Preparation method of lithium sulfide

Abstract

The present invention relates to a method for preparing lithium sulfide, according to the present invention, when preparing lithium sulfide by a reaction between a lithium raw material and hydrogen sulfide, the reaction is carried out under relatively mild conditions compared to the prior art, so that frequent maintenance or replacement due to corrosion and failure of a reactor and various pipes is not required, thereby improving the economical efficiency of the process. Further, by reusing the unreacted hydrogen sulfide from which moisture has been removed and the solvent, process costs can be reduced, and economical efficiency can be ensured during mass production. Furthermore, moisture and water vapor generated in the lithium sulfide generation reaction are effectively removed, thereby preventing a reverse reaction for generating lithium hydroxide, promoting a positive reaction, and producing high-quality lithium sulfide with high purity and high yield. In addition, the particle size can be adjusted in units, and a separate pulverizing space or pulverizing table is not required, so that convenience and mass productivity are excellent.

Description

TECHNICAL FIELD

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

[0002] Due to the high energy density and long life characteristics of lithium secondary batteries, they are widely used in electronic devices such as home appliances, notebook computers, smart phones, and recently, in electric vehicles (EV) or hybrid electric vehicles (HEV), and the range of applications thereof has greatly increased.

[0003] The lithium ion secondary battery, which is currently mainly used, has been mass-produced since 1991, and is widely used as a main power source for mobile phones, notebook computers, PCs, etc. due to its high energy density and output voltage, however, the organic electrolyte equipped to ensure the smooth movement of lithium ions has a risk of explosion in an overheated and overcharged state, and is easily ignited in the presence of a fire source, in addition, when a side reaction occurs inside the battery, the generation of gas can cause a decrease in battery performance and stability.

[0004] Therefore, in order to overcome the disadvantages of lithium ion secondary batteries, research and development on lithium all solid secondary batteries are actively being conducted. The lithium all solid secondary battery, by using a solid-state electrolyte instead of a volatile electrolyte, not only can reduce the risk of explosion, but also can use lithium metal (Li Metal) or lithium alloy (Li Alloy) as a negative electrode material, thus having the advantage of significantly improving the energy density of the battery.

[0005] Among the solid-state electrolyte candidate materials that can be mounted on all solid-state batteries today, sulfide-based solid-state electrolytes are known to be considered suitable for the preparation of high-capacity large secondary batteries due to their high ductility and high ionic conductivity, and in the preparation process of such sulfide-based solid-state electrolytes, lithium sulfide (Li2S) is considered a key material. Although there are various methods known for the synthesis of lithium sulfide, among them, the most commonly used method is a method of reacting metal lithium such as lithium hydroxide (LiOH) or lithium carbonate (Li2CO3) with hydrogen sulfide (H2S).

[0006] On the other hand, hydrogen sulfide gas is a highly corrosive gas, and if it is reacted with a lithium compound in a reactor made of a general metal material according to the existing method, the reactor and various pipes and other equipment can be corroded, requiring frequent maintenance and replacement, thus there is a problem of reducing the economic efficiency in mass-producing lithium sulfide.

[0007] Further, when a lithium compound such as lithium hydroxide is reacted with hydrogen sulfide, water vapor is inevitably generated, and the water vapor generated at this time hinders the contact of the lithium compound with the hydrogen sulfide, thereby lowering the yield of lithium sulfide. Furthermore, the water vapor accelerates the reverse reaction of lithium hydroxide, thereby lowering the purity of the produced lithium sulfide. In addition, the moisture causes aggregation between the produced lithium sulfide particles, resulting in a decrease in quality.

[0008] Accordingly, the present inventors have researched a method for economically producing lithium sulfide having a size of several micrometers to several tens of micrometers by reacting a lithium compound with hydrogen sulfide under relatively mild conditions, removing moisture by blowing a gas to promote the forward reaction, and reusing the solvent and unreacted hydrogen sulfide after removing the moisture therefrom to produce lithium sulfide, etc., thereby ensuring a process with high purity and high yield. SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION The present invention has been made to solve the above problems, and aims to provide a lithium sulfide production method that is excellent in convenience and mass productivity by designing reaction conditions and apparatuses suitable for producing lithium sulfide in a large amount with high purity and high yield by using the reaction between a lithium raw material and hydrogen sulfide (H2S), and by removing moisture to promote the forward reaction and reusing unreacted hydrogen sulfide and a solvent to ensure economy, without a separate pulverization space or a pulverization step, and thus controlling the particle diameter.

[0010] MEANS FOR SOLVING THE PROBLEMS In the present specification, a lithium sulfide production method is provided, the method including: step a) of supplying a lithium raw material to a reaction chamber provided with a solvent; step b) of supplying hydrogen sulfide (H2S) to the reaction chamber to perform a lithium sulfide (Li2S) generation reaction; and step c) of transferring a product obtained in the step b) to a lithium sulfide recovery section to obtain lithium sulfide, and pulverizing the product using an in-line mixer in a lithium sulfide recovery line.

[0011] As an example, after the step a) and before the step b), a step of maintaining the temperature in the reaction chamber in the range of 80°C to 200°C while heating for 1 hour to 5 hours, and removing the moisture in the reaction chamber can be further included.

[0012] As an example, the solvent of step a) above can be an aprotic solvent, and can be one selected from the group consisting of cycloheptane, cyclooctane, methylcyclohexane, dimethylcyclohexane, trimethylcyclohexane, ethylcyclohexane, diethylcyclohexane, propylcyclohexane, isopropylcyclohexane, dipropylcyclohexane, butylcyclohexane, tert-butylcyclohexane, methylcycloheptane, and methylcyclooctane; octane, isooctane, nonane, isononane, decane, isodecane, undecane, dodecane, hexadecane, and octadecane; toluene, o-xylene, m-xylene, p-xylene, 1,3,5-trimethylbenzene (mesitylene), 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene, ethylbenzene, propylbenzene, isopropylbenzene, butylbenzene, isobutylbenzene, tert-butylbenzene, and cyclohexylbenzene; naphthalene, decalin (decahydronaphthalene), 1-methylnaphthalene, 2-methylnaphthalene, 1-ethylnaphthalene, 2-ethylnaphthalene; tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 1,4-dioxane, dibutyl ether, isopentyl ether, dihexyl ether, 1,2-dimethoxyethane; and combinations thereof.

[0013] As an example, the volume of the solvent of step a) above can be 50% to 80% of the total volume of the reaction chamber.

[0014] As an example, the lithium raw material of step a) above can be one selected from the group consisting of lithium hydroxide (LiOH), lithium hydroxide monohydrate (LiOH·H2O), lithium carbonate (Li2CO3), and combinations thereof.

[0015] As an example, the lithium sulfide generation reaction of step b) above is shown in Equation 1 below, and the temperature in the reaction chamber can be 120°C to 300°C, the pressure can be 0.01 bar to 5.0 bar, and the reaction time can be 10 hours to 60 hours.

[0016] Equation 1: 2LiOH + H2S → Li2S + 2H2O As an example, in step b) above, the solvent supplemented during the reaction can be one selected from the group consisting of a newly supplied solvent, a solvent recovered during the process, and combinations thereof.

[0017] For example, in step c) above, the in-line mixer can be operated at a stirring speed of 300 rpm to 2,000 rpm to control the average particle size (D50) of the final lithium sulfide to be within a predetermined range.

[0018] As an example, in step c) above, a gas stream can be generated in the lithium sulfide recovery section, the solvent and impurities are removed, and the lithium sulfide is dried.

[0019] As an example, the proportion of the lithium raw material consumed through the reactions of steps a) to c) above can be 97.99% or more.

[0020] As an example, the present specification provides a lithium sulfide, which is the lithium sulfide prepared according to the above-described method, and has an average particle size (D50) of 1 to 10 m 2 / g to 14 m 2 / g of a BET surface area.

[0021] As an example, the carbon content of the above-described lithium sulfide can be less than 0.5 wt%, and the purity can be 97.99% or more.

[0022] Further, the present specification provides a lithium all-solid-state secondary battery, which includes a positive electrode, a negative electrode opposite to the positive electrode, and a sulfide-based solid electrolyte interposed between the positive electrode and the negative electrode and made of the lithium sulfide.

[0023] As an example, the lithium all-solid-state secondary battery can be applied to at least one product selected from an electric vehicle (EV), a hybrid electric vehicle (HEV), an energy storage system (ESS), urban air mobility (UAM), a mobile device, a notebook computer, an electronic device, a tablet computer, a drone, a robot, and a home appliance.

[0024] Inventive Effects According to the present invention, when lithium sulfide is prepared through a reaction between a lithium raw material and hydrogen sulfide, the reaction is performed under relatively mild conditions compared to the prior art, and thus there is no need for frequent maintenance or replacement due to corrosion and malfunction of a reactor and various pipes, thereby improving the economic efficiency of the process. Further, since unreacted hydrogen sulfide and a solvent, from which moisture has been removed, are reused, the process cost is reduced, and the economic efficiency in mass production can be secured.

[0025] Further, moisture and water vapor generated in the lithium sulfide generation reaction are effectively removed, thereby preventing the reverse reaction of lithium hydroxide generation and promoting the forward reaction, and high-quality lithium sulfide can be prepared with high purity and high yield. Further, the particle size can be adjusted in units of , without a separate pulverization space or a pulverization step, and thus convenience and mass productivity are excellent. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Schematically shows each step of a lithium sulfide preparation method according to an embodiment of the present invention.

[0027] FIGS. 2 to 3 show the results of X-ray diffraction (XRD) analysis and particle size analysis performed to confirm the presence of lithium sulfide prepared according to an embodiment of the present invention and a comparative example.

[0028] Figure 4FIG. 1 is a schematic view showing an example of a lithium sulfide production apparatus to which a lithium sulfide production method according to an embodiment of the present application can be applied.

[0029] Reference Signs Description 10: lithium raw material supply line; 20: hydrogen sulfide supply line; 30: exhaust line; 40: hydrogen sulfide re-supply line; 50: solvent re-supply line; 60: lithium sulfide recovery line; 70: inert gas supply line; WD: water (H2O) discharge line; 100: reaction chamber; 110: stirring member; 150: heating portion; 200: hydrogen sulfide supply portion; 300: condensing portion; 400: hydrogen sulfide re-supply portion; 500: solvent re-supply portion; 600: lithium sulfide recovery portion; 700: inert gas supply portion; 800: in-line mixer; F: filter member. DETAILED DESCRIPTION

[0030] Hereinafter, an embodiment of the present application will be described in detail with reference to the accompanying drawings. When adding reference numerals to components throughout the drawings, it should be noted that like reference numerals refer to the same or like components even though they are shown in different drawings. Also, detailed descriptions of related known structures or functions incorporated herein will be omitted when it is determined that the detailed descriptions can make the understanding of the embodiments of the present application more difficult.

[0031] Hereinafter, a lithium sulfide production method according to the present application, lithium sulfide produced by the method, and a lithium sulfide production apparatus will be described in more detail.

[0032] Process for the preparation of lithium sulfide The lithium sulfide production method according to an embodiment of the present application includes: a step a) of supplying a lithium raw material to a reaction chamber provided with a solvent; a step b) of supplying hydrogen sulfide (H2S) to the reaction chamber to perform a lithium sulfide (Li2S) production reaction; and a step c) of transferring a product obtained in the step b) to a lithium sulfide recovery portion to obtain lithium sulfide, and pulverizing the product using an in-line mixer in a lithium sulfide recovery line (see FIG. 1). Figure 1 ).

[0033] First, a lithium raw material is supplied to a reaction chamber provided with a solvent (step a).

[0034] The reaction chamber is a chamber having a predetermined reaction space in which a lithium sulfide production reaction is performed, and a lithium raw material and hydrogen sulfide react in the reaction space to synthesize lithium sulfide. The detailed structure of the reaction chamber will be described later.

[0035] The solvent provided in the reaction chamber is a solvent used in the wet reaction, and can be an aprotic solvent, specifically, can be one selected from the group consisting of cycloheptane, cyclooctane, methylcyclohexane, dimethylcyclohexane, trimethylcyclohexane, ethylcyclohexane, diethylcyclohexane, propylcyclohexane, isopropylcyclohexane, dipropylcyclohexane, butylcyclohexane, tert-butylcyclohexane, methylcycloheptane, and methylcyclooctane; octane, isooctane, nonane, isononane, decane, isodecane, undecane, dodecane, hexadecane, and octadecane; toluene, o-xylene, m-xylene, p-xylene, 1,3,5-trimethylbenzene (mesitylene), 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene, ethylbenzene, propylbenzene, isopropylbenzene, butylbenzene, isobutylbenzene, tert-butylbenzene, and cyclohexylbenzene; naphthalene, decalin (tetrahydronaphthalene), 1-methylnaphthalene, 2-methylnaphthalene, 1-ethylnaphthalene, 2-ethylnaphthalene; tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 1,4-dioxane, dibutyl ether, isopentyl ether, dihexyl ether, 1,2-dimethoxyethane; and combinations thereof.

[0036] In the above step, the solvent can have a volume of 50% to 80% relative to the total volume of the reaction chamber. When the volume of the above solvent is less than the above volume range, lithium sulfide particles synthesized during the lithium sulfide generation reaction can splash and adhere to the wall surface of the reaction space, or the particles can grow and become fixed. On the other hand, when the volume of the solvent exceeds the above volume range, the space occupied by inert gas or hydrogen sulfide gas (H2S) supplied to satisfy the pressure conditions required for the lithium sulfide generation reaction will decrease, thereby not only causing the control of the pressure conditions to become difficult, but also the above solvent can possibly flow back to other device configurations.

[0037] The lithium raw material of the present application is a reactant that reacts with hydrogen sulfide (H2S) supplied in the later-described step to generate lithium sulfide, and can be one selected from the group consisting of lithium hydroxide (LiOH), lithium hydroxide monohydrate (LiOH·H2O), lithium carbonate (Li2CO3), and combinations thereof. As an example, the above lithium raw material can be lithium hydroxide monohydrate (LiOH·H2O), in which case the raw material can be easily secured and is low in cost, and thus is more suitable for securing economy and mass productivity.

[0038] After the above step a, before the later-described step b, a step of removing moisture in the reaction chamber can be further included.

[0039] Specifically, the above step can prevent the conversion rate to lithium sulfide from decreasing due to the acceleration of the reverse reaction during the lithium sulfide (Li2S) generation reaction in the step b described later, by removing moisture inside the reaction chamber. As an example, the above step can be performed by maintaining the reaction space inside the reaction chamber at a temperature range of 80°C to 200°C, specifically, a temperature range of 90°C to 150°C, by the heating unit described later, and continuously heating for 1 hour to 5 hours.

[0040] In the above step, in order to selectively remove moisture inside the reaction chamber while suppressing the vaporization of the solvent to the maximum, stirring can be performed, as an example, the above stirring can be performed at a stirring speed of 300 rpm to 800 rpm. In addition, in the above step, inert gas can also be blown in order to smoothly remove moisture.

[0041] Next, hydrogen sulfide (H2S) is supplied to the reaction chamber to perform a lithium sulfide (Li2S) generation reaction (step b).

[0042] The lithium raw material supplied in the above step a performs a wet reaction with the hydrogen sulfide (H2S) gas supplied to the reaction chamber under solvent conditions in step b, thereby synthesizing lithium sulfide (Li2S), and when the lithium raw material is lithium hydroxide, the specific reaction formula can be as shown in the following formula 1.

[0043] Formula 1: 2LiOH + H2S → Li2S + 2H2O The lithium sulfide generation reaction according to an embodiment of the present application can be performed at a temperature range of 120°C to 300°C, specifically, a range of 120°C to 250°C, more specifically, a range of 120°C to 200°C, in the reaction chamber, and at a pressure range of 0.01 bar to 5.0 bar, specifically, a range of 1.5 bar to 3.0 bar, more specifically, a range of 2 bar to 2.5 bar. In addition, the above reaction can last for 10 hours to 60 hours, and stirring can be performed during the above reaction to promote the reaction.

[0044] In addition, according to an embodiment of the present application, the step b can include a process of re-supplying hydrogen sulfide to the reaction chamber after the inert gas is bubbled into the reaction chamber when the reaction reaches chemical equilibrium, and the process of bubbling the inert gas and re-supplying hydrogen sulfide of the step b can be repeated one or more times. Specifically, when hydrogen sulfide is supplied into the reaction chamber, the lithium sulfide generation reaction starts, and during the reaction, when the rates of the forward reaction and the reverse reaction are equal, a point of time at which chemical equilibrium is reached occurs. If the reaction is ended at this time, it can be difficult to obtain the desired purity of lithium sulfide, and thus the inert gas is bubbled according to the present application. The inert gas bubbling functions to discharge moisture remaining in the solvent and water vapor present in the reaction chamber to the outside of the reaction chamber, thereby breaking the chemical equilibrium and allowing the forward reaction to start again. At this time, if hydrogen sulfide is again supplied into the reaction chamber, the lithium sulfide generation reaction will proceed again. Thus, when the process of bubbling the inert gas and re-supplying hydrogen sulfide of the step b is repeated, the conversion rate of the lithium raw material to lithium sulfide can be maximized.

[0045] On the other hand, the inert gas can be supplied from one end or the bottom of the reaction chamber, and the bubbling of the inert gas can be continued for 1 to 5 hours, specifically 1 to 3 hours each time, but this can vary depending on the amount of the lithium raw material, the size of the reaction chamber, and the like. The inert gas according to an embodiment of the present application can be one selected from the group consisting of nitrogen (N2), argon (Ar), helium (He), and combinations thereof, and for example, can be nitrogen (N2). When the inert gas is nitrogen (N2), it has the advantages of being inexpensive and easy to handle, while not affecting the lithium sulfide generation reaction.

[0046] In this step, the hydrogen sulfide (H2S) supplied or re-supplied to the reaction chamber can be one selected from the group consisting of newly supplied hydrogen sulfide from a hydrogen sulfide supply unit, unreacted hydrogen sulfide recovered during the process, and combinations thereof. On the other hand, the unreacted hydrogen sulfide recovered during the process can be hydrogen sulfide that is not reacted and discharged to the outside of the reaction chamber in the step b and is re-supplied to the reaction chamber through a circulation process. The circulation of the unreacted hydrogen sulfide can refer to a process through a condenser, a hydrogen sulfide re-supply unit, and the like, which will be described later.

[0047] In addition, in this step, a portion of the solvent can be vaporized and discharged to the outside of the reaction chamber. Thus, the solvent can be replenished during the reaction, and the solvent at this time can be one selected from the group consisting of newly supplied solvent, solvent recovered during the process, and combinations thereof. On the other hand, the solvent recovered during the process can be solvent that is vaporized and discharged to the outside of the reaction chamber in the step b and is re-supplied to the reaction chamber through a circulation process. The circulation of the solvent can refer to a process through a condenser, a solvent re-supply unit, and the like, which will be described later.

[0048] Next, a process of transferring the product obtained in the above step b to a lithium sulfide recovery part to obtain lithium sulfide, and pulverizing the product using an in-line mixer in a lithium sulfide recovery line (step c) is included.

[0049] The above steps can include a process of generating a gas stream to remove the solvent and impurities and drying the lithium sulfide.

[0050] On the other hand, the product generated in the above reaction chamber is transferred to the lithium sulfide recovery part along the lithium sulfide recovery line, at which time the product is pulverized in the in-line mixer provided in the lithium sulfide recovery line. Specifically, the pulverization using the in-line mixer is performed at a stirring speed of 300 rpm to 2,000 rpm, and the in-line mixing time can be adjusted as needed. On the other hand, by controlling the stirring speed and the stirring time, the average particle size (D50) of the lithium sulfide finally obtained in the lithium sulfide recovery part can be controlled within a predetermined range of several micrometers.

[0051] In this regard, in Korean Patent Application No. 2021-0134601 (filed on October 12, 2021), a content of performing mechanical pulverization to achieve micronization by a tumbling ball mill, a ball milling, a jet milling, or the like after obtaining lithium sulfide is disclosed, and the conventional lithium sulfide particle size adjustment method is generally performed by the above steps in a separate space after finally obtaining lithium sulfide as described above. On the other hand, in the case of performing wet pulverization with simultaneous high-speed stirring accompanying the generation of lithium sulfide under solvent conditions as described in the present application, unlike the conventional method, a separate pulverization space or a separate pulverization step is not required, thus having economic efficiency, and generation of dust can also be prevented.

[0052] As described later, the above lithium sulfide recovery part can include a filtration reactor selected from at least one of a blower, an impeller, and a filter member F, or a vacuum filter capable of performing vacuum drying.

[0053] Specifically, the process of removing the solvent and the impurities can be performed by a gas stream in a horizontal direction or a vertical direction generated by the blower provided in the filtration reactor, and drying of the lithium sulfide can be simultaneously performed in the above process. The above gas stream can be a gas stream of one inert gas selected from nitrogen (N2), argon (Ar), helium (He), and combinations thereof. On the other hand, the flow rate of the above gas can be in the range of 1 kph to 10 kph. On the other hand, in the above process, the temperature of the lithium sulfide recovery part can be in the range of 80°C to 150°C, specifically, in the range of 80°C to 130°C.

[0054] On the other hand, the proportion of lithium raw material consumed by the reaction of steps a to c according to the present application can be 97.99% or more, specifically 98.99% or more, and more specifically 99.99% or more.

[0055] According to the lithium sulfide production method of the present application as described above, when lithium sulfide is produced by the reaction between lithium raw material and hydrogen sulfide, the reaction is performed under relatively mild conditions compared to the prior art, and thus there is no need for frequent maintenance or replacement due to corrosion and malfunction of reactors and various pipes, thereby improving the economic efficiency of the process. In addition, since unreacted hydrogen sulfide and solvent, from which moisture has been removed, are reused, the process cost is reduced, and the economic efficiency in mass production can be ensured.

[0056] Further, moisture and water vapor generated in the lithium sulfide production reaction are effectively removed, thereby preventing the reverse reaction of lithium hydroxide generation and promoting the forward reaction, and high-quality lithium sulfide can be produced with high purity and high yield. In addition, the particle size can be adjusted in units of , without the need for a separate pulverization space or step, and thus the convenience and mass productivity are excellent.

[0057] Lithium sulfide Lithium sulfide (Li2S) produced according to an embodiment of the present application has an average particle size (D50) in the range of 1 to 10 . In addition, the lithium sulfide (Li2S) can have a BET (Brunauer, Emmett, Teller analysis) specific surface area in the range of 1 m 2 / g to 14 m 2 / g.

[0058] In addition, the carbon content of lithium sulfide produced according to an embodiment of the present application can be less than 0.5% by weight, specifically less than 0.3% by weight, and the carbon content can be a result value of the total carbon content in the finally obtained lithium sulfide measured by an ND-IR (Non-Dispersive Infrared) analysis method. On the other hand, the purity of the finally obtained lithium sulfide according to the present application can be 97.99% or more, specifically 98.99% or more, and more specifically 99.99% or more, and the purity can be a result value measured by an XRD semi-quantitative analysis method.

[0059] Further, according to another embodiment of the present application, the lithium sulfide can be used as a core material for producing a sulfide-based solid electrolyte such as an Argyrodite series or an LPS (Li-P-S) series.

[0060] Specifically, a lithium all-solid-state secondary battery according to an embodiment of the present application can include: a positive electrode; a negative electrode opposite to the positive electrode; and a sulfide-based solid electrolyte prepared from the lithium sulfide interposed between the positive electrode and the negative electrode. In addition, the lithium all-solid-state secondary battery can be applied to at least one product / technical field selected from an electric vehicle (EV), a hybrid electric vehicle (HEV), an energy storage system (ESS), urban air mobility (UAM), a mobile device, a notebook computer, an electronic device, a tablet computer, a drone, a robot, and a home appliance.

[0061] Process for the preparation of lithium sulfide Figure 4 To show a schematic diagram of an example of a lithium sulfide preparation apparatus applicable to a lithium sulfide preparation method according to the present application. Hereinafter, the lithium sulfide preparation apparatus will be described with reference to FIG. 1. Figure 4 The preparation apparatus is described above.

[0062] The lithium sulfide preparation apparatus according to an embodiment of the present application includes a reaction chamber 100, a heating part 150, a hydrogen sulfide supply part 200, a condensation part 300, a hydrogen sulfide re-supply part 400, a solvent re-supply part 500, and a lithium sulfide recovery part 600. On the other hand, although not shown, a separately provided supply unit such as a circulation pump can be used as a unit for facilitating the movement of materials between each part within the preparation apparatus.

[0063] The reaction chamber 100 is a chamber having a predetermined reaction space in which a lithium sulfide generation reaction is performed, and a lithium raw material and hydrogen sulfide react within the reaction space to synthesize lithium sulfide (Li2S). The shape of the reaction chamber is not particularly limited as long as it has the predetermined reaction space described above. The predetermined reaction space of the reaction chamber 100 can be equipped with a solvent for a wet reaction. As described above, the solvent can be an aprotic solvent, and the specific type is as described above.

[0064] On the other hand, the lithium raw material can be supplied to the reaction space of the reaction chamber along a lithium raw material supply line 10. The supply of the lithium raw material can be performed in a manner of being loaded into the reaction chamber at once, or in order to realize an automated / semi-automated process, can be delivered through a conveyor belt provided outside the reaction chamber 100. In addition, the lithium raw material supply line 10 can be vertically or obliquely provided so that the lithium raw material moves into the reaction chamber by gravity. In addition to this, a separately provided air supply unit can be used to move the lithium raw material into the reaction chamber. A stirring member 110 for facilitating the lithium sulfide generation reaction or pulverizing the product can be provided in the reaction chamber, and the stirring member 110 can be, for example, a rotating disc, a rotor, a propeller, or the like.

[0065] The heating portion 150 can be provided in a form adjacent to or in contact with the reaction chamber to heat the predetermined reaction space described above. As an example, the heating portion 150 can be a heater, an electric heater, or an infrared heater installed on the outer surface of the reaction chamber 100 and can perform heating such that the reaction space temperature is in the range of 120°C to 300°C, specifically in the range of 120°C to 250°C, and more specifically in the range of 120°C to 200°C.

[0066] On the other hand, in order to allow the lithium raw material to sufficiently react with hydrogen sulfide, the temperature in the reaction chamber must be sufficiently increased. As a byproduct of the reaction of lithium hydroxide with hydrogen sulfide, water (H2O) is generated, as shown in Equation 1, which induces a reverse reaction of the lithium sulfide generation reaction and is located between lithium hydroxide particles or between solvents, reducing the surface area of the lithium raw material that can react with hydrogen sulfide. Therefore, by heating the reaction space to at least 120°C or more, the water or water vapor is removed, and the forward reaction can be promoted, thereby obtaining high-purity lithium sulfide. However, since the melting point of lithium hydroxide, which is one of the lithium raw materials, is 445°C, the temperature of the reaction space is preferably not more than 445°C. In addition, a high reaction temperature can cause corrosion of the reaction device and various pipes, and thus the heating needs to be controlled within the above temperature range.

[0067] On the other hand, the higher the temperature of the reaction space, the greater the risk of corrosion of the inner surface of the reaction chamber 100 and various pipes by hydrogen sulfide, and thus the reaction chamber 100 and various pipes can be made of a material having high heat resistance and corrosion resistance. For example, the reaction chamber 100 can be made of a material selected from the group consisting of Hastelloy, stainless steel (SUS), alumina, quartz, and combinations thereof, and specifically can be made of a material selected from the group consisting of Hastelloy X, stainless steel 304 (SUS304), stainless steel 310 (SUS310), stainless steel 316 (SUS316), alumina, quartz, and combinations thereof. When the reaction chamber and various pipes are made of the above-described materials and the temperature of the above-described reaction space is maintained within the above-described range, not only can the frequent maintenance or replacement of the reaction chamber 100 and various pipes and the like be prevented, but also the reaction between hydrogen sulfide and the lithium raw material can be sufficiently promoted, thereby obtaining high-purity lithium sulfide.

[0068] The hydrogen sulfide supply part 200 is configured to supply hydrogen sulfide to the reaction chamber 100. Specifically, the hydrogen sulfide supply part 200 can be a device for supplying hydrogen sulfide to one side or the lower end of one side of the reaction chamber. On the other hand, a gas sparger or an in-line dispersion device (not shown in the figure) for bubbling hydrogen sulfide can be provided on the hydrogen sulfide supply line 20 connecting the hydrogen sulfide supply part 200 and the reaction chamber 100. The above-mentioned gas sparger and in-line dispersion device can be devices that mix the supplied fluid at high pressure, and these devices can be controlled within an optimal pressure and temperature range, so that hydrogen sulfide (H2S) is supplied to the reaction chamber in a bubbling state.

[0069] The hydrogen sulfide transported into the reaction chamber along the hydrogen sulfide supply line 20 can be sprayed downward through a spray nozzle. When the hydrogen sulfide is sprayed downward, the residence time of the hydrogen sulfide (H2S) gas in the solvent increases, thereby improving the efficiency of the lithium sulfide generation reaction and reducing the proportion of unreacted hydrogen sulfide discharged to the outside of the reaction chamber.

[0070] The condensing part 300 can be used to selectively condense the gas discharged from the reaction chamber 100 along the exhaust line 30, and can be equipped with a separate cooling unit (not shown in the figure). As an example, the condensing part can be a condenser structure using a heat exchange method. For example, when the temperature of the above-mentioned condensing part is controlled to be less than 100°C, specifically less than 70°C, more specifically less than 50°C, the water vapor and the solvent discharged from the reaction chamber are liquefied, and the unreacted hydrogen sulfide passes through the above-mentioned condensing part in a gaseous state.

[0071] The hydrogen sulfide resupply part 400 can be a device for recovering unreacted hydrogen sulfide (H2S) passing through the above-mentioned condensing part and supplying the recovered unreacted hydrogen sulfide to the reaction chamber 100 along the hydrogen sulfide resupply line 40. In addition, the hydrogen sulfide resupply part 400 can include a dehumidifying part (not shown in the figure). Specifically, the unreacted hydrogen sulfide (H2S) recovered from the condensing part can be resupplied to the reaction chamber 100 in a state where moisture is completely removed when passing through the hydrogen sulfide resupply part, and thus recovering and resupplying unreacted hydrogen sulfide can improve the economic efficiency of the process. On the other hand, as long as moisture / water vapor can be removed from the recovered unreacted hydrogen sulfide gas, the structure of the dehumidifying part is not particularly limited, and for example, can be a device structure that selectively liquefies and removes water vapor by pressurizing the gas under strong pressure conditions. In this case, unlike the method of removing moisture by cooling, there is no need for a separate heating process before supplying the recovered unreacted hydrogen sulfide gas to the reaction chamber, and thus there is an advantage in terms of process economy and efficiency.

[0072] The hydrogen sulfide resupply line 40 can be directly connected to the reaction chamber 100 or connected to the hydrogen sulfide supply line 20 described above. When the hydrogen sulfide resupply line 40 is directly connected to the reaction chamber, the hydrogen sulfide resupply line 40 can be the same as the hydrogen sulfide supply line 20 and equipped with a gas sparger or an inline-disperser (not shown in the figure) for bubbling hydrogen sulfide.

[0073] The solvent resupply part 500 is a device structure that receives the mixture of liquefied solvent and water from the condensing part 300, separates them based on the difference in boiling point or specific gravity, and then selectively recovers the solvent. The solvent recovered from the solvent resupply part 500 can be resupplied to the reaction chamber 100 along the solvent resupply line 50. On the other hand, one or more solvent resupply parts can be provided, and when there are two or more solvent resupply parts, they can be provided in series or in parallel as needed. The solvent resupply part 500 can be a Dean-Stark trap or an oil-water separation device. In addition, the water separated in the above process is discharged and removed along the drain line WD.

[0074] The lithium sulfide recovery part 600 is a device structure that transfers the product generated in the reaction chamber 100 outside, and the product can be transferred along the lithium sulfide recovery line 60. In the lithium sulfide recovery part, a solvent and impurities removal and drying process can be performed before finally obtaining lithium sulfide. On the other hand, the structure of the lithium sulfide recovery part is not particularly limited, and for example, it can be a chamber structure having a cylindrical, square, rectangular, cylindrical, inverted conical, or the like shape. For example, the lithium sulfide recovery part can include a filter reactor selected from one or more of a blower, an impeller, and a filter member F, or a vacuum filter capable of performing vacuum drying.

[0075] The blower is provided at the side end or the upper end of the lithium sulfide recovery part, and is a device that generates a gas flow in the horizontal direction or the vertical direction. The gas flow generated by the blower can move the solvent and impurities remaining on the surface of the lithium sulfide in the product to the side of the filter member and remove them, and the gas supplied by the blower can be an inert gas as described above.

[0076] The impeller is provided in the lithium sulfide recovery part and can move in the upward / downward / leftward / rightward direction, and can have at least one shape selected from a paddle, a propeller, and a turbine. On the other hand, the impeller can be a device structure that operates to facilitate the process of removing impurities and drying the product transferred to the lithium sulfide recovery part.

[0077] The filter member F, which is used to discharge the solvent and impurities separated from the lithium sulfide to the outside as described above, can be made of one selected from the group consisting of Hastelloy, stainless steel, and combinations thereof, and specifically, one selected from the group consisting of Hastelloy X, stainless steel 304, stainless steel 310, stainless steel 316, and combinations thereof. In addition, the filter member F can have a mesh size of 1 The mesh filter of the above particles.

[0078] The inert gas supply part 700 is a device structure for supplying the inert gas after bubbling, and as an example, the inert gas can be supplied along the inert gas supply line 70 communicating with the lower end of the reaction chamber. The inert gas can be one selected from the group consisting of nitrogen (N2), argon (Ar), helium (He), and combinations thereof. In addition, a gas sparger or an in-line dispersing device (not shown in the drawing) for bubbling can be provided in the inert gas supply part or the inert gas supply line. In addition, the flow rate of the inert gas can be controlled to be in the range of 1 kph to 10 kph.

[0079] The above in-line mixer 800 can be provided on the lithium sulfide recovery line 60 communicating the reaction chamber 100 and the lithium sulfide recovery part 600. The in-line mixer can be used to crush the product, i.e., lithium sulfide particles, obtained by the lithium sulfide generation reaction to a desired size. Specifically, the in-line mixer is activated when the product is transferred to the lithium sulfide recovery part after the lithium sulfide generation reaction is completed, thereby crushing the lithium sulfide particles to a predetermined particle size range in the presence of a solvent. On the other hand, the in-line mixer can control the average particle size (D50) of the finally obtained lithium sulfide to be in a predetermined range by adjusting the stirring speed and the stirring time. For example, the in-line mixer can be driven at a stirring speed in the range of 300 rpm to 2,000 rpm, and can be operated for 1 hour to 20 hours at a time.

[0080] Example The present application can be implemented in various modifications and can have various embodiments, and thus specific embodiments will be illustrated below and described in detail. However, this is not intended to limit the present application to specific embodiments, but should be understood to include all modifications, equivalents, and even alternatives falling within the spirit and technical scope of the present application.

[0081] Example 1 A cylindrical reaction chamber (100 ), 28 kg (0.25 kmol) of an octane mixture was added as a solvent into the reaction chamber. Subsequently, 20 kg (0.48 kmol) of lithium hydroxide monohydrate (LiOH-H2O) was added into the above reaction chamber, and nitrogen (N2) was introduced as an inert gas at a rate of 0.2 kph using the lower gas sparger, and the reaction chamber was stirred for 2 hours under reflux. At this time, 8.6 kg of water generated was recovered / removed through an oil-water separation device (corresponding to step a).

[0082] Then, hydrogen sulfide (H2S) was introduced into the above reaction chamber at a rate of 1.5 kph while maintaining the pressure in the reaction chamber at 2 bar and the temperature at 150°C, and the reaction chamber was stirred for 20 hours under reflux. After confirming that the chemical equilibrium was reached and lithium sulfide was no longer continuously generated, the hydrogen sulfide was stopped, the pressure in the reaction chamber was reduced to 0.01 bar, and nitrogen (N2) was introduced at a rate of 1 kph using the lower gas sparger, and the reaction chamber was stirred for 1 hour under reflux. Subsequently, the nitrogen was stopped, and hydrogen sulfide (H2S) was introduced again at a rate of 1.5 kph while maintaining the pressure in the reaction chamber at 2 bar and the temperature at 150°C, and the reaction chamber was stirred for 1 hour under reflux. On the other hand, the above series of processes of nitrogen (N2) bubbling and resupply of hydrogen sulfide (H2S) were repeated three times (corresponding to step b).

[0083] After the lithium sulfide generation reaction was completed, the reaction chamber was cooled to 80°C, and then the product was passed through an in-line mixer operated at a stirring speed of 1,400 rpm, filtered using a Nutsche filter, and dried under reduced pressure at 80°C, and then 8.81 kg (0.19 kmol) of white solid lithium sulfide was obtained in a glove box (corresponding to step c).

[0084] Comparative Example 1 Except that the in-line mixing process using an in-line mixer was not performed in step c, the rest was prepared in the same manner as in Example 1 described above.

[0085] [Experiment. Measurement of physical properties of lithium sulfide] XRD measurement experiment The lithium sulfide (Li2S) recovered according to the examples and the comparative example was subjected to XRD measurement using CuKα rays, and the 2θ = 44.6 peak corresponding to lithium sulfide and the 2θ = 32.3 peak corresponding to lithium hydroxide were observed. As shown in FIG. 2, the XRD semi-quantitative analysis result of Example 1 confirmed that the purity of lithium sulfide was 99.99%.

[0086] On the other hand, as shown in FIG. 3, the XRD semi-quantitative analysis result of Comparative Example 1 confirmed that the purity of lithium sulfide was 99.99%.

[0087] BET surface area measurement experiment The lithium sulfide (Li2S) recovered according to the examples and the comparative example, respectively, was prepared, and the specific surface area was measured using Nova800 as a BET method using nitrogen gas, and as a result, the specific surface area of the lithium sulfide according to Example 1 was confirmed to be 12.8 m 2 / g.

[0088] On the other hand, the specific surface area of the lithium sulfide according to Comparative Example 1 was confirmed to be 9.3 m 2 / g.

[0089] Particle size analysis measurement experiment The lithium sulfide (Li2S) recovered according to the examples and the comparative example, respectively, was prepared, and particle size analysis was performed using a SALD-2300 device. As a result of the measurement, the average particle size (D50) of Example 1 was confirmed to be 7.7 (see FIG. 2).

[0090] On the other hand, the average particle size (D50) of the lithium sulfide of Comparative Example 1 was confirmed to be 103.4 (see FIG. 3).

[0091] The overall summary of the above experimental results is shown in Table 1 below.

[0092] Table 1

[0093] Referring to the results of Table 1 above, it can be predicted that in the case of performing online mixing after the lithium sulfide generation reaction as described in the examples of the present application, the desired average particle size (D50) of the lithium sulfide can be controlled by adjusting the stirring speed, and compared to the dry pulverization method such as jet milling, there is no need for a separate pulverization space or a pulverization step, and thus there is economic efficiency, and there is also less dust, which is also helpful for the safety of workers.

[0094] The above description is merely exemplary of the illustrative application and modifications and variations can be effected without departing from the spirit and scope of the application by a person of ordinary skill in the art. Therefore, the examples described herein are provided not only to limit the disclosure, but to explain the spirit of the disclosure, and the spirit of the disclosure is not limited to these examples. The scope of protection of the present application should be determined by the claims, and all technical spirits within the equivalent scope should be interpreted as included in the patent right of the present application.

Claims

1. A method for preparing lithium sulfide, characterized in that, include: Step a), supplying lithium feedstock to a reaction chamber containing solvent; Step b), supplying hydrogen sulfide (H2S) into the reaction chamber to carry out the lithium sulfide (Li2S) formation reaction; as well as Step c) The product obtained in step b above is transferred to the lithium sulfide recovery unit to obtain lithium sulfide, and the product is crushed in the lithium sulfide recovery line using an online mixer.

2. The method for preparing lithium sulfide according to claim 1, characterized in that, After step a and before step b, the process also includes maintaining the temperature in the reaction chamber within the range of 80°C to 200°C and heating it for 1 to 5 hours to remove moisture from the reaction chamber.

3. The method for preparing lithium sulfide according to claim 1, characterized in that, The solvent in step a above is an aprotic solvent, specifically selected from cycloheptane, cyclooctane, methylcyclohexane, dimethylcyclohexane, trimethylcyclohexane, ethylcyclohexane, diethylcyclohexane, propylcyclohexane, isopropylcyclohexane, dipropylcyclohexane, butylcyclohexane, tert-butylcyclohexane, methylcycloheptane, and methylcyclooctane; octane, isooctane, nonane, isononane, decane, isodecane, undecane, dodecane, hexadecane, and octadecane; toluene, o-xylene, m-xylene, p-xylene, and 1,3,5-trimethyloxane. Methylbenzene (trimethylbenzene), 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene, ethylbenzene, propylbenzene, isopropylbenzene, butylbenzene, isobutylbenzene, tert-butylbenzene and cyclohexylbenzene; naphthalene, decahydronaphthalene (decahydronaphthalene), 1-methylnaphthalene, 2-methylnaphthalene, 1-ethylnaphthalene, 2-ethylnaphthalene; tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 1,4-dioxane, dibutyl ether, isopentyl ether, dihexyl ether, 1,2-dimethoxyethane; and one combination thereof.

4. The method for preparing lithium sulfide according to claim 1, characterized in that, The volume of the solvent in step a above accounts for 50% to 80% of the total volume of the reaction chamber.

5. The method for preparing lithium sulfide according to claim 1, characterized in that, The lithium raw material in step a above is selected from lithium hydroxide (LiOH), lithium hydroxide monohydrate (LiOH·H2O), lithium carbonate (Li2CO3), and combinations thereof.

6. The method for preparing lithium sulfide according to claim 1, characterized in that, The lithium sulfide formation reaction in step b above is shown in Equation 1 below. The temperature inside the reaction chamber is 120°C to 300°C, the pressure is 0.01 bar to 5.0 bar, and the reaction time is 10 hours to 60 hours. Equation 1: 2LiOH + H2S → Li2S + 2H2O.

7. The method for preparing lithium sulfide according to claim 1, characterized in that, In step b above, the solvent added during the reaction is selected from a combination of newly supplied solvents, solvents recovered during the process, and solvents that are recycled during the process.

8. The method for preparing lithium sulfide according to claim 1, characterized in that, In step c above, the online mixer operates at a stirring speed of 300 rpm to 2,000 rpm to control the average particle size (D50) of the final lithium sulfide within a predetermined range.

9. The method for preparing lithium sulfide according to claim 1, characterized in that, In step c above, an airflow is generated in the lithium sulfide recovery section to remove solvents and impurities and dry the lithium sulfide.

10. The method for preparing lithium sulfide according to claim 1, characterized in that, The proportion of lithium raw materials consumed in the reactions of steps a to c above is over 97.99%.

11. A lithium sulfide, which is the lithium sulfide prepared according to claim 1, characterized in that, With 1 Up to 10 The average particle size (D50) and 1m 2 / g to 14m 2 / g of BET surface area.

12. The lithium sulfide according to claim 11, characterized in that, The carbon content of the above-mentioned lithium sulfide is less than 0.5% by weight, and the purity is above 97.99%.

13. A lithium all-solid-state secondary battery, characterized in that, include: A positive electrode; a negative electrode opposite to the aforementioned positive electrode; and a sulfide-based solid electrolyte made of lithium sulfide as described in claim 11, located between the aforementioned positive and negative electrodes.

14. The lithium all-solid-state secondary battery according to claim 13, characterized in that, The aforementioned lithium all-solid-state secondary batteries are used in at least one product selected from electric vehicles (EVs), hybrid electric vehicles (HEVs), energy storage systems (ESS), urban air mobility (UAM), mobile devices, laptops, electronic devices, tablets, drones, robots, and home appliances.

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