Preparation method of lithium sulfide

Abstract

The invention relates to a preparation method of lithium sulfide. A process for preparing a lithium-carbon compound, which may comprise a step of mixing a carbon raw material and a lithium compound to prepare a lithium-carbon compound, a step of filtering a solution in which the lithium-carbon compound and a solvent are mixed, a temperature range of 110 to 160 DEG C of the filtrate, and an inert loop (Inert Loop) The step of spray drying in the structure and the step of carrying out heat treatment on the spray-dried material after spray drying can be used for preparing lithium sulfide with the oxygen content of less than 2.8%.

Description

Technical Field

[0001] The present invention relates to an all-solid-state electrolyte. More specifically, the present invention relates to a method for preparing lithium sulfide for an all-solid-state electrolyte. Background Art

[0002] Secondary batteries are widely used in small electronic devices such as mobile phones or laptops to large devices such as electric vehicles (EVs) or energy storage systems (ESSs). As the application fields of secondary batteries expand to all aspects of life, not only high energy density, long life and other performance are required, but also stability is required.

[0003] Traditionally, the electrolytes used in lithium secondary batteries are mostly liquid electrolytes using organic solvents. However, since there are dangerous problems such as leakage or fire in the liquid electrolyte, strict encapsulation is required, and due to the strict encapsulation, there are limitations in increasing the energy density above a certain level. Therefore, there is a need for all-solid-state batteries that use inorganic solid electrolytes instead of organic liquid electrolytes.

[0004] The all-solid-state battery can exclude organic solvents such as liquid electrolytes, so that the battery unit can be safely manufactured. In addition, inorganic solid electrolytes do not decompose and have stability in a wide voltage range, so they have the advantage of being able to use high-voltage electrode materials.

[0005] The solid electrolyte is divided into oxide-based and sulfide-based. Compared with the oxide-based solid electrolyte, the sulfide-based solid electrolyte has a higher ionic conductivity. The main raw material of the sulfide-based solid electrolyte is lithium sulfide (Li2S). The synthesis method of Li2S applies a synthesis method using high-energy ball milling, a synthesis method using a wet plasma process, and a wet / dry method using lithium metal. However, for the foregoing methods, there are controversies such as difficulty in kinetic control, high starting material cost, high process cost, and environmental problems, resulting in difficulties in commercialization.

[0006] In contrast, if the carbonthermal reduction method is used, it has the advantages of environmental protection and low cost because Li2SO4 is used instead of the toxic gas H2S. However, after heat treatment in the solid-state heat treatment reduction reaction step, an extraction solvent needs to be used, so the product purity management problem must be solved through the physical property management of the extraction solution, the extraction solution drying step, the heat treatment or crystallization step.

[0007] In particular, since the drying method of the extraction solution can cause changes in the physical properties of the dried product, an appropriate drying method for the extraction solution is a key factor in obtaining high-quality lithium sulfide. Therefore, a method for synthesizing lithium sulfide by controlling the drying method of the extraction solution in which lithium sulfide is dissolved is required. Summary of the Invention

[0008] Technical Problem to be Solved

[0009] The technical problem to be solved by the present invention is to provide a drying method for preparing high-purity lithium sulfide.

[0010] Technical Solution

[0011] A method for preparing lithium sulfide according to an embodiment of the present invention may include: a step of mixing a carbon raw material and a lithium compound to prepare a lithium-carbon compound, a step of filtering a solution in which the lithium-carbon compound and a solvent are mixed, a step of spray-drying the filtrate in a temperature range of 110 to 160 °C and an inert loop structure, and a step of heat-treating the spray-dried product after spray-drying, and lithium sulfide having an oxygen content of less than 2.8% can be prepared. In one embodiment, in the step of spray-drying the filtrate in a temperature range of 110 to 160 °C and an inert loop structure, a step of controlling the average particle diameter of the spray-dried product to be 0.1 to 100 μm may be included.

[0012] In one embodiment, in the step of spray-drying the filtrate in a temperature range of 110 to 160 °C and an inert loop structure, a step of controlling the concentration of the extraction solution extracted during spray-drying to be 5 to 15 g / L may be included. In one embodiment, in the step of spray-drying the filtrate in a temperature range of 110 to 160 °C and an inert loop structure, a step of controlling the spray-dried product to be spherical may be included.

[0013] In one embodiment, in the step of filtering a solution in which the lithium-carbon compound and a solvent are mixed, the mixing ratio of the solvent to the lithium-carbon compound may be 1 to 1 / 4. In one embodiment, the step of heat-treating the spray-dried product after spray-drying may be performed at 100 to 800 °C.

[0014] In one embodiment, H2S, C3H8 or CH4 may be generated in the step of heat-treating the spray-dried product. In one embodiment, in the step of spray-drying the filtrate in a temperature range of 110 to 160 °C and an inert loop, a part of the gas generated during drying and the inert gas can be recycled and react again.

[0015] In one embodiment, in the step of spray-drying the filtrate in a temperature range of 110 to 160 °C and an inert loop structure, the inert loop structure may include a partial circulation structure for guiding the reaction of the gas generated from the spray-dried product during drying. In one embodiment, for the re-reaction, impurities can be reduced by the following reaction formula.

[0016] [Reaction formula]

[0017] 2H2S + 2LiOET → Li2S + 2EtOH

[0018] In one embodiment, the spray-dried product may contain lithium ethoxide (LiOEt, C2H5O-Li), ethanol (C2H5O-H, EtOH), and lithium bisulfide (LiSH). In one embodiment, the solvent may include at least one of ethanol, methanol, isopropanol, ethylene glycol, and butanol.

[0019] Advantageous effects

[0020] The method for preparing lithium sulfide according to an embodiment of the present invention uses spray drying and simultaneously performs a re-reaction in an inert loop structure, thereby providing a method for preparing high-purity lithium sulfide with low impurity content. Description of the drawings

[0021] Figure 1a and Figure 1b Show the XRD peaks of lithium sulfide according to the drying method.

[0022] Figures 2a to 2c Are SEM photos and particle size distribution diagrams of different magnifications (×300, ×1K) of Example 2. Figures 2d to 2g Are SEM photos and particle size distribution diagrams of different magnifications (×100, ×300, ×1K) of Example 3.

[0023] Figure 3 Show the Raman characteristics of the powder after the filtrate is dried by the preparation method of the embodiment of the present invention.

[0024] Figures 4a to 4d Shows the concentration of the gas generated during the heat treatment of the spray-dried product according to an embodiment of the present invention.

[0025] Figure 5a And Figure 5b Is a schematic diagram of the reaction process according to whether there is an Inert roop structure in the drying step.

[0026] Figure 6a And Figure 6b Shows the XRD peaks during the final heat treatment synthesis of Li2S by changing the rapid heat treatment temperature in the drying temperature control when spraying and drying the filtrate according to the embodiments and comparative examples of the present invention.

[0027] Figure 7a And Figure 7b Shows the XRD peaks during the heat treatment after spray drying of the high-concentration filtrate in the concentration control of the filtrate when spraying and drying the filtrate according to an embodiment of the present invention. Detailed Description

[0028] The terms first, second, third, etc. are used to describe each part, component, region, layer, and / or section, but these parts, components, regions, layers, and / or sections should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, without departing from the scope of the present invention, the first part, component, region, layer, or section described below can also be described as the second part, component, region, layer, or section.

[0029] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. Unless the context clearly gives the opposite meaning, the singular forms used herein are also intended to include the plural forms. The "including" used in the specification can specifically refer to a certain characteristic, field, integer, step, action, element, and / or component, but does not exclude the existence or addition of other characteristics, fields, integers, steps, actions, elements, and / or components.

[0030] If a part is described as being on top of another part, there may be other parts directly on top of or between the other part. When a part is described as being directly on top of another part, there are no other parts in between.

[0031] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. For terms defined in a dictionary, they should be interpreted as having a meaning consistent with the relevant technical literature and the content disclosed herein, and should not be interpreted in an idealized or overly formal sense. Additionally, unless otherwise specifically stated, % represents weight %, and 1 ppm is 0.0001 weight %.

[0032] Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention belongs can easily implement the present invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0033] The precursor for preparing lithium sulfide according to an embodiment of the present invention has a hollow shape. The precursor for preparing lithium is a spray product prepared by spray drying in the following lithium sulfide preparation process.

[0034] The hollow shape means a hollow form, and the precursor for preparing lithium sulfide has a hollow form. The precursor having a hollow form is characterized by the volatilization of ethanol during the spray drying process. Since the precursor has a hollow form, it has the advantage of ensuring uniformity inside and outside the particles during heat treatment.

[0035] In one embodiment, the hollow shape may have a hemispherical shape. Since the shape of the precursor has a hemispherical shape, it has the advantage of being conducive to mixing with other particles added for controlling physical properties during heat treatment.

[0036] In one embodiment, the precursor for preparing lithium sulfide may satisfy the following formula 1.

[0037] <Formula 1>

[0038] (Dmax - Dmin) / D50 ≤ 15

[0039] In the above formula 1, Dmax, Dmin, and D50 represent the maximum particle size, the minimum particle size, and the particle size when the particles accumulate to 50% by volume ratio, respectively.

[0040] In this specification, the particle size D0.9 represents the particle size when the active material particles with various particle sizes such as 0.1, 0.2, 0.3,..., 3, 5, 7,..., 10, 20, 30 μm accumulate to 0.9% by volume ratio, D10 represents the particle size when the particles accumulate to 10% by volume ratio, the D50 particle size represents the particle size when the particles accumulate to 50% by volume ratio, the D6 particle size represents the particle size when the particles accumulate to 6% by volume ratio, D95 represents the particle size when the particles accumulate to 95% by volume ratio, Dmin represents the minimum particle size, D max represents the maximum particle size.

[0041] The above formula 1 is an index indicating the degree of uniformity in the particle size distribution of the precursor. The above formula 1 can be 15 or less, specifically it can be 11.30 or less.

[0042] By satisfying the value of the above formula 1, the particle size distribution is uniform, so the reaction proceeds uniformly during heat treatment, and it has the advantage of being able to ensure the quality of lithium sulfide with a small deviation. If the value of the above formula 1 exceeds the aforementioned range, it will lead to a larger deviation in the quality of lithium sulfide. To prevent this, it is necessary to ensure the uniformity by further pulverizing the obtained lithium sulfide precursor, so there is a problem of decreased processability.

[0043] In one embodiment, the standard deviation (STD DEV) of the precursor particle size can be 11.0 or less. Specifically, the standard deviation can be 9.2 or less. By the standard deviation satisfying the aforementioned range, as described above, a uniform particle size distribution is ensured, so the reaction proceeds uniformly during heat treatment, and it has the advantage of being able to ensure the quality of lithium sulfide with a small deviation.

[0044] In one embodiment, the Dmax of the precursor can be in the range of 10 to 100 μm. Specifically, the Dmax of the precursor can be in the range of 12.82 to 66.84 μm.

[0045] In one embodiment, the Dmin of the precursor can be in the range of 0.1 to 2.5 μm. Specifically, the Dmin of the precursor can be in the range of 0.12 to 1.24 μm.

[0046] In one embodiment, for the precursor, in Raman analysis, it may include a first peak appearing at a wave number of 2600 to 3250 cm-1, a second peak appearing at a wave number of 2500 to 2600 cm-1, and a third peak appearing at a wave number of 850 to 1500 cm-1. The first peak may be the peak of EtOH, the second peak may be the peak of LiSH, and the third peak may be the peak of LiOEt.

[0047] For the precursor of the present invention, if only LiOET is included, the conversion of Li2S is less, and there is a problem that it may be converted into other impurities (Li2CO3, Li2SO4). If only LiSH is included, according to the following reaction formula, when H2S is released through the reaction, the loss of S continuously occurs, and there is a problem of decreased Li2S yield.

[0048] [Reaction formula]

[0049] LiSH + LiSH → Li2S + H2S↑

[0050] Therefore, the precursor simultaneously includes the first peak, the second peak, and the third peak, thus preventing the loss of sulfur as described below, and having the advantage of being able to prepare high-purity lithium sulfide. Specifically, the precursor simultaneously includes the first peak, the second peak, and the third peak, thus satisfying the reaction formula described below and enabling the preparation of high-purity lithium sulfide.

[0051] [Reaction formula]

[0052] LiSH + LiOEt → Li2S + EtOH

[0053] The lithium sulfide powder according to another embodiment of the present invention relates to a lithium sulfide powder for a solid-state electrolyte, which includes lithium sulfide (Li2S); and at least one impurity among lithium oxide (Li2O), lithium carbonate (Li2CO3), and lithium sulfate (Li2SO4). For high-purity lithium sulfide powder, after a heat treatment process, impurities such as lithium oxide (Li2O), lithium carbonate (Li2CO3), or lithium sulfate (Li2SO4) may be included as impurities.

[0054] In one embodiment, it is characterized in that the oxygen content in the total powder is less than 2.8%. Specifically, the oxygen content is 1.3 to 1.6%, and more specifically, it can be 1.32 to 1.60%.

[0055] If the oxygen content exceeds the foregoing range, there is a problem of a decrease in lithium conductivity when using Li2S to synthesize argyrodite. In addition, there is also a problem affected by the proportion of impurities such as Li2O, Li2CO3, Li2SO4, or LiOH.

[0056] In one embodiment, except for lithium oxide (Li2O), lithium carbonate (Li2CO3) and lithium sulfate (Li2SO4) may not exist among the impurities. In one embodiment, the content of lithium oxide (Li2O) can be 3.0% or less. Specifically, the lithium oxide (Li2O) can be 1.6% or less. The lithium oxide (Li2O) belongs to an impurity. When the content of the lithium oxide (Li2O) satisfies the foregoing range, high-purity lithium sulfide with a small amount of impurities can be achieved. If the content of the lithium oxide (Li2O) exceeds the foregoing range, there is a problem of a decrease in lithium conductivity when using Li2S to synthesize argyrodite. In one embodiment, the lithium sulfide powder of the present invention can satisfy the following formula 2.

[0057] <Formula 2>

[0058] [Li2O] × oxygen content ≤ 5.0

[0059] In the above formula 2, [Li2O] represents the content of lithium oxide in the powder.

[0060] The above formula 2 represents the relational expression between lithium oxide (Li2O) and the oxygen content, and the product of the lithium oxide and the oxygen content satisfying 5.0 or less is an index for high-purity lithium sulfide. The above formula 1 can be 5 or less, specifically it can be 2.5 or less, and more specifically it can be 0.64 to 2.11 or less.

[0061] If the value of the above formula 2 exceeds the foregoing range, there will be a problem of deterioration of the electrical characteristics when synthesizing argyrodite.

[0062] According to another embodiment of the present invention, a method for preparing lithium sulfide includes a step of mixing a carbon raw material and a lithium compound to prepare a lithium-carbon compound, a step of filtering a solution mixed with the lithium-carbon compound and a solvent, a step of spray-drying the filtrate in an Inert Loop structure, and a step of heat-treating the dried product after drying. The description of lithium sulfide can refer to the foregoing content.

[0063] In one embodiment, by way of non-limiting example, the carbon raw material may include 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 mixing the carbon raw material and the lithium compound to prepare the lithium-carbon compound can be completed by heat-treating the carbon raw material and the lithium compound.

[0064] The step of spray-drying the filtrate in an Inert Loop structure is specifically carried out by a spray-drying method. For example, the filtrate can exist in the form of a slurry, and spray-drying can be carried out by controlling the concentration of the liquid medium from which the filtrate is extracted. Through the spray-drying method, a spray-dried product with a uniform particle size can be obtained.

[0065] In one embodiment, the step of drying the filtrate can be carried out in a temperature range of 100 to 160 °C. Specifically, the temperature range can be a temperature range of 110 to 160 °C.

[0066] If it exceeds the upper limit value of the temperature range, in addition to the generated lithium sulfide compound, lithium carbonate (Li2CO3) and lithium sulfate (Li2SO4) may be generated as impurities, and there is a problem that the oxygen concentration also increases. If it exceeds the lower limit value of the temperature range, during spray-drying, the dried product that is not sufficiently dried and contains a large amount of solvent will gradually deposit in the spray-drying circulation channel, resulting in difficult circulation and a problem of deterioration of processability.

[0067] In one embodiment, the step of drying the filtrate may include the step of controlling the average particle size of the spray-dried product to 0.1 to 100 μm. Specifically, the average particle size may be controlled to 1.0 to 10.0 μm.

[0068] If the value of the average particle size exceeds the upper limit value, after obtaining the dried product by spray drying, when the dried product is heat-treated, problems may occur in the uniformity of the heat treatment. When increasing the average particle size by increasing the concentration of the spray liquid or increasing the injection speed, the spray drying nozzle may become clogged, or due to cross-spraying implemented to prevent this, there is a problem of reduced processability. If the value of the average particle size exceeds the lower limit value, the proportion of fine powder in the dried product increases, and during spray drying, there is a problem of rapid clogging of the front filter of the inhaler that circulates the powder and the solvent, resulting in reduced processability, and during heat treatment, there is a problem of loss of the heat treatment target due to the dried product being blown away by the inert gas introduced into the tube furnace.

[0069] In one embodiment, in the step of spray drying the filtrate in the temperature range of 110 to 160 °C, the step 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.

[0070] If the concentration of the extract exceeds the upper limit value, the spray drying nozzle may become clogged, or due to cross-spraying implemented to prevent this, there is a problem of reduced processability. If the concentration of the extract exceeds the lower limit value, the yield per unit time decreases, and there is a problem of consuming too much time to obtain a certain amount of dried product.

[0071] In one embodiment, the step of spray drying the filtrate in an Inert Loop structure may include the step of controlling the spray-dried product to be spherical. The step of controlling to be spherical may be controlled by methods such as adjusting the concentration of the extract, adjusting the flow rate of the inert injection gas, or adjusting the injection speed of the extract. By including the step of controlling the spray-dried product to be spherical, uniform heat transfer can be achieved during heat treatment after drying.

[0072] In one embodiment, in the step of spray-drying the filtrate in an Inert Loop structure, a part of the gas generated during drying and the inert gas can be recycled. In one embodiment, in the step of drying the filtrate, a partial recycling structure can be included to direct the reaction of the gas generated from the spray-dried product during drying. In the drying step, through the Inert Loop structure, a structure can be formed in which a part of the gas generated during the drying of the extract and the inert gas are recycled. The gas (H2S) generated from the spray-dried product during drying and the LiOET of the dried product can initiate a sufficient reaction. Specifically, as shown in the following reaction formula, H2S can participate in the reaction again.

[0073] [Reaction formula]

[0074] 2H2S + 2LiOET → Li2S + 2EtOH

[0075] Therefore, in the aforementioned Inert Loop structure, by including a partial recycling structure, the LiOEt as an impurity raw material is reduced, and the oxygen content is lowered, thus having the advantage of being able to prepare high-purity lithium sulfide.

[0076] In one embodiment, the spray-dried product may contain lithium ethoxide (LiOEt, C2H5O-Li), ethanol (C2H5O-H, EtOH), and lithium bisulfide (LiSH).

[0077] The step of heat-treating the dried product is to apply heat to the dried spray-dried product to obtain the final lithium sulfide (Li2S). In one embodiment, for the dried product, specifically the spray-dried product, it can be carried out in a temperature range of 400 to 800 °C, specifically in a temperature range of 500 to 800 °C. In one embodiment, the heating rate of the heat-treatment step can be 5 to 20 °C per minute.

[0078] In one embodiment, in the step of heat-treating the dried product, the holding time at the highest temperature can be 1 to 6 hours. In one embodiment, the step of heat-treating the dried product may include a step of natural cooling after the heat treatment for the aforementioned time.

[0079] If the upper limit values of the foregoing temperature, heating rate, and holding time are exceeded, there is a problem that lithium sulfide is converted into lithium oxide. If the lower limit values of the foregoing temperature, heating rate, and holding time are exceeded, impurities such as lithium hydroxide or lithium carbonate are not easily removed, and thus there is a problem of a decrease in the purity of lithium sulfide.

[0080] In one embodiment, the step of heat-treating the dried product may be carried out in an inert gas environment. For example, the inert gas may include at least one of helium, neon, krypton, xenon, nitrogen, and argon.

[0081] Hereinafter, specific embodiments of the present invention will be described. However, the following embodiments are merely specific embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0082] Li2S Comparison According to Drying Method

[0083] <Experimental Example>

[0084] It is carried out through the following steps: mixing carbon and lithium sulfate, and performing heat treatment in an Ar environment of an inert gas environment to obtain a carbothermal reduction step (Li2SO4 + 2C → Li2S + 2CO2↑) of a lithium sulfide-carbon mixture; mixing the lithium sulfide-carbon mixture and ethanol to prepare an extraction solution; drying the extraction solution to obtain a dried product; and heat-treating the dried product in an Ar environment of an inert gas environment to prepare lithium sulfide (Li2S). Specifically, it is described as follows.

[0085] <Example 1> - A method for preparing lithium sulfide based on a low-concentration - high-temperature - spray drying synthesis method

[0086] In the step of controlling the spraying and drying temperature of the filtrate, by adjusting the ratio of the ethanol and lithium sulfide mixture, the filtrate is sprayed under low-concentration (6 g / L, based on Li-ICP) conditions and quickly dried from room temperature to 160 °C. Except for this, the implementation manner is the same as that of the experimental example.

[0087] <Comparative Example 1> - A method for preparing lithium sulfide based on a low-concentration reduced-pressure drying synthesis method

[0088] In the step of controlling the spraying and drying temperature of the filtrate, the ratio of the ethanol and lithium sulfide mixture is adjusted, the temperature of the water bath is controlled between 45 °C and 50 °C under low-concentration (6 g / L, based on Li-ICP) conditions, and the filtrate is dried by rotary evaporation and from atmospheric pressure to a pressure of 60 mbar. Except for this, the implementation manner is the same as that of the experimental example.

[0089] Figure 1a and Figure 1bShows the XRD peaks of lithium sulfide powder according to the drying method.

[0090] Figure 1a and Figure 1b Shows the XRD peaks of Example 1 and Comparative Example 1. In Comparative Example 1, it was confirmed that lithium carbonate (Li2CO3) appeared in addition to lithium sulfide. It has been confirmed that the Li2S purity is excellent compared to other drying methods.

[0091] Average Particle Size Control of Spray According to Concentration of Extractant

[0092] Figures 2a to 2g Is the SEM photograph and particle size distribution diagram showing the average particle size according to the concentration of the extraction solution, Figures 2f to 2k Is the SEM photograph and particle size distribution diagram showing the average particle size according to the vacuum drying method.

[0093] Figures 2a to 2c Are the SEM photographs and particle size distribution diagrams of different magnifications (×300, ×1K) of Example 2. Figures 2d to 2g Are the SEM photographs and particle size distribution diagrams of different magnifications (×100, ×300, ×1K) of Example 3. Figures 2f to 2k Are the SEM photographs and particle size distribution diagrams of different magnifications (×100, ×300, ×1K) of Comparative Example 2 that performs the vacuum drying method.

[0094] <Example 2>-Low concentration-Spray-dried product

[0095] As described in the drying method of Example 1, during spray drying, the concentration of the extraction solution was controlled to a low concentration such as 6 g / L. At this time, it was confirmed that the average particle size of the dried spray product after the drying process was 1.13 μm.

[0096] <Example 3>-High concentration-Spray-dried product

[0097] As described in the drying method of Example 1, during spray drying, only the concentration of the extraction solution was changed. When the concentration of the extraction solution was controlled to a high concentration such as 10 g / L, it was confirmed that the average particle size of the dried spray product after the drying process was 8.65 μm.

[0098] <Comparative Example 2>-Low concentration-Vacuum-dried product

[0099] As described in Comparative Example 1, when performing the vacuum drying method, the particle distribution was 1.75 to 224.59 μm, and the distribution was wide. It was confirmed that the particle shape was uneven.

[0100] Table 1 below shows the particle size distribution data of the examples and comparative examples according to the present invention.

[0101]

Table 1

[0102]

[0103] Referring to Table 1 above, it was confirmed through Examples 2 and 3 that the standard deviation of the precursor for preparing lithium sulfide as the spray-dried product of the present invention is small, and the value of (Dmax - Dmin) / D50 is low, thus having a uniform particle size.

[0104] Raman Characteristic Analysis of Spray-Dried Product

[0105] Figure 3 Shows the Raman characteristics of the lithium sulfide powder produced by the preparation method of the examples of the present invention.

[0106] Figure 3 The Raman characteristics of Examples 4 and 5 are shown respectively. Specifically, from the spray-dried product, peaks of Lithium Ethoxide (LiOEt, C2H5O-Li), Ethanol (EtOH, C2H5O-H), and Lithium Bisulfide (Lithium Hydrogen Sulfide, LiSH) have been confirmed.

[0107] Example 4 - Low Concentration - High Temperature - Spray-Dried Product

[0108] In the step of controlling the spraying and drying temperature of the filtrate, by adjusting the ratio of the ethanol and lithium sulfide mixture, the filtrate is sprayed under low concentration (6 g / L, based on Li-ICP) conditions and quickly dried by heating from room temperature to 150 °C.

[0109] Example 5 - Low Concentration - Low Temperature - Spray-Dried Product

[0110] In the step of controlling the spraying and drying temperature of the filtrate, by adjusting the ratio of the ethanol and lithium sulfide mixture, the filtrate is sprayed under low concentration (6 g / L, based on Li-ICP) conditions and quickly dried by heating from room temperature to 115 °C.

[0111] Exhaust Gas Characteristics during Heat Treatment of Dried Product According to Presence of Inert Loop

[0112] Figures 4a to 4d Shows the concentration of the gas generated during the heat treatment of the spray-dried product according to an embodiment of the present invention.

[0113] Figures 4a to 4c The concentrations of C3H8, CH4, and H2S gases are shown respectively. Specifically, the concentrations of the gases generated during the heat treatment according to Example 6 and Comparative Example 3 below are illustrated. As described above, when the spray-dried product is heat-treated at 800 °C, the aforementioned gases have been confirmed to be generated.

[0114] Figure 5a and Figure 5bIt is a schematic diagram of the reaction process according to whether an inert loop structure exists in the drying step.

[0115] See also Figure 5a and Figure 5b , through the inert loop structure, the gas generated when the extract is dried and part of the inert gas are recirculated, which is a structure that guides the gas H2S generated from the spray-dried product during drying to fully react with the LiOEt of the dried product. The H2S gas participates in the reaction again, and through the reaction formula shown below, the LiOEt as an impurity raw material is reduced, thereby reducing impurities, and the result shows that the oxygen content is low. This can be confirmed by the following Table 1, which is an XRD comparison table based on different drying methods.

[0116] [Reaction formula]

[0117] 2H2S+2LiOET->Li2S+2EtOH

[0118] Example 6 - Low concentration - low temperature - spray dried

[0119] As described in Example 1, in the step of controlling the spraying and drying temperature of the filtrate, the filtrate is sprayed under low concentration (6 g / L, based on Li-ICP) conditions by adjusting the ratio of the ethanol and lithium sulfide mixture, and is quickly dried by heating from room temperature to 160°C.

[0120] <Comparative Example 3> - Low concentration - vacuum dried product

[0121] The reduced pressure drying method was performed as described 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 was adjusted, the temperature of the water bath was controlled between 45 and 50 degrees under low concentration (6 g / L, based on Li-ICP), and the filtrate was dried by rotary evaporation and reduced pressure from normal pressure to 60 mbar.

[0122] XRD Analysis of Heat-Treated Product Based on Temperature

[0123] Figure 6a and Figure 6b The XRD peaks when the rapid heat treatment temperature is controlled in the drying temperature control when the filtrate is sprayed and dried according to the embodiments and comparative examples of the present invention are shown. Specifically, compared with Example 1, as in Example 7, Comparative Example 4 and Comparative Example 5, the XRD peaks of the heat-treated filtrate spray generated when controlled at 110°C, 170°C and 180°C, respectively, are confirmed.

[0124] <Example 7> - Lithium sulfide based on low concentration-low temperature spray drying synthesis method

[0125] The drying temperature is 110 °C. Except for this, the implementation mode is the same as that of Example 1.

[0126] <Comparative Example 4> - Lithium sulfide based on low-concentration - high-temperature spray drying synthesis method

[0127] The drying temperature is 170 °C. Except for this, the implementation mode is the same as that of Example 1.

[0128] <Comparative Example 5> - Lithium sulfide based on low-concentration - high-temperature spray drying synthesis method

[0129] The drying temperature is 180 °C. Except for this, the implementation mode is the same as that of Example 1.

[0130] It is confirmed from Example 7, Comparative Example 4, and Comparative Example 5 that at temperatures above 170 °C, in addition to Li2S, Li2CO3 and Li2SO4 are generated as impurities, and it is also confirmed that the oxygen concentration increases. Thus, it is confirmed that the appropriate heat treatment temperature range is 110 to 160 °C.

[0131] <Example 8> - Lithium sulfide based on high-concentration - high-temperature spray drying synthesis method

[0132] Except that the extract concentration is high concentration (10 g / L), the implementation mode is the same as that of Example 1.

[0133] XRD Peak Analysis of Heat-Treated Product of High-Concentration Spray-Dried Product

[0134] Figure 7a and Figure 7b It shows the XRD peaks during the heat treatment after spray drying of the high-concentration (10 g / L) filtrate in the concentration control of the filtrate when spraying and drying the filtrate according to an embodiment of the present invention.

[0135] From Figure 7a and Figure 7b It is confirmed that in Example 8 with a relatively high lithium concentration, only Li2O exists in the impurity peaks after the final heat treatment.

[0136] Table 2 below shows the impurity peaks and oxygen content of lithium sulfide produced according to the examples and comparative examples of the present invention.

[0137]

Table 2

[0138]

[0139] As confirmed from the above Table 2, the lithium concentration of the extraction filtrate for drying is within the concentration range of the present invention. Specifically, when spray-drying and heat-treating the low-concentration extraction filtrate (6 g / L, Examples 1 and 7) and the high-concentration extraction filtrate (10 g / L, Example 8), Li2S with an oxygen content of approximately 1% was synthesized. For the examples of the present invention, it has been confirmed that the concentration of the extraction solution and the heat-treatment temperature satisfy the scope of the present invention. Therefore, -2 the content of Li

[0140] O is 1.6 wt% or less, and high-purity lithium sulfide with a low oxygen content can be prepared. The present invention is not limited to the above-described embodiments and / or examples and can be prepared in various different ways. Those of ordinary skill in the technical field to which the present invention pertains can understand that the present invention can be implemented in other specific ways without changing the technical idea or essential features of the present invention. Therefore, it should be understood that the above-described embodiments and / or examples are exemplary in all aspects and not restrictive.

Claims

1. A method for preparing lithium sulfide, comprising: mixing a carbon raw material and a lithium compound to prepare a lithium-carbon compound; filtering a solution mixed with the lithium-carbon compound and a solvent; spray-drying the filtrate in a temperature range of 110 to 160 °C and an inert loop structure; and performing heat treatment on the spray-dried product after spray drying, to prepare lithium sulfide with an oxygen content of less than 2.8%.

2. The method for preparing lithium sulfide according to claim 1, wherein in the step of spray-drying the filtrate in a temperature range of 110 to 160 °C and an inert loop structure, it includes a step of controlling the average particle size of the spray-dried product to be 0.1 to 100 μm.

3. The method for preparing lithium sulfide according to claim 1, wherein in the step of spray-drying the filtrate in a temperature range of 110 to 160 °C and an inert loop structure, it includes a step of controlling the concentration of the extract solution extracted during spray drying to be 5 to 15 g / L.

4. The method for preparing lithium sulfide according to claim 1, wherein in the step of spray-drying the filtrate in a temperature range of 110 to 160 °C and an inert loop structure, it includes a step of controlling the spray-dried product to be spherical.

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

6. The method for preparing lithium sulfide according to claim 1, wherein the step of performing heat treatment on the spray-dried product after spray drying is carried out at 100 to 800 °C.

7. The method for preparing lithium sulfide according to claim 1, wherein H2S, C3H8 or CH4 is generated in the step of performing heat treatment on the spray-dried product after spray drying.

8. The method for preparing lithium sulfide according to claim 1, wherein in the step of spray-drying the filtrate in a temperature range of 110 to 160 °C and an inert loop, a part of the gas generated during drying and the inert gas are recycled and react again.

9. The method for preparing lithium sulfide according to claim 1, wherein in the step of spray-drying the filtrate in a temperature range of 110 to 160 °C and an inert loop structure, the inert loop structure includes a partial circulation structure for guiding the reaction of the gas generated from the spray-dried product during drying.

10. The method for preparing lithium sulfide according to claim 8, wherein for the re-reaction, impurities are reduced through the following reaction formula, [Reaction formula] 2H2S + 2LiOET → Li2S + 2EtOH.

11. The method for preparing lithium sulfide according to claim 1, wherein the spray-dried product contains lithium ethoxide, ethanol and lithium hydrosulfide.

12. The method for preparing lithium sulfide according to claim 1, wherein the solvent includes at least one of ethanol, methanol, isopropanol, ethylene glycol and butanol.

Images