Lithium sulfide powder and its manufacturing method

Abstract

The present invention relates to lithium sulfide powder and a method for producing the same, which includes the steps of: mixing a carbon raw material minium compound to produce a lithium-carbon compound; filtering a solution obtained by mixing the lithium-carbon compound and a solvent; adding sulfur powder to the filtrate, the ratio of the number of moles of sulfur powder added to the number of moles of lithium ions being 0.01 to 0.04; drying the filtrate; and heat-treating the dried product, thereby producing lithium sulfide having an oxygen content of 1.0 to less than 3.5%.

Description

[Technical Field]

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

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

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

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

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

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

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

[0008] Typically, a method for producing high-quality lithium sulfide by reacting expensive metallic or organic lithium with high-purity hydrogen sulfide is known, and recently, a production method using relatively inexpensive lithium hydroxide has emerged as a mass production technology. Another method that can reduce production costs is to produce lithium sulfide by thermally reducing inexpensive lithium sulfate in a gas phase.

[0009] However, after thermal reduction, residual impurities are often generated during the lithium sulfide extraction process. In particular, oxygen-containing impurities remain in the final lithium sulfide product, which can affect the performance of the solid electrolyte. Summary of the Invention [Problem to be solved by the invention]

[0010] The technical problem to be solved by the present invention is to provide a lithium sulfide powder in which oxygen-containing impurities are effectively controlled.

[0011] Another technical problem to be solved by the present invention is to provide a method for producing lithium sulfide, which is a raw material for a high-purity sulfide-based solid electrolyte. [Means for solving the problem]

[0012] According to one embodiment of the present invention, the lithium sulfide powder is a lithium sulfide compound for an all-solid-state electrolyte, and may include lithium oxide (LiO) and have an oxygen content of 3.0% or less. In one embodiment, the lithium sulfide powder may satisfy Equation 1.

[0013] <Expression 1> [Li2O] × oxygen content ≦ 10.0

[0014] (In the above formula 1, [Li2O] means the intensity ratio [%] of the main XRD diffraction peak.)

[0015] In one embodiment, the lithium oxide (LiO) may be 5.6% or less by weight, and the intensity ratio of the XRD main peak of the lithium oxide (LiO) may be less than 3%.

[0016] According to another embodiment of the present invention, a method for producing lithium sulfide includes the steps of mixing a carbon source and a lithium compound to produce a lithium-carbon compound, filtering the solution obtained by mixing the lithium-carbon compound and a solvent, and adding sulfur powder to the filtrate, the ratio of the number of moles of sulfur powder added to the number of moles of lithium ions being 0.01 to 0.04, and then heat-treating the filtrate. In one embodiment, the amounts of the lithium-carbon compound and the solvent may satisfy the following formula 2:

[0017] <Expression 2> 0.10≦[Lithium-carbon compound] / [solvent]≦0.30

[0018] (In the above formula 2, [lithium-carbon compound] and [solvent] mean the content (kg) of the lithium-carbon compound and the content (L) of the solvent, respectively.)

[0019] In one embodiment, the formula 2 may satisfy 0.14 to 0.20. In one embodiment, the contents of the lithium-carbon compound and the sulfur powder may satisfy the following formula 3:

[0020] <Expression 3> 10.0≦[lithium sulfide in lithium-carbon compound] / [sulfur powder]≦100.0

[0021] (In the above formula 3, [lithium sulfide in lithium-carbon compound] and [sulfur powder] mean the amount (g) of lithium sulfide used in the lithium-carbon compound and the amount (g) of sulfur powder added, respectively.)

[0022] In one embodiment, the formula 3 may satisfy a value of 20.0 to 80.0. In one embodiment, the step of preparing the lithium-carbon compound by mixing the carbon raw material and the lithium compound may be a step of heat-treating the carbon raw material and the lithium compound at a temperature in the range of 700 to 900°C.

[0023] In one embodiment, the step of adding sulfur powder, having a ratio of moles of added sulfur powder to moles of lithium ions of 0.01 to 0.04, to the filtered material and heat-treating the sulfur powder may include drying the filtered material and heat-treating the dried material.

[0024] In one embodiment, the solvent may include at least one of ethanol, methanol, isopropyl alcohol, ethylene glycol, and butyl alcohol. In one embodiment, in the step of heat-treating the dried material, the flow rate of the inert gas atmosphere may be 5 to 15 L / min. In one embodiment, in the step of adding sulfur powder to the filtered material and heat-treating it, the sulfur powder may be added at a molar ratio of 0.012 to 0.037 relative to the molar number of lithium ions. [Effects of the Invention]

[0025] According to one embodiment of the present invention, oxygen-containing impurities generated during the purification process using an organic solvent are effectively controlled to provide a lithium sulfide compound that can be used as a raw material for sulfide-based solid electrolytes.

[0026] A method for producing a lithium sulfide compound, according to another embodiment of the present invention, provides lithium sulfide having the advantages described above. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a graph showing changes in oxygen content and impurity concentration in lithium sulfide products depending on the amount of sulfur powder added.

[0028] [Figure 2a] 1 shows the microstructures of lithium sulfide compounds according to examples of the present invention and comparative examples. [Figure 2b] 1 shows the microstructures of lithium sulfide compounds according to examples of the present invention and comparative examples. [Figure 2c] 1 shows the microstructures of lithium sulfide compounds according to examples of the present invention and comparative examples. [Figure 2d] 1 shows the microstructures of lithium sulfide compounds according to examples of the present invention and comparative examples. [Figure 2e] 1 shows the microstructures of lithium sulfide compounds according to examples of the present invention and comparative examples. [Figure 2f] 1 shows the microstructures of lithium sulfide compounds according to examples of the present invention and comparative examples. DETAILED DESCRIPTION OF THE INVENTION

[0029] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Therefore, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0030] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular form includes the plural form unless the context clearly dictates otherwise. As used in the specification, the meaning of "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components.

[0031] When a part is referred to as being "on" another part, it can mean that it is directly on top of the other part, or there can be other parts between them. In contrast, when a part is referred to as being "directly on" another part, there are no other parts between them.

[0032] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which this invention belongs. Terms defined in commonly used dictionaries are additionally interpreted as having a meaning consistent with the relevant technical literature and the presently disclosed content, and unless defined, are not interpreted as having an ideal or very formal meaning. Furthermore, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0033] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art will be able to easily understand and practice the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein.

[0034] The lithium sulfide compound according to one embodiment of the present invention relates to lithium sulfide for an all-solid-state electrolyte and includes lithium oxide (LiO). High-purity lithium sulfide can contain compounds such as lithium oxide (LiO) as impurities by undergoing a heat treatment process.

[0035] In one embodiment, the oxygen content is 3.0% or less, specifically, 1.0 to 2.6%, more specifically, 1.23 to 2.55%.

[0036] In one embodiment, the content of the lithium oxide (LiO) may be 5.6% or less. The lithium oxide (LiO) corresponds to an impurity, and when the content of the lithium oxide (LiO) satisfies the above-mentioned range, the amount of lithium oxide impurities, which are oxygen or oxygen-containing impurities, can be controlled within a certain range, thereby producing lithium sulfide suitable for use as an electrolyte raw material.

[0037] In one embodiment, the XRD main cycle peak intensity ratio of the lithium oxide (LiO) may be less than 3%, specifically, the XRD main cycle peak intensity ratio may be 2.5 or less.

[0038] If the lithium oxide (LiO) content and the XRD main cycle peak intensity ratio are outside the upper limit of the oxygen content, the lithium oxide content (oxygen impurity) exceeds the allowable range, resulting in a problem of electrolyte performance degradation. If the lithium oxide (LiO) content and the XRD main cycle peak intensity ratio are outside the lower limit of the oxygen content, lithium sulfide containing residual amorphous carbon may be produced, resulting in a problem of electrolyte performance degradation.

[0039] In one embodiment, the lithium sulfide powder of the present invention can satisfy the following formula 1:

[0040] <Expression 1> [Li2O] × oxygen content ≦ 10.0 (In the above formula 1, [Li2O] means the content of lithium oxide in the lithium sulfide powder of the XRD main peak.)

[0041] Equation 1 above represents the relationship between the XRD main peak intensity ratio of lithium oxide (LiO) and the oxygen content, and is an index for lithium sulfide applicable to sulfide-based all-solid electrolytes. Equation 1 may be 10 or less. Specifically, Equation 1 may be 6.5 or less, and more specifically, Equation 1 may satisfy a range of 1.2 to 6.4. When Equation 1 satisfies the above-mentioned range, the oxygen content is controlled within the range of the present invention, and when applied to a sulfide-based solid electrolyte, the ionic conductivity can achieve a target value. However, when Equation 1 does not satisfy the above-mentioned range, it is difficult to apply to a solid electrolyte.

[0042] According to another embodiment of the present invention, a method for producing lithium sulfide includes the steps of: mixing a carbon raw material and a lithium compound to produce a lithium-carbon compound; filtering a solution obtained by mixing the lithium-carbon compound and a solvent; and adding sulfur powder to the filtrate and heat-treating the filtrate. For details regarding lithium sulfide, please refer to the above description.

[0043] In one embodiment, the carbon source may include, but is not limited to, at least one of soft carbon, hard carbon, petroleum coke, coal-based needle coke, coal-based pitch coke, natural graphite, and artificial graphite. In one embodiment, the lithium-carbon compound may include at least one of lithium sulfate, lithium hydroxide, lithium oxide, and lithium carbonate.

[0044] The step of preparing the lithium-carbon compound by mixing the carbon raw material and the lithium compound can be performed by heat-treating the carbon raw material and the lithium compound. In one embodiment, the step of preparing the lithium-carbon compound by mixing the carbon raw material and the lithium compound can be performed by heat-treating the carbon raw material and the lithium compound at a temperature in the range of 700 to 1,200°C. In one embodiment, the heat-treating can be performed at a temperature increase rate of 5 to 10°C per minute. In one embodiment, the heat-treating can be performed by maintaining the maximum temperature for 1 to 6 hours, followed by natural cooling. When the heat-treating temperature and time for preparing the lithium-carbon compound are within the above-mentioned ranges, the lithium compound can be sufficiently reduced through carbon. When the heat-treating temperature and time are not within the above-mentioned ranges, there is a problem that the reduction reaction does not occur sufficiently.

[0045] In one embodiment, the heat treatment may be performed under an inert gas atmosphere, which may include, but is not limited to, at least one of helium, neon, krypton, xenon, nitrogen, and argon.

[0046] The step of filtering the mixed solution of the lithium-carbon compound and the solvent includes mixing the lithium-carbon compound with a solvent, followed by filtering. In one embodiment, the solvent may include, but is not limited to, at least one of ethanol, methanol, isopropyl alcohol, ethylene glycol, and butyl alcohol.

[0047] In one embodiment, in the step of filtering the mixed solution of the lithium-carbon compound and the solvent, the content of the lithium-carbon compound and the solvent may satisfy the following formula 2:

[0048] <Expression 2> 0.10≦[Lithium-carbon compound] / [solvent]≦0.30 (In the above formula 2, [lithium-carbon compound] and [solvent] mean the content (kg) of the lithium-carbon compound and the content (L) of the solvent, respectively.)

[0049] The formula 2 represents the relationship between the content of the lithium-carbon compound and the solvent. The formula 2 can be 0.1 to 0.30, specifically 0.14 to 0.20. If the mixing ratio of the solvent is high, an excessive amount of solvent is added, which reduces economic efficiency. If the mixing ratio of the solvent is low, there is a problem that filtration is not performed sufficiently.

[0050] The step of adding sulfur (S) powder to the filtered filtrate and heat-treating it includes drying the filtrate and heat-treating the dried filtrate. In one embodiment, in the step of adding sulfur powder to the filtered filtrate and heat-treating it, the step of adding sulfur powder to the filtered filtrate may be performed before the drying step. By adding sulfur powder to the filtered filtrate before the drying step, solid sulfur powder can be added to the filtrate to compensate for the lack of hydrosulfide ions during the drying process of the filtrate, and the drying process can be performed after the sulfur powder is completely dissolved.

[0051] In one embodiment, the step of adding sulfur powder to the filtered material and heat-treating the material comprises adding sulfur powder having a molar ratio of 0.01 to 0.04 relative to the molar ratio of lithium ions. Specifically, the sulfur powder may be added at a molar ratio of 0.012 to 0.037 relative to the molar ratio of lithium ions.

[0052] By adding sulfur powder to the filtered material, high-purity lithium sulfide for all-solid-state batteries that can be used in all-solid-state batteries can be produced. Specifically, by controlling the addition ratio of sulfur powder to satisfy the above-mentioned range, lithium sulfide with an oxygen content of 3 wt% or less can be produced.

[0053] In the step of adding sulfur (S8) powder to the filtered material and heat treating it, the content of the lithium-carbon compound and the sulfur powder may satisfy the following formula 3:

[0054] <Expression 3> 10.0≦[lithium sulfide in lithium-carbon compound] / [sulfur powder]≦100.0 (In the above formula 3, [lithium sulfide in lithium-carbon compound] and [sulfur powder] mean the amount (g) of lithium sulfide used in the lithium-carbon compound and the amount (g) of sulfur powder added, respectively.)

[0055] Formula 3 can satisfy 10.0 to 100.0, specifically 20.0 to 80.0, and more specifically 22.0 to 76.0. Formula 3 is a relational expression of the content of sulfur powder and the content of lithium-carbon compound, and is an index for the range of the amount of sulfur powder added, which affects the quality of the produced lithium sulfide.

[0056] If the upper limit of formula 3 is exceeded, the excess sulfur powder added may react with part of the solvent during the drying and heat treatment steps to produce undesirable organic sulfur residues in the final lithium sulfide, resulting in reduced purity.If the lower limit of formula 3 is exceeded, the effectiveness of the sulfur powder may be reduced.

[0057] The step of drying the filtrate may be a step of concentrating the filtrate under reduced pressure to dry it. In one embodiment, the step of drying the filtrate may be performed at a temperature of 40 to 70° C. In one embodiment, the step of drying the filtrate may be performed at a vacuum of 40 mbar or less.

[0058] In one embodiment, the drying of the filtrate can be performed by vacuum distillation until no more ethanol is discharged through the distiller.

[0059] The step of heat-treating the dried material involves applying heat to the dried material to obtain final lithium sulfide (LiS). In one embodiment, the dried material, specifically the dried material, may be heated at a temperature in the range of 400 to 800°C, more specifically, 500 to 800°C. In one embodiment, the heat-treating step may be performed at a temperature increase rate of 5 to 20°C per minute.

[0060] In one embodiment, the step of heat-treating the dried material may be performed at a maximum temperature for a period of 1 to 6 hours. Specifically, the period of time may be 1 to 3 hours. In one embodiment, the step of heat-treating the dried material may be performed at a temperature increase rate of 1 to 10°C / min, specifically 2 to 7°C / min. By satisfying the above-mentioned temperature, temperature increase rate, and maintenance time, lithium sulfide, which is the target of the present invention, may be appropriately produced.

[0061] In one embodiment, the heat treatment of the dried product may be performed under an inert gas atmosphere, which may include at least one of helium, neon, krypton, xenon, nitrogen, and argon.

[0062] In one embodiment, the flow rate of the inert gas atmosphere in the heat treatment of the dried product may be 5 to 15 L / min, more specifically, 8 to 12 L / min.

[0063] If the flow rate is outside the upper limit, there is a problem of product loss, and if the flow rate is outside the lower limit, there is a problem of solvent or decomposition products resulting from the solvent remaining in the dried product, which reduces the purity.

[0064] In one embodiment, the step of heat-treating the dried product may include a step of naturally cooling the dried product after heat-treating the dried product for the aforementioned time period. [Example]

[0065] Hereinafter, specific examples of the present invention will be described. However, the following examples are merely specific examples of the present invention, and the present invention is not limited to the following examples.

[0066] Experimental example

[0067] Method for producing thermal reduction products 6 kg of artificial graphite and 2 kg of lithium sulfate monohydrate were mixed uniformly and then heated to 900°C at a rate of 5°C per minute under an inert gas (Ar) atmosphere. Heat treatment was then carried out at 900°C for 2.5 hours, reducing the lithium sulfate to lithium sulfide, which was then mixed with the artificial graphite. After the heat treatment was completed, the resulting mixture was allowed to cool naturally and stored in a glove box under an inert gas atmosphere. The same amount of thermal reduction product was then used for each extraction condition.

[0068] Experiments on changing the extraction conditions for lithium sulfide When lithium sulfate is mixed with an excess amount of carbon and then heat-treated at 900°C in an inert atmosphere, the lithium sulfate is reduced to lithium sulfide, which is produced along with the excess carbon. When this mixture is added to ethanol and stirred, the lithium sulfide dissolves in the ethanol, while the carbon does not, and only the lithium sulfide can be extracted through a simple filtration process.

[0069] The filtrate is then dried to obtain a solid powder. The right side of the following reaction scheme 1 corresponds to the drying process, and the left side of the following reaction scheme 1 corresponds to the extraction process.

[0070] <Reaction Scheme 1> LiSH+Li(CH3CH2O)←→Li2S(s)+CH3CH2OH(l)

[0071] After that, any solvent remaining in the dried powder can be removed through a high-temperature heat treatment to finally obtain purified lithium sulfide. However, during the process of evaporating and drying the filtrate, some of the hydrosulfide ions may be released from the system in the form of hydrogen sulfide due to the difference in acid-basicity between the hydrosulfide ions and ethanol molecules or reactions between the hydrosulfide ions, as shown in Reactions 2 and 3 below.

[0072] <Reaction Scheme 2> LiSH+Li(CH3CH2O)+CH3CH2OH←→2Li(CH3CH2O)+H2S↑

[0073] <Reaction Scheme 3> LiSH+LiSH←→Li2S+H2S↑

[0074] This is because excess lithium ethoxide is produced in the dry powder due to a lack of hydrosulfide ions in the system, and when this is heat-treated, impurities such as lithium hydroxide, lithium oxide, or lithium carbonate may be produced due to thermal decomposition of lithium ethoxide.

[0075] In order to compensate for the lack of hydrosulfide ions during the drying process of the filtrate, solid sulfur (S) powder was added to the filtrate before the drying step, and after completely dissolving it, the drying process was carried out. At this time, the amount of sulfur powder added was adjusted to control the dry ratio of LiSH and Li(CHCHO) in the system within a certain range.

[0076] Specifically, the thermal reduction product prepared as described above was added to ethanol under an inert gas atmosphere and thoroughly stirred. After stopping the stirring, the stirred mixed slurry was filtered, and the artificial graphite that was insoluble in ethanol remained wet in the filter funnel, while the remainder was obtained in a solution state in the filter flask. At this time, the color of the solution was pale yellow-green.

[0077] Yellow sulfur (S8) powder was added to the filtrate obtained from the filtration flask and thoroughly stirred to completely dissolve. Then, using a vacuum pump, the powder was gradually poured into a round-bottom flask attached to a rotary evaporator. During this time, the vacuum was maintained at 30 mbar, and the flask was rotated in a 60°C water bath for approximately 3 hours to concentrate and dry the solution.

[0078] The dried powder was then heated at 150°C and 300°C for 2 hours each, and finally at 800°C for 2 hours to obtain lithium sulfide powder. The heat treatment temperature was increased at a rate of 5°C / min and the Ar gas flow rate was maintained at 10 L / min.

[0079] Table 1 below shows the extraction conditions, including the amounts of thermal reduction product (C-Li2S) and ethanol (EtOH) used, and the amount of sulfur (S8) powder added after filtration.

[0080] Example 1 In the experiment to change the conditions for the extraction of lithium sulfide, the amount of thermal reduction product (C-Li2S) used was 0.34 kg, the amount of ethanol (EtOH) used was 1.7 L, and the amount of sulfur (S8) added after filtration was controlled to 1.5 g.

[0081] <Example 2> The above-mentioned experiment on changing the conditions for extracting lithium sulfide was carried out in the same manner as in Example 1, except that the amount of sulfur (S8) added after filtration was controlled to 1.0 g.

[0082] Example 3 The above-mentioned experiment on changing the conditions for extracting lithium sulfide was carried out in the same manner as in Example 1, except that the amount of sulfur (S8) added after filtration was controlled to 0.5 g.

[0083] <Comparative Example 1> The above-mentioned experiment on changing the conditions for extracting lithium sulfide was carried out in the same manner as in Example 1, except that sulfur (S8) after filtration was not added.

[0084] Example 4 In the experiment to change the conditions for the extraction of lithium sulfide, the amount of thermal reduction product (C-LiS) used was 0.20 kg, the amount of ethanol (EtOH) used was 1.4 L, and the amount of sulfur (S) added after filtration was controlled to 1.0 g.

[0085] <Example 5> The above-mentioned experiment on changing the conditions for extracting lithium sulfide was carried out in the same manner as in Example 1, except that the amount of sulfur (S8) added after filtration was controlled to 0.5 g.

[0086] <Comparative Example 2> The above-mentioned lithium sulfide extraction condition change experiment was carried out in the same manner as in Example 4, except that sulfur (S8) after filtration was not added.

[0087] Table 1 below shows the results of lithium sulfide analysis in an experiment in which the extraction conditions for lithium sulfide were changed, depending on the amount of thermal reduction product (C-LiS), the amount of ethanol (EtOH), and the amount of sulfur (S) added after filtration.

[0088] Specifically, the crystalline phase of the lithium sulfide powder was analyzed using an XRD system manufactured by RIGAKU. The XRD analysis was performed by comparing the intensity of the main diffraction peak of LiS with the intensity of the main diffraction peak of each impurity crystalline phase as a 100% reference. The oxygen content in the powder was measured using an elemental analyzer, an ON836 manufactured by LECO. Specifically, to compare the oxygen distribution, reagent-grade lithium sulfide and lithium oxide powders were placed in a mortar and ground in a weight ratio of 95:5, and the resulting mixture was analyzed using an SEM / EDXS instrument.

[0089] [Table 1]

[0090] Referring to Table 1, it was confirmed that the main impurity in lithium sulfide is lithium oxide (Li2O), and it was confirmed that as the amount of sulfur powder added to the extraction solution increases, the impurity content decreases and the total oxygen content decreases. Figure 1 is a graph showing the change in oxygen content and impurity concentration in lithium sulfide product depending on the amount of sulfur powder added. Referring to Figure 1, by adjusting the number of moles of sulfur added relative to the total number of moles of lithium ions in the extraction solution to a range of 0.01 to 0.04, it was possible to control the oxygen content to 1 to 3 wt%, and the main impurity, lithium oxide, to a range of 2 to 6 wt%.

[0091] However, when sulfur was added in the amount within the above range, the lithium sulfide powder obtained at the final heat treatment had a dark gray or black color, which significantly reduced the value of the product.

[0092] 2a to 2f show the microstructures of lithium sulfide compounds according to examples of the present invention and comparative examples.

[0093] 2a to 2c show the SEM / EDXS analysis results of lithium sulfide of Example 3 prepared according to an embodiment of the present invention, and FIGS. 2d to 2f show the SEM / EDXS analysis results of lithium sulfide prepared according to a comparative example of the present invention, which is a powder prepared by mixing reagent-grade lithium sulfide and lithium oxide in a weight ratio of 95:5.

[0094] 2a to 2f, the lithium sulfide produced by the lithium sulfide production method according to one embodiment has a uniform distribution of oxygen in the microstructure and the degree of agglomeration is measured to be about 10 μm or so. In contrast, in the case of lithium sulfide produced by simple physical mixing, it was confirmed that lithium oxide particles of 50 μm or more were agglomerated.

[0095] Solid electrolyte production and performance testing The solid electrolyte (Li6PS5Cl) was synthesized using a dry milling method. Li2S, P2S5, and LiCl were mixed in a planetary mill at 300 rpm for approximately 8 hours, then pelletized at 300 MPa and heat-treated at 550°C in an Ar atmosphere.

[0096] After producing the solid electrolyte pellets, the positive electrode was attached to the top and the counter electrode (In) to the bottom, and then densified at 500 MPa. After assembling the all-solid-state battery cell, a formation cycle was performed at 0.1 C in a 30°C chamber to measure the ionic conductivity.

[0097] Example 6 In the above-mentioned solid electrolyte manufacturing and performance test, lithium sulfide with an oxygen content of 1.7 wt% was used.

[0098] <Comparative Example 3> In the above-mentioned production and performance test of the solid electrolyte, lithium sulfide with an oxygen content of 3.5 wt% was used.

[0099] <Comparative Example 4> In the above-mentioned production and performance test of the solid electrolyte, reagent-grade lithium sulfide with a purity of 99.9% and an oxygen concentration of 0.7 wt% was used.

[0100] Table 2 below compares the performance of the solid electrolytes prepared in Example 6, Comparative Example 3, and Comparative Example 4. The types of impurities were analyzed by the XRD analysis method described above, and the contents of the impurities were calculated from the oxygen concentration values.

[0101] [Table 2]

[0102] Referring to Table 2, it was confirmed that when the oxygen content is outside the range of the present invention, as in Comparative Example 3, the ionic conductivity of the solid electrolyte is low. However, when a solid electrolyte is prepared using lithium sulfide of the present invention having an oxygen content of 3 wt % or less, as in Example 6, it was confirmed that the ionic conductivity value is almost the same as that of a solid electrolyte prepared using reagent-grade lithium sulfide, as in Comparative Example 3.

[0103] The present invention is not limited to the above-described embodiments and / or examples, but can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains should understand that the present invention can be embodied in other specific forms without changing the technical concept or essential characteristics of the present invention. Therefore, it should be understood that the above-described embodiments and / or examples are illustrative in all respects and are not limiting.

Claims

1. The present invention relates to a lithium sulfide compound for an all-solid-state electrolyte, Lithium oxide (Li ２ O), Lithium sulfide powder having an oxygen content of 3.0% or less.

2. The lithium sulfide powder according to claim 1, which satisfies the following formula 1: <Formula 1> [Li] ２ O] × Oxygen content ≤ 10.0 (In the above formula 1, [Li ２ O] means the intensity ratio [%] of the main XRD diffraction peak)

3. The lithium oxide (Li ２ 2. The lithium sulfide powder according to claim 1, wherein the amount of O is 5.6% or less by weight.

4. The lithium oxide (Li ２ 2. The lithium sulfide powder according to claim 1, wherein the intensity ratio of the XRD main cycle peak of SiO is less than 3%.

5. mixing a carbon source and a lithium compound to produce a lithium-carbon compound; filtering the mixed solution of the lithium-carbon compound and the solvent; and adding sulfur powder to the filtered product, the ratio of the number of moles of sulfur powder added to the number of moles of lithium ions being 0.01 to 0.04, and then heat-treating the resulting mixture; A method for producing lithium sulfide, comprising producing lithium sulfide having an oxygen content of less than 3.5%.

6. The method for producing lithium sulfide according to claim 5, wherein the contents of the lithium-carbon compound and the solvent satisfy the following formula 2: <Formula 2> 0.10≦[lithium-carbon compound] / [solvent]≦0.30 (In the above formula 2, [lithium-carbon compound] and [solvent] mean the content (kg) of lithium-carbon compound and the content (L) of solvent, respectively.)

7. The method for producing lithium sulfide according to claim 6, wherein the formula 2 satisfies 0.14 to 0.

20.

8. The method for producing lithium sulfide according to claim 5, wherein the contents of the lithium-carbon compound and the sulfur powder satisfy the following formula 3: <Formula 3> 10.0≦[lithium sulfide in lithium-carbon compound] / [sulfur powder]≦100.0 (In the above formula 3, [lithium sulfide in lithium-carbon compound] and [sulfur powder] mean the amount (g) of lithium sulfide used in the lithium-carbon compound and the amount (g) of sulfur powder added, respectively.)

9. The method for producing lithium sulfide according to claim 8, wherein the formula 3 satisfies 20.0 to 80.

0.

10. 6. The method for producing lithium sulfide according to claim 5, wherein the step of mixing a carbon raw material and a lithium compound to produce a lithium-carbon compound comprises heat-treating the carbon element and the lithium compound at a temperature in the range of 700 to 900°C.

11. The step of adding sulfur powder to the filtered product, the ratio of the number of moles of sulfur powder added to the number of moles of lithium ions being 0.01 to 0.04, and then heat-treating the filtered product, drying the filtrate; and The method for producing lithium sulfide according to claim 5, further comprising a step of heat-treating the dried product.

12. 6. The method for producing lithium sulfide according to claim 5, wherein the solvent includes at least one of ethanol, methanol, isopropyl alcohol, ethylene glycol, and butyl alcohol.

13. 6. The method for producing lithium sulfide according to claim 5, wherein the flow rate of the inert gas atmosphere in the heat-treating the dried material is 5 to 15 L / min.

14. adding sulfur powder to the filtrate and heat treating the filtrate; 6. The method for producing lithium sulfide according to claim 5, wherein the sulfur powder is added in a ratio of the number of moles of added sulfur powder to the number of moles of lithium ions of 0.012 to 0.037.

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