Lithium sulfide manufacturing method

Abstract

The present invention relates to a method for producing lithium sulfide, which includes the steps of mixing a carbon raw material and a lithium compound to produce a lithium-carbon compound, filtering a solution obtained by mixing the lithium-carbon compound and a solvent, spray-drying the filtrate at a temperature of 110 to 160°C in an inert loop structure, and heat-treating the spray-dried product, thereby producing lithium sulfide having an oxygen content of less than 2.8%.

Description

[Technical Field]

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

[0002] Secondary batteries are widely used in a wide range of devices, from small electronic devices such as mobile phones and laptops to large devices such as electric vehicles (EVs) and energy storage systems (ESSs). As the application of secondary batteries expands to all areas of life, there is a growing demand for them to have not only high energy density and long life, but also stability.

[0003] Conventionally, most of the electrolytes used in lithium secondary batteries have been liquid electrolytes using organic solvents, but these liquid electrolytes have required strict packaging due to issues such as leakage and fire hazards, and this strict packaging has limited the ability to increase energy density beyond a certain level. Therefore, the need for all-solid-state batteries using inorganic solid electrolytes rather than organic liquid electrolytes has emerged.

[0004] The all-solid-state battery can produce safe battery cells by eliminating organic solvents used in liquid electrolytes. In addition, inorganic solid electrolytes have the advantage of being stable and not decomposed over a wide voltage range, making them suitable for use as high-voltage electrode materials.

[0005] Solid electrolytes are classified into oxide-based and sulfide-based solid electrolytes, and sulfide-based solid electrolytes are characterized by higher ionic conductivity compared to oxide-based solid electrolytes. The main raw material for sulfide-based solid electrolytes is lithium sulfide (LiS). LiS can be synthesized using a high-energy ball mill, a wet plasma process, or a wet / dry method using lithium metal. However, the above methods have problems such as difficulty in kinetic control, high costs of starting materials, high process costs, and environmental issues, making commercialization difficult.

[0006] In contrast, the carbonthermal reduction method is environmentally friendly as it does not use toxic H2S gas, and has the advantage of using inexpensive Li2SO4. However, since the extraction solvent must be used again after the heat treatment in the solid-phase heat treatment reduction reaction step, problems with product purity control must be resolved through the management of the physical properties of the extracted solution, the extraction solution drying step, heat treatment, or crystallization step.

[0007] In particular, since the physical properties of the dried product change depending on the drying method of the extract solution, an appropriate drying method for the extract solution is a key factor for obtaining high-quality lithium sulfide. Therefore, there is a need for a method for synthesizing lithium sulfide by controlling the drying method of the extract solution in which lithium sulfide is dissolved. Summary of the Invention [Problem to be solved by the invention]

[0008] The technical problem to be solved by the present invention is to provide a drying method for producing high-purity lithium sulfide. [Means for solving the problem]

[0009] A method for producing lithium sulfide according to one embodiment of the present invention includes mixing a carbon source and a lithium compound to produce a lithium-carbon compound, filtering a solution obtained by mixing the lithium-carbon compound and a solvent, spray-drying the filtrate at a temperature of 110 to 160°C in an inert loop configuration, and heat-treating the spray-dried product, thereby producing lithium sulfide having an oxygen content of less than 2.8%. In one embodiment, the method may further include spray-drying the filtrate at a temperature of 110 to 160°C in an inert loop configuration, and controlling the average particle size of the spray-dried product to 0.1 to 100 μm.

[0010] In one embodiment, the step of spray-drying the filtrate at a temperature of 110 to 160°C using an inert loop structure may include controlling the concentration of the extract extracted during spray-drying to 5 to 15 g / L. In one embodiment, the step of spray-drying the filtrate at a temperature of 110 to 160°C using an inert loop structure may include controlling the spray-dried product to be spherical.

[0011] In one embodiment, in filtering the mixed solution of the lithium-carbon compound and the solvent, the mixing ratio of the lithium-carbon compound to the solvent may be 1 to 1 / 4. In one embodiment, the heat-treating the spray-dried product may be performed at 100 to 800°C.

[0012] In one embodiment, H2S, C3H8, or CH4 may be generated during the heat treatment of the spray-dried product. In one embodiment, when the filtrate is spray-dried at a temperature of 110 to 160°C in an inert loop, some of the gases generated during drying and the inert gas may be recycled and re-reacted.

[0013] In one embodiment, the filtrate is spray-dried at a temperature of 110 to 160°C in an inert loop structure, and the inert loop structure may include a partially pure ring structure that induces a reaction of gas generated from the spray-dried product during drying. In one embodiment, the reaction may reduce impurities according to the following reaction formula: [Reaction scheme] 2H2S+2LiOET→Li2S+2EtOH

[0014] In one embodiment, the spray-dried material can include lithium ethoxide (LiOEt, CHO-Li), ethanol (CHO-H, EtOH), and lithium bisulfide (LiSH). In one embodiment, the solvent can include at least one of ethanol, methanol, isopropyl alcohol, ethylene glycol, and butyl alcohol. [Effects of the Invention]

[0015] A method for producing lithium sulfide according to one embodiment of the present invention provides a method for producing high-purity lithium sulfide with a low impurity content by utilizing spray drying and simultaneously performing a re-reaction in an inert loop structure. [Brief explanation of the drawings]

[0016] Figures 1a and 1b show the XRD peak values ​​of lithium sulfide obtained by the dry method.

[0017] 2a to 2c are SEM photographs at different magnifications (×300, ×1K) and a particle size distribution graph of Example 2. FIGS. 2d to 2g are SEM photographs at different magnifications (×100, ×300, ×1K) and a particle size distribution graph of Example 3.

[0018] FIG. 3 shows the Raman characteristics of the powder obtained by drying the filtered material according to the manufacturing method of the embodiment of the present invention.

[0019] 4a to 4d show the concentrations of gases evolved during heat treatment of a spray-dried product according to one embodiment of the present invention.

[0020] Figures 5a and 5b are schematic diagrams of the reaction process with and without an inert loop structure during the drying stage.

[0021] 6a and 6b show XRD peaks obtained when LiS was synthesized by controlling the drying temperature during spraying and drying of the filtered material in accordance with the examples and comparative examples of the present invention and by performing a final heat treatment after varying the rapid heat treatment temperature.

[0022] 7a and 7b show XRD peaks of a high-concentration filtrate during heat treatment after spray drying, in order to control the concentration of the filtrate when spraying and drying the filtrate according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, 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.

[0024] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular form includes the plural form unless the context clearly dictates otherwise. As used in the specification, the meaning of "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0025] When a part is referred to as being "on" another part, it can mean that it is directly on top of the other part, or there can be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them.

[0026] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which this invention belongs. Terms defined in commonly used dictionaries are additionally interpreted as having a meaning consistent with the relevant technical literature and the presently disclosed content, and unless defined, are not interpreted as having an ideal or very formal meaning. Furthermore, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0027] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art will be able to easily understand and practice the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0028] According to an embodiment of the present invention, a precursor for producing lithium sulfide has a hollow shape. The precursor for producing lithium is a spray prepared through spray drying during a process for producing lithium sulfide, which will be described later.

[0029] The hollow shape refers to a shape that is hollow inside, and the precursor for producing lithium sulfide has a hollow shape. The hollow shape of the precursor is a characteristic that appears when ethanol is evaporated during the spray drying process. The hollow shape of the precursor has the advantage of ensuring uniformity of the interior and exterior of the particles during heat treatment.

[0030] In one embodiment, the hollow shape may have a hemispherical shape. The hemispherical shape of the precursor has an advantage that it is easy to mix with other particles added for controlling physical properties during heat treatment.

[0031] In one embodiment, the precursor for preparing lithium sulfide may satisfy the following formula 1: <Expression 1> (Dmax-Dmin) / D50≦15 (In the above formula 1, Dmax, Dmin, and D50 are the maximum particle size, the minimum particle size, and the volume ratio, respectively, and refer to the particle size when the particles are accumulated to 50%.)

[0032] In this specification, particle size D0.9 means the particle size when particles of active material having various particle sizes distributed such as 0.1, 0.2, 0.3...3, 5, 7...10, 20, 30 μm are accumulated to 0.9% by volume, D10 means the particle size when particles are accumulated to 10% by volume, D50 particle size means the particle size when particles are accumulated to 50% by volume, D6 particle size means the particle size when particles are accumulated to 6% by volume, D95 means the particle size when particles are accumulated to 95% by volume, D min is the minimum particle size, D max means the maximum particle size.

[0033] The formula 1 is an index showing the degree of uniformity in the particle distribution of the precursor, and may be 15 or less, specifically 11.30 or less.

[0034] By satisfying the value of Equation 1, it is possible to obtain an advantage that the particle distribution is uniform and the reaction occurs uniformly during heat treatment, thereby ensuring lithium sulfide quality with little deviation. If the value of Equation 1 is outside the above range, the quality deviation of lithium sulfide may become large. To prevent this, it is necessary to ensure uniformity by additionally grinding the obtained lithium sulfide precursor, which may result in a problem of reduced processability.

[0035] In one embodiment, the standard deviation (STD DEV) of the precursor particle size may be 11.0 or less. Specifically, the standard deviation may be 9.2 or less. When the standard deviation satisfies the above range, as described above, there is an advantage in that uniform particle distribution is ensured, and the reaction occurs uniformly during heat treatment, thereby ensuring the quality of lithium sulfide with small deviation.

[0036] In one embodiment, the Dmax of the precursor may be in the range of 10 to 100 μm, specifically, in the range of 12.82 to 66.84 μm.

[0037] In one embodiment, the Dmin of the precursor may be in the range of 0.1 to 2.5 μm, specifically, in the range of 0.12 to 1.24 μm.

[0038] In one embodiment, the precursor has a wavenumber of 2,600 to 3,250 cm in Raman analysis. -1 The first peak appears at a wave number of 2,500 to 2,600 cm -1 The second peak appears at wavenumbers of 850 to 1,500 cm -1 The first peak may be a peak of EtOH, the second peak may be a peak of LiSH, and the third peak may be a peak of LiOEt.

[0039] In the case of the precursor of the present invention, when only LiOET is contained, there is a problem that LiS conversion is less and it may be converted to other impurities (LiCO, LiSO), and when only LiSH is contained, there is a problem that when HS is released in the reaction according to the following reaction formula, S loss continues and the LiS yield decreases. [Reaction scheme] LiSH+LiSH→Li2S+H2S↑

[0040] Therefore, the precursor has the advantage that it can produce high-purity lithium sulfide by simultaneously containing the first peak, the second peak, and the third peak, thereby preventing sulfur loss as described below. Specifically, the precursor has the advantage that it can produce high-purity lithium sulfide by simultaneously containing the first peak, the second peak, and the third peak, thereby satisfying the following reaction formula: [Reaction scheme] LiSH+LiOEt→Li2S+EtOH

[0041] A lithium sulfide powder according to another embodiment of the present invention relates to a lithium sulfide powder for an all-solid-state electrolyte, and includes lithium sulfide (LiS) and at least one impurity selected from the group consisting of lithium oxide (LiO), lithium carbonate (LiCO), and lithium sulfate (LiSO). High-purity lithium sulfide powder can contain impurities such as lithium oxide (LiO), lithium carbonate (LiCO), or lithium sulfate (LiSO) by undergoing a heat treatment process.

[0042] In one embodiment, the oxygen content in the whole powder is less than 2.8%, specifically, 1.3 to 1.6%, more specifically, 1.32 to 1.60%.

[0043] If the oxygen content is outside the above range, there is a problem that the lithium conductivity decreases when synthesizing argyrodite using LiS, and there is also a problem that it is affected by the ratio of impurities such as LiO, LiCO3, LiSO4, or LiOH.

[0044] In one embodiment, the impurities may be free of lithium carbonate (LiCO3) and lithium sulfate (LiSO4), excluding lithium oxide (LiO). In one embodiment, the content of lithium oxide (LiO) may be 3.0% or less. Specifically, the content of lithium oxide (LiO) may be 1.6% or less. The lithium oxide (LiO) corresponds to an impurity, and when the content of the lithium oxide (LiO) satisfies the above-mentioned range, high-purity lithium sulfide with a low impurity content can be achieved. When the content of the lithium oxide (LiO) is outside the above-mentioned range, there is a problem of reduced lithium conductivity during the synthesis of argyrodite using LiS. In one embodiment, the lithium sulfide powder of the present invention may satisfy the following formula 2: <Expression 2> [Li2O] × oxygen content ≦ 5.0 (In the above formula 2, [Li2O] means the content of lithium oxide in the powder.)

[0045] The formula 2 represents the relationship between lithium oxide (LiO) and the oxygen content, and the product of the lithium oxide and the oxygen content being 5.0 or less is an indicator of high-purity lithium sulfide. The formula 2 can be 5 or less, specifically 2.5 or less, and more specifically 0.64 to 2.11 or less.

[0046] If the value of formula 2 is outside the above range, there is a problem that electrical properties deteriorate during the synthesis of argyrodite.

[0047] According to another embodiment of the present invention, a method for producing lithium sulfide includes the steps of: mixing a carbon raw material and a lithium compound to produce a lithium-carbon compound; filtering a solution obtained by mixing the lithium-carbon compound and a solvent; spray-drying the filtrate in an inert loop structure; and heat-treating the dried product. For details about lithium sulfide, please refer to the above description.

[0048] In one embodiment, the carbon raw material may include, but is not limited to, at least one of soft carbon, hard carbon, petroleum coke, coal-based needle coke, coal-based pitch coke, natural graphite, and artificial graphite. In one embodiment, the lithium-carbon compound may include at least one of lithium sulfate, lithium hydroxide, lithium oxide, and lithium carbonate. The step of preparing the lithium-carbon compound by mixing the carbon raw material and the lithium compound may be performed by heat-treating the carbon raw material and the lithium compound.

[0049] The step of spray-drying the filtrate in an inert loop structure can be carried out by a spray-drying method. The filtrate may be in the form of a slurry, for example, and can be spray-dried by controlling the concentration of the liquid medium from which the filtrate is extracted. The spray-drying method can produce a spray-dried product with a uniform particle size.

[0050] In one embodiment, the drying of the filtered material can be carried out at a temperature ranging from 100 to 160°C. Specifically, the temperature range is from 110 to 160°C.

[0051] If the temperature is outside the upper limit of the above range, impurities such as lithium carbonate (Li2CO3) and lithium sulfide (Li2SO4) may be produced in addition to the lithium sulfide compound produced, and the oxygen concentration may also increase. If the temperature is outside the lower limit of the above range, drying may not be complete during spray drying, and dried material containing a large amount of solvent may gradually deposit in the spray drying circulation passage, making circulation difficult and reducing process efficiency.

[0052] In one embodiment, drying the filtrate may include controlling the average particle size of the spray-dried product to 0.1 to 100 μm, specifically, 1.0 to 10.0 μm.

[0053] If the average particle size is outside the upper limit, problems may occur with uniformity during heat treatment of the dried product obtained through spray drying. If the concentration of the spray liquid or the injection rate is increased to increase the average particle size, the spray drying nozzle may become clogged, and cross-spraying to prevent this may reduce processability. If the average particle size is outside the lower limit, the proportion of fine particles in the dried product may increase, which may lead to early clogging of the pre-filter of the aspirator that circulates the powder and solvent during spray drying, reducing processability. Furthermore, the dried product may be scattered by the inert gas flowing into the tube furnace during heat treatment, resulting in loss of the heat-treated product.

[0054] In one embodiment, the step of spray-drying the filtrate at a temperature of 110 to 160°C may include controlling the concentration of the extract (based on Li-ICP) extracted during spray-drying to 5 to 15 g / L. Specifically, the concentration of the extract may be controlled to 6 to 14 g / L.

[0055] If the concentration of the extract is outside the upper limit, the spray drying nozzle may be clogged, and cross-spraying to prevent this may reduce process efficiency.If the concentration of the extract is outside the lower limit, the yield per hour may be reduced, and it may take an excessively long time to obtain a certain amount of dried material.

[0056] In one embodiment, the step of spray-drying the filtrate in an inert loop structure may include controlling the shape of the spray-dried product to be spherical. The controlling the shape of the spray-dried product may be controlled by adjusting the concentration of the extract, the flow rate of the inert gas, or the injection rate of the extract. By controlling the shape of the spray-dried product to be spherical, uniform heat transfer can be achieved during heat treatment after drying.

[0057] In one embodiment, the filtrate may be spray-dried using an inert loop structure, whereby a portion of the gas generated during drying and an inert gas may be recycled. In one embodiment, the filtrate may be dried using a partially pure loop structure that induces a reaction of the gas generated from the spray-dried product during drying. The drying step may be performed using an inert loop structure, whereby a portion of the gas generated during drying of the extract and an inert gas may be recycled. During drying, the gas (HS) generated from the spray-dried product and LiOET of the dried product may be sufficiently reacted. Specifically, HS gas may participate in the re-reaction according to the following reaction formula: [Reaction scheme] 2H2S+2LiOET→Li2S+2EtOH

[0058] Therefore, the inactive loop structure described above has the advantage of containing a partially pure ring structure, reducing the amount of LiOEt, which is a raw material for impurities, and reducing the oxygen content, thereby enabling the production of high-purity lithium sulfide.

[0059] In one embodiment, the spray-dried material can include lithium ethoxide (LiOEt, CHO-Li), ethanol (CHO-H, EtOH), and lithium bisulfide (LiSH).

[0060] The step of heat-treating the dried product involves applying heat to the dried spray-dried product to obtain final lithium sulfide (LiS). In one embodiment, the dried product, specifically the spray-dried product, may be heated at a temperature in the range of 400 to 800°C, more specifically, 500 to 800°C. In one embodiment, the heat-treating step may be performed at a temperature increase rate of 5 to 20°C per minute.

[0061] In one embodiment, the heat-treating step of the dried material may be performed for 1 to 6 hours at the maximum temperature, and may include a step of naturally cooling the dried material after the heat-treating step for the above-mentioned time.

[0062] If the temperature, heating rate, and maintenance time are outside the upper limits, lithium sulfide may be converted into lithium oxide. If the temperature, heating rate, and maintenance time are outside the lower limits, impurities such as lithium hydroxide or lithium carbonate may not be easily removed, resulting in a decrease in the purity of lithium sulfide.

[0063] In one embodiment, the heat treatment of the dried product may be performed under an inert gas atmosphere, which may include at least one of helium, neon, krypton, xenon, nitrogen, and argon. [Example]

[0064] Hereinafter, specific examples of the present invention will be described. However, the following examples are merely specific examples of the present invention, and the present invention is not limited to the following examples.

[0065] Comparison of Li2S by drying method <Experimental Example> The process consisted of the following steps: a carbothermal reduction step (Li2SO4 + 2C → Li2S + 2CO2↑) in which carbon and lithium sulfate were mixed and heat-treated in an inert gas atmosphere (Ar) to obtain a lithium sulfide-carbon mixture, a step in which the lithium sulfide-carbon mixture was mixed with ethanol to make an extract, a step in which the extract was dried to obtain a dried product, and a step in which the dried product was heat-treated in an inert gas atmosphere (Ar) to produce lithium sulfide (Li2S).

[0066] Example 1: Lithium sulfide production method based on low-concentration, high-temperature, spray-drying synthesis In the step of controlling the spraying and drying temperature of the filtrate, the filtrate was sprayed at a low concentration (6 g / L, Li-ICP standard) by adjusting the ratio of the ethanol and lithium sulfide mixture, and rapidly dried at room temperature to 160°C, except that the same procedure as in the experimental example was carried out.

[0067] <Comparative Example 1> - Lithium sulfide manufacturing method based on low-concentration reduced-pressure dry synthesis method In the step of controlling the spraying and drying temperature of the filtrate, the ratio of the ethanol and lithium sulfide mixture was adjusted to a low concentration (6 g / L, Li-ICP standard) and the water bath temperature was set to between 45 and 50°C. Rotary evaporation and drying were performed by applying a reduced pressure from atmospheric pressure to 60 mbar, in the same manner as in the experimental example.

[0068] Figures 1a and 1b show the XRD peak values ​​of the dried lithium sulfide powder.

[0069] 1a and 1b show the XRD peak values ​​of Example 1 and Comparative Example 1. It was confirmed that lithium carbonate (Li2CO3) appeared in addition to lithium sulfide in Comparative Example 1. It was confirmed that this method is superior in terms of Li2S purity compared to other drying methods.

[0070] Controlling the average particle size of the spray by the concentration of the extract 2a to 2g are SEM photographs and particle size distribution graphs showing the average particle size depending on the extract concentration, and FIGS. 2f to 2k are SEM photographs and particle size distribution graphs showing the average particle size depending on the reduced pressure drying method.

[0071] Figures 2a to 2c are SEM photographs at different magnifications (300x, 1Kx) and particle size distribution graphs of Example 2. Figures 2d to 2g are SEM photographs at different magnifications (100x, 300x, 1Kx) and particle size distribution graphs of Example 3. Figures 2f to 2k are SEM photographs at different magnifications (100x, 300x, 1Kx) and particle size distribution graphs of Comparative Example 2, which was subjected to reduced pressure drying.

[0072] Example 2: Low concentration spray-dried product When spray drying was performed as in Example 1, the concentration of the extract was controlled to a low concentration of 6 g / L, and it was confirmed that the average particle size of the dried spray product after the drying process was 1.13 μm.

[0073] Example 3 - High concentration - spray dried product When spray drying was performed as in Example 1, the concentration of the extract was varied to a high concentration of 10 g / L, and it was confirmed that the average particle size of the dried spray product after the drying process was 8.65 μm.

[0074] <Comparative Example 2> - Low concentration - vacuum dried product When the reduced pressure drying method was used as in Comparative Example 1, it was confirmed that the particle size was widely distributed in the range of 1.75 to 224.59 μm and the particle shape was not uniform.

[0075] Table 1 below shows particle size distribution data according to examples of the present invention and comparative examples.

[0076] [Table 1]

[0077] From Table 1, it was confirmed that the spray-dried product of the present invention, which is a precursor for preparing lithium sulfide, has a small standard deviation and a low (Dmax-Dmin) / D50 value, and thus has a uniform particle size, through Examples 2 and 3.

[0078] Analysis of Raman characteristics of spray-dried materials FIG. 3 shows the Raman characteristics of the lithium sulfide powder produced by the manufacturing method of the embodiment of the present invention.

[0079] Figure 3 shows the Raman characteristics of Examples 4 and 5. Specifically, the spray-dried product was confirmed to exhibit peaks of lithium ethoxide (LiOEt, CHO-Li), ethanol (EtOH, CHO-H), and lithium bisulfide (LiSH).

[0080] Example 4 - Low Concentration - High Temperature - Spray Dried In the step of controlling the spraying and drying temperature of the filtrate, the filtrate was sprayed at a low concentration (6 g / L, Li-ICP standard) by adjusting the ratio of ethanol and lithium sulfide mixture, and then rapidly dried at room temperature to 150°C.

[0081] Example 5 - Low Concentration - Low Temperature - Spray Dried In the stage of controlling the spraying and drying temperature of the filtrate, the filtrate was sprayed at a low concentration (6g / L, Li-ICP standard) by adjusting the ratio of ethanol and lithium sulfide mixture, and then rapidly dried at room temperature to 115℃.

[0082] Characteristics of exhaust gases during heat treatment of dried materials with and without an inert loop. 4a-4d show the concentrations of gases evolved during heat treatment of a spray-dried product according to one embodiment of the present invention.

[0083] 4a to 4c show the concentrations of C3H8, CH4, and H2S gases, respectively. Specifically, they show the concentrations of gases generated during heat treatment in Example 6 and Comparative Example 3 described below. As such, it was confirmed that the aforementioned gases were generated when the spray-dried material was heat-treated at 800°C.

[0084] Figures 5a and 5b are schematic diagrams of the reaction process with and without the inert loop structure during the drying stage.

[0085] Referring to Figures 5a and 5b, the inert loop structure recirculates some of the gases and inert gases generated during the drying of the extract, allowing for sufficient reaction between H2S, a gas generated in the spray-dried material during drying, and the dried material, LiOEt. When H2S gas re-participates in the reaction, LiOEt, the source of impurities, is reduced according to the following reaction equation, resulting in a reduction in impurities and a decrease in oxygen content. This can be confirmed by looking at Table 1, which shows a comparison of XRD results for different drying methods. [Reaction scheme] 2H2S+2LiOET→Li2S+2EtOH

[0086] Example 6 - Low Concentration - Low Temperature - Spray Dried As in Example 1, in the step of controlling the spraying and drying temperature of the filtrate, the filtrate was sprayed under low concentration conditions (6 g / L, Li-ICP standard) by adjusting the ratio of the ethanol and lithium sulfide mixture, and then rapidly dried at room temperature to 160°C.

[0087] <Comparative Example 3> - Low concentration - dried under reduced pressure A vacuum drying method was carried out as in Comparative Example 1. In the step of controlling the spraying and drying temperature of the filtrate, the ratio of the ethanol and lithium sulfide mixture of the filtrate was adjusted to low concentration conditions (6 g / L, Li-ICP standard) with the water bath temperature set between 45 and 50°C, and rotary evaporation and drying were carried out by applying a vacuum from atmospheric pressure to 60 mbar.

[0088] XRD analysis of heat-treated materials by temperature 6a and 6b show XRD peaks obtained when the rapid thermal treatment temperature was controlled in spraying and drying the filtered material according to the examples and comparative examples of the present invention. Specifically, the XRD peaks of the filtered sprays that underwent heat treatment were confirmed when the drying temperature was controlled at 110°C, 170°C, and 180°C, as in Example 7, Comparative Example 4, and Comparative Example 5, compared to Example 1.

[0089] Example 7: Low concentration - Lithium sulfide based on low temperature spray drying synthesis method The same procedure as in Example 1 was carried out except that the drying temperature was 110°C.

[0090] <Comparative Example 4> - Lithium sulfide based on low concentration - high temperature spray drying synthesis method The same procedure as in Example 1 was carried out except that the drying temperature was 170°C.

[0091] <Comparative Example 5> - Lithium sulfide based on low concentration - high temperature spray drying synthesis method The same procedure as in Example 1 was carried out except that the drying temperature was 180°C.

[0092] In Example 7, Comparative Examples 4 and 5, it was confirmed that impurities Li2CO3 and Li2SO4 were generated in addition to Li2S at temperatures above 170°C, and the oxygen concentration also increased, confirming that the appropriate heat treatment temperature range was 110 to 160°C.

[0093] Example 8: High-concentration, high-temperature spray-drying synthesis of lithium sulfide The same procedure as in Example 1 was carried out, except that the extract concentration was high (10 g / L).

[0094] XRD peak analysis of heat-treated high-concentration spray-dried material 7a and 7b show XRD peaks of a high-concentration (10 g / L) filtrate during heat treatment after spray drying, in order to control the concentration of the filtrate when spraying and drying the filtrate according to one embodiment of the present invention.

[0095] 7a and 7b, it was confirmed that even in Example 8, where the lithium concentration was relatively high, only Li2O was present in the impurity peak after the final heat treatment.

[0096] Table 2 below shows the impurity peaks and oxygen contents of lithium sulfide produced in the examples and comparative examples of the present invention.

[0097] [Table 2]

[0098] Referring to Table 2 above, it was confirmed that when the lithium concentration of the extract filtrate for drying was within the concentration range of the present invention, specifically, when low-concentration extract filtrate (6 g / L, Examples 1 and 7) and high-concentration extract filtrate (10 g / L, Example 8) were spray-dried and heat-treated, Li2S with an oxygen content of 1% or less was synthesized in all cases. In the examples of the present invention, it was confirmed that high-purity lithium sulfide with a Li2O content of 1.6 wt% or less and a low oxygen content could be produced by using extract concentrations and heat-treatment temperatures that satisfied the ranges of the present invention.

[0099] 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 should understand that the present invention can be embodied in other specific forms without changing the technical concept or essential characteristics of the present invention. Therefore, it should be understood that the above-described embodiments and / or examples are illustrative in all respects and are not limiting.

Claims

1. mixing a carbon source and a lithium compound to produce a lithium-carbon compound; filtering the mixed solution of the lithium-carbon compound and the solvent; spray drying the filtrate in an inert loop configuration at a temperature ranging from 110 to 160°C; and heat-treating the spray-dried product; A method for producing lithium sulfide, comprising producing lithium sulfide having an oxygen content of less than 2.8%.

2. spray-drying the filtrate at a temperature of 110 to 160°C in an inert loop configuration; The method for producing lithium sulfide according to claim 1, further comprising controlling an average particle size of the spray-dried product to 0.1 to 100 μm.

3. 2. The method for producing lithium sulfide according to claim 1, further comprising the step of spray-drying the filtrate at a temperature in the range of 110 to 160°C in an inert loop structure, and controlling a concentration of an extract extracted during the spray-drying to 5 to 15 g / L.

4. spray-drying the filtrate at a temperature of 110 to 160°C in an inert loop configuration; The method for producing lithium sulfide according to claim 1 , further comprising a step of controlling the spray-dried product to have a spherical shape.

5. filtering the mixed solution of the lithium-carbon compound and the solvent; 2. The method for producing lithium sulfide according to claim 1, wherein a mixing ratio of the solvent to the lithium-carbon compound is 1 to 1 / 4.

6. 2. The method of claim 1, wherein the heat-treating the spray-dried product is performed at 100 to 800°C.

7. In the step of heat-treating the spray-dried product, H ２ S.C. ３ H ８ , or C.H. ４ The method for producing lithium sulfide according to claim 1, wherein

8. spray drying the filtrate in an inert loop at a temperature ranging from 110 to 160°C; 2. The method for producing lithium sulfide according to claim 1, wherein a part of the gas generated during drying and the inert gas are recycled and re-reacted.

9. spray-drying the filtrate at a temperature of 110 to 160°C in an inert loop configuration; 2. The method for producing lithium sulfide according to claim 1, wherein the inert loop structure includes a partially pure ring structure that induces a reaction of a gas generated from the spray-dried product during drying.

10. The method for producing lithium sulfide according to claim 8, wherein the re-reaction reduces impurities according to the following reaction formula: [Reaction formula] 2H ２ S+2LiOET→Li ２ S+2EtOH

11. The spray-dried product is lithium ethoxide (LiOEt, C ２ H ５ O—Li), ethanol (Ethanol, C ２ H ５ 2. The method for producing lithium sulfide according to claim 1, wherein the lithium sulfide is a mixture of lithium bisulfide (LiS, LiH, EtOH), lithium bisulfide (LiS, LiH), and lithium hydrogen sulfide (LiSH).

12. 2. The method for producing lithium sulfide according to claim 1, wherein the solvent includes at least one of ethanol, methanol, isopropyl alcohol, ethylene glycol, and butyl alcohol.

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