Method for producing lithium sulfide

Abstract

The present invention relates to a method for producing lithium sulfide, the method comprising: introducing a powder containing elemental lithium to a container; and reacting this powder with a gas containing elemental sulfur, while applying vibration from outside to this container in a sealed state to move the powder.

Description

Technical Field

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

Background Art

[0002] Lithium sulfide is known as a raw material for solid electrolytes used in, for example, all-solid-state lithium-ion secondary batteries.

[0003] As a method for producing lithium sulfide, for example, a method of reacting a substance (powder) containing a lithium element such as lithium hydroxide with a gas containing a sulfur element such as hydrogen sulfide is known.

[0004] For example, Patent Document 1 describes a method for producing lithium sulfide by synthesizing lithium sulfide by reacting lithium hydroxide with a gaseous sulfur source, and describes that a solid-gas reaction can be carried out by a fluidized bed. Patent Document 2 describes that lithium sulfide particles are generated by bringing a reaction gas into contact with particulate lithium hydroxide to react hydrogen sulfide gas with lithium hydroxide. Here, as a configuration in which lithium hydroxide is disposed inside a reaction tank, a configuration in which particulate lithium hydroxide is laid on the surface of a porous sheet is described.

[0005] Patent Document 3 describes a method for producing lithium sulfide by reacting a lithium raw material with hydrogen sulfide gas to continuously produce lithium sulfide, and describes that a rotary kiln can be used as a reaction tank.

[0006] Patent Document 4 describes an apparatus for producing lithium sulfide having a reaction vessel for bringing lithium hydroxide powder into contact with hydrogen sulfide gas and a stirring blade inside the reaction vessel.

[0007] Patent Document 5 describes a method for producing lithium sulfide including reacting lithium hydroxide with hydrogen sulfide without using a solvent in a disk dryer.

Prior Art Documents

[0008] [Patent Document 1] Japanese Patent Publication No. 9-278423 [Patent Document 2] Japanese Patent Application Publication No. 2016-150859 [Patent Document 3] Japanese Patent Application Publication No. 2018-35045 [Patent Document 4] International Publication No. 2016 / 098351 [Patent Document 5] Japanese Patent Publication No. 2017-222567 [Overview of the project] [Problems that the invention aims to solve]

[0009] In the production of lithium sulfide, when a substance (powder) containing lithium, such as lithium hydroxide, is reacted with a gas containing sulfur, such as hydrogen sulfide, water may be produced as a byproduct. In the methods described in Patent Documents 1 and 2, a gas flow rate exceeding the flow initiation speed is required to fluidize the lithium-containing particles, which can result in poor gas utilization efficiency. Furthermore, water tends to condense on the walls of equipment with slow gas flow rates, and when powder is scattered by the gas, it tends to adhere to the equipment walls. If powder adheres easily inside the equipment, maintenance costs tend to increase.

[0010] In the method described in Patent Document 3, the entire apparatus is rotated at a relatively low speed, which makes it easy for powder to adhere to the walls of the apparatus due to water condensation. Furthermore, when using a rotary kiln, the powder filling rate is relatively low, which can result in inferior manufacturing efficiency. Moreover, since the spaces not filled with powder are also filled with gas, the proportion of gas that does not contribute to the reaction tends to be high, which can also result in inferior gas utilization efficiency.

[0011] The methods described in Patent Documents 4 and 5 are prone to gas leakage from the shaft of the stirring blade, which can result in poor gas utilization efficiency. Furthermore, when using toxic gases, measures to prevent gas leakage are required, which tends to increase equipment costs. In addition, powder adhesion due to water coagulation is likely to occur in areas of the apparatus where there are no stirring blades.

[0012] Therefore, the present invention aims to provide a method for producing lithium sulfide with excellent productivity. [Means for solving the problem]

[0013] In other words, the present invention relates to items 1 to 8 below. 1. Putting a powder containing lithium into a container, A method for producing lithium sulfide, comprising reacting the powder with a gas containing a sulfur element while the container is sealed and the container is vibrated from the outside to move the powder. 2. A method for producing lithium sulfide according to claim 1, comprising temporarily lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction, or lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction after the reaction. 3. The method for producing lithium sulfide according to 1 or 2, wherein the pressure inside the container during the reaction is 0.100 MPa or higher. 4. The method for producing lithium sulfide according to paragraph 3, wherein the pressure at which the pressure inside the container is reduced to a level lower than the pressure inside the container during the reaction is less than 0.100 MPa. 5. A method for producing lithium sulfide according to claim 1 or 2, comprising introducing a gas containing the sulfur element into the container from a nozzle placed in the container, wherein the ejection position of the gas containing the sulfur element at the nozzle is within 50% of the height of the gas phase and within 50% of the depth of the powder, with respect to the surface of the powder. 6. The method for producing lithium sulfide according to 1 or 2, wherein the average particle size of the powder is 200 μm or more. 7. The method for producing lithium sulfide according to item 1 or 2 above, further comprising putting particles other than powder containing lithium element into the container. 8. The method for producing lithium sulfide according to item 1 or 2 above, wherein the amplitude of the vibration is 1 mm to 10 mm.

Advantages of the Invention

[0014] According to the present invention, a method for producing lithium sulfide with excellent productivity can be provided.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 is a flowchart illustrating a method for producing lithium sulfide according to the present embodiment. [Figure 2] FIG. 2 is a diagram schematically illustrating a method for producing lithium sulfide according to the present embodiment. FIG. 2(a) is a schematic cross-sectional view of the side of the container during the reaction, and FIG. 2(b) is a schematic cross-sectional view of the front of the same container as FIG. 2(a). [Figure 3] FIG. 3 is a flowchart illustrating a method for producing lithium sulfide according to the present embodiment. [Figure 4] FIG. 4 is a diagram schematically illustrating a method for producing lithium sulfide according to the present embodiment. FIG. 4(a) is a schematic cross-sectional view of the side of the container during the reaction, and FIG. 4(b) is a schematic cross-sectional view of the front of the same container as FIG. 4(a). [Figure 5] FIG. 5 is a flowchart illustrating a method for producing lithium sulfide according to the present embodiment. [Figure 6] FIG. 6 is a flowchart illustrating a method for producing lithium sulfide according to the present embodiment. FIG. 6(a) is a flowchart illustrating a method including temporarily reducing the pressure inside the container to be lower than the pressure inside the container during the reaction in the middle of the reaction, and FIG. 6(b) is a flowchart illustrating a method including reducing the pressure inside the container to be lower than the pressure inside the container during the reaction after the reaction.

Embodiments for Carrying Out the Invention

[0016] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified and implemented as appropriate without departing from the spirit of the invention. Furthermore, the "~" indicating a numerical range is used to mean that the numbers written before and after it are included as the lower limit and upper limit.

[0017] The method for producing lithium sulfide according to this embodiment (hereinafter also referred to as the "production method") includes placing a powder containing the element of lithium into a container and, while the container is sealed, reacting the powder with a gas containing the element of sulfur while vibrating the container from the outside to move the powder.

[0018] This manufacturing method involves reacting a powder containing lithium with a gas containing sulfur. Hereinafter, "powder containing lithium" and "gas containing sulfur" may be simply referred to as "powder" and "gas," respectively.

[0019] Examples of lithium-containing powders include lithium hydroxide, lithium carbonate, and lithium oxide, with lithium hydroxide being preferred from the viewpoint of being able to be processed at low temperatures. Examples of sulfur-containing gases include gases containing sulfur-containing components, for example, gases containing one or more sulfur-containing components selected from the group consisting of hydrogen sulfide and carbon disulfide. Among these, gases containing hydrogen sulfide are preferred from the viewpoint of being easy to handle because they are gases at room temperature and pressure.

[0020] For example, the reaction between lithium hydroxide and hydrogen sulfide is represented by the following reaction equation (1). In this case, lithium hydroxide (LiOH) and hydrogen sulfide (H2S) react to produce lithium sulfide (Li2S), and water (H2O) is produced as a byproduct. 2LiOH + H2S → Li2S + 2H2O (1)

[0021] The above reaction typically involves the reaction of hydrogen sulfide gas with solid lithium hydroxide to produce solid lithium sulfide and water vapor. For example, this reaction can be carried out by bringing hydrogen sulfide gas and solid lithium hydroxide into contact and heating them.

[0022] When the lithium-containing powder contains lithium hydroxide, either anhydrous lithium hydroxide or lithium hydroxide monohydrate may be used as the lithium hydroxide, or a mixture thereof may be used. When lithium hydroxide monohydrate is used, it is preferable to pre-heat the lithium hydroxide monohydrate to remove crystal water in order to improve reaction efficiency. The heat treatment may be carried out in a vibrating vessel used for lithium sulfide synthesis, or in a separate apparatus.

[0023] This manufacturing method includes placing a powder containing lithium into a container and, while the container is sealed, vibrating the container from the outside to move the powder while reacting the powder with a gas containing sulfur. In other words, this manufacturing method includes carrying out the above-described reaction between the powder and gas in a sealed container while vibrating the container from the outside to move the powder inside the container. Figure 1 is a flowchart illustrating this manufacturing method. The manufacturing method illustrated in Figure 1 includes step S11, which involves placing a powder containing lithium into a container, and step S12, which includes (i) vibrating the container from the outside while the container is sealed, and (ii) reacting the powder with a gas containing sulfur. In other words, in step S12, the powder is moved by vibrating the container from the outside while the container is sealed, and the powder is reacted with a gas containing sulfur.

[0024] As illustrated earlier, in the reaction between a lithium-containing powder and a sulfur-containing gas, water (water vapor) may be produced as a byproduct. If this moisture condenses within the reaction vessel, the powder is more likely to adhere to the inside of the vessel due to the condensed moisture, increasing maintenance costs. In contrast, this manufacturing method vibrates the vessel itself from the outside during the reaction, so the parts to which powder may adhere are vibrated, suppressing powder adhesion. This reduces maintenance costs. Furthermore, since the powder inside is moved by the vibration of the vessel, there is no need to fluidize the powder with gas, and excessive gas flow is not required. This improves the gas utilization efficiency of this manufacturing method. In addition, this manufacturing method does not require components that are prone to causing gas leaks, such as rotating mechanisms or the rotating shafts of stirring blades, so the vessel can be sealed. This makes it less likely for the gas used in the reaction to leak, resulting in superior gas utilization efficiency. Furthermore, this manufacturing method can provide a force that allows the powder to flow more efficiently in the vertical direction, thus enabling a relatively high filling rate of the powder in the container and resulting in superior manufacturing efficiency for lithium sulfide. In this manufacturing method, vibrating the container from the outside means, for example, vibrating a component such as a vibrator that is installed outside the container, either directly or indirectly in contact with the container. Furthermore, in this manufacturing method, a sealed container means that there are no parts from which gas can leak, other than the intentionally created openings such as the inlet for the lithium element powder, the gas inlet for introducing the sulfur element gas, the gas outlet for discharging the gas discharged after the reaction, and the outlet for the lithium sulfide powder synthesized after the reaction. In addition, the container in this manufacturing method does not have anything like the rotating shaft of a stirring blade. In this manufacturing method, suppression of powder adhesion to the container means both suppression of the adhesion of lithium-containing powder to the container and suppression of the adhesion of lithium sulfide powder obtained by the reaction.

[0025] Figure 2 is a schematic diagram illustrating this manufacturing method. Figure 2(a) is a schematic cross-sectional view of the side of the container during the reaction, and Figure 2(b) is a schematic cross-sectional view of the front of the same container as in Figure 2(a). However, for convenience, some components are shown only in (a) or (b), and are omitted in (b) or (a), and the same applies to Figure 4, which will be described later. Also, in Figure 2 and Figure 4, which will be described later, the arrows shown as solid black lines schematically represent the direction of gas flow. In Figure 2, the manufacturing apparatus 1 includes a container 10, and the container 10 contains a powder 5 containing lithium element inside.

[0026] The method for introducing the lithium-containing powder into the container is not particularly limited. Examples include providing the container with an openable / closable part, such as a raw material inlet, and introducing the powder through this part, or introducing the lithium-containing powder as a powder fluid along with an airflow. In the example shown in Figure 2, the container 10 is equipped with a powder raw material inlet 11. For example, the lithium-containing powder 5 can be introduced into the container 10 through the powder raw material inlet 11.

[0027] The amount of lithium-containing powder packed into the container is preferably 30% to 100% by volume relative to the container's volume, more preferably 50% to 90% by volume, and even more preferably 70% to 80% by volume. From the viewpoint of increasing the production efficiency of lithium sulfide by processing a relatively large amount per unit time, the above packing amount is preferably 30% or more by volume, more preferably 50% or more by volume, and even more preferably 70% or more by volume, relative to the container's volume. On the other hand, from the viewpoint of improving the homogeneity of the reaction and ensuring stable flow of the powder, the packing amount is preferably 100% or less by volume, more preferably 90% or less by volume, and even more preferably 80% or less by volume.

[0028] After placing the lithium-containing powder into a container, the container is sealed, and the powder is moved by vibrating the container from the outside while the powder reacts with a sulfur-containing gas. The method of sealing the container is not particularly limited, but examples include using a container that does not have a rotating shaft such as a stirring blade, or using a container made of a material that does not allow gas to pass through.

[0029] Furthermore, the method of vibrating the container is not particularly limited, but in the configuration of Figure 2, for example, the container 10 can be placed on a base 90 equipped with a vibrator 9, and the container 10 can be vibrated from the outside by vibrating the vibrator 9. At this time, the container is vibrated so that the powder inside the container moves (flows) due to the vibration. For example, in the configuration of Figure 2, when the container 10 is placed on a base 90 equipped with a vibrator 9, and the container 10 is vibrated from the outside by vibrating the vibrator 9, the powder inside the container can flow in a rotating manner when viewed in the direction of Figure 2(b), i.e., when viewed from the front. In the configuration of Figure 2, the vibrator 9 vibrates in the direction of the arrow shown in white in Figure 2, i.e., in the vertical direction of the figure. Examples of devices capable of such vibration include vibrating dryers, such as the VH and VHC type vibrating dryers manufactured by Chuo Kakoki Co., Ltd.

[0030] An example of the configuration of a vibratory drying apparatus is described below. A vibratory dryer has a configuration in which a roughly cylindrical drying container, for example, with a heating jacket attached to almost its entire surface, is positioned so that the axis of the cylinder is roughly parallel to the horizontal direction and is supported by springs. A vibration source (vibrator) is attached to the bottom of the drying container. When powdered or granular raw material is put into the drying container and the vibration source is operated in a circular motion in the circumferential direction, the powdered or granular layer is subjected to motion mainly in the circumferential vertical direction. The drying container can supply heat to the powdered or granular layer from the container wall by supplying steam, hot water, or temperature-controlled oil to the heating jacket.

[0031] In this manufacturing method, the amplitude of vibration is preferably 1 mm to 10 mm, more preferably 1.5 mm to 7 mm, and even more preferably 2 mm to 4 mm. Here, from the viewpoint of ensuring sufficient flow of the powder, the amplitude is preferably 1 mm or more, more preferably 1.5 mm or more, and even more preferably 2 mm or more. On the other hand, from the viewpoint of ease of manufacturing the apparatus, the amplitude is preferably 10 mm or less, more preferably 7 mm or less, and even more preferably 4 mm or less. Note that the amplitude of vibration refers to the width of the displacement of the container in the vertical direction (direction along the vibration).

[0032] Furthermore, the vibration frequency is preferably 10Hz to 100Hz, more preferably 15Hz to 80Hz, and even more preferably 20Hz to 60Hz. Here, from the viewpoint of ensuring sufficient flow of the powder and stabilizing the flow, the above frequencies are preferably 10Hz or higher, more preferably 15Hz or higher, and even more preferably 20Hz or higher. On the other hand, from the viewpoint of ease of manufacturing the apparatus, the vibration frequency is preferably 100Hz or lower, more preferably 80Hz or lower, and even more preferably 60Hz or lower. Note that the vibration frequency refers to the number of times the container is vibrated up and down (in the direction of vibration) per second.

[0033] In this sealed container, the powder is moved by vibrating the container from the outside, causing the powder to react with the gas. During the reaction, for example, as shown in Figure 2, a gas containing sulfur can be introduced into the container 10 from a nozzle 7 located inside the container 10. In Figure 2, the nozzle 7 is positioned to extend from the outside of the container to the inside, and has a gas inlet 12a on the outside and a gas outlet 12b on the inside. The nozzle 7 is fixed inside the container. However, the method of introducing the gas containing sulfur into the container is not limited to this. In addition, the container 10 may be equipped with a mechanism for discharging the gas inside the container 10, in addition to the mechanism for introducing the gas containing sulfur. For example, in the configuration of Figure 2, the container 10 is equipped with a gas outlet 13.

[0034] As mentioned above, any gas containing sulfur-containing components is acceptable. When a sulfur-containing gas is introduced into a container, the concentration of the sulfur-containing components may be adjusted by further adding an inert gas or the like. Examples of inert gases include nitrogen gas and argon gas. From the viewpoint of allowing sufficient reaction between the powder and the gas, the concentration of the sulfur-containing components in the sulfur-containing gas (the concentration of the sulfur-containing gas) is preferably 20% by volume or more, more preferably 50% by volume or more, and even more preferably 80% by volume or more.

[0035] When reacting powder with gas, it is preferable to heat the container to an appropriate temperature. Specifically, the temperature when reacting powder with gas is preferably 140°C to 240°C, more preferably 160°C to 230°C, and even more preferably 180°C to 220°C. Here, from the viewpoint of allowing the reaction to proceed sufficiently and preventing condensation of the generated moisture, the temperature is preferably 140°C or higher, more preferably 160°C or higher, and even more preferably 180°C or higher. On the other hand, from the viewpoint of the heat resistance of the components, the temperature is preferably 240°C or lower, more preferably 230°C or lower, and even more preferably 220°C or lower. The heating method is not particularly limited and may be a known method, such as the method using the heating jacket described above.

[0036] The reaction time between the powder and the gas is not particularly limited, as it varies depending on conditions such as the pressure inside the container, the concentration of the sulfur-containing gas, and the amount of powder filled. For example, 10 to 600 minutes is preferred, 30 to 300 minutes is more preferred, and 60 to 180 minutes is even more preferred. From the viewpoint of ensuring the reaction proceeds sufficiently, the reaction time between the powder and the gas is preferably 10 minutes or more, more preferably 30 minutes or more, and even more preferably 60 minutes or more. On the other hand, from the viewpoint of production cycle time, the reaction time is preferably 600 minutes or less, more preferably 300 minutes or less, and even more preferably 180 minutes or less.

[0037] The pressure inside the container when reacting the powder with the gas is not particularly limited, but atmospheric pressure or slight pressure is preferred, and slight pressure is more preferred. Specifically, the above pressure is preferably 0.100 MPa to 0.200 MPa, more preferably 0.105 MPa to 0.200 MPa, even more preferably 0.110 MPa to 0.160 MPa, and particularly preferably 0.120 MPa to 0.140 MPa. Here, by relatively increasing the pressure inside the container, the reaction between the powder and the gas proceeds more easily. Specifically, the pressure inside the container during the reaction is preferably 0.100 MPa or higher, more preferably 0.105 MPa or higher, even more preferably 0.110 MPa or higher, and particularly preferably 0.120 MPa or higher. On the other hand, from the viewpoint of ease of manufacture of the apparatus, the pressure inside the container during the reaction is preferably 0.200 MPa or lower, more preferably 0.160 MPa or lower, and even more preferably 0.140 MPa or lower.

[0038] The lithium-containing powder used in the reaction preferably has an average particle size of about 100 μm to 1500 μm, more preferably 200 μm to 1000 μm, even more preferably 250 μm to 800 μm, and particularly preferably 300 μm to 800 μm. Here, the average particle size is preferably 100 μm or more, more preferably 200 μm or more, even more preferably 250 μm or more, and particularly preferably 300 μm or more. When the average particle size is above the lower limit of the above, the powder flows more stably when the container is vibrated. This makes it easier for the powder and gas to react more homogeneously. In addition, since stagnation of flow within the container is suppressed, moisture is less likely to aggregate inside the container, and the adhesion of powder to the inside of the container can be suppressed. Furthermore, because the average particle size is relatively large, the powder is less likely to scatter, and the adhesion of powder to the inside of the container is suppressed. On the other hand, from the viewpoint of increasing the efficiency of the reaction, an average particle size of 1500 μm or less is more preferable, 1000 μm or less is even more preferable, and 800 μm or less is particularly preferable. Here, the average particle size of the lithium-containing powder refers to the median diameter (D50) obtained from the volume-based particle size distribution chart, which is measured using a Microtrac MT3300EXII laser diffraction particle size distribution analyzer.

[0039] Furthermore, the D90 of the lithium-containing powder is preferably 300 μm to 3000 μm, more preferably 500 μm to 2500 μm, and even more preferably 800 μm to 2000 μm. Here, the D90 is preferably 300 μm or more, more preferably 500 μm or more, and even more preferably 800 μm or more. When the D90 is above the lower limit, the powder flows more stably when the container is vibrated. This makes it easier for the powder and gas to react more homogeneously. Also, because stagnation of flow within the container is suppressed, moisture is less likely to aggregate within the container, and the adhesion of powder to the inside of the container can be suppressed. Moreover, when the D90 is above the lower limit, the powder is less likely to scatter, and the adhesion of powder to the inside of the container is suppressed. On the other hand, in order to prevent unreacted particles from remaining, the D90 is preferably 3000 μm or less, more preferably 2500 μm or less, and even more preferably 2000 μm or less. Here, D90 refers to the value of D90 obtained from the volume-based particle size distribution chart, which is acquired by measuring the particle size distribution using a Microtrac MT3300EXII laser diffraction particle size distribution analyzer.

[0040] The angle of repose of a lithium-containing powder is preferably 50° or less, more preferably 45° or less, and even more preferably 40° or less. Generally, the larger the average particle size of the powder, the smaller the angle of repose tends to be. That is, when the angle of repose is below the above value, the powder flows more stably when the container is vibrated. This makes it easier for the powder and gas to react more homogeneously. In addition, because stagnation of flow within the container is suppressed, moisture is less likely to aggregate within the container, and the adhesion of powder to the inside of the container can be suppressed. Furthermore, because the average particle size is relatively large, the powder is less likely to scatter, and the adhesion of powder to the inside of the container is suppressed. Here, the angle of repose of the powder refers to the value measured according to, for example, JIS R 9301-2-2:1999.

[0041] This manufacturing method may further include placing a media inside the container. Examples of media include particles other than the lithium element powder, and at least one of alumina particles and zirconia particles is preferred from the viewpoint of being less reactive with sulfur element gases and lithium element powders. Placing a media inside the container makes it easier for the powder to flow stably when the container is vibrated. This makes it easier for the powder and gas to react more homogeneously. In addition, since stagnation of flow inside the container is suppressed, moisture is less likely to aggregate inside the container, and the adhesion of powder to the inside of the container can be suppressed. The timing of placing the media inside the container is not particularly limited, and may be, for example, before reacting the powder and gas.

[0042] Figure 3 is a flowchart illustrating the present manufacturing method in a case where particles other than the lithium element powder (media) are placed in the container. In this case, the manufacturing method includes, for example, step S21 of placing the lithium element powder in the container, step S22 of placing particles other than the lithium element powder in the container, and step S23 of (i) vibrating the container from the outside while the container is sealed and (ii) reacting the powder with a gas containing sulfur element. Steps S21 and S22 may be performed in this order, or step S21 may be performed after step S22. Steps S21 and S22 may also be performed in parallel or simultaneously.

[0043] When introducing a gas containing sulfur elements into a container from a nozzle placed inside the container, it is preferable that the ejection position L4 of the sulfur-containing gas at the nozzle is within 50% of the gas phase height H1 and within 50% of the powder depth H2, relative to the surface L2 of the powder. The statement that the gas ejection position L4 is within 50% of the gas phase height H1, relative to the surface L2 of the powder, means the following: That is, when the gas ejection position L4 at the nozzle 7 is located in the gas phase and is not embedded in the layer of powder 5 as shown in Figure 2, the distance from the surface L2 of the powder 5 to the gas ejection position L4 is within 50% of the gas phase height H1. Here, the surface L2 of the powder refers to the height of the powder surface when the powder inside the container is leveled while the container is not being vibrated. The gas phase height H1 refers to the distance from the surface of the powder to the top surface inside the container, and in Figure 2 and Figure 4 described later, it refers to the distance H1 from L2 to L1.

[0044] Figure 4 is a schematic illustration of this manufacturing method, showing an example where only the position of the nozzle 7 is changed from the configuration in Figure 2. In Figures 2 and 4, common components and configurations are represented using common reference numerals. Figure 4(a) is a schematic cross-sectional view of the side of the container during the reaction, and Figure 4(b) is a schematic cross-sectional view of the front of the same container as in Figure 4(a). The statement that the gas ejection position L4 is within 50% of the powder depth H2, relative to the powder surface L2, means that when the gas ejection position L4 at the nozzle 7 is in contact with or embedded in the layer of powder 5, as shown in Figure 4, the distance from the surface L2 of the powder 5 to the gas ejection position L4 is within 50% of the powder depth H2. Here, the powder depth refers to the distance from the powder surface L2 to the bottom surface inside the container, and in Figures 2 and 4, it refers to the distance H2 from L2 to L3.

[0045] The gas injection point is preferably within 50% of the gas phase height, more preferably within 40%, and even more preferably within 30%. This facilitates efficient removal of moisture from the container after the reaction. Furthermore, the gas ejection point is preferably within 50% of the powder's depth, more preferably within 40%, and even more preferably within 30%. This prevents moisture generated during the reaction from causing a reverse reaction in the container, which would inhibit the formation of lithium sulfide. It also prevents stagnation of the gas flow and suppresses the aggregation of moisture in the container.

[0046] Furthermore, when introducing a gas containing sulfur elements into the container from a nozzle placed inside the container, the ejection position of the sulfur-containing gas from the nozzle is preferably within ±100 mm in height relative to the surface of the powder, more preferably within ±80 mm, and even more preferably within ±60 mm. This makes it easier to efficiently discharge moisture from the container after the reaction. It also prevents moisture generated during the reaction from causing a reverse reaction in the container and inhibiting the formation of lithium sulfide. In addition, it prevents stagnation of the gas flow and prevents moisture from accumulating in the container. Here, the positive direction of height relative to the surface of the powder refers to the direction in which the powder moves from the surface of the powder toward the gas phase side (i.e., the upper side of the container) in the height direction of the powder layer. On the other hand, the negative direction refers to the direction in which the powder moves from the surface of the powder toward the side where the powder layer is located (i.e., the bottom side of the container) in the height direction of the powder layer. For example, with the surface L2 of the powder as the reference, the upward direction in the plane of Figures 2 and 4 is the positive direction of height, and the downward direction in the plane of Figures 2 and 4 is the negative direction of height.

[0047] Since the gas ejection position is preferably within 50% of the powder's depth, it is particularly preferable that the gas ejection position be within ±100 mm of the powder's surface when the powder's depth is 200 mm or more.

[0048] It is preferable to have multiple gas ejection points within the container. This makes it easier to supply the sulfur-containing gas evenly to a wider area within the container, and facilitates a homogeneous and efficient reaction between the powder and the gas. Figures 2 and 4 illustrate configurations in which the nozzle 7 is equipped with multiple gas ejection outlets 12b, and gas is ejected from multiple locations on the nozzle 7. In other words, in Figures 2 and 4, multiple gas ejection points are arranged within the container. Furthermore, it is preferable that the direction in which the gas is ejected from each ejection point is toward the surface of the powder (the surface of the powder layer).

[0049] Figure 5 is a flowchart illustrating the present manufacturing method in which a gas containing sulfur is introduced into a container from a nozzle placed inside the container, and the ejection position of the sulfur-containing gas at the nozzle is set to a predetermined position as described above. In this case, the present manufacturing method includes, for example, step S31, which sets the gas ejection position by putting a predetermined amount of lithium-containing powder into the container, and step S32, which includes (i) vibrating the container from the outside while the container is sealed, (ii) introducing a gas containing sulfur into the container from a nozzle placed inside the container, and (iii) reacting the powder with the sulfur-containing gas.

[0050] It is preferable that the gas flow within the container is free from stagnation and blockage. By suppressing stagnation and blockage in the gas flow, the aggregation of moisture within the container is less likely to occur, and the adhesion of powder to the inside of the container can be suppressed. One way to suppress stagnation and blockage is to ensure that the powder flows more stably during the reaction, as described above.

[0051] By reacting a powder containing lithium with a gas containing sulfur in this way, lithium sulfide can be obtained as a solid.

[0052] In this manufacturing method, it is preferable to remove moisture from the container during or after the reaction between the powder and the gas. Removing moisture from the container helps to suppress the adhesion of powder to the inside of the container. Methods for removing moisture from inside the container include, for example, temporarily lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction between the powder and the gas, or lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction after the reaction between the powder and the gas. The above method is called a temporary depressurization step. By lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction through the temporary depressurization step, the gas containing moisture can be discharged from the gas discharge mechanism inside the container. The gas can be discharged, for example, through a gas outlet 13 provided in the container 10. At this time, the gas containing sulfur elements remaining after the reaction may also be discharged. In this manufacturing method, a sealable container is used, making it easy to adjust the pressure inside the container. Furthermore, even when removing moisture by temporarily lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction, a relatively large exhaust volume can be used to supply gas containing sulfur elements into the container in parallel.

[0053] Specifically, the pressure used to lower the pressure inside the container to a level lower than the pressure inside the container during the reaction is preferably 0.010 MPa to 0.100 MPa, more preferably 0.010 MPa or more and less than 0.100 MPa, even more preferably 0.020 MPa to 0.080 MPa, and particularly preferably 0.030 MPa to 0.060 MPa. That is, it is preferable to temporarily lower the pressure inside the container to 0.100 MPa or less during the reaction between the powder and the gas, or after the reaction between the powder and the gas, more preferably less than 0.100 MPa, even more preferably 0.080 MPa or less, and particularly preferably 0.060 MPa or less. On the other hand, the pressure inside the container after the reaction is preferably 0.010 MPa or higher, more preferably 0.020 MPa or higher, and even more preferably 0.030 MPa or higher, from the viewpoint of manufacturing cycle time.

[0054] Furthermore, the difference between the pressure during the reaction between the powder and the gas and the pressure after the reaction is preferably 0.005 MPa to 0.100 MPa, more preferably 0.010 MPa to 0.080 MPa, and even more preferably 0.020 MPa to 0.060 MPa. Here, from the viewpoint of effectively discharging gas containing moisture, the above pressure difference is preferably 0.005 MPa or more, more preferably 0.010 MPa or more, and even more preferably 0.020 MPa or more. On the other hand, from the viewpoint of manufacturing cycle time, the difference between the pressure during the reaction and the pressure after the reaction is preferably 0.100 MPa or less, more preferably 0.080 MPa or less, and even more preferably 0.060 MPa or less.

[0055] When removing moisture from the container, it is preferable to suppress stagnation and blockage of the gas flow, just as during the reaction. This makes it less likely for moisture to aggregate inside the container and suppresses the adhesion of powder to the inside of the container.

[0056] Figure 6 is a flowchart illustrating an example of this manufacturing method, which includes removing moisture from the container. Figure 6(a) is a flowchart illustrating a method that includes temporarily lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction, and Figure 6(b) is a flowchart illustrating a method that includes lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction after the reaction. Specifically, the manufacturing method illustrated in Figure 6(a) includes the steps of: (i) placing a powder containing lithium into a container S411; (ii) vibrating the container from the outside while the container is sealed; (ii) reacting the powder with a gas containing sulfur; and (iii) temporarily lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction. Furthermore, the manufacturing method illustrated in Figure 6(b) includes the steps of: (i) placing a powder containing lithium into a container (S421); (ii) vibrating the container from the outside while the container is sealed and (ii) reacting the powder with a gas containing sulfur (S422); and (ii) lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction (S423). In this manufacturing method, a combination of Figures 6(a) and (b) may also be used. For example, in the manufacturing method of Figure 6(a), a step similar to step S423 of Figure 6(b) may be added after step S412.

[0057] The sulfur-containing gas used in the reaction may be recovered or circulated within the apparatus for reuse. This further improves the efficiency of using the sulfur-containing gas.

[0058] After the reaction between the powder and the gas, it is preferable to remove moisture from the container and then recover the lithium sulfide from the container. Recovery can be carried out by known methods, but it is preferable to perform the recovery work in an environment where the lithium sulfide is not exposed to the atmosphere, for example, in an inert gas atmosphere. The container 10 in Figures 2 and 4 is equipped with a powder material discharge port 14. For example, the lithium sulfide after the reaction can be recovered through such a powder material discharge port. The recovered lithium sulfide can be identified, for example, by X-ray diffraction measurements.

[0059] This manufacturing method may be carried out in a batch or continuous manner. Even when carried out in a continuous manner, by appropriately dividing the process into sections, it is possible to adjust the pressure while sealing the container, such as by lowering the pressure to remove moisture from the container after the reaction. For example, the VH type vibrating dryer manufactured by Chuo Kakoki Co., Ltd. can be used for batch reactions, while the VHC type can be used for continuous reactions.

[0060] The lithium sulfide obtained by this manufacturing method is suitably used as a raw material for solid electrolytes used in all-solid-state lithium-ion secondary batteries, a raw material for positive electrode active materials, a raw material for negative electrode active materials, and an intermediate raw material for chemicals.

[0061] As explained above, the following matters are disclosed in this specification: 1. Putting a powder containing lithium into a container, A method for producing lithium sulfide, comprising reacting the powder with a gas containing a sulfur element while the container is sealed and the container is vibrated from the outside to move the powder. 2. A method for producing lithium sulfide according to claim 1, comprising temporarily lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction, or lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction after the reaction. 3. The method for producing lithium sulfide according to 1 or 2, wherein the pressure inside the container during the reaction is 0.100 MPa or higher. 4. The method for producing lithium sulfide according to paragraph 3, wherein the pressure at which the pressure inside the container is reduced to a level lower than the pressure inside the container during the reaction is less than 0.100 MPa. 5. A method for producing lithium sulfide according to any one of 1 to 4, comprising introducing a gas containing the sulfur element into the container from a nozzle placed in the container, wherein the ejection position of the gas containing the sulfur element at the nozzle is within 50% of the height of the gas phase and within 50% of the depth of the powder, with respect to the surface of the powder. 6. A method for producing lithium sulfide according to any one of items 1 to 5, wherein the average particle size of the powder is 200 μm or more. 7. A method for producing lithium sulfide according to any one of 1 to 6, further comprising placing particles other than a powder containing the element lithium into the container. 8. A method for producing lithium sulfide according to any one of 1 to 7, wherein the amplitude of the vibration is 1 mm to 10 mm. [Examples]

[0062] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Examples 1 through 8 are all examples of actual cases.

[0063] (Example 1) Lithium hydroxide powder (manufactured by Tokyo Chemical Industry Co., Ltd.) was placed in a vibrating dryer (product name VH-10, manufactured by Chuo Kakoki Co., Ltd.). The average particle size (D50) of the lithium hydroxide powder was 400 μm, and the D90 particle size was 1000 μm. The powder was added until it reached a height of 50% of the height from the bottom to the top of the reaction vessel. After adding the powder, the vibrating dryer was started with an amplitude of 3 mm and a frequency of 24 Hz. It was confirmed that the powder rotated and flowed stably under these vibration conditions. Next, a vacuum pump was used to remove the atmosphere from inside the reaction vessel through the gas outlet, and the pressure inside the reaction vessel was reduced to 0.005 MPa. Then, nitrogen was introduced through the gas inlet to create a nitrogen atmosphere inside the reaction vessel. The flow rate of nitrogen introduced through the gas inlet was set to 1 SLM (Standard Litter Min), and the pressure inside the reaction vessel was adjusted to an internal pressure of 0.105 MPa. While maintaining the gas flow rate and pressure, the temperature of the jacket surrounding the reaction vessel was raised to 200°C. After reaching the temperature, the gas introduced through the gas inlet was switched to 0.5 SLM of nitrogen and 0.5 SLM of hydrogen sulfide, and the reaction between lithium hydroxide and hydrogen sulfide was started. The pressure inside the reaction vessel was adjusted to 0.105 MPa during the reaction. The gas outlet was positioned relative to the powder surface, i.e., at 25% of the gas phase height from the powder surface to the ceiling of the vessel. The gas was flowed for 4 hours. After that, the introduced gas was switched to 1 SLM of nitrogen and held for 1 hour, then heating was stopped, the temperature was returned to room temperature, vibration was stopped, and the sample was collected. The reaction rate of the recovered lithium sulfide was found to be 94% by powder X-ray diffraction (XRD) measurement, as described later. Furthermore, observation of its adhesion to the container wall after recovery revealed no significant buildup, allowing the next batch test to begin.

[0064] (Example 2) In Example 1, the reaction with the gas was carried out continuously for 4 hours. However, in this case, the same method was used to synthesize lithium sulfide, except that the gas was first introduced and reacted for 2 hours, then the introduction of the gas was temporarily stopped, the pressure in the reaction vessel was reduced to 0.020 MPa (temporary depressurization step), the gas was then introduced again, the pressure in the reaction vessel was reduced to 0.105 MPa, and the reaction with the gas was carried out for another 2 hours. The reaction rate of the recovered lithium sulfide was found to be 99%. Furthermore, observation of its adhesion to the container wall after recovery revealed no significant buildup, allowing us to proceed with the next batch test.

[0065] (Example 3) Lithium sulfide was synthesized using the same method as in (Example 1), except that the pressure inside the reaction vessel during the reaction with the gas was changed from 0.105 MPa to 0.120 MPa. The reaction rate of the recovered lithium sulfide was found to be 96%. Furthermore, observation of its adhesion to the container wall after recovery revealed no significant buildup, allowing us to proceed with the next batch test.

[0066] (Example 4) Lithium sulfide was synthesized using the same method as in (Example 1), except that the lithium hydroxide used in (Example 1) was crushed in a mortar and classified to obtain an average particle size of 200 μm. Compared to (Example 1), there was some disturbance in the rotational motion of the powder during vibration, but lithium sulfide synthesis was still possible. The reaction rate of the recovered lithium sulfide was found to be 90%. Furthermore, observation of its adhesion to the container wall after recovery revealed no significant buildup, allowing us to proceed with the next batch test.

[0067] (Example 5) In Example 4, lithium hydroxide with an average particle size of 200 μm was mixed with the same weight of alumina particles as a media. The alumina particles used had a diameter of 3 mm. Lithium sulfide was synthesized in the same manner as in Example 1, except that this mixture was placed in a vibration dryer as a powder raw material. By incorporating alumina particles as a media, the rotational motion of the powder, which was turbulent during vibration in (Example 4), became a stable rotational flow. After synthesis, the mixture of lithium sulfide and alumina particles was recovered, and the alumina particles were removed by sieving to recover only lithium sulfide. The reaction rate of the recovered lithium sulfide was found to be 97%. Furthermore, observation of its adhesion to the container wall after recovery revealed no significant buildup, allowing us to proceed with the next batch test.

[0068] (Example 6) In Example 1, the gas nozzle was positioned at 25% of the gas phase height from the surface of the powder to the top of the container. In this case, lithium sulfide was synthesized using the same method as in Example 1, except that the nozzle was positioned at 50% of the gas phase height. The reaction rate of the recovered lithium sulfide was found to be 90%. Furthermore, observation of its adhesion to the container wall after recovery revealed no significant buildup, allowing us to proceed with the next batch test.

[0069] (Example 7) In Example 1, the gas nozzle was positioned at 25% of the gas phase height from the surface of the powder to the top of the container. However, in this case, lithium sulfide was synthesized using the same method as in Example 1, except that the gas nozzle was embedded in the powder and positioned at 25% of the powder layer thickness from the surface of the powder, i.e., 25% of the powder depth. The reaction rate of the recovered lithium sulfide was found to be 95%. Furthermore, observation of its adhesion to the container wall after recovery revealed no significant buildup, allowing us to proceed with the next batch test.

[0070] (Example 8) In Example 1, the gas nozzle was positioned at 25% of the gas phase height from the surface of the powder to the top of the container. However, in this case, lithium sulfide was synthesized using the same method as in Example 1, except that the gas nozzle was embedded in the powder and positioned at 50% of the powder layer thickness from the surface of the powder, i.e., 50% of the powder depth. The reaction rate of the recovered lithium sulfide was found to be 91%. Furthermore, observation of its adhesion to the container wall after recovery revealed no significant buildup, allowing us to proceed with the next batch test.

[0071] Based on these results, lithium sulfide could be synthesized with a reaction rate of over 90% by using appropriate vibration conditions. Furthermore, after synthesis, there was no adhesion of raw materials to the reaction vessel walls, allowing the vessel to be used directly for the next batch, thus improving manufacturing efficiency.

[0072] In Example 2, the reaction rate was higher compared to Example 1. This is thought to be because the amount of water generated during the synthesis of lithium sulfide was reduced by reducing the pressure during the synthesis process. The generated water is thought to cause a decrease in the reaction rate because it undergoes the reverse reaction, returning lithium sulfide to lithium hydroxide. Therefore, it is thought that the reaction rate was increased by removing the water generated by reducing the pressure during the reaction. Example 3 demonstrates that increasing the pressure during the reaction can increase the reaction rate to lithium sulfide. In Example 4, when using fine-grained raw materials, it was observed that the rotational flow of the powder during vibration operation became unstable. As a result, unevenness occurred in the powder's reaction with the gas, which is thought to have slightly reduced the reaction efficiency with lithium sulfide. In Example 5, a media was added to stabilize the flow during the synthesis. It is thought that the addition of the media stabilized the rotational flow, which was unstable in Example 4, and thus allowed for an increase in the reaction rate. In (Example 6), the position of the gas nozzle is changed. This demonstrates that the reaction efficiency may decrease when the gas nozzle is farther from the powder surface. Examples (7) and (8) are examples in which the gas nozzle is embedded in the powder.

[0073] (Calculation of response rate) The reaction rate to lithium sulfide was determined by XRD measurement (instrument name: SmartLab, Rigaku Corporation). Specifically, first, separately from the analysis of the sample to be measured, a sample was measured in which lithium hydroxide was mixed with lithium sulfide to a known mass percentage. Then, by comparing the peak intensity of lithium hydroxide in the sample to be measured with the peak intensity of lithium hydroxide in the mixture of lithium sulfide and lithium hydroxide to a known mass percentage, the mass percentage of lithium hydroxide contained in the sample to be measured was calculated. The reaction rate with lithium sulfide was calculated as (100 - mass of lithium hydroxide)%.

[0074] [Table 1]

[0075] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2022-064100, filed on April 7, 2022, the contents of which are incorporated herein by reference. [Explanation of Symbols]

[0076] 1 Manufacturing equipment 10 containers 11. Powdered raw material inlet 12a Gas inlet 12b Gas nozzle 13 Gas outlet 14 Powder raw material outlet 5. Powder containing lithium element 7 nozzles 9. Oscillator 90 base

Claims

1. Putting a powder containing lithium into a container, The process involves reacting the powder with a gas containing sulfur elements while the container is sealed and the container is vibrated from the outside to move the powder. The pressure inside the container during the reaction is 0.100 MPa or higher. A method for producing lithium sulfide, wherein the pressure at which the pressure inside the container is reduced to less than the pressure inside the container during the reaction is less than 0.100 MPa.

2. Putting a powder containing lithium into a container, With the container sealed, the container is vibrated from the outside to move the powder while the powder reacts with a gas containing sulfur elements. A method for producing lithium sulfide, comprising introducing a gas containing the sulfur element into the container from a nozzle placed in the container, wherein the ejection position of the gas containing the sulfur element at the nozzle is within 50% of the height of the gas phase and within 50% of the depth of the powder, with respect to the surface of the powder.

3. A method for producing lithium sulfide according to claim 1 or 2, comprising temporarily lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction, or lowering the pressure inside the container to a level lower than the pressure inside the container during the reaction, after the reaction.

4. The method for producing lithium sulfide according to claim 2, wherein the pressure inside the container during the reaction is 0.100 MPa or more.

5. The method for producing lithium sulfide according to claim 4, wherein the pressure at which the pressure inside the container is reduced to a level lower than the pressure inside the container during the reaction is less than 0.100 MPa.

6. A method for producing lithium sulfide according to claim 1 or 2, wherein the average particle size of the powder is 200 μm or more.

7. A method for producing lithium sulfide according to claim 1 or 2, further comprising placing particles other than a powder containing the element lithium into the container.

8. A method for producing lithium sulfide according to claim 1 or 2, wherein the amplitude of the vibration is 1 mm to 10 mm.

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