JP7528449B2 - Method for producing sulfide-based solid electrolyte - Google Patents

Description

The present invention relates to a method for producing a sulfide-based solid electrolyte, and an LGPS-type sulfide-based solid electrolyte obtained by the method.

In recent years, the demand for lithium-ion secondary batteries has been increasing for applications such as mobile information terminals, mobile electronic devices, electric vehicles, hybrid electric vehicles, and even stationary power storage systems. However, current lithium-ion secondary batteries use flammable organic solvents as electrolytes, and require a strong exterior to prevent the organic solvent from leaking. In addition, restrictions on the structure of devices such as portable personal computers are being imposed, such as the need to adopt a structure that addresses the risk of electrolyte leakage.

Furthermore, their use is expanding to mobile objects such as automobiles and airplanes, and large capacity is required for stationary lithium-ion secondary batteries. Under these circumstances, there is a tendency to place more importance on safety than ever before, and efforts are being made to develop all-solid-state lithium-ion secondary batteries that do not use harmful substances such as organic solvents.

For example, the use of oxides, phosphate compounds, organic polymers, sulfides, and the like as solid electrolytes in all-solid-state lithium ion secondary batteries has been considered.
Among these solid electrolytes, sulfides have the characteristics of high ionic conductivity, being relatively soft and easily forming solid-solid interfaces. They are also stable against active materials, and development is underway as a practical solid electrolyte.

One of the performance requirements for solid electrolytes is particle size. The electrode layer in an all-solid-state lithium-ion secondary battery is made by combining an electrode active material and a solid electrolyte, and a solid electrolyte with a small particle size is desired in order to form a good contact interface between the electrode active material and the solid electrolyte. Similarly, a solid electrolyte with a small particle size is desired in order to form a thinner layer in the solid electrolyte layer that separates the positive electrode layer and the negative electrode layer. For these reasons, various methods for pulverizing sulfide-based solid electrolytes are being investigated.

Known methods for pulverizing sulfide-based solid electrolytes include jet mills, bead mills, pin mills, and planetary ball mills. In Patent Document 1, an argyrodite-type solid electrolyte is pulverized with a jet mill or bead mill to obtain fine particles with small particle size and high ionic conductivity. However, when an LGPS-type solid electrolyte is pulverized using a bead mill or jet mill in a similar manner, there is a problem in that the ionic conductivity decreases.

Similarly, Patent Document 2 discloses a method for grinding LGPS-type solid electrolytes using a planetary ball mill, but even when using a planetary ball mill, there is a problem in that the ionic conductivity is significantly reduced when the grinding process is performed.

JP 2019-36536 A JP 2019-102412 A

Under these circumstances, it is desirable to provide a method for producing an LGPS-type sulfide-based solid electrolyte with high ionic conductivity and small particle size.

In view of the above problems, the inventors conducted intensive research and found that a ball mill is suitable as a method for grinding LGPS-type solid electrolytes. Planetary ball mills and jet mills are common grinding methods for obtaining powders of a few μm in size, but when grinding LGPS-type solid electrolytes, the strong grinding energy causes the crystal structure of the solid electrolyte to collapse, which in turn reduces the ionic conductivity. In contrast, a ball mill has a weaker grinding force than a planetary ball mill or a jet mill, but it can suppress the collapse of the crystal structure and the decrease in ionic conductivity. Furthermore, it was found that the LGPS-type solid electrolyte can be sufficiently finely ground even with the weak grinding force of a ball mill. This is thought to be because the LGPS-type solid electrolyte is softer than other sulfide-based solid electrolytes such as argyrodite-type. Based on the above findings, the present invention has been completed.

That is, the present invention is as follows.
＜1＞
A step of pulverizing the coarse-particle LGPS-type solid electrolyte using a ball mill to obtain a pulverized product;
heat-treating the pulverized material to obtain a pulverized and heat-treated LGPS-type solid electrolyte;
The method for producing an LGPS type solid electrolyte for an all-solid-state lithium battery includes the steps of:
＜2＞
The method for producing a solid electrolyte for an all-solid-state lithium battery according to <1>, wherein the step of obtaining the pulverized product further comprises adding a solvent to the coarse-particle LGPS-type solid electrolyte.
＜3＞
The method for producing a solid electrolyte for an all-solid-state lithium battery according to <2>, wherein the solvent is added in an amount of 10 wt % or less to the coarse-particle LGPS-type solid electrolyte.
＜4＞
The method for producing a solid electrolyte for an all-solid-state lithium battery according to <2> or <3>, wherein the solvent is one or more solvents selected from the group consisting of nitrile-based solvents, ether-based solvents, and hydrocarbon-based solvents.
＜5＞
The method for producing a solid electrolyte for an all-solid-state lithium battery according to <4>, wherein the solvent is selected from the group consisting of acetonitrile, tetrahydrofuran, and heptane.
＜6＞
The method for producing a solid electrolyte for an all-solid-state lithium battery according to any one of <1> to <5>, wherein the LGPS type solid electrolyte is composed of elemental sulfur, elemental phosphorus, elemental silicon, elemental chlorine, and elemental lithium.
＜７＞
The method for producing a solid electrolyte for an all-solid-state lithium battery according to any one of <1> to <6>, wherein the pulverized and heat-treated solid electrolyte has a decrease in ion conductivity of 2.0 mS/cm or less and a median diameter of 10 μm or less, compared to the coarse-particle LGPS-type solid electrolyte before pulverization.

The present invention provides a method for producing an LGPS-type sulfide-based solid electrolyte with high ionic conductivity and small particle size.

FIG. 1 is a schematic diagram showing the crystal structure of a sulfide-based solid electrolyte according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of an all-solid-state battery according to one embodiment of the present invention. FIG. 3 is a graph showing the results of X-ray diffraction measurement of the sulfide-based solid electrolytes obtained in Examples 1 to 5, Comparative Example 2, and Reference Example.

The present invention will be described in detail below. Note that the materials and configurations described below do not limit the present invention, and various modifications can be made within the scope of the present invention.

In this specification, the term LGPS-type solid electrolyte refers to a solid electrolyte that contains Li, P, and S and has a specific crystal structure, and examples of such solid electrolytes include solid electrolytes that contain Li, M (wherein M is one or more elements selected from the group consisting of Ge, Si, and Sn), P, and S.

The crystal structure of the LGPS-type solid electrolyte, as shown in FIG. 1, has an octahedron O composed of Li and S, a tetrahedron T1 composed of one or more elements selected from the group consisting of P, Ge, Si, and Sn and S, and a tetrahedron T2 composed of P and S, and is characterized in that the tetrahedron T1 and the octahedron O share edges, and the tetrahedron T2 and the octahedron O share vertices.

The LGPS-type solid electrolyte has peaks at least at 2θ=20.18°±0.50°, 20.44°±0.50°, 26.96°±0.50°, and 29.58°±0.50° in X-ray diffraction (CuKα: λ=1.5405 Å).

1. Production of coarse-grained LGPS-type solid electrolyte The coarse-grained LGPS-type solid electrolyte, which is the subject of the method for producing an LGPS-type solid electrolyte for an all-solid-state lithium battery of the present invention, can be produced by known methods such as the mechanical milling method described in Japanese Patent No. 5527673 and the liquid phase synthesis method described in International Publication No. WO2019/044517. Hereinafter, the production method will be described using an LGPS-type solid electrolyte having Li, Si, P, and S as constituent elements, as an example, but the embodiment of the present invention is not limited thereto.

Mechanical milling method: _{Li2S , P2S5} , and _SiS2 powders are mixed together, and then crushed and mixed using a planetary ball mill or the like to obtain a precursor of an LGPS-type solid electrolyte. Next, the obtained precursor of an LGPS-type solid electrolyte is heat-treated to obtain a coarse-grained LGPS-type solid electrolyte. The mechanical milling method is characterized by the fact that it homogenizes the composition and makes it amorphous by applying strong mechanical energy.

Liquid phase synthesis method: Li ₂ S and P ₂ S ₅ are reacted in an organic solvent such as acetonitrile or tetrahydrofuran to dissolve the Li 2 S and P 2 S 5 in the solution, and powders of Li ₂ S and SiS ₂ are added to the solution to obtain a suspension. Next, the organic solvent is distilled off to obtain a precursor of the LGPS type solid electrolyte. Then, the obtained precursor is heat-treated to obtain a coarse-grained LGPS type solid electrolyte. The liquid phase synthesis method is characterized in that the composition is homogenized and amorphous by reacting and dissolving a part or all of the raw material in an organic solvent.

2. Method for Producing LGPS-Type Solid Electrolyte for All-Solid-State Lithium Battery of the Present Invention The present invention provides a method for producing a sulfide-based solid electrolyte, more specifically, a method for producing a LGPS-type sulfide-based solid electrolyte in which the ionic conductivity is not reduced by the pulverization process.

The method for producing an LGPS type solid electrolyte for an all-solid-state lithium battery of the present invention comprises the steps of:
A step of pulverizing the coarse-particle LGPS-type solid electrolyte using a ball mill to obtain a pulverized product (hereinafter also referred to as the "pulverization step");
a step of heat-treating the pulverized product to obtain a pulverized and heat-treated LGPS-type solid electrolyte (hereinafter also referred to as a "heat-treatment step");
In the method of the present invention, the LGPS-type sulfide-based solid electrolyte is pulverized using a ball mill while suppressing the decrease in ion conductivity, and an LGPS-type solid electrolyte for an all-solid-state lithium battery having high ion conductivity and small particle size can be obtained. Specifically, solid electrolyte particles having a median diameter of 10 μm or less, particularly 5 μm or less, can be obtained. The median diameter defined in the present invention is a particle diameter at which the cumulative frequency is 50% in a particle size distribution histogram based on volume, and is sometimes called the median diameter and sometimes written as D50. In addition, examples of means for measuring particle size distribution include laser diffraction/scattering method, dynamic light scattering method, sedimentation method, and sieving method, but the median diameter defined in the present invention is a measurement value obtained by the laser diffraction/scattering method.

(1) Pulverization step As described above, the method for producing the LGPS-type solid electrolyte for an all-solid-state lithium battery of the present invention includes a step of pulverizing the coarse-particle LGPS-type solid electrolyte using a ball mill to obtain a pulverized product. In the step of obtaining the pulverized product, the pulverization conditions (temperature, rotation speed, etc.) can be appropriately adjusted in consideration of the apparatus used, the state of the solid electrolyte, etc.

The ball mill defined in this invention is a type of grinding machine, which is a device that grinds the powder to be ground into fine powder by placing hard balls such as ceramic balls and the powder to be ground in a cylindrical container and rotating them on their own axis.

In one embodiment of the present invention, the step of obtaining the pulverized product may further include adding a solvent to the coarse-particle LGPS-type solid electrolyte. That is, in one embodiment of the present invention, the step of obtaining the pulverized product may be performed by adding a solvent to the coarse-particle LGPS-type solid electrolyte, or may be performed without adding a solvent to the coarse-particle LGPS-type solid electrolyte. In one embodiment of the present invention, the step of obtaining the pulverized product is performed by adding a solvent to the coarse-particle LGPS-type solid electrolyte. In another embodiment of the present invention, the step of obtaining the pulverized product is performed without adding a solvent to the coarse-particle LGPS-type solid electrolyte. In a preferred embodiment of the present invention, the pulverization step may be performed by adding a solvent.

In one embodiment of the present invention, when a solvent is added to the pulverized product in the process of obtaining the pulverized product, the solvent can be added in an amount of 10 wt% or less relative to the coarse-particle LGPS-type solid electrolyte. When a solvent is added in the process of obtaining the pulverized product, if the amount of the solvent added is within the above range, the coarse-particle LGPS-type solid electrolyte can be pulverized more finely, and the adhesion of the solid electrolyte to the ball mill container or balls is suppressed, making it easier to recover. If the amount of the solvent added is more than the above range, the solid electrolyte may be altered and the ionic conductivity may decrease. Also, if the amount of the solvent added is more than the above range, the solid electrolyte may be strongly adhered to the container or balls of the ball mill, making recovery difficult.

In the process of obtaining the pulverized material, the amount of the solvent cannot be generally specified because it depends on the volume of the ball mill container and the type of solvent, but it is more than 0 and not more than 10 wt %, preferably 0.1 to 10 wt %, and more preferably 0.1 to 2 wt %, relative to the coarse-particle solid electrolyte.

The solvent that can be used in the process of obtaining the pulverized product is not limited as long as it can pulverize the coarse-particle LGPS-type solid electrolyte more finely, but for example, one or more solvents selected from the group consisting of nitrile-based solvents, ether-based solvents, and hydrocarbon-based solvents can be used. The above solvents may be used alone or in combination of two or more.

Examples of the nitrile-based solvent include, but are not limited to, acetonitrile, propionitrile, butyronitrile, isobutyronitrile, valeronitrile, 2-methylbutyronitrile, isovaleronitrile, pivalonitrile, hexanenitrile, heptanenitrile, and benzonitrile. In a preferred embodiment, the nitrile-based solvent may be acetonitrile.

The ether-based solvent may be, for example, tetrahydrofuran, cyclopentyl methyl ether, diisopropyl ether, diethyl ether, dimethyl ether, dioxane, or the like, but is not limited thereto. In a preferred embodiment, the ether-based solvent may be tetrahydrofuran.

The above-mentioned hydrocarbon solvents include aliphatic hydrocarbon solvents and aromatic hydrocarbon solvents. Examples of the aliphatic hydrocarbon solvents include, but are not limited to, saturated aliphatic hydrocarbon solvents having 6 to 11 carbon atoms. Examples of the saturated aliphatic hydrocarbon solvents having 6 to 11 carbon atoms include, but are not limited to, hexane, cyclohexane, heptane, octane, nonane, decane, undecane, etc. Examples of the aromatic hydrocarbon solvents include, but are not limited to, benzene, toluene, ethylbenzene, xylene, chlorobenzene, etc. In a preferred embodiment, the above-mentioned hydrocarbon solvent may be toluene or n-heptane.

The solvent used preferably has a low water content, preferably 1000 ppm or less, more preferably 100 ppm or less, and most preferably 10 ppm or less. Conventional methods such as distillation, purification using a column, and addition of molecular sieves can be used as the dehydration method.

The material of the balls used in the ball mill includes, but is not limited to, alumina, zirconia, silicon nitride, etc. The diameter of the balls is not particularly limited, but is preferably 0.1 mmφ to 30 mmφ, more preferably 0.3 mmφ to 10 mmφ, and particularly preferably 1 mmφ to 5 mmφ.

In the process of obtaining the pulverized product, the ball mill container is preferably filled with an inert gas and sealed. Examples of the inert gas include nitrogen, helium, and argon, with argon being particularly preferred. The oxygen and moisture concentrations in the inert gas are preferably low, with both being preferably 1000 ppm or less, more preferably 100 ppm or less, and particularly preferably 10 ppm or less.

The temperature inside the ball mill container is not particularly limited as long as it is a temperature at which the LGPS-type solid electrolyte does not thermally decompose and does not cause grain growth, but is preferably in the range of -10°C to 120°C, more preferably in the range of 0°C to 60°C, and particularly preferably in the range of 10°C to 40°C.

The rotation speed of the ball mill container is preferably less than the critical rotation speed, more preferably in the range of 50% to 90% of the critical rotation speed, and particularly preferably in the range of 60% to 80% of the critical rotation speed. The critical rotation speed refers to the rotation speed at which the contents (balls and objects to be ground) are pressed against the inner wall of the container by centrifugal force and the contents no longer fall. The time for the grinding process is not particularly limited, but is in the range of 1 hour to 96 hours, preferably in the range of 3 hours to 48 hours, and more preferably in the range of 6 hours to 24 hours. If the grinding time is short, the particle size may not be sufficiently small. If the grinding time is long, the crystal structure of the solid electrolyte may collapse, decreasing the ionic conductivity.

(2) Heat Treatment Step As described above, the method for producing an LGPS-type solid electrolyte for an all-solid-state lithium battery of the present invention includes a step of heat treating the pulverized material to obtain a pulverized and heat-treated LGPS-type solid electrolyte. When the pulverization step is performed, the crystallinity is reduced, and therefore the ionic conductivity is reduced. However, by performing a heat treatment step thereafter, the crystallinity is restored, and the ionic conductivity can be improved.

The heat treatment step is carried out at a temperature at which the pulverized LGPS-type solid electrolyte obtained by the pulverization step does not grow into grains. In the heat treatment step, the heat treatment conditions can be appropriately adjusted taking into consideration the equipment used and the state of the solid electrolyte. In the heat treatment step, the heat treatment temperature may be in the range of 300°C to 700°C, preferably in the range of 350°C to 650°C, and more preferably in the range of 400°C to 600°C. If the heat treatment temperature is in the above range, the desired crystals can be easily obtained. If the temperature is lower than 300°C, the desired crystals are unlikely to form, while if the temperature is higher than 700°C, crystals other than the intended one are likely to form, and the ion conductivity is likely to decrease.

The heat treatment process can be carried out in a vacuum or in an inert gas atmosphere, preferably in an inert gas atmosphere. As the inert gas, nitrogen, helium, argon, etc. can be used, among which argon is preferred. It is preferable that the concentration of oxygen and moisture is low, and both are preferably 1000 ppm or less, more preferably 100 ppm or less, and particularly preferably 10 ppm or less.

3. LGPS-type solid electrolyte for all-solid-state lithium batteries obtained by the method of the present invention The LGPS-type solid electrolyte for all-solid-state lithium batteries of the present invention obtained as described above can be formed into a desired molded body by various means and used for various applications including all-solid-state batteries described below. The molding method is not particularly limited. For example, the same molding method as the molding method for each layer constituting the all-solid-state battery described in <All-solid-state battery> described later can be used.

<All-solid-state battery>
The sulfide-based solid electrolyte of the present invention can be used, for example, as a solid electrolyte for an all-solid-state battery. According to a further embodiment of the present invention, there is provided an all-solid-state battery including the above-mentioned solid electrolyte for an all-solid-state battery.

The term "all-solid-state battery" as used herein refers to an all-solid-state lithium-ion secondary battery. FIG. 2 is a schematic cross-sectional view of an all-solid-state battery according to one embodiment of the present invention. The all-solid-state battery 10 has a structure in which a solid electrolyte layer 2 is disposed between a positive electrode layer 1 and a negative electrode layer 3. The all-solid-state battery 10 can be used in various devices including mobile phones, personal computers, automobiles, etc.

The sulfide-based solid electrolyte of the present invention may be contained as a solid electrolyte in at least one of the positive electrode layer 1, the negative electrode layer 3, and the solid electrolyte layer 2. The solid electrolyte may be composed of the sulfide-based solid electrolyte of the present invention alone, or may be used in appropriate combination with an oxide solid electrolyte (e.g., Li ₇ La ₃ Zr ₂ O ₁₂ ), a sulfide solid electrolyte (e.g., Li ₂ S-P ₂ S ₅ ), or other complex hydride solid electrolyte (e.g., LiBH ₄ , 3LiBH ₄ -LiI), as necessary. When the sulfide-based solid electrolyte of the present invention is contained in the positive electrode layer 1 or the negative electrode layer 3, the sulfide-based solid electrolyte of the present invention is used in combination with a known positive electrode active material or negative electrode active material for lithium ion secondary batteries. The amount ratio of the sulfide-based solid electrolyte of the present invention contained in the positive electrode layer 1 or the negative electrode layer 3 is not particularly limited.

The solid-state battery is produced by molding and stacking each of the layers described above, but there are no particular limitations on the method of molding and stacking each layer.

For example, there are methods in which a solid electrolyte and/or an electrode active material is dispersed in a solvent to form a slurry, which is then applied using a doctor blade or spin coater, and then rolled to form a film; gas-phase methods in which films are formed and laminated using vacuum deposition, ion plating, sputtering, laser ablation, etc.; and pressure molding methods in which powder is molded using hot pressing or cold pressing without applying heat, and then laminated.

Since the sulfide-based solid electrolyte of the present invention is relatively soft, it is particularly preferable to produce an all-solid-state battery by forming and stacking each layer by pressure molding. Pressure molding methods include hot pressing, which is performed with heating, and cold pressing, which is not performed with heating, but cold pressing can also be used to sufficiently form the electrolyte.

The present invention also includes a molded body obtained by heat-molding the sulfide-based solid electrolyte of the present invention. The molded body is preferably used as an all-solid-state battery. The present invention also includes a method for producing an all-solid-state battery, which includes a step of heat-molding the sulfide-based solid electrolyte of the present invention.

The present embodiment will be described in more detail below with reference to examples, but the present embodiment is not limited to these examples.

<X-ray diffraction measurement>
X-ray diffraction measurements were performed on the sulfide-based solid electrolyte powder in an Ar atmosphere at room temperature (25° C.) using “X'Pert3 Powder” manufactured by PANalytical Corporation, with CuKα: λ=1.5405 Å.

<Lithium ion conductivity measurement>
The sulfide-based solid electrolyte was subjected to uniaxial molding (420 MPa) to obtain a disk having a thickness of about 1 mm and a diameter of 10 mm. Then, using an all-solid-state battery evaluation cell (manufactured by Hosen Co., Ltd.), AC impedance measurement was performed by a four-terminal method ("SI1260 IMPEDANCE/GAIN-PHASE ANALYZER" manufactured by Solartron) at room temperature (25°C) to calculate the lithium ion conductivity.

Specifically, the sample was placed in a thermostatic chamber set at 25°C and held there for 30 minutes before measuring the lithium ion conductivity. The measurement frequency range was 0.1 Hz to 1 MHz, and the amplitude was 50 mV.

<Median diameter measurement>
The particle size distribution of the sulfide-based solid electrolyte powder was measured using a laser diffraction/scattering particle size distribution measurement device ("MT3300EXII" manufactured by Microtrac-Bell) to determine the median diameter (D50) on a volume basis.

Production Example First, a coarse-particle LGPS-type solid electrolyte, which is the subject of the production method of the LGPS-type solid electrolyte for an all-solid-state lithium battery of the present invention, was produced according to the steps exemplified below.

<Solubilization step 1>
In a glove box under an argon atmosphere, 1.42 g of Li ₂ S (Sigma-Aldrich, purity 99.8%) and 6.87 g of P ₂ S ₅ (Sigma-Aldrich, purity 99%) were weighed out so that the molar ratio of Li ₂ S:P ₂ S ₅ :=1:1. Next, Li ₂ S and P ₂ S ₅ were added in this order to 75 g of acetonitrile (Wako Pure Chemical Industries, ultra-dehydrated grade), and mixed at room temperature for 3 hours. The mixture gradually dissolved, and a Li-P-S homogeneous solution was obtained.

<Solubilization step 2>
In a glove box under an argon atmosphere, 4 g of _Li2S (Sigma-Aldrich, purity 99.8%) and 16 g of _SiS2 (Mitsuwa Chemical) were weighed out so that the molar ratio of _Li2S : _SiS2 was 0.5:1. Next, they were added to 610 g of acetonitrile (Wako Pure Chemical Industries, ultra-dehydrated grade) and mixed at room temperature for 24 hours. The mixture gradually dissolved, but impurities in the raw materials remained at this stage.

The resulting solution was filtered using a membrane filter (PTFE, pore size 1.0 μm) to obtain 2.0 g of filter cake and 578 g of filtrate (Li-Si-S homogeneous solution). ICP analysis of the Li-Si-S homogeneous solution revealed that the Li/Si (molar ratio) was 50.6/49.4. The concentration of (Li ₂ S + SiS ₂ ) was 3.07 wt %.

<Solution mixing step>
A homogeneous mixed solution was prepared by mixing 82.9 g of the Li-P-S homogeneous solution and 233.0 g of the Li-Si-S homogeneous solution so that the molar ratio of Si:P was 1: 1. Furthermore, 0.52 g of LiCl (Sigma-Aldrich, purity 99.99%) was added with stirring, and the mixture was mixed at room temperature for 3 hours.

<Slurrying step>
6.27 g of Li ₂ S was added to the obtained homogeneous mixed solution while stirring, and the mixture was mixed at room temperature for 12 hours to prepare a slurry liquid. A series of operations was carried out in a glove box under an argon atmosphere. The molar ratio of all the raw materials added in the above operations was Li ₂ S: P ₂ S ₅ : SiS ₂ : LiCl = 6.45: 1: 2: 0.40, and the element composition was Li _3.33 Si _0.50 P _0.50 S _3.86 Cl _0.10 .

<Drying process>
The obtained slurry liquid was dried under vacuum at 180° C. for 4 hours to remove the solvent. The solvent was removed while stirring the solution. After that, the solution was cooled to room temperature to obtain a precursor.

<Heat treatment step>
The obtained precursor was placed in a glass reaction tube in a glove box and placed in an electric tubular furnace so that the precursor was not exposed to the atmosphere. Argon (G3 grade) was blown into the reaction tube, and the temperature was raised to 475°C over 3 hours, and then the precursor was fired at 475°C for 8 hours to obtain a LGPS-type solid electrolyte.

Reference Example: As a result of X-ray diffraction measurement of the coarse-particle LGPS-type solid electrolyte produced by the above-mentioned production example, peaks were observed at 2θ=19.95°, 20.16°, 26.70°, and 29.35°, which are attributed to the crystalline phase of the LGPS-type solid electrolyte. The ionic conductivity was 6.1 mS/cm, and the median diameter was 69.7 μm.

Example 1
<Crushing process>
1 g of the coarse-particle LGPS-type solid electrolyte produced by the above-mentioned Production Example was placed in a 50 cc Duran bottle together with 80 g of zirconia balls having a diameter of 3 mm and sealed. The above-mentioned weighing, addition and sealing operations were all carried out in a glove box under an argon atmosphere, and all the equipment used had been previously dehydrated with a dryer.

The container was then rotated at 120 rpm for 12 hours at room temperature using a ball mill stand (AV-1 model, manufactured by Asahi Rika Seisakusho Co., Ltd.) to perform a pulverization process. 0.77 g of solid electrolyte was recovered, and the ionic conductivity was measured, revealing that the ionic conductivity of the solid electrolyte after the pulverization process was 2.7 mS/cm.

<Heat treatment process>
The solid electrolyte after the pulverization treatment was placed in a glass container and heat-treated at 475° C. for 4 hours under argon. As a result of X-ray diffraction measurement of the solid electrolyte after the heat treatment, peaks were observed at 2θ=19.97°, 20.17°, 26.73°, and 29.35°, which are attributed to the crystalline phase of the LGPS-type solid electrolyte. The ionic conductivity was 6.2 mS/cm, and the median diameter was 9.4 μm.

Example 2
<Crushing process>
1 g of the LGPS-type solid electrolyte produced by the above-mentioned Production Example was placed in a 50 cc Duran bottle together with 80 g of zirconia balls having a diameter of 5 mm, and then crushed in the same manner as in Example 1, except that 18 mg (1.8 wt % based on the solid electrolyte) of tetrahydrofuran (manufactured by Wako, ultra-dehydrated grade) was added as a solvent. The recovered amount of the solid electrolyte was 0.89 g.

<Heat treatment process>
The pulverized solid electrolyte was heat-treated in the same manner as in Example 1. As a result of X-ray diffraction measurement, a crystalline phase of the LGPS-type solid electrolyte was observed, as in Example 1. The ionic conductivity was 6.0 mS/cm, and the median diameter was 4.2 μm.

Example 3
<Crushing process>
The grinding treatment was carried out in the same manner as in Example 2, except that 18 mg of acetonitrile (manufactured by Wako, ultra-dehydrated grade) was added instead of tetrahydrofuran as a solvent. The recovered amount of the solid electrolyte was 0.87 g.

<Heat treatment process>
The solid electrolyte after the pulverization treatment was heat-treated in the same manner as in Example 1. As a result of X-ray diffraction measurement, a crystalline phase of the LGPS-type solid electrolyte was observed as in Example 1. The ionic conductivity was 7.4 mS/cm, and the median diameter was 8.8 μm.

Example 4
<Crushing process>
The grinding treatment was carried out in the same manner as in Example 2, except that 18 mg of toluene (manufactured by Wako, ultra-dehydrated grade) was added instead of tetrahydrofuran as a solvent. The recovered amount of the solid electrolyte was 0.83 g.

<Heat treatment process>
The solid electrolyte after the pulverization treatment was heat-treated in the same manner as in Example 1. As a result of X-ray diffraction measurement, a crystalline phase of the LGPS-type solid electrolyte was observed as in Example 1. The ionic conductivity was 5.8 mS/cm, and the median diameter was 6.3 μm.

Example 5
<Crushing process>
The pulverization treatment was carried out in the same manner as in Example 2, except that the amount of tetrahydrofuran (manufactured by Wako, ultra-dehydrated grade) added as a solvent was changed to 90 mg (9.0 wt % based on the solid electrolyte). The recovered amount of the solid electrolyte was 1.00 g.

<Heat treatment process>
The solid electrolyte after the pulverization treatment was heat-treated in the same manner as in Example 1. As a result of X-ray diffraction measurement, a crystalline phase of the LGPS-type solid electrolyte was observed as in Example 1. The ionic conductivity was 4.5 mS/cm, and the median diameter was 4.1 μm.

Comparative Example 1
<Crushing process>
The pulverization treatment was carried out in the same manner as in Example 2, except that the amount of tetrahydrofuran (manufactured by Wako, ultra-dehydrated grade) added as a solvent was changed to 180 mg (18.0 wt % relative to the solid electrolyte). After the pulverization treatment, an attempt was made to recover the solid electrolyte, but the solid electrolyte was strongly adhered to the wall surface of the container and the ball, making recovery difficult.

Comparative Example 2
<Crushing process>
10 g of the LGPS-type solid electrolyte produced by the above Production Example was pulverized using a jet mill (NJ-50, manufactured by Aisin Nano Technology Co., Ltd.) at an inlet pressure of 2.0 MPa, a pulverization pressure of 1.2 MPa, and a processing speed of 60 g/h, and 7.8 g of the pulverized solid electrolyte was recovered.

<Heat treatment process>
The solid electrolyte after the pulverization was heat-treated in the same manner as in Example 1. When X-ray diffraction measurement was performed, in addition to the LGPS type crystal structure, impurity phases belonging to argyrodite were observed at 25.30° and 29.80°. The ionic conductivity was 2.6 mS/cm, and the median diameter was 12.4 μm.

Comparative Example 3
<Crushing process>
1.5 g of the LGPS-type solid electrolyte produced by the above-mentioned production example, 53 g of zirconia beads having a diameter of 0.3 mm, 4 ml of isobutyronitrile, and 6 ml of toluene were placed in a 45 cc planetary ball mill container, and ground for 15 hours at a rotation speed of 300 rpm using a planetary ball mill (Fritsch, P-7 Classic Line). After grinding, the zirconia beads were removed to obtain a suspension. The obtained suspension was dried at 180° C. under reduced pressure for 2 hours using an evaporator, and 0.51 g of the ground solid electrolyte was collected.

<Heat treatment process>
The solid electrolyte after the pulverization was heat-treated in the same manner as in Example 1. When X-ray diffraction measurement was performed, impurity phases belonging to argyrodite were observed at 25.25° and 29.75° in addition to the LGPS type crystal structure. The ionic conductivity was 2.5 mS/cm and the median diameter was 1.9 μm.

The recovery rate, ionic conductivity, decrease in ionic conductivity compared to before grinding, and median diameter of the solid electrolytes obtained in the Reference Example, Examples 1 to 5, and Comparative Examples 1 to 3 are shown in Table 1 below, and the results of measuring the X-ray diffraction patterns are shown in Figure 3 below.

As described above, the present invention provides a method for producing an LGPS-type sulfide-based solid electrolyte having high ionic conductivity and small particle size. Furthermore, the LGPS-type sulfide-based solid electrolyte obtained by the method of the present invention is suitable for use in all-solid-state lithium batteries.

1 Positive electrode layer 2 Solid electrolyte layer 3 Negative electrode layer 10 All-solid-state battery

Claims (5)

A step of pulverizing the coarse-particle LGPS-type solid electrolyte using a ball mill to obtain a pulverized product;
heat-treating the pulverized material to obtain a pulverized and heat-treated LGPS-type solid electrolyte;
A method for producing an LGPS type solid electrolyte for an all-solid-state lithium battery, comprising:
The step of obtaining the pulverized product further includes adding a solvent to the coarse-particle LGPS-type solid electrolyte,
The method for producing an LGPS-type solid electrolyte for an all-solid-state lithium battery, wherein the solvent is added in an amount of more than 0 wt % and not more than 10 wt % to the coarse-particle LGPS-type solid electrolyte. The method for producing an LGPS-type solid electrolyte for an all-solid-state lithium battery according to claim 1, wherein the solvent is one or more solvents selected from the group consisting of nitrile-based solvents, ether-based solvents, and hydrocarbon-based solvents. The method for producing an LGPS-type solid electrolyte for an all-solid-state lithium battery according to claim 2, wherein the solvent is selected from the group consisting of acetonitrile, tetrahydrofuran, and heptane. The method for producing an LGPS-type solid electrolyte for an all-solid-state lithium battery according to claims 1 to 3, wherein the LGPS-type solid electrolyte is composed of elemental sulfur, elemental phosphorus, elemental silicon, elemental chlorine, and elemental lithium. The method for producing an LGPS-type solid electrolyte for an all-solid-state lithium battery according to claims 1 to 4, wherein the crushed and heat-treated solid electrolyte has a decrease in ion conductivity of 2.0 mS/cm or less and a median diameter of 10 μm or less, compared to the coarse-particle LGPS-type solid electrolyte before crushing.