JP7777424B2 - Inorganic solid electrolyte dispersion and method for producing inorganic solid electrolyte dispersion - Google Patents

Description

The present invention relates to an inorganic solid electrolyte dispersion and a method for producing an inorganic solid electrolyte dispersion.

Conventionally, batteries such as lithium-ion batteries (batteries using liquid electrolyte materials) have a structure in which a positive electrode material (Ni, Mn, Co, LiCoO2 _{, etc.} ) and a negative electrode material (graphite, etc.) are separated by a separator (porous resin), with a liquid binder (polymer material) sandwiched between them. To date, extensive research has been conducted into improvements to the positive electrode material, negative electrode material, separator, and binder themselves, as well as improvements to the battery packaging method.

In recent years, efforts have been made to use inorganic solid electrolytes instead of liquid binders (electrolyte materials) in liquid electrolyte materials, which require a liquid. This eliminates the need for separators, increases the degree of freedom for charge movement between the positive and negative electrode materials to generate electricity, and improves current output efficiency. Batteries that use positive and negative electrode materials and inorganic solid electrolytes are called all-solid-state batteries because they are all composed of solids. Oxide-based solid electrolytes and sulfide-based solid electrolytes are being considered as inorganic solid electrolytes for use in all-solid-state batteries.

For example, Patent Document 1 discloses a solid electrolyte composition that combines an inorganic solid electrolyte with acid-modified cellulose nanofibers.

Patent No. 6714172

While there has been much research into improving battery characteristics by making various modifications and improvements to solid electrolyte materials, as in Patent Document 1, there has not yet been much research into solid electrolyte materials that can increase productivity when manufacturing all-solid-state batteries.

For example, even if a solid electrolyte material is expected to improve battery characteristics, if the solid electrolyte material is not uniformly dispersed in the coating liquid (inorganic solid electrolyte dispersion) used to apply it to electrode materials, etc., or if the dispersibility deteriorates during storage for a certain period of time between immediately after preparation of the coating liquid and application, this can reduce productivity when manufacturing all-solid-state batteries.

The present invention aims to provide an inorganic solid electrolyte dispersion in which the inorganic solid electrolyte is uniformly dispersed and can maintain its dispersion for a long period of time, as well as a method for producing the same.

As a result of extensive research to solve the above problems, the inventors have come up with the following invention and found that it is possible to solve the above problems. Specifically, the present invention is as follows:

[1] An inorganic solid electrolyte dispersion obtained by dispersing an inorganic solid electrolyte powder used for a solid electrolyte of an all-solid-state battery in a solvent, wherein the inorganic solid electrolyte powder has a median diameter (D50) of 6.5 μm or less, as obtained from a volume-based particle size distribution measured by a laser diffraction particle size distribution measurement method, and a standard deviation (σ50) based on the median diameter (D50) of 3.5 μm or less.
[2] The inorganic solid electrolyte dispersion according to [1], wherein the content of zirconia in the inorganic solid electrolyte dispersion is 23 mass % or less.
[3] A method for producing an inorganic solid electrolyte dispersion, comprising producing the inorganic solid electrolyte dispersion according to [1] or [2] using a wet atomization device.
[4] The method for producing an inorganic solid electrolyte dispersion according to [3], wherein the chamber and nozzle of the wet atomization device are made of ceramic.

The present invention provides an inorganic solid electrolyte dispersion in which the inorganic solid electrolyte is uniformly dispersed and retains its dispersion for a long period of time, as well as a method for producing the same.

1 is a schematic diagram showing a schematic configuration of a wet atomization device according to the present embodiment. 1A and 1B are electron microscope photographs, in which (a) is an electron microscope photograph of an untreated inorganic solid electrolyte dispersion (oxide-based), and (b) is an electron microscope photograph of an inorganic solid electrolyte dispersion (oxide-based) that has been treated with a microparticle treatment device for 50 passes. Photographs showing the state of precipitation, where (a) is a photograph showing the state of precipitation in an untreated inorganic solid electrolyte dispersion (oxide-based), and (b) is a photograph of an inorganic solid electrolyte dispersion (oxide-based) after 20 passes through a microparticle processing device and 48 hours have passed. 1A and 1B are electron microscope photographs of an untreated inorganic solid electrolyte dispersion (sulfide-based), and FIG. 1B is an electron microscope photograph of an inorganic solid electrolyte dispersion (sulfide-based) after 20 passes through a microparticle processing device.

The following describes an embodiment of the present invention.

[Inorganic solid electrolyte dispersion]
The inorganic solid electrolyte dispersion according to this embodiment is prepared by dispersing an inorganic solid electrolyte powder used as a solid electrolyte material for an all-solid-state battery in a solvent.

(Inorganic solid electrolyte powder)
The inorganic solid electrolyte in the inorganic solid electrolyte powder according to this embodiment refers to an inorganic solid electrolyte, and a solid electrolyte refers to a solid electrolyte capable of transferring ions therein. Because it does not contain an organic substance as the main ion-conducting material, it is clearly distinguished from organic solid electrolytes (polymer electrolytes such as polyethylene oxide (PEO) and organic electrolyte salts such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)). Furthermore, because inorganic solid electrolytes are solid in a steady state, they are typically not dissociated or liberated into cations and anions. In this respect, they are also clearly distinguished from electrolytic solutions or inorganic electrolyte salts in which cations and anions are dissociated or liberated in a polymer (LiPF ₆ , LiBF ₄ , LiFSI, LiCl, etc.). The inorganic solid electrolyte is not particularly limited as long as it has ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, but generally does not have electronic conductivity.

The inorganic solid electrolyte powder has a median diameter (D50) obtained from the volume-based particle size distribution measured by a laser diffraction particle size distribution measurement method of 6.5 μm or less, preferably 5 μm or less, more preferably 3.5 μm or less, and even more preferably 2.5 μm or less, and preferably 2 μm or less, and more preferably 1 μm or less. Furthermore, in practice, the median diameter (D50) is 0.1 μm or more.

Furthermore, the standard deviation (σ50) based on the median diameter (D50) is 3.5 μm or less, preferably 2 μm or less, with the lower limit being practically about 0.1 μm.
If the standard deviation (σ50) exceeds 3.5 μm, it may become difficult to obtain uniform dispersion, and the long-term dispersion retention may be easily reduced.

Typical examples of inorganic solid electrolytes include (i) oxide-based inorganic solid electrolytes and (ii) sulfide-based inorganic solid electrolytes. Sulfide-based inorganic solid electrolytes are preferred in terms of high ionic conductivity and ease of interparticle interface bonding. Oxide-based solid electrolytes are also preferred in terms of low cost. When the all-solid-state battery according to this embodiment is an all-solid-state lithium-ion secondary battery, the inorganic solid electrolyte preferably has the ionic conductivity of lithium ions.

(i) Oxide-based inorganic solid electrolyte The oxide-based inorganic solid electrolyte is preferably a compound that contains oxygen atoms (O), has the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and has electronic insulation. The oxide-based inorganic solid electrolyte preferably has an ionic conductivity of 1×10 ⁻⁶ S/cm or more, more preferably 5×10 ⁻⁶ S/cm or more, and particularly preferably 1×10 ⁻⁵ S/cm or more. There is no particular upper limit, but a practical value is 1×10 ⁻¹ S/cm or less.

Specific examples of the compound include Li _xa La _ya TiO ₃ [xa=0.3 to 0.7, ya=0.3 to 0.7] (LLT), Li _xb La _yb Zr _zb Mbb _mb O _nb (Mbb is at least one element selected from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, xb satisfies 5≦xb≦10, yb satisfies 1≦yb≦4, zb satisfies 1≦zb≦4, mb satisfies 0≦mb≦2, and nb satisfies 5≦nb≦20), and Li _xc B _yc Mcc _zc O _nc (Mcc is at least one element selected from C, S, Al, Si, Ga, Ge, In, and Sn, xc satisfies 0<xc≦5, yc satisfies 0<yc≦1, zc satisfies 0<zc≦1, and nc satisfies 0<nc≦6.), Li _xd (Al,Ga) _yd (Ti,Ge) _zd Si _ad P _md O _nd (wherein 1≦xd≦3, 0≦yd≦1, 0≦zd≦2, 0≦ad≦1, 1≦md≦7, 3≦nd≦13), Li _(3-2xe) Mee _xe DeeO (xe is a number of 0 or more and 0.1 or less, Mee is a divalent metal atom, and Dee is a halogen atom or a combination of two or more halogen atoms.), Li _xf Si _yf O _zf (1≦xf≦5, 0<yf≦3, 1≦zf≦10), Li _xg S _yg O _zg (1≦xg≦3, 0<yg≦2, 1≦zg≦10), Li ₃ BO ₃ -Li ₂ SO ₄ , Li ₂ O-B ₂ O ₃ -P ₂ O ₅ , Li ₂ O-SiO ₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li ₃ PO _(4-3/2w) N _w (w is w<1), Li _3.5 Zn _0.25 GeO ₄ having a LISICON (lithium superionic conductor) type crystal structure, La _0.55 Li having a perovskite type crystal structure _{0.35TiO 3} , LiTi ₂ P ₃ O ₁₂ and Li _1+xh+yh (Al,Ga) _xh (Ti,Ge) _2-xh Si _yh P _3-yh O ₁₂ (where 0≦xh≦1, 0≦yh≦1) having a NASICON (sodium superionic conductor) type crystal structure, Li ₇ La ₃ Zr ₂ O ₁₂ (LLZ) and Li _6.25 La ₃ Zr ₂ Al _0.25 O ₁₂ (LLZO) having a garnet type crystal structure, etc. Phosphorus compounds containing Li, P, and O are also desirable. Examples include lithium phosphate ( _Li3PO4 ), LiPON _in which some of the oxygen in lithium phosphate is substituted with nitrogen, LiPOD1 (D1 is at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc.), etc. Also preferably used is LiAlON (A1 is at least one selected from Si, B, Ge, Al, C, Ga, etc.).

(ii) Sulfide-Based Inorganic Solid Electrolyte The sulfide-based inorganic solid electrolyte is preferably a compound that contains a sulfur atom (S), has the ionic conductivity of a metal belonging to Group 1 or 2 of the periodic table, and has electronic insulation. The sulfide-based inorganic solid electrolyte preferably contains at least Li, S, and P as elements and has lithium ion conductivity, but may contain elements other than Li, S, and P depending on the purpose or case.

An example of a sulfide-based inorganic solid electrolyte is a lithium ion conductive sulfide-based inorganic solid electrolyte that satisfies the composition shown in formula (1) below.

L _a1 M _b1 P _c1 S _d1 A _e1 ...Formula (1)
In the formula, L represents an element selected from Li, Na, and K, and Li is preferred. M represents an element selected from B, Zn, Sn, Si, Cu, Ga, Sb, Al, and Ge. A represents an element selected from I, Br, Cl, and F. a1 to e1 represent the composition ratio of each element, and a1:b1:c1:d1:e1 satisfies the ratio of 1-12:0-5:1:2-12:0-10. a1 is preferably 1-9, and more preferably 1.5-7.5. b1 is preferably 0-3, and more preferably 0-1. d1 is preferably 2.5-10, and more preferably 3.0-8.5. e1 is preferably 0-5, and more preferably 0-3.

The composition ratio of each element can be controlled by adjusting the compounding ratio of the raw material compounds when producing the sulfide-based inorganic solid electrolyte, as shown below.

The sulfide-based inorganic solid electrolyte may be amorphous (glass) or crystallized (glass-ceramic), or may be only partially crystallized. For example, a Li-P-S-based glass containing Li, P, and S, or a Li-P-S-based glass-ceramic containing Li, P, and S can be used.
The sulfide-based inorganic solid electrolyte can be produced by reacting at least two or more raw materials selected from the group consisting of lithium sulfide (Li ₂ S), phosphorus sulfide (e.g., diphosphorus pentasulfide (P ₂ S ₅ )), elemental phosphorus, elemental sulfur, sodium sulfide, hydrogen sulfide, lithium halides (e.g., LiI, LiBr, LiCl), and sulfides of the elements represented by M above (e.g., SiS ₂ , SnS, GeS ₂ ).

In the Li-P-S-based glass and Li-P-S-based glass ceramics, the ratio of Li ₂ S to P ₂ S ₅ , in terms of the molar ratio of Li ₂ S:P ₂ S ₅ , is preferably 60:40 to 90:10, more preferably 68:32 to 78:22. By setting the ratio of Li ₂ S to P ₂ S ₅ within this range, it is possible to increase the lithium ion conductivity. Specifically, it is possible to preferably achieve a lithium ion conductivity of 1×10 ⁻⁴ S/cm or more, more preferably 1×10 ⁻³ S/cm or more. There is no particular upper limit, but a practical upper limit is 1×10 ⁻¹ S/cm or less.

As specific examples of sulfide-based inorganic solid electrolytes, examples of combinations of raw materials are shown below. For example, Li ₂ S-P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -LiCl, Li ₂ S-P ₂ S ₅ -H ₂ S, Li ₂ S-P ₂ S ₅ -H ₂ S-LiCl, Li ₂ S-LiI-P ₂ S ₅ , Li ₂ S-LiI-Li ₂ O-P ₂ S ₅ , Li ₂ S-LiBr-P ₂ S ₅ , Li ₂ S-Li ₂ OP ₂ S ₅ , Li ₂ S-Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ S-P ₂ S ₅ -P ₂ O ₅ , Li ₂ SP ₂ S ₅ -SiS ₂ , Li ₂ S-P ₂ S ₅ -SiS ₂ -LiCl, Li ₂ S-P ₂ S ₅ -SnS, Li ₂ S-P ₂ S ₅ -Al ₂ S ₃ , Li ₂ S-GeS ₂ , Li ₂ S-GeS _{2 -ZnS} , _Li2S - _Ga2S3 , _Li2S - _{GeS2 - Ga2S3} , _Li2S - _{GeS2 - P2S5} , _Li2S - _{GeS2 - Sb2S5} , _Li2S - _{GeS2 - Al2S3} , Li ₂ S-SiS ₂ , Li ₂ S-Al ₂ Examples _of the _{sulfide-based inorganic solid electrolyte} material include _Li2S -SiS2- _Al2S3 , _Li2S - _SiS2 - _P2S5 , Li2S- _{SiS2 -P2S5- LiI} , _Li2S -SiS2 _{- LiI} , _Li2S - _{SiS2 - Li4SiO4} , _{Li2S - SiS2 - Li3PO4} , _Li10GeP2S12 , _{and Li10SnP2S12 .} However, the mixing ratio of each raw material is not important. Examples of methods for synthesizing a _sulfide -based inorganic solid electrolyte material using such a raw material composition include _an amorphization method. Examples of amorphization methods include mechanical milling, solution processing, and melt quenching. This is because processing can be carried out at room temperature, and the manufacturing process can be simplified.

(solvent)
In the inorganic solid electrolyte material dispersion, the inorganic solid electrolyte powder is dispersed in a solvent. The solvent preferably contains a non-aqueous dispersion medium. When the inorganic solid electrolyte material dispersion contains a non-aqueous dispersion medium, decomposition and deterioration of the inorganic solid electrolyte particles can be prevented, and surface oxidation of the particles can be suppressed. Furthermore, when biomass nanofibers are mixed with the inorganic solid electrolyte particles, they are more likely to be mixed uniformly.

In this embodiment, when the solvent in the inorganic solid electrolyte material dispersion contains a non-aqueous dispersion medium, this includes not only a form in which the solvent contains only a non-aqueous dispersion medium (no aqueous dispersion medium), but also a form in which the solvent contains an aqueous dispersion medium. However, when the solvent contains an aqueous dispersion medium, the water content in the solvent does not exceed 50 ppm.

A non-aqueous dispersion medium usually refers to a non-aqueous dispersion medium other than water, and includes non-aqueous dispersion mediums containing water (mixed dispersions of water and non-aqueous dispersion mediums) as long as the water content in the solvent is 50 ppm or less.

Such a non-aqueous dispersion medium may be any medium capable of dispersing the components contained in the inorganic solid electrolyte material dispersion, and examples thereof include various organic solvents. Organic solvents that can be used as non-aqueous dispersion media include alcohol compound solvents, ether compound solvents, amide compound solvents, amino compound solvents, ketone compound solvents, aromatic compound solvents, aliphatic compound solvents, nitrile compound solvents, and ester compound solvents. Among these, amide compound solvents, hydrocarbon compound solvents (aromatic compound solvents and aliphatic compound solvents), ether compound solvents, ketone compound solvents, and ester compound solvents are preferred.

Examples of alcohol compound solvents include methyl alcohol, ethyl alcohol, 1-propyl alcohol, 2-propyl alcohol, 2-butanol, ethylene glycol, propylene glycol, 1,6-hexanediol, cyclohexanediol, 1,3-butanediol, and 1,4-butanediol.

Examples of ether compound solvents include alkylene glycols (such as triethylene glycol), alkylene glycol monoalkyl ethers (such as ethylene glycol monomethyl ether), alkylene glycol dialkyl ethers (such as ethylene glycol dimethyl ether), dialkyl ethers (such as diisopropyl ether and dibutyl ether), and cyclic ethers (such as tetrahydrofuran and dioxane (including the 1,2-, 1,3-, and 1,4-isomers)).

Examples of amide compound solvents include N,N-dimethylformamide, N-methyl-2-pyrrolidone, 2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, 2-pyrrolidinone, ε-caprolactam, formamide, N-methylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, N-methylpropanamide, and hexamethylphosphoric triamide.

Examples of the amino compound solvent include triethylamine, diisopropylethylamine, and tributylamine.
Examples of ketone compound solvents include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexanone, cycloheptanone, dipropyl ketone, dibutyl ketone, diisopropyl ketone, diisobutyl ketone, isobutyl propyl ketone, sec-butyl propyl ketone, pentyl propyl ketone, and butyl propyl ketone.

Examples of aromatic compound solvents include benzene, toluene, and xylene.
Examples of the aliphatic compound solvent include hexane, heptane, octane, decane, cyclohexane, cyclooctane, paraffin, gasoline, naphtha, kerosene, and diesel.
Examples of nitrile compound solvents include acetonitrile, propylonitrile, and isobutyronitrile.
Examples of ester compound solvents include ethyl acetate, butyl acetate, propyl acetate, propyl butyrate, isopropyl butyrate, butyl butyrate, isobutyl butyrate, butyl pentanoate, ethyl isobutyrate, propyl isobutyrate, isopropyl isobutyrate, isobutyl isobutyrate, propyl pivalate, isopropyl pivalate, butyl pivalate, and isobutyl pivalate.

The non-aqueous dispersion medium contained in the solvent may be one type or two or more types, and preferably two or more types.
When the solvent contains two or more non-aqueous dispersion media, a combination of two or more non-aqueous dispersion media selected from the group consisting of hydrocarbon compound solvents, ether compound solvents, ketone compound solvents and ester compound solvents is preferred.

Taking productivity into consideration, the content of inorganic solid electrolyte powder in the inorganic solid electrolyte material dispersion is preferably 1 to 20 mass%, more preferably 1 to 15 mass%, and even more preferably 1 to 10 mass%.

Biomass nanofibers can also be added to the inorganic solid electrolyte material dispersion. Examples of biomass nanofibers include cellulose nanofibers, chitin nanofibers, chitosan nanofibers, and silk nanofibers. The average fiber diameter of the biomass nanofibers is preferably 10 to 100 nm, more preferably 10 to 40 nm, and even more preferably 10 to 25 nm. The average length of the biomass nanofibers is preferably 0.5 to 100 μm, and more preferably 1 to 30 μm.

[Method of producing inorganic solid electrolyte dispersion]
The method for producing an inorganic solid electrolyte dispersion according to this embodiment is a method for producing the above-described inorganic solid electrolyte aqueous dispersion of the present invention using a wet atomization apparatus.

(Wet type atomization device)
FIG. 1 is a schematic diagram showing the general configuration of a wet atomization device used in this embodiment.
As shown in Fig. 1, the wet atomization apparatus 1 has a raw material tank 2, a liquid supply pump 3, a pressure intensifier 4, a high-pressure filter 5, a chamber 6, and a heat exchanger 7. The raw material tank 2 stores inorganic solid electrolyte powder in a slurry state. The liquid supply pump 3 supplies the inorganic solid electrolyte powder from the raw material tank 2 to the pressure intensifier 4. The pressure intensifier 4 pressurizes the inorganic solid electrolyte powder supplied from the liquid supply pump 3. The high-pressure filter 5 filters out coarse particles from the pressurized inorganic solid electrolyte powder. The chamber 6 performs atomization by high-pressure spraying of the inorganic solid electrolyte powder from a nozzle (not shown) at a spray pressure of 100 to 245 MPa and a spray velocity of 440 to 700 m/s.

In addition, the wet atomization apparatus 1 used to process inorganic solid electrolyte powder requires a higher level of airtightness than when processing ordinary raw materials. When processing an oxide-based solid electrolyte material dispersion, for example, airtightness is required to prevent the inorganic solid electrolyte powder from oxidizing. Furthermore, when processing a sulfide-based solid electrolyte dispersion, for example, airtightness is required to prevent the release of highly toxic gases to the outside even if they are generated when the inorganic solid electrolyte powder (oxide-based) reacts with moisture or water. Furthermore, when processing inorganic solid electrolyte powder (sulfide-based), internal gas management may be required. Therefore, the wet atomization apparatus 1 requires a structure that circulates the internal gas while ensuring airtightness.

The wet atomization apparatus 1 of this embodiment is airtight by covering it with a glove box or the like. Furthermore, the wet atomization apparatus 1 can be equipped with an inert gas supply unit 8a and a gas circulation purification unit 9, thereby ensuring the safety of the gas within the glove box. An oxygen concentration meter 14 and a moisture concentration meter 15 may also be provided to adjust the ventilation and amount of inert gas, etc.

Furthermore, it is preferable to use ceramics for the chamber 6 and the nozzle (not shown) instead of conventional metals such as stainless steel. This provides superior abrasion resistance and solvent resistance compared to metals such as stainless steel, and minimizes contamination. As a result, a dispersion containing zirconia at a content of 23 mass% or less can be obtained.
The chamber 6 may be a system in which inorganic solid electrolyte powder is atomized by colliding it from a nozzle toward a ball, or a system in which inorganic solid electrolyte powder is atomized by colliding it with other inorganic solid electrolyte powders from two or more nozzles.

(Method for producing inorganic solid electrolyte dispersion using a wet atomization device)
The method for producing an inorganic solid electrolyte dispersion using a wet atomization device will be described in detail below.

In a wet-type atomization apparatus 1 partitioned by a glove box or the like, a mixture of inorganic solid electrolyte powder and a solvent is charged into a raw material tank 2 .
Next, the inorganic solid electrolyte powder in the raw material tank 2 is supplied to the pressure boosting chamber of the pressure booster 4 via the liquid supply pump 3. The supplied inorganic solid electrolyte powder is pressurized by the pressure booster 4. The pressurized inorganic solid electrolyte powder passes through a high-pressure filter 5, and is then supplied to a chamber 6 and sprayed. The atomization treatment can be repeated a required number of times, for example, about 1 to 50 times, preferably about 1 to 40 times, more preferably about 1 to 30 times, even more preferably about 1 to 20 times, and particularly preferably about 1 to 10 times.

[Method of manufacturing all-solid-state battery]
The method for producing an all-solid-state battery using the inorganic solid electrolyte dispersion of this embodiment is not particularly limited as long as it includes a step of forming a solid electrolyte-containing layer using the inorganic solid electrolyte dispersion. The solid electrolyte-containing layer can be formed, for example, by applying the dispersion to a substrate to form a coating layer, and then drying the coating layer.

The inorganic solid electrolyte dispersion of this embodiment has uniformly dispersed inorganic solid electrolyte particles in the dispersion, making it less likely for the concentration of inorganic solid electrolyte particles to become uneven during coating. Furthermore, because the dispersion maintains its dispersion for a long period of time, re-dispersion is not required even if a certain amount of time has passed between the preparation of the dispersion and coating. As a result, productivity can be improved when manufacturing all-solid-state batteries.

Substrates used for coating include, for example, current collectors and transfer sheets. Transfer sheets include, for example, resin sheets such as fluorine-based resin sheets and metal sheets. Coating methods include common methods such as doctor blade coating, die coating, gravure coating, spray coating, electrostatic coating, and bar coating.

The drying temperature is, for example, 40°C or higher, and preferably 60 to 220°C. Examples of methods for drying the coating layer include common methods such as warm air/hot air drying, infrared drying, reduced pressure drying, and dielectric heating drying. Examples of drying atmospheres include inert gas atmospheres such as Ar gas atmospheres and nitrogen gas atmospheres. Furthermore, drying may be carried out under atmospheric pressure or reduced pressure.

(Experimental Example A: Comparative Examples 1 and 2, Examples 1 to 5)
LLZO ( _{Li6.25La3Zr2Al0.25O12} ), an inorganic solid electrolyte particle (oxide-based), was mixed with an organic solvent (N- _methyl - _{2 - pyrrolidone} ) to a concentration of 5% by mass to prepare a 50 ml mixed solution. This mixed solution was subjected to wet atomization using a wet atomization apparatus (manufactured by Sugino Machine Co., Ltd., named "Starburst" except that the chamber and nozzle were made of ceramic (zirconia)) at a pressure of 200 MPa, with a 0.12 mm nozzle, and the number of passes shown in Table 1 to produce an inorganic solid electrolyte aqueous dispersion. For comparison, a mixed solution (number of passes: 0) without wet atomization was also prepared.

Next, the particle size distribution of each dispersion and mixed liquid was measured to determine the median diameter (D50) and its standard deviation (σ50). The measuring instrument used was a laser diffraction/scattering particle size distribution measuring device "LA-960" manufactured by Horiba, Ltd. The results are shown in Table 1.
The dispersion state (uniform dispersion) of the inorganic solid electrolyte particles in each dispersion and the mixed solution was observed immediately after the wet atomization treatment. Furthermore, the dispersion state (long-term dispersion retention) was also observed 48 hours after the wet atomization treatment. The results are shown in Table 1.
The evaluation criteria for each observation were as follows:
Uniform dispersion and long-term dispersion retention A: Inorganic solid electrolyte particles are dispersed, and the overall state is cloudy. B: The inorganic solid electrolyte particles are dispersed in the center and are cloudy, but the top is slightly transparent or a small amount of solid matter has accumulated at the bottom, resulting in a state in which the dispersion is not as good as A. C: The inorganic solid electrolyte particles are separated into a dispersed layer and a transparent undispersed layer, resulting in a state in which the dispersion is not as good as B.

Here, electron microscope photographs were taken (both at the same magnification) of a mixed solution that was not subjected to wet atomization treatment (Comparative Example 1) and an inorganic solid electrolyte dispersion that was subjected to 50 passes of wet atomization treatment (Example 5). The electron microscope used was an "S-2380N" electron microscope manufactured by Hitachi, Ltd.
In the micrograph of Comparative Example 1, as shown in Figure 2(a), coarse particles were partially aggregated, whereas in the micrograph of Example 5, as shown in Figure 2(b), fine particles were uniformly dispersed.

Furthermore, as shown in Figure 3, which is a photograph showing the dispersion state of Comparative Example 1 (Figure 3(a)) and a photograph showing the dispersion state of Example 2 after 48 hours (Figure 3(b)), it was found that Example 2 was able to maintain its dispersibility even after 48 hours had passed.

(Experimental Example B: Comparative Example 3, Examples 6 to 10)
Inorganic solid electrolyte aqueous dispersions were prepared in the same manner as in Experimental Example A, except that the pressure in the wet atomization treatment was 220 Pa. For each of the prepared inorganic solid electrolyte aqueous dispersions, the particle size distribution was measured in the same manner as in Experimental Example A, and the median diameter (D50) and its standard deviation (σ50) were determined. In addition, the uniform dispersion and long-term dispersion retention were evaluated. The results are shown in Table 2.

(Experimental Example C: Comparative Examples 4 and 5, Examples 11 to 15)
LSPS (Li ₁₀ SnP ₂ S ₁₂ ), an inorganic solid electrolyte particle (sulfide-based), was mixed with an organic solvent (butyl butyrate) to a concentration of 5% by mass to prepare a 20 ml mixed solution. This mixed solution was subjected to wet atomization treatment using a wet atomization device (manufactured by Sugino Machine Co., Ltd., device name "Starburst") at a pressure of 200 MPa, with a nozzle of 0.12 mm, and for the number of passes shown in Table 3, to prepare an inorganic solid electrolyte aqueous dispersion. For comparison, a mixed solution (number of passes: 0) that was not subjected to wet atomization treatment was also prepared.

The particle size distribution of the mixed solution and each of the prepared inorganic solid electrolyte aqueous dispersions was measured in the same manner as in Experimental Example A, and the median diameter (D50) and its standard deviation (σ50) were determined. Furthermore, evaluations were conducted on uniform dispersion and long-term dispersion retention. The results are shown in Table 3.

Here, electron microscope photographs were taken (at the same magnification) of a mixed solution that was not subjected to wet atomization treatment (Comparative Example 3) and an inorganic solid electrolyte dispersion that was subjected to 20 passes of wet atomization treatment (Example 12). The electron microscope used was an "S-2380N" electron microscope manufactured by Hitachi, Ltd.
In the micrograph of Comparative Example 3, as shown in Figure 4(a), coarse particles were partially aggregated, whereas in the micrograph of Example 5, as shown in Figure 4(b), fine particles were uniformly dispersed.

From the above, it can be seen that the inorganic solid electrolyte dispersion of this example has improved performance in terms of non-aggregation (uniform dispersion) and dispersion retention.

(Verification of the amount of contamination in inorganic solid electrolyte dispersion)
The wet atomization device employs a ceramic (zirconia) chamber and nozzle, and the amount of zirconia component (Zr) before and after treatment was verified.
The amount of ceramic component (Zr) in the inorganic solid electrolyte dispersion of Example 5 and the mixed solution of Comparative Example 1 was measured using an inductively coupled plasma optical emission spectrometer.
The inductively coupled plasma optical emission spectrometer used was an ICP-OES 5110 model manufactured by Algilent.
As a result, the amount of zirconia in the mixed solution of Comparative Example 1 was 20 mass %, while the amount of zirconia was 23 mass % in Example 5. Considering measurement errors, these zirconia amounts show that contamination was minimized.

It goes without saying that the present invention is not limited to the above-described embodiments, and that modifications can be made as appropriate without departing from the spirit of the present invention.

REFERENCE SIGNS LIST 1 Wet atomization device 2 Raw material tank 3 Liquid supply pump 4 Pressure booster 5 High-pressure filter 6 Chamber 7 Heat exchanger 8 Inert gas supply source 9 Gas circulation purification section 14 Oxygen concentration meter 15 Moisture concentration meter

Claims (4)

An inorganic solid electrolyte dispersion obtained by dispersing an inorganic solid electrolyte powder used for a solid electrolyte of an all-solid-state battery in a solvent,
an inorganic solid electrolyte dispersion, wherein the inorganic solid electrolyte powder has a median diameter (D50) of 0.75 μm or more and 1.51 μm or less, the standard deviation (σ50) based on the median diameter (D50) being 3.5 μm or less, and the content of the inorganic solid electrolyte powder in the inorganic solid electrolyte material dispersion is 1 to 20 mass %. The inorganic solid electrolyte dispersion according to claim 1, wherein the zirconia content of the inorganic solid electrolyte dispersion is 23 mass% or less. A method for producing an inorganic solid electrolyte dispersion, comprising producing the inorganic solid electrolyte dispersion described in claim 1 or 2 using a wet atomization device. 4. The method for producing an inorganic solid electrolyte dispersion according to claim 3, wherein the chamber and nozzle of the wet atomization device are made of ceramic.