Method for producing lithium sulfide, lithium sulfide, and method for producing sulfide solid electrolyte

Abstract

Provided are: a method for producing lithium sulfide that includes reacting lithium hydroxide with an elemental sulfur-containing dilution gas that includes an inert gas and a substance containing elemental sulfur while stirring by stirring blades to produce high-quality lithium sulfide easily and inexpensively; solvent-free lithium sulfide having a prescribed specific surface area and pore volume that makes it possible to produce a sulfide solid electrolyte efficiently; and a method for using the same.

Description

Method for producing lithium sulfide, method for producing lithium sulfide and sulfide solid electrolyte

[0001] The present invention relates to a method for producing lithium sulfide, and a method for producing lithium sulfide and a sulfide solid electrolyte.

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as their power sources has become increasingly important. Among these batteries, lithium-ion batteries have attracted attention due to their high energy density. Currently available lithium-ion batteries use electrolytes containing flammable organic solvents, necessitating the installation of safety devices to suppress temperature rise during short circuits and improvements in structure and materials to prevent short circuits. In particular, for automotive applications, higher capacity and higher output are required, raising safety concerns regarding batteries using conventional electrolytes. In contrast, all-solid-state lithium batteries, which replace the electrolyte with a solid electrolyte and achieve a fully solid-state design, do not use flammable organic solvents within the battery, thereby simplifying safety devices and improving manufacturing costs and productivity. Furthermore, sulfide solid electrolytes are known as solid electrolytes for use in such all-solid-state lithium batteries.

[0003] Lithium sulfide is used as a raw material for sulfide solid electrolytes. Known methods for producing this lithium sulfide include, for example, a method using lithium hydroxide in which lithium hydroxide is reacted with hydrogen sulfide in a nonpolar organic solvent such as toluene (see, for example, Patent Document 1), and a method in which lithium hydroxide is reacted with hydrogen sulfide without using a solvent (see, for example, Patent Document 2). Also known is a method in which hydrogen sulfide is obtained by reacting hydrogen gas with sulfur vapor in a heated porous material in a single reaction vessel, and the resulting hydrogen sulfide is then contacted with lithium hydroxide (see, for example, Patent Document 3). Patent Document 4 discloses a method in which lithium hydroxide is reacted with a hydrogen sulfide-containing gas at a reaction temperature of 350°C or higher but lower than 450°C using equipment with a rolling bed, such as a rotary kiln, to form a gas-solid reaction.

[0004] JP 2010-163356 A JP 9-278423 A JP 2016-150859 A JP 2015-137183 A

[0005] The present invention has been made in view of the above circumstances, and aims to provide a method for easily and inexpensively producing high-quality lithium sulfide, and a method for efficiently producing a sulfide solid electrolyte.

[0006] The method for producing lithium sulfide according to the present invention is a method for producing lithium sulfide, comprising reacting lithium hydroxide with a sulfur-containing diluent gas containing an inert gas and a substance containing sulfur, while stirring with a stirring blade, and the lithium sulfide according to the present invention has a specific surface area of ​​8.0 m ２ / g or more, a pore volume greater than 0.10 mL / g, and solvent-free lithium sulfide.

[0007] Furthermore, a method for producing a sulfide solid electrolyte according to the present invention is a method for producing a sulfide solid electrolyte, the method comprising: reacting lithium hydroxide with a sulfur-containing diluent gas containing an inert gas and a substance containing sulfur element while stirring with a stirring blade to obtain lithium sulfide; and reacting a raw material containing lithium sulfide.

[0008] According to the present invention, it is possible to provide a method for easily and inexpensively producing high-quality lithium sulfide, and further a method for efficiently producing a sulfide solid electrolyte.

[0009] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, the upper and lower limit values ​​of a range expressed by "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and lower limit values.

[0010] (Findings Obtained by the Inventor to Achieve the Present Invention) When lithium sulfide is used as a raw material for a solid electrolyte, high quality (hereinafter also referred to as "high quality") is naturally required of the lithium sulfide. However, the required high quality may vary depending on the desired purpose. For example, in order to efficiently obtain a solid electrolyte with superior battery performance, properties such as high purity and a large specific surface area are generally required. These properties facilitate the reaction between lithium sulfide and other solid electrolyte raw materials and facilitate the production of a high-purity sulfide solid electrolyte. In addition, in relation to high purity, it is also desirable that the lithium sulfide does not contain a solvent. This is because if lithium sulfide contains a solvent, the battery performance of the sulfide solid electrolyte obtained using this may be reduced. In addition, in order to obtain a high-quality sulfide solid electrolyte, the performance requirements for solid electrolyte raw materials such as lithium sulfide have been increasingly high in recent years.

[0011] However, the method described in Patent Document 1 uses a solvent, and when the resulting lithium sulfide is used as a raw material for a sulfide solid electrolyte, equipment and costs for removing the solvent are required to prevent a decrease in battery performance. Therefore, the method described in Patent Document 1 cannot be said to easily and inexpensively produce high-quality lithium sulfide. The method described in Patent Document 2 does not use a solvent, so it may be possible to easily and inexpensively produce high-purity lithium sulfide without using a solvent. However, it is known that when a solvent is not used, i.e., a dry production method, the specific surface area generally tends to be small, making it difficult to meet the demand for a high specific surface area. Furthermore, the lithium hydroxide used as a raw material must be adjusted to a predetermined diameter range in advance, so it cannot be said to easily and inexpensively produce high-quality lithium sulfide.

[0012] The method described in Patent Document 3 has a problem in that the apparatus used, such as a reaction tank, becomes complicated, resulting in an increase in production costs. Moreover, the method described in Patent Document 3 is also a dry production method that does not use a solvent, and it is difficult to meet the requirement for a high specific surface area. Therefore, it cannot be said that the method described in Patent Document 3 can easily and inexpensively obtain high-quality lithium sulfide.

[0013] Furthermore, in the method described in Patent Document 4, in order to achieve a high reaction temperature of 350°C or higher, it is necessary to use a rotary calciner such as a rotary kiln as equipment having a rolling bed. Moreover, the method described in Patent Document 4 is also a dry production method that does not use a solvent, and therefore it is difficult to meet the requirement for a high specific surface area. Therefore, it cannot be said that high-quality lithium sulfide can be obtained easily and inexpensively.

[0014] The dry production methods disclosed in Patent Documents 2 to 4 that do not use a solvent make it easy to produce high-purity lithium sulfide because the resulting lithium sulfide does not contain a solvent, but on the other hand, there is a problem that the specific surface area tends to be small, as mentioned above. The present inventors have investigated a method for increasing the specific surface area while taking advantage of the advantages of dry production methods that do not use a solvent. In the course of their investigations, they have focused particularly on the method of supplying and contacting the substance containing sulfur in the reaction between the raw material lithium hydroxide and the substance containing sulfur, and have found that it is effective to simultaneously supply the substance containing sulfur together with an inert gas and react them while stirring with a stirring blade.

[0015] The above-described ability to easily and inexpensively produce high-quality lithium sulfide improves the reactivity of lithium sulfide, facilitating the reaction between lithium sulfide and other solid electrolyte raw materials. As a result, the time required to easily and inexpensively produce a high-purity sulfide solid electrolyte can be shortened, and a sulfide solid electrolyte can also be produced more efficiently.

[0016] In this specification, the term "solid electrolyte" refers to an electrolyte that maintains a solid state under a nitrogen atmosphere at normal pressure at 25° C. The "sulfide solid electrolyte" of this embodiment is a solid electrolyte that contains lithium atoms, sulfur atoms, and phosphorus atoms, preferably halogen atoms, and further oxygen atoms, and has ionic conductivity due to lithium atoms.

[0017] The term "sulfide solid electrolyte" includes both crystalline sulfide solid electrolytes having a crystalline structure and amorphous sulfide solid electrolytes. In this specification, a crystalline sulfide solid electrolyte is a solid electrolyte in which a peak derived from the solid electrolyte is observed in the X-ray diffraction pattern in powder X-ray diffraction (XRD) measurement, regardless of whether or not a peak derived from the raw material of the solid electrolyte is present. That is, a crystalline sulfide 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 the crystalline sulfide solid electrolyte has the X-ray diffraction pattern described above, it may also include an amorphous sulfide solid electrolyte (also referred to as a "glass component") as a portion of the crystalline sulfide solid electrolyte. Therefore, the crystalline sulfide solid electrolyte includes so-called glass ceramics obtained by heating an amorphous solid electrolyte (glass component) above its crystallization temperature.

[0018] In this specification, the amorphous sulfide solid electrolyte (glass component) refers to a solid electrolyte in which the X-ray diffraction pattern in powder X-ray diffraction (XRD) measurement is a halo pattern in which no peaks other than those derived from the material are observed, and it does not matter whether or not there are peaks derived from the raw materials of the solid electrolyte.

[0019] (Regarding Various Forms of the Present Embodiment) A method for producing lithium sulfide according to a first form of the present embodiment is a method for producing lithium sulfide, comprising reacting lithium hydroxide with a sulfur-containing diluent gas containing an inert gas and a substance containing sulfur, while stirring with a stirring blade.

[0020] As described above, the present inventors supplied a sulfur-containing substance together with an inert gas and reacted the substances while stirring with a stirring blade. This resulted in an increase in the specific surface area while retaining the advantages of a dry production method that does not use a solvent, i.e., the advantage of obtaining high-purity lithium sulfide without the use of a solvent. The reason for the increase in specific surface area is unclear, but it is thought that the reaction between lithium hydroxide and a sulfur-containing substance, such as hydrogen sulfide, produces water as a by-product. The by-product water is rapidly desorbed by the inert gas, forming pores from which water is desorbed from the lithium sulfide particles, thereby increasing the specific surface area. Furthermore, stirring with a stirring blade is thought to promote the desorption of water, thereby increasing the specific surface area. Furthermore, as a secondary effect, the desorption of water can increase the pore volume as well as the specific surface area. This is also evident in the examples described below. Furthermore, the production method of this embodiment requires only a very simple operation of using a sulfur-containing diluent gas containing an inert gas and a substance containing sulfur, and stirring the lithium hydroxide and the diluent gas with a stirring blade. Thus, it is believed that the production method of this embodiment makes it possible to produce high-quality lithium sulfide easily and inexpensively.

[0021] A method for producing lithium sulfide according to a second aspect of the present embodiment is the same as that of the first aspect, except that the substance containing elemental sulfur is hydrogen sulfide. A method for producing lithium sulfide according to a third aspect is the same as that of the first or second aspect, except that the content of the substance containing elemental sulfur in the sulfur-containing diluent gas is 3% by volume or more and 50% by volume or less.

[0022] When the substance containing elemental sulfur is hydrogen sulfide, the reaction with lithium hydroxide proceeds more efficiently, making it easier to obtain high-quality lithium sulfide. Furthermore, when the content of the substance containing elemental sulfur contained in the sulfur-containing diluent gas is within the above range, the reaction with lithium hydroxide and the elimination of water proceed more efficiently, making it easier to obtain high-quality lithium sulfide.

[0023] The method for producing lithium sulfide according to a fourth aspect of the present embodiment is the method for producing lithium sulfide according to any one of the first to third aspects, wherein the reaction temperature of the reaction is equal to or higher than 130° C. and lower than 350° C. By setting the reaction temperature within the above temperature range, the reaction between lithium hydroxide and the sulfur-containing diluent gas proceeds more efficiently, and the elimination of water proceeds more efficiently, making it easier to obtain high-quality lithium sulfide.

[0024] The method for producing lithium sulfide according to a fifth aspect of the present embodiment is the method for producing lithium sulfide according to any one of the first to fourth aspects, wherein the lithium hydroxide is a powder having an average particle size of 0.01 mm or more and 3 mm or less. When the lithium hydroxide is a powder having an average particle size within the above range, the reaction between the lithium hydroxide and the sulfur-containing diluent gas proceeds more efficiently, and the elimination of water proceeds more efficiently, making it easier to obtain high-quality lithium sulfide.

[0025] A sixth aspect of the present embodiment is the method for producing lithium sulfide according to any one of the first to fifth aspects, wherein the reaction is carried out in the absence of a solvent.

[0026] As described above, the production method of this embodiment makes it possible to suppress a decrease in specific surface area while obtaining the advantages of a dry production method that does not use a solvent, but it is also possible to produce high-quality lithium sulfide even when a solvent is used. This is because the production method of this embodiment uses a sulfur-containing diluent gas and carries out the reaction while stirring with a stirring blade, so that even when a solvent is used, it is possible to efficiently remove the solvent along with the desorption of water. On the other hand, from the viewpoint of producing higher-quality lithium sulfide, it is preferable to carry out the reaction in the absence of a solvent.

[0027] A seventh aspect of the present embodiment provides a method for producing lithium sulfide in any one of the first to sixth aspects, wherein the lithium sulfide has a specific surface area of ​​8.0 m ２ / g or more, and the method for producing lithium sulfide according to an eighth aspect of the present embodiment is any one of the first to seventh aspects, wherein the pore volume of the lithium sulfide is more than 0.10 mL / g.

[0028] According to the method for producing lithium sulfide of the present embodiment, high-quality lithium sulfide having a specific surface area and a pore volume within the above ranges can be obtained.

[0029] A ninth aspect of the present embodiment is the method for producing lithium sulfide according to any one of the first to eighth aspects, wherein at least a part of the inert gas contained in the sulfur-containing diluent gas is supplied by a seal gas used for a shaft seal of the stirring impeller.

[0030] In the reaction in the manufacturing method of this embodiment, stirring blades are used, and shaft seals may be provided to prevent the inflow of powder into the reaction vessel equipped with the stirring blades and the leakage of hydrogen sulfide and the like into the atmosphere. Since a gas containing an inert gas is usually used for the shaft seal, this gas can be substituted for part of the inert gas used in the sulfur-containing diluent gas. By substituting the inert gas for the shaft seal, the amount of inert gas supplied solely for use in the sulfur-containing diluent gas can be reduced, and excessive supply of inert gas can be suppressed.

[0031] The lithium sulfide according to the tenth aspect of this embodiment has a specific surface area of ​​8.0 m ２ / g or more, a pore volume greater than 0.10 mL / g, and solvent-free lithium sulfide.

[0032] The lithium sulfide of this embodiment has a specific surface area and pore volume within the above ranges, and is highly pure because it does not contain a solvent, making it a high-quality lithium sulfide. Because the specific surface area and pore volume are within the above ranges, when the lithium sulfide of this embodiment is used as a solid electrolyte raw material, the reaction with other solid electrolyte raw materials is more likely to proceed, making it easier to produce a high-purity sulfide solid electrolyte. The lithium sulfide of this embodiment can be easily produced by the above-described method for producing lithium sulfide of this embodiment.

[0033] A method for producing a sulfide solid electrolyte according to an eleventh aspect of the present embodiment is a method for producing a sulfide solid electrolyte, the method including: reacting lithium hydroxide with a sulfur-containing diluent gas containing an inert gas and a substance containing sulfur element while stirring with a stirring blade to obtain lithium sulfide; and reacting a raw material containing lithium sulfide.

[0034] As described above, according to the method for producing lithium sulfide of the present embodiment, high-quality lithium sulfide can be obtained easily and inexpensively. As a result, the reaction with other solid electrolyte raw materials is facilitated, and the time required for producing a high-purity, high-quality sulfide solid electrolyte can be shortened easily and inexpensively. Therefore, a sulfide solid electrolyte can be produced more efficiently.

[0035] [Method for Producing Lithium Sulfide] Hereinafter, a method for producing lithium sulfide according to the present embodiment will be described. The method for producing lithium sulfide according to the present embodiment is a method for producing lithium sulfide, comprising reacting lithium hydroxide with a sulfur-containing diluent gas containing an inert gas and a substance containing sulfur, while stirring the mixture with a stirring blade.

[0036] (Lithium Hydroxide) The lithium hydroxide used in the production method of this embodiment may be anhydrous lithium hydroxide or a hydrate such as lithium hydroxide monohydrate. If the lithium sulfide obtained by the production method of this embodiment contains moisture, battery performance may be reduced when it is used as a raw material for a solid electrolyte. Also, from the viewpoint of reducing the burden of moisture removal, it is preferable to use anhydrous lithium hydroxide. In the case of anhydrous lithium hydroxide, the moisture content is typically 5% by mass or less, 3% by mass or less, or 1.5% by mass or less. Here, the moisture content in lithium hydroxide is a value measured using a Karl Fischer moisture meter under the vaporization method at 280°C.

[0037] The average particle size of lithium hydroxide is typically 0.01 mm or more and 3 mm or less, preferably 0.05 mm or more, more preferably 0.1 mm or more, even more preferably 0.25 mm or more, with an upper limit of preferably 2.5 mm or less, more preferably 2 mm or less, even more preferably 1.5 mm or less, and particularly preferably 1.2 mm or less. When the average particle size of lithium hydroxide is within the above range, reactivity with sulfur-containing diluent gas is improved. Furthermore, when lithium hydroxide is a powder having the above average particle size, high reactivity with other raw materials is obtained when the resulting lithium sulfide is used as a raw material for a solid electrolyte. Furthermore, the occurrence of aggregation, adhesion, scattering, etc. due to static electricity, intermolecular forces, etc. during handling is suppressed, improving ease of handling. In this specification, the average particle size refers to the particle size D50 at a cumulative volume percentage of 50% in the particle size distribution measured by laser diffraction. Specifically, the measurement can be performed using a commercially available device such as a laser diffraction particle size distribution measuring device (for example, "SALD-1000 (trade name)" (manufactured by Shimadzu Corporation), "Mastersizer 2000 (trade name)" (manufactured by Malvern Instruments Ltd.), or "LA-950 (trade name)" (manufactured by Horiba, Ltd.)).

[0038] (Sulfur-Containing Diluent Gas) In the production method of this embodiment, a sulfur-containing diluent gas containing an inert gas and a substance containing sulfur is used. In the production method of this embodiment, the substance containing sulfur that contributes to the reaction is diluted with an inert gas and supplied as a gas, thereby accelerating the reaction between lithium hydroxide and the sulfur-containing diluent gas and producing lithium sulfide with high purity and a large specific surface area. To further accelerate the reaction, it is common to supply a larger amount of the substance that contributes to the reaction, i.e., to supply the substance at a higher concentration. However, in the production method of this embodiment, the specific effect of further accelerating the reaction is achieved by deliberately diluting the substance with an inert gas and supplying it. Although the mechanism behind this unique effect is unclear, it is believed that the use of a sulfur-containing diluent gas accelerates the reaction between lithium hydroxide and the substance containing sulfur in the sulfur-containing diluent gas, as water produced as a by-product in the reaction between lithium hydroxide and the substance containing sulfur in the sulfur-containing diluent gas is rapidly desorbed by the inert gas, which does not contribute to the reaction.

[0039] The sulfur-containing substance is not particularly limited as long as it contains at least sulfur and can produce lithium sulfide by reacting with lithium hydroxide, and can be used in combination with an inert gas to form a sulfur-containing dilution gas (i.e., gas), but is preferably one containing sulfur and hydrogen. Examples of such substances include sulfur vapor and hydrogen sulfide, with hydrogen sulfide being preferred for reasons such as ease of availability and ease of stable reaction. Furthermore, when sulfur vapor is used as the sulfur-containing substance, it is preferable to use a combination of sulfur vapor and hydrogen gas. For example, commercially available hydrogen sulfide can be used as is. While hydrogen sulfide may or may not be dehydrated, it is preferable for the water content to be low in order to further reduce its influence on the reaction, and the water content may be, for example, approximately 50 ppm by mass or less.

[0040] Examples of inert gases include rare gases such as helium, neon, and argon, nitrogen, and carbon dioxide. Of these, nitrogen is preferred from the viewpoint of being cheaper and more readily available.

[0041] The content of the substance containing sulfur element in the sulfur-containing diluent gas is preferably 3% by volume or more, more preferably 5% by volume or more, and even more preferably 10% by volume or more, with the upper limit being preferably 50% by volume or less, more preferably 40% by volume or less, and even more preferably 25% by volume or less. When the content of the substance containing sulfur element is within the above range, a balanced effect of promoting the reaction between lithium hydroxide and the substance containing sulfur element in the sulfur-containing diluent gas and an effect of promoting the desorption of by-produced water can be obtained.

[0042] (Reaction) In the production method of this embodiment, it is necessary to react the lithium hydroxide and the sulfur-containing diluent gas while stirring them with stirring blades. If the reaction is not carried out while stirring with stirring blades, direct contact between the lithium hydroxide and the substance containing sulfur in the sulfur-containing diluent gas is difficult to occur, and the reaction does not proceed easily, so that lithium sulfide having high purity and a large specific surface area cannot be obtained. There are no particular limitations on the method for reacting while stirring with stirring blades, but a preferred example is a method using a reaction vessel equipped with stirring blades.

[0043] The reaction vessel is not particularly limited as long as it is equipped with at least a stirring blade, but examples thereof include a sealable tank-like vessel equipped with a heating means such as an electric heater, an oil bath, a heating jacket using a heat transfer medium such as oil or steam in its body, and also equipped with equipment capable of supplying an inert gas and a sulfur-containing diluent gas (e.g., a supply port for these gases), and further equipped with equipment capable of circulating these gases (e.g., a supply port and an outlet port for these gases). From the viewpoint of efficiently causing direct contact between lithium sulfide and a substance containing sulfur in the sulfur-containing diluent gas and further promoting the reaction, the equipment capable of supplying the inert gas and the sulfur-containing diluent gas is preferably arranged so that the supply points for these gases can be supplied so that lithium sulfide powder can be fed into the powder phase formed by stirring with the stirring blade. Furthermore, for example, a device for heating an object to be heated by circulating a heat transfer medium such as steam through the inside of a shaft and heat transfer blades provided in a dryer can also be used.

[0044] In the production method of this embodiment, it is preferable that at least a part of the inert gas contained in the sulfur-containing diluent gas is supplied by the seal gas used for the shaft seal of the stirring blade. As described above, since a part of the seal gas flows into the reaction vessel, by replacing this with a part of the inert gas used for the sulfur-containing diluent gas, the inert gas supplied solely for use in the sulfur-containing diluent gas can be reduced, and excessive supply of the inert gas can be suppressed.

[0045] As described above, water is produced as a by-product by the reaction of lithium sulfide with a substance containing sulfur in the sulfur-containing diluent gas. However, in order to further promote the reaction between lithium hydroxide and the substance containing sulfur and thereby obtain lithium sulfide with high purity and a large specific surface area, it is considered important to quickly remove the by-product water. Therefore, in order to actively remove the by-product water, the reaction vessel is preferably provided with a condenser that condenses the gas containing water and the like that is discharged. Furthermore, the provision of a condenser makes it possible to confirm whether water is being generated, i.e., to confirm whether the reaction between lithium sulfide and the substance containing sulfur in the sulfur-containing diluent gas is progressing. Furthermore, the amount of water generated can be quantified, which has the advantage of making it easy to confirm how far the reaction has progressed and whether the reaction has been completed.

[0046] The reaction vessel is preferably one that is resistant to hydrogen sulfide corrosion and has specifications such as a material that can withstand the reaction temperature described below, and may also be a vessel having a predetermined design pressure that allows the reaction to be carried out even under pressure.

[0047] Examples of the stirring blade include anchor blades, Pfaudle blades, helical blades, Maxblend blades, and disk-type blades, and any of these may be used. The stirring speed of the stirring blades can be appropriately adjusted taking into consideration the average particle size of the lithium hydroxide used, the type of sulfur-containing diluent gas, and the amount used thereof, and cannot be generally specified, but may be, for example, about 10 rpm to 1,000 rpm. Furthermore, from the viewpoint of more efficiently causing direct contact between the lithium hydroxide and the sulfur-containing substance in the sulfur-containing diluent gas and further promoting the reaction, the stirring speed is preferably 20 rpm to 500 rpm, more preferably 30 rpm to 200 rpm, and particularly preferably 40 rpm to 100 rpm.

[0048] The reaction between lithium hydroxide and sulfur-containing diluent gas may be carried out in the reaction vessel, and may be carried out in either a closed system (batch system) or a flow system. However, a flow system is preferred from the viewpoint of more rapidly desorbing the water by-product of the reaction. When the reaction is carried out in a flow system, the supply amount of the sulfur-containing substance cannot be generally specified because it can vary depending on the amount of lithium hydroxide, the volume of the reaction vessel, etc., but from the viewpoint of further promoting the reaction, it is preferably 5 N-mL / min or more, more preferably 10 N-mL / min or more, and even more preferably 20 N-mL / min or more, per 10 g of lithium hydroxide, with the upper limit being preferably 300 N-mL / min or less, more preferably 200 N-mL / min or less, and even more preferably 100 N-mL / min or less. Furthermore, when a closed system is used, the supply of sulfur-containing diluent gas may be carried out, for example, by supplying hydrogen sulfide to a reaction vessel holding lithium sulfide to a predetermined pressure, and then repeatedly supplying hydrogen sulfide when the pressure in the reaction vessel decreases to the predetermined pressure due to the reduction in hydrogen sulfide reaction.

[0049] When the reaction is carried out in a flow system, the supply amount of the sulfur-containing diluent gas is preferably 10 N-mL / min or more, more preferably 30 N-mL / min or more, and even more preferably 60 N-mL / min or more, relative to 10 g of lithium hydroxide, and the upper limit is preferably 800 N-mL / min or less, more preferably 700 N-mL / min or less, and even more preferably 500 N-mL / min or less.

[0050] The reaction temperature between lithium hydroxide and sulfur-containing diluent gas is preferably 130°C or higher, more preferably 150°C or higher, and even more preferably 180°C or higher, with the upper limit being preferably less than 350°C, more preferably 325°C or lower, and even more preferably 300°C or lower. When the reaction temperature is within the above range, not only can the reaction be further promoted from a thermochemical perspective, but also aggregation of lithium hydroxide particles is less likely to occur and substances containing sulfur element can be more easily diffused into the lithium hydroxide, thereby further accelerating the reaction. Furthermore, since elimination of water, which is a by-product of the reaction, is further promoted, lithium sulfide having high purity and a large specific surface area can be obtained and the energy required for heating can also be further reduced.

[0051] The reaction time cannot be generally defined because it can vary depending on the amounts of lithium hydroxide and the sulfur-containing substance used, their blending ratios, etc., but is usually about 1 hour to 60 hours, preferably 2 hours to 30 hours, and more preferably 3 hours to 10 hours. Here, the reaction time is defined as the time from when the supply of the sulfur-containing substance starts (also referred to as the "start of the reaction") to when the supply is stopped (also referred to as the "end of the reaction"). Note that water is produced as a by-product by the reaction of lithium hydroxide with the sulfur-containing substance in the sulfur-containing diluent gas, and the stop of the supply of the sulfur-containing substance (end of the reaction) may be specifically when or after the generation of water stops.

[0052] The reaction between lithium hydroxide and a sulfur-containing diluent gas is preferably carried out in the absence of a solvent. Conventionally, various solvents have been used in the production of lithium sulfide, and even after removal by drying, distillation, or the like, the solvent may remain. If a solvent remains in lithium sulfide, the battery performance of a sulfide solid electrolyte obtained using the lithium sulfide may be reduced due to the remaining solvent. In the production method of this embodiment, the reaction is carried out in the absence of a solvent, thereby making it possible to further reduce the content of the solvent contained in the resulting lithium sulfide.

[0053] (Modification) The production method of this embodiment may include modifying lithium sulfide. By modifying lithium sulfide, at least one property of the lithium sulfide obtained by the above reaction, such as the specific surface area or pore volume, can be improved. The modification method is not particularly limited, and examples thereof include hydrogen sulfide modification. Examples of hydrogen sulfide modification methods include contacting the lithium sulfide obtained by the above reaction with hydrogen sulfide in a solvent to produce lithium hydrosulfide, and then dehydrosulfiding the lithium hydrosulfide to produce lithium sulfide (see, for example, JP 2016-204219 A). Furthermore, from the perspective of further reducing the content of solvent contained in lithium sulfide, modification may be performed without using a solvent, for example, by a method including contacting lithium sulfide with hydrogen sulfide in the absence of a solvent to produce lithium hydrosulfide, and then dehydrosulfiding the lithium hydrosulfide to produce lithium sulfide.

[0054] (Lithium Sulfide) The lithium sulfide obtained by the production method of this embodiment has high purity and a large specific surface area. Specifically, the purity of lithium sulfide is 97.5% by mass or more, further 97.8% by mass or more, and even 98.0% by mass or more. In this specification, the purity of lithium sulfide is a value measured by potentiometric titration. The content of lithium hydroxide contained in lithium sulfide is 0.3% by mass or less, further 0.2% by mass or less, and even 0.15% by mass or less. The lower limit is not particularly limited, and is, for example, about 0.01% by mass or more. As such, since the lithium sulfide obtained by the production method of this embodiment is highly pure, when used as a raw material for a solid electrolyte, the resulting solid electrolyte has higher ionic conductivity and a solid electrolyte with better battery performance can be obtained. In this specification, the content of lithium hydroxide is a value measured by potentiometric titration.

[0055] Furthermore, the lithium sulfide obtained by the production method of this embodiment may contain water. The lower the water content in the lithium sulfide, the more preferable it is, for example, 0.5% by mass or less, further 0.3% by mass or less, and even further 0.1% by mass or less. As described above, since the lithium sulfide obtained by the production method of this embodiment has a low water content, when lithium sulfide is used as a raw material for a solid electrolyte, a decrease in ionic conductivity due to water can be suppressed, and a solid electrolyte with better battery performance can be obtained. In this specification, the water content in lithium sulfide is a value measured using a Karl Fischer moisture meter under conditions of a vaporization method at 280°C.

[0056] The specific surface area of ​​the lithium sulfide obtained by the production method of this embodiment is 8.0 m ２ / g or more, and even 10.0m ２ / g or more, 12.5m ２ / g or more, 15m ２ / g or more. Since the lithium sulfide obtained by the production method of this embodiment has a high specific surface area, when used as a raw material for a solid electrolyte, it has excellent reactivity, and therefore a solid electrolyte can be efficiently obtained. In this specification, the specific surface area is a value measured by the BET method (gas adsorption method), and either nitrogen (nitrogen method) or krypton (krypton method) may be used as the gas, and is measured by appropriately selecting depending on the size of the specific surface area. The specific surface area can be measured using, for example, a commercially available device such as a gas adsorption measuring device (e.g., AUTOSORB6 (manufactured by Sysmex Corporation)).

[0057] The pore volume of the lithium sulfide obtained by the production method of this embodiment is greater than 0.10 mL / g, even 0.12 mL / g or more, or 0.15 mL / g or more, with the upper limit typically being 1.0 mL / g or less. Because the lithium sulfide obtained by the production method of this embodiment has a high pore volume, when used as a raw material for a solid electrolyte, it has excellent reactivity, allowing for efficient production of a solid electrolyte. In this specification, the specific surface area can be measured using the same apparatus as that used to measure the specific surface area described above, and may be a value obtained by interpolating from measurement points where the relative pressure P / P0 is 0.99 or more to 0.99. The lower measurement limit of the apparatus is 0.001 mL / g.

[0058] The average particle size of lithium sulfide obtained by the production method of this embodiment is 0.1 mm or more, further 0.15 mm or more, or even 0.25 mm or more, with the upper limit being 1.5 mm or less, further 1.3 mm or less, or even 1.0 mm or less. When used as a raw material for producing a solid electrolyte, the smaller the average particle size of lithium sulfide, the better because reactivity is improved. However, as the average particle size decreases, aggregation, adhesion, scattering, etc. due to static electricity, intermolecular forces, etc., are more likely to occur during handling, which may reduce ease of handling. Considering the balance between improved reactivity and ease of handling, it is preferable to keep the average particle size within the above range.

[0059] Furthermore, the lithium sulfide obtained by the manufacturing method of this embodiment preferably does not contain a solvent. By not containing a solvent, when used as a raw material for a solid electrolyte, deterioration in battery performance due to the solvent can be suppressed. In this specification, "solvent-free" means that the lithium sulfide is substantially free of solvent, and is a concept that encompasses an embodiment in which the solvent content in the lithium sulfide is 0% by mass, as well as an embodiment in which the solvent is contained in a range of 0.1% by mass or less, which is the measurement limit. The solvent content can be measured by dissolving lithium sulfide in methanol and quantifying the amount of solvent by gas chromatography.

[0060] Examples of the solvent that is the subject of "solvent-free" include solvents that have conventionally been used in general production of lithium sulfide, such as saturated hydrocarbon solvents such as hexane, pentane, and cyclohexane; unsaturated hydrocarbon solvents such as hexene and cyclohexene; aromatic hydrocarbon solvents such as benzene, toluene, and nitrobenzene; ketone solvents such as acetone and methyl ethyl ketone; ether solvents such as diethyl ether, dibutyl ether, tetrahydrofuran, methyl cellosolve, and diethylene glycol monomethyl ether; alcohol solvents such as ethanol and butanol; ester solvents such as ethyl acetate; halogenated hydrocarbon solvents such as dichloromethane and chlorobenzene; amide solvents such as dimethylformamide and methylpyrrolidone; and nitrile solvents such as acetonitrile and isobutyronitrile.

[0061] The lithium sulfide obtained by the production method of this embodiment has high purity and a large specific surface area, and combines excellent reactivity with ease of handling, making it suitable for use as a raw material for solid electrolytes. The obtained solid electrolyte is suitable for use in lithium ion secondary batteries, more specifically, in the solid electrolytic layer of all-solid-state lithium ion secondary batteries, or as a solid electrolyte to be mixed into positive and negative electrode composites. For example, an all-solid-state lithium ion secondary battery can be obtained by providing a positive electrode, a negative electrode, and layers of solid electrolyte between the positive and negative electrodes.

[0062] [Lithium sulfide] The lithium sulfide of this embodiment has a specific surface area of ​​8.0 m ２ / g or more, a pore volume exceeding 0.10 mL / g, and no solvent is used. The specific surface area and pore volume are as described above for the lithium sulfide obtained by the production method of the present embodiment, and the absence of a solvent is also the same. Furthermore, the lithium sulfide of the present embodiment can be easily and inexpensively produced by the production method of lithium sulfide of the present embodiment. Therefore, the lithium sulfide of the present embodiment is preferably produced by the production method of lithium sulfide of the present embodiment.

[0063] The lithium sulfide of this embodiment has a large specific surface area and a large pore volume, which improves the reactivity of the lithium sulfide, thereby facilitating the reaction between the lithium sulfide and other solid electrolyte raw materials. Furthermore, the lithium sulfide of this embodiment can be preferably produced by the method for producing lithium sulfide of this embodiment described above. As a result, the lithium sulfide of this embodiment can easily and inexpensively shorten the time required to produce a high-purity sulfide solid electrolyte, and also enables more efficient production of the sulfide solid electrolyte.

[0064] Furthermore, preferred properties of the lithium sulfide of the present embodiment include the purity, the content of lithium hydroxide contained in the lithium sulfide, the water content in the lithium sulfide, and the average particle size, which are described above for the lithium sulfide obtained by the production method of the present embodiment.

[0065] [Method for Producing Sulfide Solid Electrolyte] The method for producing a sulfide solid electrolyte of the present embodiment is a method for producing a sulfide solid electrolyte, comprising: reacting lithium hydroxide with a sulfur-containing diluent gas containing an inert gas and a substance containing sulfur element while stirring with a stirring blade to obtain lithium sulfide; and reacting a raw material containing lithium sulfide.

[0066] The method for producing a sulfide solid electrolyte of this embodiment involves reacting lithium hydroxide with a sulfur-containing diluent gas containing an inert gas and a substance containing sulfur to obtain lithium sulfide, while stirring with a stirring blade, i.e., employs the method for producing lithium sulfide of this embodiment. As described above, this method makes it possible to easily and inexpensively shorten the time required to produce a high-purity sulfide solid electrolyte, and also enables more efficient production of the sulfide solid electrolyte. Obtaining lithium sulfide is as described above in the method for producing lithium sulfide of this embodiment, including preferred aspects.

[0067] (Reacting) The method for producing a sulfide solid electrolyte of this embodiment includes reacting a raw material content containing lithium sulfide obtained by the method for producing lithium sulfide of this embodiment. The raw material content is a content containing lithium sulfide, which is a solid electrolyte raw material, and other solid electrolyte raw materials. The solid electrolyte raw material that can be used in combination with lithium sulfide is not particularly limited as long as it can produce a sulfide solid electrolyte. For example, a substance containing at least one atom selected from a lithium atom, a phosphorus atom, and a sulfur atom is preferred, and a substance containing at least one atom selected from a lithium atom, a phosphorus atom, a sulfur atom, and a halogen atom is more preferred.

[0068] Such a solid electrolyte raw material is, for example, diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ Representative examples of suitable starting materials include raw materials containing at least two types of atoms selected from the above-mentioned atoms, such as phosphorus molecules and sulfur molecules, and raw materials consisting of one type of atom selected from the above-mentioned atoms. Among these, lithium sulfide and diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ Among phosphorus sulfides, phosphorus pentasulfide (P ２ S ５ ) is preferred.

[0069] The raw material may further contain a halogen atom, and examples of the raw material include substances containing a halogen atom. For example, lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ) and other halogen molecules are typically preferred.

[0070] The above solid electrolyte raw materials may be blended in a blending ratio that matches the composition of the sulfide solid electrolyte having the desired crystal structure. Examples of the blending ratio of lithium sulfide and other solid electrolyte raw materials contained in the raw material inclusions include those described in International Publication No. 2020 / 105737 (see paragraphs

[0024] to

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

[0020] to

[0022] ).

[0071] The reaction of the raw material components can be carried out, for example, by mixing (i) or by heat treatment in a pressure vessel or by heat treatment in a solvent under reflux (ii). First, the process (i) will be described.

[0072] (Regarding Production Method (i)) The method for mixing raw materials containing lithium sulfide is not particularly limited as long as it can mix the solid electrolyte raw materials. For example, it can be performed using a pulverizer, mixer, stirrer, etc. When a pulverizer is used, the raw materials are pulverized, but mixing also occurs at the same time. Mixing of raw materials can also occur when a mixer or stirrer is used. Therefore, it can be said that the sulfide solid electrolyte of this embodiment can be preferably produced by stirring, mixing, pulverizing, or a combination of any of these processes, using two or more raw materials selected from substances containing at least one atom of a lithium atom, a sulfur atom, a phosphorus atom, and a halogen atom.

[0073] The equipment used to mix the raw material components, such as a grinder, mixer, or agitator, is not particularly limited and any commonly available equipment can be used.

[0074] In the above mixing, a solvent can be added to the above raw materials and mixed. As the solvent, various solvents widely called organic solvents can be used. As the solvent, a wide range of solvents that have been conventionally used in the production of solid electrolytes can be used, and examples thereof include hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents.

[0075] In addition to the hydrocarbon solvents, examples of the solvent include solvents containing heteroatoms such as nitrogen, oxygen, sulfur, and halogen atoms, and the like, in addition to carbon and hydrogen atoms. Such solvents have the property of readily forming complexes (which can also be referred to as "electrolyte precursors" because a sulfide solid electrolyte can be obtained by removing the complexing agent from the "complex") with raw materials containing lithium, phosphorus, sulfur, oxygen, and halogen atoms (hereinafter, such solvents are also referred to as "complexing agents"). These solvents facilitate the retention of halogen atoms within the structure of the sulfide solid electrolyte, making them useful in terms of achieving higher ionic conductivity. Furthermore, the use of a complexing agent is useful because it allows the solid electrolyte raw materials to be mixed using equipment such as a mixer or agitator, i.e., without the need for a pulverizer, to proceed with the reaction of the solid electrolyte raw materials.

[0076] As the complexing agent and the hydrocarbon solvent that can be employed, for example, the complexing agents and hydrocarbon solvents exemplified in International Publication No. 2020 / 105737 can be used. Among these solvents containing heteroatoms, it is preferable to use a solvent containing a nitrogen atom as the complexing agent, more preferably an amine solvent having an amino group, and even more preferably a diamine solvent having two amino groups.

[0077] (Drying) The method for producing a sulfide solid electrolyte of this embodiment may include, when mixing is performed using a solvent, drying the fluid (usually a slurry) obtained by mixing. When a complexing agent is used as the solvent, the sulfide solid electrolyte is obtained by removing the complexing agent from a complex containing the complexing agent. When a complexing agent and a solvent are used in combination, the complexing agent is removed from a complex containing the complexing agent and then the solvent is removed. When a solvent other than a complexing agent is used, the solvent is removed to obtain the sulfide solid electrolyte.

[0078] The drying method can be any method that can remove the solvent, and can be selected from solid-liquid separation, drying by heating, drying under reduced pressure (vacuum drying), and a combination of these. When a complexing agent is used as the solvent and the complexing agent is removed from the complex (electrolyte precursor), drying by heating is preferred as the drying method, and it is preferably performed using a dryer such as a flow-type heater. This is because the complexing agent can be quickly removed from the complex (electrolyte precursor), and the generation of impurities can be more efficiently suppressed, resulting in a high-quality sulfide solid electrolyte. Preferred flow-type heaters include flash dryers, spray dryers, and fluidized dryers using a medium, with flash dryers being particularly preferred.

[0079] (Heating) The method for producing a sulfide solid electrolyte according to the present embodiment may further include heating. When an amorphous sulfide solid electrolyte (glass component) is obtained by the above-described mixing, a crystalline sulfide solid electrolyte can be obtained by heating. When a crystalline sulfide solid electrolyte is obtained, a crystalline sulfide solid electrolyte with improved crystallinity can be obtained. In either case, heating can convert the obtained sulfide solid electrolyte into a crystalline sulfide solid electrolyte, thereby improving the ionic conductivity. In other words, the heating can be considered an operation performed for crystallization.

[0080] When a complexing agent is used as a solvent during mixing, a complex containing the complexing agent is formed. However, the complexing agent can be removed from the complex by heating without performing the drying process, and a sulfide solid electrolyte can be obtained. Depending on the heating conditions, the sulfide solid electrolyte can be made amorphous or crystalline.

[0081] (Regarding Production Method (ii)) Production method (ii) is a production method in which the reaction of raw material contents is carried out by heat-treating in a solvent while heat-treating or refluxing in a pressure-resistant vessel. When the heat treatment using a pressure-resistant vessel is adopted as the production method for the sulfide solid electrolyte of this embodiment, it is a suitable method for producing a sulfide solid electrolyte having an argyrodite-type crystal structure, which will be described later. Details of the heat treatment in a solvent while heat-treating or refluxing in a pressure-resistant vessel in production method (ii) are explained in JP 2020-095953 A and the like, and these may be followed.

[0082] (Amorphous sulfide solid electrolyte) The amorphous sulfide solid electrolyte obtained by the production method of this embodiment contains lithium atoms, sulfur atoms, and phosphorus atoms, and preferably further contains halogen atoms. Representative examples include Li, ２ S-P ２ S ５ , and 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., 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-SiS ２ -P ２ S ５ In order to obtain higher ionic conductivity, a solid electrolyte such as 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 A 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.

[0083] In the amorphous sulfide solid electrolyte obtained by the production method of this embodiment, 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 with higher ionic conductivity having a thiolisiconregion II type crystal structure, an argyrodite type crystal structure, or the like, which will be described later.

[0084] (Crystalline sulfide solid electrolyte) The crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment 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. ６Crystal 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).

[0085] Preferred examples of the crystal structure include a thiolisiconregion II crystal structure and an argyrodite crystal structure. Details of these crystal structures are described, for example, in International Publication Nos. 2024 / 010078 and 2024 / 010079. The atomic composition ratio of the crystalline solid electrolyte is determined by a composition formula corresponding to the various crystal structures, and is preferably within the range of the atomic composition ratio of the amorphous solid electrolyte. When the atomic composition ratio is within this range, it is easier to form a thiolisiconregion II crystal structure or an argyrodite crystal structure among the above crystal structures.

[0086] The sulfide solid electrolyte of this embodiment has high ionic conductivity. Therefore, it is suitable for use in electrode composites and batteries, especially lithium ion batteries, and particularly all-solid-state batteries. The solid electrolyte of this embodiment may be used in a positive electrode layer, a negative electrode layer, or an electrolyte layer. Each layer can be manufactured by a known method.

[0087] 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.

[0088] (Measurement of lithium sulfide purity and lithium hydroxide content) The purity of lithium sulfide and the lithium hydroxide content in lithium sulfide were analyzed and measured by hydrochloric acid titration and silver nitrate titration. Specifically, the lithium sulfide obtained in the examples and comparative examples was weighed in a glove box (dew point: approximately −80° C., nitrogen atmosphere), dissolved in water, and measured and calculated using a potentiometric titrator ("COM-1600 (model number)", manufactured by Hiranuma Sangyo Co., Ltd.). (Measurement of average particle size) A laser diffraction particle size distribution analyzer ("LA-950 (product name)" (manufactured by Horiba, Ltd.)) was used to measure the particle size D50 at a cumulative volume percentage of 50%, and this was taken as the average particle size. (Measurement of specific surface area and pore volume) The specific surface area and pore volume were measured using a gas adsorption analyzer. An "AUTOSORB-3 (model number)" (manufactured by Anton Paar) was used as the gas adsorption analyzer. The measurement conditions for this device are as follows: Pretreatment: Vacuum evacuation treatment, 150°C for 3 hours Principle: BET multipoint by static method (nitrogen adsorption)

[0089] Example 1: A separable flask (500 mL) equipped with an anchor impeller was charged with 10 g of anhydrous lithium hydroxide (manufactured by Honjo Chemical Co., Ltd., particle size range: 0.1 mm to 1.5 mm, average particle size: 0.3 mm, moisture content: 1% by mass or less) under inert gas (nitrogen). The anchor impeller was operated at 60 rpm to stir the anhydrous lithium hydroxide, and the internal temperature (temperature of the lithium hydroxide) was heated to and maintained at 200°C using an oil bath while nitrogen was circulated at a flow rate of 360 N-mL / min. Simultaneously, the upper part of the separable flask (above the interface between the solid and gas phases) was maintained at 100°C using a ribbon heater. Next, while nitrogen was flowing, hydrogen sulfide (manufactured by Sumitomo Seika Chemicals Co., Ltd.) was supplied at a flow rate of 40 N-mL / min, and a sulfur-containing diluent gas (hydrogen sulfide content: 10% by volume) was supplied to the separable flask at a flow rate of 400 N-mL / min. The reaction between lithium hydroxide anhydride and the sulfur-containing diluent gas was carried out at a temperature of 200°C. Furthermore, water produced as a by-product by the reaction between the lithium hydroxide anhydride and hydrogen sulfide was condensed and recovered using a condenser. After the reaction had been carried out for 6 hours, 7.5 mL of water was recovered. Hydrogen sulfide was then continued to be supplied at a flow rate of 40 N-mL / min for 3 hours, but no water generation was observed. No aggregation, adhesion, or adhesion of lithium hydroxide or the product to the separable flask was observed. Next, the supply of hydrogen sulfide was stopped while the temperature was maintained at 200°C, and nitrogen was then continued to flow for 60 minutes to replace the hydrogen sulfide in the separable flask with nitrogen. The temperature in the separable flask was lowered while nitrogen was circulated, and lithium sulfide was recovered. The purity of the obtained lithium sulfide, the content of lithium hydroxide in the lithium sulfide, the specific surface area, and the pore volume were measured, and the results were 98.1 mass%, 0.3 mass%, and 14 m, respectively. ２ The average particle size was measured and found to be 300 μm (0.3 mm).

[0090] Examples 2 to 4 Lithium sulfide was produced in the same manner as in Example 1, except that the amount of anhydrous lithium hydroxide charged, the amounts of hydrogen sulfide and nitrogen supplied, and the temperature during the reaction between anhydrous lithium hydroxide and a sulfur-containing diluent gas were set to the conditions shown in Table 1 below. The purity of the obtained lithium sulfide, the content of lithium hydroxide in the lithium sulfide, the specific surface area, and the pore volume were measured. The results are shown in Table 1.

[0091] Comparative Example 1 Lithium sulfide was produced in the same manner as in Example 1, except that hydrogen sulfide was supplied at a flow rate of 100 N-mL / min, the supply of nitrogen was stopped during this period, and the reaction between anhydrous lithium hydroxide and hydrogen sulfide was carried out at a temperature of 200° C. The purity of the obtained lithium sulfide, the content of lithium hydroxide in the lithium sulfide, the specific surface area, and the pore volume were measured, and were found to be 99.3 mass%, 0.1 mass%, and 7 m, respectively. ２ / g, 0.101 cc / g.

[0092]

[0093] The results of Examples 1 to 4 confirmed that the production method of the present embodiment enables easy and inexpensive production of lithium sulfide having high purity and a large specific surface area, without the use of complicated equipment, large-scale equipment, etc. Furthermore, it was confirmed that the lithium sulfide obtained in Example 1 had an average particle size of 300 μm (0.3 mm), which suppresses deterioration in handleability due to static electricity, intermolecular forces, etc. during handling, and thus has excellent ease of handling and excellent reactivity.

[0094] The lithium sulfide of Example 4 had a small specific surface area among the lithium sulfides obtained in the Examples, and the purity of the lithium sulfide was lower than that of Comparative Example 1. However, the purity of the lithium sulfide was beneficial to the product, and a 60% improvement in pore volume was confirmed compared to that of Comparative Example 1. The lithium sulfide of Example 2 had a low purity among the lithium sulfides obtained in the Examples, and was also lower than that of Comparative Example 1. However, it was confirmed that the specific surface area and pore volume were double those of Comparative Example 1. The relatively low specific surface area and purity of the lithium sulfide in Examples 2 and 4 are thought to be due to the reaction time of 6 hours between lithium hydroxide anhydride and a sulfur-containing diluent gas. Therefore, it is thought that the purity and specific surface area of ​​the lithium sulfide increase by extending the reaction time.

[0095] On the other hand, in Comparative Example 1, in which no sulfur-containing diluent gas was used, no inert gas was supplied and no reaction between lithium hydroxide anhydride and sulfur-containing diluent gas was carried out. Therefore, although the purity of lithium sulfide was high, the specific surface area was 7 m ２ / g, and the pore volume was as small as 0.10 mL / g. In other words, the lithium sulfide obtained in Comparative Example 1 cannot be said to be lithium sulfide having high purity and a large specific surface area.

[0096] The lithium sulfide obtained by the manufacturing method of this embodiment can be suitably used as a raw material for solid electrolytes. The obtained solid electrolyte can be suitably used in lithium ion secondary batteries, more specifically, in the solid electrolytic layer of an all-solid-state lithium ion secondary battery, or as a solid electrolyte to be mixed into a positive electrode or negative electrode composite. For example, an all-solid-state lithium ion secondary battery can be obtained by providing a positive electrode, a negative electrode, or a layer of solid electrolyte between the positive electrode and the negative electrode. Furthermore, lithium ion secondary batteries (all-solid-state lithium ion secondary batteries) are used in automotive applications, information-related devices and communication devices such as personal computers, video cameras, and mobile phones, and vehicles such as automobiles.

Claims

1. A method for producing lithium sulfide, comprising reacting lithium hydroxide with a sulfur-containing diluent gas containing an inert gas and a substance containing sulfur, while stirring with a stirring blade.

2. The method for producing lithium sulfide according to claim 1, wherein the substance containing elemental sulfur is hydrogen sulfide.

3. The method for producing lithium sulfide according to claim 1 or 2, wherein the content of the substance containing elemental sulfur contained in the sulfur-containing diluent gas is 3% by volume or more and 50% by volume or less.

4. The method for producing lithium sulfide according to any one of claims 1 to 3, wherein the reaction temperature is 130°C or higher and lower than 350°C.

5. The method for producing lithium sulfide according to any one of claims 1 to 4, wherein the lithium hydroxide is a powder having an average particle size of 0.01 mm or more and 3 mm or less.

6. The method for producing lithium sulfide according to any one of claims 1 to 5, wherein the reaction is carried out in the absence of a solvent.

7. The specific surface area of ​​lithium sulfide is 8.0 m ２ The method for producing lithium sulfide according to any one of claims 1 to 6, wherein the lithium sulfide content is 1 / g or more.

8. The method for producing lithium sulfide according to any one of claims 1 to 7, wherein the lithium sulfide has a pore volume of more than 0.10 mL / g.

9. The method for producing lithium sulfide according to any one of claims 1 to 8, wherein at least a portion of the inert gas contained in the sulfur-containing diluent gas is supplied by a seal gas used to seal the shaft of the stirring blade.

10. Specific surface area is 8.0 m ２ / g or more, a pore volume greater than 0.10 mL / g, and no solvent.

11. A method for producing a sulfide solid electrolyte, comprising: reacting lithium hydroxide with an inert gas and a sulfur-containing diluent gas containing a substance containing sulfur element while stirring with a stirring blade to obtain lithium sulfide; and reacting a raw material containing the lithium sulfide.

Images