Preparation method of lithium sulfide with lithium polysulfide

Abstract

The present invention relates to a preparation method of lithium sulfide with lithium polysulfide, the method comprising the steps of: mixing a carbon-based material with a lithium sulfate aqueous solution, followed by thermal treatment; subjecting the thermally treated product to solvent extraction with a solvent including water (H2O); and obtaining lithium sulfide, wherein the step of subjecting the thermally treated product to solvent extraction comprises a step of adding S8 to the thermally treated product.

Description

Method for producing lithium sulfide using lithium polysulfide

[0001] The present invention relates to an all-solid-state electrolyte, and more particularly, to a method for producing lithium sulfide by adding lithium polysulfide.

[0002] Secondary batteries are widely used in everything from small electronic devices like mobile phones and laptops to larger devices like electric vehicles (EVs) and energy storage systems (ESS). As secondary batteries' applications expand across all aspects of daily life, the demand for them is increasing, not only for high energy density and long lifespan, but also for stability.

[0003] Conventionally, most electrolytes used in lithium secondary batteries have been liquid electrolytes utilizing organic solvents. However, due to the risk of leakage or fire hazards associated with these liquid electrolytes, strict packaging has become necessary, and this strict packaging has limited the ability to increase energy density beyond a certain level. Consequently, the need for all-solid-state batteries utilizing inorganic solid electrolytes rather than organic liquid electrolytes has emerged.

[0004] The above-mentioned all-solid-state battery can be safely manufactured by excluding organic solvents such as liquid electrolytes. Furthermore, because the inorganic solid electrolyte is stable and does not decompose over a wide voltage range, it has the advantage of enabling the use of high-voltage electrode materials.

[0005] The above solid electrolytes are classified into oxide-based and sulfide-based, and the sulfide-based solid electrolyte has the characteristic of higher ionic conductivity compared to the oxide-based solid electrolyte. The main raw material of the sulfide-based solid electrolyte is lithium sulfide (Li2S). The lithium sulfide synthesis methods utilized include a synthesis method using a high-energy ball mill, a synthesis method using a wet plasma process, and a wet / dry method using lithium metal.

[0006] Lithium sulfide, as an electrolyte, has excellent ionic conductivity and high stability, resulting in a low fire risk. Demand is growing as a raw material for solid electrolytes in all-solid-state batteries. However, the production of lithium sulfide presents challenges, including high manufacturing costs and a complex production process.

[0007] When synthesizing a sulfide-based solid electrolyte, there is a problem of excessive loss of sulfur during heat treatment due to the atmospheric stability of the material and the excessive use of lithium sulfide raw materials.

[0008] The technical problem to be solved by the present invention is to provide a method for producing lithium sulfide, which is advantageous for atmospheric stability when synthesizing a sulfide-based solid electrolyte and prevents the problem of excessive loss of sulfur due to excessive use of lithium sulfide raw material.

[0009] According to one embodiment of the present invention, a method for producing lithium sulfide includes a step of mixing a carbon-based material into lithium sulfate powder and heat-treating the mixture, a step of solvent-extracting the heat-treated resultant with water (H2O) or an aprotic polar solvent, and a step of obtaining lithium sulfide. The step of solvent-extracting the heat-treated resultant may include a step of adding sulfur source to the heat-treated resultant. In one embodiment, the step of solvent-extracting the heat-treated resultant may be such that a weight ratio of the sulfur source to Li2S in the heat-treated resultant may be 0.05 to 2.0.

[0010] In one embodiment, the sulfur source may be S8. In one embodiment, the aprotic polar solvent may include at least one of tetrahydrofuran (THF), toluene, diethyl ether, and 1-Methyl-2-pyrrolidinone (NMP). In one embodiment, the solvent extraction step may extract Li2S from the solvent-extracted result. x comprising a step of obtaining Li2S x In , x can be 4 or more.

[0011] In one embodiment, the step of obtaining lithium sulfide may include a step of drying the solvent-extracted result at 40 to 60° C. In one embodiment, the step of obtaining lithium sulfide may include a step of heat-treating the solvent-extracted result at a temperature of 400° C. or higher.

[0012] In one embodiment, in the step of mixing a carbon-based material into the lithium sulfate and heat-treating the mixture, the mixing ratio of the lithium sulfate and the carbon-based material may be C:Li2SO4 in a weight ratio of 3:1 to 7:1. In one embodiment, prior to the drying step, a step of concentrating the solvent-extracted result at a temperature range of 60 to 70°C may be included.

[0013] In one embodiment, when the solvent in the solvent extraction step is water (H2O), a step of purifying the solvent-extracted result may be included. In one embodiment, the purifying step may use a solvent including at least one of tetrahydrofuran (THF), toluene, diethyl ether, and NMP (1-Methyl-2-pyrrolidinone).

[0014] In one embodiment, the carbonaceous material may be at least one 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. In one embodiment, the step of mixing the carbonaceous material into the lithium sulfate and performing heat treatment may be performed at a temperature in the range of 800 to 1,000°C. In one embodiment, the step of mixing the carbonaceous material into the lithium sulfate aqueous solution and performing heat treatment may be performed for a period of 1 to 3 hours.

[0015] In one embodiment, when the solvent is an aprotic polar solvent in the solvent extraction step, a step of adding water (H2O) as an additive may be included. In one embodiment, the ratio of the amount of the solvent added to the amount of the water added may be 150 to 250.

[0016] A method for producing lithium sulfide according to one embodiment of the present invention uses a sulfur source in an extraction process after thermal reduction, and solvent extracts with water (H2O) or an aprotic polar solvent, thereby ensuring stability against moisture in the air when synthesizing a sulfide-based solid electrolyte, simplifying the process, and ensuring economic feasibility when applying equipment in the future.

[0017] Figure 1 is a schematic diagram of a method for producing lithium sulfide of the present invention.

[0018] Figures 2a to 2c are UV analysis graphs according to examples and comparative examples of the present invention.

[0019] Figures 3a to 3g are XRD pattern graphs of examples and comparative examples of the present invention.

[0020] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0021] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising," as used herein, specifies particular features, regions, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0022] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0023] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted as having meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed in ideal or overly formal meanings unless otherwise defined. In addition, unless specifically stated, % means weight percent, and 1 ppm is 0.0001 weight percent.

[0024] In this specification, the average particle size (D50) can be defined as a particle size corresponding to 50% of the volume accumulation amount in the particle size distribution curve. The average particle size (D50) can be measured using, for example, the laser diffraction method. The laser diffraction method can measure particle sizes from the general submicron range to several mm, and can obtain highly reproducible and highly resolvable results.

[0025] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0026] According to one embodiment of the present invention, a method for producing lithium sulfide may include a step of mixing a carbonaceous material in a lithium sulfate aqueous solution and heat-treating it, a step of solvent-extracting the heat-treated resultant, and a step of obtaining lithium sulfide. Specifically, the method for producing lithium sulfide of the present invention may be a method for synthesizing Li2S by reducing lithium sulfate (Li2SO4), which is an intermediate product generated during a lithium (Li) extraction process, using a carbonaceous material such as graphite or coke, and sequentially performing extraction-filtration-drying-heat treatment processes using a solvent, thereby producing high-purity Li2S. More specifically, the method for producing lithium sulfide of the present invention may use water (H2O) as an additive as the extraction solvent in the solvent-using extraction and filtration steps, or use water itself as a solvent to obtain Li2S. x By forming and drying, the equipment and process for blocking the atmosphere in the Li2S manufacturing process can be simplified, and it can be advantageous for scale up, especially in selecting equipment for the drying process.

[0027] In the step of heat-treating by mixing a carbonaceous material into a lithium sulfate aqueous solution, the mixing ratio of the lithium sulfate aqueous solution and the carbonaceous 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. Specifically, lithium sulfate powder and the carbonaceous material may be mixed first and stirred.

[0028] In one embodiment, the step of mixing and heat-treating the lithium sulfate powder and the carbon-based material includes pre-mixing the lithium sulfate powder and the carbon powder by stirring using a powder mixer (Universal Mixer). Specifically, the mixing may be dry mixing. In one embodiment, the step of preparing the mixed powder may include a stirring step for 30 minutes or more, specifically, 60 minutes or more. By performing the stirring step within the above time range, the carbon and the lithium sulfate aqueous solution can be easily mixed.

[0029] In one embodiment, the step of mixing lithium sulfate powder and carbon-based material and heat treating the mixture may be performed at a temperature range of 800 to 1,000°C. Specifically, the temperature range may be performed at a temperature range of 850 to 950°C.

[0030] In one embodiment, the step of mixing the lithium sulfate powder and the carbon-based material and heat-treating the mixture may be performed in an inert atmosphere. Specifically, the inert atmosphere may include, for example, a vacuum, a gas such as helium, neon, krypton, xenon, nitrogen, or argon.

[0031] In one embodiment, the step of mixing lithium sulfate powder and a carbonaceous material and performing heat treatment may be performed for a period of 1 to 3 hours. Specifically, the period of time may be performed for a period of 1.5 to 2.5 hours. By mixing the lithium sulfate aqueous solution and the carbonaceous material under the above-described temperature and time conditions, the lithium sulfate powder and the carbonaceous material are uniformly mixed, thereby facilitating the formation of C-Li2S.

[0032] In one embodiment, the step of mixing lithium sulfate powder and a carbonaceous material and heat-treating the mixture may include a step of pulverizing the carbonaceous material before mixing the lithium sulfate powder with the carbonaceous material. In one embodiment, the step of pulverizing the carbonaceous material may be a step of pulverizing the carbonaceous material using a jaw crusher or a pin mill and removing fine particles using a sieve of 200 mesh (pore size of 65 μm).

[0033] In one embodiment, the carbonaceous material may be at least one 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. Specifically, the carbonaceous material of the present invention may be artificial graphite, for example, waste resistor material from an Achtson furnace. The waste resistor material may refer to a resistor material that cannot be reused and is discarded when the coke used as a resistor material increases in electrical conductivity through an increase in crystallinity in the process of being graphitized through a 3,000°C heat treatment process and cannot perform its role as a resistor material. By using the waste resistor material, there is an environmentally friendly advantage.

[0034] The step of solvent-extracting the heat-treated result may be a step of solvent-extracting the heat-treated result with water (H2O) or an aprotic polar solvent from the step of mixing lithium sulfate powder and a carbon-based material and heat-treating them. Specifically, the heat-treated result may be a C-Li2S complex in which C and Li2S are mixed.

[0035] The aprotic polar solvent may be, for example, at least one of toluene, diethyl ether, and tetrahydrofuran (THF). Unlike conventional methods, in the solvent extraction step of the present invention, by using water or the aprotic polar solvent instead of ethanol, water evaporation can be facilitated in the subsequent drying step, thereby overcoming limitations in scale-up of the equipment.

[0036] In one embodiment, when the solvent is an aprotic polar solvent in the solvent extraction step of the heat-treated product, the extraction process may be performed using some water (H2O) as an additive. In one embodiment, the ratio of the amount of the solvent added to the amount of the water added may be 150 to 250. Specifically, the ratio may be 175 to 225. For example, the amount of water added may be 0.5 to 2 mL.

[0037] By using the above water as an additive, there is no special sealing required to block the atmosphere during the extraction process and drying process, so when considering mass production, there is an advantage in that the equipment investment cost can be reduced and the range of equipment to be selected can be expanded.

[0038] In one embodiment, when the solvent is water in the solvent extraction step of the heat-treated product, a purification step of purifying with the aprotic polar solvent may be further included. Specifically, when water is used as the solvent, an additional purification step of re-dissolving and then filtering using the aprotic polar solvent, for example, tetrahydrofuran (THF), toluene, diethyl ether, and NMP (1-Methyl-2-pyrrolidinone), may be performed after the drying step. The reason for including the purification step is that Li2S in the dried product x This is because LiOH also exists together in a certain ratio, so an excess amount of Li2SO4 exists during heat treatment.

[0039] In one embodiment, the step of solvent-extracting the heat-treated result may include a step of adding a sulfur source to the heat-treated result. Specifically, after adding the sulfur source to the heat-treated result, an extraction process may be performed using a solvent containing water.

[0040] In one embodiment, the sulfur source may be S8. By using S8 as the sulfur source, lithium polysulfide (Li2S) can be produced without using toxic gases such as H2S or CS2. x ) has the advantage of being able to form.

[0041] In one embodiment, the step of adding a sulfur source to the heat-treated result may be such that the weight ratio [g / g] of the sulfur source to Li2S in the heat-treated result may be from 0.05 to 2.0. Specifically, the weight ratio may be from 0.1 to 1.5, and more specifically, from 0.1 to 0.8. By satisfying the above-described range of weight ratio, there is an advantage in that high-yield Li2S and high-purity Li2S with a low oxygen content can be produced.

[0042] If the above weight ratio is outside the lower limit of the aforementioned range, there is a problem that the sulfur source is excessively small, and the content of Li2SO3 and Li2SO4 due to LiOH generated during the drying process increases.

[0043] In one embodiment, in the solvent extraction step, the solvent may further include at least one of tetrahydrofuran (THF), toluene, diethyl ether, and NMP (1-Methyl-2-pyrrolidinone). By making the solvent containing water an essential component in the solvent extraction step and additionally including the aforementioned solvent, there is an advantage in that the solubility of the polysulfide compound is increased, thereby increasing the yield of the final product.

[0044] In another embodiment, in the solvent extraction step, the essential solvent may include at least one of tetrahydrofuran (THF), toluene, diethyl ether, and 1-methyl-2-pyrrolidinone (NMP), and a solvent containing water may be additionally added. At this time, the solvent containing water may be additionally added in an amount of 0.1 ml or more, specifically, 0.2 to 1.0 ml, and more specifically, 0.5 to 0.7 ml. The role of the added H2O at this time can be confirmed through the following reaction formula.

[0045] [Reaction formula]

[0046] Li2S + H2O + S8→ 2Li + + SH - + OH - + S8→ 2Li + S X H - + OH -

[0047] Looking at the above reaction formula, tetrahydrofuran (THF), which is an essential solvent in the solvent extraction step, has low solubility, so that each substance is difficult to ionize and does not induce a reaction that forms polysulfide. However, when a very small amount of water (H2O) of the present invention is added to a slurry in which powders containing C-Li2S and S8 are mixed and dispersed in THF, it can be confirmed that the color of the transparent THF solution changes from green to red. This phenomenon is because Li2S is converted to Li by the addition of H2O. + Ion and SH - Wow OH - ionized, and at this time, the formed SH - S8 is reduced by ions to S x 2- It can be confirmed that ions are formed. At this time, the amount of S8 added and the ratio of SH- ions determine S x 2- The X value of is determined.

[0048] In the present invention, it was confirmed that most of the results with relatively low oxygen contents correspond to cases where the X value is 4 or higher. In the ICP analysis of the dried product of this solution, it was confirmed that the oxygen content of the final Li2S was low at 1.5% or less when the ratio of S to Li was in the range of 2:1 to 4:1. A more detailed description of this will be described later in FIGS. 2a to 2c.

[0049] By adding a sulfur source to the above heat-treated product, an oxidation-reduction reaction occurs in a solvent containing water to produce lithium sulfide (Li2S). x ) can be obtained as an aqueous solution. Specifically, the solvent extraction step is to obtain Li2S from the solvent-extracted result. x can be obtained.

[0050] In one embodiment, Li2S xIn the step of obtaining, the above x may be 4 or more. Li2S in which the above x is 4 or more x In a solvent extraction process, C-Li2S, a sulfur source, and water are mixed to obtain high-purity lithium sulfide, thereby reducing the loss of sulfur in a subsequent process.

[0051] The step of obtaining lithium sulfide includes the step of drying and the step of heat-treating the solvent-extracted result. The solvent-extracted result is Li2S. x It may be a solution containing. The solvent-extracted result may be dried and heat-treated, thereby accompanying a solidification step.

[0052] The step of drying the solvent-extracted result may be performed at a temperature range of 40 to 60°C. Specifically, the temperature range may be performed at a temperature range of 45 to 55°C.

[0053] In one embodiment, the step of drying the solvent-extracted product may be performed in a vacuum atmosphere with an atmospheric pressure of 40 mbar or less. Specifically, the drying step may utilize the reduced pressure distillation method described above in the atmospheric pressure atmosphere. By performing the drying step, a powder containing water within the solvent-extracted product can be obtained without being released.

[0054] In one embodiment, the step of heat-treating the solvent-extracted result may be performed at a temperature of 700° C. or higher. Specifically, the heat-treating step may be performed at 700° C. or higher after drying the solvent-extracted result. The step of heat-treating the solvent-extracted result may be performed to obtain Li2S through a drying process. x And it may be a step of synthesizing Li2S by performing heat treatment on a Li2CO3 mixture.

[0055] In one embodiment, the step of heat-treating the solvent-extracted result may be performed at a temperature range of 700°C or higher. As the heat-treating step is performed within the aforementioned temperature range, lithium sulfide with a 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 result exceeds the lower limit of the aforementioned temperature range, there is a problem of an increase in the oxygen content in Li2S.

[0056] In one embodiment, prior to the drying step, a step of concentrating the solvent-extracted result may be included. The concentrating step may be performed at a temperature in the range of 60 to 70°C. The drying step of the solvent-extracted result may be performed in a vacuum atmosphere having a pressure of 40 mbar or less.

[0057] The above concentration step is the solvent-extracted result Li2S x It may be a step of powdering LiOH in a solution containing . The above concentration conditions are such that when H2O is used as a solvent, the dried product is dissolved in an organic solvent such as THF in an additional purification process, and then LiOH is precipitated in the process of increasing the concentration of the solution through reduced pressure concentration, and LiOH is removed through filtration, and Li2S of relatively high purity is obtained. x The process of obtaining it is performed.

[0058] In one embodiment, a step of purifying the solvent-extracted product may be included between the concentration step and the drying step. Specifically, the purifying step may be a step of separating LiOH solidified through the concentration step, for example, in the form of a cake.

[0059] In one embodiment, the step of purifying the solvent-extracted product may be performed using a solvent. The solvent may include, for example, at least one of tetrahydrofuran (THF), toluene, diethyl ether, and 1-methyl-2-pyrrolidone (NMP). Specifically, the purifying step may be additionally performed, for example, when the solvent used in the solvent extraction process is water (H2O).

[0060] In one embodiment, the heat treatment of the above-mentioned dried product may be performed at 350°C or higher. More specifically, it may be performed in a tube-type furnace under Ar flow at 400°C or higher. Li2S x In the case of Li2S, it can be thermally decomposed into Li2S and S2 (gas) at around 350 degrees. Accordingly, the S2 in the gas phase can be recovered in the form of S8 outside the furnace.

[0061]

[0062] Specific examples of the present invention are described below. However, the following examples are merely specific examples of the present invention, and the present invention is not limited to the following examples.

[0063]

[0064] <Experimental Example>

[0065] <Example 1>

[0066] As a carbon raw material (C), waste resistors discarded from an Achison furnace of POSCO Future M were prepared. The carbon raw material (C) and lithium sulfate monohydrate were mixed in a weight ratio of 3:1, and then heat-treated at 900°C for 2 hours. Thereafter, 110 g of S8 was added to the carbon-lithium sulfide (C-Li2S) formed through the heat treatment, and a step of extraction and filtration was performed by mixing a solvent. At this time, the weight ratio of carbon-lithium sulfide (C-Li2S) and S8 was added at 10:1, and 200 ml of THF and 1 ml of ion-exchanged water (DI water) were used as the extraction solvent.

[0067] Through the above solvent extraction process, Li2S x Solution and carbon were obtained. Afterwards, Li2S was separated through a vacuum filtration process using a filter paper. x The solution containing LiOH and carbon was filtered and separated. The Li2S produced at this time X X has a value greater than or equal to 4. Specifically, x has a value of 4.

[0068] Afterwards, the separated Li2S x A solution containing LiOH was dried under reduced pressure under the conditions of a pressure (4 mbar) atmosphere, 65°C, and 1 hour. By performing the drying, Li2S x A solution and LiOH powder were obtained. Afterwards, through a purification process under reduced pressure filtration conditions, Li2S x The solution and LiOH cake were separated.

[0069] Afterwards, the separated Li2S x The solution was dried under the conditions of a reduced pressure atmosphere, 80°C, and for 3 hours. The dried product was heat-treated under the conditions of an Ar flow of 1 L / min, 400°C, and for 1 hour to produce lithium sulfide (Li2S).

[0070]

[0071] <Example 2>

[0072] The extraction was performed in the same manner as in Example 1, except that the mixing ratio of the raw materials was 110 g of heat-reduced material and 8 g of S8.

[0073]

[0074] <Example 3>

[0075] In the raw material of Example 2, 200 ml of DIW was used instead of THF as a solvent, and the solution that had undergone the filtration process was dried under reduced pressure under the conditions of a reduced pressure (4 mbar) atmosphere, 110°C, and 1 hour. The dried product was redissolved in 200 ml of THF, and then dried under a reduced pressure (4 mbar) atmosphere, 65°C, and 1 hour to obtain a dried product, except that the same procedure as Example 1 was followed.

[0076]

[0077] <Example 4>

[0078] The extraction was performed in the same manner as in Example 1, except that the mixing ratio of the raw materials was 110 g of heat-reduced material and 15 g of S8.

[0079]

[0080] <Example 4>

[0081] The same procedure as Example 4 was followed, except that the heat treatment temperature was set to 500°C.

[0082]

[0083] <Comparative Example 1>

[0084] The same procedure as Example 1 was performed except that S8 was not added in the solvent extraction step, ethanol was used as the solvent, and the heat treatment temperature was set to 800 degrees.

[0085]

[0086] <Comparative Example 2>

[0087] The mixing ratio of the raw materials was the same as in Example 1, except that 110 g of the heat-reduced material and 0.1 g of S8 were mixed.

[0088]

[0089] <Comparative Example 3>

[0090] The same procedure as Example 1 was followed, except that the mixing ratio of the raw materials was 110 g of heat-reduced material and 15 g of S8, and the heat treatment temperature was set to 350°C.

[0091]

[0092] <Comparative Example 4>

[0093] The same procedure as Example 3 was followed, except that the heat treatment temperature was set to 250°C.

[0094]

[0095] Comparative Example 5

[0096] The same procedure as Example 2 was followed, except that n-propanol, a polar solvent containing H, was used as the extraction solvent.

[0097]

[0098] <Comparative Example 6>

[0099] The same procedure as in Example 3 was followed, except that H2O was used as the extraction solvent and no additional purification using THF was performed.

[0100]

[0101] Comparative Example 7

[0102] The same procedure as Example 2 was followed, except that the heat treatment temperature was set to 500 degrees.

[0103]

[0104] <Evaluation example>

[0105] Tables 1 and 2 below show the filtrate dry matter mass, dried product ICP, Li2S mass after heat treatment, oxygen content, and yield when the conditions for solvent extraction were changed.

[0106] Oxygen content: Analyzed using a N / O analyzer from RECO.

[0107] Yield: The yield was calculated as the ratio of the mass of Li2S recovered after the final heat treatment process to the mass of Li2S contained in the C-Li2S mixture.

[0108] ICP: ICP of the dried product was analyzed using SPECTRO ARCOS from AMETEK.

[0109] XRD: XRD peak values ​​were analyzed using RIGAKU D / MAX 2500.

[0110] UV: GENESYS from Thermo Scientific TM Analysis was performed using a 180 UV-Visible Spectrophotometer.

[0111] Raw material composition, solvent extraction, amount of H2O added, purification solvent, heat treatment temperature, C-Li2S (thermal reduction product), Li2S (Li2S in thermal reduction product) Content) S8LiS8S / Li Molar ratio Extraction solvent type Addition amount Unit gggmolemole-mLmL-℃ Example 1 110101.00.2170.4662.14THF 2001-400 Example 2 110108.00.2170.6853.15THF 2001-400 Example 3 110108.00.2170.6853.15H2O 200-THF 400 Example 4 1101015.00.2170.9044.16THF 2001-400 Example 5 1101015.00.2170.9044.16THF 2001-500 Comparative Example 1 1101000.217 0.4380.5 Ethanol 2001-800 Comparative Example 2 110100.10.2170.4382.0 THF 2001-400 Comparative Example 3 1101015.00.2170.9044.16 THF 2001-350 Comparative Example 4 110108.00.2170.6853.15 H2O 200-THF 250 Comparative Example 5 110108.00.2170.6853.15 n-propanol 200--400 Comparative Example 6 110108.00.2170.6853.15 H2O 200--400 Comparative Example 7 110108.00.2170.6853.15 THF 200--500

[0112] Filtrate Dry Matter Amount Dry Product ICP Analysis Mass of Li2S after Heat Treatment Oxygen Content Yield LiS LiSS / Li Unit gwt% wt% mol / gmol / gg%% Example 1 1 200.01 20.1 18 0.00 20.00 42.18 10.78 1 Example 2 1 500.01 00.1 39 0.00 10.00 43.28 28 0.58 2.8 Example 3 600.0 240.3470.0030.0113.28.551.370Example 41500.0100.1830.0010.0064.28.460.484.6Example 51500.0100.1830.0010.0064.28.10.4281Comparative Example 1800.0190.1580.00 30.0050.457.925.279.2Comparative Example 2800.0190.1580.0030.0051.88.912.589.1Comparative Example 31500.0100.1830.0010.0064.294.51094.5Comparative Example 4600.0240.3470.0030.0113. 25.671256.7Comparative Example 5600.0240.3470.0030.0113.24.592.081.5Comparative Example 6600.0240.3470.0030.0113.23.782037.8Comparative Example 70.80.1903.2870.0270.1033.80.12.01.0

[0113] Looking at Tables 1 and 2 above, the ICP analysis of the dried product after solvent extraction confirmed that the oxygen content of Li2S was low and the yield was high under conditions where the S:Li ratio was 2 to 4. Specifically, in the case of Examples 1, 3, 4, and 5 using THF as a solvent, the oxygen content in the final product, lithium sulfide, was less than 1%, confirming a very high purity quality. In Examples 1, 3, 4, and 5, Li2S could be obtained in a high yield of 80% or more. In addition, in the case of Example 3 using water as a solvent, Li2S with a relatively high purity of about 70% could be obtained with an oxygen content of 1.3% through a purification process using THF. Through this, it was confirmed that high-purity Li2S could be obtained even in an air-exposed state, and that there was an advantage in scale-up when selecting extraction and drying process equipment. Specifically, Comparative Examples 4 and 5 in which the heat treatment temperature was excessively low, Comparative Example 2 in which ethanol was used as an extraction solvent without adding S8, Comparative Example 3 in which the content of S8 was excessively low, Comparative Examples 6 and 7 in which THF was not used as an extraction solvent, and Comparative Example 8 in which no water was added at all during solvent extraction were confirmed to have a high oxygen content and thus a low purity compared to Examples 1 to 4. In addition, it was confirmed that Examples 1, 2, and 4 had an oxygen content of less than 1.0%.

[0114] As in Example 5, Li2S xIt was confirmed that the temperature at which Li2S and S2 (gas) are decomposed through thermal decomposition is sufficiently achieved at a temperature of 400°C or higher. In the case of Comparative Example 1, solvent extraction was performed using ethanol without adding S8 through the existing thermal reduction process, and there is a problem that it is difficult to obtain high-purity lithium sulfide because the oxygen content is high compared to the examples, and an equipment structure that requires airtightness to thoroughly prevent exposure to the atmosphere during processes such as extraction and drying is required, and there is a problem that there is a limitation in the scale up of the condensation equipment for recovering ethanol.

[0115] In the case of Comparative Example 2 where the weight ratio of Li2S and S was 10:0.1, the ICP analysis result of the dried product confirmed that the molar ratio of S:Li was 1.8, which is less than 2. In this case, the UV analysis result confirmed that a polysulfide having an X value of 3 was formed. Specifically, when the dried product in which Li2S and Li2S3 were mixed was heat-treated while some LiOH was mixed, it was confirmed that Li2SO4 was formed, and ultimately Li2S containing relatively high impurities with an oxygen content of 2.5% was obtained.

[0116] In the case of Comparative Example 3, where the heat treatment temperature is 350°C, it can be confirmed that it has an oxygen content of 10% compared to Example 4. This was confirmed to be due to the decomposition of the solvent and LiOH without decomposition of the polysulfide at a temperature of 350°C.

[0117] In Comparative Example 4, where H2O was used as the solvent and a purification process was performed with THF, followed by heat treatment at 250°C, the oxygen content was found to be 12% higher and the yield was also lower than in Example 3. This was confirmed to be due to the use of H2O as the solvent, which affected the oxygen content even after the purification process due to LiOH and Li2CO3 present in the extraction solution.

[0118] In Comparative Example 5, which used n-propanol in the solvent extraction process, when the solution was dried after extraction, the weight was relatively high at around 8.73 g, but the yield after heat treatment was low at around 60% and the oxygen content was also high. This was confirmed to be due to the severe weight loss caused by the thermal decomposition of lithium alkoxide present in the extraction solution and the formation of Li2CO3 produced by the thermal decomposition of lithium alkoxide.

[0119] Comparative Example 6, which used H2O as a solvent in the solvent extraction process and did not perform a separate purification process, was confirmed to have a very high oxygen content and low yield compared to Example 3, which underwent a redissolution and purification process with THF. This is because, in the case where a purification process was not performed, the contents of LiOH and Li2CO3 present in the solution were high, resulting in the presence of many impurities even after drying, and it was confirmed that various types of impurities containing a high level of oxygen were present even after heat treatment at 400°C.

[0120] Comparative Example 7, in which H2O was not added during the solvent extraction process, is SH - It was confirmed that dissolution through reduction of S8 did not occur because no ions were formed. Heat treatment was performed on a very small amount of dried material, but it was confirmed that Li2S could not be obtained with a final yield of 1%.

[0121] Figures 2a to 2c are UV analysis graphs according to examples and comparative examples of the present invention.

[0122] Figure 2a is a UV analysis result when the S / Li molar ratio is 2 or more, Figure 2b is a UV analysis result when the S / Li molar ratio is 3 or more, and Figure 2c is a UV analysis graph when the S / Li molar ratio is lower than 2.

[0123] Referring to FIG. 2a and FIG. 2b, as in Example 3, the UV spectra for the extraction solution show that when the molar ratio of S / Li is 2 to 4, the polysulfide in the solution is S4. 2- , S6 2- It was confirmed that it exists in ionic form. UV analysis was performed on the filtered solution diluted in DMSO solution.

[0124] Referring to Fig. 2c, when the ratio of S / Li is 1.8, as in Comparative Examples 1 and 2, S3 is added to the extraction solution. 2- It was confirmed that S exists. Through this, in the extraction solution of the example x 2- I heard S4 2- Through S6 2- It was confirmed through UV analysis that it was formed.

[0125] Figures 3a to 3g are XRD pattern graphs of examples and comparative examples of the present invention.

[0126]

[0127] Figures 3a to 3g sequentially show XRD patterns of Example 2, Example 3, Comparative Example 2, Comparative Example 3, Comparative Example 4, Comparative Example 5, and Comparative Example 6.

[0128] Referring to FIGS. 3a and 3b, it can be confirmed that a trace amount of Li2O is observed in Example 3. This shows an oxygen content of 1.3%, which is somewhat higher than that of Examples 1, 2, and 4, but it can be confirmed that it shows a lower oxygen content compared to the comparative examples.

[0129] Referring to Fig. 3c, it was confirmed that peaks of Li2SO4 were observed together with Li2S. Comparative Example 2 has a relatively high oxygen content, which can be confirmed to be due to Li2SO4. Referring to Figs. 3d and 3f, peaks such as Li2CO3 and Li2SO4 were confirmed in Comparative Examples 3 to 5 due to oxygen. Referring to Fig. 3f, it was confirmed that S8 was also observed in Comparative Example 6 along with LiOH, Li2CO3, and Li2SO4.

[0130]

[0131] The present invention is not limited to the above-described embodiments and / or examples, but can be manufactured in various different forms. Those skilled in the art will understand that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the above-described embodiments and / or examples should be understood as illustrative in all respects and not restrictive.

Claims

1. A step of mixing a carbon-based material into lithium sulfate powder and performing heat treatment; A step of solvent extracting the heat-treated resultant product with water (H2O) or an aprotic polar solvent; and Comprising a step of obtaining lithium sulfide, A method for producing lithium sulfide, wherein the step of solvent extracting the heat-treated result includes a step of adding a source to the heat-treated result.

2. In paragraph 1, A method for producing lithium sulfide, wherein the step of solvent extracting the heat-treated resultant has a weight ratio of the sulfur source to Li2S in the heat-treated resultant of 0.05 to 2.

0.

3. In paragraph 1, The above sulfur source is a method for producing lithium sulfide having S8.

4. In paragraph 1, A method for producing lithium sulfide, wherein in the solvent extraction step, the aprotic polar solvent includes at least one of tetrahydrofuran (THF), toluene, diethyl ether, and NMP (1-Methyl-2-pyrrolidinone).

5. In paragraph 1, The above solvent extraction step is to extract Li2S from the solvent extracted result. x Comprising a step of obtaining, The above Li2S x A method for producing lithium sulfide wherein x is 4 or more.

6. In paragraph 1, A method for producing lithium sulfide, wherein the step of obtaining the lithium sulfide comprises a step of drying the solvent-extracted resultant at 40 to 60° C.

7. In paragraph 1, A method for producing lithium sulfide, wherein the step of obtaining the lithium sulfide includes a step of heat-treating the solvent-extracted resultant at a temperature of 400° C. or higher.

8. In paragraph 1, A method for producing lithium sulfide, wherein in the step of mixing a carbon-based material into the lithium sulfate and performing heat treatment, the mixing ratio of the lithium sulfate and the carbon-based material is C:Li2SO4 of 3:1 to 7:1 by weight.

9. In paragraph 5, Before the above drying step, A method for producing lithium sulfide, comprising a step of concentrating the solvent-extracted resultant at a temperature range of 60 to 70° C.

10. In paragraph 1, In the solvent extraction step, if the solvent is water (H20), A method for producing lithium sulfide, comprising a step of purifying the solvent-extracted result.

11. In Article 10, A method for producing lithium sulfide, wherein the purifying step uses a solvent containing at least one of tetrahydrofuran (THF), toluene, diethyl ether, and NMP (1-Methyl-2-pyrrolidinone).

12. In paragraph 1, A method for producing lithium sulfide, wherein the carbonaceous material is at least one 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.

13. In paragraph 12, The above artificial graphite is a method for producing lithium sulfide, a waste resistance material of Achison.

14. In paragraph 1, A method for producing lithium sulfide, wherein the step of mixing a carbon-based material into the lithium sulfate and heat-treating the mixture is performed at a temperature range of 800 to 1,000°C.

15. In paragraph 1, A method for producing lithium sulfide, wherein the step of mixing a carbon-based material into the lithium sulfate aqueous solution and performing heat treatment is performed for a period of 1 to 3 hours.

16. In paragraph 1, In the solvent extraction step, if the solvent is an aprotic polar solvent, A method for producing lithium sulfide, comprising the step of adding water (H2O) as an additive.

17. In paragraph 17, A method for producing lithium sulfide, wherein the ratio of the amount of the solvent added to the amount of water added is 150 to 250.

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