Method for producing lithium sulfide

Abstract

The present invention relates to a method for producing lithium sulfide and, more specifically, to a wet method for producing lithium sulfide, in which a lithium raw material and hydrogen sulfide are converted into lithium sulfide in the presence of a polar solvent, and then particle size can be adjusted and purity can be also increased through purification using lithium sulfide recrystallization.

Description

Method for producing lithium sulfide

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0106414, filed August 8, 2024, the entire disclosure of which is incorporated herein by reference.

[0003]

[0004] The present invention relates to a method for producing lithium sulfide.

[0005]

[0006] Lithium sulfide (Li2S) is a key raw material for the solid electrolyte used in all-solid-state batteries, a promising next-generation battery technology. It can also serve as the cathode active material for lithium-sulfur batteries. With the anticipated surge in demand for next-generation batteries, demand for Li2S is also expected to increase. Consequently, active research is underway into the commercial production of Li2S.

[0007]

[0008] Lithium sulfide (Li2S) is manufactured using lithium raw materials and sulfur raw materials. Lithium carbonate, lithium oxide, metallic lithium, lithium hydroxide, etc. are used as lithium raw materials, and sulfur raw materials include sulfur (Molten Sulfur), hydrogen sulfide (H2S), and carbon disulfide (C). S 2) etc. are used. Among these, the method of producing lithium sulfide by reacting lithium hydroxide monohydrate (LiOH·H2O) and hydrogen sulfide (H2S) is the most studied because the reaction conditions are relatively mild.

[0009]

[0010] Conventional synthetic methods using lithium hydroxide monohydrate (LiOH·H2O) include a dry method in which lithium hydroxide solids are directly brought into contact with hydrogen sulfide gas at high temperatures without using a solvent; a method in which lithium hydroxide is dissolved in a polar solvent and then reacted; and a wet method in which lithium hydroxide is dispersed within a non-polar solvent and reacted. The dry method has the advantage of not using a solvent, but there is a problem in that the raw materials may clump together, and the moisture generated as a byproduct may not drain away well, causing the synthesized lithium sulfide to react adversely and generate lithium hydroxide as an impurity. The wet method has the advantage of a low reaction temperature by dispersing the lithium raw material in a solvent, which promotes the reaction with hydrogen sulfide; however, there is a problem in that side reactions occur when some polar solvents are used.

[0011]

[0012] Meanwhile, the purity and particle size of lithium sulfide are important for use as a solid electrolyte raw material. If the lithium sulfide particle size is too large, unreacted lithium sulfide may be generated when synthesizing the solid electrolyte, and if the particles are too small, handling becomes difficult due to dust. Therefore, lithium sulfide particle size control technology for producing lithium sulfide (Li2S) with particles of appropriate size is very important. Milling of raw materials or lithium sulfide is usually used to control the particle size of lithium sulfide, but this method is difficult to commercialize in large quantities, and milling lithium sulfide can damage crystallinity, which can reduce its performance as a battery material raw material.

[0013]

[0014] Furthermore, lithium hydroxide monohydrate, used as a raw material, is easily converted to lithium carbonate by carbon dioxide when exposed to the atmosphere. Because lithium carbonate has a higher decomposition temperature than lithium hydroxide, the reaction temperature between lithium hydroxide and hydrogen sulfide alone does not convert it to lithium sulfide. Furthermore, lithium carbonate present within lithium sulfide can act as an impurity that degrades performance during the manufacture of solid electrolytes.

[0015]

[0016] Accordingly, research is needed on a method for producing high-purity lithium sulfide while solving the above-mentioned problems and controlling the particle size of the produced lithium sulfide.

[0017]

[0018] The present invention relates to a wet lithium sulfide production method, which can control particle size and also increase purity through a purification process utilizing recrystallization of lithium sulfide (Li2S) after converting lithium raw material and hydrogen sulfide into lithium sulfide (Li2S) in the presence of a solvent.

[0019]

[0020] The present invention provides a method for producing lithium sulfide, comprising the steps of: converting lithium hydroxide monohydrate into anhydrous lithium hydroxide, reacting the anhydrous lithium hydroxide with hydrogen sulfide in the presence of a solvent to produce lithium sulfide; a first filtration step (step 2) of dissolving the lithium sulfide in a solvent to produce a solution, and then removing insoluble matter through filtration to obtain a filtrate; a step (step 3) of concentrating the filtrate; a second filtration step (step 4) of filtering the concentrated filtrate to obtain a solid; and a step (step 5) of drying the solid.

[0021]

[0022] In addition, the present invention provides lithium sulfide manufactured according to the manufacturing method of the present invention.

[0023]

[0024] The method for producing lithium sulfide according to the present invention can produce high-purity lithium sulfide by controlling the particle size of lithium sulfide and minimizing impurities. More specifically, through a purification step including filtration and concentration steps, the particle size of lithium sulfide can be controlled, and high-performance lithium sulfide with reduced impurities can be produced.

[0025]

[0026] FIG. 1 is a graph showing the results of X-ray diffraction analysis (XRD) of lithium sulfide manufactured according to one embodiment and commercial lithium sulfide.

[0027]

[0028] In the present invention, terms such as first, second, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from another.

[0029] Additionally, the terms used herein are for the purpose of describing exemplary embodiments only and are not intended to limit the present invention.

[0030] Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0031] In this specification, the terms “comprise,” “include,” or “have” are intended to describe a feature, number, step, component, or combination thereof implemented, but do not exclude the possibility of one or more other features, numbers, steps, components, combinations, or additions thereof.

[0032] Additionally, in this specification, when each layer or element is referred to as being formed “on” or “over” each layer or element, it means that each layer or element is formed directly on each layer or element, or that other layers or elements may be additionally formed between each layer, on the object, or on the substrate.

[0033] The present invention is susceptible to various modifications and takes various forms. Specific embodiments are illustrated and described in detail below. However, this does not limit the invention to a specific disclosed form, but rather encompasses all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0034]

[0035] Hereinafter, the present invention will be described in detail.

[0036]

[0037] The present invention provides a method for producing lithium sulfide, comprising the steps of: converting lithium hydroxide monohydrate into anhydrous lithium hydroxide, reacting the anhydrous lithium hydroxide with hydrogen sulfide in the presence of a solvent to produce lithium sulfide; a first filtration step (step 2) of dissolving the lithium sulfide in a solvent to produce a solution, and then removing insoluble matter through filtration to obtain a filtrate; a step (step 3) of concentrating the filtrate; a second filtration step (step 4) of filtering the concentrated filtrate to obtain a solid; and a step (step 5) of drying the solid.

[0038]

[0039] The present invention can be divided into the reaction step of step 1 and the purification steps of steps 2 to 5. The inventors of the present invention have completed the present invention by confirming that the particle size of lithium sulfide produced by reacting a lithium raw material with hydrogen sulfide to produce lithium sulfide can be controlled while simultaneously reducing impurities through a series of purification steps including filtration, concentration, filtration, and drying.

[0040]

[0041] Step 1 of the present invention is a step of converting lithium hydroxide monohydrate into anhydrous lithium hydroxide, and reacting anhydrous lithium hydroxide with hydrogen sulfide in the presence of a solvent to produce lithium sulfide.

[0042]

[0043] Lithium hydroxide monohydrate has a lower decomposition temperature than other lithium salts, allowing for the synthesis of lithium sulfide under relatively mild conditions, making it suitable for use as a lithium precursor in the production of lithium sulfide. However, lithium hydroxide monohydrate is hygroscopic and, when exposed to the air, is rapidly converted to lithium carbonate (Li2CO3) by carbon dioxide (CO2). The converted lithium carbonate decomposes only at high temperatures, making it difficult to remove using conventional methods. Furthermore, it can remain as an impurity even after the production of lithium sulfide, adversely affecting the performance of solid electrolytes, such as a decrease in ionic conductivity.

[0044]

[0045] Accordingly, step 1 of the present invention includes a step of converting lithium hydroxide monohydrate, which is a lithium raw material, into anhydrous lithium hydroxide before the reaction between hydrogen sulfide and the lithium raw material. Preferably, in step 1, lithium hydroxide monohydrate can be converted into anhydrous lithium hydroxide under a temperature condition of 150°C to 450°C in the presence of an inert gas. When the temperature is less than 150°C, it is not easy to remove moisture from lithium hydroxide monohydrate, so that moisture in the raw material cannot sufficiently escape, which may cause adverse effects such as causing a reverse reaction during lithium sulfide synthesis, and when the temperature exceeds 450°C, the lithium hydroxide raw material may melt, so it is preferable to proceed within the above range. Preferably, the conversion of the anhydrous lithium hydroxide can be carried out at a temperature of 170°C or higher, 200°C or higher, 230°C or higher, 250°C or higher, or 270°C or higher, but not more than 420°C, not more than 400°C, not more than 380°C, not more than 360°C, or not more than 340°C.

[0046]

[0047] In addition, there is no particular limitation on examples of the above inert gas, but for example, nitrogen, argon, helium, and a mixed gas thereof can be used.

[0048]

[0049] Next, the present invention produces lithium sulfide by reacting the anhydrous lithium hydroxide with hydrogen sulfide in the presence of a solvent.

[0050]

[0051] As described above, the reaction between lithium hydroxide and hydrogen sulfide gas can proceed with or without a solvent. A solvent-free process has the advantage of eliminating the need for solvent removal or recovery steps. However, the removal of the reaction water generated by the acid-base reaction is difficult and the reaction temperature is high, making the use of a solvent advantageous from a process economic perspective.

[0052]

[0053] The solvent is not particularly limited, but when a single type of polar solvent is used, the thermal decomposition rate of the intermediate product LiSH may be slow, and a high thermal decomposition temperature may be required, which may cause a side reaction between the polar solvent and the lithium raw material, resulting in the generation of unintended impurities. Accordingly, it is preferable to use a nonpolar solvent having low reactivity with the raw material and high thermal stability. Specifically, the solvent may include a nonpolar aromatic hydrocarbon solvent and / or a nonpolar aliphatic hydrocarbon solvent, and more specifically, may include at least one selected from the group consisting of toluene, xylene, ethylbenzene, decalin, 1,2,3,4-tetrahydronaphthalene, hexane, pentane, 2-ethyl hexane, heptane, octane, decane, cyclohexane, methyl cyclohexane, hexene, heptene, and cyclohexene.

[0054]

[0055] In addition, the mass ratio of the lithium hydroxide monohydrate and the solvent may be used in a range of 1:5 to 1:20. When lithium hydroxide monohydrate and the solvent are used in the amounts within the above range, high dispersion of the raw material is induced, which is advantageous for controlling the particle size of the lithium sulfide produced. Preferably, lithium hydroxide and the solvent may be used in a mass ratio of 1:5.5 to 1:18, 1:6 to 1:16, or 1:6.5 to 1:14.

[0056]

[0057] Meanwhile, the anhydrous lithium hydroxide and hydrogen sulfide are manufactured into lithium sulfide through a gas-liquid phase reaction. At this time, the molar ratio of the anhydrous lithium hydroxide and the hydrogen sulfide may be 1:1 to 1:30. If the molar ratio of the hydrogen sulfide gas to the lithium hydroxide raw material is less than 1:1, the reactivity of the hydrogen sulfide and the anhydrous lithium hydroxide is low, so the reaction time is prolonged and the process efficiency may decrease, and if it exceeds 1:30, the process cost may increase due to the excessive supply of hydrogen sulfide gas, and the reaction occurs rapidly, making it difficult to smoothly discharge the by-product moisture. Preferably, the hydrogen sulfide gas may be first introduced so that the molar ratio of the anhydrous lithium hydroxide and the hydrogen sulfide gas is 1:1 to 1:25, or 1:1 to 1:20, or 1:1 to 1:15.

[0058]

[0059] Additionally, in step 1, the reaction of the anhydrous lithium hydroxide and hydrogen sulfide may proceed at a temperature of 120°C to 300°C. More specifically, it may proceed at a temperature of 125°C or higher, 130°C or higher, 135°C or higher, or 140°C or higher, but not more than 250°C, not more than 230°C, not more than 200°C, or not more than 170°C.

[0060]

[0061] Meanwhile, the reaction of Step 1 can proceed while removing water. By removing the water generated by the reaction of the lithium hydroxide raw material and hydrogen sulfide gas from the reaction system, the reaction can be promoted by preventing the phenomenon of clumping due to moisture absorption of lithium hydroxide. In this way, a technique widely known in the art can be utilized as a method for removing water in the reaction step. For example, water can be removed by condensing the vaporous water generated together with the hydrogen sulfide gas using a condenser to remove it in a liquid form and then reintroducing the gaseous hydrogen sulfide into the reactor. If even a small amount of water is not properly removed during the above process, the lithium sulfide may be converted back to lithium hydroxide due to a reverse reaction, and lithium hydroxide may remain in the reaction product containing lithium sulfide. In this way, Step 1 of the present invention can be performed by observing whether water is generated and proceeding until no water is generated.

[0062]

[0063] In addition, the reactors available in step 1 are not particularly limited, but examples thereof include a batch reactor, a continuous stirred-tank reactor (CSTR), a flow reactor, and a fluidized reactor.

[0064]

[0065] In the present invention, after producing lithium sulfide through the above reaction step, the lithium sulfide purification step of steps 2 to 5 of the present invention is performed.

[0066]

[0067] Step 2 of the present invention is a first filtration step in which a solution is prepared by dissolving the lithium sulfide in a solvent, and then insoluble matters are removed through filtration to obtain a filtrate. The first filtration step is a step in which a solution containing the lithium sulfide is prepared, and then the solution is passed through a filter to separate insoluble matters such as lithium carbonate that are not dissolved in the solution from a liquid phase containing the lithium sulfide, thereby obtaining a filtrate.

[0068]

[0069] The solvent is not particularly limited as long as it is a solvent that selectively dissolves lithium sulfide while not dissolving impurities, but may include, for example, one or more selected from the group consisting of methanol, ethanol, propanol, isopropanol, butanol, isobutanol, and pentanol.

[0070]

[0071] Additionally, the insoluble matter removed through the above filtration may be lithium carbonate, for example.

[0072]

[0073] Additionally, the filter applied in step 2 of the present invention may be a filter commonly used in the art that can separate liquid filtrate and solid insoluble matter. Furthermore, the first filtration step may be conducted at atmospheric pressure, and a vacuum pump may be provided or a connected filtration device may be used to enhance the filtration speed.

[0074]

[0075] Next, a step (step 3) of concentrating the filtrate, which is a solution containing lithium sulfide from which the insoluble matter has been removed, is performed. Through step 3 of the present invention, as the solvent evaporates, the lithium sulfide dissolved in the filtrate undergoes recrystallization and grows into crystals. In this way, by controlling the concentration conditions in step 3 of the present invention, the growth rate of the lithium sulfide crystals can be controlled, and the particle size of the final lithium sulfide can be adjusted.

[0076]

[0077] Preferably, step 3 can be performed under temperature conditions of 40°C to 80°C for 1 to 15 hours. Specifically, step 3 can be performed under temperature conditions of 45°C or higher, 50°C or higher, 55°C or higher, or 60°C or higher, and 75°C or lower, 70°C or lower, or 65°C or lower. In addition, step 3 can be performed in the above-described temperature range for 2 to 14 hours, 3 to 12 hours, or 3 to 8 hours. Performing step 3 at the above-described temperature and time range facilitates particle size control of lithium sulfide, thereby obtaining lithium sulfide having a desired particle size distribution.

[0078]

[0079] Meanwhile, if necessary, the first filtration step of step 2 of the present invention and the concentration step of step 3 may be independently performed several times.

[0080]

[0081] Next, after step 3, a second filtration step (step 4) is performed to filter the concentrated filtrate to obtain a solid. As described above, lithium sulfide crystals grow in the concentrated filtrate and exist as a solid, and this is the step of obtaining this through the second filtration step. Meanwhile, the solid may include trace amounts of solvents, etc., along with lithium sulfide.

[0082]

[0083] The filter applied in the second filtration step can be any filter commonly used in the industry capable of separating solvents and solids. Furthermore, the second filtration step, like the first filtration step, can be conducted at atmospheric pressure, or a vacuum pump or connected filtration device can be used to enhance the filtration speed.

[0084]

[0085] Next, a step (step 5) of drying the solid obtained in step 4 is performed. By performing the drying step, trace amounts of solvent present in the solid can be removed.

[0086]

[0087] Preferably, step 5 can be carried out at a temperature of 80°C to 300°C. If carried out at a temperature lower than 80°C, the solvent may not be easily removed, and if carried out at a temperature higher than 300°C, there may be a problem of lithium sulfide degeneration or lowered process efficiency. More preferably, step 5 can be carried out at a temperature of 100°C or higher, 120°C or higher, 140°C or higher, 160°C or higher, or 180°C or higher, and 380°C or lower, 350°C or lower, 330°C or lower, 300°C or lower, 250°C or lower, or 230°C or lower.

[0088]

[0089] Additionally, step 5 may be performed for 12 to 48 hours, 15 to 40 hours, 20 to 35 hours, or 25 to 33 hours in the temperature range described above.

[0090]

[0091] According to one embodiment of the present invention, the average particle diameter (D) of lithium hydroxide monohydrate in step 1 50 ) is 50 um to 100 um, and the average particle size (D) of the manufactured lithium sulfide 50 ) can be 1 um to 30 um. In this specification, the average particle diameter (D 50 ) means the particle diameter at the 50% point of the cumulative distribution of particle counts according to particle size (particle diameter). The average particle diameter (D 50 ) can be measured using a laser diffraction scattering particle size distribution measuring device, and the particle size at the point where the cumulative particle number distribution according to particle size is 50% is calculated, and this is the average particle diameter (D 50 ) is defined as.

[0092] When the average particle size of lithium sulfide is controlled within the above range, it is easy to synthesize a solid electrolyte manufactured using lithium sulfide as a raw material, and the purity and ionic conductivity can be increased. Preferably, the average particle size (D of the lithium hydroxide monohydrate) 50 ) may be 55 um or more, or 60 um or more, and 90 um or less, or 80 um or less, and the average particle size (D) of the lithium sulfide 50 ) may be 2 um or more, 3 um or more, 4 um or more, 5 um or more, 6 um or more, and 29 um or less, 28 um or less, 27 um or less, or 26 um or less.

[0093]

[0094] In addition, according to one embodiment of the present invention, the average particle size reduction rate calculated by the following equation 1 may be 50 to 99%, and specifically, 55% to 95%, 60% to 90%:

[0095] [Formula 1]

[0096] Average particle size reduction rate = [(D 50,i - D 50,f ) / D 50,i ] * 100

[0097] In the above equation 1,

[0098] D 50,i is the average particle diameter (D) of lithium hydroxide monohydrate 50 ) is the value,

[0099] D 50,f is the average particle size of lithium sulfide (D 50 ) is the value.

[0100]

[0101] According to the method for producing lithium sulfide of the present invention described above, the produced lithium sulfide can contain lithium carbonate in an amount of 3,500 ppm or less based on the mass of the produced lithium sulfide as a result of IC (Ion chromatography) analysis. Preferably, the produced lithium sulfide can contain lithium carbonate in an amount of 3,000 ppm or less, 2,500 ppm or less, 2,000 ppm or less, 1,500 ppm or less, or 1,000 ppm or less based on the mass of the lithium sulfide.

[0102]

[0103] Meanwhile, the present invention provides lithium sulfide manufactured according to the above-described manufacturing method. As described above, the lithium sulfide of the present invention has a particle size controlled to a certain level, an amount of carbonate impurities that are not easy to remove is 3,500 ppm or less, and an average particle size (D 50 ) is 1 um to 30 um, and can achieve excellent performance when manufacturing solid electrolyte materials.

[0104]

[0105] Hereinafter, the functions and effects of the invention will be described in more detail through specific examples. However, these examples are provided merely as examples of the invention and do not define the scope of the invention.

[0106]

[0107] [Example]

[0108] Example 1

[0109] 50 g of lithium hydroxide monohydrate was placed in a reactor, and dried at 300°C for 8 hours while injecting N2 to obtain anhydrous lithium hydroxide (LiOH). 500 g of xylene was added to the reactor containing the purified anhydrous lithium hydroxide (LiOH), and while stirring, hydrogen sulfide (H2S) was introduced so that the molar ratio of anhydrous lithium hydroxide and hydrogen sulfide was 1:1, and the reaction was carried out at 150°C. The moisture generated during the reaction was removed by liquefaction through a condenser while being discharged to the top of the reactor, and the reaction was carried out until no more moisture was produced, and then solid lithium sulfide was obtained.

[0110] A purification step was performed on the lithium sulfide obtained above. Specifically, lithium sulfide was dissolved in ethanol at a mass ratio of lithium sulfide to ethanol of 1:10. Thereafter, the ethanol-lithium sulfide solution of the first filtration step was filtered to remove solid insoluble matter. Thereafter, the filtrate was concentrated by increasing the temperature at 60°C for 3 hours. When crystals were formed in the solution after concentration, filtration of the second filtration step was performed. The residual solid was dried at 200°C for 30 hours in a N2 environment to obtain purified lithium sulfide. Subsequently, XRD analysis results confirmed that lithium sulfide was synthesized without other impurities.

[0111]

[0112] Example 2

[0113] Lithium sulfide was prepared in the same manner as in Example 1, except that after filtering the ethanol-lithium sulfide solution, the filtrate was concentrated at 60°C for 5 hours.

[0114]

[0115] Example 3

[0116] Lithium sulfide was prepared in the same manner as in Example 1, except that after filtering the ethanol-lithium sulfide solution, the filtrate was concentrated at 60°C for 8 hours.

[0117]

[0118] Comparative Example 1

[0119] After the reaction step, lithium sulfide was prepared in the same manner as in Example 1, except that the purification step was not performed.

[0120]

[0121] Comparative Example 2

[0122] In the purification step, lithium sulfide was prepared in the same manner as in Example 1, except that solid impurities were not removed through filtration prior to concentration.

[0123]

[0124] Experimental example

[0125] (1) Size analysis

[0126] The particle size (D) of lithium hydroxide monohydrate and manufactured lithium sulfide used in the examples and comparative examples was measured using a laser diffraction particle size measuring device. 10 , D 50 , D 90 ) was measured.

[0127] Additionally, the average particle size reduction rate was calculated according to Equation 1 below.

[0128] [Formula 1]

[0129] Average particle size reduction rate = [(D 50,i - D 50,f ) / D 50,i ] * 100

[0130] In the above equation 1,

[0131] D 50,i is the average particle diameter (D) of lithium hydroxide monohydrate 50 ) is the value,

[0132] D 50,f is the average particle size of lithium sulfide (D 50 ) is the value.

[0133]

[0134] (2) Purity analysis

[0135] The unreacted lithium hydroxide and lithium carbonate (Li2CO3) contents based on the mass of lithium sulfide prepared in the above examples and comparative examples were measured using ion chromatography (IC). The IC analyzer used was Thermofisher's ICS-6000.

[0136]

[0137] The above measurement results are shown in Table 1 below.

[0138]

[0139] Item Li2CO3 content (ppm) Particle size (μm) Average particle size reduction rate (%) D 10 D 50 D 90 Raw material (LiOH·H2O) 3,900 1367 270 - Example 1 965 471 289.6 Example 2 988 71 42 479.1 Example 3 989 10 265 161.2 Comparative example 13,700 1264 2624.5 Comparative example 23,655 381 188.1

[0140] As can be confirmed in Table 1 above, the results of particle size analysis of lithium sulfide show that the longer the concentration time of the ethanol-lithium sulfide solution, the larger the crystal size, and it was confirmed that the Li2CO3 impurity in the lithium sulfide can be removed through the filtering step during the concentration process. Meanwhile, in the case of Comparative Example 1, which did not go through a lithium sulfide purification process, it was confirmed that the size of the manufactured lithium sulfide particles was similar to the particle size of the raw material lithium hydroxide monohydrate, and in the case of Comparative Example 2, which did not perform filtering, it was confirmed that a lot of the impurity Li2CO3 remained.

[0141]

Claims

1. A step of converting lithium hydroxide monohydrate into anhydrous lithium hydroxide and reacting anhydrous lithium hydroxide with hydrogen sulfide in the presence of a solvent to produce lithium sulfide (step 1); A first filtration step (step 2) of dissolving the lithium sulfide in a solvent to prepare a solution and then removing insoluble matter through filtration to obtain a filtrate; Step of concentrating the above filtrate (step 3); A second filtration step (step 4) of filtering the concentrated filtrate to obtain a solid; and Comprising a step of drying the above solid (step 5), Method for producing lithium sulfide.

2. In paragraph 1, In step 1, lithium hydroxide monohydrate is converted into anhydrous lithium hydroxide under temperature conditions of 150°C to 450°C in the presence of an inert gas. Method for producing lithium sulfide.

3. In paragraph 1, The solvent of step 1 comprises at least one selected from the group consisting of toluene, xylene, ethylbenzene, decalin, 1,2,3,4-tetrahydronaphthalene, hexane, pentane, 2-ethyl hexane, heptane, octane, decane, cyclohexane, methyl cyclohexane, hexene, heptene and cyclohexene. Method for producing lithium sulfide.

4. In paragraph 1, In step 1, the molar ratio of anhydrous lithium hydroxide and hydrogen sulfide is 1:1 to 1:30, Method for producing lithium sulfide.

5. In paragraph 1, In step 1, the reaction of anhydrous lithium hydroxide and hydrogen sulfide is carried out under temperature conditions of 120°C to 300°C. Method for producing lithium sulfide.

6. In paragraph 1, The solvent of step 2 comprises at least one selected from the group consisting of methanol, ethanol, propanol, isopropanol, butanol, isobutanol and pentanol. Method for producing lithium sulfide.

7. In paragraph 1, Step 3 is carried out for 1 to 15 hours under temperature conditions of 40 to 80°C. Method for producing lithium sulfide.

8. In paragraph 1, Step 5 is carried out under temperature conditions of 80 ℃ to 300 ℃. Method for producing lithium sulfide.

9. In paragraph 1, The average particle size (D) of lithium hydroxide monohydrate in step 1 50 ) is 50 um to 100 um, The average particle size of manufactured lithium sulfide (D 50 ) is 1 um to 30 um, Method for producing lithium sulfide.

10. In paragraph 9, The average particle size reduction rate calculated by the following equation 1 is 50 to 99%, Method for producing lithium sulfide: [Formula 1] Average particle size reduction rate = [(D 50,i - D 50,f ) / D 50,i ] * 100 In the above equation 1, D 50,i is the average particle diameter (D) of lithium hydroxide monohydrate 50 ) is the value, D 50,f is the average particle size of lithium sulfide (D 50 ) is the value.

11. In paragraph 1, According to the IC (Ion chromatography) analysis results, the mass of the manufactured lithium sulfide contains lithium carbonate of 3,500 ppm or less. Method for producing lithium sulfide.

12. Lithium sulfide manufactured by a manufacturing method according to any one of claims 1 to 11.

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