Method for preparing lithium sulfide

Abstract

The present invention relates to a method for preparing lithium sulfide, the method comprising the steps of: preparing a lithium-carbon compound by mixing a carbon reducing agent and a lithium compound; filtering a solution in which the lithium-carbon compound and a solvent are mixed; and drying the filtrate, wherein the carbon reducing agent comprises natural graphite.

Description

Method for manufacturing lithium sulfide

[0001] The present invention relates to a method for manufacturing lithium sulfide, comprising a method for purifying lithium sulfide. This application claims priority to Korean Patent Application No. 10-2024-0190832 filed on December 19, 2024, the entire contents of which are incorporated herein by reference.

[0002] 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.

[0003] 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.

[0004] 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.

[0005] 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.

[0006] In manufacturing the above lithium sulfide, a reducing agent can be utilized. At this time, solvent extraction is used to remove the residual reducing agent. Specifically, solvent extraction is used to increase the purity even in low-purity lithium sulfide.

[0007] However, there is a problem in that the purification effect is insufficient due to the loss of sulfur during the drying process after solvent extraction.

[0008] The technical problem that the present invention aims to solve is to provide a method for manufacturing lithium sulfide that can increase the purity of the manufactured lithium sulfide.

[0009] A method for producing lithium sulfide according to one embodiment of the present invention comprises the steps of: mixing a carbon reducing agent and a lithium compound to produce a lithium-carbon compound; filtering a solution mixed with the lithium-carbon compound and a solvent; and drying the filtrate, wherein the carbon reducing agent may include natural graphite.

[0010] In one embodiment, the natural graphite may have an average particle size of 10 μm or less. In one embodiment, the natural graphite has a specific surface area of ​​3.5 m² 2 It can be more than / g.

[0011] In one embodiment, the weight of the carbon reducing agent may be less than the weight of the lithium compound. In one embodiment, the weight ratio of the carbon reducing agent to the lithium compound (weight ratio of carbon reducing agent to lithium compound) may be 1:2 to 1:5.

[0012] In one embodiment, the molar ratio of the carbon reducing agent to the lithium compound (molar ratio of carbon reducing agent to lithium compound) may be 6:1 to 2:1. In one embodiment, the step of preparing the lithium-carbon compound may be performed at a temperature of 700 to 900 °C.

[0013] In one embodiment, the step of preparing the lithium-carbon compound may be performed at a heating rate of 3 to 7 °C / min. In one embodiment, the step of preparing the lithium-carbon compound may be performed in a vacuum atmosphere.

[0014] In one embodiment, the step of filtering the solution mixed with the lithium-carbon compound and the solvent can control the concentration of lithium in the solution to 9.54 g / L or higher. In one embodiment, the step of filtering the solution mixed with the lithium-carbon compound and the solvent can have a ratio of solvent to lithium-carbon compound (solvent (mL) / lithium-carbon compound (g)) of 30 or less.

[0015] In one embodiment, the content of the solvent may be 340 mL or less. In one embodiment, the step of drying the filtrate may be performed in an inert gas atmosphere.

[0016] A method for manufacturing lithium sulfide according to one embodiment of the present invention uses natural graphite as a carbon reducing agent to produce a lithium-carbon compound with a small amount of carbon, thereby enabling the production of lithium sulfide with high purity using less carbon.

[0017] According to another embodiment of the present invention, a method for producing lithium sulfide can produce high-purity lithium sulfide by appropriately controlling the ethanol content with respect to the aforementioned lithium-carbon compound to increase the lithium concentration of the extraction solution.

[0018] Figure 1 shows the XRD peak values ​​of the thermal reduction product according to an embodiment of the present invention.

[0019] Figure 2 shows the XRD peak values ​​of lithium sulfide according to an embodiment of the present invention.

[0020] 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.

[0021] 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.

[0022] When it is stated that one part is "on" or "on" another part, it may be directly on or on the other part, or another part may be involved in between. In contrast, when it is stated that one part is "directly on" another part, no other part is interposed in between.

[0023] 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 %.

[0024] 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.

[0025] According to one embodiment of the present invention, the lithium sulfide powder relates to a lithium sulfide powder for an all-solid-state electrolyte and may include lithium sulfide (Li2S) and lithium oxide (Li2O). Specifically, the lithium sulfide powder may include lithium oxide (Li2O) by undergoing drying and heat treatment processes.

[0026] In one embodiment, based on 100 wt% of lithium sulfide powder, the oxygen content in the lithium sulfide powder may be 4.0 wt% or less. Specifically, the oxygen content may be 3.5 wt% or less, more specifically, 1.0 wt% or less.

[0027] 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. Additionally, there is a problem that is affected by the ratio of impurities such as Li2O, Li2CO3, Li2SO4, or LiOH. 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.

[0028] In one embodiment, the lithium oxide (Li2O) may satisfy an XRD ratio (H%) of 5.0% or less. Specifically, the lithium oxide (Li2O) may satisfy an XRD ratio (%) of 3.0% or less, more specifically, 1.5% or less.

[0029] 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) falls outside the aforementioned range, the purity of the lithium sulfide powder may decrease, and there is a problem of reduced atmospheric stability of the solid electrolyte.

[0030] According to another embodiment of the present invention, a method for producing lithium sulfide may include the steps of mixing a carbon reducing agent and a lithium compound to produce a lithium-carbon compound, filtering a solution mixed with the lithium-carbon compound and a solvent, and drying the filtered material. The inventors have discovered that when natural graphite is used as a carbon reducing agent in producing the lithium sulfide of the present invention, a low content of the carbon reducing agent is used, unlike in the past, thereby simplifying the carbon reduction procedure in subsequent processes and, consequently, obtaining a high-purity dried material and lithium sulfide.

[0031] In one embodiment, the carbon reducing agent may include natural graphite. Specifically, the natural graphite may have an average particle size (D50) of 10 μm or less. The average particle size (D50) refers to a particle size corresponding to 50% of the volume of the natural graphite powder. The average particle size (D50) of the natural graphite may be 8 μm or less, specifically 3 to 8 μm or less.

[0032] In one embodiment, the natural graphite has a specific surface area of ​​3.5 m² 2 It may be greater than / g. Specifically, the specific surface area is 4.5 m² 2 / g or more, more specifically, 5.0 to 6.0 m 2 / g can be.

[0033] In one embodiment, the natural graphite may have a tap density of 0.8 g / mL or less. Specifically, the tap density may be 0.5 g / mL or less, more specifically, 0.1 to 0.4 g / mL.

[0034] The carbon reducing agent of the present invention includes natural graphite having the aforementioned characteristics, thereby allowing for the addition of a smaller amount of carbon reducing agent compared to conventional methods, and accordingly, the proportion of lithium sulfate monohydrate can be increased to obtain lithium sulfide of higher purity.

[0035] In one embodiment, the lithium compound may include at least one of lithium sulfate monohydrate, lithium sulfate, lithium hydroxide, lithium oxide, and lithium carbonate. Specifically, the lithium compound may be lithium sulfate monohydrate.

[0036] In one embodiment, in the step of preparing a lithium-carbon compound by mixing a carbon reducing agent and a lithium compound, the weight of the carbon reducing agent may be less than the weight of the lithium compound. By including the aforementioned natural graphite as the carbon reducing agent, a smaller amount of the carbon reducing agent than the lithium compound can be used, and accordingly, fewer processes or procedures are required to remove residual carbon in subsequent processes.

[0037] In one embodiment, the weight ratio of the carbon reducing agent to the lithium compound (weight ratio of carbon reducing agent to lithium compound) may be 1:2 to 1:5. Specifically, the weight ratio may be 1:3 to 1:5, and more specifically, 1:3.5 to 1:4.5.

[0038] In one embodiment, the molar ratio of the carbon-based reducing agent to the lithium compound (molar ratio of carbon reducing agent to lithium compound) may be 1:2 to 1:5. Specifically, the molar ratio may be 6:1 to 2:1, specifically 4:1 to 2:1, and more specifically 3.5:1 to 2.5:1.

[0039] By satisfying the aforementioned weight and molar ratios, a higher proportion of lithium sulfate monohydrate can be charged into the mixture, thereby improving productivity, and by reducing the carbon content and minimizing the formation of impurities, the purity of lithium sulfide can be increased.

[0040] If the above weight and molar ratios exceed the upper limits, there is a problem where unreacted lithium compound raw materials remain in the lithium-carbon compound after heat treatment. If the above weight ratio exceeds the lower limit, the amount of carbon raw material used is large, resulting in a disadvantage in terms of process cost.

[0041] In one embodiment, the step of preparing the lithium-carbon compound may be performed by heat-treating a carbon reducing agent and a lithium compound. Specifically, the heat treatment may be performed in a temperature range of 700 to 900 ℃. More specifically, the temperature may be performed in a temperature range of 740 to 810 ℃.

[0042] In one embodiment, the step of preparing the lithium-carbon compound may be performed at a heating rate of 3 to 7 ℃ / min. Specifically, the heating rate may be performed at a heating rate of 4 to 6 ℃ / min.

[0043] In one embodiment, the step of preparing the lithium-carbon compound may be performed in a vacuum atmosphere. Specifically, the vacuum atmosphere is 9.9 × 10⁻⁶ -2 Up to 0.1 × 10 -3 It can be performed under Torr pressure.

[0044] As the step of preparing the above lithium-carbon compound is performed under the aforementioned conditions, a high-purity dried product can be easily produced. The step of filtering the solution mixed with the lithium-carbon compound and the solvent may be a step of controlling the content of lithium oxide in lithium sulfide through a solvent extraction method. Specifically, solvent extraction may be performed to separate the reducing agent remaining in the dried product obtained after reducing lithium sulfate monohydrate by heat treatment using a carbon reducing agent.

[0045] In one embodiment, the concentration of lithium in the solution can be controlled to 9.54 g / L or higher. Specifically, the concentration of lithium can be controlled to satisfy 9.54 g / L or higher, specifically 9.8 g / L or higher, more specifically 10.0 g / L or higher, and even more specifically 10.0 to 11.0 g / L. By controlling the concentration of lithium in the solution to the aforementioned range, the purity of the final-produced lithium sulfide can be increased.

[0046] In one embodiment, the step of filtering the solution mixed with the lithium-carbon compound and the solvent may have a ratio of solvent to the lithium-carbon compound (solvent (mL) / lithium-carbon compound (g)) of 30 or less. Specifically, the ratio may be 28.5 or less, more specifically, 24 to 27. By satisfying the above-mentioned range, lithium sulfide with low oxygen concentration, low impurity content, and excellent ion conductivity can be produced.

[0047] In one embodiment, the content of the solvent may be 340 mL or less. The content of the solvent may be 335 mL or less, specifically 300 mL or less, more specifically 270 mL or less, and even more specifically 240 to 270 mL or less. Even if the content of the solvent is controlled within the aforementioned range, the purity of lithium sulfide can be increased to an appropriate range in the present invention by using a small amount of carbon reducing agent.

[0048] The solvent may be a polar protic solvent. The polar protic solvent may be a solvent having hydrogen atoms capable of forming hydrogen bonds and having polarity within the molecule. As a non-limiting example, the solvent may include ethanol, methanol, propanol, glycerol, water, acetic acid, ammonia, ethylene glycol, or a combination thereof.

[0049] In one embodiment, the solvent extraction step may be performed in a range of 0 to 60 ℃. Specifically, the filtration step may be performed in a range of 10 to 50 ℃, more specifically, in a range of 20 to 45 ℃.

[0050] In one embodiment, the filtration step may be performed in an inert atmosphere. Specifically, the inert atmosphere may be performed in an inert atmosphere such as Ar, H2, He, or N2.

[0051] In one embodiment, the filtration step may extract Li2S by dissolving the thermal reduction product in a solvent and stirring at room temperature for 1 to 30 hours, specifically 16 to 25 hours. As the solvent extraction step is performed for the aforementioned time, lithium sulfide with low sulfur loss can be produced.

[0052] The step of drying the above-mentioned filtrate can be performed in a temperature range of 20 to 300 ℃. Specifically, the temperature range can be performed in a temperature range of 50 to 200 ℃, and more specifically, in a temperature range of 40 to 150 ℃.

[0053] The step of drying the above-mentioned filtrate may be a step of slowly drying the solution containing lithium sulfide extracted through filtration by evaporating it. Through the drying step, the solution containing lithium sulfide evaporates, and a white powder may be obtained.

[0054] In one embodiment, the step of drying the filtrate may be performed at a vacuum pressure in the range of 15 to 300 mbar. Specifically, the vacuum pressure may be performed in the range of 30 to 200 mbar.

[0055] In one embodiment, the maximum temperature holding time in the step of heat-treating the dried product may be performed for 0.5 to 6 hours. In one embodiment, the step of heat-treating the dried product may include a step of natural cooling after performing heat treatment for the aforementioned time.

[0056] In one embodiment, the step of heat-treating the dried product may be performed in an inert gas atmosphere. The inert gas may include, for example, at least one of helium, neon, krypton, xenon, nitrogen, and argon.

[0057] Subsequently, the method may include a step of heat-treating the dried powder at 700°C or higher to obtain lithium sulfide powder. Specifically, the dried powder may be heat-treated at 750°C or higher to obtain lithium sulfide powder.

[0058] In one embodiment, the step of obtaining lithium sulfide powder by heat-treating the dried powder at 700°C or higher may be performed for 1 to 5 hours. Specifically, the time may be performed for 1.5 to 3 hours.

[0059] In one embodiment, the heating rate of the dried powder may be 5 ℃ / min or higher. Specifically, the heating rate may be 8 ℃ / min or higher.

[0060] In one embodiment, the step of heat-treating the dried powder at 700°C or higher to obtain lithium sulfide powder may be performed under an inert gas atmosphere. The inert gas may include, for example, Ar or nitrogen (N2), and the flow rate may be performed in the range of 1.0 to 5 L / min.

[0061] By heat-treating the powder dried under the aforementioned conditions, high-purity lithium sulfide with minimized impurity and oxygen content can be obtained.

[0062]

[0063] 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.

[0064]

[0065] <Experimental Example 1> : Carbon reducing agent ratio

[0066] <Example 1>

[0067] Natural graphite and lithium sulfate monohydrate, which are carbon reducing agents, were evenly mixed in a weight ratio of 1:2, then placed in a graphite crucible and 9.9 × 10⁻⁶ under a vacuum atmosphere -2 Up to 0.1 × 10-3 The temperature is raised to 800°C at a rate of 5°C per minute under Torr pressure.

[0068] Afterwards, when heat-treated at a temperature of 800 ℃ for 3 hours, lithium sulfate is reduced to lithium sulfide and obtained in a mixed state with graphite.

[0069] 1 g of the obtained thermal reduction product was dissolved in 50 mL of ethanol and filtered under reduced pressure through a 1 μm filter paper. The filter cake formed on the filter paper was dried in a convection oven at 150 °C for 24 hours to calculate the yield of the thermal reduction product.

[0070] At this time, the natural graphite has an average particle size (D50) of 5.21 μm and a specific surface area of ​​5.5 m 2 / g, and a tap density of 0.31 g / mL was used.

[0071]

[0072] <Comparative Example 1> - Excess amount of carbon reducing agent ratio

[0073] The procedure was performed in the same manner as Example 1, except that artificial graphite was used as the carbon reducing agent and the weight ratio of artificial graphite to lithium sulfate monohydrate was controlled to 3:1.

[0074] In this case, the artificial graphite has a particle size of 2 mm or less and a specific surface area of ​​3.3 m² 2 / g, and a tap density of 1.0 g / mL was used.

[0075]

[0076] <Experimental Example 2>: Control of Carbon Reducing Agent Content

[0077] <Example 2>

[0078] The procedure was performed in the same manner as Example 1, except that the weight ratio of natural graphite to lithium sulfate monohydrate was controlled to 1:3.

[0079]

[0080] <Example 3>

[0081] The procedure was performed in the same manner as Example 1, except that the weight ratio of natural graphite to lithium sulfate monohydrate was controlled to 1:4.

[0082]

[0083] <Example 4>

[0084] The procedure was performed in the same manner as Example 1, except that the weight ratio of natural graphite to lithium sulfate monohydrate was controlled to 1:5.

[0085]

[0086] Table 1 below shows the yield, yield rate, and impurity content of lithium sulfide according to the examples and comparative examples.

[0087] The yield, yield rate, and impurity content of lithium sulfide were measured or calculated by the following method.

[0088] Yield of lithium sulfide:

[0089] Actual yield of lithium sulfide = Weight of thermal reduction product - Weight of dry filter cake

[0090] Theoretical yield of lithium sulfide = Weight of input lithium sulfate monohydrate × ((Molar mass of lithium sulfide) / (Molar mass of lithium sulfate monohydrate))

[0091] Yield [%]: (Actual yield of lithium sulfide / Theoretical yield of lithium sulfide) × 100

[0092] Impurity content [H%]: The intensity of the lithium sulfide peak at 2θ = 27° on the XRD pattern of the thermal reduction product was set to 100, and the intensity ratio of each peak was expressed as H%.

[0093] Figure 1 is an XRD peak graph for the thermal reduction product of Example 4.

[0094] Mixing Ratio of Carbon Reducing Agent Type (Carbon Reducing Agent : (Lithium Sulfate Monohydrate) Yield Unreacted Residual Carbon Reducing Agent Specific Impurities [H%] [Weight Ratio] [Molar Ratio] [%] Li2O (33.7°) Li2CO3 (31.8°) Li2SO4 (22.29°) Example 1 Natural Graphite 1:25.33:188.647 0.900 Comparative Example 1 Artificial Graphite 3:132:126.89 1.8026.9326.8 Example 2 Natural Graphite 1:33.55:191.329 0.500 Example 3 Natural Graphite 1:42.66:191.215 0.600 Example 4 Natural Graphite 1:52.13:182.712 0.100.1

[0095] Looking at Table 1 and Figure 1 above, it was confirmed that when natural graphite and artificial graphite are used as carbon reducing agents, the amount of carbon reducing agent used can be significantly reduced compared to the conventional method of producing lithium sulfide. Specifically, it was confirmed that when natural graphite or artificial graphite is used as in Example 1 and Comparative Example 1, high-purity dried material and lithium sulfide can be obtained with a small amount because the amount of carbon reducing agent that needs to be filtered in the extraction process is small, even if less carbon reducing agent is used. In the case of Example 4, it was confirmed that the ratio of unreacted residual carbon reducing agent and the impurity content are lower than in Comparative Example 1 and Example 1, but it was confirmed that the yield is somewhat lower compared to Examples 2 and 3. In the case of Examples 2 and 3, although there is no significant difference in yield and quality, there is an advantage of high productivity as the proportion of lithium sulfate monohydrate in the raw material mixture increases, allowing more lithium sulfate monohydrate to be loaded into a crucible of limited volume.

[0096] In addition, the proportion of unreacted residual carbon in the thermal reduction product is the lowest, which has the advantage of increasing productivity by minimizing the amount of ethanol filtrate remaining in the filter cake during subsequent extraction and filtration processes.

[0097]

[0098] <Experimental Example 2>: Control of ethanol concentration in subsequent process

[0099] <Experimental Example 2-1>

[0100] 0.42 g of solid sulfur was mixed with 10 g of the thermally reduced product prepared according to Example 4 above, added to 350 mL of ethanol solvent, and stirred sufficiently at room temperature for 24 hours. After stopping the stirring, the mixed slurry was filtered, and the graphite that does not dissolve in ethanol remained in a wet state in the filter funnel, while the remainder was obtained in a solution state in the filter flask.

[0101] Subsequently, the prepared filtrate was transferred to a 1 L round-bottom flask, mounted on a rotary evaporator, and the solution was evaporated and concentrated using a vacuum pump to proceed with the drying process. During this process, the experiment was conducted under vacuum conditions at a drying temperature of 120 ℃ for a total of 30 minutes.

[0102] Specifically, the vacuum pressure was controlled within the range of 15–300 mbar, and an external constant temperature bath was used for drying. When drying at temperatures below 60 ℃, a heated water bath was used, and when temperatures above 80 ℃ were required, a constant temperature bath containing silicone oil was used. The powder dried in this manner was heat-treated at 800 ℃ for 2 hours to obtain lithium sulfide powder. The heating rate for heat treatment was 10 ℃ / min, and the flow rate of Ar gas was 2.5 L / min.

[0103]

[0104] <Experimental Example 2-2>

[0105] The above Experimental Example 2-1 was performed in the same manner as Experimental Example 2-1, except that the ethanol was controlled to 335 mL.

[0106]

[0107] <Experimental Example 2-3>

[0108] The experiment was performed in the same manner as Experiment 2-1, except that the ethanol was controlled to 285 mL.

[0109]

[0110] <Experimental Example 2-4>

[0111] The experiment was performed in the same manner as Experimental Example 2-1, except that the ethanol was controlled to 250 mL.

[0112] Figure 2 is an XRD peak graph of lithium sulfide prepared according to Experimental Example 2-4 of the present invention.

[0113]

[0114] <Experimental Example 2-5>

[0115] The above Experimental Example 2-1 was performed in the same manner as Experimental Example 2-1, except that the ethanol was controlled to 229 mL.

[0116] Thermal reduction product [g] Ethanol [mL] Li concentration in solution [g / L] Oxygen concentration [wt%] Impurities [H%] Ionic conductivity [mS / cm] Remarks Li2O (33.7°) Li2CO3 (31.8°) Li2SO4 (22.29°) Experimental Example 2-1 103 50 9.2 28 3.6 9 54.8 0 2.19 Comparative Example Experimental Example 2-2 103 35 9.5 4 3.5 1 2.7 0 2.43 Comparative Example Experimental Example 2-3 102 85 9.8 16 2.3 1 1.6 0 2.46 Example Experimental Example 2-4 102 50 10.5 6 0.5 4 0 0 3.33 Example Experimental Example 2-5 102 29 11.5 9 21.1 8 0.8 0 3.1 83 Example

[0117] Referring to Table 2 and Figure 2 above, it was confirmed that the purity of the heat-treated final lithium sulfide increased as the Li concentration of the extraction solution increased. In the case of Experimental Examples 2-4 and 2-5, it was confirmed that the ionic conductivity was high, exceeding 3.00 (10 mS / cm). However, compared to Experimental Example 2-4, it was confirmed that in Experimental Example 2-5, the lithium sulfide did not dissolve sufficiently in ethanol, and some remained in the filter cake along with unreacted graphite. 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 present invention can be implemented in other specific forms without altering the technical spirit 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 a lithium-carbon compound by mixing a carbon reducing agent and a lithium compound; A step of filtering the solution obtained by mixing the above lithium-carbon compound and solvent; and The above filtrate includes a step of drying, The above carbon reducing agent is a method for producing lithium sulfide containing natural graphite.

2. In Paragraph 1, The above natural graphite is a method for manufacturing lithium sulfide having an average particle size of 10 μm or less.

3. In Paragraph 1, The above natural graphite has a specific surface area of ​​3.5 m² 2 Method for manufacturing lithium sulfide with a content of / g or more.

4. In Paragraph 1, The above natural graphite is a method for manufacturing lithium sulfide having a tap density of 0.8 g / mL or less.

5. In Paragraph 1, A method for manufacturing lithium sulfide in which the weight of the carbon reducing agent is less than the weight of the lithium compound.

6. In Paragraph 1, A method for producing lithium sulfide in which the weight ratio of the carbon reducing agent to the lithium compound (weight ratio of carbon reducing agent to lithium compound) is 1:2 to 1:

5.

7. In Paragraph 1, A method for producing lithium sulfide in which the molar ratio of the carbon reducing agent to the lithium compound (molar ratio of carbon reducing agent to lithium compound) is 6:1 to 2:

1.

8. In Paragraph 1, A method for manufacturing lithium sulfide in which the step of manufacturing the above lithium-carbon compound is performed at a temperature of 700 to 900 ℃.

9. In Paragraph 1, A method for manufacturing lithium sulfide powder in which the step of manufacturing the above lithium-carbon compound is performed at a heating rate of 3 to 7 ℃ / min.

10. In Paragraph 1, A method for manufacturing lithium sulfide in which the step of manufacturing the above lithium-carbon compound is performed in a vacuum atmosphere.

11. In Paragraph 1, The step of filtering the solution mixed with the lithium-carbon compound and solvent is, A method for producing lithium sulfide by controlling the concentration of lithium in the above solution to 9.54 g / L or higher.

12. In Paragraph 1, The step of filtering the solution mixed with the lithium-carbon compound and solvent is, A method for producing lithium sulfide in which the ratio of solvent to the lithium-carbon compound (solvent (mL) / lithium-carbon compound (g)) is 30 or less.

13. In Paragraph 12, A method for manufacturing lithium sulfide in which the content of the above solvent is 340 mL or less.

14. In Paragraph 1, A method for manufacturing lithium sulfide powder in which the step of drying the above-mentioned filter is performed in an inert gas atmosphere.

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