Method for preparing alkali metal sulfide

Abstract

The present invention relates to a method for preparing an alkali metal sulfide, comprising the steps of: mixing a precursor and a first reducing agent to form a mixture; reducing the mixture together with a second reducing agent to obtain an alkali metal sulfide; dissolving and purifying the obtained alkali metal sulfide in a polar solvent; and drying the purified alkali metal sulfide.

Description

Method for producing alkali metal sulfide

[0001] The present invention relates to a method for producing alkali metal sulfide.

[0002] Methods for producing lithium sulfide are known, for example, by reducing lithium sulfate. The method for reducing lithium sulfate involves reducing lithium sulfate by reacting it with a reducing agent containing carbon, thereby producing lithium sulfide.

[0003] However, when reducing lithium sulfate using a reducing agent containing carbon, there is a problem in that, since lithium has a high reactivity during the manufacturing process, an excessive amount of impurities that react with lithium are generated, which reduces the yield of alkali metal sulfide and lowers its purity.

[0004] In addition, when lithium sulfate is reduced using a reducing agent containing carbon, the amount of carbon used increases, which causes the problem of generating large amounts of compounds that affect the Earth's atmospheric environment, such as CO2.

[0005] The problem to be solved by the present invention is to provide a method for producing high-purity alkali metal sulfide by using hydrogen together with carbon as a reducing agent, while reducing the amount of carbon used.

[0006] According to one aspect of the present invention, a method for producing an alkali metal sulfide is provided, comprising: a step (S10) of forming a mixture by mixing a precursor, which is a compound containing an alkali metal element and a sulfur element, and a first reducing agent; a step (S20) of reducing the mixture with a second reducing agent to obtain an alkali metal sulfide; a step (S30) of dissolving the obtained alkali metal sulfide in a polar solvent to purify it; and a step (S40) of drying the purified alkali metal sulfide.

[0007] According to one embodiment of the present invention, even if the amount of carbon used is reduced, the reduction effect is maximized by using hydrogen as a reducing agent together with carbon, and by reducing the amount of carbon used, environmental pollution by carbon dioxide, etc. can be prevented, and high-purity alkali metal sulfide can be manufactured.

[0008] Additionally, by using carbon and hydrogen as reducing agents, alkali metal sulfides can be produced at relatively low temperatures.

[0009] Figure 1 is a flowchart showing a method for producing alkali metal sulfide according to one embodiment of the present invention.

[0010] Figure 2 is a graph showing the results of analyzing the alkali metal sulfides of Comparative Examples 1 to 3 using XRD.

[0011] Figure 3 is a graph showing the results of XRD analysis of alkali metal sulfides of Examples 1 and 2.

[0012] Figure 4 is a graph showing the results of XRD analysis of alkali metal sulfides of Examples 3 and 4.

[0013] Figure 5 is a graph showing the results of XRD analysis of alkali metal sulfides of Examples 3 and 5.

[0014] Figure 6 is a graph showing the results of XRD analysis of alkali metal sulfides of Examples 3 and 6.

[0015] Figure 7 is a graph showing the results of XRD analysis of alkali metal sulfides of Examples 7 and 8.

[0016] Figure 8 is a graph showing the results of XRD analysis of alkali metal sulfides of Examples 3 and 8.

[0017] Figure 9 is a graph showing the results of XRD analysis of alkali metal sulfides of Examples 8 and 9.

[0018] According to one aspect of the present invention, a method for producing an alkali metal sulfide is provided, comprising: a step (S10) of forming a mixture by mixing a precursor, which is a compound containing an alkali metal element and a sulfur element, and a first reducing agent; a step (S20) of reducing the mixture with a second reducing agent to obtain an alkali metal sulfide; a step (S30) of dissolving the obtained alkali metal sulfide in a polar solvent to purify it; and a step (S40) of drying the purified alkali metal sulfide.

[0019] According to one embodiment of the present invention, a method for producing an alkali metal sulfide is provided, which further includes a drying step after the step of forming the mixture (S10).

[0020] According to one embodiment of the present invention, a method for producing an alkali metal sulfide is provided, wherein the precursor is any one of lithium sulfate, sodium sulfate and potassium sulfate.

[0021] According to one embodiment of the present invention, a method for producing an alkali metal sulfide is provided, wherein the first reducing agent is a carbon-based reducing agent.

[0022] According to one embodiment of the present invention, a method for producing an alkali metal sulfide is provided, wherein the first reducing agent includes at least one of solid carbonaceous materials such as coal, coke, graphite, carbon black, fullerene, carbon tube, charcoal, carbide, simple carbon, and its isotropes.

[0023] According to one embodiment of the present invention, a method for producing an alkali metal sulfide is provided, wherein in the step (S20) of reducing the mixture with a second reducing agent to obtain an alkali metal sulfide, the reduction temperature is 700°C to 800°C.

[0024] According to one embodiment of the present invention, a method for producing an alkali metal sulfide is provided, wherein the molar ratio of the precursor and the first reducing agent (precursor: first reducing agent) is 1:1.5 to 1:2.

[0025] According to one embodiment of the present invention, a method for producing an alkali metal sulfide is provided, wherein the hydrogen concentration is 2 vol% to 4 vol% and the flow rate of the second reducing agent is 50 cc / min to 100 cc / min.

[0026] According to one embodiment of the present invention, a method for producing an alkali metal sulfide is provided, wherein the second reducing agent comprises at least one selected from the group consisting of carbon monoxide, nitrogen, argon, helium, neon, methane, ethane, propane, and butane and hydrogen.

[0027] According to one embodiment of the present invention, a method for producing an alkali metal sulfide is provided, which further includes a step of crystallizing the dried alkali metal sulfide after the step of drying the purified alkali metal sulfide (S40).

[0028] According to one embodiment of the present invention, a method for producing an alkali metal sulfide is provided, wherein peaks exist at diffraction angles (2θ) of 27°±1.0°, 31°±1.0°, 45°±1.0°, and 53°±1.0° in an X-ray diffraction (XRD) analysis graph of the alkali metal sulfide, and the alkali metal sulfide satisfies the following equation 1.

[0029] [Formula 1]

[0030] I background ≤ I min

[0031] I min In the graph analyzed by X-ray diffraction (XRD), the height of the lowest peak among the Li2S peaks corresponding to the diffraction angles (2θ) of 27°±1.0°, 31°±1.0°, 45°±1.0°, and 53°±1.0° is I background is the height of the highest peak between diffraction angles (2θ) of 20° and 25° in the graph analyzed by X-ray diffraction (XRD).

[0032] The present invention is capable of various modifications and embodiments. Specific embodiments are illustrated in the drawings and described in detail in the detailed description. The effects and features of the present invention, as well as the methods for achieving them, will become clearer with reference to the embodiments described in detail below, along with the drawings. However, the present invention is not limited to the embodiments disclosed below and can be implemented in various forms.

[0033] In the examples below, the terms first, second, etc. are not used in a limiting sense, but are used for the purpose of distinguishing one component from another.

[0034] In the examples below, singular expressions include plural expressions unless the context clearly indicates otherwise.

[0035] In the examples below, terms such as “include” or “have” mean that a feature or component described in the specification is present, and do not preclude the possibility that one or more other features or components may be added.

[0036] In the following examples, when a part such as a film, region, component, etc. is said to be on or above another part, it includes not only a case where it is directly on top of the other part, but also a case where another film, region, component, etc. is interposed in between.

[0037] For convenience of explanation, the sizes of components in the drawings may be exaggerated or reduced. For example, the sizes and thicknesses of each component shown in the drawings are arbitrarily indicated for convenience of explanation, and thus the present invention is not necessarily limited to what is shown.

[0038] Hereinafter, embodiments of the present invention will be described in detail with reference to the attached drawings, and when describing with reference to the drawings, identical or corresponding components will be given the same drawing reference numerals.

[0039] Method for producing alkali metal sulfide

[0040] Figure 1 is a flowchart showing a method for producing alkali metal sulfide according to one embodiment of the present invention.

[0041] Referring to FIG. 1, a method for producing an alkali metal sulfide (S1) may include a step of forming a mixture by mixing a precursor and a first reducing agent (S10), a step of reducing the mixture with a second reducing agent to obtain an alkali metal sulfide (S20), a step of dissolving the obtained alkali metal sulfide in a polar solvent to purify it (S30), and a step of drying the purified alkali metal sulfide (S40).

[0042] In the step (S10) of forming a mixture by mixing a precursor and a first reducing agent, the precursor may be a compound containing an alkali metal element and a sulfur element. For example, the alkali metal element may be lithium ion (Li), sodium element (Na), potassium element (K), etc., and the precursor may be lithium sulfate, sodium sulfate, potassium sulfate, etc. The precursor may be a hydrate or an anhydride.

[0043] The first reducing agent may contain carbon. The first reducing agent is a carbon-based reducing agent, and its material is not particularly limited, and may be in a gaseous, liquid, or solid state. Furthermore, the first reducing agent may contain non-carbon atoms as long as it can be a source of carbon. For example, the first reducing agent may contain at least one of solid carbonaceous materials, such as coal, coke, graphite, carbon black, fullerene, carbon tubes, charcoal, carbide, simple carbon, and its allotropes.

[0044] A solvent may be used to mix the precursor and the first reducing agent, for example, an organic solvent may be used, for example, selected from the group consisting of ethanol, cyclohexane, hexane, n-heptane, and combinations thereof.

[0045] The precursor and the first reducing agent mixed with the organic solvent can be uniformly mixed using milling, stirring, a homogenizer, ultrasonic waves, etc. For example, the mixing of the precursor and the first reducing agent can be performed by a milling process. The milling process can be selected from the group consisting of a ball mill, an attrition mill, a vibration mill, a disk mill, a jet mill, a rotor mill, a pearl mill, and combinations thereof.

[0046] Meanwhile, the precursor and the first reducing agent may be mixed at a constant ratio. For example, the precursor and the first reducing agent may be mixed at a molar ratio of 1:1.5 to 1:2, and specifically, the precursor and the first reducing agent may be mixed at a molar ratio of 1:1.5. If the content of the first reducing agent is too low, the reduction efficiency may be reduced, and conversely, if the content of the first reducing agent is excessively high, an excessive amount of impurities may be generated, which may reduce the manufacturing efficiency. Therefore, it is important that the precursor and the first reducing agent be mixed at a constant molar ratio.

[0047] As an optional embodiment, after the step of forming the mixture (S10), a drying step for removing the solvent may be further included. For example, the drying may include various methods such as vacuum drying, hot air drying, freeze-drying, and spray drying. The drying temperature for removing the solvent may be 40 to 60°C, and the drying atmosphere may be a vacuum atmosphere with an air pressure of 40 mbar or less.

[0048] In the step (S20) of reducing the mixture with a second reducing agent to obtain an alkali metal sulfide, the mixture can be reduced by heat treatment with the second reducing agent.

[0049] The second reducing agent may be a reducing gas, and the reducing gas may include hydrogen. For example, the reducing gas may be a mixture of hydrogen and at least one selected from the group consisting of carbon monoxide, nitrogen, argon, helium, neon, methane, ethane, propane, and butane. By supplying a reducing gas containing hydrogen to a mixture containing the first reducing agent, the reducing effect can be further enhanced, thereby significantly reducing the amount of the first reducing agent containing carbon, which affects the atmospheric environment, compared to before. As a result, the amount of carbon compounds generated during the reaction process is reduced, thereby alleviating the problem of atmospheric pollution caused by carbon compounds.

[0050] When the mixture is heat-treated with a second reducing agent, the reduction temperature may be 700°C to 800°C. Specifically, the lower limit of the reduction temperature may be 700°C, 710°C, 720°C, 730°C, 740°C, or 750°C, and the upper limit of the reduction temperature may be 800°C, 790°C, 780°C, 770°C, or 760°C. When the above reduction temperature range is satisfied, lithium sulfide having a small amount of impurities and strong crystallinity can be obtained.

[0051] When the hydrogen concentration is 2 vol% to 4 vol%, the flow rate of the second reducing agent may be 50 cc / min to 100 cc / min. Specifically, the lower limit of the flow rate of the second reducing agent may be, for example, 50 cc / min, 55 cc / min, 60 cc / min, 65 cc / min, or 70 cc / min, and the upper limit of the flow rate of the second reducing agent may be, for example, 100 cc / min, 95 cc / min, 90 cc / min, 85 cc / min, or 80 cc / min. When the flow rate range of the second reducing agent is satisfied, even if the content of the first reducing agent is reduced, high-purity lithium sulfide (Li2S) can be obtained with almost no impurities.

[0052] Meanwhile, the mixture can be loaded into a tube having an outer diameter of 30 mm to 70 mm and a length of 400 mm to 800 mm, and a reducing gas containing hydrogen at a hydrogen concentration of 2 vol% to 4 vol% can be supplied to the tube loaded with the mixture at a rate of 50 cc / min to 100 cc / min, and at the same time, the mixture can be heat-treated at 700 to 900°C for 1 to 24 hours. By supplying the reducing gas at a rate of 50 cc / min to 100 cc / min to the tube having an outer diameter of 30 mm to 70 mm and a length of 400 mm to 800 mm in this way, contact between the complex powder generated by the precursor and the first reducing agent and the reducing gas is promoted, so that the reduction reaction can proceed efficiently.

[0053] In the step (S30) of purifying the obtained alkali metal sulfide by dissolving it in a polar solvent, the obtained alkali metal sulfide dissolves in the solvent, and unreacted precursors and impurities may settle out without dissolving in the solvent. In this way, the impurities that have settled out without dissolving can be removed, and only the purified, high-purity alkali metal sulfide can be extracted.

[0054] At this time, the solvent used in the purification may be a polar solvent. For example, the polar solvent may have a polarity index of 4.3 to 6.2. The polar solvent may be, for example, ethanol or 1-propanol. In such a solvent, only the obtained alkali metal sulfide dissolves, and the remaining impurities settle, so that the alkali metal sulfide and impurities can be easily separated, thereby obtaining a high-purity alkali metal sulfide.

[0055] As an optional embodiment, the purification may include a centrifugation step. The centrifugation step may be performed at about 1000 to about 5000 rpm for about 5 to about 60 minutes, and specifically, at 1000 to 4000, 1000 to 3000, 2000 to 5000, 2000 to 4000, 2000 to 3000, 3000 to 5000, or 3000 to 4000 rpm for 5 to 50, 5 to 40, 5 to 30, 10 to 60, 10 to 50, 10 to 40, 10 to 30, 20 to 60, 20 to 50, 20 to 40, 30 to 60, or 30 to 50 minutes.

[0056] Meanwhile, as an optional example, the obtained alkali metal sulfide and impurities can be purified by various methods such as filtering, dehydration by compression, and filter pressing.

[0057] In the step of drying the purified alkali metal sulfide (S40), the remaining solvent can be removed from the purified alkali metal sulfide by vacuum drying, hot air drying, freeze drying, spray drying, etc.

[0058] As an optional embodiment, a step of crystallizing the dried alkali metal sulfide may be further included.

[0059] Alkali metal sulfide from which the solvent has been removed in the crystallization step can be crystallized by heat treatment. The heat treatment temperature may be 300°C to 930°C. Meanwhile, the purity of the alkali metal sulfide can be further improved by supplying at least one reducing gas from the group consisting of carbon monoxide, nitrogen, hydrogen, argon, helium, neon, methane, ethane, propane, and butane during the heat treatment for crystallization.

[0060] alkali metal sulfides

[0061] According to the above method for producing alkali metal sulfide, a high-purity alkali metal sulfide containing almost no impurities can be obtained. The alkali metal sulfide can be, for example, lithium sulfide, sodium sulfide, potassium sulfide, etc., and the impurities can be lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), lithium hydroxide (LiOH), or lithium oxide (Li2O).

[0062] High purity alkali metal sulfide may have a purity of 95% or greater. Specifically, the purity of the alkali metal sulfide may be 95% or greater, 95.5% or greater, 96% or greater, 96.5% or greater, 97% or greater, 97.5% or greater, 98% or greater, 98.5% or greater, 99% or greater, or 99.5% or greater.

[0063] In the X-ray diffraction (XRD) analysis graph of the alkali metal sulfide manufactured by the method for manufacturing the alkali metal sulfide according to the present invention, peaks exist at diffraction angles (2θ) of 27°±1.0°, 31°±1.0°, 45°±1.0°, and 53°±1.0°, and can satisfy the following equation 1.

[0064] [Formula 1]

[0065] I background ≤ I min

[0066] I min In the graph analyzed by X-ray diffraction (XRD), the height of the lowest peak among the Li2S peaks corresponding to the diffraction angles (2θ) of 27°±1.0°, 31°±1.0°, 45°±1.0°, and 53°±1.0° is I background is the height of the highest peak between diffraction angles (2θ) of 20° and 25° in the graph analyzed by X-ray diffraction (XRD).

[0067] In the XRD analysis results of the alkali metal sulfide obtained by supplying a reducing gas (hydrogen concentration 3 vol%) at a molar ratio of lithium sulfate and carbon of 1:2 and 50 cc / min, and the alkali metal sulfide obtained by supplying a reducing gas (hydrogen concentration 3 vol%) at a molar ratio of lithium sulfate and carbon of 1:1.5 and 100 cc / min, it can be confirmed that almost no peaks of impurities are observed, and the peaks of lithium sulfide are observed in the same way. Therefore, when performing a reduction reaction using carbon and hydrogen as reducing agents at the same time in an appropriate ratio, the amount of carbon used can be reduced as hydrogen replaces some of the carbon, and even if the amount of carbon is reduced as the first reducing agent, the production of impurities can be reduced by increasing the amount of hydrogen as the second reducing agent. As a result, atmospheric pollution caused by carbon compounds generated during the manufacturing process can be reduced, and high-purity alkali metal sulfide can be manufactured.

[0068] Hereinafter, examples are presented to help understand the present invention, but the examples are only illustrative of the present disclosure, and the scope of the present application is not construed as being limited to the examples described below, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0069]

[0070] Example 1

[0071] Anhydrous lithium sulfate (Li2SO4anhydrous) was used as the precursor, and Super P, a type of carbon, was used as the first reducing agent, and mixed in a molar ratio of 1:2. At this time, the mixing process was performed by ball milling with 3 mm balls for 24 hours using ethanol as the solvent in the atmosphere.

[0072] Afterwards, the ball-milled mixture was dried in a vacuum at 60°C through a drying process, and a composite powder was obtained by removing the balls.

[0073] The obtained complex powder was reduced at 800°C for 12 hours using a reduction process, in which an Ar-H2 mixture containing Ar, a type of inert gas, and 3% hydrogen was flowed at a rate of 50 cc / min to produce an alkali metal sulfide (a composite particle containing a mixture of black and white particles).

[0074] XRD was measured for the alkali metal sulfide (composite particles containing black and white particles) manufactured after the reduction process.

[0075]

[0076] Example 2

[0077] An alkali metal sulfide (composite particle containing black and white particles) was manufactured in the same manner as in Example 1, except that an N2-H2 mixed gas was used instead of an Ar-H2 mixed gas in the reduction process.

[0078] XRD was measured for the alkali metal sulfide (composite particles containing black and white particles) manufactured after the reduction process.

[0079]

[0080] Example 3

[0081] An alkali metal sulfide (composite particle containing a mixture of black and white particles) was manufactured in the same manner as Example 1, except that ethanol as a solvent was not used in the mixing process, the drying process was not performed accordingly, and N2-H2 mixed gas was used instead of Ar-H2 mixed gas in the reduction process.

[0082] XRD was measured for the alkali metal sulfide (composite particles containing black and white particles) manufactured after the reduction process.

[0083]

[0084] Example 4

[0085] After measurement in a glove box with an Ar atmosphere, a mixing process was performed in the glove box, and an alkali metal sulfide (composite particles containing a mixture of black and white particles) was manufactured in the same manner as in Example 1, except that N2-H2 mixed gas was used instead of Ar-H2 mixed gas in the reduction process.

[0086] XRD was measured for the alkali metal sulfide (composite particles containing black and white particles) manufactured after the reduction process.

[0087]

[0088] Example 5

[0089] A purification process was performed in which the alkali metal sulfide (composite particles containing a mixture of black and white particles) obtained in Example 3 was dissolved in ethanol and dried to obtain a white powder. Subsequently, a recrystallization process was performed, heat treatment was performed at 600°C for 12 hours in an Ar atmosphere to finally obtain a crystallized alkali metal sulfide (white powder).

[0090] The finally obtained crystallized alkali metal sulfide (white powder) was subjected to XRD measurement to determine the degree of reduction, crystallinity, and impurities.

[0091]

[0092] Example 6

[0093] An alkali metal sulfide (composite particle containing a mixture of black and white particles) was manufactured in the same manner as in Example 1, except that the composite powder obtained in the drying process was reduced by flowing a mixed gas of N2-H2 at 50 cc / min for 12 hours at 750°C.

[0094] XRD was measured for the alkali metal sulfide (composite particles containing black and white particles) manufactured after the reduction process.

[0095]

[0096] Example 7

[0097] Anhydrous lithium sulfate (Li2SO4anhydrous) was used as the precursor, Super P, a type of carbon, was used as the first reducing agent, and the mixture was mixed at a molar ratio of 1:1.5. An alkali metal sulfide (composite particles containing black and white particles) was manufactured in the same manner as Example 1, except that N2-H2 mixed gas was used instead of Ar-H2 mixed gas in the reduction process.

[0098] XRD was measured for the alkali metal sulfide (composite particles containing black and white particles) manufactured after the reduction process.

[0099]

[0100] Example 8

[0101] Anhydrous lithium sulfate (Li2SO4anhydrous) was used as the precursor, Super P, a type of carbon, was used as the first reducing agent, and the mixture was mixed at a molar ratio of 1:1.5. In addition, an N2-H2 mixed gas was flowed twice as fast as the Ar-H2 mixed gas at 100 cc / min during the reduction process, and an alkali metal sulfide (composite particle containing a mixture of black and white particles) was manufactured in the same manner as in Example 1.

[0102] XRD was measured for the alkali metal sulfide (composite particles containing black and white particles) manufactured after the reduction process.

[0103]

[0104] Example 9

[0105] An alkali metal sulfide (composite particle containing black and white particles) was manufactured in the same manner as Example 1, except that a N2-H2 mixed gas was flowed at 100 cc / min instead of an Ar-H2 mixed gas in the reduction process.

[0106] XRD was measured for the alkali metal sulfide (composite particles containing black and white particles) manufactured after the reduction process.

[0107]

[0108] Comparative Example 1

[0109] Lithium sulfate monohydrate (Li2SO4monohydrate) was used as the precursor, and Super P, a type of carbon, was used as the first reducing agent, and mixed at a molar ratio of 1:4. At this time, the mixing process was performed by ball milling with 3 mm balls for 24 hours using ethanol in the air.

[0110] Afterwards, the ball-milled mixture was dried at 60°C in a vacuum through a drying process, and a composite powder was obtained by removing the balls.

[0111] The obtained complex powder was reduced at 800°C for 12 hours using an inert gas, Ar, flowing at a rate of 50 cc / min to produce an alkali metal sulfide (a composite particle containing a mixture of black and white particles).

[0112] A purification process was performed to obtain a white powder by dissolving alkali metal sulfide (a composite particle containing black and white particles) in ethanol and drying it.

[0113] Afterwards, through a recrystallization process, a crystallized alkali metal sulfide (white powder) was finally obtained by heat treatment in an Ar atmosphere at 600°C for 12 hours.

[0114] The finally obtained crystalline alkali metal sulfide (white powder) was subjected to XRD measurement to determine the degree of reduction, crystallinity, and impurities.

[0115]

[0116] Comparative Example 2

[0117] By not adding Super P, a type of carbonaceous material, as the first reducing agent, the mixing and drying processes were omitted, and an Ar-H2 mixed gas containing Ar and 3% hydrogen was used instead of Ar gas in the reduction process, and a crystallized alkali metal sulfide (white powder) was finally obtained in the same manner as in Comparative Example 1.

[0118] The finally obtained crystallized alkali metal sulfide (white powder) was subjected to XRD measurement to determine the degree of reduction, crystallinity, and impurities.

[0119]

[0120] Comparative Example 3

[0121] An alkali metal sulfide (white powder) crystallized was finally obtained in the same manner as in Comparative Example 1, except that an Ar-H2 mixed gas containing Ar, a type of inert gas, and 3% hydrogen was used instead of Ar gas in the reduction process.

[0122] The finally obtained crystallized alkali metal sulfide (white powder) was subjected to XRD measurement to determine the degree of reduction, crystallinity, and impurities.

[0123]

[0124] Evaluation Example: X-ray diffraction (XRD) analysis

[0125] The alkali metal sulfides obtained in Comparative Examples 1 to 3 and Examples 1 to 9 were subjected to X-ray diffraction (XRD) analysis using Aeris from Marvern, and Cu K α radiation was used for the X-ray diffraction (XRD) analysis. Graphs of XRD analysis of the metal sulfides of Comparative Examples 1 to 3 and Examples 1 to 9 are shown in FIGS. 2 to 9.

[0126]

[0127] Mixing process Drying process Precursor system 1 Reducing agent molar ratio Example 1 Anhydride Super P 1:2O Example 2 Anhydride 1:2O Example 3 Anhydride 1:2- Example 4 Anhydride 1:2O Example 5 Anhydride 1:2- Example 6 Anhydride 1:2O Example 7 Anhydride 1:1.5O Example 8 Anhydride 1:1.5O Example 9 Anhydride 1:2O Comparative Example 11 Hydrate Super P 1:4O Comparative Example 21 Hydrate--- Comparative Example 31 Hydrate Super P 1:4O

[0128] Reduction processPurification processDrying processRecrystallization processType of second reducing agentContent of second reducing agentReduction temperatureExample 1Ar-H250cc / min800℃-Example 2N2-H250cc / min800℃-Example 3N2-H250cc / min800℃-Example 4N2-H250cc / min800℃-Example 5N2-H250cc / min800℃OExample 6N2-H250cc / min750℃-Example 7N2-H250cc / min800℃-Example 8N2-H2100cc / min800℃-Example 9N2-H2100cc / min800℃-Comparative example 1Ar50cc / min800℃OComparative example 2Ar-H250cc / min800℃OComparative example 3Ar-H250cc / min800℃O

[0129]

[0130] Referring to Figure 2, the height of the lowest peak among the Li2S peaks corresponding to the diffraction angles (2θ) of 27°±1.0°, 31°±1.0°, 45°±1.0°, and 53°±1.0° in the X-ray diffraction (XRD) analyzed graph is I min I, the height of the highest peak between diffraction angles (2θ) 20° and 25° background It can be seen that it is lower. That is, in the case of Comparative Example 1, which used only the first reducing agent in large quantities, and Comparative Example 2, which used only the second reducing agent, it can be confirmed that lithium sulfide (Li2S) was partially reduced, but a large amount of impurities were generated in both cases. In addition, in the case of Comparative Example 3, which applied Comparative Examples 1 and 2 together, it can be confirmed that the amount of carbon was excessive due to the simultaneous use of an excessive amount of the first reducing agent and the second reducing agent, which resulted in an increase in impurities.

[0131] However, referring to FIG. 3, in the case of Example 1 in which the first reducing agent and the second reducing agent were used in an appropriate ratio, lithium carbonate, which is an impurity, was hardly generated, so that high-purity lithium sulfide (Li2S) could be obtained.

[0132] And, if lithium sulfide (Li2S) is reduced to lithium (Li), it can be re-oxidized by N2 gas to produce lithium nitride (Li3N). However, referring to Example 1 using Ar-H2 mixed gas and Example 2 using N2-H2 mixed gas, it can be confirmed that lithium nitride (Li3N) is not substantially produced in Example 2. Therefore, it can be seen that high-purity lithium sulfide (Li2S) can be obtained by using a relatively inexpensive N2-H2 mixed gas based on N2 gas instead of the Ar-H2 mixed gas.

[0133] In addition, referring to FIG. 4, in the case of Example 3, it can be confirmed that the method for producing alkali metal sulfide according to the present invention can be applied to both dry and wet mixing processes, as almost no impurities were generated even though ethanol, a solvent, was not used in the mixing process.

[0134] Meanwhile, in the case of Example 3, which was mixed / dried in the air, and Example 4, which was mixed / dried in a glove box, which is a moisture-controlled environment, it was confirmed that when mixed / dried in a controlled environment like Example 4, impurities were more controlled, and lithium sulfide (Li2S) of higher purity could be synthesized.

[0135] Referring to FIG. 5, it can be confirmed that in Example 5, the reduced alkali metal sulfide (composite particles mixed with black and white particles) from Example 3 was dissolved in ethanol, a polar solvent, and then precipitated to remove carbon and effectively purify lithium sulfide (Li2S).

[0136] And, referring to FIG. 6, in the case of Example 6, which was heat-treated at 750°C in the reduction process, it can be confirmed that even if the reduction temperature is lowered to 750°C, which is lower than 800°C, by using the first reducing agent and the second reducing agent in an appropriate ratio, the reduction effect is maintained, so that high-purity lithium sulfide (Li2S) can be obtained.

[0137] In particular, referring to FIGS. 7 and 8, in the case of Example 7 where the molar ratio of the precursor and the first reducing agent was 1:1.5, some new impurities were generated, but in the case of Example 8 where the flow rate of the second reducing agent (100 cc / min) was doubled compared to Example 7 (50 cc / min), a purity similar to that of when the molar ratio of the precursor and the first reducing agent was 1:2 was obtained, so it can be confirmed that the effect of the decrease in the first reducing agent can be overcome by increasing the second reducing agent.

[0138] Finally, referring to FIG. 9, in Example 9 where the molar ratio of the precursor and the first reducing agent is 1:2 and the flow rate of the second reducing agent (100 cc / min) is increased, it can be seen that a large amount of carbon, which is the first reducing agent, is suitable for synthesizing highly crystalline lithium sulfide (Li2S) when the amount of hydrogen is increased. However, it can be confirmed that the amount of impurities slightly increases as the amount of carbon increases compared to Example 8.

Claims

1. A step (S10) of forming a mixture by mixing a precursor, which is a compound containing an alkali metal element and a sulfur element, and a first reducing agent; A step (S20) of reducing the above mixture with a second reducing agent to obtain an alkali metal sulfide; Step (S30) of purifying the obtained alkali metal sulfide by dissolving it in a polar solvent; and A method for producing an alkali metal sulfide, comprising a step (S40) of drying the purified alkali metal sulfide.

2. In paragraph 1, A method for producing an alkali metal sulfide, further comprising a drying step after the step of forming the mixture (S10).

3. In paragraph 1, A method for producing an alkali metal sulfide, wherein the precursor is any one of lithium sulfate, sodium sulfate and potassium sulfate.

4. In paragraph 1, A method for producing an alkali metal sulfide, wherein the first reducing agent is a carbon-based reducing agent.

5. In paragraph 1, A method for producing an alkali metal sulfide, wherein the first reducing agent comprises at least one of solid carbonaceous materials such as coal, coke, graphite, carbon black, fullerene, carbon tube, charcoal, carbide, simple carbon and its isotropes.

6. In paragraph 1, A method for producing an alkali metal sulfide, wherein in the step (S20) of reducing the above mixture with a second reducing agent to obtain an alkali metal sulfide, the reduction temperature is 700°C to 800°C.

7. In paragraph 1, A method for producing an alkali metal sulfide, wherein the molar ratio of the precursor and the first reducing agent (precursor:first reducing agent) is 1:1.5 to 1:

2.

8. In paragraph 1, A method for producing an alkali metal sulfide, wherein the hydrogen concentration is 2 vol% to 4 vol% and the flow rate of the second reducing agent is 50 cc / min to 100 cc / min.

9. In paragraph 1, A method for producing an alkali metal sulfide, wherein the second reducing agent comprises hydrogen and at least one selected from the group consisting of carbon monoxide, nitrogen, argon, helium, neon, methane, ethane, propane, and butane.

10. In paragraph 1, A method for producing an alkali metal sulfide, further comprising a step of crystallizing the dried alkali metal sulfide after the step (S40) of drying the purified alkali metal sulfide.

11. In paragraph 1, In the X-ray diffraction (XRD) analysis graph of the above alkali metal sulfide, peaks exist at diffraction angles (2θ) of 27°±1.0°, 31°±1.0°, 45°±1.0°, and 53°±1.0°, and a method for producing an alkali metal sulfide satisfying the following equation 1: [Formula 1] I background ≤ I min I min In the graph analyzed by X-ray diffraction (XRD), the height of the lowest peak among the Li2S peaks corresponding to diffraction angles (2θ) of 27°±1.0°, 31°±1.0°, 45°±1.0°, and 53°±1.0° is I background is the height of the highest peak between diffraction angles (2θ) of 20° and 25° in an X-ray diffraction (XRD) analysis graph.

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