Carbon-lithium compound and method of manufacturing lithium sulfide

Abstract

The present invention relates to a carbon-lithium compound and a method of manufacturing lithium sulfide, wherein the carbon-lithium compound is an intermediate product for preparing a lithium sulfide powder having a pellet form, and comprises an oxide, the oxide being 1.0% or less based on the second XRD peak value of the lithium sulfide (Li2S).

Description

Method for producing carbon-lithium compounds and lithium sulfide

[0001] The present invention relates to a method for producing lithium sulfide, and to a method for producing a carbon-lithium compound, which is an intermediate product for producing lithium sulfide, and high-quality lithium sulfide.

[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] Specifically, among the methods for producing lithium sulfide, CTR (Carbo-thermal reduction) is a method for synthesizing lithium sulfide by heat-treating a mixed powder of carbon and lithium sulfate. The method for producing lithium sulfide by thermal reduction of lithium sulfate has the advantage of reducing process costs, and the lithium sulfide produced through the aforementioned reduction reaction remains mixed with an excess of carbon powder. The lithium sulfide can be dissolved in a solvent to extract it, the extracted solution can be dried, and then heat-treated to ultimately obtain lithium sulfide.

[0007] However, in the case of the thermal reduction process during the lithium sulfide manufacturing process, a process of heat treatment at high temperature using an inert gas is included, and after the thermal reduction process, oxides are easily generated, which causes an increase in the oxygen concentration of the final product, lithium sulfide.

[0008] Therefore, research is needed to reduce the oxygen concentration by controlling the conditions of the thermal reduction process during the lithium sulfide manufacturing process.

[0009] The technical problem to be solved by the present invention is to provide a carbon-lithium compound having significantly improved impurity and oxygen content by effectively suppressing oxides generated during thermal reduction of a mixed powder of carbon and lithium sulfide.

[0010] Another technical problem to be solved by the present invention is to provide a method for producing lithium sulfide from a carbon-lithium compound having the aforementioned advantages.

[0011] According to one embodiment of the present invention, a carbon-lithium compound is an intermediate product for manufacturing lithium sulfide powder having a pellet shape, and includes an oxide, and the oxide may be 1.0% or less based on the second XRD peak value of lithium sulfide (Li2S).

[0012] In one embodiment, the oxide may not include Li2SO4. In one embodiment, the oxide may not include Li2CO3. In one embodiment, the oxide may include Li2O, and the Li2O may be 1.0% or less based on the second XRD peak value of lithium sulfide (Li2S).

[0013] According to another embodiment of the present invention, a method for producing lithium sulfide includes a step of mixing a carbon raw material and a lithium compound and performing thermal reduction, and the resulting carbon-lithium compound may have a pellet shape.

[0014] In one embodiment, in the step of mixing the carbon raw material and the lithium compound and performing thermal reduction, the ratio of the carbon raw material to the lithium compound may be 3.0 or more and 5.0 or less. In one embodiment, the step of mixing the carbon raw material and the lithium compound and performing thermal reduction may be performed in a vacuum atmosphere.

[0015] In one embodiment, the vacuum atmosphere is 1 × 10 -3 It can be performed under partial pressure conditions of 5 Torr. In one embodiment, after the step of mixing the carbon raw material and the lithium compound and performing thermal reduction, the step of filtering a solution in which the thermally reduced carbon-lithium compound and the solvent are mixed; and the step of drying and then heat-treating the filtrate may be included. In one embodiment, in the step of mixing the carbon raw material and the lithium compound and performing thermal reduction, when the carbon raw material and the lithium compound are mixed, a mixture in the shape of pellets having a size of 1 mm to 5.0 mm can be formed.

[0016] In one embodiment, the step of mixing the carbon raw material and the lithium compound and performing thermal reduction may be performed at a temperature range of 860 to 1,100° C. In one embodiment, the carbon-lithium compound produced in the step of mixing the carbon raw material and the lithium compound and performing thermal reduction may include an oxide, and the oxide may be 1.0% or less based on the second XRD peak value of lithium sulfide (Li2S). In one embodiment, the oxide may include Li2O, and the Li2O may be 1.0% or less based on the second XRD peak value of lithium sulfide (Li2S). In one embodiment, the oxide may not include Li2SO4.

[0017] According to one embodiment of the present invention, a carbon-lithium compound is provided that effectively suppresses oxides generated during thermal reduction by controlling process conditions in a thermal reduction process during the production of lithium sulfide, thereby providing a carbon-lithium compound with greatly improved impurity and oxygen content.

[0018] According to another embodiment of the present invention, a method for producing lithium sulfide is provided, which controls the mixed shape of carbon and lithium sulfate in the form of pellets and controls process conditions during thermal reduction, thereby effectively suppressing oxides generated during thermal reduction and producing lithium sulfide with greatly improved impurity and oxygen content.

[0019] FIG. 1 illustrates a pellet-shaped carbon-lithium compound obtained by pelletizing a mixed powder of a carbon-lithium compound according to one embodiment of the present invention.

[0020] FIG. 2 illustrates an XRD result graph of a carbon-lithium compound having a pellet shape according to a mixing ratio of carbon and lithium compounds according to one embodiment of the present invention.

[0021] FIG. 3 illustrates an XRD result graph according to process temperature of a carbon-lithium compound having a pellet shape according to one embodiment of the present invention.

[0022] FIG. 4 illustrates a graph of XRD results according to process time of a carbon-lithium compound having a pellet shape according to one embodiment of the present invention.

[0023] Figures 5 to 7 show XRD peak values ​​of carbon-lithium compounds according to process conditions.

[0024] 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 only 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] FIG. 1 illustrates a pellet-shaped carbon-lithium compound obtained by pelletizing a mixed powder of a carbon-lithium compound according to one embodiment of the present invention.

[0030] Referring to FIG. 1, according to one embodiment of the present invention, the carbon-lithium compound may have a pellet shape. The pellet shape refers to a sphere shape. The carbon-lithium compound is manufactured in a pellet shape from a mixed powder phase, thereby increasing the uniformity of the process and improving the processability when manufacturing lithium sulfide.

[0031] In one embodiment, the carbon-lithium compound may have a pellet shape having a size of 1 mm to 5.0 mm. Specifically, the carbon-lithium compound may have a pellet shape having a size of 0.5 to 5.0 mm. More specifically, the size may be 0.5 to 3.0 mm. The size of the pellet shape refers to a size measured using a vernier caliper.

[0032] If the size of the pellet shape exceeds the upper limit of the aforementioned range, there is a problem in that the carbon-lithium compound excessively aggregates, thereby reducing the uniformity of the reaction. If the size of the pellet shape exceeds the lower limit of the aforementioned range, there is a problem in that the pellet shape is not maintained.

[0033] According to one embodiment of the present invention, the carbon-lithium compound comprises an oxide. Specifically, the carbon-lithium compound may be an intermediate product produced during the process of manufacturing lithium sulfide (Li2S). More specifically, the intermediate product may be produced by mixing carbon and a lithium compound, followed by a thermal reduction step. For example, the carbon-lithium compound may be, for example, C-Li2S.

[0034] The carbon raw material may include, for example, at least one of soft carbon, hard carbon, petroleum coke, coal-based needle coke, coal-based pitch coke, natural graphite, and artificial graphite. The lithium compound may include at least one of lithium sulfate, lithium hydroxide, lithium oxide, and lithium carbonate. In the present embodiment, when lithium sulfate is used as the lithium compound, the cost of the raw material is low, so the economic feasibility of the lithium sulfide manufacturing process can be improved.

[0035] In one embodiment, the carbon-lithium compound may include an oxide. Specifically, the oxide may be an impurity generated during thermal reduction of a mixed powder of carbon and lithium sulfate. In one embodiment, the oxide may be a material containing oxygen, such as Li2O.

[0036] In one embodiment, the oxide may be 1.0% or less based on the second XRD peak value of lithium sulfide (Li2S). Specifically, the oxide may be 0.9% or less. The second XRD peak value of lithium sulfide (Li2S) was confirmed to be the second peak value among the XRD peak values ​​of lithium sulfide (Li2S) as a peak value clearly distinguishable from the carbon peak.

[0037] By ensuring that the ratio of the above oxides satisfies the aforementioned range, high-purity lithium sulfide can be produced. If the ratio of the above oxides exceeds the aforementioned range, lithium sulfide with a high impurity content is produced, making it difficult to utilize in all-solid-state batteries.

[0038] In one embodiment, the oxide may not contain Li2SO4. Li2SO4 may be a substance that remains in lithium sulfide (Li2S), thereby increasing the oxygen content and generating impurities during the synthesis of an all-solid-state electrolyte, thereby causing problems such as lowering ionic conductivity. Since the oxide does not contain Li2SO4, it is possible to provide high-purity lithium sulfide, and has the advantage of being applicable to the field of all-solid-state batteries.

[0039] According to another embodiment of the present invention, a method for producing lithium sulfide comprises a step of mixing a carbon raw material and a lithium compound and performing thermal reduction. Specifically, by including the step of mixing the carbon raw material and the lithium compound and performing thermal reduction, an intermediate product of the above-described carbon-lithium compound can be produced, and lithium sulfide can be provided using the intermediate product. High-purity lithium sulfide (Li2S) can be provided from the above-described intermediate product.

[0040] The step of mixing and thermally reducing a carbon raw material and a lithium compound may comprise a step of mixing the carbon raw material and the lithium compound in powder form, respectively, and a step of thermally reducing the mixed resultant product. By thermally reducing the mixed powder, there is an advantage of improving the uniformity of the reaction compared to mixing in an existing aqueous solution state and thermally reducing it.

[0041] The step of mixing the carbon raw material and the lithium compound, respectively, includes a step of pelletizing the carbon raw material and the lithium compound. Specifically, the step of pelletizing the carbon raw material and the lithium compound may be a method of pelletizing a mixed powder of the carbon raw material and the lithium compound by adding water to the powder and rotating a cylindrical device to agglomerate the powder. By pelletizing the carbon raw material and the lithium compound, the content of impurities including oxygen is advantageously reduced compared to when the carbon raw material and the lithium compound are in a mixed powder state.

[0042] In one embodiment, the ratio of the water content (mL) to the weight (g) of the powder may be 0.05 to 0.50, specifically, 0.10 to 0.40, and more specifically, 0.20 to 0.30. By mixing the powder and the water in the above-described ratio, the carbon raw material and the lithium compound can be easily pelletized.

[0043] The step of mixing the carbon raw material and the lithium compound may be performed such that the ratio of the carbon raw material to the lithium compound is 3.0 or more and 5.0 or less. Specifically, the ratio may be 3 or more and 4.0 or less.

[0044] The step of mixing the carbon raw material and the lithium compound may involve either dry mixing or wet mixing. Specifically, the mixing step may utilize a known mixer, such as a stirring, rotary, or wind-driven mixer. For example, the carbon raw material and the lithium compound may be mixed using a mixing method such as mechanochemical treatment.

[0045] The step of mixing the carbon raw material and the lithium compound can be performed at a mixing speed of 5.0 to 50.0 rpm. Specifically, the mixing speed can be performed at 20.0 to 30.0 rpm.

[0046] In one embodiment, the step of thermally reducing the mixed powder may be performed at a temperature range of 860 to 1,100°C. Specifically, the temperature range may be performed at a temperature range of 860 to 1,000°C, more specifically, at a temperature range of 880 to 920°C, and even more specifically, at a temperature range of 895 to 905°C.

[0047] If the temperature range exceeds the upper limit, there is a problem that the synthesized Li2S powder sublimates, resulting in a decrease in yield. If the temperature range exceeds the lower limit, there is a problem that the reaction is not sufficiently performed, resulting in residual raw materials.

[0048] In one embodiment, the step of thermally reducing the mixed powder may be performed for 2 hours or more. Specifically, the time may be 2 to 3 hours.

[0049] If the above time range exceeds the upper limit, there is a problem of increased process time and cost. If the above time range exceeds the lower limit, there is a problem of unreacted raw materials remaining in the carbon raw material and Li2S mixture.

[0050] The above thermal reduction step can be performed in a vacuum atmosphere. By performing the thermal reduction step in a vacuum atmosphere, byproducts such as CO or CO2 generated during the thermal reduction reaction of the mixed powder of carbon and lithium compounds are rapidly discharged, thereby suppressing the formation of oxides and increasing the uniformity of the reaction of the mixed powder, thereby enabling the production of high-purity lithium sulfide.

[0051] In one embodiment, the vacuum atmosphere is 1 × 10 -3A method for producing lithium sulfide, which is performed under partial pressure conditions of 5 Torr. The partial pressure conditions are 1 × 10 -3 It can be up to 1 Torr.

[0052] If the upper limit of the above partial pressure condition is exceeded, there is a problem of increased oxide residue. If the lower limit of the above partial pressure condition is exceeded, there is a problem of increased cost of the device for depressurization.

[0053] After the step of mixing and thermally reducing the above carbon raw material and lithium compound, the step of filtering a solution containing the thermally reduced carbon-lithium compound and a solvent, and the step of drying and then heat-treating the filtrate may be included. Specifically, the mixed powder obtained from the heat treatment process is transferred to an extraction reactor under non-exposed atmospheric conditions, and the solvent is mixed to perform the extraction process.

[0054] The step of filtering a solution containing a thermally reduced carbon-lithium compound and a solvent may be a step of mixing the thermally reduced carbon-lithium compound, for example, C-Li2S, with a solvent. The solvent may include at least one of ethanol, methanol, isopropyl alcohol, ethylene glycol, and butyl alcohol.

[0055] In one embodiment, the mixing ratio of the solvent [L] to the carbon lithium compound [g] may be 4 to 10. Specifically, the mixing ratio may be 6 to 8.

[0056] If the above mixing ratio exceeds the upper limit of the above-mentioned range, there is a problem of reduced economic efficiency due to excessive solvent use. If the above mixing ratio exceeds the lower limit of the above-mentioned range, there is a problem of reduced extraction rate due to insufficient dissolution of the Li2S powder.

[0057] The step of drying the filtrate and then heat-treating it is a step of heat-treating the filtered material to obtain the final lithium sulfide (Li2S). The step of drying the filtrate and then heat-treating it can be performed at a temperature range of 400 to 800°C. Specifically, the temperature range can be performed at 500 to 800°C.

[0058] In one embodiment, the step of drying the filtrate and then heat treating it can be performed by heat treating it at a maximum temperature of 5 to 20° C. per minute for a maximum temperature maintenance time of 1 to 6 hours, followed by natural cooling.

[0059] In the heat treatment step after drying the above-mentioned filtrate, if the temperature exceeds the upper limit of the aforementioned temperature range, there is a problem of lithium sulfide being converted to lithium oxide. If the temperature exceeds the lower limit of the aforementioned temperature range, there is a problem of the purity of the final product, lithium sulfide, being reduced due to the temperature not being sufficient to convert or remove lithium sulfide to lithium hydroxide or lithium carbonate.

[0060] At this time, the step of drying the filtrate and then heat-treating it may be performed in an inert gas atmosphere. The inert gas atmosphere may include, for example, at least one of helium, neon, krypton, xenon, nitrogen, and argon.

[0061] Lithium sulfide manufactured in this way can be used as a raw material for a sulfide-based solid electrolyte.

[0062]

[0063] 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.

[0064]

[0065] <Experimental Example 1>: Evaluation example according to mixture shape in a vacuum atmosphere

[0066] <Comparative Example 1>

[0067] As a carbon raw material (C), Achisonro waste resistor material from POSCO Future M was prepared. The carbon raw material (C) in powder form and lithium sulfate (Li2SO4) powder were mixed at a weight ratio of 3:1 so that the total amount was 40 g, and vacuum (10 -3 Torr), heat treatment was performed at 900 ℃ for 2 hours and then naturally cooled to obtain a carbon-lithium compound in powder form, C+Li2S.

[0068] The above carbon-lithium compound was mixed with ethanol as a solvent, filtered, and the filtrate was dried. Then, in an Ar atmosphere, which is an inert gas atmosphere, heat treatment was performed at 800°C at a heating rate of 10°C per minute for a maximum temperature retention time of 2 hours, and then naturally cooled to produce lithium sulfide (Li2S).

[0069]

[0070] Comparative Example 2

[0071] In the step of thermally reducing the carbon raw material and lithium sulfate mixed powder, the carbon raw material (C) in powder form and lithium sulfate (Li2SO4) powder were mixed to have a weight ratio of 3:1, and the process was performed under atmospheric pressure conditions rather than vacuum conditions, and the process was performed in the same manner as Example 1 except that the argon (Ar) flow was 0.5 LPM.

[0072]

[0073] <Example 1>

[0074] In the step of thermally reducing the mixed powder of carbon raw material and lithium sulfate, the reduction process was performed in the same manner as in Comparative Example 1, except that the mixed powder was pelletized by adding water to the mixed powder of carbon and lithium sulfate and rotating it to a size of 1 to 3 mm.

[0075] Specifically, the step of adding water to the powder was to add water at a ratio of 50 mL of water to 200 g of powder, and then rotate the powder in a cylindrical device to form pellets. At this time, the density of the pellets was measured using the Archimedes method, and it was confirmed that the density of the pellets was approximately 1.7 g / mL.

[0076]

[0077] Table 1 below shows the weight ratio of carbon raw material (C) powder: lithium sulfate (Li2SO4) powder and the process conditions in the thermal reduction process. Table 2 below shows the XRD peak intensity ratio (%) of C-Li2S and the XRD peak intensity ratio (%) of lithium sulfide (Li2S) manufactured according to the process conditions in Table 1 below.

[0078] XRD of the powder (C+Li2S) after the thermal reduction step showed 2 of lithium sulfide. nd The ratio of oxygen compounds is indicated based on the peak. The main XRD peaks of carbon and lithium sulfide are 26.61 and 27.0°, respectively, and the peak value of carbon is very large, making it difficult to distinguish between the two. The main peak and 2 nd Since the peak size ratio is 100:23.6, the size of the main peak is 2 nd The size of the main peak was assumed by dividing the peak size by 0.236. The peak size ratio of the remaining oxides was compared with the calculated value.

[0079] The XRD peak intensity ratios in Table 2 below were measured using the Theta-2theta mode method using XRD diffraction analysis equipment.

[0080] Classification form C: Li2SO4 Weight process conditions Temperature (℃) Time (hr) Pressure Partial pressure [torr] Ar flow Comparative example 1 Mixed powder 3:1900 2 Vacuum 10 -3 0Comparative Example 2 Mixed Powder 3:19002 Normal Pressure - 0.5 LPM Example 1 (Example 2) Pellet 3:19002 Vacuum 10 -3 0

[0081] Classification (C+Li2S) XRD peak intensity ratio (%, Li2S 2 nd (peak standard) Li2S XRD peak intensity ratio (%, Li2S 1) st (peak standard) Li2CO3Li2OLi2SO4sumLi2CO3Li2OLi2SO4sumComparative example 100.60.51.101.501.5Comparative example 20201.421.4016.1016.1Example 100.500.500.400.4

[0082] Looking at Tables 1 and 2 above, looking at Comparative Examples 1 and 2, it was confirmed that under the thermal reduction process conditions, when the pressure was under vacuum conditions rather than atmospheric pressure, the content of oxides was lower, resulting in a higher purity of lithium sulfide. In addition, looking at Comparative Example 1 and Example 1, it was confirmed that when the carbon-lithium compound was in the form of pellets rather than mixed powder, the content of oxides was lower.

[0083] <Experimental Example 2>: Process Condition Control in Pellet Shape

[0084] <Reference Example 1>

[0085] The reduction process was performed in the same manner as in Example 1, except that the powder having a weight ratio of C:Li2SO4 of 2:1 was pelletized into a size of 1 to 3 mm by adding water to a mixture of carbon and lithium sulfate powder and rotating it.

[0086]

[0087] <Example 2>

[0088] The reduction process was performed in the same manner as Example 1, except that only pellets larger than 1 mm in size were input by classifying the powder size using a sieve.

[0089]

[0090] <Example 3>

[0091] The reduction process was performed in the same manner as Example 1, except that only pellets smaller than 1 mm in size were input by classifying the powder size using a sieve.

[0092]

[0093] <Example 4>

[0094] The same procedure as Example 1 was followed, except that the weight ratio of C:Li2SO4 was 4:1.

[0095]

[0096] <Reference Example 2>

[0097] The process was performed in the same manner as Example 2, except that the process temperature was changed to 850°C.

[0098]

[0099] <Example 5>

[0100] The process was performed in the same manner as Example 2, except that the process temperature was changed to 875 ℃.

[0101]

[0102] <Reference Example 3>

[0103] The process was performed in the same manner as Example 2, except that the process time was changed to 1 hour.

[0104]

[0105] <Reference Example 4>

[0106] The process was performed in the same manner as Example 2, except that the process time was changed to 1.5 hours.

[0107]

[0108] Table 3 below shows the weight ratio of carbon raw material (C) powder: lithium sulfate (Li2SO4) powder and the process conditions in the thermal reduction process, and Table 4 below shows the XRD peak intensity ratio (%) of C-Li2SO4 powder manufactured according to the conditions of Table 3 below and the XRD peak intensity ratio (%) of lithium sulfide (Li2S).

[0109] FIG. 2 illustrates an XRD result graph of a carbon-lithium compound having a pellet shape according to a mixing ratio of carbon and lithium compounds according to one embodiment of the present invention.

[0110] FIG. 3 illustrates an XRD result graph according to process temperature of a carbon-lithium compound having a pellet shape according to one embodiment of the present invention.

[0111] FIG. 4 illustrates a graph of XRD results according to process time of a carbon-lithium compound having a pellet shape according to one embodiment of the present invention.

[0112] Figures 5 to 7 show XRD peak values ​​of carbon-lithium compounds according to process conditions.

[0113] Fig. 5 shows XRD graphs according to the weight of carbon and lithium compounds in a carbon-lithium compound. Specifically, XRD peak values ​​are sequentially shown from the bottom when the weight ratios of carbon and lithium compounds are 2:1, 3:1, and 4:1. More specifically, Fig. 5 shows XRD graphs for Reference Example 1, Example 2, and Example 4 of the present invention.

[0114] Fig. 6 shows XRD graphs according to process temperature. Specifically, XRD peak values ​​at process temperatures of 900°C, 875°C, and 850°C are shown sequentially from the bottom. More specifically, Fig. 6 shows XRD graphs for Example 2, Example 5, and Reference Example 2 of the present invention.

[0115] Fig. 7 shows XRD graphs according to process time. Specifically, XRD peak values ​​for process times of 1 hour, 1.5 hours, and 2 hours are shown sequentially from the bottom. More specifically, Fig. 7 shows XRD graphs for Reference Example 3, Reference Example 4, and Example 2 of the present invention.

[0116]

[0117] Classification Type Pellet Size C: Li2SO4 Weight Process Condition Temperature (℃) Time (hr) Pressure Pressure Partial pressure [torr] Reference Example 1 Pellet > 1 mm2: 1900 2 Vacuum 10 -3 Example 2 Pellet > 1 mm 3: 1900 2 Vacuum 10 -3 Example 3 Pellet <1 mm3:19002 Vacuum 10 -3 Example 4 Pellet > 1 mm 4: 1900 2 Vacuum 10 -3 Reference Example 2 Pellet > 1 mm 3: 1850 2 Vacuum 10 -3 Example 5 Pellet > 1 mm3: 18752 Vacuum 10 -3 Reference Example 3 Pellet > 1 mm 3: 1900 1 Vacuum 10 -3 Reference Example 4 Pellet > 1 mm3: 1900 1.5 Vacuum 10 -3

[0118] Classification (C+Li2S) XRD peak intensity ratio (%, Li2S 2 nd (peak standard) Li2S XRD peak intensity ratio (%, Li2S 1) st (peak standard) Li2CO3Li2OLi2SO4sumLi2CO3Li2OLi2SO4sumReference Example 103.90.64.50.33.203.5Example 200.600.600.500.5Example 300.400.400.400.4Example 401.001.000.700.7Reference Example 203.40.43.80.32.803.1Example 500.900.901.001.0Reference Example 303.40.64.00.33.303.6Reference Example 401.50.92.40.22.102.3

[0119] Looking at Table 3, Table 4 and FIGS. 2 to 7 above, it was confirmed that in the carbon-lithium compounds having a pellet shape in Reference Example 1 and Examples 2 to 4, when the proportion of the carbon raw material was excessively low, the proportion of Li2O was high and the reaction of Li2SiO4 was not completed. In Examples 2, 5, and Reference Example 2, it was confirmed that when the process temperature was as low as 850°C, the proportion of Li2O was high and the reaction of Li2SiO4 was not completed. In Examples 2 and Reference Examples 3 and 4, it was confirmed that the reaction was completed when the process time was 2 hours or more, and the proportion of the remaining oxide decreased. The present invention is not limited to the above-described embodiments and / or examples, but can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential characteristics thereof. Therefore, it should be understood that the above-described embodiments and / or examples are exemplary in all respects and not restrictive.

Claims

1. As an intermediate product for manufacturing lithium sulfide powder having a pellet shape, Contains oxides, The above oxide is a carbon-lithium compound having a content of 1.0% or less based on the second XRD peak value of lithium sulfide (Li2S).

2. In paragraph 1, The above oxide is a carbon-lithium compound that does not contain Li2SO4.

3. In paragraph 2, The above oxide is a carbon-lithium compound that does not contain Li2CO3.

4. In paragraph 1, The above oxide comprises Li2O, The above Li2O is a carbon-lithium compound having a content of 1.0% or less based on the second XRD peak value of lithium sulfide (Li2S).

5. In paragraph 1, A carbon-lithium compound having a size of 1 mm to 5.0 mm.

6. A step of mixing carbon raw material and lithium compound and performing thermal reduction, A method for producing lithium sulfide having a pellet shape as a carbon-lithium compound as a result of thermal reduction.

7. In paragraph 6, A method for producing lithium sulfide, wherein in the step of mixing the carbon raw material and the lithium compound and performing thermal reduction, the ratio of the carbon raw material to the lithium compound is 3.0 or more and 5.0 or less.

8. In paragraph 6, A method for producing lithium sulfide, wherein the step of mixing the carbon raw material and the lithium compound and performing thermal reduction is performed in a vacuum atmosphere.

9. In paragraph 8, The above vacuum atmosphere is 1 × 10 -3 A method for producing lithium sulfide, which is performed under partial pressure conditions of 5 Torr.

10. In paragraph 6, After the step of mixing the above carbon raw material and lithium compound and performing thermal reduction, A step of filtering a solution containing a heat-reduced carbon-lithium compound and a solvent; and A method for producing lithium sulfide, comprising the step of drying the above filtrate and then performing a heat treatment.

11. In paragraph 6, In the step of mixing the carbon raw material and lithium compound and performing thermal reduction, A method for producing lithium sulfide, wherein when the above carbon raw material and the above lithium compound are mixed, a mixture in the shape of pellets having a size of 1 mm to 5.0 mm is formed.

12. In paragraph 6, A method for producing lithium sulfide, wherein the step of mixing the carbon raw material and the lithium compound and performing thermal reduction is performed at a temperature range of 860 to 1,100°C.

13. In paragraph 6, The carbon-lithium compound produced in the step of mixing the above carbon raw material and lithium compound and performing thermal reduction contains an oxide, A method for producing lithium sulfide, wherein the oxide content is 1.0% or less based on the second XRD peak value of lithium sulfide (Li2S).

14. In paragraph 13, Containing the above oxide Li2O, A method for producing lithium sulfide, wherein the above Li2O is 1.0% or less based on the second XRD peak value of lithium sulfide (Li2S).

15. In paragraph 6, The above oxide is a method for producing lithium sulfide not containing Li2SO4.

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