Method for preparing lithium sulfide

Abstract

In the method for preparing lithium sulfide, a solid sulfur layer and a lithium source layer are sequentially arranged in a reactor. And injecting gas into the reactor along a single direction to obtain a product containing lithium sulfide. The lithium sulfide-containing product is dissolved in an anhydrous solvent to form a lithium sulfide-containing solution. And separating the lithium sulfide from the solution containing the lithium sulfide. And the gas sequentially passes through the solid sulfur layer and the lithium source layer, so that high-purity lithium sulfide can be effectively prepared.

Description

Technical Field

[0001] The present invention relates to a method for preparing lithium sulfide, and more particularly to a method for preparing high-purity lithium sulfide. Background Art

[0002] In recent years, secondary batteries have been widely used and developed as power sources for portable electronic communication devices such as camcorders, mobile phones, and laptop computers, and vehicles such as hybrid cars and electric cars. Among secondary batteries, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous in terms of charging speed and light weight, and are therefore being actively developed and applied.

[0003] All-solid batteries using solid electrolytes in secondary batteries do not contain flammable liquid electrolytes, so they are safe. In addition, the energy density and life of all-solid batteries are higher than those of existing secondary batteries using liquid electrolytes. Due to the high energy density and long life characteristics, all-solid batteries are being actively studied in recent years.

[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 prepared from lithium sulfide.

[0005] However, lithium sulfide needs to be produced by synthesis rather than from natural minerals. In the synthesis process of lithium sulfide, when metallic lithium is used as the lithium source, there are problems in terms of price, and when lithium hydroxide is used as the lithium source, the reaction efficiency may be reduced or side reactions may occur. In addition, hydrogen sulfide (H2S) as a sulfur source 2 S) is toxic and difficult to handle. Therefore, it is necessary to design a process for effectively preparing high-purity lithium sulfide. Summary of the invention

[0006] 1. Technical issues to be resolved

[0007] A technical problem of the present invention relates to a method for effectively preparing high-purity lithium sulfide.

[0008] (II) Technical solution

[0009] In a method for preparing lithium sulfide according to an exemplary embodiment, a solid sulfur layer and a lithium source layer are sequentially arranged in a reactor. A gas is injected into the reactor in a single direction to obtain a product containing lithium sulfide. The product containing lithium sulfide is dissolved in an anhydrous solvent to form a solution containing lithium sulfide. Lithium sulfide is separated from the solution containing lithium sulfide.

[0010] In some embodiments, the gas may be injected from one end of the reactor and sequentially pass through the solid sulfur layer and the lithium source layer.

[0011] In some embodiments, the lithium source layer may include at least one of lithium hydroxide, lithium hydroxide hydrate, lithium oxide, and lithium oxide hydrate.

[0012] In some embodiments, the lithium source contained in the lithium source layer may be a lithium source recovered from waste positive electrode materials of a lithium secondary battery.

[0013] In some embodiments, a ratio of the total number of moles of lithium atoms included in the lithium source layer to the total number of moles of sulfur atoms included in the solid sulfur layer may be 1 to 3.

[0014] In some embodiments, the gas may be free of oxygen and moisture.

[0015] In some embodiments, the gas may include nitrogen, hydrogen, or a mixture of nitrogen and hydrogen.

[0016] In some embodiments, the gas may include a mixed gas of the nitrogen and hydrogen, and the volume ratio of the nitrogen in the mixed gas of the nitrogen and hydrogen may be 30-100 volume %.

[0017] In some embodiments, the reaction temperature in the reactor may be 300-500°C.

[0018] In some embodiments, the reaction pressure in the reactor may be 0.1-5 bar.

[0019] In some embodiments, the anhydrous solvent may include a solvent having a moisture content of 0.5% or less.

[0020] In some embodiments, the anhydrous solvent may include at least one of anhydrous ethanol, acetone, ethyl acetate, dimethyl sulfoxide, and dimethylformamide.

[0021] In some embodiments, the step of separating lithium sulfide from the solution containing lithium sulfide may include removing the anhydrous solvent by evaporation.

[0022] In some embodiments, the reactor may include a first reactor and a second reactor.

[0023] In some embodiments, the solid sulfur layer may be disposed in the first reactor, the lithium source layer may be disposed in the second reactor, and the gas may be supplied from the first reactor to the second reactor to sequentially contact the solid sulfur layer and the lithium source layer.

[0024] (III) Beneficial effects

[0025] According to the above exemplary embodiment, a solid sulfur layer and a lithium source layer are sequentially disposed in a reactor, and gas is injected in a single direction to sequentially contact the layers, so that high-purity lithium sulfide can be prepared under mild conditions.

[0026] According to an exemplary embodiment, by using a lithium source generated during the treatment of waste batteries, high-purity lithium sulfide can be obtained in an environmentally friendly and low-cost manner.

[0027] According to an exemplary embodiment, solid sulfur can be obtained from byproducts produced after oil refining processing, so lithium sulfide can be prepared in an environmentally friendly manner. In addition, solid sulfur is easy to control and operators do not directly contact harmful gases, so lithium sulfide can be prepared efficiently.

[0028] According to the exemplary embodiment, an anhydrous solvent is used without a side reaction and the preparation time is shortened, so that lithium sulfide can be effectively separated. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a schematic process sequence diagram for explaining a method for preparing lithium sulfide according to an exemplary embodiment.

[0030] Figure 2 is a schematic process flow diagram for explaining a method for preparing lithium sulfide according to an exemplary embodiment.

[0031] Figure 3 is a schematic process flow diagram for illustrating a method of preparing lithium sulfide according to some embodiments.

[0032] Description of Reference Numerals

[0033] 100: Reactor 100a: First reactor

[0034] 100b: Second reactor 110: Solid sulfur layer

[0035] 120: lithium source layer 140: gas supply unit

[0036] 150: Product Collection Department DETAILED DESCRIPTION

[0037] Embodiments of the present invention provide, for example, a method for preparing lithium sulfide from solid sulfur and lithium sources with high purity and high yield.

[0038] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, but this is merely exemplary, and the present invention is not limited to the specific embodiments described exemplarily.

[0039] Figure 1 is a schematic process sequence diagram for explaining a method for preparing lithium sulfide according to an exemplary embodiment. Figure 2 is a schematic process flow diagram for explaining a method for preparing lithium sulfide according to an exemplary embodiment.

[0040] Reference Figure 1 , a solid sulfur layer and a lithium source layer can be formed sequentially inside the reactor (eg, S10 process).

[0041] Reference Figure 2 The reactor 100 may include a solid sulfur layer 110 and a lithium source layer 120 , and the reactor 100 may face a gas supply part 140 and a product collection part 150 .

[0042] For example, Figure 2 As shown, the reactor 100 may be filled to sequentially arrange the solid sulfur layer 110 and the lithium source layer 120. According to the arrangement, the gas may sequentially pass through the above layers.

[0043] The form in which the solid sulfur layer 110 and the lithium source layer 120 are arranged is not particularly limited. For example, the solid sulfur layer 110 and the lithium source layer 120 may be arranged in separately distinguished spaces, or may be arranged in the same space in a state of being distinguished by a separator. For example, the solid sulfur layer 110 and the lithium source layer 120 may be in contact with the separator, respectively, and exist in a state of being in contact with each other. In some embodiments, the solid sulfur layer 110 and the lithium source layer 120 may be in direct contact with each other without a separator.

[0044] In an exemplary embodiment, each of the solid sulfur layer 110 and the lithium source layer 120 may exist in a state of being separated from each other. When the layers exist separately, a flow of gas may be generated, so that lithium sulfide may be efficiently prepared.

[0045] For example, the solid sulfur layer 110 and the lithium source layer 120 may be separated so that an air layer or a bead layer of a non-reactive substance may be formed between the solid sulfur layer 110 and the lithium source layer 120. The air layer or the bead layer of the non-reactive substance may facilitate the flow of gas, thereby facilitating the contact between the lithium source layer and the gas.

[0046] For example, a reactive substance layer may not be included between the solid sulfur layer 110 and the lithium source layer 120. When a reactive substance layer is included, a product may change or generation of impurities may increase, and a reaction time may increase.

[0047] After the solid sulfur layer 110 and the lithium source layer 120 are sequentially arranged, gas may be injected in a single direction. Gas may be injected from the gas supply part 140 into one end of the reactor 100 in a single direction to collect a product containing lithium sulfide from the other end of the reactor 100 (eg, S20 process).

[0048] In an exemplary embodiment, the gas may be injected from one end of the reactor 100 and pass through the solid sulfur layer 110 and the lithium source layer 120 in sequence.

[0049] The gas may be injected in one direction to produce a unidirectional flow.

[0050] For example, when the gas is completely injected from two directions of the reactor 100 (for example, from the solid sulfur layer to the lithium source layer and from the lithium source layer to the solid sulfur layer), gas flow may not be generated or the residence time of the gas may be prolonged, and thus high-purity lithium sulfide may not be prepared.

[0051] When the gas does not sequentially pass through the solid sulfur layer 110 and the lithium source layer 120 , lithium sulfide may not be prepared, or the purity of the prepared lithium sulfide may be significantly reduced.

[0052] For example, when the lithium source layer 120 and the solid sulfur layer 110 are disposed in this order and the gas passes in this order, a reaction may not occur, and thus lithium sulfide may not be prepared.

[0053] For example, the other end of the reactor 100 may be connected to the reactor 100 as a whole, or may exist in a separate state. For example, the other end may be connected to the reactor 100 through a pipeline in a separate space. Alternatively, the other end may exist in a state where it is connected to the reactor and merged.

[0054] The other end may include, for example, a product collecting portion 150. The product collecting portion 150 may be located at the opposite side of the gas supply portion 140, and the solid sulfur layer 110 and the lithium source layer 120 disposed in the reactor 100 are located between the product collecting portion 150 and the gas supply portion 140.

[0055] In an exemplary embodiment, the product collecting section 150 may be located on the opposite side of the gas supplying section 140. The gas may sequentially pass through the solid sulfur layer 110 and the lithium source layer 120, and may form a product containing lithium sulfide through gas phase synthesis. The product containing lithium sulfide may be obtained in the product collecting section 150.

[0056] The product containing lithium sulfide may be dissolved in an anhydrous solvent. The product containing lithium sulfide may be dissolved in an anhydrous solvent to form a solution containing lithium sulfide (eg, S30 process).

[0057] For example, the solution containing lithium sulfide may contain 20 wt % or more of lithium sulfide relative to the total weight.

[0058] In an exemplary embodiment, the solution containing lithium sulfide may contain 30 wt % or more of lithium sulfide relative to the total weight. The content of lithium sulfide contained in the solution may vary somewhat depending on the reaction conditions.

[0059] The lithium sulfide dissolved in the anhydrous solvent may be separated from the anhydrous solvent (eg, S40 process).

[0060] For example, the lithium sulfide may be separated by evaporating the anhydrous solvent used to form the solution containing the lithium sulfide.

[0061] In an exemplary embodiment, the purity of the lithium sulfide remaining after separation of the anhydrous solvent can be 95% or more. For example, the purity of the lithium sulfide remaining after evaporation of the anhydrous solvent can be 97% or more, 98% or more, 99% or more, 99.5% or more, 99.8% or more, or 99.9% or more. The purity can be the purity measured by XRD Rietveld refinement.

[0062] In an exemplary embodiment, a solid sulfur layer 110 may be provided inside the reactor 100 so that the gas first passes through the solid sulfur layer 110. The solid sulfur contained in the solid sulfur layer 110 may be solid sulfur in all forms regardless of form, particle size, particle distribution, and the like.

[0063] The solid sulfur may be prepared, for example, in a desulfurization process of petroleum, crude oil, etc. For example, the desulfurization process may include wet desulfurization by physical absorption treatment using sodium hydroxide, polyethylene glycol, potassium carbonate, ferrous chloride, etc.; dry desulfurization by chemical adsorption using an adsorbent such as silica gel; biological desulfurization using sulfur oxidizing bacteria such as Thiobacillus, etc.

[0064] Solid sulfur produced as a byproduct in the desulfurization process is used, so that lithium sulfide can be produced in an environmentally friendly and low-cost manner. In addition, solid sulfur is easy to control, so it can be sequentially arranged in a reactor, and the generation of harmful gases during the preparation of lithium sulfide can be reduced.

[0065] In an exemplary embodiment, the lithium source may include at least one of lithium hydroxide, lithium hydroxide hydrate, lithium oxide, and lithium oxide hydrate.

[0066] In one embodiment, the lithium source may comprise lithium hydroxide hydrate or lithium oxide hydrate.

[0067] The lithium hydroxide, lithium hydroxide hydrate, lithium oxide or lithium oxide hydrate may be present in the lithium source layer 120 alone or in a mixed state. For example, powders 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 included in the form of powder, the average particle diameter may be 2 mm or less.

[0068] As the lithium source, at least one of lithium hydroxide hydrate or lithium oxide hydrate may be included, thereby promoting the preparation of lithium sulfide without adding additional reactants.

[0069] In an exemplary embodiment, the lithium source included in the lithium source layer 120 may use a lithium source recovered from waste positive electrode materials.

[0070] For example, the lithium source may be obtained by preparing a spent positive electrode active material mixture from spent positive electrode materials, reacting the spent positive electrode active material mixture with a gas to form a primary precursor mixture, and then selectively recovering a lithium precursor from the primary precursor mixture to obtain the lithium source.

[0071] 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.

[0072] The conductive material may include carbon-based materials such as graphite, carbon black, graphene, carbon nanotubes, etc. The adhesive may include resin materials such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, etc.

[0073] For example, the waste positive electrode active material mixture can be generated by pulverization. For example, the waste positive electrode active material mixture can be heat-treated, and impurities contained in the waste positive electrode active material mixture can be removed or reduced by heat treatment. Therefore, the purity of the primary precursor mixture can be improved, and the purity of the recovered lithium precursor can be improved.

[0074] For example, the gas reacting with the spent positive electrode active material mixture may be a reducing gas. The primary precursor mixture prepared by reacting with the spent positive electrode active material mixture may include, for example, lithium hydroxide, lithium oxide, transition metals or transition metal oxides.

[0075] The primary precursor mixture may be subjected to a water washing treatment with water to recover the lithium precursor, and the lithium precursor may be separated and recovered from the transition metal through the water washing treatment. The lithium precursor may include lithium hydroxide or a hydrate thereof.

[0076] The recovered lithium precursor may be crystallized by a dry process or the like.

[0077] As the lithium source, a substance recovered from waste positive electrode materials can be used, so that lithium sulfide can be prepared in an environmentally friendly manner.

[0078] In an exemplary embodiment, the reactor 100 may include a reactor into which gas can be injected in one direction. For example, the reactor 100 may include a tubular reactor, a tower reactor, a stirred tank reactor, a fluidized bed reactor, and the like.

[0079] In an exemplary embodiment, the reactor 100 may include a fluidized bed reactor. A reactor body having a diameter that increases gradually or gradually from the bottom may be included to enhance mixing of gas and solids.

[0080] For example, when a fluidized bed reactor is used as the reactor 100 used in the process of preparing the lithium sulfide, the lithium source can be recovered from the waste positive electrode material and lithium sulfide can be prepared in the same reactor. Therefore, the efficiency of preparing lithium sulfide can be improved.

[0081] In addition, when a fluidized bed reactor is used, the product collecting part 150 may exist in a state of being combined with the fluidized bed reactor, and may have a constant inclination angle and gradually increase in diameter in a direction from the gas supply part 140 to the product collecting part 150. As the diameter changes, the fluidization efficiency is improved, thereby increasing the yield of lithium sulfide.

[0082] In an exemplary embodiment, a ratio of the total number of moles of lithium atoms included in the lithium source layer 120 to the total number of moles of sulfur atoms included in the solid sulfur layer 110 may be 1 to 3.

[0083] 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. Lithium sulfide may be prepared by making the molar ratio of lithium atoms to sulfur atoms within the above range.

[0084] The gas injected into the reactor may include, for example, hydrogen, a mixed gas of nitrogen and hydrogen, argon, nitrogen, helium and other inert gases.

[0085] In an exemplary embodiment, the gas may not contain oxygen and moisture, thereby reducing the generation of impurities.

[0086] In an exemplary embodiment, the gas may include nitrogen, hydrogen, or a mixed gas of nitrogen and hydrogen. For example, the gas may include nitrogen, hydrogen, nitrogen and hydrogen, nitrogen and argon, hydrogen and argon, etc.

[0087] In an exemplary embodiment, the gas may include a mixed gas of nitrogen and hydrogen, and the volume ratio of nitrogen in the mixed gas of nitrogen and hydrogen may be 30-100 volume %.

[0088] In an exemplary embodiment, the temperature of the step of injecting the gas to obtain a product containing lithium sulfide may be 300-500° C. In some embodiments, the temperature may be 300-450° C.

[0089] When the temperature is lower than 300° C., even if the gas contacts solid sulfur, the reaction may not be activated or the activation level may be low, so that the yield of lithium sulfide may be low, and a side reaction may occur, so that the purity of lithium sulfide may be reduced. When the temperature exceeds 500° C., a constant flow rate of the gas cannot be maintained, so that the yield of lithium sulfide may be reduced, and the prepared lithium sulfide may solidify, so that the yield may be reduced.

[0090] In an exemplary embodiment, the pressure of the step of injecting the gas to obtain a product containing lithium sulfide may be 0.1-5 bar.

[0091] The pressure can be maintained at a level similar to atmospheric pressure, or can be maintained at a level slightly higher than atmospheric pressure depending on the amount of gas injected. In some embodiments, the pressure can be 0.5-4 bar, 1-3 bar. Within the above pressure range, high-purity lithium sulfide can be prepared.

[0092] In an exemplary embodiment, the reaction time of the step of injecting the gas to obtain a product containing lithium sulfide may be less than 5 hours.

[0093] In some embodiments, the reaction time of the step of injecting the gas to obtain a product containing lithium sulfide can be 0.5-4 hours or 1-4 hours. The reaction time can be reduced by injecting the gas in a single direction, so that lithium sulfide can be effectively prepared. The reaction time can be partially adjusted according to the reaction temperature, but the reaction time can be adjusted within the above range.

[0094] For example, when the reaction time is prolonged, sulfur compounds other than lithium sulfide may be produced.

[0095] The product containing lithium sulfide may contain some impurities other than lithium sulfide.

[0096] The anhydrous solvent may use a solvent that dissolves lithium sulfide, thereby removing impurities that are insoluble in the anhydrous solvent. For example, among the compounds generated after the reaction, compounds that are insoluble in the anhydrous solvent may remain in the filter, and the remaining compounds may be separated and removed.

[0097] In an exemplary embodiment, the anhydrous solvent may include a solvent having a moisture content of 0.5% or less.

[0098] For example, the anhydrous solvent may include anhydrous alcohol, acetone, ether, dimethylformamide, dimethylacetamide, acetonitrile, dichloromethane, diethylamine, dimethylsulfoxide, hexane, cyclohexane, ethyl acetate, isopropyl alcohol, toluene, N-methyl caprolactam, N-methylpyrrolidone, etc.

[0099] In an exemplary embodiment, the anhydrous solvent may include at least one of anhydrous ethanol, acetone, ethyl acetate, dimethyl sulfoxide, and dimethylformamide.

[0100] In an exemplary embodiment, the lithium sulfide may be separated by evaporating the anhydrous solvent from the solution containing the lithium sulfide.

[0101] For example, lithium sulfide may be dissolved in an anhydrous solvent and the anhydrous solvent may be removed by evaporation, thereby purifying and separating the lithium sulfide without side reactions. For example, without using an anhydrous solvent, lithium sulfide may react again with moisture contained in the solvent to generate sulfate, so the purity and yield of lithium sulfide may be reduced.

[0102] Figure 3 is a schematic process flow diagram for illustrating a method of preparing lithium sulfide according to some embodiments.

[0103] Reference Figure 3 , the reactor 100 may include a first reactor 100a and a second reactor 100b.

[0104] The first reactor 100a and the second reactor 100b may be the same as or different from each other, and may be the same as the reactor.

[0105] The first reactor 100a may be connected to the gas supply part 140, and the second reactor 100b may be connected to the product collecting part 150. The first reactor 100a and the second reactor 100b may be connected to each other.

[0106] The method of connecting the first reactor 100a and the second reactor 100b is not particularly limited, and may include all connection methods within the range of not exposing gas, reactants, etc. and not causing changes in the reaction.

[0107] The first reactor 100 a and the second reactor 100 b may be connected to each other so that the gas supplied to the first reactor 100 a may be supplied to the second reactor 100 b .

[0108] The first reactor 100a and the second reactor may be arranged in the same direction. Gas may be supplied to the first reactor 100a in a single direction through the gas supply unit 140. The gas may be supplied in a direction toward the second reactor 100b connected to the first reactor 100a, thereby forming a single direction flow of gas from the first reactor 100a to the second reactor 100b.

[0109] In an exemplary embodiment, the solid sulfur layer 110 may be disposed in the first reactor 100a, and the lithium source layer 120 may be disposed in the second reactor 100b.

[0110] 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 according to the position inside the reactor. Alternatively, the solid sulfur layer 110 in the first reactor 100a and the lithium source layer 120 in the second reactor 100b may be arranged in a state of being separated from each other by a predetermined distance or more.

[0111] After the above layers are provided, a gas may be supplied to sequentially contact the solid sulfur layer 110 and the lithium source layer 120 .

[0112] Even if the solid sulfur layer 110 and the lithium source layer 120 exist in physically separated reactors, lithium sulfide can be efficiently produced according to a single direction flow of gas.

[0113] In an exemplary embodiment, the product containing lithium sulfide as described above may be obtained in the product collecting part 150 , and may be dissolved in an anhydrous solvent to form a solution containing lithium sulfide as described above.

[0114] In an exemplary embodiment, no solvent may be used when providing the solid sulfur layer 110 and the lithium source layer 120. For example, the solid sulfur layer 110 and the lithium source layer 120 may not contain a solvent, and an anhydrous solvent may be used in the product containing lithium sulfide in the product collecting part 150.

[0115] The solid sulfur layer 110 and the lithium source layer 120 do not contain an organic solvent in the preparation process, and the anhydrous solvent used in the product collecting part 150 can be removed by evaporation, so lithium sulfide can be prepared in an environmentally friendly manner.

[0116] Below, specific experimental examples are presented to help understand the present invention, but this is only used to illustrate the present invention and is not used to limit the claims. Various changes and modifications can be made to the embodiments within the scope of the present invention and the technical concept. This is obvious to those skilled in the art, and it is natural that such changes and modifications fall within the scope of the claims.

[0117] Example 1

[0118] Solid sulfur and lithium hydroxide monohydrate (LiOH·H 2 O). Nitrogen (100% by volume) was injected into the reactor to contact the solid sulfur layer and the lithium hydroxide layer in sequence. When the nitrogen was injected, the reaction pressure was maintained at 2 bar, the reaction temperature was maintained at 400° C., and the reaction was carried out for 1 hour. The reactor was moved to a glove box, the product located at the upper part was dissolved in anhydrous ethanol, and the substance insoluble in anhydrous ethanol was separated and removed. Then, the anhydrous ethanol was evaporated to obtain lithium sulfide.

[0119] Example 2

[0120] The reaction was carried out by the same process as in Example 1, except that the reaction temperature was 350°C.

[0121] Example 3

[0122] The reaction was carried out by the same process as in Example 1, except that the reaction temperature was 300°C.

[0123] Example 4

[0124] The reaction was carried out by the same process as in Example 1, except that a mixed gas of nitrogen (50 volume %) and hydrogen (50 volume %) was used as the gas.

[0125] Comparative Example 1

[0126] The reaction was carried out by the same process as in Example 1, except that lithium hydroxide and solid sulfur were filled in the reactor in this order, so that the gas contacted the lithium hydroxide layer and the solid sulfur layer in sequence.

[0127] Comparative Example 2

[0128] The reaction was carried out by the same process as in Example 1, except that the reaction temperature was 120°C.

[0129] Comparative Example 3

[0130] The reaction was carried out by the same process as in Example 1, except that the reaction temperature was 250°C.

[0131] Comparative Example 4

[0132] The reaction was carried out by the same process as in Example 1, except that the reaction temperature was 600°C.

[0133] Comparative Example 5

[0134] The reaction was carried out by the same process as in Example 1, except that the product was not dissolved in anhydrous ethanol and the subsequent steps were not performed.

[0135] Experimental example

[0136] The products obtained in the above-mentioned Examples and Comparative Examples were measured for X-ray diffraction (XRD), and their crystal structures were analyzed by the Rietveld refinement method.

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

[0138] [Table 1]

[0139]

[0140] Referring to Table 1, according to the embodiment, the product prepared by contacting the gas with the solid sulfur layer and the lithium hydroxide layer in sequence is dissolved in anhydrous ethanol and then separated. Therefore, high-purity lithium sulfide is obtained efficiently. In addition, according to the embodiment, high-purity lithium sulfide is obtained within the reaction temperature range of 300-450°C.

[0141] In Comparative Example 1, in which the gas sequentially contacted the lithium hydroxide layer and the solid sulfur layer instead of sequentially contacting the solid sulfur layer and the lithium hydroxide layer, no reaction occurred.

[0142] In Comparative Example 2 where the reaction temperature was low, most of the product dissolved in anhydrous ethanol, so that the recovery rate after separation and purification was high, but the reaction for preparing lithium sulfide hardly occurred, so that the content of lithium sulfide was confirmed to be less than 20%.

[0143] In Comparative Example 3 where the reaction temperature was increased compared to Comparative Example 2 but was lower than 300° C., most of the product was dissolved in anhydrous ethanol, resulting in a high recovery rate after separation and purification, but the content of the prepared lithium sulfide was less than 60%.

[0144] In Comparative Example 4, where the reaction temperature was high, the content of lithium sulfide was 90% or more, but lithium sulfide solidified in the product collection section, resulting in loss during the recovery of lithium sulfide. In addition, due to the high reaction temperature, it was confirmed that some lithium hydroxide did not react and remained.

[0145] In Comparative Example 5 in which separation and purification were not performed, a large amount of sulfate was contained in addition to lithium sulfide, so that the purity of lithium sulfide was low.

Claims

1. A method for preparing lithium sulfide, comprising the following steps: A solid sulfur layer and a lithium source layer are sequentially arranged in a reactor; injecting gas into the reactor in a single direction to obtain a product containing lithium sulfide; dissolving the product containing lithium sulfide in an anhydrous solvent to form a solution containing lithium sulfide; as well as Lithium sulfide is separated from the solution containing lithium sulfide.

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

3. The method for preparing lithium sulfide according to claim 1, wherein: The lithium source layer contains at least one of lithium hydroxide, lithium hydroxide hydrate, lithium oxide, and lithium oxide hydrate.

4. The method for preparing lithium sulfide according to claim 3, wherein: The lithium source contained in the lithium source layer is a lithium source recovered from waste positive electrode materials of lithium secondary batteries.

5. The method for preparing lithium sulfide according to claim 1, wherein: The ratio of the total number of moles of lithium atoms included in the lithium source layer to the total number of moles of sulfur atoms included in the solid sulfur layer is 1 to 3.

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

7. The method for preparing lithium sulfide according to claim 1, wherein: The gas includes nitrogen, hydrogen or a mixed gas of nitrogen and hydrogen.

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

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

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

11. The method for preparing lithium sulfide according to claim 1, wherein: The anhydrous solvent includes a solvent having a water content of 0.5% or less.

12. The method for preparing lithium sulfide according to claim 1, wherein: The anhydrous solvent comprises at least one of anhydrous ethanol, acetone, ethyl acetate, dimethyl sulfoxide and dimethylformamide.

13. The method for preparing lithium sulfide according to claim 1, wherein: The step of separating lithium sulfide from the solution containing lithium sulfide comprises removing the anhydrous solvent by evaporation.

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

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

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