Precursor for preparing lithium sulfide and lithium sulfide powder

Abstract

The present invention relates to a method for preparing lithium sulfide, comprising the steps of: mixing a carbon raw material and a lithium compound to prepare a lithium-carbon compound; a step for filtering a solution obtained by mixing the lithium-carbon compound and a solvent; a step of spray-drying the filtrate in an inert loop (Inert Loop) structure at a temperature in the range of 110 to 160 DEG C; and a step of thermally treating the spray-dried product after spray drying to produce lithium sulfide having an oxygen content of less than 2.8%.

Description

Technical Field

[0001] The present invention relates to all-solid-state electrolytes, and more particularly, to precursors for preparing lithium sulfide and lithium sulfide powder for all-solid-state electrolytes. Background Art

[0002] Secondary batteries are widely used in small electronic devices such as mobile phones or laptop computers, as well as large devices such as electric vehicles (EVs) or energy storage systems (ESSs). As the application fields of secondary batteries expand to all areas of daily life, not only are requirements for performance such as high energy density and long life put forward, but the demand for safety is also increasing day by day.

[0003] Most of the electrolytes conventionally used in lithium secondary batteries are liquid electrolytes using organic solvents. However, due to safety problems such as leakage or fire of the liquid electrolyte, strict encapsulation is required, and this strict encapsulation limits the improvement of energy density to a higher level. Therefore, there is a need for an all-solid-state battery using an inorganic solid electrolyte instead of an organic liquid electrolyte.

[0004] The all-solid-state battery can safely prepare battery cells by excluding organic solvents such as liquid electrolytes. In addition, since the inorganic solid electrolyte does not decompose and remains stable within a wide voltage range, it has the advantage of applying electrode materials at high voltages.

[0005] The solid electrolyte can be divided into an oxide-based and a sulfide-based. Compared with the oxide-based solid electrolyte, the sulfide-based solid electrolyte has higher ionic conductivity. The main raw material of the sulfide-based solid electrolyte is lithium sulfide (Li2S). The synthesis methods of Li2S include a synthesis method using high-energy ball milling, a synthesis method using a wet plasma process, and a wet / dry method using metallic lithium. However, for these methods, it is difficult to commercialize because of difficulties in kinetic control, high starting material costs, high production process costs, and environmental problems.

[0006] In contrast, when using the carbonthermal reduction method, since it does not use the toxic gas H2S, it has environmental friendliness, and at the same time, it has the advantage of using low-cost Li2SO4. However, after heat treatment in the solid-phase heat treatment reduction reaction stage, an extraction solvent still needs to be used again. Therefore, product purity management problems must be solved through physical property management of the extraction solution, extraction solution drying step, heat treatment, or crystallization step.

[0007] In particular, since different drying methods 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, it is necessary to synthesize lithium sulfide by controlling the drying method of the extraction solution in which lithium sulfide is dissolved. 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 lithium sulfide precursor capable of preparing high-purity lithium sulfide powder.

[0010] Another technical problem to be solved by the present invention is to provide lithium sulfide powder as a raw material for a high-purity sulfide-based solid electrolyte.

[0011] Technical Solution

[0012] A precursor for preparing lithium sulfide powder according to an embodiment of the present invention relates to a precursor used in the preparation of lithium sulfide powder, and the precursor has a hollow shape.

[0013] Satisfies the following formula 1:

[0014] <Formula 1>

[0015] (Dmax - Dmin) / D50 ≤ 15

[0016] (In the above formula 1, Dmax, Dmin and D50 respectively represent the maximum particle size, the minimum particle size, and the particle size at which the volume ratio accumulates to 50%. )

[0017] In one embodiment, the hollow shape can be a hemispherical shape. In one embodiment, the particle size standard deviation (STDDEV) is 11.0 or less.

[0018] In one embodiment, the precursor includes a first peak appearing at a wave number of 2600 to 3250 cm -1 in Raman analysis, 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 In one embodiment, the first peak is the peak of EtOH, the second peak is the peak of LiSH, and the third peak is the peak of LiOEt.

[0019] In one embodiment, the Dmax can be in the range of 10 to 100 μm. In one embodiment, the Dmin is in the range of 0.1 to 2.5 μm. In one embodiment, the formula 1 is 11.30 or less.

[0020] Lithium sulfide powder according to an embodiment of the present invention, the lithium sulfide powder is a lithium sulfide compound for an all-solid electrolyte, wherein the lithium sulfide powder is obtained from a hollow-shaped precursor for preparing lithium sulfide powder, contains lithium sulfide (Li2S), and at least one impurity among lithium oxide (Li2O), lithium carbonate (Li2CO3), and lithium sulfate (Li2SO4), and the oxygen content is less than 2.8%. In one embodiment, among the impurities, except for lithium oxide (Li2O), there is no lithium carbonate (Li2CO3) and lithium sulfate (Li2SO4).

[0021] In one embodiment, the lithium sulfide powder can satisfy the following formula 2,

[0022] <Formula 2>

[0023] [Li2O] × oxygen content ≤ 5.0

[0024] (In the above formula 2, [Li2O] represents the content of lithium oxide in the lithium sulfide powder.)

[0025] In one embodiment, the formula 2 can be 2.5 or less. In one embodiment, the formula 2 can be 0.64 to 2.11. In one embodiment, the lithium oxide (Li2O) can be 1.6% or less by weight%.

[0026] Advantageous Effects

[0027] According to an embodiment of the present invention, by controlling the drying method of the extraction solution dissolved with lithium sulfide, a high-purity precursor used as a raw material for a sulfide-based solid electrolyte is provided.

[0028] According to another embodiment of the present invention, a high-purity lithium sulfide powder prepared from a precursor having the above advantages is provided. Brief Description of the Drawings

[0029] Figure 1a and Figure 1b Shows the XRD peaks of lithium sulfide according to the drying method.

[0030] Figures 2a to 2c Are SEM photos and particle size distribution diagrams of Example 2 at magnifications (×300, ×1K). Figures 2d to 2g Are SEM photos and particle size distribution diagrams of Example 3 at magnifications (×100, ×300, ×1K).

[0031] Figure 3 Shows the Raman characteristics of the powder obtained by drying the filtrate according to the preparation method of the embodiment of the present invention.

[0032] Figures 4a to 4f Shows the gas concentration generated during the heat treatment of the spray-dried product according to an embodiment of the present invention.

[0033] Figure 5a and Figure 5b are schematic diagrams of the reaction process according to whether there is an Inert roop structure in the drying stage.

[0034] Figure 6a and Figure 6b show the XRD peaks when synthesizing Li2S by final heat treatment after rapid temperature change heat treatment during the injection and drying of the filtrate and during the control of the drying temperature, according to the embodiments and comparative examples of the present invention.

[0035] Figure 7a and Figure 7b show the XRD peaks during the post-heat treatment of spray drying of a high-concentration filtrate during the injection and drying of the filtrate and during the control of the filtrate concentration, according to the embodiments of the present invention. Detailed Description

[0036] The terms first, second, third, etc. are used to describe various parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, and / or segment from another part, component, region, layer, and / or segment. Therefore, without departing from the scope of the present invention, the first part, component, region, layer, and / or segment described below can also be described as the second part, component, region, layer, and / or segment.

[0037] The terms used herein are only for describing specific embodiments and are not intended to limit the present invention. Unless otherwise clearly indicated to the contrary in the context, the singular forms used are also intended to include the plural forms. It should also be understood that the term "comprising" 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.

[0038] If a part is described as being above another part, it can be directly above the other part or there can be other parts in between. When a part is described as being directly above another part, there will be no other parts in between.

[0039] Unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. 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. In addition, unless otherwise described, % represents weight %, and 1 ppm represents 0.0001 weight %.

[0040] 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 pertains 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.

[0041] The precursor for preparing lithium sulfide powder according to an embodiment of the present invention has a hollow shape. The precursor for preparing lithium is a spray obtained by spray drying in the lithium sulfide preparation process described later.

[0042] The hollow shape refers to a shape with an empty interior, and the precursor for preparing lithium sulfide has a shape with an empty interior. The precursor having a shape with an empty interior is a characteristic exhibited due to the volatilization of ethanol during spray drying. Since the precursor has a shape with an empty interior, it has the advantage of being able to ensure uniformity inside and outside the particles during heat treatment.

[0043] In one embodiment, the above hollow shape can have a hemispherical shape. Since the shape of the precursor is hemispherical, it has the advantage of being conducive to mixing with other particles added to control physical properties during heat treatment.

[0044] In one embodiment, the precursor for preparing lithium sulfide satisfies the following formula 1,

[0045] <Formula 1>

[0046] (Dmax - Dmin) / D50 ≤ 15

[0047] (In the above formula 1, Dmax, Dmin, and D50 respectively represent the maximum particle size, the minimum particle size, and the particle size at which the volume ratio cumulative reaches 50%. )

[0048] In the specification, the particle size D0.9 refers to the particle size when the active substance particles with various particle size distributions (such as 0.1, 0.2, 0.3... 3, 5, 7... 10, 20, 30 μm) are cumulatively distributed by volume to 0.9%; D10 is the particle size when cumulatively distributed by volume to 10%, D50 is the particle size when cumulatively distributed by volume to 50%, D6 is the particle size when cumulatively distributed by volume to 6%, D95 is the particle size when cumulatively distributed by volume to 95%, Dmin is the minimum particle size, and Dmax is the maximum particle size.

[0049] The formula 1 is an index indicating the degree of uniformity in the particle size distribution of the precursor. The formula 1 can be 15 or less, specifically, it can be 11.30 or less.

[0050] By satisfying the value of the above formula (1), the particle size distribution is uniform, and the reaction proceeds uniformly during heat treatment, ensuring a lithium sulfide quality with a small deviation. If the value of the formula (1) exceeds the aforementioned range, the deviation of the lithium sulfide quality will increase. To prevent this, it is necessary to further pulverize the obtained lithium sulfide precursor to ensure uniformity, resulting in a problem of reduced processability.

[0051] 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 satisfying the standard deviation range, as described above, the particle size distribution is ensured to be uniform, and the reaction proceeds uniformly during heat treatment, having the advantage of ensuring a lithium sulfide quality with a small deviation.

[0052] 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.

[0053] 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.

[0054] In one embodiment, the precursor may include a first peak appearing at a wavenumber of 2600 to 3250 cm -1 a second peak appearing at a wavenumber of 2500 to 2600 cm -1 and a third peak appearing at a wavenumber of 850 to 1500 cm -1 in Raman analysis. 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.

[0055] In the precursor of the present invention, when only LiOET is contained, there is a problem that the conversion of Li2S is insufficient and it may be converted into other impurities (Li2CO3, Li2SO4). When only LiSH is contained, according to the following reaction formula, there is a problem that the yield of Li2S decreases due to the continuous loss of S caused by the release of H2S during the reaction.

[0056] [Reaction formula]

[0057] LiSH + LiSH → Li2S + H2S↑

[0058] Thus, the precursor includes the first peak, the second peak, and the third peak at the same time, so that the loss of sulfur can be prevented as described below, having the advantage of being able to prepare high-purity lithium sulfide. Specifically, by including the first peak, the second peak, and the third peak at the same time, the precursor satisfies the following reaction formula and can prepare high-purity lithium sulfide.

[0059] [Reaction formula]

[0060] LiSH + LiOEt → Li2S + EtOH

[0061] The lithium sulfide powder according to another embodiment of the present invention relates to a lithium sulfide powder for a solid-state electrolyte, and contains at least one impurity among lithium sulfide (Li2S), lithium oxide (Li2O), lithium carbonate (Li2CO3), and lithium sulfate (Li2SO4). High-purity lithium sulfide powder may contain impurities such as lithium oxide (Li2O), lithium carbonate (Li2CO3), or lithium sulfate (Li2SO4) during the heat treatment process.

[0062] In one embodiment, it is characterized in that the oxygen content in the whole powder is less than 2.8%. Specifically, in terms of volume, the oxygen content can be 1.3 to 1.6%, and more specifically, it can be 1.32 to 1.60%.

[0063] If the oxygen content exceeds the above range, there will be a problem of decreased lithium conductivity when synthesizing argyrodite using Li2S. In addition, there is also a problem affected by the proportion of impurities such as Li2O, Li2CO3, Li2SO4, or LiOH.

[0064] In one embodiment, except for lithium oxide (Li2O), there is no lithium carbonate (Li2CO3) and lithium sulfate (Li2SO4) among the impurities. In one embodiment, the content of lithium oxide (Li2O) can be 3.0% or less. Specifically, the content of lithium oxide (Li2O) can be 1.6% or less. The lithium oxide (Li2O) belongs to an impurity, and when the content of lithium oxide (Li2O) meets the above range, high-purity lithium sulfide with a low impurity content can be achieved. If the content of lithium oxide (Li2O) exceeds the above range, there will be a problem of decreased lithium conductivity when synthesizing argyrodite using Li2S. In one embodiment, the lithium sulfide powder of the present invention can satisfy Formula 2 below.

[0065] <Formula 2>

[0066] [Li2O] × oxygen content ≤ 5.0

[0067] (In the above Formula 2, [Li2O] represents the content of lithium oxide in the lithium sulfide powder.)

[0068] The above Formula 2 represents the relational formula between lithium oxide (Li2O) and the oxygen content, and the product of the lithium oxide and the oxygen content satisfies 5.0 or less, which is an index of 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.

[0069] When the value of the formula 2 exceeds the range, problems of degradation of electrical performance characteristics occur during the synthesis of argyrodite.

[0070] A method for preparing lithium sulfide according to another embodiment of the present invention includes the steps of mixing a carbon raw material and a lithium compound to prepare a lithium-carbon compound; filtering a solution obtained by mixing the lithium-carbon compound with a solvent; spray-drying the filtered material in an Inert Loop; and heat-treating the spray-dried product after spray-drying.

[0071] Regarding the description of lithium sulfide, reference may be made to the foregoing content. In one embodiment, non-limiting examples of 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 may be carried out by heat-treating the carbon raw material and the lithium compound.

[0072] The step of spray-drying the filtered material in an Inert Loop structure is specifically carried out by a spray-drying method. The filtered material may exist in a slurry form, for example, and the concentration of the liquid medium extracted from the filtered material may be controlled for spray-drying. By the spray-drying method, a spray-dried product with a uniform particle size can be obtained.

[0073] In one embodiment, the step of drying the filtered material may be carried out in a temperature range of 100 to 160 °C. Specifically, the temperature range may be carried out in a temperature range of 110 to 160 °C.

[0074] If the temperature range exceeds the upper limit value, in addition to the formation of lithium sulfide compounds, impurity lithium carbonate (Li2CO3) and lithium sulfate (Li2SO4) may also be generated, and the oxygen concentration will also increase. If the temperature range is lower than the lower limit value, during spray-drying, insufficient drying causes the dried product containing a large amount of solvent to gradually deposit in the spray-drying circulation channel, resulting in inconvenient circulation, thereby reducing the processability.

[0075] In one embodiment, the step of drying the filtered material includes the step of controlling the average particle size of the spray-dried product to be 0.1 to 100 μm. Specifically, the average particle size may be controlled to be 1.0 to 10.0 μm.

[0076] If the average particle size value exceeds the upper limit value, problems may occur in the heat treatment uniformity when the dried product is heat-treated after obtaining the dried product by spray drying; if the concentration of the spray liquid is increased or the injection speed is increased to increase the average particle size, it may cause clogging of the spray drying nozzle. Or cross-jetting is performed to prevent clogging, thereby reducing the processability. If the average particle size value is less than the lower limit value, the proportion of fine powder in the dried product increases, and during spray drying, the front filter of the inhaler for the circulating powder and solvent clogs quickly, thereby reducing the processability; during heat treatment, due to the inert gas flowing into the tubular furnace, the dried product scatters, resulting in loss of the object to be heat-treated.

[0077] In one embodiment, in the step of spray-drying the filtrate in the temperature range of 110 to 160 °C, it may include the step of controlling the concentration of the extract (based on Li-ICP) extracted during spray drying to be 5 to 15 g / L. Specifically, the concentration of the extract may be controlled to be 6 to 14 g / L.

[0078] If the concentration of the extract exceeds the upper limit value, it may cause clogging of the spray drying nozzle, or cross-jetting is performed to prevent clogging, thereby reducing the processability. If the concentration of the extract is lower than the lower limit value, there is a problem that the yield per unit time decreases and it takes too much time to obtain a certain amount of dried product.

[0079] In one embodiment, the step of spray-drying the filtrate in an Inert Loop structure may include the step of controlling the above spray-dried product to be spherical. The step of controlling to be spherical can be adjusted 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 above spray-dried product to be spherical, uniform heat transfer can be achieved during heat treatment after drying.

[0080] In one embodiment, in the step of spray-drying the above filtrate in an Inert Loop structure, the gas generated during drying and part of the inert gas can be recycled. In one embodiment, in the step of drying the filtrate, it may include a partial circulation structure that induces the reaction of the gas generated from the spray-dried product during drying. By using an Inert Loop structure in the drying step, a structure can be formed in which the gas generated during the drying of the extract and part of the inert gas are recycled. During drying, the gas (H2S) generated in the spray-dried product can induce a sufficient reaction with the LiOET of the dried product. Specifically, the H2S gas can participate in the re-reaction according to the following reaction formula.

[0081] [Reaction formula]

[0082] 2H2S + 2LiOET → Li2S + 2EtOH

[0083] Therefore, in the inert loop structure, a partial circulation structure is included, which has the advantage of reducing LiOEt as an impurity raw material and lowering the oxygen content, thereby preparing high-purity lithium sulfide.

[0084] In one embodiment, the spray-dried product may include lithium ethoxide (LiOEt, C2H5O-Li), ethanol (C2H5O-H, EtOH), and lithium bisulfide (LiSH).

[0085] The step of heat-treating the dried product is to heat the dried spray-dried product to obtain the final lithium sulfide (Li2S). In one embodiment, the dried product, specifically the spray-dried product, can be carried out in the temperature range of 400 to 800 °C, specifically in the temperature range of 500 to 800 °C. In one embodiment, the heating rate of the heat-treatment step can be carried out at a rate of 5 to 20 °C per minute.

[0086] In one embodiment, in the step of heat-treating the dried product, the time for maintaining the maximum temperature can be carried out between 1 and 6 hours. In one embodiment, the step of heat-treating the dried product may include a step of natural cooling after performing the heat treatment for the above time.

[0087] If the upper limit values of the temperature, heating rate, and maintenance time are exceeded, there will be a problem that lithium sulfide is converted into lithium oxide. If the lower limit values of the temperature, heating rate, and maintenance time are below, there will be a problem of reduced purity of lithium sulfide because impurities such as lithium hydroxide or lithium carbonate cannot be easily removed.

[0088] In one embodiment, the step of heat-treating the dried product can be carried out in an inert gas atmosphere. The inert gas, for example, may include at least one of helium, neon, krypton, xenon, nitrogen, or argon.

[0089] Hereinafter, specific embodiments of the present invention will be described. However, the following embodiments are only specific examples of the present invention, and the present invention is not limited to the following embodiments.

[0090] Comparison of Li2S according to drying method

[0091] <Experimental Example>

[0092] After mixing carbon and lithium sulfate, heat treatment is carried out in an Ar environment under an inert gas atmosphere to obtain the carbothermal reduction step of the lithium sulfide-carbon mixture (Li2SO4 + 2C → Li2S + 2CO2↑); the step of preparing an extract by mixing the lithium sulfide-carbon mixture with ethanol; the step of drying the extract to obtain a dried product; the step of heat-treating the dried product in an Ar environment under an inert gas atmosphere to prepare lithium sulfide (Li2S). Specifically as follows.

[0093] <Example 1> - A method for producing lithium sulfide based on low-concentration - high-temperature - spray drying synthesis

[0094] In the step of controlling the injection and drying temperature of the filtrate, except by adjusting the ratio of the ethanol-lithium sulfide mixture to be injected under low-concentration conditions (6 g / L, based on Li-ICP) and rapidly drying from room temperature to 160 °C, it is the same as the experimental example.

[0095] <Comparative Example 1> - A method for producing lithium sulfide based on low-concentration reduced-pressure drying synthesis

[0096] In the step of controlling the injection and drying temperature of the filtrate, by adjusting the ratio of the ethanol-lithium sulfide mixture in the filtrate, under low-concentration conditions (6 g / L, Li-ICP standard), the water bath temperature is controlled between 45 °C and 50 °C, and drying is carried out by rotary evaporation and reduction from atmospheric pressure to 60 mbar. Except for this, other operations are the same as the experimental example.

[0097] Figure 1a and Figure 1b shows the XRD peaks of lithium sulfide powder according to the drying method.

[0098] Figure 1a and Figure 1b respectively show the XRD peaks of Example 1 and Comparative Example 1, in which in Comparative Example 1, in addition to lithium sulfide, lithium carbonate (Li2CO3) was also confirmed. Compared with other drying methods, Li2S was confirmed to be superior in terms of purity.

[0099] Controlling the average spray particle size according to the extract concentration

[0100] Figures 2a to 2g are SEM images and particle size distribution diagrams of the average particle size according to the extract concentration, Figures 2f to 2k are SEM images and particle size distribution diagrams of the average particle size according to the reduced-pressure drying method.

[0101] Figures 2a to 2c are SEM images and particle size distribution diagrams of different magnifications (×300, ×1K) of Example 2. Figures 2d to 2gSEM images and particle size distribution diagrams at different magnification ratios (×100, ×300, ×1K) for Example 3. Figures 2f to 2k SEM images and particle size distribution diagrams at different magnification ratios (×100, ×300, ×1K) for Comparative Example 2 which performs the vacuum drying method.

[0102] <Example 2> - Low concentration - Spray - dried product

[0103] For the drying method as described in Example 1, during spray drying, the concentration of the extract was controlled at a low concentration of 6 g / L. It was confirmed that the average particle size of the dried spray after the drying treatment was 1.13 μm.

[0104] <Example 3> - High concentration - Spray - dried product

[0105] According to the drying method of Example 1, during spray drying, only changing the concentration of the extract, when the concentration of the extract was controlled at a high concentration of 10 g / L, it was confirmed that the average particle size of the dried spray product after the drying process was 8.65 μm.

[0106] <Comparative Example 2> - Low concentration - Vacuum - dried product

[0107] As described in Comparative Example 1, when performing the vacuum drying method, it was confirmed that the particle distribution range was wide, from 1.75 to 224.59 μm, and the particle shapes were uneven.

[0108] The following Table 1 shows the particle size distribution data of the examples and comparative examples according to the present invention.

[0109]

Table 1

[0110]

[0111] As can be seen from Table 1 above, through Example 2 and Example 3, for the spray - dried products of the present invention, which are used to prepare the precursor of lithium sulfide, the standard deviation is small, and (Dmax - Dmin) / D50 has a low value, and it is confirmed that they have a uniform particle size.

[0112] Raman analysis of spray-dried product

[0113] Figure 3 Shows the Raman characteristics of lithium sulfide powder produced by the preparation method according to the examples of the present invention.

[0114] Figure 3The Raman characteristics of Example 4 and Example 5 are shown respectively. Specifically, when observing the spray-dried product, peaks of Lithium Ethoxide (LiOEt, C2H5O-Li), Ethanol (EtOH, C2H5O-H), and Lithium bisulfide (Lithium hydrogen sulfide, LiSH) were confirmed.

[0115] Example 4 - Low Concentration - High Temperature - Spray-Dried Product

[0116] In the step of controlling the spraying and drying temperature of the filtrate, by adjusting the ratio of ethanol to lithium sulfide in the filtrate, spraying was carried out under low concentration conditions (6 g / L, Li-ICP standard), and rapid drying was performed from room temperature to 150 °C.

[0117] Example 5 - Low Concentration - Low Temperature - Spray-Dried Product

[0118] In the step of controlling the spraying and drying temperature of the filtrate, by adjusting the ratio of ethanol to lithium sulfide in the filtrate, spraying was carried out under low concentration conditions (6 g / L, Li-ICP standard), and rapid drying was performed from room temperature to 115 °C.

[0119] Exhaust characteristics during heat treatment drying of products with or without an Inert Loop

[0120] Figures 4a to 4d Shows the gas concentrations generated when heat-treating the spray-dried product according to an embodiment of the present invention.

[0121] Figures 4a to 4c The concentrations of C3H8, CH4, and H2S gases are shown respectively. Specifically, the gas concentrations generated during heat treatment according to Example 6 and Comparative Example 3 are shown. Thus, when the spray-dried product was heat-treated at 800 °C, the generation of the above gases was confirmed.

[0122] Figure 5a and Figure 5b Are schematic diagrams of the reaction process according to the presence or absence of an Inert roop structure in the drying stage.

[0123] Refer to Figure 5a and Figure 5b, through an Inert roop structure, the gas generated during the drying of the extraction solution and some inert gas are circulated, so that the H2S gas generated from the spray-dried product during drying can react sufficiently with LiOEt in the dried product. The H2S gas participates in the re-reaction, and through the following reaction formula, the LiOEt as an impurity raw material is reduced, thereby showing a reduction in impurities and a decrease in oxygen content. This can be confirmed by the XRD comparison according to the difference in drying methods in Table 1 below.

[0124] [Reaction formula]

[0125] 2H2S + 2LiOET --> Li2S + 2EtOH

[0126] Example 6 - Low concentration - Low temperature - Spray-dried product

[0127] Same as Example 1, in the step of controlling the spraying of the filtrate and the drying temperature, by adjusting the ratio of ethanol to lithium sulfide in the filtrate, spraying was carried out under low concentration conditions (6 g / L, Li-ICP standard), and rapid drying was carried out from room temperature to 160 °C.

[0128] <Comparative Example 3> - Low concentration - Vacuum-dried product

[0129] Vacuum drying was carried out in the same manner as in Comparative Example 1. In the step of controlling the spraying of the filtrate and the drying temperature, by adjusting the ratio of ethanol to lithium sulfide in the filtrate, under low concentration conditions (6 g / L, Li-ICP standard), the water bath temperature was controlled between 45 and 50 degrees Celsius, and drying was carried out by rotary evaporation and reduction from atmospheric pressure to 60 mbar.

[0130] XRD analysis of heat-treated products according to temperature

[0131] Figure 6a and Figure 6b Shows the XRD peaks when controlling the rapid heat treatment temperature during the drying temperature control when spraying and drying the filtrate according to the examples and comparative examples of the present invention. Specifically, compared with Example 1, when Examples 7, Comparative Example 4, and Comparative Example 5 were controlled at 110 °C, 170 °C, and 180 °C respectively, the XRD peaks of the filtered spray product generated after heat treatment were confirmed.

[0132] <Example 7> - Lithium sulfide based on low concentration - Low temperature spray drying synthesis method

[0133] Except that the drying temperature was set to 110 °C, the rest were the same as in Example 1.

[0134] <Comparative Example 4> - Lithium sulfide based on low concentration - High temperature spray drying synthesis method

[0135] Except that the drying temperature was set at 170 °C, the rest was the same as in Example 1.

[0136] <Comparative Example 5>- Lithium sulfide based on low-concentration-high-temperature spray drying synthesis method

[0137] Except that the drying temperature was set at 180 °C, the rest was the same as in Example 1.

[0138] By observing Example 7, Comparative Example 4, and Comparative Example 5, it was found that when the temperature was above 170 °C, in addition to Li2S, impurities Li2CO3 and Li2SO4 were also generated, and the oxygen concentration also increased. It can be confirmed from this that the appropriate heat treatment temperature range is 110 to 160 °C.

[0139] <Example 8>- Lithium sulfide based on high-concentration-high-temperature spray drying synthesis method

[0140] Except that the extract concentration was high concentration (10 g / L), the rest was the same as in Example 1.

[0141] XRD analysis of heat-treated products of high-temperature spray-dried products

[0142] Figure 7a and Figure 7b is an XRD peak during the heat treatment after spray drying of a high-concentration (10 g / L) filtrate when controlling the filtrate concentration during the spraying and drying of the filtrate according to an embodiment of the present invention.

[0143] Observation Figure 7a and Figure 7b , it can be confirmed that even in Example 8 with a relatively high lithium concentration, only Li2O exists in the impurity peaks after the final heat treatment.

[0144] 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.

[0145]

Table 2

[0146]

[0147]

[0148] As can be seen from Table 2 above, in order for the lithium concentration of the dried extract filtrate to be within the concentration range of the present invention, specifically, when performing spray drying and heat treatment on a low-concentration extract filtrate (6 g / L, Examples 1 and 7) and a high-concentration extract filtrate (10 g / L, Example 8), Li2S with an oxygen content of about 1% can be synthesized. In the examples of the present invention, since the concentration of the extract and the heat treatment temperature satisfy the range of the present invention, it is confirmed that high-purity lithium sulfide with an Li2O content of 1.6 wt% or less and a low oxygen content can be prepared.

[0149] The present invention is not limited to the above-described embodiments and / or comparative examples, but can be implemented in various different forms. Those of ordinary skill in the art to which the present invention pertains should understand that the present invention can be implemented in other specific forms without changing the technical idea or basic characteristics of the present invention. Therefore, it should be understood that the embodiments and / or comparative examples are exemplary in all respects and not restrictive.

Claims

1. A precursor for preparing lithium sulfide powder, wherein, the precursor is in a hollow shape, satisfying Formula 1, [Formula 1] (Dmax - Dmin) / D50 ≤ 15 (In the above Formula 1, Dmax, Dmin and D50 respectively represent the maximum particle size, the minimum particle size, and the particle size at which the volume ratio accumulates to 50%. ) 2. The precursor for preparing lithium sulfide powder according to Claim 1, wherein, the hollow shape is a hemispherical shape.

3. The precursor for preparing lithium sulfide powder according to Claim 1, wherein, the particle size standard deviation (STD DEV) is 11.0 or less.

4. The precursor for preparing lithium sulfide powder according to Claim 1, wherein, The precursor includes, in Raman analysis, a first peak appearing at a wavenumber of 2600 to 3250 cm -1 a second peak appearing at a wavenumber of 2500 to 2600 cm -1 and a third peak appearing at a wavenumber of 850 to 1500 cm -1 ​ 5. The precursor for preparing lithium sulfide powder according to Claim 4, wherein, the first peak is the peak of EtOH, the second peak is the peak of LiSH, and the second peak is the peak of LiOEt.

6. The precursor for preparing lithium sulfide powder according to Claim 1, wherein, the Dmax is in the range of 10 to 100 μm.

7. The precursor for preparing lithium sulfide powder according to Claim 1, wherein, the Dmin is in the range of 0.1 to 2.5 μm.

8. The precursor for preparing lithium sulfide powder according to Claim 1, wherein, Formula 1 is 11.30 or less.

9. A lithium sulfide powder, the lithium sulfide powder being a lithium sulfide compound for a solid-state electrolyte, wherein, the lithium sulfide powder is obtained from a hollow-shaped precursor for preparing lithium sulfide powder, contains lithium sulfide (Li2S), and at least one impurity among lithium oxide (Li2O), lithium carbonate (Li2CO3), and lithium sulfate (Li2SO4), and the oxygen content is less than 2.8%.

10. The lithium sulfide powder according to Claim 9, wherein, among the impurities, except for lithium oxide (Li2O), there is no lithium carbonate (Li2CO3) and lithium sulfate (Li2SO4).

11. The lithium sulfide powder according to Claim 9, wherein, it satisfies Formula 2, [Formula 2] [Li2O] × oxygen content ≤ 5.0 (In the above Formula 2, [Li2O] represents the content of lithium oxide in the lithium sulfide powder.) 12. The lithium sulfide powder according to Claim 11, wherein, Formula 2 is 2.5 or less.

13. The lithium sulfide powder according to Claim 11, wherein, Formula 2 is 0.64 to 2.

11.

14. The lithium sulfide powder according to Claim 9, wherein, the lithium oxide (Li2O) is 1.6% or less by weight%.

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