JP7698526B2 - Amorphous powder, powder packing containing the same, method for producing amorphous powder, and method for producing solid electrolyte - Google Patents

Description

This invention relates to an amorphous powder and a powder package containing the same, a method for producing the amorphous powder, and a method for producing a solid electrolyte.

As a solid electrolyte used in an all-solid-state battery, there is an ion conductor having a NASICON type crystal structure with high ionic conductivity. One known solid electrolyte having a NASICON type crystal structure is, for example, a solid electrolyte containing lithium, aluminum, germanium, phosphorus, and oxygen and represented by the general formula Li1 _{+ xAlxGe2 -x} ( _PO4 ) ₃ (x ranges from 0<x≦1, hereinafter sometimes referred to as "LAGP").

A solid electrolyte having a NASICON crystal structure may be provided as a coating 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. For example, Patent Documents 1 and 2 propose a method of forming this coating by using an amorphous powder containing, for example, lithium, aluminum, germanium, phosphorus, and oxygen. Here, the amorphous powder is crystallized to change the crystal structure from amorphous to NASICON type, and the NASICON type solid electrolyte is formed as a coating on the particle surface of the electrode active material. By changing the crystal structure to NASICON type, the solid electrolyte exhibits ionic conductivity, and by having this solid electrolyte exist as a coating on the surface of the electrode active material, high ionic conductivity can be obtained in the electrode layer of an all-solid-state battery.

JP 2018-37341 A JP 2019-50083 A

When mixing electrode active material powder and amorphous powder, it is important to mix the powders uniformly and reduce the variation in the mixed state from the viewpoint of uniformly forming a solid electrolyte coating on the particle surface of the electrode active material powder. In this regard, it has been confirmed that when the amorphous powder is mixed directly with the electrode active material powder, the powder cannot be mixed uniformly and the variation in the mixed state becomes large. As a result, a bias in ion conductivity occurs in the electrode layer, and not only is it not possible to obtain excellent battery characteristics in the ultimately manufactured all-solid-state battery, but the variation in the battery characteristics can also become large. In other words, it is sometimes impossible to stably obtain excellent battery characteristics in the all-solid-state battery.

The present invention aims to provide a technology that reduces the variation in the mixed state of amorphous powder when it is mixed with electrode active material powder.

The inventors conducted research to solve the above-mentioned problems and discovered that by adjusting the amount of moisture contained in the amorphous powder, it is possible to reduce the variation in the mixed state when the amorphous powder is mixed with the electrode active material powder.

The first aspect of the present invention is a method for producing a cellular membrane comprising the steps of:
An amorphous powder containing lithium, aluminum, germanium, phosphorus and oxygen,
The amorphous powder has a moisture content of 0.08 to 4 mass %.

A second aspect of the present invention is a method for producing a composition comprising the steps of:
The moisture content of the amorphous powder is 3% by mass or less.

A third aspect of the present invention is a method for producing a composition comprising the steps of:
The moisture content of the amorphous powder is 0.3 to 1% by mass.

A fourth aspect of the present invention is a method for producing a composition according to any one of the first to third aspects,
The amorphous powder 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;
The material contains phosphorus in an amount of 10 mass % or more and 30 mass % or less.

A fifth aspect of the present invention is a method for producing a composition comprising the steps of:
An amorphous powder according to any one of the first to fourth aspects;
A container for storing the amorphous powder in a sealed state,
The amorphous powder is contained in the container so that the moisture content of the powder is maintained at 0.08 to 4 mass %.

A sixth aspect of the present invention is the fifth aspect,
The container contains a hydrated material together with the amorphous powder.

A seventh aspect of the present invention is a method for producing a composition comprising the steps of:
A method for producing an amorphous powder containing lithium, aluminum, germanium, phosphorus and oxygen, comprising the steps of:
A moisture content adjusting step of adjusting the moisture content of the amorphous powder to 0.08% by mass to 4% by mass.
A method for producing an amorphous powder.

An eighth aspect of the present invention is the seventh aspect,
In the moisture content adjusting step, the moisture content of the amorphous powder is adjusted to 3 mass % or less.

A ninth aspect of the present invention is the seventh aspect,
In the moisture content adjusting step, the moisture content of the amorphous powder is adjusted to 0.3% by mass to 1% by mass.

A tenth aspect of the present invention is a method for producing a composition according to any one of the seventh to ninth aspects,
In the moisture content adjustment step, an amorphous powder having a moisture content of 0.05% by mass or less is exposed to an atmosphere containing moisture, thereby causing the amorphous powder to absorb water.

An eleventh aspect of the present invention is a method for producing a composition according to any one of the seventh to tenth aspects,
In the moisture content adjustment step, an amorphous powder having a moisture content of 0.05% by mass or less is accommodated in a container in a sealed state together with a hydrated member, thereby allowing the amorphous powder to absorb water.

A twelfth aspect of the present invention is a method for producing a composition according to any one of the eighth to eleventh aspects,
Before the moisture content adjustment step,
A mixing and slurrying step of obtaining a mixed slurry containing lithium, aluminum, germanium, and phosphorus;
a drying step of drying the mixed slurry to obtain a dry powder;
and a heat treatment step of heat treating the dry powder at 300° C. or higher and 500° C. or lower to obtain an amorphous powder having a moisture content of 0.05 mass % or less.

A thirteenth aspect of the present invention is a method for producing a composition comprising the steps of:
The method for producing a solid electrolyte having a NASICON crystal structure includes a calcination step of calcining the amorphous powder of any one of the first to fourth aspects to crystallize the powder.

According to the present invention, it is possible to reduce the variation in the mixed state of an amorphous powder when it is mixed with an electrode active material powder.

FIG. 1 is a schematic diagram for explaining the water content adjusting step in the examples. FIG. 2 is an XRD spectrum of the amorphous powder according to Example 1.

<One embodiment of the present invention>
An embodiment of the present invention will be described below. In this specification, each "particle" constitutes a "powder", and "powder" refers to a collection of "particles". In the following description, as a general rule, the term "particle" is used when focusing on the individual components that constitute the powder, and the term "powder" or "powder of particles" is used when focusing on the whole collection of particles.

(Amorphous powder)
The amorphous powder according to the present embodiment contains at least lithium, aluminum, germanium, phosphorus and oxygen as constituent elements. This amorphous powder is a precursor powder that is amorphous and forms a solid electrolyte having a NASICON crystal structure by crystallization. The powder having a NASICON crystal structure can be used as a solid electrolyte for an all-solid-state battery because it exhibits high ionic conductivity. Here, a solid electrolyte is a solid that can move ions (charged substances) by an externally applied electric field. The amorphous powder according to the present embodiment can be uniformly mixed with the electrode active material powder by adjusting the moisture content within a predetermined range. The composition and moisture content of the amorphous powder will be described in detail below.

The amorphous powder contains lithium, aluminum, germanium, phosphorus, oxygen, and other elements as necessary. There are no particular limitations on the content of these elements as long as they become a solid electrolyte having a NASICON crystal structure when crystallized. From the viewpoint of obtaining a solid electrolyte having a NASICON crystal structure that exhibits higher ionic conductivity, it is preferable that the content of each element in the amorphous powder be within the following ranges.

Lithium is an element that contributes to the formation of a NASICON-type crystal structure when the amorphous powder is crystallized. The lower limit of the lithium content is preferably 1.0 mass% or more, more preferably 1.5 mass% or more, and even more preferably 1.8 mass% or more. The upper limit is preferably 4.0 mass% or less, preferably 3.5 mass% or less, and even more preferably 3.3 mass% or less.

Aluminum is an element that contributes to the formation of a NASICON-type crystal structure when the amorphous powder is crystallized. The lower limit of the aluminum content is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, and even more preferably 2.0 mass% or more. The upper limit is preferably 6.0 mass% or less, more preferably 5.5 mass% or less, and even more preferably 5.0 mass% or less.

Germanium is an element that contributes to the formation of amorphous in the amorphous powder, and also contributes to the formation of a NASICON crystal structure when the amorphous powder is crystallized. The lower limit of the germanium content is preferably 15% by mass or more, more preferably 20% by mass or more, even more preferably 22% by mass or more, and most preferably 23.5% by mass or more. The upper limit is preferably 35% by mass or less, more preferably 33% by mass or less, and even more preferably 30% by mass or less.

Phosphorus is an element that contributes to the formation of amorphous in the amorphous powder, and also contributes to the formation of a NASICON crystal structure when the amorphous powder is crystallized. The lower limit of the phosphorus content is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. The upper limit is preferably 30% by mass or less, more preferably 28% by mass or less, and even more preferably 25% by mass or less.

The amorphous powder may contain elements other than the above-mentioned lithium, aluminum, germanium, and phosphorus, so long as they form a NASICON-type crystal structure when crystallized. The other elements may include, for example, at least one of titanium, zirconium, and silicon. The total content of the other elements is preferably 5% by mass or less, and more preferably 3% by mass or less.

Oxygen is the remainder of lithium, aluminum, germanium, phosphorus, and other elements. The oxygen content is the total content of each constituent element contained in the amorphous powder minus (100% by mass - total mass% of each constituent element), and is preferably 40% by mass or more and 55% by mass or less.

The amorphous powder may contain impurity elements other than those mentioned above, as long as the effect is not impaired.

The amorphous powder of this embodiment is configured to have a moisture content of 0.08% to 4% by mass. Since the amorphous powder is produced through drying and heat treatment, the moisture content tends to decrease after heat treatment due to heating, and is at most about 0.05% by mass. In this regard, in this embodiment, as described below, the moisture content is adjusted to 0.08% by mass or more. This improves the dispersibility of the amorphous powder in the electrode active material powder, and allows them to be mixed uniformly. On the other hand, if the moisture content is excessively high, the amorphous powder may aggregate, resulting in a decrease in dispersibility. However, by setting the moisture content to 4% by mass or less, the aggregation of the amorphous powder can be suppressed, and the mixability with the electrode active material powder can be maintained at a high level. From the viewpoint of further improving the mixability with the electrode active material, the moisture content is preferably 0.08% to 3% by mass, and more preferably 0.3% to 1% by mass.

The moisture content of the amorphous powder is a value measured using a Karl Fischer moisture analyzer, as described below. The moisture content obtained by this measurement mainly indicates the amount of moisture adhering to the surface of the amorphous powder.

The fact that an amorphous powder is amorphous means that, when the amorphous powder is subjected to powder X-ray diffraction (XRD) measurement, a halo is observed in the region of 2θ: 15° to 40°. Note that a halo is a gentle fluctuation in X-ray intensity, which is observed as a broad rise in an X-ray chart. The half-width of the halo is 2θ: 2° or more.

There are no particular limitations on the particle size of the amorphous powder, but it is preferable that the volume-based particle size distribution of the amorphous powder is measured using a laser diffraction scattering type particle size distribution measuring device, and the volume-based cumulative 50% particle size (D50) obtained by the measurement is 0.5 μm or more and 30 μm or less. By setting the particle size in this range, it becomes possible to suitably use the powder as a solid electrolyte in an all-solid-state battery.

The BET specific surface area of the amorphous powder is preferably 10 m ² /g or more and 100 m ² /g or less. By setting the BET specific surface area in this range, it becomes possible to suitably use the powder as a solid electrolyte of an all-solid-state battery.

(Method of producing amorphous powder)
Next, the above-mentioned method for producing the amorphous powder will be described in the order of (1) raw material aqueous solution preparation step, (2) mixing slurry step, (3) drying step, (4) heat treatment step, and (5) moisture content adjustment step. Note that (1) to (4) are not limited to the methods described below, and for example, the moisture content of the amorphous powder obtained using the manufacturing methods described in JP-A-2018-37341 and JP-A-2019-50083 may be adjusted.

(1) Raw material aqueous solution preparation step First, raw materials containing lithium, aluminum, germanium, phosphorus, and other elements as necessary, which are elements constituting the amorphous powder, are dissolved in water to prepare raw material aqueous solutions containing the respective constituent elements. The raw materials containing the respective constituent elements may be conventionally known. For example, it is advisable to prepare an aqueous solution in which germanium oxide such as germanium dioxide is dissolved, and an aqueous solution in which lithium nitrate, aluminum nitrate nonahydrate, ammonium dihydrogen phosphate, or the like is dissolved.

(2) Mixing and Slurrying Step Next, the raw material aqueous solution prepared in (1) is mixed according to the composition of the target amorphous powder, and a slurry containing the constituent elements of the solid electrolyte is obtained by the so-called coprecipitation method. 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, a slurry containing lithium, aluminum, germanium, phosphorus, etc. can be obtained by the coprecipitation method.

According to the coprecipitation method, the ion concentration product of the constituent elements in the slurry mixed with the raw material aqueous solution becomes supersaturated, where the solubility product is higher than the ion concentration product, and the number of nuclei of the precipitates increases, so that the particle size of the precipitates can be reduced, which makes it possible to make the BET specific surface area of the amorphous powder 20 ^m2 /g or more.

(3) Drying Step Next, the slurry obtained in (2) is dried to evaporate the water in the slurry, thereby obtaining a dry powder. The drying method is not particularly limited, but spray drying using a spray dryer or the like is preferable. According to the spray drying, the constituent elements present as ions in the slurry can be rapidly precipitated in a short time, and the non-uniformity of the precipitation caused by the difference in solubility between the constituent elements can be reduced. This makes it possible to obtain a dry powder with a uniform composition, and to more reliably form an amorphous powder in which the generation of germanium dioxide is suppressed. The drying temperature may be appropriately set to a temperature at which no water remains in the obtained dry powder. For example, 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°C or higher.

(4) Heat Treatment Step Next, the dry powder obtained in (3) is heat treated to vitrify it to obtain an amorphous powder. For example, the dry powder is placed in an alumina container 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.

The amorphous powder obtained by heat treatment has a reduced moisture content due to the heating during the above-mentioned (3) drying step and (4) heat treatment step. For example, the moisture content of the amorphous powder after heat treatment is 0.05% by mass or less.

(5) Moisture Content Adjustment Step Next, in this embodiment, the moisture content of the amorphous powder obtained in (4) is adjusted. Specifically, the amorphous powder after the heat treatment and having a moisture content of 0.05% by mass or less is exposed to a moisture-containing atmosphere for a predetermined time to allow the amorphous powder to absorb water and adjust the moisture content of the amorphous powder to 0.08% by mass to 4% by mass. In this way, the amorphous powder of this embodiment is obtained.

The water absorption method is not particularly limited, but may be a method of directly spraying water on the amorphous powder to absorb water, or a method of indirectly absorbing water by exposing the amorphous powder to an atmosphere containing water. In the indirect water absorption method, for example, a hydrated member (e.g., paper soaked in water) may be enclosed in a container together with the amorphous powder and sealed. To adjust the moisture content of the amorphous powder, if the powder is directly absorbed, the amount of water sprayed may be adjusted. If the powder is indirectly absorbed, the amount of moisture in the hydrated member may be adjusted. From the viewpoint of increasing the mixability of the amorphous powder with the electrode active material powder, the indirect water absorption method is preferred. This is because the indirect water absorption method makes it easier to adjust the moisture content and suppresses the aggregation of the amorphous powder due to water absorption, compared to the direct water absorption method.

The container used when indirectly absorbing water is not particularly limited as long as it can be sealed and can suppress moisture permeation, and any known container can be used.

In addition, a particle size adjustment step for adjusting the particle size of the amorphous powder may be provided between the heat treatment step (4) and the moisture content adjustment step (5). For example, when the solid electrolyte is formed into a sheet, the particle size may be appropriately adjusted according to the target sheet thickness. Although a known method can be used for particle size adjustment, wet pulverization using a bead mill or the like is preferable. When wet pulverization is performed, solid-liquid separation is performed after the wet pulverization process, and the amorphous powder after wet pulverization is dried. The particle size of the amorphous powder obtained by drying after particle size adjustment is not particularly limited, but it is more preferable that the cumulative 50% particle size (D ₅₀ ) based on volume determined by laser diffraction scattering type particle size distribution measurement is 0.5 μm to 5 μm.

(Powder packaging)
The above-mentioned amorphous powder may vary in moisture content by decreasing or increasing the moisture content due to exposure to the atmosphere. If the moisture content fluctuates excessively, the amorphous powder may aggregate, which may impair the mixability with the electrode active material powder. Therefore, from the viewpoint of maintaining the moisture content of the amorphous powder at 0.08% by mass to 4% by mass and ensuring long-term storage stability, it is preferable to store the amorphous powder in a container and make it into a powder package. The powder package will be specifically described below.

The powder packaging of this embodiment includes an amorphous powder and a container that contains the amorphous powder in a sealed state, and is configured to maintain the moisture content of the amorphous powder at 0.08 to 4% by mass. By sealing the amorphous powder in the container, the moisture can be retained within the container even if moisture evaporates from the amorphous powder. This makes it possible to suppress a reduction in the moisture content of the amorphous powder and maintain the moisture content at 0.08 to 4% by mass.

It is preferable that the powder package contains a hydrated member in a container together with the amorphous powder. The hydrated member allows the amorphous powder to absorb water in the container, and fluctuations in the moisture content can be more reliably suppressed. This allows the amorphous powder to be more reliably stored for long periods of time.

From the viewpoint of indirectly absorbing water into the amorphous powder, it is preferable to prevent the hydrated member from coming into direct contact with the amorphous powder. For example, a tray or a tub may be placed on the amorphous powder, and the hydrated member may be placed on top of the tray. The amount of water in the hydrated member may be changed as appropriate depending on the desired amount of water in the amorphous powder.

When storing hydrated members in a powder package, for example, amorphous powder with a moisture content of 0.05% by mass or less after the heat treatment process and a member containing a predetermined amount of moisture may be stored in a container, and the amorphous powder may be allowed to absorb water in the container and stored so as to maintain the predetermined moisture content. Alternatively, for example, amorphous powder that has been adjusted to a predetermined moisture content in advance may be stored in a container together with the hydrated member, and stored so as to maintain the predetermined moisture content.

There are no particular limitations on the container used for the powder packaging, so long as it can be sealed and can suppress moisture permeation. For example, known containers such as resin-laminated aluminum bags can be used.

The material to be hydrated is not particularly limited as long as it is capable of absorbing and retaining moisture, and it is advisable to use well-known materials such as paper.

(Mixed powder for electrode layer and electrode layer)
Next, a mixed powder for an electrode layer obtained by mixing the above-mentioned amorphous powder and electrode active material powder will be described.

The mixed powder for the electrode layer is obtained by mixing the amorphous powder and the electrode active material powder described above. As described above, the amorphous powder of this embodiment has excellent mixability (uniformity of mixing) with the electrode active material powder, so that the uneven distribution of the amorphous powder and the electrode active material powder can be suppressed in the mixed powder for the electrode layer. Specifically, when a predetermined amount of samples are taken from the mixed powder for the electrode layer and the concentration of the component derived from the amorphous powder contained in each sample or the concentration of the element derived from the electrode active material powder is measured, the standard deviation σ of these concentrations can be preferably 1.0 or less, more preferably 0.5 or less, and even more preferably 0.3 or less. In other words, the variation in the concentration of the predetermined element in each sample can be suppressed and the concentration can be made uniform.

There are no particular limitations on the electrode active material powder, so long as it is used as a positive electrode active material or a negative electrode active material, and any conventionally known material can be used. There are no particular limitations on the particle size of the electrode active material powder, and it is preferable that it be, for example, 0.5 μm to 20 μm.

The electrode layer can be produced, for example, by forming the mixed powder for the electrode layer into a sheet and firing it at a temperature exceeding 500°C to crystallize the amorphous powder. The resulting electrode layer is configured so that the surface of the electrode active material powder is uniformly coated with a solid electrolyte having a NASICON type crystal structure. Therefore, in the electrode layer, high ionic conductivity can be obtained while minimizing the bias. Moreover, when multiple electrode layers are produced, the variation in the ionic conductivity of each layer can be reduced. By employing such an electrode layer in an all-solid-state battery, it is possible to stably obtain excellent battery characteristics in the all-solid-state battery.

The reason why high ionic conductivity can be obtained in the electrode layer of this embodiment is presumably because the solid electrolyte forms a NASICON-type crystal structure to exhibit high ionic conductivity, and the mixed powder for the electrode layer has little variation in its mixed state, i.e., the powders are not unevenly distributed and there is little bias in their concentrations. This means that the number of interfaces between the solid electrolyte and the active material in the electrode layer formed from the mixed powder for the electrode layer is greater than when the mixed state varies greatly, making it easier for ionic conduction to occur.

The solid electrolyte of the NASICON crystal structure contains lithium, aluminum, germanium, and phosphorus, which are the constituent elements of the amorphous powder before crystallization described above. Whether or not a solid electrolyte 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 Centre for Diffraction Data) using a computer attached to the XRD device.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these in any way.

<Production of amorphous powder>
In the present examples, the amorphous powders of Examples 1 to 6 and Comparative Examples 1 and 2 were produced by carrying out the following steps in this order: (1) raw material aqueous solution preparation step, (2) mixing and slurrying step, (3) drying step, (4) heat treatment step, (5) particle size adjustment step, and (6) moisture content adjustment step, as shown below.

Example 1
(1) Raw Material Aqueous Solution Preparation Step First, (I) a germanium aqueous solution and (II) an aqueous solution containing lithium, aluminum, and phosphorus were prepared as raw material aqueous solutions. Each of these will be described below.

(I) Aqueous solution of germanium compound 385 g of germanium dioxide (99.999% manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added to 8000 g of pure water, and the mixture was heated to 40° C. with stirring. 195 g of ammonia water (28% manufactured by Nacalai Tesque, Inc.) with a concentration of 28% by mass was further added as an alkali to dissolve germanium dioxide, thereby preparing an aqueous solution of a germanium compound. The pH value of the prepared aqueous solution was 10.7, which was alkaline.

(II) Lithium, aluminum, and phosphorus-containing aqueous solution 217 g of lithium nitrate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., 98.0+%), 394 g of aluminum nitrate nonahydrate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., 98.0+%), and 725 g of ammonium dihydrogen phosphate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., 98.0+%) were added to 1500 g of pure water to prepare a lithium, aluminum, and phosphorus-containing aqueous solution. The pH value of the prepared lithium, aluminum, and phosphorus-containing aqueous solution was 1.4, which was acidic.

(2) Mixing and Slurrying Step 7200 g of the alkaline germanium aqueous solution was taken and heated to 40° C. while stirring, and the entire amount (2837 g) of the prepared lithium, aluminum, and phosphorus-containing aqueous solution was added thereto. The aqueous solution became cloudy immediately after the addition, and a white mixed slurry of lithium, aluminum, germanium, phosphorus, ammonia, and water was obtained. The pH value of the obtained white slurry was 4.3.

(3) Drying step The mixed slurry was spray-dried using a spray dryer (SD-1000 manufactured by Tokyo Rikakikai Co., Ltd.) to evaporate the water in the mixed 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 a mixed slurry addition rate of 10 g/min.

(4) Heat Treatment Step 50 g of the dried powder obtained by spray drying was placed in an alumina container, and the temperature was increased from room temperature to 400° C. at a heating rate of 5° C./min. After the temperature reached 400° C., the mixture was heat-treated for 120 minutes in an air atmosphere to obtain a heat-treated powder.

(5) Particle size adjustment step 400 g of the heat-treated powder was loaded into a bead mill together with 1600 g of φ1 mm Zr beads and 943.2 g of isopropyl alcohol (IPA) and wet-milled for 120 minutes. The wet-milled heat-treated powder was then placed in a dryer and dried at 100 ° C for 3 hours to remove the IPA and obtain a dry powder with adjusted particle size. The moisture content of the particle size-adjusted dry powder obtained in this step was measured in the same manner as the moisture content analysis described below, and was 0.04% by mass.

(6) Moisture content adjustment process The moisture content adjustment process was carried out as shown in FIG. 1. Specifically, first, a nylon inner bag and an outer bag (width 450 mm, length 700 mm) were prepared, and the inner bag was placed in the outer bag to form a double layer to form a container 11. Next, 200 g of the particle size-adjusted dry powder 10 after the particle size adjustment was taken and placed in the nylon inner bag in the container 11. In addition, a paper rag (product name JK Wiper, manufactured by Nippon Paper Crecia Co., Ltd.) was impregnated with 0.12 g of pure water to prepare a hydrated member, and then a stainless steel deep bat 13 containing the hydrated member was prepared and placed on the particle size-adjusted dry powder 10 in the inner bag, and the inlets of the inner bag and outer bag were sealed and left to stand for 12 hours. After standing, the stainless steel deep bat 13 containing the hydrated member 12 was removed from the inner bag, the inlet of the container 11 was sealed again, the container 11 was shaken, and left to stand for 1 hour to obtain the amorphous powder of Example 1.

Example 2
In Example 2, an amorphous powder was obtained in the same manner as in Example 1, except that in (6) Adjustment of Moisture Content in Example 1, the moisture content adjustment condition was changed from 0.12 g to 0.52 g in the amount of pure water impregnated into the paper cloth.

Example 3
In Example 3, an amorphous powder was obtained in the same manner as in Example 1, except that in (6) Adjustment of Moisture Content in Example 1, the moisture content adjustment condition was changed from 0.12 g to 0.92 g in the amount of pure water impregnated into the paper cloth.

Example 4
In Example 4, the same procedure as in Example 1 was followed, except that in (6) Adjustment of Moisture Content in Example 1, the moisture content adjustment condition was changed to 1.52 g of pure water impregnated into the paper cloth from 0.12 g, and an amorphous powder was obtained.

Example 5
In Example 5, an amorphous powder was obtained in the same manner as in Example 1, except that in (6) Adjustment of Moisture Content in Example 1, the moisture content adjustment condition was changed to the amount of pure water impregnated into the paper cloth from 0.12 g to 1.92 g.

Example 6
In Example 6, an amorphous powder was obtained in the same manner as in Example 1, except that in (6) Adjustment of Moisture Content in Example 1, the moisture content adjustment condition was changed to the amount of pure water impregnated into the paper cloth from 0.12 g to 5.92 g.

Comparative Example 1
In Comparative Example 1, an amorphous powder was obtained in the same manner as in Example 1, except that in (6) Adjustment of Moisture Content in Example 1, the moisture content adjustment condition was changed from 0.12 g to 9.92 g of pure water to be impregnated into the paper cloth.

Comparative Example 2
In Comparative Example 2, an amorphous powder was obtained in the same manner as in Example 1, except that in (6) Adjustment of Moisture Content in Example 1, the moisture content adjustment condition was changed from 0.12 g to 0.02 g in the amount of pure water impregnated into the paper cloth.

<Evaluation method>
Next, the obtained amorphous powders of the Examples and Comparative Examples were subjected to moisture content analysis, XRD measurement of the amorphous powder, elemental analysis, particle diameter _D50 measurement, and BET specific surface area measurement. The obtained amorphous powders of the Examples and Comparative Examples were mixed with an electrode active material to evaluate the mixability. Furthermore, the obtained amorphous powders of the Examples and Comparative Examples were crystallized to prepare pressed powder sintered bodies, and XRD measurement of the pressed powder sintered bodies was performed to evaluate whether they were solid electrolytes with a NASICON type crystal structure. Each method and result will be described below.

(moisture content analysis)
The moisture content of the amorphous powder was measured under the following measurement conditions, and the measurement results are shown in Table 1.
Measurement equipment: Karl Fischer moisture analyzer (Hiranuma trace moisture analyzer AQ-2100 and moisture vaporizer EV-2000, manufactured by Hiranuma Sangyo Co., Ltd.)
Measurement sample amount: 0.3 g
Carrier gas: Nitrogen gas
Carrier gas flow rate: 0.3 L/min
Interval time: 15sec
Vaporization chamber temperature: 100°C

(XRD Measurement of Amorphous Powder)
XRD measurement of the amorphous powder was carried out under the following 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

(Elemental analysis)
0.1 g of the amorphous powder according to the obtained Examples and Comparative Examples and 1 g of NaK carbonate were weighed into a platinum crucible and melted at about 900°C. After melting, the solution was infused with hot water, and 10 mL of nitric acid was added to dissolve the solution, which was then diluted 500 times to prepare one solution sample. One solution sample was subjected to elemental analysis using ICP-OES, and the analytical values of each constituent element are shown in Table 1. The amount of oxygen present is considered to be the amount obtained by subtracting the total content of each constituent element analytical value contained in the amorphous powder by elemental analysis (100% by mass - the total value of the mass% of each constituent element). This also applies to Examples 2 to 6 and Comparative Examples 1 and 2, which will be described later.

(Particle diameter _D50 measurement)
The volumetric particle size distribution of the obtained amorphous powders of the Examples and Comparative Examples was measured 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 size ( _D50 ). The measurement results are shown in Table 1.

(BET specific surface area measurement)
The BET specific surface area of the amorphous powders obtained in the Examples and Comparative Examples was measured using a BET specific surface area measuring device (Macsorb, manufactured by Mountec Co., Ltd.). After degassing by flowing nitrogen gas into the measuring device for 20 minutes at 105°C, the measurement was performed by the BET single point method while flowing a mixed gas of nitrogen and helium ( _N2 : 30 volume %, He: 70 volume %). The measured BET specific surface area values are shown in Table 1.

(mixability)
The amorphous powders of the examples and comparative examples obtained were mixed with an electrode active material, and the uniformity of the mixture with the electrode active material was analyzed. The uniformity of the mixture was measured by preparing five samples of mixed powders mixed with an electrode active material powder containing a Co element, which is an element not contained in the amorphous powder of Example 1 obtained, dissolving the five mixed powder samples, and determining the standard deviation σ of the Co element content contained in the solution. The smaller the value of the standard deviation σ, the more uniformly the amorphous powder and the electrode active material are mixed, and the higher the mixing uniformity. The reason for measuring the Co element content is that Co is an element that is not common to the amorphous powder and the electrode active material powder, and the variation in the Co content can be used to grasp the variation in the mixed state of the amorphous powder and the electrode active material powder.

Specifically, first, 16 g of the amorphous powder of the examples and comparative examples and 4 g of LiNiCoMnO ₂ powder (manufactured by MTI) with a D ₅₀ of 6.9 μm as an electrode active material were mixed using a micro-type see-through V-type mixer (manufactured by Tsutsui Rikagaku Kikai Co., Ltd., model VM-2 mixing container V-C) under conditions of a rotation speed of 70 rpm and a rotation time of 5 minutes. Then, five samples were prepared by taking 0.5 g of each of the obtained mixed powder. Then, for the five samples, 0.1 g of the sample and 1 g of NaK carbonate were weighed out in a platinum crucible and melted at about 900 ° C., and after melting, the solution was leached in hot water, and 10 mL of nitric acid was added to dissolve the solution, which was then diluted 500 times to prepare five solution samples. The amount of Co in the solution was measured for the five solution samples using ICP-OES. The standard deviation σ of the Co amount in the five obtained solutions was determined, and the determined standard deviation σ is shown in Table 2. When preparing a solution sample by diluting the solution, the obtained solution was transferred to a 250-ml volumetric flask and made to volume with pure water, and then 5 ml of the constant volume solution was taken, 5 ml of nitric acid was added, and the volume was made to volume with pure water in a 100-ml volumetric flask.

(XRD measurement of compacted powder sintered body)
First, 0.5 g of each of the amorphous powders obtained in the Examples and Comparative Examples was sampled and placed in a cylindrical container with a diameter of 10 mm, and pressed at 360 MPa using a press to obtain a green compact. The green compact of the obtained amorphous powder was fired for 120 minutes after the furnace temperature reached 800° C., producing a crystallized green compact.

The obtained pressed and sintered body was subjected to XRD measurement under the same measurement conditions as the "XRD measurement of amorphous powder" described above, and by comparing it with the JCPDS card No. 01-080-1922 of LAGP, a solid electrolyte with a NASICON type crystal structure, it was confirmed whether the crystal structure of the pressed and sintered body was NASICON type.

<Evaluation Results>
The results obtained by the above-mentioned evaluation methods are summarized in Tables 1 and 2 below.

As shown in Table 1, it was confirmed that the amorphous powders in Examples 1 to 6, Comparative Example 1, and Comparative Example 2 all contained 2.43 mass% Li, 3.02 mass% Al, 25.1 mass% Ge, and 21.7 mass% P as constituent elements. It was also confirmed that the particle diameter D ₅₀ was 1.8 μm and the BET specific surface area was 27 m ² /g. It was also confirmed that the moisture content of the amorphous powder was 0.1 mass% in Example 1, 0.3 mass% in Example 2, 0.5 mass% in Example 3, 0.08 mass% in Example 4, 1 mass% in Example 5, 3 mass% in Example 6, 5 mass% in Comparative Example 1, and 0.05 mass% in Comparative Example 2 by changing the amount of moisture impregnated into the paper cloth in the moisture content adjustment.

XRD measurements were also performed on the amorphous powder of Example 1, and the XRD spectrum shown in Figure 2 was obtained. In the XRD spectrum of Figure 2, a halo with a half-width of 2θ:2° or more was observed in the region of 2θ:15° to 40°. This confirmed that the amorphous powder of Example 1 was amorphous. The amorphous powders of the other Examples and Comparative Examples were also confirmed to be amorphous.

In addition, when XRD measurements were performed on the pressed and sintered bodies formed using the amorphous powders of the examples and comparative examples, the crystal peak of LAGP, a solid electrolyte with a NASICON crystal structure, was observed in all pressed and sintered bodies. This confirmed that the amorphous powders of the examples and comparative examples are precursor powders that, when crystallized, form a solid electrolyte with a NASICON crystal structure.

In addition, when the mixability of the amorphous powders of the examples and comparative examples was evaluated, it was confirmed that, when five samples were taken for each of Examples 1 to 6 in which the moisture content of the amorphous powder was within the range of 0.08% by mass to 4% by mass, the standard deviation σ of the Co content in each sample was 0.5 or less, as shown in Table 2. In other words, it was confirmed that the variation in the Co content in each sample was small, and the variation in the mixed state of the amorphous powder and the electrode active material was small, and they were mixed uniformly.
In contrast, in Comparative Example 1 in which the moisture content of the amorphous powder was 5% by mass and Comparative Example 2 in which the moisture content was 0.05% by mass, the standard deviations σ were 1.43 and 1.49, respectively, and it was confirmed that the amorphous powder and the electrode active material were not mixed uniformly. This is presumably because the moisture content of the amorphous powder was excessively low or high, causing the amorphous powder to aggregate and resulting in low mixability with the electrode active material powder.

In addition, in Examples 2 to 5, the standard deviation σ was made smaller, and it was confirmed that the amorphous powder and the electrode active material could be mixed more uniformly by setting the moisture content of the amorphous powder to 0.3% by mass to 1% by mass.

As described above, the amorphous powder with a moisture content of 0.08% to 4% by mass can be mixed uniformly with the electrode active material, and when an electrode layer is formed, a coating film made of a solid electrolyte can be formed uniformly on the surface of the electrode active material, thereby suppressing bias in ion conductivity in the electrode layer and realizing excellent battery characteristics.

Claims (15)

An amorphous powder containing lithium, aluminum, germanium, phosphorus and oxygen,
The moisture content of the amorphous powder is 0.08 to 4% by mass,
The amorphous powder is a precursor powder for forming a solid electrolyte having a NASICON type crystal structure . 2. The amorphous powder according to claim 1, which is used for mixing with an electrode active material powder and for firing the mixed powder for an electrode layer obtained by said mixing. The moisture content of the amorphous powder is 3% by mass or less.
3. The amorphous powder according to claim 1 or 2 . The moisture content of the amorphous powder is 0.3 to 1% by mass or less.
4. The amorphous powder according to claim 1 . The amorphous powder 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;
Contains phosphorus in an amount of 10% by mass or more and 30% by mass or less;
5. The amorphous powder according to claim 1 . The amorphous powder according to any one of claims 1 to 5 ,
A container for storing the amorphous powder in a sealed state,
The amorphous powder is contained in the container so that the moisture content thereof is maintained at 0.08 to 4% by mass.
Powder packaging. The container contains a hydrated material together with the amorphous powder.
The powder package according to claim 6 . A method for producing an amorphous powder containing lithium, aluminum, germanium, phosphorus and oxygen, comprising the steps of:
A moisture content adjusting step of adjusting the moisture content of the amorphous powder to 0.08% by mass to 4% by mass ,
The amorphous powder is a precursor powder for forming a solid electrolyte having a NASICON type crystal structure.
Method for producing amorphous powder. The method for producing an amorphous powder according to claim 8, which is used for mixing with an electrode active material powder and for firing the mixed powder for an electrode layer obtained by said mixing. In the moisture content adjustment step, the moisture content of the amorphous powder is adjusted to 3% by mass or less.
The method for producing an amorphous powder according to claim 8 or 9 . In the moisture content adjustment step, the moisture content of the amorphous powder is adjusted to 0.3% by mass to 1% by mass.
The method for producing an amorphous powder according to any one of claims 8 to 10 . In the moisture content adjustment step, an amorphous powder having a moisture content of 0.05% by mass or less is exposed to an atmosphere containing moisture, thereby causing the amorphous powder to absorb water.
The method for producing an amorphous powder according to any one of claims 8 to 11 . In the moisture content adjustment step, an amorphous powder having a moisture content of 0.05% by mass or less is accommodated in a container in a sealed state together with a hydrated member, thereby allowing the amorphous powder to absorb moisture.
The method for producing an amorphous powder according to any one of claims 8 to 12 . Before the moisture content adjustment step,
A mixing and slurrying step of obtaining a mixed slurry containing lithium, aluminum, germanium, and phosphorus;
a drying step of drying the mixed slurry to obtain a dry powder;
A heat treatment step of heat treating the dry powder at 300° C. or more and 500° C. or less to obtain an amorphous powder having a moisture content of 0.05% by mass or less.
The method for producing an amorphous powder according to any one of claims 8 to 13 . The method includes a firing step of firing a mixed powder for an electrode layer obtained by mixing the amorphous powder according to any one of claims 1 to 5 with an electrode active material powder,
In the calcination step, an amorphous powder, which is a precursor powder for forming the solid electrolyte having a NASICON crystal structure, is calcined and crystallized .