This is because IPA volatilizes during drying after grinding, and does not remain in the amorphous solid electrolyte precursor powder. When a bead mill is used for grinding, zirconia beads are preferable as the beads. It is preferable to dry the amorphous solid electrolyte precursor powder after wet grinding at a temperature that is equal to or higher than the boiling point of the solvent used and equal to or lower than the firing temperature in the above-mentioned "(5) firing" to remove the solvent used.

(7) Production of solid electrolyte having NASICON type crystal structure To obtain the solid electrolyte having NASICON type crystal structure according to the present invention from the amorphous solid electrolyte precursor powder according to the present invention, the amorphous solid electrolyte precursor powder obtained in the above "(6) Particle size adjustment" may be placed in a container made of alumina, for example, or may be formed into a pellet or sheet, and then crystallized at a temperature exceeding 500°C. A solid electrolyte having NASICON type crystal structure can be obtained by crystallizing the amorphous solid electrolyte precursor powder by firing at a temperature of preferably 550°C to 900°C. The solid electrolyte having NASICON type crystal structure is preferably single-phase. This is because the ionic conductivity of the solid electrolyte is easily increased by being single-phase.
The obtained solid electrolyte having a NASICON type crystal structure can be used, for example, as a solid electrolyte in an all-solid-state battery.

The rate of temperature rise during firing is not particularly important, but is preferably 1 to 20°C/min. There are no particular restrictions on the firing atmosphere, but it is preferable to use an air atmosphere. The firing time is not particularly important, but it is preferable to set the firing time to 30 to 300 minutes after the temperature exceeds 500°C and reaches 900°C or less. It is presumed that during the firing, the nitrogen contained in the amorphous solid electrolyte precursor powder of the present invention functions as a sintering aid, causing crystal growth, reducing the number of crystal grain boundaries in the solid electrolyte, and improving ionic conductivity.

The solid electrolyte of the NASICON crystal structure contains lithium, aluminum, germanium, and phosphorus, which are the constituent elements of the amorphous solid electrolyte precursor powder before crystallization described above. Whether the solid electrolyte of the present invention has the NASICON crystal structure can be determined from the XRD profile measured using an XRD device. Specifically, the obtained XRD profile can be identified by comparing it with PDF (Powder Diffraction File) No. 01-080-1922 of the ICDD (International Center for Diffraction Data) using a computer attached to the XRD device, and it can also be confirmed whether it is a single phase.

Example 1
According to the flow showing the manufacturing process of the amorphous solid electrolyte precursor powder described above, the amorphous solid electrolyte precursor powder according to Example 1 was manufactured. Then, the manufactured amorphous solid electrolyte precursor powder according to Example 1 was analyzed and its characteristics were evaluated.

(1) Preparation of raw aqueous solutions In Example 1, (I) a germanium-containing aqueous solution and (II) a lithium, aluminum, and phosphorus-containing aqueous solution were prepared as raw aqueous solutions. Each of them will be described below.

(I) Germanium-containing aqueous solution 192.5 g of germanium dioxide was added to 4000 g of pure water, and the mixture was heated to 40° C. with stirring, and 97.5 g of ammonia water having a concentration of 28% by mass was further added as an alkali to dissolve the germanium oxide, thereby preparing a germanium-containing aqueous solution. The pH of the prepared aqueous solution was 10.7, which was alkaline.

(II) Lithium, aluminum, and phosphorus-containing aqueous solution: 15.5 g of lithium nitrate and 4.2 g of lithium hydroxide monohydrate were added to 336.3 g of pure water.
38.7 g of aluminum nitrate nonahydrate and 71.2 g of ammonium dihydrogen phosphate were added to prepare an aqueous solution containing lithium, aluminum, and phosphorus. The pH of the aqueous solution containing lithium, aluminum, and phosphorus thus prepared was 1.8, which was acidic.

(2) Mixing 720 g of the alkaline germanium-containing aqueous solution was taken and heated to 40° C. while stirring, and the entire amount (283.7 g) of the acidic lithium, aluminum, and phosphorus-containing aqueous solution was added thereto. The aqueous solution became cloudy immediately after the addition, and a white mixed slurry containing lithium, aluminum, germanium, phosphorus, ammonia, and water was obtained. The pH of the resulting mixed slurry was 4.7.

(3) pH Adjustment The mixed slurry was stirred while adding 5 g of nitric acid having a concentration of 60% by mass to adjust the pH to 4.3, thereby obtaining a pH-adjusted slurry. The temperature of the slurry at this time was 40° C.
Here, since 0.58 mol of nitric acid and 0.46 mol of ammonia were added before obtaining the pH-adjusted slurry, the molar ratio of the added nitric acid and ammonia (NO ₃ /NH ₃ ) was 1.27.

In the present invention, the pH value of the liquid was measured in accordance with JIS Z8802. A glass electrode hydrogen ion concentration indicator (model D-53) manufactured by Horiba Estec was used, calibrated with oxalate and phthalate buffer solutions in the acidic range, neutral phosphate and phosphate buffer solutions in the neutral range, and borate and carbonate buffer solutions in the alkaline range, as pH standard solutions.

(4) spray drying;
The pH-adjusted slurry was spray-dried using a spray dryer (SD-1000 manufactured by Tokyo Rikakikai Co., Ltd.) to evaporate the water in the pH-adjusted slurry and precipitate it in a solid phase at once, thereby obtaining a white powder. The spray-drying conditions were an inlet temperature of 180° C., an outlet temperature of 90° C., and an addition rate of the pH-adjusted slurry of 10 g/min.

(5) Calcination The dried powder obtained by the spray drying was placed in an alumina container, and the container was heated from room temperature to 400° C. at a heating rate of 5° C./min. After the temperature reached 400° C., the container was calcined for 120 minutes in an air atmosphere to obtain an amorphous solid electrolyte precursor powder.

(6) Particle Size Adjustment 40 g of the amorphous solid electrolyte precursor powder was loaded into a bead mill together with 160 g of φ1 mm Zr beads and 94.32 g of IPA, and wet-pulverized for 120 minutes. The powder was then placed in a dryer and dried at 100° C. for 3 hours to obtain an amorphous solid electrolyte precursor powder according to Example 1.
The amorphous solid electrolyte precursor powder according to Example 1 was subjected to volumetric particle size distribution measurement at a dispersion pressure of 5 bar using a laser diffraction scattering type particle size distribution measurement device (SYMPATEC's HELOS & RODOS (airflow type dispersion module)) to determine the volumetric cumulative 50% particle diameter (D ₅₀ ) of 1.8 μm.
A SEM photograph of the amorphous solid electrolyte precursor powder according to Example 1 at 30,000 times magnification is shown in FIG.

(7) Analysis and Characterization of Amorphous Solid Electrolyte Precursor Powder The amorphous solid electrolyte precursor powder obtained according to Example 1 was subjected to (I) elemental analysis, (II) nitrogen content analysis, (III) XRD measurement of the amorphous solid electrolyte precursor powder, and (IV) Raman spectrum measurement of the amorphous solid electrolyte precursor powder. Each method and result will be described below.
In the amorphous solid electrolyte precursor powder, the remainder of the amount of each element present by the above (I) elemental analysis and the amount of nitrogen present by the above (II) nitrogen amount analysis is considered to be the amount of oxygen present. This also applies to Examples 2 to 8 and Comparative Examples 1 to 3 described below.

(I) Elemental Analysis Sodium carbonate was added as a melting agent to the amorphous solid electrolyte precursor powder of Example 1 and melted to prepare an alkaline molten salt. Next, this molten salt was dissolved in nitric acid, and elemental analysis was performed on this solution using an ICP-OES device (ICP-720 manufactured by Agilent). The analytical values of each of the constituent elements, lithium, aluminum, phosphorus, germanium, titanium, zirconia, and silicon, are shown in Table 1.

(II) Nitrogen Content Analysis The nitrogen content in the amorphous solid electrolyte precursor powder according to Example 1 was analyzed using a nitrogen analyzer (EMGA-920 manufactured by Horiba, Ltd.) The nitrogen content analysis values are shown in Table 1.

(III) XRD Measurement of Amorphous Solid Electrolyte Precursor Powder XRD measurement was carried out under the following measurement conditions for the amorphous solid electrolyte precursor powder according to Example 1. The obtained XRD spectrum is shown in FIG.
<XRD Measurement Conditions>
Measuring device: XRD-6100 (manufactured by Shimadzu Corporation)
Tube: Cu
Tube voltage: 40 kV
Tube current: 30mA
Divergence slit: 1.0°
Scattering slit: 1.0°
Receiving slit: 0.3 mm
Step width: 0.02°/step
Measurement time: 0.25 sec

From Figure 1, it can be seen that the XRD spectrum of the amorphous solid electrolyte precursor powder of Example 1 shows a halo with a half-width of 2θ:2° or more in the region of 2θ:15° to 40°, confirming that it is amorphous. Note that all of the amorphous solid electrolyte precursor powders of Examples 2 to 8 and Comparative Examples 1 to 3 described below also show a halo with a half-width of 2θ:2° or more in the region of 2θ:15° to 40°, confirming that they are also amorphous.

(IV) Raman Spectroscopic Measurement of Amorphous Solid Electrolyte Precursor Powder The amorphous solid electrolyte precursor powder according to Example 1 was subjected to Raman spectroscopy at a laser wavelength of 532 nm using a laser Raman spectrophotometer (NRS-4500 manufactured by JASCO Corporation). The Raman spectrum obtained by the measurement is shown in FIG. 2. In the obtained Raman spectrum, a peak due to the symmetric stretching of nitrous acid (NO ₂ ) was detected at 1285 cm ⁻¹ , and it was found that the nitrogen contained in the amorphous solid electrolyte precursor powder was in the form of nitrous acid. The cases where a peak due to the symmetric stretching of nitrous acid (NO ₂ ) was detected were marked with ◯, and cases where no peak was detected were marked with ×, and are shown in Table 1.

In the amorphous solid electrolyte precursor powders according to Examples 2 to 8 described below, a peak due to symmetric stretching of nitrous acid (NO ₂ ) was detected at 1285 cm ⁻¹ ±5, indicating that the nitrogen contained therein is also in the form of nitrous acid. On the other hand, no peak was detected in the amorphous solid electrolyte precursor powders according to Comparative Examples 1 to 3.

(8) Production of solid electrolyte having NASICON type crystal structure and evaluation of its characteristics With respect to the solid electrolyte having NASICON type crystal structure, which is a compacted and sintered body obtained by sintering and crystallizing a compact of the amorphous solid electrolyte precursor powder according to Example 1, (I) production of the solid electrolyte having NASICON type crystal structure and evaluation by XRD measurement, and (II) evaluation of the ionic conductivity of the solid electrolyte having NASICON type crystal structure were carried out. Each method and result will be described below.

(I) Production of solid electrolyte having NASICON type crystal structure and evaluation by XRD measurement 0.5 g of the amorphous solid electrolyte precursor powder according to Example 1 was placed in a cylindrical container having a diameter of 10 mm and pressed at 360 MPa by a press to obtain a green compact. The green compact obtained was fired for 120 minutes after the furnace temperature reached 800° C. to produce a crystallized fired green compact.

The produced pressed and sintered body was subjected to XRD measurement under the same measurement conditions as in "(V) XRD measurement of amorphous solid electrolyte precursor powder" described above, and the result was compared with ICDD (International Center for Diffraction Data) PDF (Powder Diffraction File) No. 01-080-1922. As a result, the same diffraction peak as that of LiGe ₂ (PO ₄ ) ₃ , which is a solid electrolyte having a NASICON type crystal structure, was observed, and it was found that the pressed and sintered body obtained by crystallizing the amorphous solid electrolyte precursor powder according to Example 1 has a NASICON type crystal structure and is a single-phase solid electrolyte.

In addition, in the pressed and sintered bodies obtained by crystallizing the amorphous solid electrolyte precursor powders according to Examples 2 to 8 and Comparative Examples 1 to 3 described below, the crystal peak of LAGP, a solid electrolyte with a NASICON crystal structure, was observed, and it was found that the solid electrolyte had a NASICON crystal structure and was a single-phase solid electrolyte.

(II) Evaluation of ionic conductivity of solid electrolyte having NASICON crystal structure The solid electrolyte having NASICON crystal structure according to Example 1 was measured in the range of 100 Hz to 4 MHz by an AC impedance method using a potentio/galvanostat (1470E manufactured by Solartron) and a frequency response analyzer (1255B manufactured by Solartron) in an air atmosphere at a temperature of 25° C. Then, the resistance value of the solid electrolyte having NASICON crystal structure was obtained from a Cole-Cole plot (complex impedance plane plot) of the measured value, and the ionic conductivity of the solid electrolyte having NASICON crystal structure according to Example 1 was calculated from the obtained resistance value, and the calculated value is shown in Table 1.

Example 2
An amorphous solid electrolyte precursor powder according to Example 2 was obtained in the same manner as in Example 1, except that in "(3) pH adjustment" of Example 1, 10 g of nitric acid having a concentration of 60 mass % was added while stirring the obtained mixed slurry, thereby obtaining a pH-adjusted slurry having a pH adjusted to 3.9.
Here, since 0.63 mol of nitric acid and 0.46 mol of ammonia were added before the pH-adjusted slurry of Example 2 was obtained, the molar ratio (NO ₃ /NH ₃ ) of the added nitric acid and ammonia was 1.37.

The amorphous solid electrolyte precursor powder obtained according to Example 2 was subjected to the following analyses in the same manner as in Example 1: (7) Analysis and Characterization of Amorphous Solid Electrolyte Precursor Powder (I) Elemental Analysis, (II) Nitrogen Content Analysis, (III) XRD Measurement of Amorphous Solid Electrolyte Precursor Powder, (IV) Raman Spectral Measurement of Amorphous Solid Electrolyte Precursor Powder,
(8) Production of solid electrolyte having NASICON type crystal structure and evaluation of its characteristics (I) Production of solid electrolyte having NASICON type crystal structure and evaluation by XRD measurement, (II) Evaluation of ionic conductivity of solid electrolyte having NASICON type crystal structure,
The measurement results, including the elemental analysis results, the nitrogen content, the electrical conductivity, the pH value and (NO ₃ /NH ₃ ) ratio in the pH-adjusted slurry, and the presence or absence of a nitrite peak, are shown in Table 1.

Example 3
An amorphous solid electrolyte precursor powder according to Example 3 was obtained in the same manner as in Example 1, except that in "(3) pH adjustment" of Example 1, 20 g of nitric acid having a concentration of 60 mass % was added while stirring the obtained mixed slurry, thereby obtaining a pH-adjusted slurry in which the pH was adjusted to 3.6.
Here, since 0.73 mol of nitric acid and 0.46 mol of ammonia were added before the pH-adjusted slurry of Example 3 was obtained, the molar ratio (NO ₃ /NH ₃ ) of the added nitric acid and ammonia was 1.58.

The amorphous solid electrolyte precursor powder obtained in Example 3 was subjected to the same procedure as in Example 1.
"(7) Analysis and Characterization of Amorphous Solid Electrolyte Precursor Powder (I) Elemental Analysis, (II) Nitrogen Content Analysis, (III) XRD Measurement of Amorphous Solid Electrolyte Precursor Powder, (IV) Raman Spectroscopic Measurement of Amorphous Solid Electrolyte Precursor Powder,
(8) Production of solid electrolyte having NASICON type crystal structure and evaluation of its characteristics (I) Production of solid electrolyte having NASICON type crystal structure and evaluation by XRD measurement, (II) Evaluation of ionic conductivity of solid electrolyte having NASICON type crystal structure,
The measurement results, including the elemental analysis results, the nitrogen content, the electrical conductivity, the pH value and (NO ₃ /NH ₃ ) ratio in the pH-adjusted slurry, and the presence or absence of a nitrite peak, are shown in Table 1.

Example 4
An amorphous solid electrolyte precursor powder according to Example 4 was obtained in the same manner as in Example 1, except that in "(3) pH adjustment" of Example 1, 35 g of nitric acid having a concentration of 60 mass % was added while stirring the obtained mixed slurry, thereby obtaining a pH-adjusted slurry in which the pH was adjusted to 3.1.
Here, since 0.87 mol of nitric acid and 0.46 mol of ammonia were added before the pH-adjusted slurry of Example 4 was obtained, the molar ratio (NO ₃ /NH ₃ ) of the added nitric acid and ammonia was 1.89.

The amorphous solid electrolyte precursor powder according to Example 4 thus obtained was subjected to the same procedure as in Example 1.
"(7) Analysis and Characterization of Amorphous Solid Electrolyte Precursor Powder (I) Elemental Analysis, (II) Nitrogen Content Analysis, (III) XRD Measurement of Amorphous Solid Electrolyte Precursor Powder, (IV) Raman Spectroscopic Measurement of Amorphous Solid Electrolyte Precursor Powder,
(8) Production of solid electrolyte having NASICON type crystal structure and evaluation of its characteristics (I) Production of solid electrolyte having NASICON type crystal structure and evaluation by XRD measurement, (II) Evaluation of ionic conductivity of solid electrolyte having NASICON type crystal structure,
The measurement results, including the elemental analysis results, the nitrogen content, the electrical conductivity, the pH value and (NO ₃ /NH ₃ ) ratio in the pH-adjusted slurry, and the presence or absence of a nitrite peak, are shown in Table 1.

Example 5
An amorphous solid electrolyte precursor powder according to Example 5 was obtained in the same manner as in Example 1, except that in "(3) pH adjustment" of Example 1, 55 g of nitric acid having a concentration of 60 mass % was added while stirring the obtained mixed slurry, thereby obtaining a pH-adjusted slurry in which the pH was adjusted to 2.5.
Here, since 1.06 mol of nitric acid and 0.46 mol of ammonia were added before the pH-adjusted slurry of Example 5 was obtained, the molar ratio (NO ₃ /NH ₃ ) of the added nitric acid and ammonia was 2.30.

The amorphous solid electrolyte precursor powder according to Example 5 thus obtained was subjected to the same procedure as in Example 1.
"(7) Analysis and Characterization of Amorphous Solid Electrolyte Precursor Powder (I) Elemental Analysis, (II) Nitrogen Content Analysis, (III) XRD Measurement of Amorphous Solid Electrolyte Precursor Powder, (IV) Raman Spectroscopic Measurement of Amorphous Solid Electrolyte Precursor Powder,
(8) Production of solid electrolyte having NASICON type crystal structure and evaluation of its characteristics (I) Production of solid electrolyte having NASICON type crystal structure and evaluation by XRD measurement, (II) Evaluation of ionic conductivity of solid electrolyte having NASICON type crystal structure,
The measurement results, including the elemental analysis results, the nitrogen content, the electrical conductivity, the pH value and (NO ₃ /NH ₃ ) ratio in the pH-adjusted slurry, and the presence or absence of a nitrite peak, are shown in Table 1.

Example 6
In the "(1) Preparation of raw material aqueous solutions", "(I) Aqueous germanium solution" and "(II) Aqueous lithium, aluminum, and phosphorus-containing solution" were prepared in the same manner as in Example 1. In Example 6, "(III) Aqueous titanium-containing solution" was also prepared, which will be described.

(III) Titanium-containing aqueous solution 3.0 g of 28% ammonia water was added to 35.8 g of 35% hydrogen peroxide solution, and then 1.51 g of metatitanic acid was added and stirred until completely dissolved. The solution was added with "(II) lithium, aluminum, and phosphorus-containing aqueous solution" prepared in the same manner as in Example 1 to prepare a lithium, aluminum, phosphorus, and titanium-containing aqueous solution. The pH of the solution at this point was 4.0.

(2) Mixing 684 g of the alkaline germanium aqueous solution was taken and heated to 40° C. while stirring, and the entire amount of the lithium-, aluminum-, phosphorus-, and titanium-containing aqueous solution was added thereto. The aqueous solution became cloudy immediately after the addition, and a white mixed slurry was obtained. The pH of the resulting mixed slurry was 7.0.

(3) pH Adjustment 13 g of nitric acid having a concentration of 60% by mass was added to the resulting mixed slurry while stirring, to obtain a pH-adjusted slurry having a pH of 3.9.
Here, since 0.66 mol of nitric acid and 0.50 mol of ammonia were added before the pH-adjusted slurry of Example 6 was obtained, the molar ratio (NO ₃ /NH ₃ ) of the added nitric acid and ammonia was 1.33.

The obtained pH-adjusted slurry was used in the same manner as in Example 1 to obtain an amorphous solid electrolyte precursor powder according to Example 6.
The amorphous solid electrolyte precursor powder according to Example 6 thus obtained was subjected to the same procedure as in Example 1.
"(7) Analysis and Characterization of Amorphous Solid Electrolyte Precursor Powder (I) Elemental Analysis, (II) Nitrogen Content Analysis, (III) XRD Measurement of Amorphous Solid Electrolyte Precursor Powder, (IV) Raman Spectroscopic Measurement of Amorphous Solid Electrolyte Precursor Powder,
(8) Production of solid electrolyte having NASICON type crystal structure and evaluation of its characteristics (I) Production of solid electrolyte having NASICON type crystal structure and evaluation by XRD measurement, (II) Evaluation of ionic conductivity of solid electrolyte having NASICON type crystal structure,
The measurement results, including the elemental analysis results, the nitrogen content, the electrical conductivity, the pH value and (NO ₃ /NH ₃ ) ratio in the pH-adjusted slurry, and the presence or absence of a nitrite peak, are shown in Table 1.

Example 7
In the same manner as in Example 1, in "(1) Preparation of raw material aqueous solution", "(I) Germanium aqueous solution" and "(II) Lithium, aluminum, phosphorus-containing aqueous solution" were prepared. Then, in "(2) Mixing", 684 g of the alkaline "germanium aqueous solution" was taken and heated to 40° C. with stirring, and 4.1 g of zirconium oxynitrate was added and completely dissolved. When the entire amount of the "lithium, aluminum, phosphorus-containing aqueous solution" was added thereto, the aqueous solution became cloudy immediately after the addition, and a white mixed slurry was obtained. The pH of the resulting mixed slurry was 4.6.

(3) pH Adjustment 5 g of nitric acid having a concentration of 60% by mass was added to the resulting mixed slurry while stirring, to obtain a pH-adjusted slurry having a pH of 3.9.
Here, since 0.61 mol of nitric acid and 0.45 mol of ammonia were added before the pH-adjusted slurry of Example 7 was obtained, the molar ratio (NO ₃ /NH ₃ ) of the added nitric acid and ammonia was 1.37.

The obtained pH-adjusted slurry was used in the same manner as in Example 1 to obtain an amorphous solid electrolyte precursor powder according to Example 7.
The amorphous solid electrolyte precursor powder according to Example 7 thus obtained was subjected to the same procedure as in Example 1.
"(7) Analysis and Characterization of Amorphous Solid Electrolyte Precursor Powder (I) Elemental Analysis, (II) Nitrogen Content Analysis, (III) XRD Measurement of Amorphous Solid Electrolyte Precursor Powder, (IV) Raman Spectroscopic Measurement of Amorphous Solid Electrolyte Precursor Powder,
(8) Production of solid electrolyte having NASICON type crystal structure and evaluation of its characteristics (I) Production of solid electrolyte having NASICON type crystal structure and evaluation by XRD measurement, (II) Evaluation of ionic conductivity of solid electrolyte having NASICON type crystal structure,
The measurement results, including the elemental analysis results, the nitrogen content, the electrical conductivity, the pH value and (NO ₃ /NH ₃ ) ratio in the pH-adjusted slurry, and the presence or absence of a nitrite peak, are shown in Table 1.

Example 8
As in Example 1, in "(1) Preparation of raw material aqueous solution", "(I) Germanium aqueous solution" and "(II) Lithium, aluminum, phosphorus-containing aqueous solution" were prepared. Then, in "(2) Mixing", 720 g of the alkaline germanium aqueous solution was taken out, and _{10.2 g} of _Li2O11Si5 solution (Sigma-Aldrich) was added. The liquid was heated to 40°C while stirring, and the entire amount of the "lithium, aluminum, phosphorus-containing aqueous solution" was added thereto. The aqueous solution became cloudy immediately after the addition, and a white mixed slurry was obtained. The pH of the resulting mixed slurry was 4.4.

(3) pH Adjustment 9 g of nitric acid having a concentration of 60% by mass was added to the resulting mixed slurry while stirring, to obtain a pH-adjusted slurry having a pH of 3.9.
Here, since 0.62 mol of nitric acid and 0.46 mol of ammonia were added before the pH-adjusted slurry of Example 8 was obtained, the molar ratio (NO ₃ /NH ₃ ) of the added nitric acid and ammonia was 1.35.

The obtained pH-adjusted slurry was used in the same manner as in Example 1 to obtain an amorphous solid electrolyte precursor powder according to Example 8.
The amorphous solid electrolyte precursor powder according to Example 8 thus obtained was subjected to the same procedure as in Example 1.
"(7) Analysis and Characterization of Amorphous Solid Electrolyte Precursor Powder (I) Elemental Analysis, (II) Nitrogen Content Analysis, (III) XRD Measurement of Amorphous Solid Electrolyte Precursor Powder, (IV) Raman Spectroscopic Measurement of Amorphous Solid Electrolyte Precursor Powder,
(8) Production of solid electrolyte having NASICON type crystal structure and evaluation of its characteristics (I) Production of solid electrolyte having NASICON type crystal structure and evaluation by XRD measurement, (II) Evaluation of ionic conductivity of solid electrolyte having NASICON type crystal structure,
The measurement results, including the elemental analysis results, the nitrogen content, the electrical conductivity, the pH value and (NO ₃ /NH ₃ ) ratio in the pH-adjusted slurry, and the presence or absence of a nitrite peak, are shown in Table 1.

Comparative Example 1
An amorphous solid electrolyte precursor powder according to Comparative Example 1 was obtained by the same operation as in Example 1, except that in "(3) pH adjustment" of Example 1, 20 g of ammonia water having a concentration of 28 mass % was added while stirring the obtained slurry, and a pH-adjusted slurry was obtained in which the pH was adjusted to 5.5.
A SEM photograph of the amorphous solid electrolyte precursor powder according to Comparative Example 1 at a magnification of 30,000 times is shown in FIG.
Here, since 0.53 mol of nitric acid and 0.79 mol of ammonia were added before obtaining the pH-adjusted slurry according to Comparative Example 1, the molar ratio (NO ₃ /NH ₃ ) of the added nitric acid and ammonia was 0.68.

The amorphous solid electrolyte precursor powder obtained according to Comparative Example 1 was subjected to the following analyses in the same manner as in Example 1: "(7) Analysis and Characterization of Amorphous Solid Electrolyte Precursor Powder (I) Elemental Analysis, (II) Nitrogen Content Analysis, (III) XRD Measurement of Amorphous Solid Electrolyte Precursor Powder, (IV) Raman Spectral Measurement of Amorphous Solid Electrolyte Precursor Powder,
(8) Production of solid electrolyte having NASICON type crystal structure and evaluation of its characteristics (I) Production of solid electrolyte having NASICON type crystal structure and evaluation by XRD measurement, (II) Evaluation of ionic conductivity of solid electrolyte having NASICON type crystal structure,
The measurement results, including the elemental analysis result, the nitrogen content, the electrical conductivity, the pH value and the ( _NO3 / _NH3 ) ratio in the pH-adjusted slurry, and the presence or absence of a nitrite peak, are shown in Table 1. The nitrogen content was less than the measurement limit (0.01% by mass).

Comparative Example 2
32.3 g of germanium dioxide was added to 652.9 g of pure water and stirred, and 18.3 g of ammonia water with a concentration of 28% by mass was further added to dissolve germanium dioxide. 21.1 g of lithium acetate, 38.7 g of aluminum nitrate nonahydrate, 71.2 g of ammonium dihydrogen phosphate, and 95 g of nitric acid with a concentration of 60% by mass were further added in this order to obtain a raw aqueous solution with a pH of 0.2, and further ammonia water was added to adjust the pH to 5.3, thereby obtaining a raw aqueous solution with a pH adjustment. The obtained raw aqueous solution with a pH adjustment was transparent, not a slurry.
Here, since 1.21 mol of nitric acid and 4.61 mol of ammonia were added before obtaining the pH-adjusted transparent raw material aqueous solution according to Comparative Example 2, the molar ratio of the added nitric acid and ammonia ( _NO3 / _NH3 ) was 0.26.

Moisture was removed from the pH-adjusted transparent raw material aqueous solution according to Comparative Example 2 at 100° C. for 24 hours, and then the solution was further dried at 260° C. for 5 hours to obtain a dry powder. The dry powder obtained was calcined in a hydrogen atmosphere at 450° C. for 2 hours, and the calcined powder obtained was pulverized in the same manner as in Example 1 to obtain an amorphous solid electrolyte precursor powder according to Comparative Example 2.
A SEM photograph of the amorphous solid electrolyte precursor powder according to Comparative Example 2 at a magnification of 10,000 times is shown in FIG.

The amorphous solid electrolyte precursor powder obtained according to Comparative Example 2 was subjected to the same procedure as in Example 1.
"(7) Analysis and Characterization of Amorphous Solid Electrolyte Precursor Powder (I) Elemental Analysis, (II) Nitrogen Content Analysis, (III) XRD Measurement of Amorphous Solid Electrolyte Precursor Powder, (IV) Raman Spectroscopic Measurement of Amorphous Solid Electrolyte Precursor Powder,
(8) Production of solid electrolyte having NASICON type crystal structure and evaluation of its characteristics (I) Production of solid electrolyte having NASICON type crystal structure and evaluation by XRD measurement, (II) Evaluation of ionic conductivity of solid electrolyte having NASICON type crystal structure,
The measurement results, including the elemental analysis result, the nitrogen content, the electrical conductivity, the pH value and the ( _NO3 / _NH3 ) ratio in the pH-adjusted slurry, and the presence or absence of a nitrite peak, are shown in Table 1. The nitrogen content was less than the measurement limit (0.01% by mass).

Comparative Example 3
410 g of Ge(OEt) and 33.25 g of Al(OBt) were added to 97.68 g of butanol to obtain a germanium-aluminum solution in which germanium and aluminum were dissolved. Also, 32.61 g of lithium acetate and 9.098 g of ammonium dihydrogen phosphate were added to 379.64 g of pure water to obtain a lithium-phosphorus aqueous solution in which lithium and phosphorus were dissolved.

The germanium/aluminum solution and the lithium/phosphorus solution were mixed to obtain a mixed solution. The mixed solution was dried under an atmosphere of 100° C., and then vacuum dried at 110° C. to obtain a dry powder. The dry powder was fired at 400° C. under a nitrogen atmosphere, and the fired powder was pulverized in the same manner as in Example 1 to obtain an amorphous solid electrolyte precursor powder according to Comparative Example 3.
In Comparative Example 3, the solvent of the mixed solution was an organic solvent, which is different from the other Examples and Comparative Examples, and since pH adjustment with nitric acid was not required, the pH value of the mixed solution was not measured.

The amorphous solid electrolyte precursor powder obtained according to Comparative Example 3 was subjected to the following analyses in the same manner as in Example 1: "(7) Analysis and Characterization of Amorphous Solid Electrolyte Precursor Powder (I) Elemental Analysis, (II) Nitrogen Content Analysis, (III) XRD Measurement of Amorphous Solid Electrolyte Precursor Powder, (IV) Raman Spectral Measurement of Amorphous Solid Electrolyte Precursor Powder,
(8) Production of solid electrolyte having NASICON type crystal structure and evaluation of its characteristics (I) Production of solid electrolyte having NASICON type crystal structure and evaluation by XRD measurement, (II) Evaluation of ionic conductivity of solid electrolyte having NASICON type crystal structure,
The results of the measurements, including the elemental analysis result, the nitrogen content, the electrical conductivity, and the presence or absence of a nitrite peak, are shown in Table 1. The nitrogen content was less than the measurement limit (0.01% by mass).

<summary>

From Table 1, it was found that the solid electrolytes having a NASICON type crystal structure obtained by crystallizing the amorphous solid electrolyte precursor powders according to Examples 1 to 8 containing a predetermined amount of nitrogen exhibit higher ionic conductivity than the solid electrolytes having a NASICON type crystal structure obtained by crystallizing the amorphous solid electrolyte precursor powders according to Comparative Examples 1 to 3. The amorphous solid electrolyte precursor powder according to the present invention is an amorphous precursor powder containing lithium, aluminum, germanium, and phosphorus that can be crystallized to obtain a solid electrolyte exhibiting high ionic conductivity, and can be suitably used as a precursor powder for a solid electrolyte used in an all-solid-state battery.

Claims (10)

Lithium is 1% by mass or more and 4% by mass or less,
Aluminum: 0.5% by mass or more and 6% by mass or less;
germanium, 15% by mass or more and 35% by mass or less;
Phosphorus: 10% by mass or more and 30% by mass or less;
Contains 0.05% by mass or more and 3% by mass or less of nitrogen, with the remainder being oxygen;
Amorphous solid electrolyte precursor powder. The amorphous solid electrolyte precursor powder according to claim 1, wherein the amorphous solid electrolyte precursor powder contains 2.5 mass% or less of nitrogen. The amorphous solid electrolyte precursor powder according to claim 1 or 2, wherein the amorphous solid electrolyte precursor powder contains 0.1 mass % or more of nitrogen. The amorphous solid electrolyte precursor powder according to any one of claims 1 to 3, wherein the amorphous solid electrolyte precursor powder contains 1.5 mass% or less of nitrogen and 23.5 mass% or more of germanium. The amorphous solid electrolyte precursor powder according to any one of claims 1 to 4, containing the nitrogen in the form of nitrous acid. The amorphous solid electrolyte precursor powder according to any one of claims 1 to 5, further comprising one or more elements selected from the group consisting of titanium, zirconium and silicon in a total amount of 5 mass% or less. 1. A method for producing an amorphous solid electrolyte precursor powder comprising lithium, aluminum, germanium, phosphorus, nitrogen, and oxygen, the powder containing 1% by mass or more and 4% by mass or less of lithium, 0.5% by mass or more and 6% by mass or less of aluminum, 15% by mass or more and 35% by mass or less of germanium, 10% by mass or more and 30% by mass or less of phosphorus, 0.05% by mass or more and 3% by mass or less of nitrogen, and the remainder being oxygen,
A step of adjusting the pH of a liquid containing lithium, aluminum, germanium, phosphorus, and ammonia to 2 or more and less than 4.5 to obtain a pH-adjusted slurry;
spray drying the pH adjusted slurry to obtain a dry powder;
and calcining the dried powder at 300° C. or more and 500° C. or less. 8. The method for producing an amorphous solid electrolyte precursor powder according to claim 7, wherein a molar ratio of nitric acid to ammonia (NO ₃ /NH ₃ ) in the pH-adjusted slurry is 1.0 or more and 3.0 or less. The method for producing an amorphous solid electrolyte precursor powder according to claim 7 or 8, further comprising adding one or more elements selected from the group consisting of titanium, zirconium and silicon to the liquid containing lithium, aluminum, germanium, phosphorus and ammonia, so that the amorphous solid electrolyte precursor powder contains one or more elements selected from the group consisting of titanium, zirconium and silicon in a total amount of 5 mass% or less. A method for producing a solid electrolyte having a NASICON crystal structure, comprising a step of calcining the amorphous solid electrolyte precursor powder according to any one of claims 1 to 6 at a temperature higher than 500°C.