Method for producing lithium sulfide

Abstract

The present invention addresses the problem of providing a method for producing lithium sulfide, with which the reaction efficiency between a lithium hydroxide starting material and a sulfur-containing gas is improved as compared with a conventional method. In a method for producing lithium sulfide according to the present invention, lithium sulfide is produced by bringing a lithium hydroxide starting material into contact with a sulfur-containing gas so as to cause a reaction therebetween, while pulverizing the lithium hydroxide starting material. It is preferable that the lithium hydroxide starting material is a lithium hydroxide hydrate. It is preferable that the lithium hydroxide starting material is pulverized by a high shear pulverizer. It is also preferable that the high shear pulverizer is a rotary blade type pulverizer.

Description

Lithium sulfide manufacturing method

[0001] The present invention relates to a method for producing lithium sulfide.

[0002] In recent years, secondary batteries have been attracting attention as an effort to prevent global warming by reducing carbon dioxide emissions. Among these, solid-state batteries are expected to be put into practical use as batteries that combine safety and high energy density. Sulfide solid electrolytes are known as one of the solid electrolytes used in solid-state batteries. Sulfide solid electrolytes are produced using, for example, lithium sulfide as a raw material. Lithium sulfide is generally produced by reacting hydrogen sulfide with a lithium source compound. For example, Patent Documents 1 and 2 describe a method for producing lithium sulfide by reacting lithium hydroxide, a lithium source, with hydrogen sulfide under heating.

[0003] Patent Document 1 describes a method for producing lithium sulfide, including a preparation step of placing lithium hydroxide powder in a reaction vessel equipped with a gas inlet and a gas outlet, and a reaction step of introducing hydrogen sulfide gas into the reaction vessel through the gas inlet to react with the lithium hydroxide and exhausting unreacted hydrogen sulfide gas through the gas outlet, wherein the concentration Cin of the hydrogen sulfide gas at the gas inlet is maintained within a range of 5 to 50%. The document also describes that this configuration suppresses the occurrence of cracks due to shrinkage of lithium sulfide powder in the synthesis of lithium sulfide by a dry method, thereby improving the production efficiency of lithium sulfide.

[0004] Patent Document 2 describes a technique in which lithium hydroxide is charged into a reaction vessel, the temperature of the inner wall of the reaction vessel that is in contact with the lithium hydroxide is maintained at 140 to 230°C, the temperature of the lid of the reaction vessel is maintained at 100°C or higher, and the lithium hydroxide is reacted with hydrogen sulfide gas while stirring so as not to retain the lithium hydroxide. This document also describes that this configuration makes it possible to prevent aggregation of lithium hydroxide and adhesion of the product to the reaction vessel without using a solvent.

[0005] JP 2023-14712 A International Publication No. 2016 / 098351 Pamphlet

[0006] In a method for synthesizing lithium sulfide by reacting a lithium hydroxide raw material with a sulfur-containing gas, water generated during heating or the progress of the reaction causes lithium hydroxide raw material particles to adhere to each other, forming agglomerates, with lithium sulfide formed only on the surface side of the agglomerates, hindering the progress of the reaction. The formation of agglomerates is particularly pronounced when lithium hydroxide hydrate is used as the lithium hydroxide raw material. However, the methods described in Patent Documents 1 and 2 are insufficient in terms of effectively resolving the problem with the lithium hydroxide raw material. In particular, the methods described in Patent Documents 1 and 2 do not fully consider techniques that can improve production efficiency by progressing the reaction even when lithium hydroxide hydrate is used.

[0007] Therefore, an object of the present invention is to provide a method for producing lithium sulfide that can overcome the various drawbacks of the prior art described above.

[0008] The present invention provides a method for producing lithium sulfide, which comprises pulverizing a lithium hydroxide raw material while bringing the material into contact with a sulfur-containing gas to react with the material to produce lithium sulfide.

[0009] The present invention will be described below based on preferred embodiments. In the method for producing lithium sulfide of the present invention, a lithium hydroxide raw material is pulverized and brought into contact with a sulfur-containing gas to react with the material to produce lithium sulfide.

[0010] In the present invention, the sulfur-containing gas used is, for example, hydrogen sulfide (H ２ Examples of sulfur-containing gases include hydrogen sulfide (S) gas and sulfur (S) gas. These gases may be used alone or in combination of two or more. These gases may be used as they are or may be diluted with an inert gas. Among them, it is preferable to use a gas containing hydrogen sulfide as the sulfur-containing gas from the viewpoint of ease of handling since it is a gas at room temperature and atmospheric pressure. The pressure of the sulfur-containing gas in the reaction system may be atmospheric pressure, or may be a pressure below or above atmospheric pressure. Generally, sulfurization of the lithium hydroxide raw material can be successfully carried out by flowing a sulfur-containing gas through the reaction system under atmospheric pressure.

[0011] In this production method, the amount of sulfur-containing gas used per mole of lithium atoms is, for example, preferably 0.5 moles or more, more preferably 1.0 moles or more, and even more preferably 1.5 moles or more, calculated as the sulfur atoms in the sulfur-containing gas. On the other hand, the amount of sulfur-containing gas used per mole of lithium atoms is, for example, preferably 10.0 moles or less, more preferably 7.0 moles or less, and even more preferably 4.0 moles or less, calculated as the sulfur atoms in the sulfur-containing gas. When the amount of sulfur-containing gas used per mole of lithium atoms is within the above range, high-purity lithium sulfide can be obtained. In addition, the production cost can be reduced, the production amount can be improved, and the equipment maintenance load can be further reduced.

[0012] In the present invention, the concentration of the sulfur-containing gas in the reaction vessel is preferably, for example, 50% by volume or more, more preferably 70% by volume or more, in order to promote the reaction with the lithium hydroxide raw material during pulverization. Furthermore, the concentration of the sulfur-containing gas in the reaction vessel is preferably 100% by volume or less, more preferably 90% by volume or less, in order to improve the pulverization efficiency of the lithium hydroxide raw material. Examples of gas components other than the sulfur-containing gas in the reaction vessel include inert gases such as nitrogen and argon.

[0013] The lithium hydroxide raw material used in the production method of the present invention includes anhydrous lithium hydroxide and lithium hydroxide hydrate. The lithium hydroxide raw material is a solid. The term "solid lithium hydroxide raw material" is intended to exclude lithium hydroxide in the form of an aqueous solution. Therefore, lithium hydroxide raw material that has absorbed water contained in the air is included in the category of solid lithium hydroxide raw material. The reaction between lithium hydroxide and hydrogen sulfide is represented by the following reaction formula (1). In this case, lithium hydroxide (LiOH) and hydrogen sulfide (H ２ S) reacts to form lithium sulfide (Li ２ S) is produced, and water (H ２ In this reaction, solid lithium sulfide is obtained from solid lithium hydroxide. ２ S → Li ２ S+2H２ O (1)

[0014] When a lithium hydroxide raw material is reacted with a sulfur-containing gas, the lithium hydroxide raw material is hygroscopic, and as described above, the lithium hydroxide raw material absorbs moisture, forming a mass in which raw material particles adhere to each other. If lithium sulfide is produced, the reaction product, lithium sulfide, is also deliquescent and therefore present in the mass. When such a mass is produced, the lithium hydroxide raw material particles or the lithium hydroxide raw material particles and lithium sulfide particles are stuck together, making it difficult for the sulfur-containing gas to penetrate into the particles, and the reaction progresses slowly. The present inventors have found that when the lithium hydroxide raw material is lithium hydroxide hydrate, the generation of a mass during the reaction of the above formula (1) is significant. When the lithium hydroxide raw material is lithium hydroxide monohydrate, the reaction formula is as follows: 2LiOH·H ２ O+H ２ S → Li ２ S+4H ２ O (2) Thus, when a hydrate is used as the lithium hydroxide raw material, the amount of water produced is more than twice as much as in the case of an anhydrous material, and the tendency for the formation of the agglomerates becomes significant.

[0015] In the prior art, when the lithium hydroxide raw material is a hydrate, it is common to dry the lithium hydroxide raw material to remove water of crystallization before reacting it with a sulfur-containing gas. In contrast, the present invention can effectively promote the progress of the reaction even when lithium hydroxide hydrate is used. As a result, the present invention can omit the step of drying lithium hydroxide hydrate before reacting it with a sulfur-containing gas, thereby reducing the cost of producing lithium sulfide compared to the prior art. For this reason, the present invention preferably uses lithium hydroxide hydrate as the lithium hydroxide raw material. From the above viewpoint, the water content of the lithium hydroxide raw material is preferably 0.001% by mass or more, more preferably 0.01% by mass or more. The water content of the lithium hydroxide raw material may be 45% by mass or less, which is preferable from the viewpoint of reaction progress, and may be 43% by mass or less. The water content here includes the amount of water of crystallization.

[0016] The problems of high costs for drying and removing moisture from the lithium hydroxide raw material and the difficulty in proceeding with the reaction with a sulfur-containing gas when using a lithium hydroxide raw material are particularly significant when producing lithium sulfide on a large scale industrially by reacting a sulfur-containing gas with a lithium hydroxide raw material. From this perspective, in the present invention, the internal volume of the reaction vessel is preferably, for example, 3 L or more, more preferably 20 L or more, and particularly preferably 150 L or more. The internal volume of the reaction vessel can be, for example, 4000 L or less.

[0017] The amount of lithium hydroxide raw material packed in the reaction vessel is, for example, preferably 500 g or more, more preferably 540 g or more, per 1 L of vessel volume, from the viewpoint of grinding efficiency, and is preferably 630 g or less, more preferably 600 g or less, from the viewpoint of grinding efficiency as well.

[0018] In the present invention, there is no particular limitation on the particle size of the lithium hydroxide raw material used in the reaction, but it is preferable in terms of pulverization efficiency that the particle size at the start of the reaction is at least a certain value. From this viewpoint, the volume cumulative particle size D of the lithium hydroxide raw material at a cumulative volume of 50% by volume measured by a laser diffraction / scattering particle size distribution measurement method is ５０ is, for example, preferably 1 μm or more, more preferably 10 μm or more, and even more preferably 100 μm or more. ５０ For example, the particle size is preferably 1000 μm or less in terms of reactivity with sulfur-containing gas, more preferably 800 μm or less, and even more preferably 600 μm or less.

[0019] When reacting the sulfur-containing gas with the lithium hydroxide raw material, it is preferable to heat the inside of the container to an appropriate temperature. Specifically, the temperature inside the container when reacting the sulfur-containing gas with the lithium hydroxide raw material is preferably 100 ° C. or higher, more preferably 120 ° C. or higher, and even more preferably 150 ° C. or higher, from the viewpoint of sufficiently progressing the reaction. Furthermore, the temperature when reacting the sulfur-containing gas with the lithium hydroxide raw material is preferably 450 ° C. or lower, more preferably 400 ° C. or lower, and even more preferably 350 ° C. or lower, from the viewpoint of preventing the lithium hydroxide from melting. The heating method is not particularly limited, and examples include a method of passing a heat medium against the wall surface of the reaction container.

[0020] For example, the temperature inside the container during grinding, which will be described later, may be the same as or different from the temperature inside the container when grinding is not being performed. If they are different, the temperature inside the container during grinding may be higher or lower than the temperature inside the container when grinding is not being performed.

[0021] The reaction time between the sulfur-containing gas and the lithium hydroxide raw material is preferably 10 minutes or more, more preferably 30 minutes or more, because the purity of the resulting lithium sulfide is high. In addition, the reaction time between the sulfur-containing gas and the lithium hydroxide raw material is preferably shorter in terms of shortening the production time, for example, preferably 720 minutes or less, more preferably 600 minutes or less.

[0022] In the present invention, in order to solve the problem of improving the reaction efficiency between a lithium hydroxide raw material and a sulfur-containing gas compared to conventional methods, the lithium hydroxide raw material is pulverized and brought into contact with a sulfur-containing gas to cause a reaction. By pulverizing a mass formed by a strong solidification of the lithium hydroxide raw material (particularly lithium hydroxide hydrate) containing lithium sulfide, a new surface where the lithium hydroxide is exposed to the outside is created, and the reaction proceeds quickly as this surface reacts with the sulfur-containing gas. In particular, pulverization can effectively improve a state in which lithium sulfide is generated on the surface of the mass, making the reaction difficult.

[0023] Here, "pulverization" in this specification refers to pulverizing, by high shear force, impact force, compression force, and friction force, a solid mass of lithium hydroxide raw material containing lithium sulfide formed as the reaction between the lithium hydroxide raw material and the sulfur-containing gas proceeds. This operation breaks up the mass containing the lithium hydroxide raw material and lithium sulfide, exposing new surfaces of the lithium hydroxide raw material to the sulfur-containing gas, thereby effectively promoting the lithium hydroxide reaction. Therefore, "pulverization" in this specification is different from simply vibrating or stirring the lithium hydroxide raw material during the reaction to prevent lithium hydroxide particles from adhering to each other or lithium hydroxide powder from adhering to the reaction vessel. It is also different from using a medium in combination with vibration to help the lithium hydroxide raw material powder acquire fluidity. Operations such as simple vibration, stirring, or imparting fluidity usually do not sufficiently promote the reaction when a hydrate is used as the lithium hydroxide raw material.

[0024] For the above reasons, the preferred method for pulverizing the lithium hydroxide raw material is dry pulverization using a high-shear pulverizer. Examples of high-shear pulverizers include rotary blade pulverizers. Pulverization using a rotary blade pulverizer is preferred because it can efficiently pulverize lumps of the lithium hydroxide raw material, resulting in good production efficiency when the production method of the present invention is carried out on a large scale, and because it can not only pulverize the lithium hydroxide raw material but also increase its fluidity, thereby improving the reactivity with sulfur-containing gas and thereby enhancing the effects of the present invention. As the rotary blade pulverizer, one that rotates a rotating shaft equipped with blades around the rotating shaft is used. Specifically, a single-shaft rotary shear pulverizer, a double-shaft rotary shear pulverizer, a multi-shaft screw pulverizer, or a rotary blade high-shear mixer (FM Mixer (manufactured by Nippon Coke and Engineering Co., Ltd.), a high-speed mixer (manufactured by Earth Technica Corporation), or a super mixer (manufactured by Kawata Corporation)) can be used.

[0025] In the pulverization using a rotary blade pulverizer, the peripheral speed of the stirring blade is preferably 450 m / min or more, more preferably 700 m / min or more, and the rotation speed of the stirring blade is preferably 5400 m / min or less, more preferably 4500 m / min or less.

[0026] The pulverization is preferably carried out for, for example, 30 seconds or more, more preferably 60 seconds or more. In the case of a batch method, the pulverization is preferably carried out for, for example, 720 minutes or less from the viewpoint of shortening the production time and preventing granulation and reagglomeration, and more preferably 600 minutes or less. Here, when pulverization is carried out intermittently, the pulverization time is the sum of the pulverization times for each pulverization.

[0027] In the present invention, the volume cumulative particle size D of the lithium hydroxide raw material at a cumulative volume of 50% by volume measured by a laser diffraction / scattering particle size distribution measurement method one minute after the start of pulverization is ５０ However, D at the start of the grinding operation ５０ The pulverization is preferably carried out by an operation in which the volume cumulative particle size D of the lithium hydroxide raw material at a cumulative volume of 50% by volume is measured by a laser diffraction / scattering particle size distribution measurement method one minute after the start of pulverization. ５０ However, D at the start of the grinding operation ５０ It is preferable that the ratio is 10% or more.

[0028] When introducing the lithium hydroxide raw material and the sulfur-containing gas into the reaction system, the pulverization operation of the lithium hydroxide raw material may be started, for example, before the lithium hydroxide raw material and the sulfur-containing gas come into contact, or may be started simultaneously with the contact of the lithium hydroxide raw material and the sulfur-containing gas, or may be started after the contact of the lithium hydroxide raw material and the sulfur-containing gas begins. Among these, starting simultaneously with the contact of the lithium hydroxide raw material and the sulfur-containing gas, or after the contact of the lithium hydroxide raw material and the sulfur-containing gas begins, is preferred in terms of preventing excessively small particle size of the lithium hydroxide raw material at the start of the reaction, which may conversely lead to a rapid increase in moisture and make the lithium hydroxide raw material more likely to adhere to the wall of the reaction vessel, and in terms of preventing particle granulation and re-agglomeration. From this viewpoint, it is particularly preferable to start pulverization after the contact of the lithium hydroxide raw material and the sulfur-containing gas begins.

[0029] The pulverization operation may be started after lithium sulfide begins to be produced by the reaction between the lithium hydroxide raw material and the sulfur-containing gas, or may be started before lithium sulfide is produced.

[0030] The pulverization operation of the lithium hydroxide raw material may be carried out, for example, continuously or intermittently during the reaction. The pulverization operation may be carried out once or twice or more times.

[0031] A nozzle for introducing a sulfur-containing gas may be provided so that the gas is sprayed from the vicinity of the grinding position of the lithium hydroxide raw material. For example, if the outlet of the nozzle for introducing the sulfur-containing gas is located at a height position within ±3 cm from the height position of the stirring blade in the grinding device, the contact between the new cross section of the lithium hydroxide raw material and the sulfur-containing gas is excellent, thereby increasing the reaction efficiency. The height position of the stirring blade here refers to the position ranging from the highest position to the lowest position of the stirring blade in the height direction of the grinding device.

[0032] Furthermore, when the lithium hydroxide raw material is pulverized, the reaction vessel may be vibrated to further increase the reaction efficiency between the sulfur-containing gas and the lithium hydroxide raw material.

[0033] The moisture content in the reaction vessel can be reduced by known techniques, such as reducing the pressure inside the vessel or heating the vessel wall.

[0034] The lithium sulfide obtained by this production method is useful, for example, as a raw material for a sulfide solid electrolyte of a lithium ion battery. ２ S ５ ) or other sulfides by mechanical milling reaction to obtain, for example, Li ７ P ３ S １１ and LiPS ４ Alternatively, a crystalline solid electrolyte, for example, a solid electrolyte having a crystal phase with an argyrodite crystal structure, can be synthesized by firing a mixture of lithium sulfide, diphosphorus pentasulfide, and a lithium halide such as lithium chloride (LiCl) and / or lithium bromide (LiBr) under an inert gas atmosphere or a hydrogen sulfide atmosphere. The substance to be reacted with lithium sulfide to synthesize the solid electrolyte is not particularly limited. For example, in addition to the above-mentioned diphosphorus pentasulfide, silicon sulfide (SiS ２ ), germanium sulfide (GeS ２ ) etc.

[0035] With respect to the above-described embodiments, the present invention further discloses the following methods for producing lithium sulfide. [1] A method for producing lithium sulfide, comprising contacting a lithium hydroxide raw material with a sulfur-containing gas while pulverizing the raw material to cause a reaction and produce lithium sulfide. [2] The method for producing lithium sulfide according to [1], wherein the lithium hydroxide raw material is lithium hydroxide hydrate. [3] The method for producing lithium sulfide according to [1] or [2], wherein the lithium hydroxide raw material is pulverized using a high-shear pulverizer. [4] The method for producing lithium sulfide according to [3], wherein the high-shear pulverizer is a rotary blade pulverizer.

[0036] As described above in detail, the production method of the present invention provides a method for producing lithium sulfide in which the reaction efficiency between a lithium hydroxide raw material and a sulfur-containing gas is improved compared to conventional methods.

Claims

1. A method for producing lithium sulfide by crushing lithium hydroxide raw material and contacting it with a sulfur-containing gas to react with it to produce lithium sulfide.

2. The method for producing lithium sulfide according to claim 1, wherein the lithium hydroxide raw material is lithium hydroxide hydrate.

3. The method for producing lithium sulfide according to claim 1 or 2, wherein the lithium hydroxide raw material is pulverized using a high-shear pulverizer.

4. The method for producing lithium sulfide according to claim 3, wherein the high-shear crusher is a rotary blade crusher.