Method for producing sulfide solid electrolyte

Abstract

To provide a method for producing a high-quality sulfide solid electrolyte free from the risk of contamination with foreign matter.SOLUTION: A method for producing a sulfide solid electrolyte, the method comprising: pulverizing a raw material inclusion containing a lithium atom, a sulfur atom, and a phosphorus atom with a pulverizer to obtain a raw material mixture; and subsequently firing a firing object using a device at least a part of the inside of which is coated with ceramics.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a sulfide solid electrolyte. [Background technology]

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become increasingly important. Among these batteries, lithium-ion batteries have attracted attention due to their high energy density. Currently available lithium-ion batteries use electrolytes containing flammable organic solvents, which necessitates the installation of safety devices to suppress temperature rise during short circuits, as well as improvements in structure and materials to prevent short circuits. In particular, for automotive applications, there is a demand for higher capacity and higher output, making it increasingly important to consider safety aspects of batteries that use conventional electrolytes. In contrast, lithium-ion batteries, which use solid electrolytes and are completely solid-state, do not use flammable organic solvents within the battery, which allows for simplified safety devices and is thought to be superior in terms of manufacturing cost and productivity.

[0003] Sulfide solid electrolytes are known as solid electrolytes used in lithium-ion batteries. Various crystal structures are known for sulfide solid electrolytes, one of which is the argyrodite crystal structure. Sulfide solid electrolytes with the argyrodite crystal structure are known to be highly stable and have high ionic conductivity.

[0004] As a method for producing a sulfide solid electrolyte, for example, Patent Document 1 describes a method for producing a solid electrolyte having an argyrodite-type crystal structure, which includes heat-treating a raw material mixture containing lithium, sulfur, phosphorus, and a halogen in a solvent using a pressure-resistant container or under reflux, removing the solvent, and firing the treated product obtained by the heat treatment. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-95953 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a method for producing a high-quality sulfide solid electrolyte without the risk of contamination with foreign matter. [Means for solving the problem]

[0007] The method for producing a sulfide solid electrolyte according to the present invention includes the steps of: A raw material containing lithium atoms, sulfur atoms, and phosphorus atoms is pulverized by a pulverizer to obtain a raw material mixture; and The method for producing a sulfide solid electrolyte includes firing an object to be fired using a device having at least a portion of its interior coated with ceramic. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing a high-quality sulfide solid electrolyte without the risk of contamination with foreign matter. [Brief explanation of the drawings]

[0009] [Figure 1A] 1 shows photographs of the appearance of a test piece in Comparative Example 1 (before and after a corrosion test). [Figure 1B] 1 shows photographs of the appearance of a test piece in Comparative Example 2 (before and after a corrosion test). [Figure 1C] 1 shows photographs of the appearance of a test piece in Example 1 (before and after a corrosion test). [Figure 1D] 3 shows photographs of the appearance of a test piece in Example 2 (before and after a corrosion test). [Figure 2]1 shows an XRD pattern of a test piece in Comparative Example 1 after a corrosion test. [Figure 3] 1 is a chart showing the results of surface observation by SEM-EDS of a test piece in Comparative Example 1 ((a) before corrosion test, (b) gas phase portion after corrosion test, and (c) solid phase portion after corrosion test). [Figure 4] 1 shows an XRD pattern of a test piece in Comparative Example 2 after a corrosion test. [Figure 5] 1 is a chart showing the results of surface observation by SEM-EDS of a test piece in Comparative Example 2 ((a) before corrosion test, (b) gas phase portion after corrosion test, and (c) solid phase portion after corrosion test). [Figure 6] 1 shows an XRD pattern of a test piece in Example 1 after a corrosion test. [Figure 7] 1 is a chart showing the results of surface observation by SEM-EDS of a test piece in Example 1 ((a) before corrosion test, (b) gas phase portion after corrosion test, and (c) solid phase portion after corrosion test). [Figure 8] 1 shows an XRD pattern of a test piece in Example 2 after a corrosion test. [Figure 9] 1 is a chart showing the results of surface observation by SEM-EDS of a test piece in Example 2 ((a) before corrosion test, (b) gas phase portion after corrosion test, and (c) solid phase portion after corrosion test). DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, the upper and lower limit values ​​of a range of values ​​expressed as "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and lower limit values.

[0011] (Findings Obtained by the Inventors to Achieve the Invention) As a result of extensive research aimed at solving the above problems, the present inventors have discovered the following and have completed the present invention. Sulfide solid electrolytes having a stable crystal structure, such as an argyrodite-type crystal structure, require heat treatment (calcination) at high temperatures (e.g., 400°C) during production, which generates sulfide gas. Therefore, the interior of the equipment (calcination equipment) used during the heat treatment is exposed to a severely corrosive environment. The inventors used a rotary kiln, a type of calcination equipment, to calcinate a sulfur-containing material at 400°C or higher for approximately 72 hours. As a result, they found that a large amount of black sulfide corrosion material was discharged from the outlet of the furnace tube. Furthermore, observation of the interior of the furnace tube revealed that the interior of the furnace tube had partially peeled off. If the corrosion inside the calcination equipment progresses, the interior of the equipment peels off and is mixed into the resulting sulfide solid electrolyte, potentially degrading the quality of the sulfide solid electrolyte. Such peeling can occur anywhere inside the equipment that comes into contact with the sulfur-containing material, but is particularly pronounced inside the calcination equipment, which is exposed to a high-temperature environment.

[0012] The main countermeasures for the above-mentioned peeling inside the device are to review the materials of the device itself and the environmental conditions. However, reviewing the materials leads to an increase in the cost of the device. Furthermore, reviewing the environmental conditions is extremely difficult to achieve while also affecting the quality of the resulting sulfide solid electrolyte, and therefore cannot be said to have an immediate effect. After extensive investigation, the inventors of the present invention have focused on using equipment with an internal coating. Coating eliminates the need to reconsider the materials of the entire equipment, and can suppress increases in equipment costs. Furthermore, since it does not require reviewing environmental conditions, this can be an effective solution.

[0013] Patent Document 1 does not consider the above problem.

[0014] Based on the above-mentioned investigations, the present inventors have found that, when firing an object to be fired that contains sulfur atoms, by using equipment at least a part of the interior of which is coated with ceramics, the interior of the equipment has excellent corrosion resistance, and therefore a high-quality sulfide solid electrolyte can be produced without the risk of foreign matter being mixed in.

[0015] (Various aspects of this embodiment) A method for producing a sulfide solid electrolyte according to a first aspect of the present embodiment includes the steps of: A raw material containing lithium atoms, sulfur atoms, and phosphorus atoms is pulverized by a pulverizer to obtain a raw material mixture; and The method for producing a sulfide solid electrolyte includes firing an object to be fired using a device having at least a portion of its interior coated with ceramic.

[0016] In this specification, the term "sintering object" refers to an object to be subjected to sintering, and may include a raw material mixture containing sulfur atoms and a processed product obtained by heat treatment. The sintering object is different from the raw material alone contained in the raw material inclusion and from the sulfide solid electrolyte obtained by the method for producing a sulfide solid electrolyte of this embodiment. The sintering object may contain Li3PS4, as described below. The calcined material can be confirmed by, for example, analyzing it by FT-IR (diffuse reflectance spectroscopy) and detecting a peak that is different from both the raw material and the sulfide solid electrolyte, or by powder X-ray diffraction (XRD) measurement and detecting a similar peak.

[0017] As described above, the inventors have discovered that coating at least a portion of the interior of equipment used in firing a firing object containing sulfur atoms with a ceramic provides excellent corrosion resistance to the interior of the equipment. Therefore, the method for producing a sulfide solid electrolyte of this embodiment uses the above equipment when firing a firing object containing sulfur atoms, thereby producing a high-quality sulfide solid electrolyte without the risk of foreign matter being mixed in. Furthermore, because the interior of the above equipment has excellent corrosion resistance, the frequency of maintenance of the equipment can be reduced, allowing for efficient production of a sulfide solid electrolyte. Furthermore, by coating at least a portion of the interior of the device with ceramics, the corrosion resistance of the interior of the device can be increased, which allows the device to be made of metallic materials and enables the adoption of various firing methods.

[0018] A method for producing a sulfide solid electrolyte according to a second aspect of the present embodiment is the same as the first aspect, except that: The equipment is a firing furnace; That is it.

[0019] As described above, the inside of equipment that comes into contact with a material to be fired that contains sulfur atoms, particularly the inside of firing equipment that is in a high-temperature environment, is exposed to a severely corrosive environment. The equipment used in this embodiment has excellent corrosion resistance because at least a portion of its interior is coated with a ceramic. Such equipment is preferably equipment that comes into contact with a material to be fired that contains sulfur atoms, and among these, a firing furnace is more preferable from the viewpoint of further demonstrating the effects of the present invention.

[0020] A method for producing a sulfide solid electrolyte according to a third aspect of the present embodiment is the same as the second aspect, except that: The firing furnace is a rotary kiln. That is it.

[0021] When the firing furnace is a rotary kiln, the effects of the present invention can be more effectively exhibited, and a sulfide solid electrolyte having an argyrodite-type crystal structure can be more easily obtained.

[0022] A method for producing a sulfide solid electrolyte according to a fourth aspect of the present embodiment is the same as the third aspect, except that: The rotary kiln is provided with a furnace tube, and the inside of the furnace tube is coated with ceramics. That is it.

[0023] When a rotary kiln is used as the above-mentioned equipment, the material to be burned containing sulfur atoms is heated in a furnace tube provided in the rotary kiln, and the furnace tube is exposed to a particularly severe corrosive environment. Therefore, by coating the inside of the furnace tube with a ceramic material, the effects of the present invention can be more effectively achieved.

[0024] A method for producing a sulfide solid electrolyte according to a fifth aspect of the present embodiment is any one of the first to fourth aspects, The ceramics include at least one selected from the group consisting of metal oxide, metal nitride, metal carbonitride, metal carbide, and amorphous carbon. A method for producing a sulfide solid electrolyte according to a sixth aspect of the present embodiment is the same as any one of the first to fourth aspects, The ceramic contains at least one selected from the group consisting of zirconium oxide, chromium oxide, aluminum oxide, silicon oxide, titanium oxide, yttrium oxide, titanium nitride, titanium aluminum nitride, chromium nitride, titanium carbonitride, silicon carbide, titanium carbide, and amorphous carbon. That is it.

[0025] From the viewpoint of further improving corrosion resistance and further exerting the effects of the present invention, the ceramic used for coating the inside of the device preferably contains at least one selected from the group consisting of metal oxide, metal nitride, metal carbonitride, metal carbide, and amorphous carbon, and more preferably contains at least one selected from the group consisting of zirconium oxide, chromium oxide, aluminum oxide, silicon oxide, titanium oxide, yttrium oxide, titanium nitride, titanium aluminum nitride, chromium nitride, titanium carbonitride, silicon carbide, titanium carbide, and amorphous carbon.

[0026] A seventh aspect of the present embodiment provides a method for producing a sulfide solid electrolyte in any one of the first to sixth aspects, The heating temperature of the firing is 350°C or higher and 500°C or lower. That is it.

[0027] In the method for producing a sulfide solid electrolyte of this embodiment, the corrosion resistance of the equipment used is excellent even when the object to be fired containing sulfur atoms is heated within the above temperature range, so the effects of the present invention can be exerted. Furthermore, by heating the object to be fired containing sulfur atoms within the above temperature range, a sulfide solid electrolyte having an argyrodite-type crystal structure is easily obtained.

[0028] A method for producing a sulfide solid electrolyte according to an eighth aspect of the present embodiment is any one of the first to seventh aspects, The firing is carried out in an inert gas atmosphere or a reduced pressure atmosphere. That is it.

[0029] In the method for producing a sulfide solid electrolyte of the present embodiment, a sulfide solid electrolyte having a higher quality argyrodite-type crystal structure is more easily obtained by firing an object to be fired that contains sulfur atoms in an inert gas atmosphere or a reduced pressure atmosphere.

[0030] A ninth aspect of the present embodiment provides a method for producing a sulfide solid electrolyte in any one of the first to eighth aspects, In obtaining the raw material mixture, the raw material content is pulverized in a solvent using a pulverizer to obtain a raw material mixture slurry. That is it.

[0031] In the method for producing a sulfide solid electrolyte of the present embodiment, in obtaining the raw material mixture, it is preferable to pulverize the raw material contents in a solvent using a pulverizer to obtain a raw material mixture slurry, from the viewpoint of reducing aggregation of the raw materials.

[0032] A tenth aspect of the present embodiment provides a method for producing a sulfide solid electrolyte according to the ninth aspect, After obtaining the raw material mixture, heat-treating the raw material mixture in the raw material mixture slurry using a pressure vessel or under reflux. That is it.

[0033] In the method for producing a sulfide solid electrolyte of the present embodiment, after obtaining the raw material mixture, the raw material mixture is heat-treated in the raw material mixture slurry using a pressure-resistant vessel or under reflux, which makes it easier to obtain a sulfide solid electrolyte having an argyrodite-type crystal structure more efficiently.

[0034] A method for producing a sulfide solid electrolyte according to an eleventh aspect of the present embodiment is the same as the tenth aspect, except that: After the heat treatment, the treated product obtained by the heat treatment is dried. That is it.

[0035] In the method for producing a sulfide solid electrolyte of the present embodiment, it is preferable to include drying the treated product obtained by the heat treatment after the heat treatment, from the viewpoint of efficiently removing the solvent from the treated product.

[0036] A method for producing a sulfide solid electrolyte according to a twelfth aspect of the present embodiment is the method for producing a sulfide solid electrolyte according to the eleventh aspect, The drying is performed by fluidized drying using media particles as a medium. That is it.

[0037] In the method for producing a sulfide solid electrolyte of this embodiment, the drying is preferably carried out by fluidized drying using media particles as a medium, since this allows drying to be carried out in a shorter time.

[0038] (Sulfide solid electrolyte) In this specification, the term "sulfide solid electrolyte" refers to an electrolyte that contains sulfur atoms and maintains a solid state under a nitrogen atmosphere at 25° C. The sulfide solid electrolyte in this embodiment is a sulfide solid electrolyte that contains lithium atoms, sulfur atoms, and phosphorus atoms, and preferably contains halogen atoms, and has ionic conductivity due to the lithium atoms.

[0039] The term "sulfide solid electrolyte" includes crystalline sulfide solid electrolytes. In this specification, a crystalline sulfide solid electrolyte refers to a sulfide solid electrolyte in which a peak derived from the solid electrolyte is observed in an X-ray diffraction pattern in an X-ray diffraction measurement, regardless of whether or not a peak derived from a raw material of the sulfide solid electrolyte is present. That is, the crystalline sulfide solid electrolyte includes a crystalline structure derived from the solid electrolyte, and a part of the crystalline structure may be derived from the solid electrolyte, or the entire crystalline structure may be derived from the solid electrolyte.

[0040] The method for producing the sulfide solid electrolyte of this embodiment will be described in more detail below in accordance with the above aspects.

[0041] [Method for producing sulfide solid electrolyte] The method for producing the sulfide solid electrolyte of this embodiment (hereinafter also simply referred to as the “production method of this embodiment”) is as follows: A raw material containing lithium atoms, sulfur atoms, and phosphorus atoms is pulverized by a pulverizer to obtain a raw material mixture; and The method for producing a sulfide solid electrolyte includes firing an object to be fired using a device having at least a portion of its interior coated with ceramic.

[0042] (Obtaining raw material mixture) The manufacturing method of this embodiment includes pulverizing a raw material containing lithium atoms, sulfur atoms, and phosphorus atoms using a pulverizer to obtain a raw material mixture. The raw material inclusions may contain solid electrolyte raw materials selected depending on the sulfide solid electrolyte to be obtained, and preferably contain lithium atoms, sulfur atoms, and phosphorus atoms. Furthermore, since sulfide solid electrolytes preferably contain halogen atoms from the viewpoint of improving ionic conductivity, the raw material inclusions preferably further contain halogen atoms. More specifically, the raw material inclusions are inclusions containing substances containing these atoms (hereinafter also referred to as "solid electrolyte raw materials"), and preferably contain two or more solid electrolyte raw materials.

[0043] Representative examples of the solid electrolyte raw material contained in the raw material-containing material include lithium sulfide, phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5), and other raw materials containing at least two types of atoms selected from the above-mentioned atoms, as well as raw materials consisting of one type of atom selected from the above-mentioned atoms, such as elemental phosphorus and elemental sulfur. Among these, lithium sulfide and phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5) are preferred, and among the phosphorus sulfides, diphosphorus pentasulfide (P2S5) is preferred.

[0044] The raw material may further contain a halogen atom, and examples of the raw material include substances containing halogen atoms, such as lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; and elemental halogens such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I).

[0045] Li3PS4, which has a PS4 structure, can also be used as the solid electrolyte raw material. Specifically, Li3PS4 can be prepared in advance by manufacturing or the like and used as the raw material. In this case, preferred combinations of solid electrolyte raw materials contained in the raw material contents include a combination of Li3PS4 and the lithium halide, a combination of Li3PS4 and the elemental halogen, and a combination of Li3PS4 and the lithium halide and elemental halogen.

[0046] The above solid electrolyte raw materials may be blended in a blending ratio that matches the composition of the sulfide solid electrolyte having the desired crystal structure. The blending ratio of lithium sulfide and other solid electrolyte raw materials contained in the raw material content may be, for example, the blending ratio described in International Publication No. 2020 / 105737 (see paragraphs

[0024] to

[0028] ). Furthermore, the solid electrolyte raw material may be appropriately selected from the materials exemplified in International Publication No. 2020 / 105737 (see paragraphs

[0020] to

[0022] ).

[0047] The raw material components are preferably pulverized in advance to adjust the particle size. When pulverized in advance, the average particle size is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 12 μm or less. A pulverizer can be used to pulverize the raw material, and a container-driven pulverizer such as a ball mill or a bead mill is also preferred, as it has a short processing time and allows for continuous pulverization.

[0048] The raw material components are preferably pre-mixed. There are no particular limitations on the mixer that can be used for pre-mixing, but preferred examples include a mechanical stirring mixer, a Nauta mixer which is a conical screw mixer, and an FM mixer which is a high-speed stirring mixer.

[0049] The raw material mixture is pulverized using a pulverizer to obtain a raw material mixture. The above-mentioned pulverizer can also perform stirring and mixing at the same time as pulverization. The method of performing mixing accompanied by pulverization using a pulverizer has conventionally been adopted as a solid-phase method (mechanical milling method). As the pulverizer, for example, a media-type pulverizer using a pulverization medium can be used.

[0050] The raw material mixture is preferably pulverized in a solvent using a pulverizer to obtain a raw material mixture slurry, from the viewpoint of reducing aggregation of the solid electrolyte raw materials. The above-mentioned pulverizer is preferably a wet pulverizer that can handle wet pulverization. Representative examples of wet grinders include wet bead mills, wet ball mills, and wet vibration mills. Wet bead mills, which use beads as grinding media, are preferred because they allow for free adjustment of grinding operation conditions and are easily adaptable to smaller particle sizes.

[0051] Alternatively, a flow-through mill can be used, which is capable of circulating the slurry to be pulverized as needed. Specifically, a mill that circulates the slurry between a mill (pulverizing mixer) that pulverizes the slurry and a temperature holding tank (reaction vessel) can be used.

[0052] The size of the beads or balls used in the ball mill or bead mill may be appropriately selected depending on the desired particle size, processing amount, etc. For example, the diameter of the beads is usually 0.05 mm or more, preferably 0.1 mm or more, more preferably 0.3 mm or more, with the upper limit being usually 5.0 mm or less, preferably 3.0 mm or less, more preferably 2.0 mm or less. The diameter of the balls is usually 2.0 mm or more, preferably 2.5 mm or more, more preferably 3.0 mm or more, with the upper limit being usually 20.0 mm or less, preferably 15.0 mm or less, more preferably 10.0 mm or less. Examples of materials for the beads and balls include metals such as stainless steel, chrome steel, and tungsten carbide; ceramics such as zirconia and silicon nitride; and minerals such as agate.

[0053] When a ball mill or a bead mill is used, the peripheral speed varies depending on the scale of the processing, so it is difficult to generalize, but it is usually 0.3 m / s or more, preferably 1.5 m / s or more, and more preferably 3.0 m / s or more, and the upper limit is usually 15.5 m / s or less, preferably 14.0 m / s or less, and more preferably 12.5 m / s or less. In this case, the grinding time varies depending on the scale of the treatment and cannot be generalized, but is usually 0.5 hours or more, preferably 1 hour or more, more preferably 5 hours or more, and even more preferably 10 hours or more, and the upper limit is usually 100 hours or less, preferably 72 hours or less, more preferably 48 hours or less, even more preferably 36 hours or less, even more preferably 24 hours or less, and even more preferably 10 hours or less.

[0054] By selecting the size and material of the medium (beads, balls) used, the rotor peripheral speed (the rotation speed of the tip of the stirring blade), and the time, etc., it is possible to perform mixing, stirring, pulverization, or a combination of these processes, and to adjust the particle size, etc. of the solid electrolyte raw material.

[0055] (solvent) As the solvent, for example, nonpolar solvents such as hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents, and polar solvents such as solvents containing heteroatoms are preferably used, and it is preferable to use a combination of a nonpolar solvent and a polar solvent. When a combination of a nonpolar solvent and a polar solvent is used, aromatic hydrocarbon solvents, especially toluene and ethylbenzene, are preferred as the nonpolar solvent, and nitrile solvents, which have the property of forming an azeotrope with aromatic hydrocarbon solvents such as toluene and are easily removed together with aromatic hydrocarbon solvents such as toluene, are preferred as the polar solvent.

[0056] The content of the nonpolar solvent in the solvent is preferably 95% by mass or more, and when a nonpolar solvent and a polar solvent are used in combination, the content of the polar solvent in the solvent is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more, with the upper limit being preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0057] (Heat treatment) In obtaining the raw material mixture, when the raw material contents are pulverized in a solvent using a pulverizer to obtain a raw material mixture slurry, it is preferable to include, after obtaining the raw material mixture, heat-treating the raw material mixture in the raw material mixture slurry using a pressure-resistant vessel or under reflux, because this makes it easier to obtain a sulfide solid electrolyte having an argyrodite-type crystal structure more efficiently. When the heating temperature exceeds the boiling point of the solvent used, it is preferable to use an autoclave as the pressure vessel. The heating temperature in the heat treatment may be appropriately selected depending on the type of solid electrolyte raw material used, and is, for example, preferably 150° C. or higher, more preferably 160° C. or higher, even more preferably 170° C. or higher, and even more preferably 180° C. or higher, with the upper limit being preferably 300° C. or lower, more preferably 280° C. or lower, even more preferably 270° C. or lower, and even more preferably 260° C. or lower. The heating time is preferably 10 minutes to 6 hours, more preferably 10 minutes to 3 hours, and even more preferably 30 minutes to 2 hours.

[0058] When the heat treatment is carried out while refluxing the solvent, the method is not particularly limited, and for example, a cooler (such as a Dimroth cooler) that cools the vapor and returns it to the solvent can be used.

[0059] (to dry) From the viewpoint of efficiently removing the solvent from the treated product, it is preferable to include drying the treated product obtained by the heat treatment after the heat treatment. There are no particular limitations on the method for drying the treated product, but fluidized drying using media particles as a medium is preferred because it allows drying in a shorter time. From the viewpoint of further increasing productivity, the fluidized drying is preferably carried out using a fluidized medium dryer having a mechanism for fluidizing media particles with a gas. Examples of media used in media fluidized bed dryers include media particles such as ceramic balls, zirconia beads, etc. Media fluidized bed dryers are dryers that heat the material to be dried using a fluidized bed formed by these media particles, and a heated airflow is used to form the fluidized bed.

[0060] As the gas used for the heated gas flow, it is preferable to use an inert gas such as nitrogen or argon from the viewpoint of suppressing deterioration of the material to be treated due to oxidation, and it is more preferable to use nitrogen in consideration of cost.

[0061] The temperature of the gas supplied to the medium fluidized dryer is usually about 60 to 200°C, and from the viewpoint of drying in a shorter time, it is preferably 70 to 180°C, more preferably 80 to 160°C, and even more preferably 90 to 150°C.

[0062] The gas supply rate is usually about 0.5 to 10.0 m / s based on the supply temperature, and from the viewpoint of maintaining good fluidity of the media particles, it is preferably 1.0 to 8.0 m / s, more preferably 1.5 to 5.0 m / s, and even more preferably 2.0 to 3.5 m / s. The gas supply rate is the linear velocity relative to the cross-sectional area of ​​the fluidized bed of media particles serving as the medium, in the direction perpendicular to the gas flow direction.

[0063] (Firing) The manufacturing method of this embodiment includes firing an object to be fired using a device having at least a portion of its interior coated with ceramic. The equipment is not particularly limited as long as it has excellent corrosion resistance, but is preferably a calcination furnace from the viewpoint of further demonstrating the effects of the present invention. Examples of calcination furnaces include batch calcination furnaces such as muffle furnaces, tubular furnaces, and atmosphere furnaces; and continuous calcination furnaces such as tunnel kilns, pusher kilns, roller hearth kilns, and rotary kilns. Among these, continuous calcination furnaces are preferred, and rotary kilns are more preferred, from the viewpoint of more efficient mass production.

[0064] As described above, in the manufacturing method of this embodiment, when the firing object is fired, the firing device is one in which at least a portion of the interior is coated with ceramics, as described above. When there are multiple devices in which the firing object is fired, it is preferable that at least one of the devices is one in which at least a portion of the interior is coated with ceramics, and it is more preferable that all of the devices are one in which at least a portion of the interior is coated with ceramics.

[0065] The rotary kiln includes a furnace tube including a heating section for firing the material to be fired, and a rotary drive section for rotating the furnace tube. The rotary kiln has a supply port at one end and a discharge port at the other end. The furnace tube is installed so that the discharge port side of the furnace tube is lower than the supply port side. The material to be fired is fed into the inclined and rotating furnace tube, transported to the heating section, heated (fired), and then transported to the discharge port.

[0066] Since the material to be fired is heated by a heating section of the furnace tube, the inside of the furnace tube is exposed to a severely corrosive environment, and therefore, from the viewpoint of further improving corrosion resistance, the inside of the furnace tube is preferably coated with ceramics, which makes it easier to obtain a high-quality sulfide solid electrolyte without the risk of foreign matter being mixed in.

[0067] The material of the furnace tube is not particularly limited, and examples thereof include metals such as carbon steel and stainless steel; ceramics such as silicon carbide, alumina, mullite and silicon nitride; SUS; and quartz.

[0068] The rotary kiln may be equipped with a raw material supplying device such as a feeder and a product collecting device such as a hopper. Since the interior of these devices comes into contact with the material to be fired, the interior of the devices is preferably coated with ceramics in order to enhance the corrosion resistance of the interior of the devices and to further demonstrate the effects of the present invention.

[0069] From the viewpoint of further improving corrosion resistance and further exerting the effects of the present invention, the ceramic used for coating the inside of the device preferably contains at least one selected from the group consisting of metal oxide, metal nitride, metal carbonitride, metal carbide, and amorphous carbon, and more preferably contains at least one selected from the group consisting of zirconium oxide, chromium oxide, aluminum oxide, silicon oxide, titanium oxide, yttrium oxide, titanium nitride, titanium aluminum nitride, chromium nitride, titanium carbonitride, silicon carbide, titanium carbide, and amorphous carbon.

[0070] The coating method for forming a ceramic coating on the inside of the device is not particularly limited, but examples thereof include spray coating, immersion, etc. Devices whose insides have been coated in advance may be used, or uncoated devices may be used by coating the insides later.

[0071] By heating (firing) the firing object, an argyrodite-type crystal structure is formed and the crystallinity is improved, so that a high-quality sulfide solid electrolyte having an argyrodite-type crystal structure can be obtained.

[0072] The heating temperature in the calcination may be appropriately selected depending on the composition of the sulfide solid electrolyte to be obtained, and is, for example, preferably 350° C. or higher and 500° C. or lower, more preferably 380° C. or higher and 500° C. or lower, even more preferably 400° C. or higher and 490° C. or lower, and still more preferably 410° C. or higher and 490° C. or lower. In the production method of this embodiment, even if the calcination target containing sulfur atoms is calcined within the above temperature range, the corrosion resistance of the equipment used is excellent, and therefore the effects of the present invention can be exerted. The heating time is preferably from 1 minute to 6 hours, more preferably from 1 minute to 2 hours, and even more preferably from 5 minutes to 1 hour.

[0073] The firing is preferably carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere or an argon atmosphere) or a reduced pressure atmosphere (particularly in a vacuum), which makes it easier to obtain a sulfide solid electrolyte having a higher quality argyrodite-type crystal structure.

[0074] (Sulfide solid electrolyte) The sulfide solid electrolyte obtained by the production method of this embodiment preferably has an argyrodite-type crystal structure. The argyrodite-type crystal structure basically has the structural skeleton of Li7PS6, with some of the P substituted with Si. The composition formula of the argyrodite crystal structure is, for example, Li 7-x P 1-y Si y S6, Li7+x P 1-y Si y Examples include S6 (where x is from -0.6 to 0.6 and y is from 0.1 to 0.6). The alditol-type crystal structure represented by these compositional formulas is cubic or orthorhombic, preferably cubic, and in X-ray diffraction measurement using CuKα radiation, it has peaks mainly appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0°.

[0075] As the compositional formula of the alditol-type crystal structure, Li 7-x-2y PS 6-x-y Cl x (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5) can be mentioned. The alditol-type crystal structure represented by this compositional formula is preferably cubic, and in X-ray diffraction measurement using CuKα radiation, it has peaks mainly appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Also, as the compositional formula of the alditol-type crystal structure, Li 7-x PS 6-x Ha x (Ha is Cl or Br, and x is preferably from 0.2 to 1.8) can also be mentioned. The alditol-type crystal structure represented by this compositional formula is preferably cubic, and in X-ray diffraction measurement using CuKα radiation, it has peaks mainly appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0°. Note that these peak positions may shift within a range of ±0.5°.

[0076] Here, when the sulfide solid electrolyte obtained by the manufacturing method of the present embodiment contains lithium atoms, sulfur atoms, phosphorus atoms and halogen atoms, the above "Li 7-x P 1-y Si y S6, Li 7+x P 1-y Si yIn the compositional formula of "S6 (where x is -0.6 to 0.6 and y is 0.1 to 0.6)", and when using an atom other than a chlorine atom as the halogen atom, "Li 7-x-2y PS 6-x-y Cl x In the compositional formula of "(0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5)", it may not be shown. However, when having the same diffraction peaks as the diffraction peaks described as the diffraction peaks of the above "al-djerroudite type crystal structure", it can be said that the sulfide solid electrolyte obtained by the production method of the present embodiment preferably has an al-djerroudite type crystal structure formed by lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms.

[0077] In the sulfide solid electrolyte obtained by the production method of the present embodiment, the composition ratio (molar ratio) of lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms is preferably 1.0 to 1.8:0.1 to 0.8:1.0 to 2.0:0.01 to 0.6, more preferably 1.1 to 1.7:0.2 to 0.6:1.2 to 1.8:0.05 to 0.5, and still more preferably 1.2 to 1.6:0.25 to 0.5:1.3 to 1.7:0.08 to 0.4.

[0078] When using bromine and iodine, or using bromine and chlorine in combination as the halogen atom, the composition ratio (molar ratio) of lithium atoms, phosphorus atoms, sulfur atoms, bromine, and chlorine (or iodine) is preferably 1.0 to 1.8:0.1 to 0.8:1.0 to 2.0:0.01 to 0.3:0.01 to 0.3, more preferably 1.1 to 1.7:0.2 to 0.6:1.2 to 1.8:0.02 to 0.25:0.02 to 0.25, still more preferably 1.2 to 1.6:0.25 to 0.5:1.3 to 1.7:0.03 to 0.2:0.03 to 0.2, and even more preferably 1.35 to 1.45:0.3 to 0.45:1.4 to 1.7:0.04 to 0.18:0.04 to 0.18. Note that the types and composition ratios (molar ratios) of the atoms constituting the sulfide solid electrolyte obtained by the production method of the present embodiment can be confirmed by, for example, an ICP emission spectroscopic analyzer.

[0079] The shape of the sulfide solid electrolyte obtained by the production method of this embodiment is not particularly limited, but may be, for example, particulate. The average particle diameter (D 50 ) can be, for example, in the range of 0.01 μm to 500 μm, or 0.1 to 200 μm.

[0080] (to crush) The sulfide solid electrolyte obtained by the production method of this embodiment may be further pulverized, which allows the average particle size to be adjusted according to the application.

[0081] The sulfide solid electrolyte may be pulverized using a pulverizer, which may be appropriately selected from the pulverizers exemplified above as pulverizers that can be used to pulverize the raw materials, and a container-driven pulverizer such as a ball mill or a bead mill is preferably used. The grinding energy is preferably 0.05 kWh / kg or more, more preferably 0.1 kWh / kg or more, and even more preferably 0.15 kWh / kg or more, with the upper limit being preferably 1.5 kWh / kg or less, more preferably 1.25 kWh / kg or less, and even more preferably 1.0 kWh / kg or less. When the grinding energy is within the above range, it is easy to adjust the average particle size according to the desired application.

[0082] (Application) The sulfide solid electrolyte obtained by the manufacturing method of this embodiment may be used in a positive electrode layer, a negative electrode layer, or an electrolyte layer. Each layer can be manufactured by a known method.

[0083] (electrode composite material) When the sulfide solid electrolyte obtained by the production method of this embodiment is used as an electrode mixture, it can be used as an electrode mixture containing the sulfide solid electrolyte and an electrode active material. As the electrode active material, a positive electrode active material or a negative electrode active material is adopted depending on whether the electrode mixture is used for a positive electrode or a negative electrode. As the positive electrode active material and the negative electrode active material, materials conventionally used as these active materials can be used. In addition to the sulfide solid electrolyte and the electrode active material, other components such as a conductive material and a binder may also be included.

[0084] (Lithium-ion battery) When the sulfide solid electrolyte obtained by the production method of this embodiment is used as a battery, it can be used as a lithium ion battery containing at least one selected from the sulfide solid electrolyte and the electrode mixture. The battery preferably includes a current collector in addition to the positive electrode layer, electrolyte layer, and negative electrode layer, and a known current collector can be used. For example, a layer of a material that reacts with the solid electrolyte, such as Au, Pt, Al, Ti, or Cu, coated with Au or the like can be used. [Example]

[0085] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples in any way.

[0086] (Production Example 1: Production of treated material containing sulfur atoms) Lithium sulfide (manufactured by Idemitsu Kosan Co., Ltd.) was pulverized under a nitrogen atmosphere using a pin mill equipped with a constant volume feeder (model "100UPZ" manufactured by Hosokawa Micron Corporation) to an average particle size of 7.7 μm. Similarly to lithium sulfide, diphosphorus pentasulfide (manufactured by Thermophos Corporation, average particle size: 125 μm), lithium chloride (manufactured by Honjo Chemical Co., Ltd., average particle size: 308 μm), and lithium bromide (manufactured by Honjo Chemical Co., Ltd., average particle size: 38 μm) were also pulverized using a pin mill to an average particle size of 8.7 μm, 10.0 μm, and 5.0 μm, respectively.

[0087] In a nitrogen-atmosphere glove box, the solid electrolyte raw materials (lithium sulfide, diphosphorus pentasulfide, lithium chloride, and lithium bromide) were weighed out to a total of 110 g in a molar ratio of 47.5:12.5:25.0:15.0. A total of 110 g was then placed in a glass container and roughly mixed by shaking. The roughly mixed raw materials were dispersed in a mixed solvent of 1140 mL of dehydrated toluene (Fujifilm Wako Pure Chemical Industries, Ltd.) and 7 mL of dehydrated isobutyronitrile (Kishida Chemical Co., Ltd.) under a nitrogen atmosphere to produce a slurry (approximately 10% by mass of the raw materials). The slurry was then fed into a bead mill (model LMZ015, Ashizawa Finetech Co., Ltd.) and milled at a rotor peripheral speed of 12 m / s for 1 hour to obtain a raw material mixture slurry containing the milled raw materials.

[0088] The raw material mixture slurry was then placed in an autoclave (volume: 2000 mL, made of SUS316) equipped with a stirrer and a heating oil bath, and heat-treated at 200°C for 2 hours while stirring (rotation speed: 200 rpm). After heat treatment in the solvent, the slurry was transferred to a Schlenk flask purged with nitrogen, and the solvent was distilled off by drying under reduced pressure to obtain a treated product containing sulfur atoms.

[0089] (Corrosion resistance evaluation) (1) Preparation of test specimens As test pieces for Comparative Example 1, Comparative Example 2 and Example 1, Example 2, the test pieces shown below were prepared. Comparative Example 1: SUS304 (50 mm length x 25 mm width x 6 mm thickness) was used as a test piece for Comparative Example 1. Comparative Example 2: SUS316 (50 mm length x 25 mm width x 6 mm thickness) was used as a test piece for Comparative Example 2. Example 1: The test piece for Example 1 was a SUS304 (length 50 mm x width 25 mm x thickness 6 mm) with a zirconia coating applied to the entire surface. Example 2: The test piece for Example 2 was a SUS316 (length 50 mm x width 25 mm x thickness 6 mm) with a zirconia coating applied to the entire surface.

[0090] (2) Corrosion test The sulfur atom-containing treatment product obtained in Production Example 1 was placed in an alumina sagger (body: outer dimensions 110 mm × 110 mm × 90 mm (height), inner dimensions 106 mm × 106 mm × 86 mm (height); lid: outer dimensions 110 mm × 110 mm × 4 mm (height), inner dimensions 100 mm × 100 mm × 5 mm (height)) so that it was approximately 25 mm high from the bottom of the sagger. A test piece was placed in the sulfur atom-containing treatment product in the sagger so that half of its vertical surface was buried, and the sagger was then covered with aluminum foil. The portion of the test piece buried in the sulfur atom-containing treatment product was designated the solid phase portion, and the unburied portion was designated the gas phase portion. The sagger wrapped in aluminum foil was then placed in an electric furnace ("F-1404-P (model number)" manufactured by Tokyo Glass Instruments Co., Ltd.) and heated at a firing temperature of 410°C for 72 hours (12 hours of heating per day was repeated for 6 days). Next, the test piece was removed from the sagger, and the sulfide solid electrolyte attached to the test piece was removed.

[0091] (3) Exterior photo Photographs of the appearance of two longitudinal surfaces (front and back surfaces) of the test specimens before and after the corrosion test (2) above were taken. Fig. 1A is a photograph of the appearance of the test specimen in Comparative Example 1 (before and after the corrosion test), and Fig. 1B is a photograph of the appearance of the test specimen in Comparative Example 2 (before and after the corrosion test). Fig. 1C is a photograph of the appearance of the test specimen in Example 1 (before and after the corrosion test), and Fig. 1D is a photograph of the appearance of the test specimen in Example 2 (before and after the corrosion test).

[0092] (4) X-ray diffraction measurement (XRD) X-ray diffraction measurements were performed on the test specimens after the corrosion test in (2) above using an X-ray diffractometer (D8 DISCOVER Plus, manufactured by Bruker) under the following conditions. The XRD pattern of the test specimen in Comparative Example 1 after the corrosion test is shown in FIG. 2, and the XRD pattern of the test specimen in Comparative Example 2 after the corrosion test is shown in FIG. 4. The XRD pattern of the test specimen in Example 1 after the corrosion test is shown in FIG. 6, and the XRD pattern of the test specimen in Example 2 after the corrosion test is shown in FIG. 8. (Measurement conditions) Tube voltage: 45kV Tube current: 120mA X-ray wavelength: Cu-Kα ray (1.5418Å) Optical system: parallel beam method Slit configuration: Light source side solar slit 2.5°, divergence slit 0.2 mm, Twin Secondary 5.2mm, solar slit 4.0° on the light receiving side Detector: Semiconductor detector Eiger2R500K (1D mode) Measurement range: 2θ=5-80deg Step width, scan speed: 0.02 deg, 0.6 sec / step

[0093] (5) Elemental analysis using a scanning electron microscope-energy dispersive X-ray spectrometer (SEM-EDS) Elemental analysis was performed on the gas phase and solid phase portions of the test specimens before the corrosion test (2) above and after the corrosion test (2) above using an energy dispersive X-ray spectrometer (EDS) analyzer attached to the SEM apparatus. Fig. 3 is a chart showing the results of surface observation by SEM-EDS of the test specimens in Comparative Example 1 ((a) before the corrosion test, (b) the gas phase portion after the corrosion test, and (c) the solid phase portion after the corrosion test), and Fig. 5 is a chart showing the results of surface observation by SEM-EDS of the test specimens in Comparative Example 2 ((a) before the corrosion test, (b) the gas phase portion after the corrosion test, and (c) the solid phase portion after the corrosion test). FIG. 7 is a chart showing the results of surface observation by SEM-EDS of the test piece in Example 1 ((a) before the corrosion test, (b) the gas phase portion after the corrosion test, and (c) the solid phase portion after the corrosion test), and FIG. 9 is a chart showing the results of surface observation by SEM-EDS of the test piece in Example 2 ((a) before the corrosion test, (b) the gas phase portion after the corrosion test, and (c) the solid phase portion after the corrosion test).

[0094] 1A and 1B, it was confirmed that the test pieces in Comparative Examples 1 and 2 had both turned black after the corrosion test. By comparing the XRD patterns of the test pieces after the corrosion test shown in FIGS. 2 and 4 with the reference peaks shown below, peaks indicating Fe sulfides, FeNi sulfides, and FeCr sulfides were confirmed. This indicated that Fe sulfides, FeNi sulfides, and FeCr sulfides had both been formed on the surface of the test pieces in Comparative Examples 1 and 2. Furthermore, the charts showing the results of surface observation of the test pieces by SEM-EDS shown in FIGS. 3 and 5 indicated that the weight percentage of sulfur in the gas phase and solid phase of the test pieces in Comparative Examples 1 and 2 had significantly increased after the corrosion test. On the other hand, as shown in FIGS. 1C and 1D, no black discoloration was observed in any of the test pieces in Examples 1 and 2 after the corrosion test. By comparing the XRD patterns of the test pieces after the corrosion test shown in FIGS. 6 and 8 with the reference peaks shown below, no peaks indicating sulfides were confirmed, indicating that no sulfides were formed on the surfaces of any of the test pieces in Examples 1 and 2. Furthermore, as shown in the charts of FIGS. 7 and 9, which show the results of surface observation of the test pieces by SEM-EDS, sulfur was not detected in the gas phase or solid phase of any of the test pieces in Examples 1 and 2 after the corrosion test. Therefore, it can be said that the method for producing a sulfide solid electrolyte of this embodiment can produce a high-quality sulfide solid electrolyte without the risk of foreign matter being mixed in. [Industrial Applicability]

[0095] The method for producing a sulfide solid electrolyte according to the present embodiment can produce a high-quality sulfide solid electrolyte without the risk of foreign matter being mixed in. The obtained sulfide solid electrolyte is suitable for use in lithium ion batteries, particularly those used in automotive applications, as well as in information-related devices and communication devices such as personal computers, video cameras, and mobile phones, and is particularly suitable for use in all-solid-state batteries.

Claims

1. A raw material containing lithium atoms, sulfur atoms, and phosphorus atoms is pulverized by a pulverizer to obtain a raw material mixture; and A method for producing a sulfide solid electrolyte, comprising: firing an object to be fired using equipment having at least a portion of its interior coated with ceramic.

2. The method for producing a sulfide solid electrolyte according to claim 1 , wherein the equipment is a calcination furnace.

3. The method for producing a sulfide solid electrolyte according to claim 2 , wherein the firing furnace is a rotary kiln.

4. The method for producing a sulfide solid electrolyte according to claim 3 , wherein the rotary kiln includes a furnace tube, and the inside of the furnace tube is coated with ceramics.

5. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 4, wherein the ceramic comprises at least one selected from the group consisting of metal oxide, metal nitride, metal carbonitride, metal carbide, and amorphous carbon.

6. The ceramics are selected from the group consisting of zirconium oxide, chromium oxide, aluminum oxide, silicon oxide, titanium oxide, yttrium oxide, titanium nitride, titanium aluminum nitride, chromium nitride, titanium carbonitride, silicon carbide, titanium carbide, and amorphous carbon. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 4, comprising at least one selected from the group consisting of:

7. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 6, wherein the heating temperature for the firing is 350 ° C or higher and 500 ° C or lower.

8. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 7, wherein the firing is carried out in an inert gas atmosphere or a reduced pressure atmosphere.

9. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 8, wherein in obtaining the raw material mixture, the raw material content is pulverized in a solvent by a pulverizer to obtain a raw material mixture slurry.

10. 10. The method for producing a sulfide solid electrolyte according to claim 9, comprising, after obtaining the raw material mixture, heat-treating the raw material mixture in the raw material mixture slurry using a pressure-resistant vessel or under reflux.

11. The method for producing a sulfide solid electrolyte according to claim 10, further comprising, after the heat treatment, drying the treated product obtained by the heat treatment.

12. The method for producing a sulfide solid electrolyte according to claim 11 , wherein the drying is performed by fluidized drying using media particles as a medium.

Images