Lithium sulfide for solid electrolyte and manufacturing method thereof

Abstract

A lithium sulfide for a solid electrolyte according to an embodiment disclosed herein has a content of at least one element A, selected from the group consisting of Group 1 elements and Group 2 elements, of 8 mol% or less as measured by inductively coupled plasma spectroscopy (ICP). According to an embodiment disclosed herein, a lithium sulfide can be prepared without using a highly toxic raw material.

Description

Lithium sulfide for solid electrolyte and method for producing the same

[0001] The present disclosure relates to lithium sulfide for solid electrolyte and a method for producing the same.

[0002] Recently, development of all-solid-state batteries containing solid electrolytes has been ongoing. These all-solid-state batteries, which incorporate solid electrolytes instead of conventional liquid electrolytes, offer superior safety against explosions and fires and enhanced energy density. Solid electrolytes applicable to these all-solid-state batteries include polymer-based solid electrolytes, oxide-based solid electrolytes, and sulfide-based solid electrolytes.

[0003] Among these, sulfide-based solid electrolytes are attracting attention as electrolytes with high potential for commercialization due to their relatively high ionic conductivity. Accordingly, there is a growing demand for technologies capable of efficiently manufacturing sulfide-based solid electrolytes.

[0004] According to one aspect of the present disclosure, a method for producing lithium sulfide without using highly toxic raw materials is provided.

[0005] According to another aspect of the present disclosure, lithium sulfide can be produced using low-cost raw materials.

[0006] According to another aspect of the present disclosure, a method for producing lithium sulfide, which is easy to synthesize on a large scale, is provided.

[0007] According to another aspect of the present disclosure, a raw material for manufacturing a sulfide-based solid electrolyte can be manufactured with high purity.

[0008] Lithium sulfide for a solid electrolyte according to one embodiment has a content of at least one element A selected from the group consisting of Group 1 elements and Group 2 elements of 8 mol% or less when analyzed by inductively coupled plasma spectroscopy (ICP).

[0009] In some embodiments, the element A may correspond to A in a compound represented by the following chemical formula 1.

[0010] [Chemical Formula 1]

[0011] AB y

[0012] In the above chemical formula 1, A is at least one selected from the group consisting of group 1 elements and group 2 elements, and B is a group 17 element, NO3 - and BF4 - At least one selected from the group consisting of , and y is 1 or 2.

[0013] In some embodiments, the lithium sulfide for the solid electrolyte may have binding energies different from those of a peak representing the compound represented by the chemical formula 1 and a peak representing lithium sulfide when analyzed by a scanning electron microscope (SEM) and an energy-dispersive X-ray spectrometer (EDS).

[0014] In some embodiments, when the lithium sulfide for the solid electrolyte is analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS), the region representing the compound represented by the chemical formula 1 and the region representing lithium sulfide in the EDS mapping image may be different from each other.

[0015] In some embodiments, the compound represented by the above formula 1 may be sodium chloride (NaCl).

[0016] Lithium sulfide for a solid electrolyte according to one embodiment may have a content of 20% or less of a compound represented by the following chemical formula 1 according to X-ray diffraction (XRD) analysis and the Rietveld Refinement Method.

[0017] [Chemical Formula 1]

[0018] AB y

[0019] In the above chemical formula 1, A is at least one selected from the group consisting of group 1 elements and group 2 elements, and B is a group 17 element, NO3- and BF4 - At least one selected from the group consisting of , and y is 1 or 2.

[0020] In some embodiments, the lithium sulfide for the solid electrolyte may have binding energies different from those of a peak representing the compound represented by the chemical formula 1 and a peak representing lithium sulfide when analyzed by a scanning electron microscope (SEM) and an energy-dispersive X-ray spectrometer (EDS).

[0021] In some embodiments, when the lithium sulfide for the solid electrolyte is analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS), the region representing the compound represented by the chemical formula 1 and the region representing lithium sulfide in the EDS mapping image may be different from each other.

[0022] In some embodiments, the compound represented by the above formula 1 may be sodium chloride (NaCl).

[0023] A method for producing lithium sulfide for a solid electrolyte according to one embodiment comprises the steps of: preparing a solution by mixing a sulfur compound represented by the following chemical formula 2 and a lithium compound represented by the following chemical formula 3 with a solvent; cooling the solution to 25°C or lower; removing the compound represented by the following chemical formula 1 from the cooled solution to obtain lithium sulfide; and heat-treating the obtained lithium sulfide.

[0024] [Chemical Formula 1]

[0025] AB y

[0026] In the above chemical formula 1, A is at least one selected from the group consisting of group 1 elements and group 2 elements, and B is a group 17 element, NO3 - and BF4 - At least one selected from the group consisting of , and y is 1 or 2.

[0027] [Chemical Formula 2]

[0028] A x S

[0029] In the above chemical formula 2, A has the same meaning as A in the above chemical formula 1, S is sulfur, and x is 1 or 2.

[0030] [Chemical Formula 3]

[0031] LiB

[0032] In the above chemical formula 3, Li is lithium, and B has the same meaning as B in the above chemical formula 1.

[0033] In some embodiments, the solvent may include at least one selected from the group consisting of alcohol-based solvents, tetrahydrofuran-based solvents, and phosphoramide-based solvents.

[0034] In some embodiments, the step of heat treating the lithium sulfide may be performed at 400°C to 900°C.

[0035] In some embodiments, the heat-treated lithium sulfide may have a content of at least one element A selected from the group consisting of Group 1 elements and Group 2 elements of 8 mol% or less when analyzed by inductively coupled plasma spectroscopy (ICP).

[0036] In some embodiments, the heat-treated lithium sulfide may have a content of the compound represented by the chemical formula 1 of 20% or less according to the Rietveld Refinement Method when analyzed by X-ray diffraction (XRD).

[0037] According to one embodiment of the present disclosure, lithium sulfide can be produced without using highly toxic raw materials.

[0038] According to another embodiment of the present disclosure, lithium sulfide can be manufactured with excellent economic efficiency.

[0039] According to another embodiment of the present disclosure, large-scale synthesis can be facilitated in the production of lithium sulfide.

[0040] According to another embodiment of the present disclosure, a raw material used in the manufacture of a sulfide-based solid electrolyte can be manufactured with high purity.

[0041] Figures 1a to 1c are drawings showing the results of analyzing lithium sulfide (Figure 1a), cation A (Figure 1b), and anion B (Figure 1c) using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS) for lithium sulfide of a comparative example, respectively.

[0042] Figure 1d is a diagram showing the results of analyzing the peaks of each component according to binding energy using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS) for lithium sulfide of a comparative example.

[0043] Figures 2a to 2c are drawings showing the results of analyzing lithium sulfide (Figure 2a), cation A (Figure 2b), and anion B (Figure 2c) of lithium sulfide of Example 2 using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS), respectively.

[0044] Figure 2d is a diagram showing the results of analyzing the peaks of each component according to binding energy using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS) for lithium sulfide of Example 2.

[0045] Hereinafter, the technology disclosed in this specification and its implementation examples will be described in detail with reference to the attached drawings. However, the embodiments of the technology may be modified in various other forms, and the scope is not limited to the implementation examples described below. Furthermore, the technology disclosed in this specification may be applied not only by being limited to the configurations of the implementation examples described below, but also by selectively combining all or some of the implementation examples to enable various modifications.

[0046] As described above, there is a need for the development of a technology capable of efficiently manufacturing a sulfide-based solid electrolyte. The sulfide-based solid electrolyte can be manufactured using lithium sulfide (Li2S) as a raw material, and the lithium sulfide (Li2S) is composed of hydrogen sulfide (H2S), lithium sulfate (Li2S), and the like. 2- It can be synthesized with SO4, etc.

[0047] When hydrogen sulfide (H2S) is used in the synthesis of the lithium sulfide (Li2S), the lithium sulfide (Li2S) can be produced by reacting hydrogen sulfide (H2S) with lithium hydroxide (LiOH) or alkyl lithium (Li-R). However, in this case, there is a problem in that highly toxic hydrogen sulfide (H2S) must be used as a direct reactant.

[0048] Meanwhile, when synthesizing the lithium sulfide (Li2S), lithium sulfate (Li 2- When using SO4), the lithium sulfide (Li2S) is combined with carbon (C) and lithium sulfate (Li) which act as a reducing agent. 2- SO4) can be produced by reacting (see reaction scheme 1 below).

[0049] [Reaction Formula 1]

[0050] Li2SO4+ 2C -> Li2S + 2CO2

[0051] However, the above-described reaction may not control the degree of reduction by carbon, and impurities such as polysulfide compounds may be synthesized in addition to lithium sulfide (Li2S) through the reaction. Since the polysulfide compounds do not have a large difference in solubility from lithium sulfide (Li2S), it may be difficult to isolate pure lithium sulfide (Li2S).

[0052] According to one embodiment of the present disclosure, a method for producing high-purity lithium sulfide on a large scale without using highly toxic raw materials is provided. Hereinafter, embodiments of the technology disclosed in the present disclosure will be described in detail with reference to FIGS. 1A to 2D.

[0053] Figures 1a to 1c are drawings showing the results of analyzing lithium sulfide (Figure 1a), cation A (Figure 1b), and anion B (Figure 1c) using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS) for lithium sulfide of a comparative example, respectively.

[0054] Figure 1d is a diagram showing the results of analyzing the peaks of each component according to binding energy using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS) for lithium sulfide of a comparative example.

[0055] Figures 2a to 2c are drawings showing the results of analyzing lithium sulfide (Figure 2a), cation A (Figure 2b), and anion B (Figure 2c) using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS) for lithium sulfide of a comparative example, respectively.

[0056] Figure 2d is a diagram showing the results of analyzing the peaks of each component according to binding energy using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS) for lithium sulfide of Example 2.

[0057] Lithium sulfide for solid electrolytes

[0058] Lithium sulfide for a solid electrolyte according to one embodiment has a content of at least one element A selected from the group consisting of Group 1 elements and Group 2 elements of 8 mol% or less when analyzed by inductively coupled plasma spectroscopy (ICP).

[0059] The lithium sulfide for the solid electrolyte is a high-purity lithium sulfide with a low impurity content, and may have a relatively low content of the element A. In some embodiments, the element A may be included in a compound represented by the following chemical formula 1. Specifically, the element A may correspond to A in the compound represented by the following chemical formula 1.

[0060] [Chemical Formula 1]

[0061] AB y

[0062] In the above chemical formula 1, A is at least one selected from the group consisting of group 1 elements and group 2 elements, and B is a group 17 element, NO3 - and BF4 - At least one selected from the group consisting of , and y is 1 or 2.

[0063] The compound represented by the above chemical formula 1 can be produced in the process of manufacturing lithium sulfide by reaction of a sulfur compound represented by the following chemical formula 2 and a lithium compound represented by the following chemical formula 3.

[0064] [Chemical Formula 2]

[0065] A x S

[0066] In the above chemical formula 2, A has the same meaning as A in the above chemical formula 1, S is sulfur, and x is 1 or 2.

[0067] [Chemical Formula 3]

[0068] LiB

[0069] In the above chemical formula 3, Li is lithium, and B has the same meaning as B in the above chemical formula 1.

[0070] In some embodiments, the compound represented by Chemical Formula 1 may be sodium chloride (NaCl). Furthermore, in some embodiments, the compound represented by Chemical Formula 2 may be sodium sulfide (Na2S), and the compound represented by Chemical Formula 3 may be lithium chloride (LiCl).

[0071] The lithium sulfide for the above solid electrolyte has a content of element A of 8 mol% or less when analyzed by inductively coupled plasma spectrometry (ICP). According to the inductively coupled plasma spectrometry (ICP) analysis, the content of the element included in the analysis target can be quantitatively measured. The inductively coupled plasma spectrometry (ICP) analysis device is not particularly limited. For example, the inductively coupled plasma spectrometry (ICP) analysis can be performed using an Agilent 700s or an Agilent 5800.

[0072] In some embodiments, the lithium sulfide for the solid electrolyte may have a content of the element A of 7.5 mol% or less or 7 mol% or less, and may be 0.001 mol% or more, 0.01 mol% or more, 0.1 mol% or more, 1 mol% or more, 3 mol% or more, or 6 mol% or more, as analyzed by inductively coupled plasma spectroscopy (ICP). When the content of the compound represented by the chemical formula 1 is as described above, the lithium sulfide for the solid electrolyte may be a high-purity lithium sulfide with a small amount of impurities.

[0073] In some embodiments, the lithium sulfide for the solid electrolyte may not include the element A. Specifically, the lithium sulfide for the solid electrolyte may be a high-purity lithium sulfide that does not include impurities and has a content of the element A of about 0 mol% as determined by inductively coupled plasma spectroscopy (ICP).

[0074] According to another embodiment, lithium sulfide for solid electrolyte has a content of 20% or less of a compound represented by the following chemical formula 1 according to X-ray diffraction (XRD) analysis and Rietveld Refinement Method.

[0075] [Chemical Formula 1]

[0076] AB y

[0077] In the above chemical formula 1, A is at least one selected from the group consisting of group 1 elements and group 2 elements, and B is a group 17 element, NO3 - and BF4 - At least one selected from the group consisting of , and y is 1 or 2.

[0078] The above-mentioned lithium sulfide for solid electrolyte is a high-purity lithium sulfide with a low impurity content, and the content of the compound represented by the above-mentioned chemical formula 1 may be relatively low. A detailed description of the compound represented by the above-mentioned chemical formula 1 is omitted as it overlaps with the above-mentioned content.

[0079] The lithium sulfide for the above solid electrolyte has a content of 20% or less of the compound represented by the above chemical formula 1 according to X-ray diffraction (XRD) analysis and the Rietveld Refinement Method. According to the Rietveld Refinement Method, the entire diffraction pattern derived from the XRD analysis of the measurement target can be analyzed at once without the need to separate each peak. Accordingly, more accurate crystallographic analysis results can be derived during analysis by the Rietveld Refinement Method, and differences in chemical properties resulting from the composition and crystal structure of the measurement target can be analyzed more precisely.

[0080] The above X-ray diffraction (XRD) analysis equipment, conditions, etc. are not particularly limited. For example, the above X-ray diffraction (XRD) analysis can be performed under the following conditions.

[0081] - Equipment: PANalytical EMPYREAN

[0082] - Specifications: Power 4kW

[0083] - OPTIC: Bragg-Brentano HD, PIXcel3D Detector

[0084] - Area: 10°~120°

[0085] - Step size: 0.00625°

[0086] - Scan speed: 0.98° / min

[0087] - Wavelength: Cu Ka 1,560

[0088] The programs used for the above Rietveld refinement method are not particularly limited. For example, the above Rietveld refinement method can be performed using the HighScore Plus program and the pseudo-Voight function model.

[0089] In some embodiments, the lithium sulfide for solid electrolyte may have a content of the compound represented by the chemical formula 1 of 16% or less, 15% or less, 12% or less, or 10% or less, and may have a content of 0.001% or more, 0.01% or more, 0.1% or more, 1% or more, 5% or more, or 7% or more, as determined by X-ray diffraction (XRD) analysis and Rietveld refining. When the content of the compound represented by the chemical formula 1 is as described above, the lithium sulfide for solid electrolyte may be a high-purity lithium sulfide with a small amount of impurities.

[0090] In some embodiments, the lithium sulfide for the solid electrolyte may not include the compound represented by the above chemical formula 1. Specifically, the lithium sulfide for the solid electrolyte may be a high-purity lithium sulfide that does not include impurities and has a content of the compound represented by the above chemical formula 1 of about 0% according to X-ray diffraction (XRD) analysis and Rietveld refining method.

[0091] In some embodiments, the lithium sulfide for the solid electrolyte may have binding energies different from those of a peak representing the compound represented by Chemical Formula 1 and a peak representing lithium sulfide when analyzed by SEM-EDS using a scanning electron microscope (SEM) and an energy-dispersive X-ray spectrometer (EDS). For example, the peak representing the compound represented by Chemical Formula 1 may be a peak corresponding to A and B in Chemical Formula 1, and the peak representing lithium sulfide may be a peak representing sulfur (S).

[0092] As shown in FIGS. 1d and 2d, in some embodiments, the lithium sulfide for the solid electrolyte can be clearly distinguished from the peaks corresponding to A and B in the chemical formula 1 and the peak representing sulfur (S) when analyzed by SEM-EDS.

[0093] In some embodiments, the peak corresponding to A in the above chemical formula 1 may appear at a binding energy of 0.5 to 1.5 keV in the SEM-EDS analysis. For example, the peak corresponding to A in the above chemical formula 1 may appear at a binding energy of 1.041 keV in the SEM-EDS analysis. In this case, the A is sodium (Na + ) can be judged to be.

[0094] In some embodiments, the peak corresponding to B in the above chemical formula 1 may appear at a binding energy of 2.5 to 3.5 keV in the SEM-EDS analysis. For example, the peak corresponding to B in the above chemical formula 1 may appear at a binding energy of 2.621 keV in the SEM-EDS analysis. In this case, the B is sodium (Cl - ) can be judged to be.

[0095] In some embodiments, a peak representing sulfur (S) may appear at a binding energy of 1.5 to 2.5 keV during SEM-EDS analysis. Specifically, a peak representing sulfur (S) may appear at a binding energy of 2.307 keV during SEM-EDS analysis.

[0096] In some embodiments, when the lithium sulfide for the solid electrolyte is analyzed by SEM-EDS using a scanning electron microscope (SEM) and an energy-dispersive X-ray spectrometer (EDS), the region corresponding to A and the region corresponding to B of the compound represented by the chemical formula 1 may be different from each other in the EDS mapping image. For example, the region representing the compound represented by the chemical formula 1 may be the region corresponding to A and the region corresponding to B in the chemical formula 1, and the region representing the lithium sulfide may be the region representing sulfur (S).

[0097] The distinction of the area representing each component in the above EDS mapping image can be made by quantifying the point where each component is detected in the EDS mapping image and saving the image of the area where the target component is detected.

[0098] As shown in FIGS. 1A to 1C and 2A to 2C, in some implementations, the lithium sulfide for the solid electrolyte can be clearly distinguished from the region corresponding to A and B in the chemical formula 1 and the region representing sulfur (S) in the EDS mapping image when analyzed by SEM-EDS.

[0099] The above SEM-EDS analysis equipment, conditions, etc. are not particularly limited. For example, the SEM-EDS analysis can be performed using a Bruker FlatQuad equipped with EDS equipment linked to an SEM under conditions of an acceleration voltage of 5 kV, a pulse throughput of 130 kcps, and a working distance of 15 mm.

[0100] Lithium sulfide for solid electrolyte according to the above-described embodiments can be manufactured by the method described below.

[0101] Method for producing lithium sulfide for solid electrolyte

[0102] A method for producing lithium sulfide for a solid electrolyte according to one embodiment comprises the steps of: preparing a solution by mixing a sulfur compound represented by the following chemical formula 2 and a lithium compound represented by the following chemical formula 3 with a solvent; cooling the solution to 25°C or lower; removing the compound represented by the following chemical formula 1 from the cooled solution to obtain lithium sulfide; and heat-treating the obtained lithium sulfide.

[0103] [Chemical Formula 1]

[0104] AB y

[0105] In the above chemical formula 1, A is at least one selected from the group consisting of group 1 elements and group 2 elements, and B is a group 17 element, NO3 - and BF4 - At least one selected from the group consisting of , and y is 1 or 2.

[0106] [Chemical Formula 2]

[0107] A x S

[0108] In the above chemical formula 2, A has the same meaning as A in the above chemical formula 1, S is sulfur, and x is 1 or 2.

[0109] [Chemical Formula 3]

[0110] LiB

[0111] In the above chemical formula 3, Li is lithium, and B has the same meaning as B in the above chemical formula 1.

[0112] The above method for producing lithium sulfide for solid electrolytes can produce high-purity lithium sulfide with high economic efficiency by using inexpensive raw materials instead of highly toxic hydrogen sulfide (H2S). Furthermore, the method for producing lithium sulfide for solid electrolytes can facilitate large-scale synthesis by utilizing a liquid-phase synthesis reaction. Each step of the method for producing lithium sulfide for solid electrolytes is described in detail below.

[0113] <Solution preparation steps>

[0114] The above solution preparation step is a sulfur compound represented by the above chemical formula 2 (A x S) and a lithium compound (LiB) represented by the above chemical formula 3 may be reacted to synthesize lithium sulfide (Li2S). The solution may be a mixture of lithium sulfide (Li2S) synthesized by the reaction of compounds represented by chemical formulas 2 and 3 and a compound represented by chemical formula 1 (AB y ) may be included. The sulfur compound (A) represented by the above chemical formula 2 x S) and the lithium compound (LiB) represented by the above chemical formula 3 can be prepared in a molar ratio of 1:2 for the synthesis of lithium sulfide (Li2S).

[0115] In some embodiments, the solution preparation step may be performed at a temperature above room temperature. For example, the solution preparation step may be performed at a temperature above 25°C and below the boiling point of the solvent.

[0116] In some embodiments, the solvent may be a polar solvent. For example, the solvent may include at least one selected from the group consisting of an alcohol-based solvent, a tetrahydrofuran-based solvent, and a phosphoramide-based solvent.

[0117] The alcohol-based solvent is not particularly limited as long as it is an alcohol compound having a hydroxyl group (-OH). For example, the alcohol-based solvent may be methanol, ethanol, isopropanol, etc.

[0118] The tetrahydrofuran-based solvent is not particularly limited as long as it is a compound having a pentagonal heterocycle in which four carbon atoms and an oxygen atom are connected by a single bond. For example, the tetrahydrofuran-based solvent may be at least one selected from tetrahydrofuran; and compounds having at least one functional group bonded to the 2nd or 3rd carbon position of the tetrahydrofuran. For example, the compound having at least one functional group bonded to the 2nd or 3rd carbon position of the tetrahydrofuran may be 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 2-(isocyanomethyl)tetrahydrofuran, 3-(aminomethyl)tetrahydrofuran, etc.

[0119] The above phosphoramide solvent is not particularly limited as long as it is a compound having a structure in which a phosphorus atom connected to an oxygen atom by a double bond is connected to an oxygen atom or a nitrogen atom by three single bonds. For example, the phosphoramide solvent may be phosphoramide, diethyl phosphoramidate, hexamethyl phosphoramide, etc.

[0120] In some embodiments, the concentration of the solution may be 0.1 to 0.5 M. If the concentration of the solution is less than 0.1 M, a large amount of ABy, which is an impurity, may be contained in the final product, which may be problematic, and if the concentration of the solution is more than 0.5 M, the yield of lithium sulfide may be reduced, which may be problematic.

[0121] <Solution cooling stage>

[0122] The above solution cooling step is a step of cooling the solution prepared as described above to 25°C or lower, and may be a step of lowering the temperature of the solution to room temperature or lower to lower the solubility of impurities (compounds represented by the above chemical formula 1) other than lithium sulfide (Li-2S) contained in the solution and precipitating them.

[0123] In some embodiments, the solution cooling step may be a step of cooling the solution to -10°C to 25°C. Specifically, in the solution cooling step, the solution may be cooled to 10°C or lower or 5°C or lower. If the temperature of the solution is lowered below -10°C, the solubility of lithium sulfide (Li2S) may also be lowered, thereby reducing the yield of lithium sulfide (Li2S). If the temperature of the solution is higher than 25°C, impurities other than lithium sulfide (Li-2S) (compounds represented by the above chemical formula 1) may not be well precipitated, making it difficult to obtain high-purity lithium sulfide (Li2S).

[0124] <Lithium sulfide obtaining step>

[0125] The above lithium sulfide obtaining step is a step of removing the compound represented by the above chemical formula 1 from a solution that has undergone a cooling process and obtaining lithium sulfide (Li2S). The compound represented by the above chemical formula 1 may be removed by filtration after being precipitated in the solution by the cooling process. The filtration of the solution may be performed under an inert gas environment such as argon (Ar).

[0126] The above lithium sulfide (Li2S) can be obtained by removing the solvent through drying of a solution that has undergone a filtration process. Lithium sulfide (Li2S) is dissolved in the solution from which impurities have been removed through the filtration process, and when the solvent is removed through a drying process, high-purity lithium sulfide (Li2S) can be obtained.

[0127] The drying process of the above solution may be carried out at a temperature above the boiling point of the solvent used, which is sufficient to remove the solvent. In some embodiments, the drying process of the solution may be carried out at a temperature of 70°C or higher, and at a temperature of 200°C or lower.

[0128] <Lithium sulfide heat treatment step>

[0129] The above lithium sulfide heat treatment step is a step of applying heat treatment to the obtained lithium sulfide (Li2S), and the purity of the lithium sulfide (Li2S) can be improved through the above lithium sulfide heat treatment step.

[0130] In some embodiments, the step of heat-treating the lithium sulfide may be performed at a temperature of 400°C to 900°C. For example, the step of heat-treating the lithium sulfide may be performed at a temperature of 550°C or higher and at a temperature of 850°C or lower.

[0131] In some embodiments, the heat-treated lithium sulfide may have a content of at least one element A selected from the group consisting of Group 1 elements and Group 2 elements of 8 mol% or less when analyzed by inductively coupled plasma spectroscopy (ICP). A detailed description of the inductively coupled plasma spectroscopy (ICP) analysis of the lithium sulfide and the element content of the compound represented by the chemical formula 1 is omitted as it overlaps with the above-described content.

[0132] In some embodiments, the heat-treated lithium sulfide may have a content of the compound represented by the chemical formula 1 according to the Rietveld Refinement Method of 20% or less when analyzed by X-ray diffraction (XRD). A detailed description of the content of the compound represented by the chemical formula 1 according to the Rietveld Refinement Method and the X-ray diffraction (XRD) analysis of the lithium sulfide overlaps with the above-described content and is therefore omitted.

[0133] Sulfide-based solid electrolyte

[0134] A sulfide-based solid electrolyte according to one embodiment is manufactured from lithium sulfide (Li2S) according to any one of the above-described embodiments. The sulfide-based solid electrolyte is Li2S-P2S5, Li2S-P2S5-LiX (X is a halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (m, n are positive numbers, Z is one of Ge, Zn or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li p MO q (p, q are positive numbers, M is one of P, Si, Ge, B, Al, Ga In), Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2) and Li 7-x PS 6-x I x There can be at least one selected from (0≤x≤2).

[0135] The above sulfide-based solid electrolyte may be an argyrodite-based solid electrolyte. The above argyrodite-based solid electrolyte may be a compound represented by the following chemical formula 4.

[0136] [Chemical Formula 4]

[0137] Li a + A + b Q c X -d

[0138] In the above chemical formula 4, 1≤a≤12, 0≤b≤5, 0≤c≤10, 0≤d≤2, A is at least one of P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta, Q is at least one of S, Se, or Te, and X is at least one of Cl, Br, I, F, CN, OCN, SCN, or N3.

[0139] Specifically, the above argyrodite-based solid electrolyte is Li 7-x PS 6-x Cl x (0≤x≤2), Li 7-x PS 6-x Br x (0≤x≤2), Li 7-x PS 6-x I x (0≤x≤2), Li6PS5Cl, Li6PS5Br, , Li6PS5I, Li 6.5 Sb 0.5 Ge 0.5 S5I, Li 5.7 PS 4.7 Cl 1.3 , Li 6.6 Sb 0.5 Si 0.6 It may be a compound represented by a chemical formula such as S5I.

[0140] The present disclosure may also relate to the following aspects:

[0141] Aspect 1) Lithium sulfide for solid electrolyte may have a content of at least one element A selected from the group consisting of Group 1 elements and Group 2 elements of 8 mol% or less when analyzed by inductively coupled plasma spectroscopy (ICP).

[0142] Aspect 2) In aspect 1, the element A may correspond to A in a compound represented by the following chemical formula 1.

[0143] [Chemical Formula 1]

[0144] AB y

[0145] In the above chemical formula 1, A is at least one selected from the group consisting of group 1 elements and group 2 elements, and B is a group 17 element, NO3 - and BF4 - At least one selected from the group consisting of , and y is 1 or 2.

[0146] Aspect 3) In aspect 2, when the lithium sulfide for the solid electrolyte is analyzed by SEM-EDS using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS), the binding energy of the peak representing the compound represented by the chemical formula 1 and the peak representing lithium sulfide may be different from each other.

[0147] Aspect 4) In Aspect 2 or 3, when the lithium sulfide for the solid electrolyte is analyzed by SEM-EDS using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS), the region representing the compound represented by the chemical formula 1 and the region representing lithium sulfide in the EDS mapping image may be different from each other.

[0148] Aspect 5) In any one of aspects 2 to 4, the compound represented by the chemical formula 1 may be sodium chloride (NaCl).

[0149] Aspect 6) Lithium sulfide for solid electrolyte may have a content of 20% or less of a compound represented by the following chemical formula 1 according to X-ray diffraction (XRD) analysis and the Rietveld Refinement Method.

[0150] [Chemical Formula 1]

[0151] AB y

[0152] In the above chemical formula 1, A is at least one selected from the group consisting of group 1 elements and group 2 elements, and B is a group 17 element, NO3 - and BF4 - At least one selected from the group consisting of , and y is 1 or 2.

[0153] Aspect 7) In aspect 6, when the lithium sulfide for the solid electrolyte is analyzed by SEM-EDS using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS), the binding energy of the peak representing the compound represented by the chemical formula 1 and the peak representing lithium sulfide may be different from each other.

[0154] Aspect 8) In aspect 6 or 7, when the lithium sulfide for the solid electrolyte is analyzed by SEM-EDS using a scanning electron microscope (SEM) and an energy dispersive X-ray spectrometer (EDS), the region representing the compound represented by the chemical formula 1 and the region representing lithium sulfide in the EDS mapping image may be different from each other.

[0155] Aspect 9) In any one of aspects 6 to 8, the compound represented by the chemical formula 1 may be sodium chloride (NaCl).

[0156] Aspect 10) A method for producing lithium sulfide for a solid electrolyte may include a step of mixing a sulfur compound represented by the following chemical formula 2 and a lithium compound represented by the following chemical formula 3 with a solvent to produce a solution; a step of cooling the solution to 25°C or lower; a step of removing a compound represented by the following chemical formula 1 from the cooled solution to obtain lithium sulfide; and a step of heat-treating the obtained lithium sulfide.

[0157] [Chemical Formula 1]

[0158] AB y

[0159] In the above chemical formula 1, A is at least one selected from the group consisting of group 1 elements and group 2 elements, and B is a group 17 element, NO3 - and BF4 - At least one selected from the group consisting of , and y is 1 or 2.

[0160] [Chemical Formula 2]

[0161] A x S

[0162] In the above chemical formula 2, A has the same meaning as A in the above chemical formula 1, S is sulfur, and x is 1 or 2.

[0163] [Chemical Formula 3]

[0164] LiB

[0165] In the above chemical formula 3, Li is lithium, and B has the same meaning as B in the above chemical formula 1.

[0166] Aspect 11) In aspect 10, the solvent may include at least one selected from the group consisting of an alcohol-based solvent, a tetrahydrofuran-based solvent, and a phosphoramide-based solvent.

[0167] Side 12) In side 10 or 11, the step of heat treating the lithium sulfide can be performed at 400°C to 900°C.

[0168] Aspect 13) In any one of aspects 10 to 12, the heat-treated lithium sulfide may have a content of at least one element A selected from the group consisting of Group 1 elements and Group 2 elements of 8 mol% or less when analyzed by inductively coupled plasma spectroscopy (ICP).

[0169] Side 14) In any one of Sides 10 to 13, the heat-treated lithium sulfide may have a content of 20% or less of the compound represented by the chemical formula 1 according to the Rietveld Refinement Method when analyzed by X-ray diffraction (XRD).

[0170] Example

[0171] 1. Manufacturing of lithium sulfide (Li2S)

[0172] 1) Example 1

[0173] Sodium sulfide (Na2S) and lithium chloride (LiCl), weighed in a molar ratio of 1:2, were prepared as sulfur compounds and lithium compounds. The sodium sulfide (Na2S) and lithium chloride (LiCl) were mixed with ethanol as a solvent at a temperature exceeding 25°C (55°C to 70°C) to prepare a solution having a concentration of 0.3 M. The solution was stirred using a magnetic stirrer and then cooled to 25°C to precipitate sodium chloride (NaCl). The precipitated sodium chloride (NaCl) was then removed by filtration under an argon (Ar) environment, and the solution was dried at 70°C or higher to remove the solvent, thereby recovering lithium sulfide (Li2S) in powder form. The recovered lithium sulfide (Li2S) in powder form was heat-treated at 600°C to obtain high-purity lithium sulfide (Li2S) crystals.

[0174] 2) Example 2

[0175] Lithium sulfide (Li2S) crystals were obtained in the same manner as in the above example, except that the solution was cooled to 0°C.

[0176] 3) Comparative example

[0177] Lithium sulfide (Li2S) crystals were obtained in the same manner as in the above example, except that sodium chloride (NaCl) was removed by filtration under an argon (Ar) environment without a process of cooling the solution.

[0178] 2. Evaluation of lithium sulfide (Li2S)

[0179] 1) Inductively Coupled Plasma Spectroscopy (ICP) Analysis

[0180] After measuring a certain amount of weight that would not cause a safety problem for workers due to hydrogen sulfide generated from lithium sulfide, the lithium sulfide of the examples and comparative examples of the corresponding content was dissolved in tertiary distilled water that did not contain any ions and sufficiently reacted to convert all of the lithium sulfide into lithium hydroxide (LiOH), and then analyzed by ICP. This is because the concentration of lithium element or element A in the lithium sulfide sample does not change even if it reacts with distilled water. At this time, dissolving lithium sulfide in distilled water and reacting it was performed by the following method.

[0181] 1. Mix 20 mg of sample with 15 mL of distilled water by shaking well. If any floating matter is present, remove it with a 0.45 um syringe filter.

[0182] 2. Add 5 drops of nitric acid and mix evenly.

[0183] Afterwards, inductively coupled plasma spectrometry (ICP) analysis was performed to determine the concentrations of lithium element and element A, and the results are shown in Table 1 below. At this time, the ICP analysis was performed using Agilent 700s under the following conditions.

[0184] - RF Power (W): 1200

[0185] - Coolant gas (L / min): 15

[0186] - Auxiliary gas(L / min): 1.5

[0187] - Carrier gas (L / min): 0.75

[0188] ICP analysis results Comparative examples Example 1 Example 2 Weight-based content of lithium element (ppm) 2889.6 1704.6 1470.6 Weight-based content of element A (Na) (ppm) 862.2 216.6 170.3 Molar concentration of lithium element (mol%) 84.7 mol% 92.9 mol% 93.5 mol% Molar concentration of element A (Na) (mol%) 15.3 mol% 7.1 mol% 6.5 mol%

[0189] 2) X-ray diffraction (XRD) analysis

[0190] In order to prevent contact with the atmosphere, lithium sulfide samples of examples and comparative examples for XRD analysis were prepared inside a glove box, and XRD analysis and analysis according to the Rietveld refining method were performed using an X-ray diffraction (XRD) analyzer, and the results are shown in Table 2 below. At this time, the XRD analysis was performed under the following conditions.

[0191] - Equipment: PANalytical EMPYREAN

[0192] - Specifications: Power 4kW

[0193] - OPTIC: Bragg-Brentano HD, PIXcel3D Detector

[0194] - Area: 10°~120°

[0195] - Step size: 0.00625°

[0196] - Scan speed: 0.98° / min

[0197] - Wavelength: Cu Ka 1,560

[0198] XRD analysis results Comparative examples Example 1 Example 2 Content of Li2S (%) 48.6 86.3 71.2 Compound AB y (NaCl) content (%)51.413.79.4

[0199] Referring to Table 1 and Table 2 above, the lithium sulfide of the comparative example manufactured without a separate solution cooling step contains an impurity compound (AB y ) content is relatively high, so it can be confirmed that the purity is low. On the other hand, lithium sulfide of Examples 1 and 2 manufactured by a process including a solution cooling step in the manufacture of lithium sulfide contains an impurity compound (AB y ) content is relatively low, and it can be confirmed that the purity is high.

[0200] In particular, it can be confirmed that the lithium sulfide of Example 2, which was manufactured by a process including a step of cooling the solution to below room temperature (0°C), has very high purity characteristics.

[0201] 3) SEM-EDS analysis

[0202] In order to prevent contact with the atmosphere, lithium sulfide samples of the examples and comparative examples for SEM-EDS analysis were prepared in a powder state inside a glove box, and then SEM-EDS analysis was performed on the lithium sulfides of the comparative examples and Example 2 using a scanning electron microscope (SEM) and an energy-dispersive X-ray spectrometer (EDS). The results are shown in Figs. 1a to 2d. At this time, the SEM-EDS analysis was performed using a Bruker FlatQuad equipped with an EDS device linked to an SEM under the conditions of an acceleration voltage of 5 kV, a pulse throughput of 130 kcps, and a working distance of 15 mm.

[0203] Referring to Figure 1d, in the comparative lithium sulfide manufactured without a separate solution cooling step, the impurity compound (AB) y ) appears relatively high, confirming that the purity of lithium sulfide is low. On the other hand, referring to Figure 2d, the lithium sulfide of Example 2 manufactured by a process including a solution cooling step in the manufacture of lithium sulfide contains an impurity compound (AB y) can be confirmed by the relatively low peak indicating the high lithium sulfide.

[0204] As described above, the features of the present invention can be applied in whole or in part to lithium sulfide for solid electrolyte and a method for producing the same.

Claims

1. As lithium sulfide for solid electrolyte, The lithium sulfide for the solid electrolyte has a content of at least one element A selected from the group consisting of Group 1 elements and Group 2 elements of 8 mol% or less when analyzed by inductively coupled plasma spectroscopy (ICP). Lithium sulfide for solid electrolytes.

2. In paragraph 1, The above element A corresponds to A in the compound represented by the following chemical formula 1. Lithium sulfide for solid electrolytes. [Chemical Formula 1] AB y In the above chemical formula 1, A is at least one selected from the group consisting of group 1 elements and group 2 elements, and B is a group 17 element, NO3 - and BF4 - At least one selected from the group consisting of , and y is 1 or 2.

3. In paragraph 2, When analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS), the binding energies of the peak representing the compound represented by the chemical formula 1 and the peak representing lithium sulfide are different from each other. Lithium sulfide for solid electrolytes.

4. In paragraph 2, When SEM-EDS analysis was performed using a scanning electron microscope (SEM) and an energy-dispersive X-ray spectrometer (EDS), the area representing the compound represented by the chemical formula 1 and the area representing lithium sulfide in the EDS mapping image were different from each other. Lithium sulfide for solid electrolytes.

5. In paragraph 2, The compound represented by the above chemical formula 1 is sodium chloride (NaCl). Lithium sulfide for solid electrolytes.

6. As lithium sulfide for solid electrolyte, The lithium sulfide for the above solid electrolyte has a content of 20% or less of a compound represented by the following chemical formula 1 according to X-ray diffraction (XRD) analysis and the Rietveld Refinement Method. Lithium sulfide for solid electrolytes. [Chemical Formula 1] AB y In the above chemical formula 1, A is at least one selected from the group consisting of group 1 elements and group 2 elements, and B is a group 17 element, NO3 - and BF4 - At least one selected from the group consisting of , and y is 1 or 2.

7. In paragraph 6, When analyzed by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS), the binding energies of the peak representing the compound represented by the chemical formula 1 and the peak representing lithium sulfide are different from each other. Lithium sulfide for solid electrolytes.

8. In paragraph 6, When SEM-EDS analysis was performed using a scanning electron microscope (SEM) and an energy-dispersive X-ray spectrometer (EDS), the area representing the compound represented by the chemical formula 1 and the area representing lithium sulfide in the EDS mapping image were different from each other. Lithium sulfide for solid electrolytes.

9. In paragraph 6, The compound represented by the above chemical formula 1 is sodium chloride (NaCl). Lithium sulfide for solid electrolytes.

10. A step of preparing a solution by mixing a sulfur compound represented by the following chemical formula 2 and a lithium compound represented by the following chemical formula 3 with a solvent; A step of cooling the above solution to 25°C or lower; A step of removing a compound represented by the following chemical formula 1 from the cooled solution and obtaining lithium sulfide; and A step of heat treating the obtained lithium sulfide, Method for producing lithium sulfide for solid electrolyte. [Chemical Formula 1] AB y In the above chemical formula 1, A is at least one selected from the group consisting of group 1 elements and group 2 elements, and B is a group 17 element, NO3 - and BF4 - At least one selected from the group consisting of , and y is 1 or 2. [Chemical Formula 2] A x S In the above chemical formula 2, A has the same meaning as A in the above chemical formula 1, S is sulfur, and x is 1 or 2. [Chemical Formula 3] LiB In the above chemical formula 3, Li is lithium, and B has the same meaning as B in the above chemical formula 1.

11. In paragraph 10, The solvent comprises at least one selected from the group consisting of alcohol-based solvents, tetrahydrofuran-based solvents, and phosphoramide-based solvents. Method for producing lithium sulfide for solid electrolyte.

12. In paragraph 10, The step of heat treating the lithium sulfide is performed at 400°C to 900°C. Method for producing lithium sulfide for solid electrolyte.

13. In paragraph 10, The above heat-treated lithium sulfide has a content of at least one element A selected from the group consisting of Group 1 elements and Group 2 elements of 8 mol% or less when analyzed by inductively coupled plasma spectroscopy (ICP). Method for producing lithium sulfide for solid electrolyte.

14. In paragraph 10, The above heat-treated lithium sulfide has a content of 20% or less of the compound represented by the above chemical formula 1 according to the Rietveld Refinement Method when analyzed by X-ray diffraction (XRD). Method for producing lithium sulfide for solid electrolyte.

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