Method of preparing lithium sulfide

Abstract

To provide an efficient method of preparing high-purity lithium sulfide.SOLUTION: In a method for preparing lithium sulfide, a solid sulfur layer and a lithium source layer are sequentially arranged in a reactor. A gas feed is injected into the reactor in a single direction to obtain a lithium sulfide-containing product. The lithium sulfide-containing product is dissolved in an anhydrous solvent to form a lithium sulfide-containing solution. Lithium sulfide is separated from the lithium sulfide-containing solution. The gas feed sequentially passes through the solid sulfur layer and the lithium source layer, such that high-purity lithium sulfide may be efficiently prepared.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for producing lithium sulfide, and more particularly to a method for producing high purity lithium sulfide. [Background technology]

[0002] Recently, secondary batteries have been widely applied and developed as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptops, as well as vehicles such as hybrid cars and electric cars. As secondary batteries, lithium secondary batteries have been actively developed and applied due to their high operating voltage and energy density per unit weight, as well as their advantages in terms of charging speed and weight reduction.

[0003] Among secondary batteries, all-solid batteries that use solid electrolytes are highly safe because they do not contain flammable liquid electrolytes. In addition, the energy density and lifespan of all-solid batteries are higher than those of conventional secondary batteries that use liquid electrolytes. All-solid-state batteries have recently been actively researched due to their characteristics of high energy density and long lifespan.

[0004] Sulfide-based solid electrolytes have high lithium ion conductivity and are safe over a wide voltage range. 2 SP 2 S 5、 Li 2 SP 2 S 5 -LiCl etc. and is produced from lithium sulfide.

[0005] However, lithium sulfide cannot be produced from natural minerals and must be produced synthetically. In the synthesis process of lithium sulfide, if metallic lithium is used as the lithium source, there is a problem in terms of cost, and if lithium hydroxide is used, there is a problem of reduced reaction efficiency and side reactions. In addition, hydrogen sulfide (H 2Since lithium sulfide is toxic and difficult to handle, there is a need to design a process for efficiently producing high-purity lithium sulfide. Summary of the Invention [Problem to be solved by the invention]

[0006] One object of the present disclosure is to provide an efficient method for producing high purity lithium sulfide. [Means for solving the problem]

[0007] In a method for producing lithium sulfide according to an exemplary embodiment, a solid sulfur layer and a lithium source layer are sequentially disposed in a reactor, a gas is unidirectionally injected into the reactor to obtain a lithium sulfide-containing product, the lithium sulfide-containing product is dissolved in an anhydrous solvent to form a lithium sulfide-containing solution, and lithium sulfide is separated from the lithium sulfide-containing solution.

[0008] In some embodiments, the gas can be injected into one end of the reactor and passed sequentially through the solid sulfur layer and the lithium source layer.

[0009] In some embodiments, the lithium source layer can include at least one of lithium hydroxide, lithium hydroxide hydrate, lithium oxide, and lithium oxide hydrate.

[0010] In some embodiments, the lithium source contained in the lithium source layer may be recovered from waste positive electrode material of lithium secondary batteries.

[0011] In some embodiments, the ratio of the total moles of lithium atoms contained in the lithium source layer to the total moles of sulfur atoms contained in the solid sulfur layer may be 1-3.

[0012] In some embodiments, the gas may be free of oxygen and moisture.

[0013] In some embodiments, the gas may include nitrogen, hydrogen, or a nitrogen-hydrogen mixture.

[0014] In some embodiments, the gas includes the nitrogen-hydrogen mixed gas, and the volume ratio of nitrogen in the nitrogen-hydrogen mixed gas may be 30 vol % to 100 vol %.

[0015] In some embodiments, the reaction temperature in the reactor may be from 300°C to 500°C.

[0016] In some embodiments, the reaction pressure in the reactor may be from 0.1 bar to 5 bar.

[0017] In some embodiments, the anhydrous solvent can include a solvent having a water content of 0.5% or less.

[0018] In some embodiments, the anhydrous solvent can include at least one of absolute ethanol, acetone, ethyl acetate, dimethylsulfoxide, and dimethylformamide.

[0019] In some embodiments, separating lithium sulfide from the lithium sulfide-containing solution can include evaporating off the anhydrous solvent.

[0020] In some embodiments, the reactor can include a first reactor and a second reactor.

[0021] In some embodiments, the solid sulfur layer is disposed in the first reactor and the lithium source layer is disposed in the second reactor, and the gas can be supplied from the first reactor to the second reactor to sequentially contact the solid sulfur layer and the lithium source layer. Effect of the Invention

[0022] According to the exemplary embodiment, a solid sulfur layer and a lithium source layer are sequentially placed in a reactor, and gas is injected in a single direction to sequentially contact the layers, thereby producing high purity lithium sulfide under mild conditions.

[0023] According to an exemplary embodiment, high purity lithium sulfide can be obtained at low cost and in an environmentally friendly manner by using a lithium source generated during the processing of waste batteries.

[0024] According to an exemplary embodiment, the solid sulfur is obtained from a by-product generated after refining oil processing, so that lithium sulfide can be produced in an environmentally friendly manner. In addition, the solid sulfur is easy to control and does not directly contact harmful gases with workers, so that lithium sulfide can be produced efficiently.

[0025] According to the exemplary embodiment, lithium sulfide can be efficiently separated using anhydrous solvents without side reactions, with reduced production time. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 is a schematic process flow diagram illustrating a method for producing lithium sulfide in accordance with an exemplary embodiment. [Diagram 2] FIG. 2 is a schematic process flow diagram illustrating a method for producing lithium sulfide in accordance with an exemplary embodiment. [Diagram 3] FIG. 3 is a schematic process flow diagram illustrating a method for producing lithium sulfide according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Embodiments of the present disclosure provide, for example, a method for producing lithium sulfide in high purity and yield from solid sulfur and lithium sources.

[0028] DETAILED DESCRIPTION OF THE DRAWINGS In the following, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings, which are illustrative only, and the present disclosure is not limited to the specific embodiments illustratively described.

[0029] 1 is a schematic process flow diagram for illustrating a method for producing lithium sulfide according to an exemplary embodiment. FIG. 2 is a schematic process flow diagram for illustrating a method for producing lithium sulfide according to an exemplary embodiment.

[0030] Referring to FIG. 1, a solid sulfur layer and a lithium source layer can be formed sequentially in a reactor (eg, step S10).

[0031] Referring to FIG. 2, the reactor 100 may include a solid sulfur layer 110 and a lithium source layer 120 facing a gas supply section 140 and a product collection section 150 .

[0032] For example, as shown in Figure 2, a solid sulfur layer 110 and a lithium source layer 120 can be packed in a reactor 100 in a sequential manner, such that the gas can pass through the layers in sequence.

[0033] The arrangement of the solid sulfur layer 110 and the lithium source layer 120 is not particularly limited. For example, the solid sulfur layer 110 and the lithium source layer 120 may be arranged in separate spaces, or may be arranged in the same space separated by a separation film. For example, the solid sulfur layer 110 and the lithium source layer 120 may be in contact with each other by contacting a separation film. In some embodiments, the solid sulfur layer 110 and the lithium source layer 120 may be in direct contact with each other without a separation film.

[0034] In an exemplary embodiment, the solid sulfur layer 110 and the lithium source layer 120 can be spaced apart from each other, allowing a gas flow to be generated and lithium sulfide to be efficiently produced.

[0035] For example, the solid sulfur layer 110 and the lithium source layer 120 can be separated to form an air layer or a bead layer of a non-reactive material between the solid sulfur layer 110 and the lithium source layer 120. The air layer or the bead layer of a non-reactive material facilitates the flow of gas and helps the lithium source layer to contact the gas.

[0036] For example, it is not necessary to include a reactive material layer between the solid sulfur layer 110 and the lithium source layer 120. The inclusion of a reactive material layer may result in a change in the product or an increase in the production of impurities, and an increase in the reaction time.

[0037] After the solid sulfur layer 110 and the lithium source layer 120 are sequentially arranged, gas can be injected unidirectionally. By injecting gas unidirectionally from the gas supply unit 140 into one end of the reactor 100, lithium sulfide-containing products can be collected from the other end of the reactor 100 (e.g., step S20).

[0038] In an exemplary embodiment, the gas may be injected into one end of the reactor 100 and passed sequentially through the solid sulfur layer 110 and the lithium source layer 120 .

[0039] The gas can be injected in one direction to create a unidirectional flow.

[0040] For example, if the gas is injected from both directions into the reactor 100 (e.g., from the solid sulfur layer to the lithium source layer and from the lithium source layer to the solid sulfur layer), the gas flow may not be generated or the gas residence time may be long, making it impossible to produce high-purity lithium sulfide.

[0041] If the gas does not pass through the solid sulfur layer 110 and the lithium source layer 120 in sequence, lithium sulfide may not be produced or the purity of the produced lithium sulfide may be significantly reduced.

[0042] For example, if the lithium source layer 120 and the solid sulfur layer 110 are arranged in this order and gas passes through them in this order, no reaction may occur and lithium sulfide may not be produced.

[0043] For example, the other end of the reactor 100 may be in a state where it is integrally connected to the reactor 100 or in a state where it is separate from the reactor 100. For example, the other end may be connected to the reactor 100 through a tube in a separate space. Alternatively, the other end may be connected to the reactor and be merged.

[0044] The other end may include, for example, a product collecting section 150. The product collecting section 150 may be located on the opposite side of the gas supplying section 140 across the solid sulfur layer 110 and the lithium source layer 120 disposed in the reactor 100.

[0045] In an exemplary embodiment, the product collecting section 150 may be located on the opposite side to the gas supplying section 140. The gas may be passed through the solid sulfur layer 110 and the lithium source layer 120 in sequence to form a lithium sulfide-containing product by gas-phase synthesis. In the product collecting section 150, the lithium sulfide-containing product may be obtained.

[0046] The lithium sulfide-containing product can be dissolved in an anhydrous solvent to form a lithium sulfide-containing solution (eg, step S30).

[0047] For example, the lithium sulfide-containing solution may contain 20% by weight or more of lithium sulfide based on the total weight.

[0048] In an exemplary embodiment, the lithium sulfide-containing solution may contain 30% or more by weight of lithium sulfide based on the total weight of the solution. The amount of lithium sulfide contained in the solution may vary depending in part on the reaction conditions.

[0049] The lithium sulfide dissolved in the anhydrous solvent can be separated from the anhydrous solvent (eg, step S40).

[0050] For example, lithium sulfide can be separated by evaporating the anhydrous solvent used to form the lithium sulfide-containing solution.

[0051] In exemplary embodiments, the lithium sulfide remaining after separation of the anhydrous solvent may have a purity of 95% or greater. For example, the lithium sulfide remaining after evaporation of the anhydrous solvent may have a purity of 97% or greater, 98% or greater, 99% or greater, 99.5% or greater, 99.8% or greater, or 99.9% or greater. The purity may be as measured by XRD Rietveld refinement.

[0052] In an exemplary embodiment, a solid sulfur layer 110 can be disposed within the reactor 100 such that the gas passes through the solid sulfur layer 110. The solid sulfur contained in the solid sulfur layer 110 can be any form of solid sulfur, regardless of morphology, particle size, particle distribution, and the like.

[0053] The solid sulfur may be, for example, a material produced in a desulfurization process of petroleum, crude oil, etc. For example, the desulfurization process may include wet desulfurization in which the sulfur is physically absorbed using sodium hydroxide, polyethylene glycol, potassium carbonate, ferrous chloride, etc.; dry desulfurization in which the sulfur is chemically absorbed using an adsorbent such as silica gel; and biological desulfurization using sulfur-oxidizing bacteria such as Thiobacillus.

[0054] By using solid sulfur as a by-product produced in the desulfurization process, lithium sulfide can be produced in an environmentally friendly and low-cost manner. In addition, solid-state sulfur is easy to control and can be sequentially arranged in the reactor, which can reduce the generation of harmful gases in the lithium sulfide production process.

[0055] In an exemplary embodiment, the lithium source can include at least one of lithium hydroxide, lithium hydroxide hydrate, lithium oxide, and lithium oxide hydrate.

[0056] In one embodiment, the lithium source may include lithium hydroxide hydrate or lithium oxide hydrate.

[0057] The lithium hydroxide, lithium hydroxide hydrate, lithium oxide, or lithium oxide hydrate may be present separately or in a mixed state in the lithium source layer 120. For example, a powder of lithium hydroxide, lithium hydroxide hydrate, lithium oxide, or lithium oxide hydrate may be used. When the lithium hydroxide, lithium hydroxide hydrate, lithium oxide, lithium oxide hydrate, or a combination thereof is contained in a powder form, the average particle size may be 2 mm or less.

[0058] By including at least one of lithium hydroxide hydrate or lithium oxide hydrate as the lithium source, the production of lithium sulfide can be facilitated without the input of additional reactants.

[0059] In an exemplary embodiment, the lithium source included in lithium source layer 120 may be a lithium source recovered from waste cathode material.

[0060] For example, the lithium source can be obtained by preparing a waste cathode active material mixture from a waste cathode material, reacting the waste cathode active material mixture with a gas to form a pre-precursor mixture, and then selectively recovering a lithium precursor from the pre-precursor mixture.

[0061] For example, the waste positive electrode material may include a positive electrode current collector (eg, aluminum (Al)) and a positive electrode active material layer, and the positive electrode active material layer may include a positive electrode active material, a conductive material, and a binder.

[0062] The conductive material may include, for example, a carbon-based material such as graphite, carbon black, graphene, carbon nanotubes, etc. The binder may include a resin material such as polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, etc.

[0063] For example, the waste cathode active material mixture can be produced by pulverization. For example, the waste cathode active material mixture can be heat-treated, and impurities contained in the waste cathode active material mixture can be removed or reduced by the heat treatment. This can improve the purity of the preliminary precursor mixture, and can improve the purity of the recovered lithium precursor.

[0064] For example, the gas reacting with the waste positive electrode active material mixture may be a reducing gas. The preliminary precursor mixture produced by reacting with the waste positive electrode active material mixture may include, for example, lithium hydroxide, lithium oxide, a transition metal, or a transition metal oxide.

[0065] The pre-precursor mixture can be washed with water to recover the lithium precursor, which can be separated from the transition metal by the water washing process. The lithium precursor can include lithium hydroxide or a hydrate thereof.

[0066] The recovered lithium precursor can be crystallized, such as by a dry process.

[0067] The lithium source can be a material recovered from waste positive electrode material, and lithium sulfide can be produced in an environmentally friendly manner.

[0068] In an exemplary embodiment, reactor 100 can include a reactor that allows for unidirectional gas injection. For example, reactor 100 can include a tubular reactor, a column reactor, a stirred tank reactor, a fluidized bed reactor, etc.

[0069] In an exemplary embodiment, the reactor 100 can include a fluidized bed reactor. The reactor body can include a stepped or gradual increase in diameter from the bottom to promote gas-solid mixing.

[0070] For example, when a fluidized bed reactor is used as the reactor 100 used in the lithium sulfide production process, a lithium source can be recovered from the waste cathode material and lithium sulfide can be produced in the same reactor. Therefore, the production efficiency of lithium sulfide can be improved.

[0071] In addition, when a fluidized bed reactor is used, the product collector 150 may be combined with the fluidized bed reactor, and the diameter may be gradually increased with a certain inclination angle from the gas supply 140 to the product collector 150. The change in diameter may improve the fluidization efficiency and the yield of lithium sulfide.

[0072] In an exemplary embodiment, the ratio of the total moles of lithium atoms contained in the lithium source layer 120 to the total moles of sulfur atoms contained in the solid sulfur layer 110 may be 1-3.

[0073] In some embodiments, the ratio of the total moles of lithium atoms contained in the lithium source layer 120 to the total moles of sulfur atoms contained in the solid sulfur layer 110 may be 1.2 to 2.8, 1.4 to 2.6, or 1.5 to 2.5. The molar ratio of lithium atoms and sulfur atoms falls within the above ranges, and lithium sulfide can be produced.

[0074] The gases injected into the reactor can include, for example, hydrogen, nitrogen-hydrogen mixtures, inert gases such as argon, nitrogen, helium, and the like.

[0075] In an exemplary embodiment, the gas may be free of oxygen and moisture, which may reduce the generation of impurities.

[0076] In an exemplary embodiment, the gas may include nitrogen, hydrogen, or a nitrogen-hydrogen mixture. For example, the gas may include nitrogen, hydrogen, nitrogen-hydrogen, nitrogen-argon gas, hydrogen-argon gas, etc.

[0077] In an exemplary embodiment, the gas may include a nitrogen-hydrogen mixed gas, and the volume ratio of nitrogen in the nitrogen-hydrogen mixed gas may be between 30 vol% and 100 vol%.

[0078] In an exemplary embodiment, the temperature of the step of injecting the gas to obtain the lithium sulfide-containing product may be between 300° C. and 500° C. In some embodiments, the temperature may be between 300° C. and 450° C.

[0079] If the temperature is less than 300° C., the reaction may not be activated even when the gas contacts the solid sulfur, or the activation level may be low, resulting in a low yield of lithium sulfide, and side reactions may occur, resulting in a low purity of lithium sulfide.If the temperature exceeds 500° C., a constant gas flow rate cannot be maintained, resulting in a low yield of lithium sulfide, or the produced lithium sulfide may solidify, resulting in a low yield.

[0080] In an exemplary embodiment, the pressure of the step of injecting the gas to obtain the lithium sulfide-containing product may be between 0.1 bar and 5 bar.

[0081] The pressure can be close to atmospheric pressure or can be maintained somewhat above atmospheric pressure depending on the amount of gas injected. In some embodiments, the pressure can be between 0.5 bar and 4 bar, between 1 bar and 3 bar. In the pressure range, lithium sulfide can be produced in high purity.

[0082] In an exemplary embodiment, the reaction time for the step of injecting a gas to obtain a lithium sulfide-containing product may be less than 5 hours.

[0083] In some embodiments, the reaction time of the step of injecting the gas to obtain the lithium sulfide-containing product may be 0.5 to 4 hours, or 1 to 4 hours. The reaction time can be shortened by injecting the gas in a single direction, and lithium sulfide can be produced efficiently. The reaction time can be adjusted in part by the reaction temperature, and can be adjusted within the above range.

[0084] For example, if the reaction time is long, sulfur compounds may be produced in addition to lithium sulfide.

[0085] The lithium sulfide-containing product may contain impurities other than lithium sulfide.

[0086] As the anhydrous solvent, a solvent capable of dissolving lithium sulfide can be used, and impurities that are not soluble in the anhydrous solvent can be removed. For example, among the compounds produced after the reaction, those that are not soluble in the anhydrous solvent remain in the filter, and the remaining compounds can be separated and removed.

[0087] In an exemplary embodiment, the anhydrous solvent can include a solvent having a water content of 0.5% or less.

[0088] For example, the anhydrous solvent may include anhydrous ethanol, acetone, ether, dimethylformamide, dimethylacetamide, acetonitrile, dichloromethane, diethylamine, dimethylsulfoxide, hexane, cyclohexane, ethyl acetate, isopropyl alcohol, toluene, N-methyl caprolactam, and N-methylpyrrolidone.

[0089] In an exemplary embodiment, the anhydrous solvent can include at least one of absolute ethanol, acetone, ethyl acetate, dimethylsulfoxide, and dimethylformamide.

[0090] In an exemplary embodiment, lithium sulfide can be separated from the lithium sulfide-containing solution by evaporation of the anhydrous solvent.

[0091] For example, lithium sulfide can be purified and separated without side reactions by dissolving lithium sulfide in an anhydrous solvent and removing the anhydrous solvent by evaporation. For example, if an anhydrous solvent is not used, lithium sulfide may re-react with moisture contained in the solvent to produce sulfate, which may reduce the purity and yield of lithium sulfide.

[0092] FIG. 3 is a schematic process flow diagram illustrating a method for producing lithium sulfide according to some embodiments.

[0093] Referring to FIG. 3, the reactor 100 can include a first reactor 100a and a second reactor 100b.

[0094] The first reactor 100a and the second reactor 100b may be the same or different, and may be the same as the reactors described above.

[0095] The first reactor 100a can be connected to a gas supply 140, and the second reactor 100b can be connected to a product collection section 150. The first reactor 100a and the second reactor 100b can be connected to each other.

[0096] The method of connecting the first reactor 100a and the second reactor 100b is not particularly limited, and may include any connecting method as long as the gas, reactants, etc. are not exposed and the reaction is not changed.

[0097] The first reactor 100a and the second reactor 100b are connected to each other, so that the gas supplied to the first reactor 100a can be supplied to the second reactor 100b.

[0098] The first reactor 100a and the second reactor may be arranged in the same direction. A gas may be supplied unidirectionally to the first reactor 100a through a gas supply unit 140. The gas may be supplied in a direction toward the second reactor 100b connected to the first reactor 100a, forming a unidirectional gas flow from the first reactor 100a to the second reactor 100b.

[0099] In an exemplary embodiment, the solid sulfur layer 110 may be disposed in a first reactor 100a and the lithium source layer 120 may be disposed in a second reactor 100b.

[0100] For example, the solid sulfur layer 110 in the first reactor 100a and the lithium source layer 120 in the second reactor 100b may be adjacent to each other depending on the position in the reactor, or the solid sulfur layer 110 in the first reactor 100a and the lithium source layer 120 in the second reactor 100b may be disposed apart from each other by a certain distance or more.

[0101] After the layers are in place, gas can be supplied to sequentially contact the solid sulfur layer 110 and the lithium source layer 120 .

[0102] Even though the solid sulfur layer 110 and the lithium source layer 120 are in physically separate reactors, lithium sulfide can still be produced efficiently by unidirectional gas flow.

[0103] In an exemplary embodiment, a lithium sulfide-containing product as described above can be obtained in product collection 150 and dissolved in an anhydrous solvent to form a lithium sulfide-containing solution as described above.

[0104] In an exemplary embodiment, the deposition of the solid sulfur layer 110 and the lithium source layer 120 may be solvent-free. For example, the solid sulfur layer 110 and the lithium source layer 120 may be solvent-free, and an anhydrous solvent may be used for the lithium sulfide-containing product in the product collection portion 150.

[0105] Since the solid sulfur layer 110 and the lithium source layer 120 do not contain organic solvents during the manufacturing process, and the anhydrous solvent used in the product collector 150 can be removed by evaporation, lithium sulfide can be manufactured in an environmentally friendly manner.

[0106] Below, preferred examples are presented to aid in understanding the present invention. However, these examples are merely illustrative of the present invention and do not limit the scope of the appended claims. It will be apparent to those skilled in the art that various changes and modifications to the examples are possible within the scope of the scope and technical spirit of the present invention, and it is natural that such changes and modifications also fall within the scope of the appended claims.

[0107] Example 1 In the reactor, solid sulfur and lithium hydroxide monohydrate (LiOH H 2O) were sequentially filled into the reactor. Nitrogen gas (100 vol%) was injected into the reactor so that the solid sulfur layer and the lithium hydroxide layer were in contact with each other in that order. While injecting nitrogen gas, the reaction pressure was maintained at 2 bar and the reaction temperature at 400°C for 1 hour. The reactor was transferred to a glove box, and the product located at the top was dissolved in absolute ethanol, and the material that was not dissolved in absolute ethanol was separated and removed. The absolute ethanol was then evaporated to obtain lithium sulfide.

[0108] Example 2 The reaction was carried out in the same manner as in Example 1, except that the reaction temperature was 350°C.

[0109] Example 3 The reaction was carried out in the same manner as in Example 1, except that the reaction temperature was 300°C.

[0110] Example 4 The reaction was carried out in the same manner as in Example 1, except that a mixed gas of nitrogen (50 vol%) / hydrogen (50 vol%) was used as the gas.

[0111] Comparative Example 1 The reaction was carried out in the same manner as in Example 1, except that the reactor was filled with lithium hydroxide and then solid sulfur, and the gas was brought into contact with the lithium hydroxide layer and then the solid sulfur layer.

[0112] Comparative Example 2 The reaction was carried out in the same manner as in Example 1, except that the reaction temperature was 120°C.

[0113] Comparative Example 3 The reaction was carried out in the same manner as in Example 1, except that the reaction temperature was 250°C.

[0114] Comparative Example 4 The reaction was carried out in the same manner as in Example 1, except that the reaction temperature was 600°C.

[0115] Comparative Example 5 The reaction was carried out in the same manner as in Example 1, except that the product was not dissolved in absolute ethanol and the subsequent steps were not carried out.

[0116] Experimental Example The products obtained in the above-mentioned Examples and Comparative Examples were subjected to XRD (X-Ray Diffraction) measurement and the crystal structure was analyzed by Rietveld refinement. The analysis results are shown in Table 1 below.

[0117] [Table 1]

[0118] Referring to Table 1, according to the embodiment, the product produced by contacting the gas with the solid sulfur layer and the lithium hydroxide layer in this order was dissolved in anhydrous ethanol and then separated. Therefore, high-purity lithium sulfide could be obtained with high efficiency. Also, according to the embodiment, high-purity lithium sulfide was obtained in the reaction temperature range of 300°C to 450°C.

[0119] In Comparative Example 1, in which the gas contacted the lithium hydroxide layer and the solid sulfur layer in this order, rather than the solid sulfur layer and the lithium hydroxide layer in this order, no reaction occurred.

[0120] In Comparative Example 2, in which the reaction temperature was low, most of the products were dissolved in anhydrous ethanol, and the recovery rate after separation and purification was high. However, it was confirmed that the reaction producing lithium sulfide hardly occurred, and the lithium sulfide content was less than 20%.

[0121] In Comparative Example 3, where the reaction temperature was increased compared to Comparative Example 2 but was less than 300°C, most of the product was dissolved in absolute ethanol, resulting in a high recovery rate after separation and purification, but the lithium sulfide content was less than 60%.

[0122] In Comparative Example 4, where the reaction temperature was high, the lithium sulfide content was 90% or more, but the lithium sulfide solidified in the product collection section, resulting in losses in the lithium sulfide recovery process. In addition, it was confirmed that some lithium hydroxide remained unreacted due to the high reaction temperature.

[0123] In Comparative Example 5, in which separation and purification was not performed, many sulfates were contained in addition to lithium sulfide, and the purity of lithium sulfide was low. [Explanation of symbols]

[0124] 100: Reactor 100a: First reactor 100b: Second reactor 110: Solid sulfur layer 120: Lithium source layer 140: Gas supply unit 150: Product collection section

Claims

1. sequentially disposing a solid sulfur layer and a lithium source layer in a reactor; injecting gas unidirectionally into the reactor to obtain a lithium sulfide-containing product; dissolving the lithium sulfide-containing product in an anhydrous solvent to form a lithium sulfide-containing solution; and separating lithium sulfide from the lithium sulfide-containing solution.

2. 2. The method for producing lithium sulfide according to claim 1, wherein the gas is injected into one end of the reactor and passes through the solid sulfur layer and the lithium source layer in sequence.

3. 2. The method of claim 1, wherein the lithium source layer comprises at least one of lithium hydroxide, lithium hydroxide hydrate, lithium oxide, and lithium oxide hydrate.

4. The method for producing lithium sulfide according to claim 3, wherein the lithium source contained in the lithium source layer is recovered from a waste positive electrode material of a lithium secondary battery.

5. 2. The method for producing lithium sulfide according to claim 1, wherein a ratio of a total mole number of lithium atoms contained in the lithium source layer to a total mole number of sulfur atoms contained in the solid sulfur layer is 1 to 3.

6. The method for producing lithium sulfide according to claim 1 , wherein the gas does not contain oxygen and moisture.

7. The method for producing lithium sulfide according to claim 1, wherein the gas comprises nitrogen, hydrogen, or a nitrogen-hydrogen mixed gas.

8. The method for producing lithium sulfide according to claim 7, wherein the gas contains the nitrogen-hydrogen mixed gas, and a volume ratio of nitrogen in the nitrogen-hydrogen mixed gas is 30 vol% to 100 vol%.

9. The method for producing lithium sulfide according to claim 1, wherein the reaction temperature in the reactor is 300°C to 500°C.

10. 2. The method for producing lithium sulfide according to claim 1, wherein the reaction pressure in the reactor is 0.1 bar to 5 bar.

11. 2. The method for producing lithium sulfide according to claim 1, wherein the anhydrous solvent contains a solvent having a water content of 0.5% or less.

12. 2. The method of claim 1, wherein the anhydrous solvent comprises at least one of anhydrous ethanol, acetone, ethyl acetate, dimethylsulfoxide, and dimethylformamide.

13. 2. The method for producing lithium sulfide according to claim 1, wherein the step of separating lithium sulfide from the lithium sulfide-containing solution comprises evaporating off the anhydrous solvent.

14. The method for producing lithium sulfide according to claim 1 , wherein the reactor includes a first reactor and a second reactor.

15. the solid sulfur layer is disposed in the first reactor and the lithium source layer is disposed in the second reactor; 15. The method for producing lithium sulfide according to claim 14, wherein the gas is supplied from the first reactor to the second reactor so as to sequentially contact the solid sulfur layer and the lithium source layer.

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