Lithium sulfide and preparation method therefor

Abstract

The present invention relates to lithium sulfide and a preparation method therefor, which comprises the steps of: mixing a carbon-based material with a lithium compound that contains lithium, and heat-treating same; and purifying a heat-treated product, wherein the step of purifying a heat-treated product includes a step of mixing the heat-treated product, a sulfur-containing additive and a first solvent so as to obtain an extraction solution.

Description

Lithium sulfide and method of manufacturing the same

[0001] The present invention relates to a method for manufacturing lithium sulfide, and more specifically, to high-purity lithium sulfide and a method for manufacturing the same.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0191920, filed on December 19, 2024, the entire contents of which are incorporated herein by reference.

[0003] Secondary batteries are widely used in everything from small electronic devices such as mobile phones or laptops to large devices such as electric vehicles (EVs) or energy storage systems (ESS). As the application fields of secondary batteries expand to all areas of daily life, there is a growing demand for not only performance such as high energy density and long lifespan, but also stability.

[0004] Conventionally, most electrolytes used in lithium-ion batteries were liquid electrolytes utilizing organic solvents. However, due to risks such as leakage or fire associated with these liquid electrolytes, strict packaging was required; consequently, there were limitations in increasing energy density beyond a certain level due to this strict packaging. Consequently, the need for all-solid-state batteries utilizing inorganic solid electrolytes instead of organic liquid electrolytes has emerged.

[0005] The above-mentioned all-solid-state battery allows for the safe fabrication of battery cells by excluding organic solvents such as liquid electrolytes. Furthermore, since inorganic solid electrolytes maintain stability without decomposing over a wide voltage range, they offer the advantage of enabling the use of high-voltage electrode materials.

[0006] The above solid electrolytes are classified into oxide-based and sulfide-based types, and the sulfide-based solid electrolytes have the characteristic of having high ionic conductivity compared to the oxide-based solid electrolytes. The main raw material for the sulfide-based solid electrolytes is lithium sulfide (Li2S). The synthesis methods for the lithium sulfide include a synthesis method using a high-energy ball mill, a synthesis method using a wet plasma process, and wet / dry methods using lithium metal.

[0007] Specifically, when converting lithium sulfate to lithium sulfide using the carbon thermal reduction method, solvent extraction is performed to remove residual carbon. Subsequently, the extracted lithium sulfide solution is dried and heat-treated to obtain lithium sulfide powder.

[0008] Ethanol is primarily used in the aforementioned solvent extraction, but it is one of the high-cost materials in the manufacturing process. For this reason, research has been conducted to reduce the amount of ethanol used by recovering it during the drying process and reusing it in the solvent extraction process to lower the process unit cost.

[0009] However, this study has a problem in that it is difficult to lower process unit costs because purification costs are incurred when the recovered ethanol is purified and reused.

[0010] The technical problem that the present invention aims to solve is to provide a method for manufacturing lithium sulfide that can be used in sulfide-based solid electrolytes, which reduces the amount of ethanol used to lower process costs and simultaneously produces high-purity lithium sulfide.

[0011] A method for manufacturing lithium sulfide according to one embodiment of the present invention comprises the steps of mixing a carbonaceous material with a lithium compound containing lithium and heat-treating the mixture, and purifying the heat-treated product. The step of purifying the heat-treated product may include the step of mixing the heat-treated product, a sulfur-containing additive, and a first solvent to obtain an extraction solution. In one embodiment, the step of purifying the heat-treated product may include, after the step of obtaining the extraction solution, the step of drying the extraction solution to obtain a lithium sulfide dried product and a second solvent, and the step of recovering the second solvent to replace at least a portion of the first solvent in the step of obtaining the extraction solution and mixing it.

[0012] In one embodiment, the step of obtaining the extraction solution may have a weight ratio of the sulfur-containing additive to the lithium sulfide (Li2S) in the heat-treated product (weight of sulfur-containing additive [g] / weight of lithium sulfide in the heat-treated product [g]) of 1.5 to 7.5. In one embodiment, the sulfur-containing additive may be in powder form.

[0013] In one embodiment, the sulfur-containing additive may include at least one of sulfur (S8), disulfides (S2), tetrasulfur (Cyclo-S4, S4), hydrogen sulfide (H2S), polysulfides, sulfides, and carbon disulfide. In one embodiment, in the step of mixing the second solvent to recover the second solvent to obtain the extraction solution, the ratio of the second solvent may be 30 to 90 vol% based on the sum of the first solvent and the second solvent, which is 100 vol%.

[0014] In one embodiment, the step of drying the extraction solution to obtain a lithium sulfide dry product and the second solvent may be performed at a temperature of 160 to 280 °C. In one embodiment, the step of drying the extraction solution to obtain a lithium sulfide dry product and the second solvent may be performed in a dryer having an internal pressure of 20 to 40 mbar.

[0015] In one embodiment, the step of purifying the heat-treated product may include, after the step of drying the extraction solution to obtain a lithium sulfide dry product and the second solvent, a step of heat-treating the lithium sulfide dry product. In one embodiment, the step of heat-treating the lithium sulfide dry product may be performed at 800 to 1,000 ℃.

[0016] In one embodiment, the step of heat-treating the extracted lithium sulfide dried product may be performed in a range of 1 to 5 hours. In one embodiment, the step of heat-treating the extracted lithium sulfide dried product is performed in a reduced pressure atmosphere, and the reduced pressure atmosphere is 10 -1 to 10 -3 It can be performed in torr.

[0017] In one embodiment, the step of mixing a carbon-based material with the lithium compound containing lithium and heat-treating it may include the step of preparing the lithium compound and the carbon-based material, and the step of mixing the lithium compound and the carbon-based material and heat-treating it. In one embodiment, the lithium compound containing lithium may include lithium sulfate (Li2SO4).

[0018] According to another embodiment of the present invention, the lithium sulfide may have a total amount of lithium oxide (Li2O) and lithium sulfate (Li2SO4) of 0.4 H% or less. In one embodiment, based on 100 wt% of lithium sulfide, the oxygen content may be 1.4 wt% or less. In one embodiment, based on 100 wt% of lithium sulfide, the carbon content may be 0.15 wt% or less.

[0019] A method for manufacturing lithium sulfide according to one embodiment of the present invention uses an additive instead of the conventional distillation purification method for recovered ethanol, thereby producing high-purity lithium sulfide without the need for separate energy costs, obtaining high-quality lithium sulfide, and simultaneously ensuring economic feasibility.

[0020] According to another embodiment of the present invention, lithium sulfide can be manufactured by the method described above to provide high-purity lithium sulfide.

[0021] Figure 1 is a schematic diagram of the method for manufacturing lithium sulfide according to the present invention.

[0022] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, the first part, component, region, layer, or section described below may be referred to as the second part, component, region, layer, or section without departing from the scope of the present invention.

[0023] The technical terms used herein are for the reference of specific embodiments only and are not intended to limit the invention. The singular forms used herein include plural forms unless phrases clearly indicate otherwise. As used in the specification, the meaning of “comprising” specifies certain characteristics, areas, integers, steps, actions, elements, and / or components, and does not exclude the presence or addition of other characteristics, areas, integers, steps, actions, elements, and / or components.

[0024] When it is stated that one part is "above" or "on" another part, it may be directly above or on the other part, or other parts may be involved in between. In contrast, when it is stated that one part is "directly above" another part, no other parts are interposed in between.

[0025] Unless otherwise defined, all terms used herein, including technical and scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with relevant technical literature and the present disclosure, and are not interpreted in an ideal or highly formal sense unless otherwise defined. Additionally, unless specifically noted, % means weight %, and 1 ppm is 0.0001 weight %.

[0026] Hereinafter, embodiments of the present invention are described in detail so that those skilled in the art can easily implement the invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0027] A method for manufacturing lithium sulfide according to one embodiment of the present invention may include the step of mixing a carbon-based material with a lithium compound containing lithium and heat-treating it, and the step of purifying the heat-treated product. By adding a sulfur-containing additive together with a solvent during the step of purifying the heat-treated product, the method for manufacturing lithium sulfide according to the present invention obtains a method for manufacturing lithium sulfide with high purity and economic feasibility by not undergoing a separate additional purification process.

[0028] The above lithium compound is a lithium compound including a sulfide system, for example, lithium sulfate (Li2SO4). , It may be lithium sulfate monohydrate (LiSO4·H2O). Specifically, the lithium compound may be lithium sulfate.

[0029] The carbon-based material may be graphite. Specifically, the carbon-based material may be one or more selected from the group consisting of coke, artificial graphite, carbon powder, graphene, activated carbon, and carbon black, having a carbon content of 99.9% or more.

[0030] In one embodiment, the step of mixing a carbon-based material with a lithium compound and heat-treating it may involve mixing a carbon-based material with a lithium compound and heat-treating it, wherein the mixing ratio of the lithium compound and the carbon-based material may be C:Li2SO4 in a weight ratio of 3:1 to 7:1. Specifically, the weight ratio may be 4:1 to 6:1.

[0031] Specifically, the step of mixing a carbon-based material with a lithium compound and heat-treating it may, for example, involve mixing lithium sulfate powder or an aqueous lithium sulfate solution with a carbon-based material and mixing it dry or wet while stirring.

[0032] In the case of the above dry mixing, the lithium sulfate powder and the carbon-based material are pre-mixed by stirring using a powder mixer (Universal Mixer). In the case of the above wet mixing, the carbon-based material is added to the lithium sulfate aqueous solution and pre-mixed by stirring using a stirrer such as a mixer.

[0033] In one embodiment, the step of preparing the mixed product may include a stirring step of 30 minutes or more, specifically 60 minutes or more. By performing the stirring step within the time range, carbon and lithium sulfate can be easily mixed.

[0034] In one embodiment, the step of mixing a lithium compound and a carbon-based material and heat-treating it may be performed in a temperature range of 800 to 1,000 ℃. Specifically, the temperature range may be performed in a temperature range of 850 to 950 ℃.

[0035] In one embodiment, the step of mixing the lithium compound and the carbon-based material and heat-treating them may be performed in an inert atmosphere. Specifically, the inert atmosphere may include, for example, a vacuum and a gas such as helium, neon, krypton, xenon, nitrogen, or argon.

[0036] In one embodiment, the step of mixing the lithium compound and the carbon-based material and heat-treating them may be performed in a range of 1 to 3 hours. Specifically, the time range may be performed in a range of 1.5 to 2.5 hours. Under the aforementioned temperature and time conditions, a carbon-lithium sulfide (C-Li2S) composite, which is the result of heat-treating the lithium compound and the carbon-based material by uniformly mixing them, can be easily obtained.

[0037] In one embodiment, the step of mixing the lithium compound and the carbon-based material and heat-treating them may include the step of grinding the carbon-based material before mixing the carbon-based material with the lithium sulfate powder. In one embodiment, the step of grinding the carbon-based material may be the step of grinding the carbon-based material using a jaw crusher or a pin mill and removing fine particles using a sieve of 200 mesh (pore size 65 μm).

[0038] The step of purifying the heat-treated product may be a step of purifying the carbon-lithium sulfide complex to obtain lithium sulfide. Specifically, the step of purifying the heat-treated product may be a step of mixing the heat-treated product, a sulfur-containing additive, and a first solvent to extract and filter lithium sulfide from the carbon-lithium sulfide complex. It has been found that by using a sulfur-containing additive together with a solvent in the step of purifying the heat-treated product of the present invention, the solvent can be reused, thereby enabling the economical acquisition of low-cost, high-purity lithium sulfide.

[0039] The above-mentioned sulfur-containing additive comprises sulfur as a source, and, as a non-limiting example, sulfur (Sulfur Powder, S8) and disulfides (Disulfides, S 2 ), tetrasulfide (Tetrasulfur, Cyclo-S4, S 4 It may include at least one of hydrogen sulfide (H2S), polysulfides, sulfides, and carbon disulfide. Specifically, the additive that adds the sulfur may be sulfur. In one embodiment, the additive containing sulfur may be in powder form.

[0040] In one embodiment, the first solvent may be a polar solvent. Specifically, the polar solvent may be, as a non-limiting example, alcohols such as methanol, propanol, or butanol; ketones such as acetone or methyl ethyl ketone (MEK); ethers such as diethyl ether or tetrahydrofuran (THF); polar protic solvents such as ethanol, water (H2O), or glycerol; polar aprotic solvents such as dimethyl sulfoxide (DMSO) or dimethylformamide (DMF); or solvents such as acetonitrile or pyridine. Specifically, the first solvent may be ethanol.

[0041] The step of solvent extraction of the heat-treated product may be a step of solvent extraction of the heat-treated product with water (H2O) or an aprotic polar solvent from the step of mixing lithium sulfate powder and a carbon-based material and heat-treating the mixture. Specifically, the heat-treated product may be a C-Li2S composite in which C and Li2S are mixed.

[0042] In one embodiment, the weight ratio of the sulfur-containing additive to the lithium sulfide (Li2S) in the heat-treated product (weight of sulfur-containing additive [g] / weight of lithium sulfide in the heat-treated product [g]) may be 1.5 to 7.5. Specifically, the weight ratio may be 3.0 to 6.0, more specifically 4.1 to 5.0, even more specifically 4.1 to 4.3, and even more specifically 4.1 to 4.2. By satisfying the aforementioned ranges, the sulfur-containing additive can easily react with the carbon-lithium sulfide composite, which is the heat-treated product, thereby minimizing or suppressing the loss of sulfur during the drying and heat treatment steps after extraction, and thus obtaining high-purity lithium sulfide.

[0043] If the above weight ratio deviates from the lower limit of the aforementioned range, the sulfur-containing additive is excessively low, resulting in a problem where the effect manifested by adding the additive is insufficient. If the above weight ratio deviates from the upper limit of the aforementioned range, the sulfur-containing additive is excessively high, leading to reduced economic efficiency and a problem where a large amount of residual carbon is generated during the heat treatment step following the extraction and drying steps, thereby degrading the quality of the lithium sulfide product.

[0044] In one embodiment, the step of purifying the heat-treated product includes the step of drying the extraction solution after the step of obtaining the extraction solution. Specifically, the step of drying the extraction solution may involve drying the extraction solution from which lithium sulfide is extracted from a carbon-lithium sulfide complex. More specifically, the step of drying the extraction solution may involve solidifying the extracted lithium sulfide solution to obtain a dried product.

[0045] In one embodiment, the step of drying the extraction solution may include, after the step of obtaining the extraction solution, a step of drying the extraction solution to obtain a lithium sulfide dry product and a second solvent, and a step of recovering the second solvent to obtain the extraction solution, a step of mixing these two, wherein at least a portion of the first solvent is replaced and mixed. Specifically, in the step of drying the extraction solution, a second solvent, which is a solvent, may be obtained in addition to the lithium sulfide dry product. The second solvent may be the same solvent as the first solvent. For example, the second solvent may be ethanol.

[0046] The method for manufacturing lithium sulfide according to the present invention has the advantage of reducing process unit costs by reusing the second solvent recovered from the drying step in the step of obtaining the extraction solution. In addition, by using a sulfur-containing additive in the step of obtaining the extraction solution, the process of separately purifying the recovered second solvent is not performed, thereby having the advantage of reducing process unit costs.

[0047] Specifically, when the second solvent is reused and a sulfur additive is used, lithium ethoxide in the lithium sulfide dissolved in the solvent reacts with the added sulfur to produce ethanol, as shown in Reaction Scheme 1 below. Subsequently, by allowing the ethanol to be recovered without decomposition during the drying step after extraction, lithium sulfide could be obtained economically without a separate process of purifying the second solvent.

[0048] (Reaction Equation 1)

[0049] LiSH + LiOEt + (x-1)S → 2Li + + S x 2- + EtOH → Li2S x + EtOH

[0050] In one embodiment, in the step of recovering the second solvent to obtain the extraction solution, the ratio of the second solvent may be 30 to 90 vol% based on the total amount of the first solvent and the second solvent, which is 100 vol%. For example, if the ratio of the second solvent is 30 vol%, the ratio of the first solvent may be 70 vol%. Specifically, the ratio of the second solvent may be 40 to 85 vol%, more specifically 60 to 85 vol%, and even more specifically 70 to 80 vol%.

[0051] By including the proportion of the second solvent within the aforementioned range, economic feasibility can be secured while simultaneously producing high-purity lithium sulfide. If the proportion of the second solvent is excessively high, there is a problem of reduced purity of the obtained lithium sulfide, and if the proportion of the second solvent is excessively low, there is a problem of reduced economic feasibility.

[0052] In one embodiment, the step of drying the extraction solution to obtain a lithium sulfide dry product and the second solvent may be performed at a temperature of 160 to 280 °C. Specifically, the temperature may be 190 to 260 °C, more specifically 200 to 250 °C. By performing the drying step at the temperature within the aforementioned range, a lithium sulfide dry product can be easily obtained, and high-purity lithium sulfide can be obtained.

[0053] If the above temperature is excessively high, the oxygen content remaining in the lithium sulfide dried product becomes excessively high, which can lower the purity of the lithium sulfide. If the above temperature is excessively low, the solvent is not removed smoothly, leading to a problem where the lithium sulfide dried product cannot be easily obtained.

[0054] In one embodiment, the step of drying the extraction solution to obtain a lithium sulfide dry product and the second solvent may be performed in an atmosphere with an internal pressure of 25 to 40 mbar. Specifically, the internal pressure may be 25 to 35 mbar. More specifically, the internal pressure may be 27 to 35 mbar, and even more specifically, the internal pressure may be 30 to 35 mbar. As the drying step is performed within the aforementioned internal pressure range, a lithium sulfide dry product of high purity can be easily obtained.

[0055] In one embodiment, the step of purifying the heat-treated product may include a step of heat-treating the lithium sulfide dried product after the step of drying the extraction solution to obtain the lithium sulfide dried product and the second solvent. Specifically, the step of heat-treating the lithium sulfide dried product may be a step of synthesizing the dried product obtained during the drying process into lithium sulfide.

[0056] Specifically, the step of heat-treating the lithium sulfide dried product can be performed at a temperature of 800 to 1,000 ℃. Specifically, the temperature can be performed at a temperature of 850 to 950 ℃.

[0057] In one embodiment, the step of heat-treating the lithium sulfide dried product may be performed for 1 to 5 hours. Specifically, the step of heat-treating the lithium sulfide dried product may be performed for 2 to 4 hours.

[0058] In one embodiment, the step of heat-treating the lithium sulfide dried product may be performed in a reduced pressure atmosphere. Specifically, the step of heat-treating the lithium sulfide dried product is 10 -1 to 10 -3 It can be performed in a reduced pressure atmosphere of torr.

[0059] As described above, since the step of heat-treating the dried lithium sulfide is performed under the aforementioned heat treatment conditions, lithium sulfide with low oxygen content can be synthesized and the yield of lithium sulfide from lithium can be increased. If the step of heat-treating the solvent-extracted product deviates from the lower limit of the aforementioned temperature range, there is a problem in that the oxygen content in Li2S increases.

[0060] According to another embodiment of the present invention, lithium sulfide can be produced by the manufacturing method described above. Specifically, the lithium sulfide may have a total amount of lithium oxide (Li2O) and lithium sulfate (Li2SO4) of 0.4 H% or less. Specifically, the total amount may be 0.2 H% or less. By satisfying the above range for the total amount, lithium sulfide of high purity can be provided.

[0061] In one embodiment, the lithium sulfide may have an oxygen content of 1.4 weight% or less based on 100 weight% of lithium sulfide. Specifically, the oxygen content may be 1.2 weight% or less, more specifically, 0.9 weight% or less.

[0062] In one embodiment, the carbon content of the lithium sulfide may be 0.15 weight% or less based on 100 weight% of the lithium sulfide. Specifically, the carbon content may be 0.13 weight% or less, more specifically, 0.11 weight% or less.

[0063] The lithium sulfide of the present invention can provide lithium sulfide applicable to batteries by including the oxygen content and the carbon content within the aforementioned ranges.

[0064] Specific embodiments of the present invention are described below. However, the following embodiments are merely specific examples of the present invention, and the present invention is not limited to the following embodiments.

[0065]

[0066] Experimental Example 1: Adding a sulfur additive to the purification step

[0067] <Example 1>

[0068] Complex formation stage

[0069]

[0070] After mixing carbon raw material (C) and lithium sulfate (Li2SO4) monohydrate in a weight ratio of 3:1, heat treatment was performed at 900°C for 2 hours.

[0071]

[0072] purification step

[0073] <Step to obtain extraction solution>

[0074]

[0075] After 72, a step was performed to obtain an extraction solution by mixing 4.8 kg of carbon-lithium sulfide (C-Li2S) formed through heat treatment with 18 L of ethanol, which is the first solvent, and sulfur powder (S8), which is an additive containing sulfur, and then extracting and filtering. At this time, the weight ratio of sulfur powder (S8 [g] / Li2S [g]) to lithium sulfide (Li2S) in the carbon-lithium sulfide resulting from heat treatment was adjusted to 4.3.

[0076]

[0077] <Drying Stage>

[0078] The extraction solution obtained through the extraction and filtration steps was introduced into a thin-film dryer maintained at a predetermined temperature and pressure to obtain lithium sulfide dried material and ethanol, a second solvent separated from the extraction solution. At this time, the temperature was 240 ℃ and the internal pressure of the dryer was controlled to 30 mbar.

[0079]

[0080] <Heat Treatment Step>

[0081] Subsequently, the dried lithium sulfide was heat-treated under reduced pressure to obtain white lithium sulfide powder. At this time, the reduced pressure condition was 10 -1 to 10 -2 It was controlled by torr, the heat treatment temperature was controlled to 900 ℃, and the heat treatment time was controlled to 3 hours.

[0082]

[0083] <Comparative Example 1>

[0084] The procedure was carried out in the same manner as Example 1, except that no sulfur-containing additives were included in the step of obtaining the extraction solution.

[0085]

[0086] Experimental Example 2: Extraction Condition Control

[0087] <Comparative Example 2>

[0088] In the step of obtaining the extraction solution, the extraction solution was obtained by additionally mixing the second solvent recovered from the drying step with the lithium carbon-sulfide formed through heat treatment and the first solvent. At this time, ethanol, which is the second solvent, was used in an amount of 50% of the amount of ethanol, which is the first solvent.

[0089] The remaining processes were performed in the same manner as Comparative Example 1.

[0090]

[0091] <Comparative Example 3>

[0092] In the step of obtaining the extraction solution, the extraction solution was obtained by additionally mixing the second solvent recovered from the drying step with the lithium carbon-sulfide formed through heat treatment and the first solvent. At this time, ethanol, which is the second solvent, was used at 100% of the amount of ethanol, which is the first solvent.

[0093] The remaining processes were performed in the same manner as Comparative Example 1.

[0094]

[0095] <Example 2>

[0096] In the extraction solution obtaining step, an extraction solution was obtained by additionally mixing lithium carbon-sulfide formed through heat treatment, a sulfur-containing additive, and a second solvent recovered from the drying step in addition to the first solvent. At this time, ethanol, the second solvent, was used at 40% of the amount of ethanol, the first solvent. The remaining processes were carried out in the same manner as in Example 1.

[0097]

[0098] <Example 3>

[0099] In the step of obtaining the extraction solution, the extraction solution was obtained by additionally mixing the carbon-lithium sulfide formed through heat treatment, an additive containing sulfur, and a second solvent recovered from the drying step in addition to the first solvent. At this time, ethanol, the second solvent, was used at 80% of the amount of ethanol, the first solvent. In addition, the weight ratio of sulfur powder to lithium sulfide (Li2S) in the carbon-lithium sulfide resulting from heat treatment (S8 [g] / Li2S [g]) was controlled to 4.2.

[0100] The remaining processes were performed in the same manner as in Example 1.

[0101]

[0102] <Comparative Example 4>

[0103] In the extraction solution acquisition step, an extraction solution was obtained by additionally mixing a second solvent recovered from the drying step in addition to the carbon-lithium sulfide formed through heat treatment, an additive containing sulfur, and the first solvent. At this time, ethanol, the second solvent, was used at 80% of the amount of ethanol, the first solvent. In addition, the weight ratio of sulfur powder to lithium sulfide (Li2S) in the carbon-lithium sulfide resulting from heat treatment (S8 [g] / Li2S [g]) was controlled to 1.1.

[0104] The remaining processes were performed in the same manner as in Example 1.

[0105]

[0106] <Comparative Example 5>

[0107] In the step of obtaining the extraction solution, the extraction solution was obtained by additionally mixing the carbon-lithium sulfide formed through heat treatment, an additive containing sulfur, and a second solvent recovered from the drying step in addition to the first solvent. At this time, ethanol, the second solvent, was used at 80% of the amount of ethanol, the first solvent. In addition, the weight ratio of sulfur powder to lithium sulfide (Li2S) in the carbon-lithium sulfide resulting from heat treatment (S8 [g] / Li2S [g]) was controlled to 8.0.

[0108] The remaining processes were performed in the same manner as in Example 1.

[0109]

[0110] Experimental Example 3: Drying Condition Control

[0111] <Example 4>

[0112] The procedure was performed in the same manner as Example 2, except that the drying temperature was controlled to 200 ℃ and the internal pressure of the dryer was controlled to 27 mbar during the drying step.

[0113]

[0114] <Comparative Example 6>

[0115] The procedure was performed in the same manner as Example 2, except that the drying temperature was controlled to 150 ℃ and the internal pressure of the dryer was controlled to 20 mbar during the drying step.

[0116]

[0117] <Comparative Example 7>

[0118] The procedure was performed in the same manner as Example 2, except that the drying temperature was controlled to 300 ℃ during the drying step.

[0119]

[0120] <Evaluation Example>

[0121] Table 1 below shows the temperature conditions of the solvent extraction, drying, and heat treatment steps, and Table 2 shows the analysis results for lithium sulfide, which is the heat-treated product according to Table 1.

[0122] Oxygen content and carbon content: Analyzed using a RECO N / O analyzer.

[0123] Impurity content ratio (Li2O, Li2SO4): Using RIGAKU's XRD equipment, the intensity of the main diffraction peak line of Li2S was analyzed as a relative comparison value of the intensity of the main diffraction peak line of each impurity with respect to 100%.

[0124] Filtration and extraction step Drying step Heat treatment C-Li2S Li2S content Total solvent (ethanol) usage Ratio of second solvent (recovered ethanol) Additive / Li2S ratio Heating temperature Internal pressure Temperature (g) (L) (%) (wt%) (°C) (mbar) (°C) Comparative Example 1 552 1800 240 30900 Comparative Example 2 552 18500 240 30900 Comparative Example 3 552 181000 240 30900 Example 1 552 180 4.32 40 30900 Example 2 552 1840 4.324030900 Example 355218804.224030900 Comparative Example 455218801.124030900 Comparative Example 555218808.024030900 Example 455218404.320027900 Comparative Example 655218404.315020900 Comparative Example 755218404.330030900

[0125] Analysis of Heat-Treated Material (Li2S) Impurity Content Ratio Oxygen Content Carbon Content Li2OL | Li2SO4 (H%) (H%) (wt%) (wt%) Comparative Example 1: 0.50 | 1.50.09 Comparative Example 2: 5.20.26.40.10 Comparative Example 3: 9.10.39.60.08 Example 1: 0.10 | 1.30.11 Example 2: 0.00.90.13 Example 3: 0.00.80.13 Comparative Example 4: 0.70 | 1.80.11 Comparative Example 5: 0.00.60.17 Example 4: 0.00 | 1.00.11 Comparative Example 6: 1.20 | 3.70.17 Comparative Example 7: 1.20 | 3.00.06

[0126] Looking at Tables 1 and 2 above, it was confirmed that the purity of the lithium sulfide obtained in Comparative Example 1 and Example 1 is excellent when sulfur powder is additionally mixed in during the filtration and extraction process. Furthermore, looking at Examples 2 to 4 and Comparative Examples 2 to 6, it was confirmed that high-purity lithium sulfide can be obtained when recovered ethanol, which is the second solvent recovered from the drying step, is used to replace a portion of the first solvent in the filtration and extraction step. Specifically, looking at Comparative Examples 2 and 3, it was confirmed that when sulfur powder is not used as an additive in the filtration and extraction step, the purity of the obtained lithium sulfide is inferior compared to the lithium sulfide obtained from the Examples. Looking at Examples 2 to 4 and Comparative Example 4 and Comparative Example 5, it was confirmed that high-purity lithium sulfide can be obtained when a certain proportion of the total solvent used in the filtration and extraction step is replaced with recovered ethanol, which is the solvent recovered from the drying step. However, as in Comparative Example 4, when the ratio of additives is excessively low, it was confirmed that the purity of impurities is somewhat inferior compared to Examples 2 and 3. In addition, as in Comparative Example 5, when the ratio of additives is excessively high, it was confirmed that the purity of lithium sulfide is somewhat inferior compared to Examples 1 to 3 because the carbon content is somewhat higher and the powder is gray.

[0127] Upon examining Example 4, Comparative Example 6, and Comparative Example 7, it was confirmed that high-purity lithium sulfide can be obtained when the drying temperature satisfies the range of the present invention. However, it was confirmed that Comparative Example 6 had a gray powder with a carbon content that was somewhat higher than that of the other examples. It was determined that this could lead to a slight decrease in performance when manufacturing a solid electrolyte.

[0128]

[0129] The present invention is not limited to the above embodiments and / or examples but can be manufactured in various different forms, and those skilled in the art will understand that the invention can be implemented in other specific forms without changing the technical concept or essential features of the invention. Therefore, the embodiments and / or examples described above should be understood as illustrative in all respects and not restrictive.

Claims

1. A step of mixing a carbon-based material with a lithium compound containing lithium and heat-treating it; and It includes a step of purifying the heat-treated product above, The step of refining the heat-treated product above is, A method for producing lithium sulfide comprising the step of mixing the heat-treated product, a sulfur-containing additive, and a first solvent to obtain an extraction solution.

2. In Paragraph 1, The step of refining the heat-treated product above is, After the step of obtaining the above extraction solution, A step of drying the above extraction solution to obtain a lithium sulfide dry product and a second solvent; and A method for producing lithium sulfide comprising the step of recovering the second solvent to obtain the extraction solution, and the step of replacing at least a portion of the first solvent with the second solvent.

3. In Paragraph 1, The step of obtaining the above extraction solution is, A method for producing lithium sulfide in which the weight ratio of the sulfur-containing additive to the lithium sulfide (Li2S) in the heat-treated product (weight of sulfur-containing additive [g] / weight of lithium sulfide in the heat-treated product [g]) is 1.5 to 7.

5.

4. In Paragraph 1, A method for manufacturing lithium sulfide in powder form using the above-mentioned sulfur-containing additive.

5. In Paragraph 1, A method for producing lithium sulfide comprising at least one of the following: sulfur (S8), disulfides (S2), tetrasulfides (Cyclo-S4, S4), hydrogen sulfide (H2S), polysulfides, sulfides, and carbon disulfide.

6. In Paragraph 2, A method for producing lithium sulfide, wherein the ratio of the second solvent is 30 to 90 vol% based on the sum of the first solvent and the second solvent, 100 vol%, in the step of recovering the second solvent and mixing it to obtain the extraction solution.

7. In Paragraph 2, The step of drying the above extraction solution to obtain a dried lithium sulfide product and the second solvent is, A method for producing lithium sulfide by performing the above extraction solution at a temperature of 160 to 280 ℃.

8. In Paragraph 2, The step of drying the above extraction solution to obtain a dried lithium sulfide product and the second solvent is, A method for producing lithium sulfide carried out in a dryer with an internal pressure of 25 to 40 mbar.

9. In Paragraph 2, The step of refining the heat-treated product above is, After the step of drying the above extraction solution to obtain a lithium sulfide dry product and the above second solvent, A method for manufacturing lithium sulfide comprising the step of heat-treating the above-mentioned lithium sulfide dried product.

10. In Paragraph 9, A method for manufacturing lithium sulfide in which the step of heat-treating the above-mentioned lithium sulfide dried product is performed at 800 to 1,000 ℃.

11. In Paragraph 9, A method for manufacturing lithium sulfide in which the step of heat-treating the extracted lithium sulfide dried product is performed in the range of 1 to 5 hours.

12. In Paragraph 9, The step of heat-treating the above-extracted lithium sulfide dry product is performed in a reduced pressure atmosphere, and The above reduced pressure atmosphere is 10 -1 to 10 -3 A method for manufacturing lithium sulfide performed in torr.

13. In Paragraph 9, The step of mixing a carbon-based material with the lithium compound containing the above lithium and heat-treating it is Step of preparing the above lithium compound and the above carbon-based material; A method for manufacturing lithium sulfide comprising the step of mixing the above lithium compound and the above carbon-based material and heat treating.

14. In Paragraph 1, A method for producing lithium sulfide containing lithium sulfate (Lithium Sulfate, Li2SO4), wherein the lithium compound containing the above lithium is a lithium compound.

15. Lithium sulfide obtained by any one of claims 1 to 14, Lithium sulfide having a combined content of lithium oxide (Li2O) and lithium sulfate (Li2SO4) of 0.4 H% or less.

16. In Paragraph 15, Lithium sulfide having an oxygen content of 1.4 weight% or less based on 100 weight% of lithium sulfide.

17. In Paragraph 15, Lithium sulfide having a carbon content of 0.15 weight% or less based on 100 weight% of lithium sulfide.

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