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. Furthermore, 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.

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 their applications 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 will 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 with lithium sulfide, thereby lowering the purity of the produced lithium sulfide. In addition, the moisture causes aggregation between the particles of the produced lithium sulfide, 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 bubbling a gas to promote the forward reaction, and further removing moisture from unreacted hydrogen sulfide and a solvent and reusing the same for the production of 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 the present invention aims to provide a method for producing lithium sulfide, which can economically mass-produce high-purity, high-yield lithium sulfide by designing reaction conditions and apparatuses suitable for mass-producing lithium sulfide with high purity and high yield using the reaction between a lithium raw material and hydrogen sulfide (H2S), and further removing moisture by bubbling hydrogen sulfide to promote the forward reaction, and removing moisture from unreacted hydrogen sulfide and a solvent and reusing the same.

[0010] MEANS FOR SOLVING THE PROBLEMS In the present specification, a method for producing lithium sulfide is provided, which includes: 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) production reaction, and including a process of bubbling the unreacted hydrogen sulfide recovered during the process to maintain the pressure in the reaction chamber within a predetermined range; and step c) of transferring the product obtained in the above step b) to a lithium sulfide recovery section to obtain lithium sulfide.

[0011] As an example, 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 to remove moisture in the reaction chamber can be further included after the above step a) and before step b).

[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, isoamyl 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 For example, in step b above, when the unreacted hydrogen sulfide recovered during the process is introduced in a bubbling manner, new hydrogen sulfide can be additionally supplied to maintain the pressure in the reaction chamber within a predetermined range.

[0017] As an example, in step b above, the solvent supplemented during the reaction can be one selected from the group consisting of newly supplied solvent, solvent recovered during the process, and combinations thereof.

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

[0019] As an example, the proportion of lithium raw material consumed through the reactions of the above steps a to c 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 method, and has an average particle size (D50) of 1 to 200 m / g to 14 m / g of a BET surface area. 2 2

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

[0022] In addition, the present specification provides a lithium full solid-state secondary battery, the lithium full solid-state secondary battery including: a positive electrode; a negative electrode opposite to the positive electrode; and a sulfide-based solid-state electrolyte interposed between the positive electrode and the negative electrode and made of the lithium sulfide.

[0023] As an example, the lithium full 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 lithium raw material and hydrogen sulfide, the reaction is performed under relatively mild conditions compared to the prior art, so that frequent maintenance or replacement due to corrosion and failure of reactors and various pipes is not required, thereby improving the economic efficiency of the process. In addition, since unreacted hydrogen sulfide and solvents, from which moisture has been removed, are reused, the process cost is reduced, and the economic efficiency at the time of mass production can be secured.

[0025] Furthermore, 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. 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 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 application and a comparative example.

[0028] Figure 4 FIG. 1 shows a schematic diagram of a lithium sulfide preparation apparatus according to an embodiment of the present application.

[0029] BEST MODE FOR CARRYING OUT THE INVENTION 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; 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 of all the drawings, it should be noted that the same components are designated by the same reference numerals even if they are illustrated in different drawings. Also, when it is determined that a detailed description of related known structures or functions impedes understanding of the embodiment of the present application, a detailed description thereof will be omitted.

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

[0032] Process for the preparation of lithium sulfide The lithium sulfide preparation method according to an embodiment of the present application includes: step a) of supplying a lithium raw material to a reaction chamber provided with a solvent; step b) of supplying hydrogen sulfide (H2S) into the reaction chamber to perform a lithium sulfide (Li2S) generation reaction, and including a process of bubbling unreacted hydrogen sulfide recovered during the process to maintain the pressure in the reaction chamber within a predetermined range; and step c) of transferring the product obtained in the above step b) to a lithium sulfide recovery portion to obtain lithium sulfide (see 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 the lithium sulfide generation reaction is performed, and the 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, and 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, decaline (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.

[0036] In the above step, the solvent can have a volume of 50% to 80% with respect to the total volume of the reaction chamber, and when the volume of the solvent is less than the above range, the 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 be fixed. On the other hand, when the volume of the solvent exceeds the above volume range, the space occupied by the 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 solvent can be refluxed to other device configurations.

[0037] The lithium raw material of the present application is a reactant that reacts with the hydrogen sulfide (H2S) supplied in the later 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 lithium raw material can be lithium hydroxide monohydrate (LiOH·H2O), and in this 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 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 of 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, a process (step b) including supplying hydrogen sulfide (H2S) into the reaction chamber to perform a lithium sulfide (Li2S) generation reaction, and including passing unreacted hydrogen sulfide recovered during the process in a bubbling manner, thereby maintaining the pressure inside the reaction chamber within a predetermined range.

[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 Formula 1 below.

[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, inside 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 be continued for 10 hours to 60 hours, and stirring can be performed during the above reaction to promote the reaction.

[0044] In addition, the introduction of the unreacted hydrogen sulfide recovered in the process of the above step b can be performed at any point of time after the start of the reaction, but according to an embodiment of the present application, it can be continuously performed from the time when the lithium sulfide generation reaction reaches chemical equilibrium. Specifically, when hydrogen sulfide is supplied into the reaction chamber, the lithium sulfide generation reaction starts to proceed, and during the progress of the above reaction, there is a point of time when the rates of the forward reaction and the reverse reaction are equal, and chemical equilibrium is reached. If the reaction is ended at this time, it can be difficult to obtain the desired level of purity of lithium sulfide, and therefore the introduction of the unreacted hydrogen sulfide (H2S) recovered in the process according to the present application is performed. The introduction of the unreacted hydrogen sulfide recovered in the process serves to remove water 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, the unreacted hydrogen sulfide recovered in the process is also used as a reactant to react with the lithium raw material, and therefore the lithium sulfide generation reaction starts to proceed again. Therefore, if the introduction is continued, the conversion rate of the lithium raw material to lithium sulfide can be maximized.

[0045] For example, the amount of unreacted hydrogen sulfide recovered in the above introduction process can be an amount corresponding to the amount of hydrogen sulfide consumed in the above lithium sulfide production reaction. However, since the amount of unreacted hydrogen sulfide recovered in the above introduction process can be less than the amount of hydrogen sulfide consumed in the above lithium sulfide generation reaction, new hydrogen sulfide can be additionally supplied to maintain the pressure in the reaction chamber within a predetermined range. On the other hand, the new hydrogen sulfide can be hydrogen sulfide newly supplied from a hydrogen sulfide supply unit to be described later, and the unreacted hydrogen sulfide recovered in the process can be hydrogen sulfide that is supplied to the reaction chamber again through a circulation process after being discharged to the outside of the reaction chamber in the above step b, and the circulation of the unreacted hydrogen sulfide can refer to a process through a condensation unit, a hydrogen sulfide resupply unit, etc. to be described later.

[0046] In addition, in the present step, a portion of the solvent can be vaporized and discharged to the outside of the reaction chamber. Therefore, the solvent can be replenished during the reaction, and the solvent at this time can be one selected from among newly supplied solvent, solvent recovered in the process, and combinations thereof. On the other hand, the solvent recovered in the process can be solvent that is supplied to the reaction chamber again through a circulation process after being vaporized and discharged to the outside of the reaction chamber in the above step b, and the circulation of the solvent can refer to a process through a condensation unit, a solvent resupply unit, etc. to be described later.

[0047] Next, the product obtained in the above step b is transferred to a lithium sulfide recovery unit to obtain lithium sulfide (step c).

[0048] The above step can include a process of generating a gas stream to remove the solvent and impurities and dry the lithium sulfide.

[0049] As described later, the lithium sulfide recovery section can include a filter reactor including at least one selected from a blower, an impeller, and a filter member F, or a vacuum filter capable of performing vacuum drying.

[0050] Specifically, the solvent and impurity removal process can be performed by a horizontal or vertical gas flow generated by a blower provided in the filter reactor, and drying of the lithium sulfide can be simultaneously performed in the above process. The gas flow can be a flow of an inert gas selected from nitrogen (N2), argon (Ar), helium (He), and combinations thereof. On the other hand, the flow rate of the 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 section can be in the range of 80°C to 150°C, specifically, in the range of 80°C to 130°C.

[0051] 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.

[0052] According to the lithium sulfide production method of the present application as described above, when lithium sulfide is produced by 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 frequent maintenance or replacement due to corrosion and malfunction of a reactor and various pipes is not required, thereby improving the economic efficiency of the process. In addition, since unreacted hydrogen sulfide and a solvent from which moisture has been removed are reused, the process cost is reduced, and economic efficiency in mass production can be ensured.

[0053] Further, moisture and water vapor generated in the lithium sulfide production reaction are effectively removed, thereby preventing a reverse reaction of lithium hydroxide production and promoting a forward reaction, and high-quality lithium sulfide can be produced at high purity and high yield.

[0054] 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 200 , specifically, an average particle size (D50) in the range of 1 to 120 . 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.

[0055] In addition, the carbon content of the lithium sulfide prepared 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 a non-dispersive infrared (ND-IR) 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 a semi-quantitative XRD analysis method.

[0056] Further, according to another embodiment of the present application, the lithium sulfide can be used as a core material for preparing a sulfide-based solid electrolyte such as an argyrodite series or an LPS (Li-P-S) series.

[0057] Specifically, the lithium full solid-state secondary battery according to an embodiment of the present application can include a cathode, an anode opposite to the cathode, and a sulfide-based solid electrolyte prepared from the lithium sulfide interposed between the cathode and the anode. In addition, the lithium full 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.

[0058] Process for the preparation of lithium sulfide Figure 4 To show a schematic view of an example of a lithium sulfide preparation apparatus applicable to the lithium sulfide preparation method according to the present application. Hereinafter, the lithium sulfide preparation apparatus according to an embodiment of the present application will be described with reference to FIG. 1. Figure 4 The preparation apparatus will be described.

[0059] 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 in the preparation apparatus.

[0060] The reaction chamber 100 is a chamber having a predetermined reaction space in which a lithium sulfide generation reaction is performed, and lithium raw material reacts with hydrogen sulfide in the reaction space to synthesize lithium sulfide (Li2S). The shape of the reaction chamber is not particularly limited as long as it has the above-described predetermined reaction space. The above-described reaction space of the reaction chamber 100 can be provided 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.

[0061] On the other hand, the lithium raw material can be supplied to the reaction space of the reaction chamber along the 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 once, or in order to realize an automated / semi-automated process, can be transported by a transport 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 separate 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 above-described stirring member 110 can be, for example, a rotating disc, a rotor, a propeller, or the like.

[0062] The heating portion 150 can be provided in a form adjacent to or in contact with the reaction chamber to heat the above-described predetermined reaction space. As an example, the heating portion 150 can be a heater, an electric heating wire, or an infrared heater installed on the outer surface of the reaction chamber 100, and can perform heating so that the temperature of the reaction space 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.

[0063] On the other hand, in order for the lithium raw material to sufficiently react with hydrogen sulfide, the temperature in the reaction chamber must be sufficiently increased. As shown in the above-described Equation 1, as a byproduct of the reaction of lithium hydroxide with hydrogen sulfide, water (H2O) is generated, which can induce a reverse reaction of the lithium sulfide generation reaction, and at the same time, 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, removing moisture or water vapor, the forward reaction can be facilitated, and thus high-purity lithium sulfide can be obtained. 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-described temperature range.

[0064] 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 the various pipes by hydrogen sulfide, and thus the reaction chamber 100 and the 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 (SUS 304), stainless steel 310 (SUS 310), stainless steel 316 (SUS 316), alumina, quartz, and combinations thereof. When the reaction chamber and the 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 frequent maintenance or replacement of the reaction chamber 100 and the 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.

[0065] 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, on the hydrogen sulfide supply line 20 connecting the hydrogen sulfide supply part 200 and the reaction chamber 100, a sparger or an inline-disperser (not shown in the drawing) for bubbling hydrogen sulfide can be provided. The above-described sparger and inline-disperser 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 inside of the reaction chamber in a bubbling state.

[0066] Hydrogen sulfide delivered to the inside of the reaction chamber along the hydrogen sulfide supply line 20 can be sprayed downward through a spray nozzle. When hydrogen sulfide is sprayed downward, the residence time of 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.

[0067] 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 drawing). As an example, the condensing part can be a condenser structure using a heat exchange method. For example, when the temperature of the above-described condensing part is controlled to be less than 100°C, specifically less than 70°C, and 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-described condensing part in a gaseous state.

[0068] The hydrogen sulfide resupply part 400 can be a device for recovering unreacted hydrogen sulfide (H2S) passing through the condensing part described above, and resupplying 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 the unreacted hydrogen sulfide can improve the economic efficiency of the process. On the other hand, as long as the 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 in which the gas is selectively liquefied and removed by pressurizing the gas under a strong pressure condition. In this case, unlike the method of removing moisture by cooling, there is no need for a separate heating process before the recovered unreacted hydrogen sulfide gas is supplied to the reaction chamber, and thus there is an advantage in terms of process economy and efficiency.

[0069] 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 equipped with an aerator or an in-line dispersion device (not shown in the figure) for blowing hydrogen sulfide, like the hydrogen sulfide supply line 20 described above.

[0070] The solvent resupply part 500 is a device structure that receives a 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 described above 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.

[0071] The lithium sulfide recovery part 600 is a device structure that transports and discharges the product generated in the reaction chamber 100, and the product can be transported and discharged along the lithium sulfide recovery line 60. In the lithium sulfide recovery part, a solvent and impurities can be removed and dried before finally obtaining lithium sulfide. The structure of the lithium sulfide recovery part is not particularly limited, and for example, can be a chamber structure having a cylindrical, square, rectangular, cylindrical, or inverted conical shape. For example, the lithium sulfide recovery part described above 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.

[0072] The blower is provided at the side end or the upper end of the lithium sulfide recovery part, and is a device for generating a gas stream in a horizontal direction or a vertical direction. The gas stream 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. The gas supplied by the blower can be an inert gas as described above.

[0073] The impeller is provided in the lithium sulfide recovery part, and can move in upward, downward, left, and right directions, 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 when removing impurities and drying the product transferred to the lithium sulfide recovery part, to facilitate the process.

[0074] The filter member F is used to discharge the solvent and impurities separated from the lithium sulfide to the outside as described above, and can be made of one selected from Hastelloy, stainless steel, and combinations thereof, specifically one selected from 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 above mesh filter of the particles.

[0075] The inert gas supply part 700 is a device structure for supplying inert gas after bubbling to the reaction chamber. 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 nitrogen (N2), argon (Ar), helium (He), and combinations thereof. In addition, an aerator or an in-line dispersion device (not shown in the figure) 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 stream can be controlled to be in the range of 1 kph to 10 kph.

[0076] Example The present application can be implemented in various modifications and can have various embodiments, and thus specific embodiments will be exemplified 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.

[0077] 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-H20) was added into the above reaction chamber, and nitrogen (N2) was supplied as an inert gas at a rate of 0.2 kph using the lower aerator, 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).

[0078] Then, hydrogen sulfide (H2S) was supplied 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 under reflux stirring, and when the pressure in the reaction chamber decreased, the unreacted hydrogen sulfide recovered during the process was continuously supplied by bubbling at a rate of 0.2 kph to 0.5 kph to maintain the above internal pressure, and the reaction chamber was stirred under reflux for 12 hours under the above conditions. At this time, 8.35 kg of water generated was recovered through an oil-water separation device (corresponding to step b).

[0079] After the lithium sulfide generation reaction was completed, the reaction chamber was cooled to 80°C, filtered using a Nutsche filter, and dried under reduced pressure at 80°C, and then 9.71 kg (0.21 kmol) of white solid lithium sulfide was obtained in a glove box (corresponding to step c).

[0080] Comparative Example 1 The same procedure as in Example 1 was followed, except that in step b, bubbling of unreacted hydrogen sulfide (H2S) recovered during the process was not performed.

[0081] [Experiment. Measurement of physical properties of lithium sulfide] XRD measurement experiment Lithium sulfide (Li2S) recovered according to the examples and the comparative example was prepared, respectively, and XRD measurement was performed using CuKa rays, and peaks corresponding to 2θ = 44.6 of lithium sulfide and 2θ = 32.3 of lithium hydroxide were observed. As shown in FIG. 2, the results of XRD semi-quantitative analysis of Example 1 confirmed that the purity of lithium sulfide was 99.99%.

[0082] On the other hand, as shown in FIG. 3, the results of XRD semi-quantitative analysis of Comparative Example 1 confirmed that lithium sulfide was 97.00% and lithium hydroxide was 3.00%.

[0083] BET surface area measurement experiment Lithium sulfide (Li2S) recovered according to the examples and the comparative example was prepared, respectively, and the specific surface area was measured using Nova 800, which is a BET method using nitrogen gas, and the results confirmed that the specific surface area of lithium sulfide according to Example 1 was 8.7 m 2 / g.

[0084] On the other hand, the specific surface area of the lithium sulfide according to Comparative Example 1 was 9.3 m 2 / g.

[0085] Particle size analysis measurement experiment The lithium sulfide (Li2S) recovered according to the examples and comparative examples was prepared, respectively, and particle size analysis was performed using a SALD-2300 apparatus. The measurement results confirmed that the average particle size (D50) of Example 1 was 98.8 (see FIG. 2).

[0086] On the other hand, the average particle size (D50) of the lithium sulfide according to Comparative Example 1 was 109.2 (see FIG. 3).

[0087] The overall summary of the above experimental results is shown in Table 1 below.

[0088] Table 1

[0089] As can be seen from the results of Table 1 above, when the lithium sulfide generation reaction reaches chemical equilibrium as shown in the examples of the present application, by continuously blowing unreacted hydrogen sulfide (H2S) recovered in the process into the reaction chamber to maintain a predetermined pressure, moisture in the reaction chamber can be removed, the chemical equilibrium can be broken and the forward reaction can be promoted, and thus the purity of the lithium sulfide finally obtained can be significantly improved compared to the comparative examples.

[0090] The above description is merely exemplary of the illustrative techniques to implement the present application and numerous modifications and alterations to the illustrative embodiments are possible without departing from the spirit and scope of the present application. Accordingly, the summary of the embodiments described herein is intended for purposes of illustration only and should not be construed as in any way limiting the spirit and scope of the present disclosure. The scope of the present application should be determined by the following claims and should not be limited by the above description. Within the equivalent range of the technical spirit, all technical spirits should be interpreted as included in the patent right of the present application.

Claims

1. A process for the preparation of lithium sulfide, characterized in that, comprising: Step a) supplying a lithium raw material to a reaction chamber provided with a solvent; Step b) supplying hydrogen sulfide (H2S) into the reaction chamber to perform a lithium sulfide (Li2S) generation reaction, and including a process of bubbling the unreacted hydrogen sulfide recovered during the process to maintain the pressure in the reaction chamber within a predetermined range; and Step c) transferring the product obtained in the above step b) to a lithium sulfide recovery section to obtain lithium sulfide.

2. The lithium sulfide production method according to claim 1, wherein, after the above step a) and before step b), a step of maintaining the temperature in the reaction chamber within a range of 80°C to 200°C while heating for 1 hour to 5 hours to remove moisture in the reaction chamber is further included.

3. The lithium sulfide production method according to claim 1, wherein, the solvent in the above step a) is an aprotic solvent, and is 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, decaline (tetrahydro-naphthalene), 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.

4. The lithium sulfide production method according to claim 1, wherein, the volume of the solvent in the above step a) is 50% to 80% of the total volume of the reaction chamber.

5. The lithium sulfide production method according to claim 1, wherein, the lithium raw material in the above step a) is one selected from the group consisting of lithium hydroxide (LiOH), lithium hydroxide monohydrate (LiOH-H2O), lithium carbonate (Li2CO3), and combinations thereof.

6. The lithium sulfide production method according to claim 1, wherein, the lithium sulfide generation reaction in the above step b) is represented by the following formula 1, the temperature in 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, Formula 1: 2LiOH + H2S → Li2S + 2H2O.

7. The lithium sulfide production method according to claim 1, wherein, in the above step b), while bubbling the unreacted hydrogen sulfide recovered during the process, new hydrogen sulfide is additionally supplied to maintain the pressure in the reaction chamber within a predetermined range.

8. The lithium sulfide production method according to claim 1, wherein, ​ ​ ​ ​ ​ ​ In the above step b, the solvent supplemented during the reaction is one selected from the group consisting of a newly supplied solvent, a solvent recovered during the process, and a combination thereof. 9.The lithium sulfide production method of claim 1, wherein the lithium sulfide is produced by a process comprising: a step of preparing a lithium source; a step of preparing a sulfur source; a step of mixing the lithium source and the sulfur source; a step of heating the mixture to a predetermined temperature; a step of adding a solvent to the mixture; a step of reacting the mixture; and a step of recovering the lithium sulfide. In the above step c, a gas stream is generated in the lithium sulfide recovery section, the solvent and impurities are removed, and the lithium sulfide is dried. 10.The lithium sulfide production method of claim 1, wherein the lithium sulfide is produced by a process comprising: a step of preparing a lithium source; a step of preparing a sulfur source; a step of mixing the lithium source and the sulfur source; a step of heating the mixture to a predetermined temperature; a step of adding a solvent to the mixture; a step of reacting the mixture; a step of recovering the lithium sulfide; and a step of drying the lithium sulfide. The proportion of the lithium source consumed through the above steps a to c is 97.99% or more.

11. Lithium sulfide produced by the method of claim 1, characterized in that, having a mean particle size (D50) of 1 to 200 average particle size (D50) of 1 m 2 g to 14 m 2 g BET surface area. 12.The lithium sulfide of claim 11, wherein the lithium sulfide has a carbon content of less than 0.5% by weight and a purity of 97.99% or more. The lithium sulfide of claim 11.

13. A lithium all-solid-state secondary battery characterized by comprising: 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 of claim 11. 14.The lithium full solid-state secondary battery of claim 13, wherein the lithium full solid-state secondary battery is applied to at least one product selected from the group consisting of an electric vehicle (EV), a hybrid electric vehicle (HEV), an energy storage system (ESS), an urban air mobility (UAM), a mobile device, a notebook computer, an electronic device, a tablet computer, a drone, a robot, and a home appliance. The lithium full solid-state secondary battery is applied to at least one product selected from the group consisting of an electric vehicle (EV), a hybrid electric vehicle (HEV), an energy storage system (ESS), an urban air mobility (UAM), a mobile device, a notebook computer, an electronic device, a tablet computer, a drone, a robot, and a home appliance. ​

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