Method for producing lithium sulfide

Abstract

The present invention relates to a method for producing lithium sulfide, the method comprising the steps of: preparing lithium sulfide containing impurities; and removing the impurities from the lithium sulfide, wherein the step of removing the impurities comprises a step of pyrolyzing at least one of lithium carbonate (Li2CO3) and lithium sulfate (Li2SO4).

Description

Method for manufacturing lithium sulfide

[0001] The present invention relates to lithium sulfide, and more specifically to a method for manufacturing lithium sulfide through purification and drying processes.

[0002] This application claims priority to Korean Patent Application No. 10-2024-0191859 filed on December 19, 2024, the entire contents of said prior application are incorporated herein by reference.

[0003]

[0004] 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.

[0005] 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.

[0006] 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.

[0007] The above solid electrolytes are classified into oxide-based and sulfide-based types, and the sulfide-based solid electrolytes have the characteristic of high ionic conductivity compared to the oxide-based solid electrolytes. The main raw material for the sulfide-based solid electrolytes is lithium sulfide (Li2S). Various methods are utilized for the synthesis of lithium sulfide, such as synthesis methods using a high-energy ball mill, synthesis methods using a wet plasma process, and wet / dry methods using lithium metal.

[0008] Specifically, methods for manufacturing lithium sulfide include a wet process using a solvent and a dry process using a gas without a solvent. Among the various processes mentioned above, carbonthermal reduction is a process for manufacturing lithium sulfate using a carbon-containing powder source, such as coke or artificial graphite, and a source containing Li and S, such as lithium sulfate (Li2SO4).

[0009] However, the lithium sulfate produced through the above process has a problem in that its purity is reduced by a small amount of oxide, which has poor thermal stability.

[0010] Another technical problem that the present invention aims to solve is to provide a method for providing lithium sulfide having the aforementioned advantages.

[0011] A method for manufacturing lithium sulfide according to one embodiment of the present invention comprises the step of preparing lithium sulfide containing impurities and a process for removing impurities from the lithium sulfide, wherein the process for removing impurities may include a process for thermally decomposing at least one of lithium carbonate (Li2CO3) and lithium sulfate (Li2SO4).

[0012] In one embodiment, the process of removing impurities from the lithium sulfide can be performed at 930 to 1,150 ℃.

[0013] In one embodiment, the process of removing impurities from the lithium sulfide can be performed for 2 to 5 hours.

[0014] In one embodiment, the process of removing impurities from the lithium sulfide is 10 -1 to 10 -5 It can be performed within a pressure range of Torr.

[0015] In one embodiment, the lithium oxide (Li2O) in the lithium sulfide produced may be 5.5% or less as an XRD ratio (%).

[0016] In one embodiment, the step of preparing lithium sulfide containing the impurities may include a thermal reduction process in which a lithium compound and a reducing agent powder are mixed and heat-treated.

[0017] In one embodiment, the content of the lithium compound in the thermal reduction process may be less than the content of the reducing agent powder.

[0018] In one embodiment, the weight ratio of the reducing agent powder and the lithium compound in the thermal reduction process may satisfy 1:1 to 1:10.

[0019] In one embodiment, the thermal reduction process may be performed at 700 to 1,000 ℃.

[0020] In one embodiment, the thermal reduction process may be performed for 1.5 to 5.0 hours.

[0021] In one embodiment, the process of removing impurities from the lithium sulfide can be performed in a magnesia crucible.

[0022] In one embodiment, the lithium sulfide powder produced through the thermal reduction process may be at least one of Li2SO4-rich or Li2O-rich.

[0023] According to another embodiment of the present invention, a method for manufacturing lithium sulfide can provide a method for manufacturing high-purity lithium sulfide in which oxides with poor thermal stability are easily removed by performing an impurity removal process within an optimal time and temperature range.

[0024] Figure 1 is an XRD peak graph of lithium sulfide prepared according to Example 1 and Example 3 of the present invention.

[0025] Figure 2 is an XRD peak graph of lithium sulfide prepared according to Comparative Example 1 of the present invention.

[0026] Figure 3 is an XRD peak graph of lithium sulfide prepared according to Comparative Example 5 of the present invention.

[0027] Figure 4 is an XRD peak graph of lithium sulfide prepared according to Example 4 of the present invention.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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 %.

[0032] 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.

[0033] According to one embodiment of the present invention, the lithium sulfide may be high-purity lithium sulfide containing impurities. Specifically, the lithium sulfide may be high-purity lithium sulfide mixed with a trace amount of impurities.

[0034] According to one embodiment of the present invention, lithium sulfide may include lithium sulfide (Li2S) and lithium oxide (Li2O). Specifically, lithium sulfide may include a trace amount of lithium oxide (Li2O) after undergoing an impurity removal process.

[0035] In one embodiment, based on 100 wt% of lithium sulfide, the oxygen content in the lithium sulfide may be 3.5 wt% or less. Specifically, the oxygen content may be up to 3.3 wt% or less, more specifically 3.0 wt% or less, and even more specifically 1.0 wt% or less.

[0036] If the oxygen content falls outside the aforementioned range, there is a problem in that the ion conductivity retention rate decreases before and after atmospheric exposure during the synthesis of argyrodite using Li2S, and the problem is affected by the ratio of impurities such as Li2O, Li2CO3, or Li2SO4. Specifically, even if the oxygen content within the aforementioned range is satisfied, if Li2CO3 is present above a certain level in addition to Li2O, there is a problem in that the ion conductivity retention rate decreases due to atmospheric exposure.

[0037] In one embodiment, the lithium oxide (Li2O) may satisfy an XRD ratio (%) of 5.5% or less. Specifically, the lithium oxide (Li2O) may satisfy an XRD ratio (%) of 3.5% or less, more specifically 3.0% or less, and even more specifically 0.1 to 1.1%.

[0038] When the XRD ratio (%) of the above lithium oxide (Li2O) satisfies the aforementioned range, the decrease in ionic conductivity is small, allowing for the securing of lithium sulfide that can be used as a raw material for a solid electrolyte with excellent atmospheric stability. If the above lithium oxide (Li2O) deviates from the upper limit of the aforementioned range, the purity of the lithium sulfide powder may decrease, and if it deviates from the lower limit of the aforementioned range, there is a problem with the reduced atmospheric stability of the solid electrolyte.

[0039] According to another embodiment of the present invention, a method for manufacturing lithium sulfide may include the step of preparing lithium sulfide containing impurities and a process for removing impurities from the lithium sulfide. By including a heat treatment process for removing impurities from the lithium sulfide, the method for manufacturing lithium sulfide according to the present invention can increase the purity of the lithium sulfide by removing oxides with relatively poor thermal stability.

[0040] The step of preparing the lithium sulfide above may include a thermal reduction process in which a lithium compound and a reducing agent powder are mixed and heat-treated. The lithium compound may include at least one of lithium sulfate, lithium hydroxide, lithium oxide, and lithium carbonate. The reducing agent may be a carbon raw material, and the carbon raw material may include, as a non-limiting example, at least one of soft carbon, hard carbon, petroleum coke, coal needle coke, coal pitch coke, natural graphite, and artificial graphite.

[0041] In one embodiment, the weight ratio of the reducing agent powder and the lithium compound in the thermal reduction process may satisfy 1:1 to 1:10. Specifically, the reducing agent powder may be mixed in less than the lithium compound. More specifically, the weight ratio of the reducing agent powder and the lithium compound may be 1:5.5 to 1:8.5.

[0042] By satisfying the aforementioned weight ratio within the range, the impurity removal process described later can be easily performed, thereby enabling the production of high-purity lithium sulfide. If the ratio exceeds the upper limit, there is a problem where unreacted lithium compound raw materials, specifically lithium sulfate, remain within the lithium-carbon compound after heat treatment. If the ratio exceeds the lower limit, the amount of carbon raw material used increases, resulting in a disadvantage in terms of process cost.

[0043] By performing a thermal reduction process at the above weight ratio, the lithium sulfide powder produced through the thermal reduction process may be at least one of Li2SO4-rich or Li2O-rich. Since the lithium sulfide powder that has undergone the thermal reduction process contains at least one of Li2SO4-rich or Li2O-rich, the impurity removal process described later can be easily performed, thereby enabling the production of high-purity lithium sulfide.

[0044] In one embodiment, a thermal reduction process in which a lithium compound and a reducing agent powder are mixed and heat-treated can be performed at a temperature range of 700 to 1,000 °C. Specifically, it can be performed at a temperature range of 730 to 950 °C, and more specifically, at a temperature range of 750 to 850 °C. Since the thermal reduction process in which the lithium compound and the reducing agent powder are mixed and heat-treated is performed within the aforementioned temperature range, the impurity removal process described later can be easily performed, thereby enabling the production of high-purity lithium sulfide.

[0045] In one embodiment, a thermal reduction process in which a lithium compound and a reducing agent powder are mixed and heat-treated can be performed for 1.5 to 5.0 hours. Specifically, it can be performed for 1.5 to 5.0 hours, and more specifically, for 1.5 to 5.0 hours. As the time is performed within the aforementioned range, the impurity removal process described later can be easily performed to produce high-purity lithium sulfide.

[0046] In one embodiment, the thermal reduction process for heat-treating the mixture of the carbon raw material and the lithium compound may be performed at a heating rate of 3 to 8 ℃ / min. Specifically, the heating rate may be performed at a heating rate of 4 to 6 ℃ / min. By satisfying the heat treatment temperature and heating rate, a thermal reduction material that facilitates the removal of impurities during the impurity process can be produced.

[0047] The process for removing impurities in the lithium sulfide described above may be a step of removing oxides in the low-purity lithium sulfide obtained through the aforementioned thermal reduction process. Specifically, the process for removing impurities in the lithium sulfide may be a step of removing oxides containing lithium in the low-purity lithium sulfide, which has relatively poor thermal stability.

[0048] In one embodiment, the process of removing impurities from the lithium sulfide can be performed at 930 to 1,150 ℃. Specifically, the process of removing impurities from the lithium sulfide can be performed at 950 to 1,100 ℃, more specifically at 980 to 1,050 ℃. Since the process of removing impurities from the lithium sulfide is performed within the aforementioned temperature range, additional processes such as solvent extraction and drying steps in subsequent processes are unnecessary, thereby simplifying the process steps and allowing for the easy removal of impurities such as oxides from the lithium sulfide.

[0049] If the process for removing impurities from the lithium sulfide exceeds the upper limit of the aforementioned range, there is a problem in that the recovery rate of lithium sulfide decreases. If the process for removing impurities from the lithium sulfide exceeds the lower limit of the aforementioned range, there is a problem in that the impurities are not sufficiently removed.

[0050] In one embodiment, the process of removing impurities from the lithium sulfide can be performed for 2 to 5 hours. Specifically, it can be performed for 2 to 4.8 hours, and more specifically, for 2 to 4.5 hours. As the time is performed within the aforementioned range, impurities such as oxides in the lithium sulfide can be easily removed.

[0051] In one embodiment, the process of removing impurities from the lithium sulfide can be performed in a reduced pressure atmosphere. Specifically, the reduced pressure atmosphere is 10 -1 to 10 -5It can be performed in a pressure range of Torr. More specifically, the reduced pressure atmosphere is 10 -2 to 10 -4 It can be performed within a pressure range of Torr. As the above-mentioned reduced pressure atmosphere is performed within the aforementioned range, oxides contained in lithium sulfide can be easily removed.

[0052] If the above reduced pressure atmosphere exceeds the upper limit of the aforementioned range, there is a problem in that process costs increase due to the need for an additional vacuum pump. If the above reduced pressure atmosphere exceeds the lower limit of the aforementioned range, there is a problem in that impurities are not sufficiently removed at the same temperature.

[0053] In one embodiment, the impurity removal process may be a process of thermally decomposing at least one of lithium carbonate (Li2CO3) and lithium sulfate (Li2SO4). Specifically, the impurity removal process may be a process of thermally decomposing lithium carbonate and lithium sulfate among lithium-containing oxides in each temperature range by the following mechanism. The following mechanism was confirmed by analyzing the gas generated during high-temperature heat treatment of the sample using TPD-MS thermogravimetric mass spectrometry.

[0054] 700-800℃: Li2CO 3(s) → Li2O (s) + CO 2(g)

[0055] 800-1000℃: Li2SO 4(s) → Li2O (s) + SO x(g) (x=2,3)

[0056] In one embodiment, the process for removing the impurities may be a step in which lithium oxide (Li2O) undergoes a phase change. Specifically, the process for removing the impurities may be a step in which the lithium oxide is sublimated and removed in a gaseous state. Specifically, the lithium oxide may be removed from lithium sulfide by the following mechanism.

[0057] 900-1000℃: Li2O (s) → Li2O (g)

[0058] In one embodiment, the process of removing impurities may be performed in an alumina or magnesia crucible. Specifically, the process of removing impurities may be performed in a magnesia crucible. Since the process of removing impurities is performed in a magnesia crucible, the problem of lithium oxide (Li2O) reacting with the alumina crucible to form lithium aluminate and re-forming impurities can be prevented.

[0059] Thus, the present invention can produce high-purity lithium sulfide by performing a multi-stage heat treatment process including a thermal reduction process and a heat treatment process for removing impurities, and can simplify the process by not including additional steps such as conventional solvent extraction and drying steps.

[0060]

[0061] 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.

[0062]

[0063] <Experimental Example 1> : Heat Treatment Temperature and Time Control

[0064] <Example 1> - 1,000 ℃, 2 hours

[0065] 200 g of powder, mixed with carbon raw materials graphite and lithium sulfate monohydrate in a weight ratio of 1:6, was loaded into a graphite crucible containing a quartz tube, and the graphite crucible containing the powder was heated from room temperature to 800 ℃ at a rate of 5 ℃ / min in an Ar inert gas atmosphere. After reaching 800 ℃, a thermal reduction process was performed by maintaining the temperature and pressure for 3 hours. At this time, it was confirmed through X-ray diffraction that the prepared lithium sulfide powder was a Li2O-rich sample.

[0066] Subsequently, 1g of the manufactured lithium sulfide powder was loaded into an alumina (Al2O3) crucible containing a stainless steel (SUS) tube, and the temperature was increased from room temperature to 1,000℃ at a rate of 5℃ / min under a vacuum atmosphere. At a temperature of 1,000℃ and 10 -3 A process to remove impurities was performed by heat treatment for 2 hours under a pressure of Torr. At this time, it was confirmed through X-ray diffraction analysis that lithium oxide, which is an oxide, was sublimated and removed as a gaseous phase during the high-temperature vacuum heat treatment process.

[0067]

[0068] <Example 2> - Sample: Li2SO4-rich

[0069] The procedure was carried out in the same manner as Example 1, except that the lithium sulfide powder produced from the above thermal reduction process was a Li2SO4-rich sample. The Li2SO4-rich sample was prepared by mixing graphite and lithium sulfate monohydrate in a weight ratio of 1:8.

[0070]

[0071] <Example 3> - 1,000 ℃, 4 hours

[0072] The process for removing the above impurities was performed in the same manner as Example 1, except that the heat treatment time was changed from 2 hours to 4 hours.

[0073]

[0074] <Comparative Example 1> - Impurity removal process not performed

[0075] The procedure was performed in the same manner as Example 1, except that the process of removing the above impurities was not performed.

[0076]

[0077] <Comparative Example 2> - Impurity removal process not performed

[0078] The procedure was performed in the same manner as Example 2, except that the process of removing the above impurities was not performed.

[0079]

[0080] <Comparative Example 3> - 1,000 ℃, 1 hour

[0081] The process for removing the above impurities was performed in the same manner as Example 1, except that the heat treatment time was changed from 2 hours to 1 hour.

[0082]

[0083] <Comparative Example 4> - 1,000 ℃, 6 hours

[0084] The process for removing the above impurities was performed in the same manner as Example 1, except that the heat treatment time was changed from 2 hours to 6 hours.

[0085]

[0086] <Comparative Example 5>

[0087] The process for removing the above impurities was performed in the same manner as Example 1, except that the heat treatment temperature was changed to 1,200 ℃ and the heat treatment atmosphere was performed for 1 hour under pressure conditions of 0.1 to 0.9 atm.

[0088]

[0089] <Comparative Example 6>

[0090] The process for removing the above impurities was performed in the same manner as Example 1, except that the heat treatment temperature was changed to 1,200 ℃.

[0091]

[0092] Figure 1 is an XRD peak graph of lithium sulfide prepared according to Example 1 and Example 3 of the present invention.

[0093] Figure 2 is an XRD peak graph of lithium sulfide prepared according to Comparative Example 2 of the present invention.

[0094] Figure 3 is an XRD peak graph of lithium sulfide prepared according to Comparative Example 5 of the present invention.

[0095] Table 1 below shows the recovery rate of lithium sulfide prepared according to the examples and comparative examples, the content of impurities in the lithium sulfide, and the oxygen content.

[0096] The above recovery rate, the above impurity content, and the above oxygen content were measured by the following method.

[0097] Impurity content (H%): For the lithium sulfide powder prepared according to the examples and comparative examples, a powder X-ray diffraction measuring device D / Max-2500V 18 kW from Rigaku was used under the following conditions, and the height ratio of the XRD peak values ​​was measured as the impurity content.

[0098] Tube voltage: 40 kV

[0099] Tube current: 200 mA

[0100] X-ray wavelength: Cu-Kα line (1.5418 Å)

[0101] Measurement range: 2θ = 10 - 80 deg

[0102] Step width, Scan speed: 0.02 deg, 4 deg / min

[0103] Oxygen (O) content (wt%): Measured using elemental analysis with a LECO ON836-LC instrument.

[0104] Impurity Removal Process Conditions Recovery Rate Impurity and Oxygen Content Sample Temperature [°C] Time [h] Pressure [Torr] Li2CO3 [H%] Li2O [H%] Li2SO4 [H%] O [wt%] Example 1 Li2O-rich 1,000 210 -3 91.401.103.01 Example 2 Li2SO4-rich 1,000210 -3 80.900.600.984 Example 3 Li2O-rich 1,000 410 -3 85.40 0.30 0.837 Comparative Example 1 Li2O-rich ---- 0.56 8.20 61 7.295 Comparative Example 2 Li2SO4-rich ---- 0.70 84.86 925 Comparative Example 3 Li2O-rich 1,000 110 -393.50203.89 Comparative Example 4Li2O-rich 1,000610 -3 74.30000.621 Comparative Example 5 Li2O-rich 1,20020.1~0.9 atm 97.10000.516 Comparative Example 6 Li2O-rich 1,200210 -3 52.70000.523

[0105] Looking at Table 1 above, it was confirmed that Examples 1 and 2, which underwent an impurity removal process, had a lower content of impurities such as oxides compared to Comparative Example 1, which did not undergo an impurity removal process. When comparing Examples 1 and 2 with Comparative Examples 1 and 2, it was confirmed that when lithium oxide was present in excess in lithium sulfide after the thermal reduction process, lithium oxide, an impurity in lithium sulfide, was removed by performing the impurity removal process. Furthermore, when comparing Examples 1 and 2 with Comparative Examples 1 and 2, it was confirmed that when lithium sulfate was present in excess in lithium sulfide after the thermal reduction process, lithium oxide, an impurity in lithium sulfide, was removed by performing the impurity removal process. Thus, it was confirmed that the lower impurity content in Examples 1 and 2 compared to Comparative Examples 1 and 2 was due to lithium carbonate (Li2CO3) and lithium sulfate (Li2SO4) being removed in the gaseous phase after thermal decomposition according to the chemical formula below.

[0106] Li2CO 3(s) → Li2O (s) + CO 2(g)

[0107] Li2SO 4(s) → Li2O (s) + SO x(g) (x=2,3)

[0108] Li2O (s) → Li2O (g)

[0109] Looking at Examples 1 to 3 and Comparative Examples 3 and 4, it was confirmed that when the heat treatment time in the impurity removal process deviates from the upper and lower limits of the present invention, an excessive amount of impurities in lithium sulfide is generated. Looking at Examples 1 to 3 and Comparative Examples 5 and 6, it was confirmed that when the heat treatment temperature or pressure in the impurity removal process deviates from the range of the present invention, the content of impurities in lithium sulfide is high.

[0110] In addition, in the case of Comparative Example 5, although the quality and recovery rate are excellent, there is a problem of relatively high heat treatment costs and poor processability due to the high heat treatment temperature. In the case of Comparative Example 6, although the quality improves as the heat treatment temperature increases, there is a problem of low recovery rate because thermal decomposition of lithium sulfide itself, rather than impurities, also occurs.

[0111]

[0112] <Experimental Example 2> : Magnesia Example

[0113] <Example 4>

[0114] The process was carried out in the same manner as in Example 1, except that the thermal reduction process and the impurity removal process were performed in a magnesia crucible instead of an alumina crucible.

[0115] Figure 4 is an XRD peak graph of lithium sulfide prepared according to Example 4 of the present invention.

[0116]

[0117] Table 2 below shows the recovery rate, impurities, and oxygen content according to the impurity removal process conditions of Example 1 and Example 4.

[0118] Impurity Removal Process Conditions Recovery Rate Impurity and Oxygen Content Crucible Temperature [°C] Time [h] Pressure [Torr] Li2CO3 [H%] Li2O [H%] Li2SO4 [H%] O [wt%] Example 1 Alumina 1,000 210 -3 85.401.103.01 Example 4 Magnesia 1,000210 -3 97.60000.483

[0119] Looking at Table 2 above, it was confirmed that Example 4 has a lower impurity content and a higher recovery rate than Example 1. This is because in the case of Example 1, lithium oxide reacts with the alumina crucible during the thermal reduction and impurity removal processes to form lithium aluminate, resulting in relatively lower quality and recovery rates of the purified product. In the case of Example 4, the likelihood of lithium aluminate formation is low, allowing for the acquisition of high-purity lithium sulfide with a low impurity content and a high recovery rate.

[0120]

[0121] 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 preparing lithium sulfide containing impurities; and The method includes a process for removing impurities from the lithium sulfide mentioned above, A method for producing lithium sulfide in which the process of removing the above impurities is a process of thermally decomposing at least one of lithium carbonate (Li2CO3) and lithium sulfate (Li2SO4).

2. In Paragraph 1, A method for manufacturing lithium sulfide in which the process of removing impurities from the lithium sulfide is performed at 930 to 1,150 ℃.

3. In Paragraph 1, A method for manufacturing lithium sulfide in which the process of removing impurities from the lithium sulfide is performed for 2 to 5 hours.

4. In Paragraph 1, The process of removing impurities from the above lithium sulfide is 10 -1 to 10 -5 A method for manufacturing lithium sulfide performed in a pressure range of Torr.

5. In Paragraph 1, A method for producing lithium sulfide in which the lithium oxide (Li2O) in the produced lithium sulfide is 5.5% or less as an XRD ratio (%).

6. In Paragraph 1, A method for manufacturing lithium sulfide comprising a thermal reduction process in which a lithium compound and a reducing agent powder are mixed and heat-treated, in the step of preparing lithium sulfide containing the above impurities.

7. In Paragraph 6, A method for producing lithium sulfide in which the content of the lithium compound in the above thermal reduction process is less than the content of the reducing agent powder.

8. In Paragraph 6, A method for producing lithium sulfide in which the weight ratio of the reducing agent powder and the lithium compound in the above thermal reduction process satisfies 1:1 to 1:

10.

9. In Paragraph 6, The above thermal reduction process is a method for manufacturing lithium sulfide performed at 700 to 1,000 ℃.

10. In Paragraph 6, A method for producing lithium sulfide in which the above thermal reduction process is performed for 1.5 to 5.0 hours.

11. In Paragraph 1, A method for manufacturing lithium sulfide in which the process of removing impurities from the lithium sulfide is performed in a magnesia crucible.

12. In Paragraph 6, A method for producing lithium sulfide powder through the above thermal reduction process, wherein the lithium sulfide powder is at least one of Li2SO4-rich or Li2O-rich.

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