Method for cleaning sulfur atom-containing substance and apparatus for producing sulfide solid electrolyte or lithium sulfide

Abstract

Provided is a method that is for safely and efficiently cleaning a sulfur atom-containing substance adhering to the inside of a device constituting an apparatus for producing a sulfide solid electrolyte, and that can reduce the amount of wastewater, the method comprising: cooling the inside of the device; and supplying steam to the inside of the device.

Description

Method for cleaning sulfur atom-containing materials and apparatus for producing sulfide solid electrolyte or lithium sulfide

[0001] The present invention relates to a method for cleaning a sulfur atom-containing substance and an apparatus for producing a sulfide solid electrolyte or lithium sulfide.

[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 for use as their power sources has become increasingly important. Traditionally, batteries used for such applications have used electrolytes containing flammable organic solvents. However, because the electrolytes are liquid and flammable, safety concerns regarding leakage, fire, and other issues have arisen when used in batteries. In particular, for automotive applications, high capacity and high output are required, and safety concerns regarding batteries using conventional electrolytes are becoming increasingly serious. Therefore, all-solid-state batteries in which the electrolyte is replaced with a solid electrolyte layer are being developed because such batteries eliminate the use of flammable organic solvents, simplify safety devices, and offer superior manufacturing costs and productivity.

[0003] As a method for producing a solid electrolyte used in a solid electrolyte layer, mass production has been investigated, and a production method using a complexing agent has attracted attention as a method that is easily adaptable to scale-up. For example, a solid production method including using a specific compound having an amino group as a complexing agent and mixing the complexing agent with a solid electrolyte raw material to prepare an electrolyte precursor (see, for example, Patent Document 1), and a solid electrolyte production method including drying a slurry containing the complexing agent and the electrolyte precursor by fluidized drying using media particles (see, for example, Patent Document 2) are known. Furthermore, Patent Document 3 discloses a method for producing lithium sulfide used as a raw material for the solid electrolyte, in which lithium hydroxide and hydrogen sulfide are reacted in a nonpolar organic solvent such as toluene.

[0004] Furthermore, with regard to cleaning of equipment, Patent Document 4 discloses a method for cleaning the inside of a paint tank filled with solvent-containing paint, in which the solvent evaporated from the paint is condensed on the inner wall in a space within the tank, and the condensed solvent dissolves the paint adhering to the wall surface and causes it to flow down.

[0005] International Publication No. 2020 / 105737 Pamphlet International Publication No. 2021 / 230189 Pamphlet Japanese Patent Application Laid-Open No. 2010-163356 Japanese Patent Application Laid-Open No. 9-255088

[0006] The present invention has been made in view of the above circumstances, and aims to provide a method for cleaning sulfur atom-containing substances adhering to the inside of equipment in a production apparatus for a sulfide solid electrolyte or lithium sulfide, which can be done safely and efficiently and can also reduce the amount of wastewater, and an apparatus for producing a sulfide solid electrolyte or lithium sulfide.

[0007] A method for cleaning sulfur atom-containing substances according to the present invention is a method for cleaning sulfur atom-containing substances adhering to the inside of a device constituting an apparatus for producing a sulfide solid electrolyte or lithium sulfide, the method comprising cooling the inside of the device and supplying steam to the inside of the device.

[0008] Furthermore, the present invention provides an apparatus for producing a sulfide solid electrolyte or lithium sulfide, the apparatus comprising: a cooling device that cools the inside of the apparatus; and a cleaning facility having a steam supply device that supplies steam to the inside of the apparatus.

[0009] According to the present invention, it is possible to provide a method for cleaning sulfur atom-containing substances adhering to the inside of equipment in a manufacturing apparatus for a sulfide solid electrolyte or lithium sulfide, which can be done safely and efficiently and can also reduce the amount of wastewater, and an apparatus for manufacturing a sulfide solid electrolyte or lithium sulfide.

[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 numerical range expressed as "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​of the examples can also be used as the upper and lower limit values. Furthermore, preferred specifications can be arbitrarily adopted. In other words, one preferred specification can be adopted in combination with one or more other preferred specifications. It can be said that a combination of preferred items is more preferable.

[0011] (Findings Obtained by the Inventors to Achieve the Present Invention) The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found the following, which has led to the completion of the present invention.

[0012] As research into the practical application of all-solid-state batteries progresses, mass production of sulfide solid electrolytes has become an urgent issue. In recent years, as demand for sulfide solid electrolytes has increased, full-scale operations have begun, shifting from lab-scale facilities to plant-scale facilities for mass production, creating a need for efficient maintenance of these facilities. Maintenance work primarily involves repairing and replacing the equipment and various components used in the equipment, as well as cleaning the interior of the equipment. Sulfide solid electrolyte production equipment handles sulfur-containing materials (hereinafter also referred to as "sulfur-containing substances"), such as solid electrolyte raw materials such as lithium sulfide and diphosphorus pentasulfide, intermediates such as electrolyte precursors, and the final product, sulfide solid electrolyte. These sulfur-containing substances may react with moisture in the air to generate hydrogen sulfide, so safety considerations are necessary. Furthermore, lithium sulfide production equipment, which is the raw material for sulfide solid electrolytes, is also in a similar situation to the sulfide solid electrolyte production equipment, and lithium sulfide produced by this lithium sulfide production equipment is one of the sulfur-containing substances.

[0013] Until now, cleaning the inside of equipment before the above-mentioned maintenance work has been done by passing water through the inside of the equipment to be maintained and then draining it. However, in order to safely perform the maintenance work, multiple water flushes are required, which consumes a large amount of water and generates a large amount of wastewater. As the scale of facilities increases, the amount of water used and the amount of wastewater generated by cleaning the equipment continue to increase, making it necessary to reduce the amount of water used and the amount of wastewater generated.

[0014] Regarding equipment cleaning methods, Patent Document 3, as mentioned above, discloses a paint tank and its interior cleaning method, in which, in a paint tank filled with solvent-containing paint, the solvent evaporated from the paint is condensed on the inner wall in a space within the tank, and the condensed solvent dissolves the paint adhering to the wall surface and allows it to flow down. However, since the equipment to be cleaned internally is a "paint tank," it is different from the "equipment constituting an apparatus for producing sulfide solid electrolytes or lithium sulfide" that is the target of cleaning in the present invention. Furthermore, the target of cleaning in the internal cleaning method described in Patent Document 3 is the "paint" that is the content of the "paint tank," which is completely different from the "sulfur atom-containing substance" that is the target of the present invention.

[0015] In relation to the contents to be cleaned, Patent Document 3 mentions avoiding adverse effects on the human body and the environment due to the evaporation of the solvent, but does not anticipate any event requiring attention to safety in terms of the generation of hydrogen sulfide caused by the sulfur atom-containing substance targeted by the present invention through reaction with moisture in the atmosphere, etc. Furthermore, since Patent Document 3 uses a solvent for cleaning, it does not present any issues regarding reducing the amount of water used and wastewater discharged when washing the equipment.

[0016] The inventors of the present invention have conducted extensive research into how to efficiently clean sulfur-atom-containing substances adhering to the interior of equipment in order to reduce the amount of wastewater discharged. As a result, they have focused on steam as a cleaning medium. When steam is supplied to the interior of an equipment to be cleaned, the steam disperses so as to fill the interior of the equipment evenly. By cooling the steam uniformly dispersed inside the equipment, water adheres evenly and thoroughly to the interior of the equipment, and the adhering water turns into droplets and flows downward inside the equipment. Then, when the water droplets flowing evenly down the interior of the equipment come into contact with the sulfur-atom-containing substances adhering to the interior, the sulfur-atom-containing substances are deactivated, and the generation of hydrogen sulfide is suppressed and the sulfur-atom-containing substances are discharged together with the water droplets. In other words, they have discovered that by using steam as a cleaning medium, it is possible to clean the sulfur-atom-containing substances adhering to the interior of the equipment by deactivating them and washing them off.

[0017] Furthermore, when steam is used as a cleaning medium, even a small amount of steam can be used to evenly deposit water inside the equipment to be cleaned, forming water droplets, thereby reducing the amount of water used. As a result, the amount of wastewater can also be reduced. Thus, according to the cleaning method for sulfur atom-containing substances of the present invention, it is possible to safely and efficiently clean sulfur atom-containing substances adhering to the inside of equipment while further reducing the amount of wastewater.

[0018] (Regarding various aspects of the present embodiment) A method for cleaning a sulfur atom-containing substance according to a first aspect of the present embodiment is a method for cleaning a sulfur atom-containing substance adhering to the inside of a device constituting an apparatus for producing a sulfide solid electrolyte or lithium sulfide, the method including cooling the inside of the device and supplying steam to the inside of the device.

[0019] As described above, by supplying steam to the inside of the equipment and cooling the inside of the equipment, the supplied steam causes water to adhere evenly to the inside of the equipment, forming water droplets, thereby making it possible to deactivate and wash away sulfur atom-containing substances adhering to the inside of the equipment while reducing the amount of water used. Furthermore, by utilizing the dispersibility of steam, the amount of water used can be reduced, which also makes it possible to reduce the amount of water discharged. As a result, the cleaning method of this embodiment makes it possible to safely and efficiently clean sulfur atom-containing substances adhering to the inside of the equipment while further reducing the amount of water discharged.

[0020] A method for cleaning sulfur atom-containing substances according to a second aspect of the present embodiment is a method for cleaning sulfur atom-containing substances adhering to the inside of equipment according to the first aspect, wherein the cooling is carried out by at least one means selected from the group consisting of a cooling jacket and supply of water.

[0021] There are no particular limitations on the method for cooling the inside of the device, but from the viewpoint of more efficient cooling, preferred methods include using a cooling jacket and supplying water to the inside of the device.

[0022] A method for cleaning sulfur atom-containing substances according to a third aspect of the present embodiment is a method for cleaning sulfur atom-containing substances adhering to the inside of equipment according to the first or second aspect, comprising starting cooling the inside of the equipment and then starting the supply of steam.

[0023] In the cleaning method of this embodiment, by cooling the inside of the equipment in advance, the steam to be supplied subsequently can be more efficiently converted into water droplets, which makes it possible to clean the sulfur atom-containing substances adhering to the inside of the equipment while further reducing the amount of steam supplied, thereby reducing the amount of wastewater.

[0024] A method for cleaning a sulfur atom-containing substance according to a fourth aspect of the present embodiment is a method for cleaning a sulfur atom-containing substance adhering to the inside of equipment according to any one of the first to third aspects, wherein the sulfur atom-containing substance is at least one substance selected from a raw material inclusion, an intermediate, and a sulfide solid electrolyte.

[0025] The object to be cleaned in the cleaning method of the present embodiment can be any substance containing sulfur atoms that flows through an apparatus for producing a sulfide solid electrolyte or lithium sulfide. Typical examples include raw material-containing substances, intermediates, and sulfide solid electrolytes.

[0026] A cleaning method for sulfur atom-containing substances according to a fifth aspect of the present embodiment is the cleaning method for sulfur atom-containing substances adhering to the inside of equipment according to any one of the first to fourth aspects, wherein, in supplying the steam, the steam is supplied so that the pressure inside the equipment is 0.0 MPa or more and 0.35 MPa or less.

[0027] In the cleaning method of this embodiment, if steam is supplied so that the pressure inside the equipment is within the above range, it becomes possible to more efficiently clean the sulfur atom-containing substances adhering to the inside of the equipment, and to reduce the amount of wastewater.

[0028] A cleaning method for sulfur atom-containing substances according to a sixth aspect of the present embodiment is a cleaning method for sulfur atom-containing substances adhering to the inside of equipment according to any one of the first to fifth aspects, in which the steam is condensed and drained.

[0029] As described above, the cleaning method of this embodiment is a method for cleaning sulfur atom-containing substances with steam, in which steam supplied to the inside of an equipment adheres to the cooled interior of the equipment as water droplets, and the water droplets can wash away the sulfur atom-containing substances while deactivating them. That is, the steam supplied to the inside of the equipment condenses into water droplets, and the water droplets are drained to the outside of the equipment. The sixth embodiment clarifies this. Furthermore, when attention is paid to the state of the steam, it is supplied to the inside of the equipment, condenses, and is drained, which results in more safe and efficient cleaning of sulfur atom-containing substances attached to the inside of the equipment, and the amount of drainage can be reduced.

[0030] A method for cleaning sulfur atom-containing substances according to a seventh aspect of the present embodiment is the method for cleaning sulfur atom-containing substances adhering to the inside of equipment according to any one of the first to sixth aspects, wherein the steam is alkaline.

[0031] If the steam supplied to the inside of the equipment is alkaline, the cleaning effect on sulfur atom-containing substances is improved and the deactivation effect on sulfur atom-containing substances is also improved, making it possible to more safely and efficiently clean sulfur atom-containing substances adhering to the inside of the equipment, and reducing the amount of wastewater.

[0032] An apparatus for producing a sulfide solid electrolyte or lithium sulfide according to an eighth aspect of the present embodiment is a production apparatus including a cooling device that cools the inside of the apparatus, and a cleaning facility having a steam supply device that supplies steam to the inside of the apparatus.

[0033] The apparatus for producing a sulfide solid electrolyte or lithium sulfide according to the present embodiment is equipped with a cleaning facility having a cooling device and a steam supply device, thereby enabling the method for cleaning a sulfur atom-containing substance according to the present embodiment to be carried out. As a result, the apparatus is capable of producing a sulfide solid electrolyte or lithium sulfide, and is capable of cleaning sulfur atom-containing substances adhering to the interior of the apparatus safely and efficiently, while also reducing the amount of wastewater.

[0034] A ninth aspect of the present embodiment is the apparatus for producing a sulfide solid electrolyte or lithium sulfide according to the eighth aspect, further including a drainage system for draining condensed water of steam supplied to the inside of the apparatus.

[0035] When steam is supplied to the inside of the equipment from the steam supply device, the steam condenses and adheres to the inside of the cooled equipment as water droplets, and these water droplets can deactivate and wash away sulfur atom-containing substances. By providing the drainage facility, after the steam supplied to the inside of the equipment turns into water droplets, the water droplets can be easily drained, making it possible to more safely and efficiently wash away sulfur atom-containing substances adhering to the inside of the equipment and reducing the amount of wastewater.

[0036] The solid electrolyte of this embodiment will be described in more detail below in accordance with the above embodiment.

[0037] In this specification, the term "solid electrolyte" refers to an electrolyte that maintains a solid state at 25°C under a nitrogen atmosphere. The solid electrolyte in this embodiment preferably contains lithium atoms, phosphorus atoms, and sulfur atoms, and more preferably contains halogen atoms, and is a solid electrolyte that uses lithium atoms as conductive species and has ionic conductivity due to the lithium atoms. Here, those containing sulfur atoms are also called "sulfide solid electrolytes."

[0038] The term "solid electrolyte" includes both crystalline solid electrolytes and amorphous solid electrolytes. In this specification, a crystalline solid electrolyte is a solid electrolyte in which peaks derived from the solid electrolyte are observed in an X-ray diffraction pattern in X-ray diffraction measurement, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present. That is, a crystalline solid electrolyte includes a crystalline structure derived from the solid electrolyte, and a portion of the crystalline structure may be derived from the solid electrolyte, or the entire crystalline structure may be derived from the solid electrolyte. Furthermore, as long as a crystalline solid electrolyte has the X-ray diffraction pattern described above, it may also contain an amorphous solid electrolyte in part. Therefore, crystalline solid electrolytes include so-called glass ceramics obtained by heating an amorphous solid electrolyte to a temperature equal to or higher than its crystallization temperature. Furthermore, in this specification, an amorphous solid electrolyte is an electrolyte in which a halo pattern in X-ray diffraction measurement shows substantially no peaks other than those derived from the material, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present.

[0039] [Method for Cleaning Sulfur-Atom-Containing Substances] The method for cleaning sulfur-atom-containing substances of the present embodiment is a method for cleaning sulfur-atom-containing substances adhering to the inside of a device constituting an apparatus for producing a sulfide solid electrolyte or lithium sulfide, the method including cooling the inside of the device and supplying steam to the inside of the device.

[0040] The equipment constituting the sulfide solid electrolyte production apparatus to be cleaned by the method for cleaning a sulfur atom-containing material of this embodiment varies depending on the production method of the sulfide solid electrolyte, but mainly includes reaction equipment used for the reaction of the solid electrolyte raw material; heating equipment for removing the solvent (including a complexing agent) from a slurry or solution containing an intermediate such as the solid electrolyte raw material and / or an electrolyte precursor and the solvent (including a complexing agent) when a solvent (including a complexing agent) is used; heating equipment for crystallization, etc.; separation equipment for separating the sulfide solid electrolyte; particle size adjustment equipment for adjusting the particle size of the sulfide solid electrolyte; when heat treatment is performed using a pressure-resistant container, heating equipment for firing the pressure-resistant container and the heat-treated product; and piping connecting these devices. These equipment will be described in detail in the description of the production method and production apparatus for the sulfide solid electrolyte.

[0041] When an apparatus for producing a sulfide solid electrolyte is operated, sulfur atom-containing substances, such as solid electrolyte raw materials, intermediates such as an electrolyte precursor when a complexing agent is used, and even the finished sulfide solid electrolyte, adhere to the interior of the equipment and piping. In the method for cleaning sulfur atom-containing substances of the present embodiment, all of the equipment to which sulfur atom-containing substances may adhere by configuring and operating the apparatus for producing a sulfide solid electrolyte is subject to cleaning.

[0042] The sulfur atom-containing substances removed from the inside of equipment by the cleaning method of this embodiment include, as already described, sulfur atom-containing substances in a sulfide solid electrolyte production apparatus; intermediates such as a solid electrolyte raw material; an electrolyte precursor when a complexing agent is used; or a heat-treated product obtained by heat treatment using a pressure-resistant container when a pressure-resistant container is used; and a sulfide solid electrolyte product. These sulfur atom-containing substances may adhere individually to the inside of the equipment, or multiple types of sulfur atom-containing substances may adhere to the inside of a single equipment. For example, the solid electrolyte raw material and the sulfide solid electrolyte, or the electrolyte precursor when a complexing agent is used, adhere to the inside of the reaction equipment; the remaining solid electrolyte raw material, the electrolyte precursor, and the sulfide solid electrolyte produced by removing the complexing agent from the electrolyte precursor adhere to the inside of the heating equipment; the heat-treated product adheres to the inside of the pressure-resistant container; and the sulfide solid electrolyte, as well as intermediates such as the remaining solid electrolyte raw material, the electrolyte precursor, and the heat-treated product adhere to the separation equipment. In this way, in the cleaning method of this embodiment, the sulfur atom-containing substance removed from the inside of the equipment is at least one substance selected from a solid electrolyte raw material containing sulfur atoms, an intermediate such as an electrolyte precursor or a heat-treated product, and a sulfide solid electrolyte. Details of these sulfur atom-containing substances will also be described in detail in the description of the method and apparatus for producing a sulfide solid electrolyte.

[0043] Furthermore, the equipment constituting an apparatus for producing lithium sulfide, which is to be cleaned by the method for cleaning a sulfur atom-containing material of this embodiment, may vary depending on the method for producing lithium sulfide, but representative examples include a reaction vessel in which lithium hydroxide is produced by reacting with hydrogen sulfide and in which the reaction mainly takes place between lithium hydroxide and hydrogen sulfide; drying equipment when a solvent is used during the reaction; piping connecting these devices; piping connecting these devices with peripheral devices (auxiliary equipment); etc. Examples of sulfur atom-containing materials removed from the inside of equipment by the cleaning method of this embodiment include lithium sulfide obtained by reacting lithium hydroxide with hydrogen sulfide as a sulfur atom-containing material in an apparatus for producing lithium sulfide, and sulfur that can be used as a raw material.

[0044] When an apparatus for producing lithium sulfide is operated, sulfur atom-containing substances such as sulfur as a raw material and lithium sulfide as a product adhere to the inside of the equipment and piping, as in the case of the above-mentioned apparatus for producing a sulfide solid electrolyte. In the method for cleaning sulfur atom-containing substances of the present embodiment, all of the equipment constituting the apparatus for producing lithium sulfide and operating it are targets for cleaning.

[0045] (Cooling the inside of the equipment) The method for cleaning a sulfur atom-containing material of this embodiment includes cooling the inside of the equipment constituting the apparatus for producing a sulfide solid electrolyte or lithium sulfide. By cooling the inside of the equipment, steam supplied to the inside of the equipment can be cooled, and water droplets can be generated by condensation of the steam, allowing the sulfur atom-containing material to be quickly cleaned with the water droplets.

[0046] The method for cooling the inside of the device is not particularly limited as long as it can cool the inside of the device. From the viewpoint of easy and efficient cooling, preferred examples include a method of cooling from the outside of the device using a cooling jacket, and a method of supplying water.

[0047] The refrigerant used in the cooling jacket may be water, an antifreeze such as ethylene glycol, or a liquefied gas such as liquid nitrogen or liquid helium, with water being preferred in consideration of the desired cooling temperature and ease of handling. Water may be supplied either by spraying it directly into the equipment or by spraying it using a spray nozzle or the like.

[0048] The temperature inside the equipment cannot be generally determined because it varies depending on the temperature of the refrigerant used in the cooling jacket and the temperature of the supplied water, but is preferably 1°C or higher, more preferably 3°C or higher, and the upper limit is set to a temperature below room temperature in summer (for example, 35°C or lower), preferably 30°C or lower, more preferably 15°C or lower, and even more preferably 10°C or lower. Here, the temperature inside the equipment is basically the same as the temperature of the refrigerant used in the cooling jacket and the temperature of the supplied water, so the temperature of the refrigerant and the temperature of the supplied water are preferably set within the above ranges. By cooling the temperature inside the equipment to within the above ranges, condensation of steam can be promoted, making it possible to more efficiently wash sulfur atom-containing substances and reduce the amount of wastewater.

[0049] (Supplying Steam to the Inside of the Equipment) The cleaning method for sulfur atom-containing substances of this embodiment includes supplying steam to the inside of the equipment. By combining the cooling and supplying steam to the inside of the equipment, the sulfur atom-containing substances can be efficiently cleaned with water droplets generated by condensation of the steam, and the amount of wastewater can be reduced.

[0050] The steam supplied to the inside of the equipment has a steam pressure (absolute pressure) of preferably 0.05 MPa or more, more preferably 0.1 MPa or more, and even more preferably 0.31 MPa or more, with the upper limit being preferably 5.0 MPa or less, more preferably 3.0 MPa or less, and even more preferably 1.0 MPa or less. When the steam pressure is within the above range, it is possible to more efficiently wash the sulfur atom-containing substance, and it is possible to reduce the amount of wastewater.

[0051] The steam supplied to the inside of the equipment is preferably alkaline. By using alkaline steam, it is possible to more efficiently clean sulfur atom-containing substances and reduce the amount of wastewater. For example, the alkaline steam can be made alkaline by using a nitrogen-containing compound such as ammonia or hydrazine. The pH of the steam is preferably 7.5 or higher, more preferably 8.5 or higher, with an upper limit of preferably 13 or lower, more preferably 10 or lower, and the pH can be adjusted to within the above range by using the nitrogen-containing compound.

[0052] The steam supplied to the inside of the equipment is preferably supplied so that the pressure inside the equipment is 0.0 MPa or more, more preferably 0.01 MPa or more, even more preferably 0.05 MPa or more, with the upper limit being preferably 0.35 MPa or less, more preferably 0.3 MPa or less, even more preferably 0.2 MPa or less. The pressure inside the equipment is determined by the balance between the amount of steam supplied and the amount of steam condensed into water droplets, and can be adjusted by the amount of steam supplied, the cooling temperature inside the equipment, etc. When the pressure inside the equipment is within the above range, the generation of water droplets due to condensation of steam proceeds quickly, and it can be said that the sulfur atom-containing substance is efficiently washed.

[0053] In the cleaning method for sulfur atom-containing substances of this embodiment, there is no particular limitation on the order in which cooling the inside of the equipment (hereinafter may be simply referred to as "cooling") and supplying steam to the inside of the equipment (hereinafter may be simply referred to as "steam supply") are performed. For example, cooling may be started and then steam supply may be started, or steam supply may be started and then cooling may be started, or cooling and steam supply may be started simultaneously. Furthermore, cooling and steam supply may be performed simultaneously; for example, cooling may be started and then steam supply may be started while continuing cooling, or steam supply may be started and cooling may be started while continuing steam supply.

[0054] In the cleaning method for sulfur atom-containing substances of this embodiment, it is preferable to start cooling the inside of the equipment and then start supplying steam. This is because the generation of water droplets by condensation of steam proceeds more efficiently. From the same viewpoint, it is more preferable to start cooling the inside of the equipment and then start supplying steam, so that cooling the inside of the equipment and supplying steam are carried out simultaneously.

[0055] When steam is supplied into the interior of the equipment, the steam forms water droplets and flows down inside the equipment. The water droplets that flow down may be discharged directly from the bottom of the equipment, or may be discharged all at once after accumulating to a certain extent at the bottom of the equipment. In this way, when focusing on the steam supplied into the interior of the equipment, the steam condenses to form water droplets, which flow down to the bottom of the equipment together with the sulfur atom-containing substance and are discharged from the equipment. From the viewpoint of adjusting the pressure inside the equipment to the above range and more efficiently cleaning the sulfur atom-containing substance, it is preferable to discharge all at once the water that has accumulated at the bottom of the equipment at regular intervals.

[0056] The cleaning method of the present embodiment may include supplying an alkaline aqueous solution to the interior of the equipment. Supplying the alkaline aqueous solution can improve the deactivation effect of sulfur atom-containing substances adhering to the interior of the equipment. Supplying the alkaline aqueous solution to the interior of the equipment may be performed before or after supplying steam.

[0057] From the viewpoint of more efficiently deactivating the sulfur atom-containing material, preferred alkaline aqueous solutions include aqueous solutions of compounds such as hydroxides and carbonates of alkali metals and hydroxides of alkaline earth metals, and aqueous solutions of nitrogen-containing compounds such as ammonia and hydrazine, other than these compounds. As alkali metals, sodium and potassium are preferred, and sodium is more preferred. As alkaline earth metals, calcium and magnesium are preferred. Hydroxides are also preferred. From the same viewpoint, the content of the above-mentioned compounds contained in the alkaline aqueous solution is such that the pH of the alkaline aqueous solution is preferably 7.5 or more, more preferably 8.5 or more, and preferably 13 or less, more preferably 10 or less. The same applies to the content when a nitrogen-containing compound is used.

[0058] [Method for Producing Sulfide Solid Electrolyte] As described above, the cleaning method of this embodiment can efficiently clean sulfur atom-containing substances adhering to the interior of equipment. Therefore, when the purpose of maintenance is to clean the interior of equipment, the maintenance itself can be performed efficiently. Furthermore, when the maintenance is to repair the interior of equipment, the maintenance can be started more quickly. Furthermore, when starting operation of a production apparatus for sulfide solid electrolytes and lithium sulfide, the dew point inside the equipment is lowered to suppress reaction of sulfur atom-containing substances with moisture in the atmosphere. According to the cleaning method of this embodiment, the amount of water used can be reduced compared to conventional cleaning methods, and the amount of water present inside the equipment can be reduced, making it easier to lower the dew point inside the equipment. Therefore, operation of the production apparatus can be started more quickly after maintenance. As described above, the cleaning method of this embodiment can further shorten the time required for maintenance, i.e., the downtime of the production apparatus can be further reduced. Therefore, even if the same production apparatus is used, sulfide solid electrolytes and lithium sulfide can be produced with a higher operating rate.

[0059] The sulfur atom-containing substance to be cleaned by the cleaning method of this embodiment and the equipment to which the sulfur atom-containing substance adheres may vary depending on the method for producing the sulfide solid electrolyte and lithium sulfide, as described above. Hereinafter, the sulfur atom-containing substance and the equipment to which the sulfur atom-containing substance adheres will be described in more detail along with the method for producing the sulfide solid electrolyte. Next, the method for producing lithium sulfide will also be described.

[0060] The sulfide solid electrolyte can be produced by using a sulfide solid electrolyte production apparatus, and from the viewpoint of producing a sulfide solid electrolyte with a higher operating rate, it is preferable to carry out a method for producing a sulfide solid electrolyte, the method including cleaning sulfur atom-containing substances adhering to the inside of devices constituting the sulfide solid electrolyte production apparatus by the cleaning method of the above-described embodiment, and then using the sulfide solid electrolyte production apparatus.

[0061] The method for producing a sulfide solid electrolyte includes cleaning sulfur atom-containing substances adhering to the inside of devices constituting an apparatus for producing a sulfide solid electrolyte by the cleaning method of the present embodiment, which enables production of a sulfide solid electrolyte with a higher operating rate, even when the same production apparatus is used, as described above.

[0062] The method for producing a sulfide solid electrolyte includes, following the above-mentioned cleaning, using a sulfide solid electrolyte production apparatus. The sulfide solid electrolyte production apparatus employed in the method for producing a sulfide solid electrolyte includes cleaning equipment used to clean at least sulfur atom-containing substances adhering to the interior of the equipment, the cleaning equipment including a cooling device for cooling the interior of the equipment to be cleaned and a steam supply device for supplying steam to the interior of the equipment. Furthermore, the sulfide solid electrolyte production apparatus employed in the method for producing a sulfide solid electrolyte further includes, in addition to the above-mentioned cleaning equipment, various devices according to the production method used to obtain a sulfide solid electrolyte by reacting solid electrolyte raw materials.

[0063] (Washing the sulfur atom-containing substance) The sulfur atom-containing substance is washed by the method for washing the sulfur atom-containing substance of the present embodiment. The specific washing method is as described above in the method for washing the sulfur atom-containing substance of the present embodiment.

[0064] (Use of an Apparatus for Producing a Sulfide Solid Electrolyte) In the method for producing a sulfide solid electrolyte, using an apparatus for producing a sulfide solid electrolyte essentially means producing a sulfide solid electrolyte, that is, obtaining a sulfide solid electrolyte by reacting solid electrolyte raw materials. As described above, the apparatus for producing a sulfide solid electrolyte includes various devices according to the production method used to obtain a sulfide solid electrolyte by reacting solid electrolyte raw materials. Below, the apparatus for producing a sulfide solid electrolyte will be described in terms of obtaining a sulfide solid electrolyte by reacting solid electrolyte raw materials.

[0065] In obtaining a sulfide solid electrolyte by reacting the solid electrolyte raw materials, the reaction of the solid electrolyte raw materials may be carried out by a known method such as a mechanical milling method, a melt-cooling method, or a slurry method (including a solution method).

[0066] (Mechanical Milling Method) When the mechanical milling method is employed, the apparatus for producing the sulfide solid electrolyte may include at least a reaction device equipped with a pulverizer that pulverizes the solid electrolyte raw materials to cause a reaction, and further, as necessary, a heating device that performs heating for crystallization, etc. The sulfide solid electrolyte and remaining solid electrolyte raw materials may adhere to the inside of the reaction device equipped with the pulverizer and the heating device.

[0067] As the pulverizer, a media-type pulverizer using a pulverizing medium can be used. Media-type pulverizers are broadly classified into container-driven pulverizers and media-agitation pulverizers. Examples of container-driven pulverizers include agitation tanks, grinding tanks, and combinations thereof, such as ball mills and bead mills. Examples of media-agitation pulverizers include impact pulverizers such as cutter mills, hammer mills, and pin mills; tower-type pulverizers such as tower mills; agitation tank pulverizers such as attritors, aquamizers, and sand grinders; flow tank pulverizers such as Viscomill and pearl mills; flow pipe pulverizers; annular pulverizers such as Coball mills; continuous dynamic pulverizers; and single- or multi-shaft kneaders. Considering the ease of adjusting the particle size of the resulting sulfide, the ball mills and bead mills exemplified as container-driven pulverizers are preferred, and planetary pulverizers are particularly preferred.

[0068] Furthermore, when a solvent is used to pulverize the solid electrolyte raw material and the material to be pulverized is in a liquid or slurry state, a flow-through pulverizer capable of circulating the material as needed can also be used. Specific examples of the flow-through pulverizer include a pulverizer that circulates the slurry between a pulverizer (pulverizer mixer) that pulverizes the slurry and a temperature holding tank (reaction vessel).

[0069] When a solvent is used during mechanical milling of the solid electrolyte raw material, drying may be performed to remove the solvent. When removing the solvent, various dryers can be used, such as vacuum dryers; pneumatic dryers such as stationary dryers, fluidized dryers, medium-fluidized dryers, and spray dryers; and dryers combining these types. The heating temperature in this case cannot be generalized because it varies depending on the type of solvent to be removed and the pressure conditions during drying. However, it is usually 5 to 100°C, preferably 10 to 85°C, and more preferably 15 to 70°C, and reduced-pressure drying (vacuum drying) is preferred. Drying can also be performed by filtration using a glass filter or the like, solid-liquid separation by decantation, or solid-liquid separation using a centrifuge or the like. Drying using the above-mentioned various dryers and drying by solid-liquid separation can also be performed in combination.

[0070] As described above, heating for crystallization or the like may be performed. Examples of heating equipment used in this case include a hot plate, a vacuum heating device, an argon gas atmosphere furnace, a baking furnace, a vacuum baking furnace, etc., depending on the scale of the treatment. In addition, various dryers used for drying to remove the solvent can also be used, and the heating equipment for removing the solvent and the heating equipment for crystallization or the like may be shared.

[0071] The heating temperature for crystallization cannot be generalized because it varies depending on the crystal structure to be obtained, but is usually preferably 130° C. or higher, more preferably 135° C. or higher, and even more preferably 140° C. or higher, and although there is no particular upper limit, it is preferably 600° C. or lower, more preferably 550° C. or lower, and even more preferably 500° C. or lower. Heating for crystallization can be carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere or an argon atmosphere) or a reduced pressure atmosphere (particularly in vacuum).

[0072] (Melt quenching method) When the melt quenching method is adopted, the apparatus for producing a sulfide solid electrolyte may include at least a reaction device including a heater for reacting solid electrolyte raw materials, and a quenching device including a quenching tank for quenching the fired product (melted product) fired by the heating device. The sulfide solid electrolyte, remaining solid electrolyte raw materials, and the fired product serving as an intermediate may adhere to the inside of the reaction device including a heater and the quenching device including a quenching tank.

[0073] The heating device is not particularly limited as long as it can heat the solid electrolyte raw material to a temperature at which it can melt (preferably 400 to 1000°C, more preferably 800 to 900°C), and can be appropriately selected from the heating devices exemplified as heating devices used for heating for crystallization in the mechanical milling method described above. The quenching tank can be a tank that can cool the molten solid electrolyte raw material to a temperature at which it can be quenched (preferably 10°C or less, more preferably 0°C or less), for example, a tank that can hold a refrigerant such as ice or liquid nitrogen.

[0074] (Slurry Method) When a slurry method (including a solution method) is employed, for example, when a solid electrolyte raw material is reacted while being mixed in a solvent (complexing agent) containing a heteroatom, the sulfide solid electrolyte production apparatus may include a reaction device equipped with a reaction vessel having a stirring blade for mixing the solid electrolyte raw material with the solvent (complexing agent) containing a heteroatom to produce an intermediate electrolyte precursor; a heating device for removing the complexing agent from the electrolyte precursor; a heating device for crystallization, etc. When a slurry method (including a solution method) is employed, the electrolyte precursor and remaining solid electrolyte raw material may adhere to the inside of the reaction vessel equipped with the reaction vessel, and the sulfide solid electrolyte, remaining solid electrolyte raw material, and electrolyte precursor may adhere to the inside of the heating device for removing the complexing agent and the heating device for crystallization, etc.

[0075] The reaction equipment may be, for example, a mechanically agitated mixer equipped with an agitating blade inside a reaction vessel. Examples of mechanically agitated mixers include high-speed agitation mixers and double-arm mixers. High-speed agitation mixers are preferably used from the viewpoint of improving the uniformity of the solid electrolyte raw material in a mixture of the solid electrolyte raw material and the solvent (complexing agent) containing a heteroatom, thereby obtaining higher ionic conductivity. Examples of high-speed agitation mixers include vertical-axis rotary mixers and horizontal-axis rotary mixers, and either type of mixer may be used.

[0076] In the above-mentioned reactor, a mixture (slurry) containing the electrolyte precursor, residual complexing agent that does not contribute to the reaction with the solid electrolyte raw material, and other solvents used as needed is obtained. When a slurry method is employed, a dryer may be provided to remove the residual complexing agent and other solvents used as needed from the mixture (slurry). Furthermore, when a slurry method (including a solution method) is employed, a grinding device may be provided to grind and mix the mixture (slurry) obtained in the above-mentioned reactor. The grinding device can be appropriately selected from the various grinders exemplified as grinders that can be used to grind and react the solid electrolyte raw material in the above-mentioned mechanical milling method.

[0077] An amorphous sulfide solid electrolyte is obtained by removing the complexing agent from the electrolyte precursor. The complexing agent can be removed from the electrolyte precursor by heating. The heating device used in this process can be appropriately selected from the various dryers exemplified as dryers that can be used to remove the solvent in the mechanical milling method. From the viewpoint of more efficiently removing the complexing agent from the electrolyte precursor, it is preferable to use a flash dryer. Furthermore, when removing the residual complexing agent and other solvents used as needed from the mixture (slurry), the dryer used to remove the solvent can also be appropriately selected from the various dryers exemplified as dryers that can be used to remove the solvent in the mechanical milling method.

[0078] The heating equipment for crystallization, etc. can be appropriately selected from the various heating equipments exemplified as heating equipment for heating for crystallization, etc. in the mechanical milling method described above. Various dryers used for removing the complexing agent can also be used, and the heating equipment for removing the complexing agent and the heating equipment for crystallization, etc. can be shared. The heating temperature for crystallization, etc. can be appropriately selected from the temperature range exemplified as the heating temperature for heating for crystallization, etc. in the mechanical milling method described above.

[0079] The heating equipment for crystallization or the like may also be used as a heating equipment for obtaining an amorphous sulfide solid electrolyte. In this case, for example, after removing the complexing agent from the electrolyte precursor using a heating equipment for removing the complexing agent, heating may be performed using a heating equipment for crystallization or the like. When the complexing agent cannot be sufficiently removed from the electrolyte precursor using a heating equipment for removing the complexing agent, and the electrolyte precursor remains, a more homogeneous amorphous sulfide solid electrolyte can be obtained by heating using a heating equipment for crystallization or the like. When a crystalline sulfide solid electrolyte is to be obtained, further heating using a heating equipment for crystallization or the like is sufficient. When a heating equipment for crystallization or the like is used to remove the complexing agent from the electrolyte precursor, the removal of the complexing agent and crystallization may be performed using the same heating equipment.

[0080] (Method Using a Pressure-Resistant Container) The reaction of the solid electrolyte raw materials can also be carried out by heat-treating them in a solvent using a pressure-resistant container or while refluxing (hereinafter, this may be referred to as the "method using a pressure-resistant container"). These heat-treatment methods are effective in producing a sulfide solid electrolyte having an argyrodite-type crystal structure, as described below. When this method is employed, the sulfide solid electrolyte production apparatus may include at least a reaction device equipped with a pressure-resistant container for heat-treating the solid electrolyte raw materials in a solvent; a cooling device for refluxing the solvent; and a calcination device for calcining the heat-treated product obtained by the heat treatment. An intermediate (heat-treated product) that can become a sulfide solid electrolyte by calcination in the subsequent calcination device, as well as remaining solid electrolyte raw materials, may adhere to the inside of the reaction device equipped with the pressure-resistant container. Furthermore, the sulfide solid electrolyte, remaining solid electrolyte raw materials, and the intermediate (heat-treated product) may adhere to the inside of the calcination device.

[0081] When the heat treatment is carried out using a pressure vessel, if the heating temperature exceeds the boiling point of the solvent used, it is preferable to use a heating device such as an autoclave. When the heat treatment is carried out while refluxing the solvent, the method is not particularly limited, and for example, a cooling device (e.g., a Dimroth device) that cools the vapor and returns it to the solvent can be used.

[0082] It is preferable to remove the solvent after the heat treatment in the solvent. By performing the heat treatment, a slurry containing the solvent and the heat-treated product is obtained, and by removing the solvent from the slurry, the heat-treated product is obtained. For example, the solvent can be removed by using an appropriate dryer selected from the various dryers exemplified as dryers for removing the solvent in the mechanical milling method.

[0083] The heat-treated product obtained by removing the solvent is preferably calcined. This allows a solid electrolyte, preferably a crystalline solid electrolyte, to be produced. The heating temperature in calcining the heat-treated product may be appropriately selected depending on the composition of the solid electrolyte to be obtained, and is, for example, preferably 300°C or higher, more preferably more than 300°C, even more preferably 320°C or higher, even more preferably 350°C or higher, particularly preferably 380°C or higher, with the upper limit being preferably 470°C or lower, more preferably 460°C or lower, even more preferably 450°C or lower, still more preferably 440°C or lower, particularly preferably 430°C or lower.

[0084] The firing can be carried out using a heating device such as a firing furnace, including a stationary hearth kiln and a rotary kiln, etc. 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).

[0085] (Other Equipment) The solid electrolyte raw material can be pulverized whether the reaction of the solid electrolyte raw material is carried out by the mechanical milling method, the melt quenching method, the slurry method, or the method using a pressure-resistant container. The solid electrolyte raw material may adhere to the inside of the pulverizer used to pulverize the solid electrolyte raw material. The pulverizer used to pulverize the solid electrolyte raw material can be appropriately selected from the various pulverizers exemplified as the pulverizer used to pulverize the solid electrolyte raw material for reaction in the mechanical milling method. A pin mill is also preferred because it has a short processing time and allows for continuous pulverization operations.

[0086] Whether the reaction of the solid electrolyte raw materials is carried out by the mechanical milling method, the melt quenching method, the slurry method, or a method using a pressure-resistant vessel, the solid electrolyte raw materials can be preliminarily mixed. The solid electrolyte raw materials may adhere to the inside of a mixer used for premixing the solid electrolyte raw materials. Mixers that can be used for premixing can be appropriately selected from the various reaction vessels exemplified as reaction vessels equipped with stirring blades used to mix the solid electrolyte raw materials and the heteroatom-containing solvent (complexing agent) in the slurry method. Mixers of various types, such as a rotating container mixer or a fixed container mixer, as well as a Nauta mixer, which is a conical screw mixer, or an FM mixer, which is a high-speed stirring mixer, can also be used.

[0087] Whether the reaction of the solid electrolyte raw materials is carried out by the mechanical milling method, the melt quenching method, the slurry method, or the method using a pressure vessel, the sulfide solid electrolyte production apparatus may be equipped with a particle size adjustment device such as a grinder or a classifier for particle size adjustment, such as fine particle size adjustment, depending on the application of the sulfide solid electrolyte. The sulfide solid electrolyte, remaining solid electrolyte raw materials, and electrolyte precursor may adhere to the inside of the particle size adjustment device for particle size adjustment. The particle size adjustment device can be appropriately selected from the various grinders exemplified as the grinders that grind the solid electrolyte raw materials to cause reaction in the mechanical milling method.

[0088] When a flash dryer is used as the heating device, particularly when a slurry method (including a solution method) is used, the sulfide solid electrolyte can be separated from the airflow. A preferred example of a separation device for separating the sulfide solid electrolyte is a bag filter. This allows the powder to be easily separated from a fluid containing the heated airflow used in the flash dryer and the powder dried by the flash dryer. The sulfide solid electrolyte, remaining solid electrolyte raw materials, and electrolyte precursor may adhere to the inside of the separation device.

[0089] As the bag filter, commercially available bag filters can be used without any particular restrictions. The bag filter may also have a brushing means, for example, a pulsating counterpressure system or a pulse jet system is preferred, with a pulse jet system being preferred. An induced draft fan may be provided in the line from the exhaust port of the bag filter to forcibly exhaust the gas exhausted from the exhaust port. By exhausting the gas using an induced draft fan or the like, filtration in the bag filter proceeds smoothly, and the slurry can be dried in a shorter time.

[0090] The solid electrolyte raw materials, solvents, etc. used in the method for producing the sulfide solid electrolyte will be described below.

[0091] (Solid electrolyte raw material) The solid electrolyte raw material used in the above reaction may be selected depending on the solid electrolyte to be obtained, and preferably includes a solid electrolyte raw material containing at least one atom selected from lithium atoms, phosphorus atoms, and sulfur atoms, and it is preferable to use multiple types of solid electrolyte raw materials. Furthermore, from the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte, a solid electrolyte raw material further containing a halogen atom is also preferred. As the raw material used in the vapor sulfide solid electrolyte production apparatus, a content containing multiple types of the above solid electrolyte raw materials (hereinafter sometimes referred to as a "raw material content") can be preferably used.

[0092] Examples of the solid electrolyte raw material include lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides; raw materials containing at least two atoms selected from the above-mentioned atoms, and fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ Representative examples of the raw material include a halogen element such as halogen, phosphorus, sulfur, and the like; and a raw material consisting of one atom selected from the above-mentioned elements.

[0093] Among the above, examples of the solid electrolyte raw material containing lithium atoms, sulfur atoms, and phosphorus atoms include lithium sulfide; diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ Among the phosphorus sulfides, diphosphorus pentasulfide is preferred.

[0094] Among the above, lithium sulfide, diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides, fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ and lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide are preferred. When oxygen atoms are introduced into the solid electrolyte, lithium oxide, lithium hydroxide, and phosphate compounds such as lithium phosphate are preferred.

[0095] Among the above, either a simple halogen or a lithium halide can be preferably used as the solid electrolyte raw material containing a halogen atom, because the use of a solid electrolyte raw material containing a halogen atom can improve the ionic conductivity of the sulfide solid electrolyte.

[0096] As the lithium halide, lithium chloride, lithium bromide, and lithium iodide are more preferred. When attempting to obtain a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure, it is preferable to use at least one of lithium chloride and lithium bromide, and it is more preferable to use lithium chloride and lithium bromide in combination. Furthermore, when attempting to obtain a crystalline sulfide solid electrolyte having a thiolicon region II-type crystal structure, it is preferable to use at least one of lithium bromide and lithium iodide, and it is more preferable to use lithium bromide and lithium iodide in combination.

[0097] The halogen element is chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２) is more preferred. When attempting to obtain a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure, it is preferable to use at least one of chlorine and bromine, and it is more preferred to use chlorine and bromine in combination. When attempting to obtain a crystalline sulfide solid electrolyte having a thiolicon region II-type crystal structure, it is preferable to use at least one of bromine and iodine, and it is more preferred to use bromine and iodine in combination.

[0098] Preferred examples of the combination of solid electrolyte raw materials contained in the raw material inclusions include a combination of lithium sulfide, phosphorus sulfide, and lithium halide, a combination of lithium sulfide, phosphorus sulfide, and a simple halogen, and a combination of lithium sulfide, phosphorus sulfide, lithium halide, and a simple halogen. More preferred examples include a combination of lithium sulfide, phosphorus pentasulfide, and a lithium halide, and a combination of lithium sulfide, phosphorus pentasulfide, and a simple halogen. Among the above combinations, preferred lithium halides are lithium chloride, lithium bromide, and lithium iodide, and preferred simple halogens are chlorine, bromine, and iodine. As mentioned above, the solid electrolyte raw materials containing halogen atoms can be selected depending on the type of solid electrolyte to be obtained.

[0099] P.S. ４ Li containing structure ３ P.S. ４ can also be used as a solid electrolyte raw material. ３ P.S. ４ In this case, the combination of the solid electrolyte raw materials contained in the raw material contents may be Li ３ P.S. ４ and the lithium halide, Li ３ P.S. ４ and the above-mentioned elemental halogens, Li ３ P.S. ４ and the lithium halide and the elemental halogen.

[0100] When the raw material contains lithium sulfide, diphosphorus pentasulfide, and lithium halide as solid electrolyte raw materials, the ratio of lithium sulfide to the total of lithium sulfide and diphosphorus pentasulfide is preferably 60 mol% or more, more preferably 65 mol% or more, even more preferably 70 mol% or more, and even more preferably 74 mol% or more, from the viewpoint of obtaining higher chemical stability and higher ionic conductivity, and the upper limit is preferably 85 mol% or less, more preferably 83 mol% or less, and even more preferably 80 mol% or less. The range is typically preferably 60 to 85 mol%, more preferably 65 to 83 mol%, even more preferably 70 to 80 mol%, and even more preferably 74 to 80 mol%. Furthermore, when attempting to obtain a sulfide solid electrolyte having a thiolicon region II type crystal structure, in addition to the above ranges, particularly 74 to 78.5 mol%, 74 to 78 mol%, and 74 to 76 mol% are preferred, and when attempting to obtain a sulfide solid electrolyte having an argyrodite type crystal structure, in addition to the above ranges, particularly 76 to 83 mol%, 77 to 80 mol%, and 78 to 80 mol% are preferred.

[0101] When the raw material content includes lithium sulfide, diphosphorus pentasulfide, lithium halide, and other raw materials used as necessary as solid electrolyte raw materials, the content of lithium sulfide and diphosphorus pentasulfide relative to the total is preferably 50 mol% or more, more preferably 55 mol% or more, and even more preferably 60 mol% or more, with the upper limit being preferably 100 mol% or less, more preferably 90 mol% or less, even more preferably 85 mol% or less, and even more preferably 80 mol% or less. The range is typically preferably 50 to 100 mol%, more preferably 55 to 90 mol%, even more preferably 60 to 85 mol%, and even more preferably 60 to 80 mol%. Furthermore, when attempting to obtain a sulfide solid electrolyte having a thiolicon region II type crystal structure, in addition to the above ranges, particularly 65 to 90 mol%, 70 to 85 mol%, and 75 to 83 mol% are preferred, and when attempting to obtain a sulfide solid electrolyte having an argyrodite type crystal structure, in addition to the above ranges, particularly 50 to 78 mol%, 55 to 70 mol%, and 55 to 65 mol% are preferred.

[0102] (Solvent) Preferred examples of the solvent used in the reaction include polar solvents such as solvents containing heteroatoms. Polar solvents such as solvents containing heteroatoms are preferably used in the slurry method. Heteroatoms such as nitrogen atoms, oxygen atoms, halogen atoms such as chlorine atoms, and sulfur atoms have a high affinity with lithium atoms and tend to bond with the solid electrolyte raw materials contained in the raw material contents to form complexes (hereinafter also simply referred to as "complexes"). Therefore, as mentioned above, solvents containing heteroatoms can also be called "complexing agents." A solvent (complexing agent) containing a heteroatom forms a complex with the solid electrolyte raw materials, which makes it easier to maintain the uniform dispersion state of the solid electrolyte raw materials, particularly the dispersion state of the halogen atoms, and as a result, it is thought that a sulfide solid electrolyte with high ionic conductivity can be obtained.

[0103] Among the above, nitrogen and oxygen atoms are preferred as heteroatoms contained in the complexing agent. Examples of solvents containing nitrogen atoms as heteroatoms include solvents having a group containing a nitrogen atom, such as an amino group, an amide group, a nitro group, or a nitrile group. Solvents having a group containing a nitrogen atom are preferably used in the slurry method (a method for forming a complex), and among these, solvents having an amino group are preferred.

[0104] As the solvent having an amino group, an aliphatic amine is preferred from the viewpoint of obtaining higher ionic conductivity. Examples of the aliphatic amine include ethylenediamine, diaminopropane, dimethylethylenediamine, diethylethylenediamine, dimethyldiaminopropane, tetramethyldiaminomethane, tetramethylethylenediamine (TMEDA), tetramethyldiaminopropane (TMPDA), tetraethylethylenediamine, and tetraethyldiaminopropane. Among these aliphatic amines, a polyamine having two or more amino groups is preferred, and a diamine having two amino groups is preferred.

[0105] The solvent having an amino group is preferably a tertiary amine having a tertiary amino group as the amino group, more preferably a tertiary diamine having two tertiary amino groups, even more preferably a tertiary diamine having two tertiary amino groups at both ends, and even more preferably an aliphatic tertiary diamine having tertiary amino groups at both ends. As the aliphatic tertiary diamine, the above-mentioned tetramethylethylenediamine, tetraethylethylenediamine, tetramethyldiaminopropane, and tetraethyldiaminopropane are preferred, and tetramethylethylenediamine and tetraethylethylenediamine are more preferred.

[0106] Preferred examples of solvents other than those having an amino group include aliphatic nitrile solvents such as acetonitrile, acrylonitrile, propionitrile, chloropropionitrile, isobutyronitrile, tert-butyronitrile, capronitrile, isocapronitrile, malononitrile, and fumaronitrile; alicyclic nitrile solvents such as cyclohexylnitrile; and aromatic nitrile solvents such as benzonitrile and fluorobenzonitrile. These nitrile solvents are preferably used in the above-mentioned reaction of the solid electrolyte raw material in a method using a pressure-resistant vessel, and are more preferably used in combination with a non-polar solvent such as a hydrocarbon solvent described below. In this case, among the above-mentioned nitrile solvents, aliphatic nitrile solvents are preferred, and propionitrile, isobutyronitrile, and isocapronitrile are more preferred.

[0107] Preferred examples of the solvent other than the solvent having an amino group include solvents containing a nitrogen atom, such as dimethylformamide, nitrobenzene, and dimethylacetamide.

[0108] Preferred examples of the complexing agent include ether solvents and ester solvents containing an oxygen atom as a heteroatom, as well as alcohol solvents, aldehyde solvents, and ketone solvents. As the complexing agent containing an oxygen atom, from the viewpoint of obtaining higher ionic conductivity, ether solvents and ester solvents are preferred, and ether solvents are more preferred. Preferred ether solvents include aliphatic ethers such as dimethyl ether, diethyl ether, tert-butyl methyl ether, dimethoxymethane, dimethoxyethane, diethylene glycol dimethyl ether (diglyme), triethylene oxide glycol dimethyl ether (triglyme), diethylene glycol, and triethylene glycol; and alicyclic ethers such as ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, and dioxane. Among these, alicyclic ethers are more preferred, and tetrahydrofuran is preferred in view of availability and other factors.

[0109] Among the reactions of the above-mentioned solid electrolyte raw materials, in the method using a pressure vessel, aliphatic ethers and alicyclic ethers are preferred, and diethyl ether and tetrahydrofuran are particularly preferred.

[0110] Preferred examples of the ester solvent include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate; and aliphatic esters such as methyl propionate, ethyl propionate, dimethyl oxalate, diethyl oxalate, dimethyl malonate, diethyl malonate, dimethyl succinate, and diethyl succinate.

[0111] Preferred examples of the solvent include alcohol solvents such as ethanol and butanol; aldehyde solvents such as formaldehyde, acetaldehyde and dimethylformamide; and ketone solvents such as acetone and methyl ethyl ketone. When a solution method is employed, it is preferable to use an alcohol solvent. Among solvents having a group containing an oxygen atom, alcohol solvents are preferably used in the solution method.

[0112] Furthermore, as the solvent, a non-polar solvent such as a hydrocarbon solvent can also be used as a solvent other than the above-mentioned solvent containing a hetero atom. Examples of hydrocarbon solvents include saturated or unsaturated aliphatic hydrocarbons such as hexane, hexene, pentane, 2-ethylhexane, heptane, heptene, octane, decane, undecane, dodecane, and tridecane; saturated or unsaturated alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, and cyclohexene; and aromatic hydrocarbon solvents such as benzene, toluene, xylene, mesitylene, ethylbenzene, and tert-butylbenzene. Among these, aromatic hydrocarbon solvents are preferred, and toluene and xylene are more preferably used.

[0113] In the method using the pressure vessel, it is preferable to use a combination of a polar solvent such as the above-mentioned heteroatom-containing solvent (complexing agent) and a non-polar solvent such as a hydrocarbon solvent. In this case, the non-polar solvent is preferably an aromatic hydrocarbon solvent, particularly toluene or ethylbenzene, and the polar solvent is preferably a nitrile solvent, which has the property of forming an azeotrope with an aromatic hydrocarbon solvent such as toluene and is easily removed together with the aromatic hydrocarbon solvent such as toluene.

[0114] (Amorphous Solid Electrolyte) The sulfide solid electrolyte obtained by the above-mentioned method for producing a sulfide solid electrolyte can be either an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte, depending on the firing conditions. The amorphous sulfide solid electrolyte obtained by the above-mentioned method preferably contains lithium atoms, sulfur atoms, and phosphorus atoms, and more preferably further contains halogen atoms, and representative examples thereof include Li, ２ S-P ２ S ５ , Li ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５-LiI-LiBr, etc., sulfide solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide; and solid electrolytes further containing other atoms such as oxygen atoms and silicon atoms, for example, Li ２ S-P ２ S ５ -Li ２ O-LiI, Li ２ S-P ２ S ５ -Li ２ O-LiI-LiBr, Li ２ S-SiS ２ -P ２ S ５ In order to obtain higher ionic conductivity, a sulfide solid electrolyte such as LiI is preferable. ２ S-P ２ S ５ - LiI, Li ２ S-P ２ S ５ -LiCl, Li ２ S-P ２ S ５ - LiBr, Li ２ S-P ２ S ５ A sulfide solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as LiI-LiBr, is preferred. The types of atoms constituting the amorphous sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0115] In the amorphous sulfide solid electrolyte obtained by the above production method, the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.6, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.05 to 0.5, and even more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.08 to 0.4. Further, when bromine and iodine are used in combination as halogen atoms, the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, bromine, and iodine is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.3: 0.01 to 0.3, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.02 to 0.25: 0.02 to 0.25, more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.03 to 0.2: 0.03 to 0.2, and even more preferably 1.35 to 1.45: 1.4 to 1.7: 0.3 to 0.45: 0.04 to 0.18: 0.04 to 0.18. By setting the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range, it becomes easier to obtain a solid electrolyte having a higher ionic conductivity and a crystal structure described below, particularly a thiolisiconregion II crystal structure or an argyrodite crystal structure.

[0116] The shape of the amorphous sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle size (D ５０ The average particle size (D) is, for example, 0.01 μm or more, further 0.03 μm or more, 0.05 μm or more, or 0.1 μm or more, and the upper limit is 5 μm or less, further 3.0 μm or less, 1.5 μm or less, 1.0 μm or less, or 0.5 μm or less. ５０ ) is the particle size at which 50% (volume basis) of the total particle size is reached when the particle sizes are sequentially added together starting from the smallest particle size when an integrated particle size distribution curve is drawn, and the volume distribution refers to an average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device.

[0117] (Crystalline sulfide solid electrolyte) The crystalline sulfide solid electrolyte obtained by the above-mentioned production method may be a so-called glass ceramic obtained by heating an amorphous sulfide solid electrolyte to a crystallization temperature or higher, and its crystalline structure may be Li ３ P.S. ４ Crystal structure, Li ４ P ２ S ６ Crystal structure, Li ７ P.S. ６ Crystal structure, Li ７ P ３ S １１ Examples of such structures include a crystal structure having peaks at 2θ=approximately 20.2° and 23.6° (for example, JP 2013-16423 A).

[0118] Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure (Kanno et al., Journal of the Electrochemical Society, 148(7)A742-746(2001)), Li ４－ｘ Ge １－ｘ P ｘ S ４ Examples of the crystal structure include a crystal structure similar to the thio-LISICON Region II type (see Solid State Ionics, 177 (2006), 2721-2725). The crystal structure of the crystalline sulfide solid electrolyte obtained by the above method is preferably the thio-LISICON Region II type crystal structure among the above, in that higher ionic conductivity can be obtained. Here, the "thio-LISICON Region II type crystal structure" refers to a crystal structure in which Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-LISICON Region II crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４This indicates that the thiolisicon region II type crystal structure has a similar crystal structure to the thiolisicon region II type. As will be described later, the thiolisicon region II type crystal structure and the similar crystal structure have similar diffraction peaks, and are therefore very close to each other. Therefore, it is technically reasonable to treat the "thiolisicon region II type crystal structure" as including the thiolisicon region II type crystal structure and the similar crystal structure.

[0119] Here, the above "Li ４－ｘ Ge １－ｘ P ｘ S ４ The notation of the crystal structure "thio-LISICON Region II type" means that it was discovered in the above document as a crystal structure composed of Li, Ge, P, and S atoms. The sulfide solid electrolyte obtained by the above production method contains lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms, and therefore is not a "Li ４－ｘ Ge １－ｘ P ｘ S ４ "Li in thio-LISICON Region II type" ４－ｘ Ge １－ｘ P ｘ S ４ However, when the sulfide solid electrolyte obtained by the above production method has the same diffraction peak as the above-mentioned "thiolisiconregion II type crystal structure" (including the above-mentioned "similar crystal structure"), it can be said that the sulfide solid electrolyte has a thiolisiconregion II type crystal structure formed by lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms. The same applies to the argyrodite type crystal structure described below.

[0120] The crystalline sulfide solid electrolyte obtained by the above-mentioned production method may contain the above-mentioned thiolicon region II type crystal structure or may contain it as a main crystal, but from the viewpoint of obtaining higher ionic conductivity, it is preferable that it contains it as a main crystal. In this specification, "containing it as a main crystal" means that the proportion of the target crystal structure among the crystal structures is 80% or more, preferably 90% or more, and more preferably 95% or more. Furthermore, from the viewpoint of obtaining higher ionic conductivity, the crystalline sulfide solid electrolyte obtained by the above-mentioned production method contains crystalline Li ３ P.S. ４ (β-Li ３ P.S. ４ It is preferable that the main crystal does not contain thiolicon region II crystal structure. Although the above-mentioned main crystal is explained using the thiolicon region II crystal structure as an example, the same applies to other crystal structures.

[0121] In X-ray diffraction measurement using CuKα radiation, Li ３ P.S. ４ Diffraction peaks of the crystal structure appear, for example, at 2θ=17.5°, 18.3°, 26.1°, 27.3°, and 30.0°. ４ P ２ S ６ Diffraction peaks of the crystal structure appear, for example, at 2θ=16.9°, 27.1°, and 32.5°. ７ P.S. ６ Diffraction peaks of the crystal structure appear, for example, at 2θ=15.3°, 25.2°, 29.6°, and 31.0°. ７ P ３ S １１ Diffraction peaks of the crystal structure appear, for example, at 2θ=17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°, and Li ４－ｘ Ge １－ｘ P ｘ S ４ The diffraction peaks of the thio-LISICON Region II crystal structure appear, for example, at 2θ=20.1°, 23.9°, and 29.5°, and Li ４－ｘ Ge １－ｘ P ｘ S４ Diffraction peaks of a crystal structure similar to that of thio-LISICON Region II type appear, for example, at 2θ=20.2° and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0122] The above Li ７ P.S. ６ A preferred example of the crystalline sulfide solid electrolyte is an argyrodite-type crystal structure having a structural skeleton in which part of P is substituted with Si. The composition formula of the argyrodite-type crystal structure is, for example, the composition formula Li ７－ｘ P １－ｙ Si ｙ S ６ and Li ７＋ｘ P １－ｙ Si ｙ S ６ (x is −0.6 to 0.6, y is 0.1 to 0.6) The argyrodite-type crystal structure represented by this composition formula is a cubic or orthorhombic crystal, preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°.

[0123] The composition formula of the argyrodite-type crystal structure is Li ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ (0.8≦x≦1.7, 0<y≦−0.25x+0.5) is also included. The argyrodite-type crystal structure represented by this composition formula is preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. The composition formula of the argyrodite-type crystal structure is preferably the composition formula Li ７－ｘ P.S. ６－ｘ Ha ｘ(Ha is Cl or Br, and x is preferably 0.2 to 1.8). The argyrodite-type crystal structure represented by this composition formula is preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, it has peaks that appear mainly at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Note that these peak positions may vary within a range of ±0.5°.

[0124] The atomic composition ratios contained in the crystalline sulfide solid electrolyte are those according to the composition formulas corresponding to the various crystal structures, and are preferably within the range of the atomic composition ratios of the amorphous sulfide solid electrolyte. When the atomic composition ratios are within the range, the thiolicon region II crystal structure or the argyrodite crystal structure is likely to be formed among the above crystal structures.

[0125] (Solvent Content) When a solvent is used in the reaction of the solid electrolyte raw materials, the content of the solvent contained in the obtained crystalline sulfide solid electrolyte is preferably 0 mass %, i.e., no solvent is contained at all. However, from the viewpoint of efficiently obtaining a sulfide solid electrolyte having high ionic conductivity, the content is usually 10 mass % or less, further 8 mass % or less, 5 mass % or less, 3 mass % or less, or 1 mass % or less, and the lower limit is about 0.01 mass % or more.

[0126] [Apparatus for Producing Sulfide Solid Electrolyte] The apparatus for producing a sulfide solid electrolyte according to the present embodiment, which is used in the above-described method for producing a sulfide solid electrolyte, is an apparatus including cleaning equipment having at least a cooling device that cools the inside of a device to be cleaned and a steam supplying device that supplies steam to the inside of the device.

[0127] The sulfide solid electrolyte manufacturing apparatus is provided with a cleaning facility, which can further reduce the time required for maintenance, i.e., the downtime of the manufacturing apparatus. Therefore, even if the same manufacturing apparatus is used, it is possible to manufacture a sulfide solid electrolyte with a higher operating rate.

[0128] The sulfide solid electrolyte production apparatus only needs to be equipped with the cleaning equipment, and the equipment other than the water supply device for cleaning the equipment may vary depending on the method for producing a sulfide solid electrolyte employed. The cooling equipment for cooling the interior of the equipment to be cleaned and the steam supply device for supplying steam to the interior of the equipment, which the cleaning equipment has, are as described in the method for cleaning a sulfur atom-containing material of this embodiment. Furthermore, the equipment that the sulfide solid electrolyte production apparatus may have is as described in the method for producing a sulfide solid electrolyte.

[0129] In addition to the cleaning equipment, the sulfide solid electrolyte production apparatus of this embodiment preferably further includes a drainage equipment for draining condensed water of the steam supplied to the inside of the apparatus. By including the drainage equipment, it is possible to quickly drain the condensed water of the steam used to clean the inside of the apparatus.

[0130] Preferred examples of the equipment included in the drainage system include a drainage tank that collects condensed water discharged from the equipment as wastewater, a storage device that stores wastewater such as a drainage pit, and piping from the equipment to the storage device. Furthermore, since drainage from the equipment can be performed using a drain valve included in the equipment or a drain valve provided on the piping connecting the equipment, no additional equipment is required for drainage from the equipment. The wastewater stored in the storage device is treated as needed and can be reused as needed.

[0131] (Applications) The sulfide solid electrolyte obtained by the above-mentioned production method is suitable for use in an electrode mixture and in batteries, particularly lithium ion batteries, and particularly all-solid-state batteries. The sulfide solid electrolyte obtained by the above-mentioned production method may be used in the positive electrode layer or negative electrode layer of a lithium ion battery, or in the electrolyte layer of an all-solid-state battery in addition to the positive electrode tank and negative electrode tank. Each layer can be produced by a known method.

[0132] [Electrode Mixture] The sulfide solid electrolyte obtained by the above-described production method can be used for an electrode mix, as described above. The electrode mix using the sulfide solid electrolyte obtained by the above-described production method is an electrode mix containing the above-described solid electrolyte and an electrode active material.

[0133] 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, and as the positive electrode active material and the negative electrode active material, materials conventionally used as these active materials can be used.

[0134] The compounding ratio (mass ratio) of the solid electrolyte to the electrode active material in the electrode mixture is preferably 99.5:0.5 to 40:60, more preferably 99:1 to 50:50, and even more preferably 98:2 to 60:40, in order to improve battery performance and in consideration of production efficiency.

[0135] The electrode composite using the sulfide solid electrolyte obtained by the above-described production method may contain, in addition to the sulfide solid electrolyte obtained by the above-described production method and the electrode active material, other components such as a conductive material such as a carbon-based material, a thermoplastic elastomer, a binder such as a resin, etc.

[0136] [Lithium Ion Battery] A lithium ion battery using the sulfide solid electrolyte obtained by the above production method includes at least one of the sulfide solid electrolyte obtained by the above production method and an electrode mixture containing the sulfide solid electrolyte.

[0137] The lithium ion battery using the sulfide solid electrolyte obtained by the above-mentioned production method is not particularly limited in its configuration, as long as it contains either the sulfide solid electrolyte obtained by the above-mentioned production method or an electrode composite containing the same, and for example, a solid electrolyte of another form or an electrode composite containing the same may be used. Furthermore, the configuration of the lithium ion battery may be any configuration of a commonly used lithium ion battery.

[0138] The lithium ion battery using the sulfide solid electrolyte obtained by the above manufacturing method preferably includes, for example, a positive electrode layer, a negative electrode layer, an electrolyte layer, and a current collector. The positive electrode layer and the negative electrode layer preferably use an electrode mixture using the sulfide solid electrolyte obtained by the above manufacturing method, and the electrolyte layer preferably uses the sulfide solid electrolyte obtained by the above manufacturing method. A lithium ion battery using a solid electrolyte as the electrolyte layer is also called an all-solid-state battery.

[0139] The battery preferably includes a current collector in addition to the positive electrode layer, the electrolyte layer, and the 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.

[0140] [Method for Producing Lithium Sulfide] Lithium sulfide can be produced by using an apparatus for producing lithium sulfide. From the viewpoint of producing lithium sulfide with a higher operating rate, the method for producing lithium sulfide is preferably carried out by a method for producing lithium sulfide, which includes cleaning sulfur atom-containing substances adhering to the inside of devices constituting the apparatus for producing lithium sulfide by the cleaning method of the present embodiment described above, and then using the apparatus for producing lithium sulfide.

[0141] The method for producing lithium sulfide includes cleaning sulfur atom-containing substances adhering to the inside of devices constituting an apparatus for producing lithium sulfide by the cleaning method of the present embodiment. As a result, as described above, even if the same production apparatus is used, lithium sulfide can be produced with a higher operating rate.

[0142] The method for producing lithium sulfide includes using an apparatus for producing lithium sulfide following the above-mentioned cleaning. The apparatus for producing lithium sulfide employed in the method for producing lithium sulfide is equipped with cleaning equipment that is used to clean at least sulfur atom-containing substances adhering to the inside of the equipment, and that includes a cooling device that cools the inside of the equipment to be cleaned and a steam supply device that supplies steam to the inside of the equipment. Furthermore, the apparatus for producing lithium sulfide employed in the method for producing lithium sulfide further includes, in addition to the above-mentioned cleaning equipment, various devices according to the production method used to obtain lithium sulfide by reacting raw materials such as lithium hydroxide.

[0143] In the method for producing lithium sulfide, using a lithium sulfide production apparatus essentially means producing lithium sulfide, that is, obtaining lithium sulfide by reacting raw materials such as lithium hydroxide. As described above, the lithium sulfide production apparatus is equipped with various devices according to the production method when obtaining lithium sulfide by reacting raw materials such as lithium hydroxide. Hereinafter, the lithium sulfide production apparatus will be described in conjunction with obtaining lithium sulfide by reacting raw materials such as lithium hydroxide.

[0144] As a raw material, lithium hydroxide is preferably used as a lithium source. For example, industrially produced and commercially available lithium hydroxide can be used as the lithium hydroxide. Commercially available lithium hydroxide has a high purity, and the purity of the resulting lithium sulfide is improved.

[0145] A preferred example of the sulfur source used as a raw material is hydrogen sulfide. Hydrogen sulfide is highly reactive with lithium hydroxide, allowing for more efficient production of lithium sulfide. Lithium hydroxide and hydrogen sulfide can be reacted in a reaction vessel. The reaction between lithium hydroxide and hydrogen sulfide can be carried out in the presence or absence of a solvent. When the reaction is carried out in the presence of a solvent, for example, the reaction can be carried out by placing lithium hydroxide in the solvent and blowing in hydrogen sulfide.

[0146] Sulfur can also be used as the sulfur source. In this case, for example, sulfur is placed in a heating container, heated to gasify the sulfur, and hydrogen is supplied to the heating container to react with the gaseous sulfur to produce hydrogen sulfide, which can be used in the reaction with lithium hydroxide.

[0147] Therefore, the lithium sulfide manufacturing apparatus may include a reaction vessel for reacting lithium hydroxide with hydrogen in the presence or absence of a solvent; a heating vessel for heating sulfur to form gaseous sulfur, into which hydrogen can be introduced as needed to produce hydrogen sulfide; and a reaction vessel for reacting the gaseous sulfur generated in the heating vessel with hydrogen. Furthermore, a porous catalyst such as zeolite or alumina may be used as needed for the reaction of gaseous sulfur with hydrogen; that is, the heating vessel and the reaction vessel for reacting gaseous sulfur with hydrogen may be filled with a catalyst. Because lithium sulfide may adhere to the inside of the reaction vessel and sulfur may adhere to the inside of the heating vessel, the reaction vessel, the heating vessel, and the piping connecting these vessels are targets for cleaning by the cleaning method of this embodiment.

[0148] [Apparatus for Producing Sulfide Solid Electrolyte or Lithium Sulfide] The apparatus for producing a sulfide solid electrolyte or lithium sulfide of this embodiment includes a cleaning facility having a cooling device that cools the interior of the device and a steam supply device that supplies steam to the interior of the device. The cooling device that cools the interior of the device to be cleaned and the steam supply device that supplies steam to the interior of the device that the cleaning facility includes are as described above in the method for cleaning a sulfur atom-containing material of this embodiment. Furthermore, the equipment that may be included in the apparatus for producing a sulfide solid electrolyte or lithium sulfide is as described above in the method and apparatus for producing a sulfide solid electrolyte and the method for producing lithium sulfide.

[0149] Furthermore, the apparatus for producing a sulfide solid electrolyte or lithium sulfide according to this embodiment preferably further includes, in addition to the cleaning equipment, a drainage equipment for draining condensed water of steam supplied to the inside of the apparatus. The drainage equipment is as described above in connection with the apparatus for producing a sulfide solid electrolyte.

[0150] The lithium sulfide obtained by the lithium sulfide production method of the present embodiment is suitably used as a solid electrolyte raw material in the sulfide solid electrolyte production method. Therefore, by combining the lithium sulfide production apparatus described above with the sulfide solid electrolyte production apparatus described above, it is possible to efficiently produce lithium sulfide, which is a raw material for the sulfide solid electrolyte, and to efficiently produce the sulfide solid electrolyte.

[0151] 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.

[0152] Example 1 After stopping the production of a sulfide solid electrolyte using a sulfide solid electrolyte production apparatus, sulfur atom-containing substances adhering to the inside of a stirring / mixing vessel in which solid electrolyte raw materials were mixed in a solvent were washed as follows. The stirring / mixing vessel was placed in a closed environment, and cooling of the inside of the stirring / mixing vessel was initiated using a water-cooled jacket attached to the outer wall of the stirring / mixing vessel, and the temperature inside the vessel was adjusted to 5°C. Next, steam (pressure (absolute pressure): 0.45 MPa, ammonia content: 0.5 mass ppm, hydrazine content: 0.02 mass ppm, pH 9 (25°C)) was supplied from a steam supply port attached to the stirring / mixing vessel so as to maintain the pressure inside the vessel at 0.1 MPa. The steam supply was continued for 30 minutes and then stopped. The drain valve at the bottom of the stirring / mixing vessel was opened, and the water accumulated in the stirring / mixing vessel was drained and recovered. This was considered the first cleaning. The total amount of wastewater recovered was 31.0 kg, and 1,119.2 g of sulfur atom-containing substances were measured from the wastewater. Next, the drain valve of the stirring / mixing tank was closed to create a closed environment again, and the second cleaning was performed in the same manner as the first cleaning, except that steam supply was continued for 15 minutes. 73.6 g of sulfur atom-containing substances were measured from the wastewater. The same procedure as the second cleaning was repeated four times, for a total of six cleanings. Furthermore, water (water temperature: 25°C) was supplied from the supply port at the top of the stirring / mixing tank until it was full, and then the drain valve at the bottom was opened to drain and recover the water from inside the stirring / mixing tank, thereby performing a normal cleaning. 0.3 g of sulfur atom-containing substances was measured from the recovered wastewater. The results from the first to sixth cleanings, as well as the results of the normal cleaning, are shown in Table 1.

[0153]

[0154] According to the results of Example 1, since only 0.3 g of sulfur atom-containing substances was found in the final normal cleaning, it was confirmed that 99.97 mass % of the sulfur atom-containing substances adhering to the inside of the equipment could be cleaned by six cleanings. Furthermore, even after six cleanings, the amount of wastewater was 89.0 kg, which was a reduction of about 87 to 91% compared to the normal cleaning, which discharged 700 kg to 1000 kg.

[0155] Comparative Example 1 After stopping the production of sulfide solid electrolyte using the sulfide solid electrolyte production apparatus, sulfur atom-containing substances adhering to the inside of a stirring / mixing vessel in which solid electrolyte raw materials were mixed in a solvent were washed as follows. The stirring / mixing vessel was placed in a closed environment, and nitrogen (temperature: 80°C) was supplied through a nitrogen supply port provided in the stirring / mixing vessel to perform washing. The nitrogen supply was continued for 30 minutes, then stopped, and powder (sulfur atom-containing substances) was recovered from the bottom of the stirring / mixing vessel. The recovered powder weighed 8.4 g. This was the first operation, and was repeated three times (a total of four times). Next, water was supplied through a supply port at the top of the stirring / mixing vessel to fill it up, and then drained from the bottom. The content of sulfur atom-containing substances in the drainage water was 20.4 g. The results of the first to fourth washings, as well as the results of washing with water, are shown in Table 2.

[0156]

[0157] The results of Comparative Example 1 show that cleaning with nitrogen only removed about 32 mass% of sulfur atom-containing substances, and that cleaning with nitrogen alone is difficult to remove sulfur atom-containing substances.

[0158] (Comparative Example 2) After stopping the production of a sulfide solid electrolyte using the sulfide solid electrolyte production apparatus, sulfur atom-containing substances adhering to the inside of the stirring and mixing tank in which the solid electrolyte raw materials were mixed in a solvent, the heat exchanger, and the mill were washed as follows. First, 200 kg of water was supplied to the stirring and mixing tank, and water circulation was started using a pump. After 10 minutes, the drain valve at the bottom of the stirring and mixing tank was opened, and the water was drained and recovered. This was designated as the first washing. The total amount of recovered wastewater was 200 kg, and 1,568 g of sulfur atom-containing substances were measured from the wastewater. Next, a circulation line was formed between the stirring and mixing tank and the mill, and 200 kg of water was supplied into the circulation line. After 10 minutes, the drain valve at the bottom of the stirring and mixing tank was opened, and the water was drained and recovered. This was designated as the second washing. The total amount of recovered wastewater was 200 kg, and 367 g of sulfur atom-containing substances were measured from the wastewater. Next, a circulation line was formed between the stirring and mixing tank, the heat exchanger, and the mill. 200 kg of water was supplied into the circulation line, and water circulation was started using a pump. After 10 minutes, the drain valve at the bottom of the stirring and mixing tank was opened, and the water was drained and recovered. This was designated the third washing. The total amount of recovered wastewater was 200 kg, and 494 g of sulfur atom-containing substances were measured from the recovered wastewater. Next, the same washing as the third washing was repeated five times (a total of eight washings) except that the amount of water supplied in the third washing was 50 kg, and the amount of sulfur atom-containing substances contained in the wastewater recovered in each washing was measured. The results from the first to eighth washings are shown in Table 3.

[0159]

[0160] From the results of Comparative Example 2, it was confirmed that although it is possible to wash away sulfur atom-containing substances by washing with water, a large amount of water, 850 kg, is required.

[0161] Example 2 After stopping the production of a sulfide solid electrolyte using the sulfide solid electrolyte production apparatus, sulfur atom-containing substances adhering to the inside of a powder collector (bag filter) in which solid electrolyte raw materials are mixed in a solvent were washed as follows. Water (water temperature: 25°C) was sprayed into the inside of the powder collector to bring the temperature to 25°C. Next, steam (pressure (absolute pressure): 0.45 MPa, ammonia content: 0.5 mass ppm, hydrazine content: 0.02 mass ppm, pH 9 (25°C)) was supplied from a steam supply port provided in the powder collector so as to maintain the pressure inside the equipment at 0.1 MPa. During this time, the drain valve at the bottom of the powder collector was open. The steam supply was continued for 10 minutes and then stopped, and the water discharged from the bottom of the powder collector was recovered. This was used as the first cleaning. The total amount of wastewater recovered was 6.2 kg, and 545 g of sulfur atom-containing substances were measured from the wastewater. Next, the drain valve of the powder collector was closed to create a closed environment again, and the second cleaning was performed in the same manner as the first cleaning, except that the steam supply was continued for 30 minutes. 16 g of sulfur atom-containing substances was measured from the wastewater. The same operation as the second cleaning was repeated twice, except that the steam supply time in the second cleaning was 40 minutes, for a total of four cleanings. The results from the first to fourth cleanings are shown in Table 4.

[0162]

[0163] From the results of Example 2, it was confirmed that the desired areas were sufficiently cleaned by four cleaning steps.

[0164] The method for washing a sulfur atom-containing material according to the present embodiment is suitable for use in an apparatus for producing a sulfide solid electrolyte. Furthermore, the sulfide solid electrolyte obtained by the apparatus for producing a sulfide solid electrolyte has high ionic conductivity, and therefore is suitable for use as a solid electrolyte or electrode composite in lithium ion batteries, particularly in all-solid-state batteries, used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones, as well as in vehicles such as automobiles.

Claims

1. A method for cleaning sulfur atom-containing substances adhering to the inside of equipment constituting an apparatus for producing a sulfide solid electrolyte or an apparatus for producing lithium sulfide, the method comprising cooling the inside of the equipment and supplying steam to the inside of the equipment.

2. The method for washing a sulfur atom-containing material according to claim 1, wherein the cooling is carried out by at least one means selected from the group consisting of a cooling jacket and the supply of water.

3. The method for cleaning a sulfur atom-containing material according to claim 1 or 2, wherein cooling of the inside of the equipment is started, and then supplying of the steam is started.

4. The method for cleaning a sulfur atom-containing substance according to any one of claims 1 to 3, wherein the sulfur atom-containing substance is at least one substance selected from the group consisting of a raw material component, an intermediate, and a sulfide solid electrolyte.

5. A method for cleaning sulfur-atom-containing materials according to any one of claims 1 to 4, wherein the steam is supplied so that the pressure inside the equipment is 0.0 MPa or more and 0.35 MPa or less.

6. The method for washing a sulfur atom-containing material according to any one of claims 1 to 5, wherein the vapor is condensed and drained.

7. The method for cleaning a sulfur atom-containing substance according to any one of claims 1 to 6, wherein the steam is alkaline.

8. A sulfide solid electrolyte or lithium sulfide manufacturing device equipped with a cooling device for cooling the inside of the device and a cleaning facility having a steam supply device for supplying steam to the inside of the device.

9. The apparatus for producing a sulfide solid electrolyte or lithium sulfide according to claim 8, further comprising a drainage system for draining condensed water from steam supplied to the inside of the apparatus.

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