Preparation method of high-performance lithium sulfide and high-performance lithium sulfide prepared therefrom

Abstract

The present invention relates to a preparation method of lithium sulfide having excellent performance as a solid electrolyte raw material, and lithium sulfide prepared therefrom. Specifically, the present invention relates to: a preparation method of lithium sulfide, comprising adjusting, during preparation of lithium sulfide, the particle size of raw materials and reaction conditions so as to minimize residual impurities in lithium sulfide, and improving the flow characteristics and aggregation characteristics of particles, thereby providing an excellent solid electrolyte raw material; and lithium sulfide.

Description

Method for producing high-performance lithium sulfide and high-performance lithium sulfide produced thereby

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2024-0097431, filed July 23, 2024, the entire disclosure of which is incorporated herein by reference.

[0003]

[0004] The present invention relates to a method for producing lithium sulfide and lithium sulfide produced thereby.

[0005]

[0006] With the recent development of the secondary battery industry, interest in all-solid-state batteries, which offer superior performance and fire safety compared to conventional lithium-ion batteries, is growing. All-solid-state batteries require the use of solid electrolytes instead of liquid ones. Among these, sulfide-based solid electrolytes are recognized for their high ionic conductivity and stability over a wide voltage range compared to other solid electrolytes (oxides, polymers).

[0007]

[0008] Sulfide-based solid electrolytes are generally synthesized using lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), and lithium chloride (LiCl) as raw materials, so research on the production of lithium sulfide (Li2S) is actively being conducted. Lithium sulfide (Li2S) is manufactured by reacting a lithium precursor and a sulfur precursor. Previous research on the production of lithium sulfide has mainly focused on synthesis methods according to the type of raw precursor. Recently, research has been actively conducted on the production of lithium sulfide using lithium hydroxide monohydrate (LiOH H2O) and hydrogen sulfide (H2S) as raw precursors. Most of the synthesis methods proposed are those that synthesize in the presence of a solvent or that flow hydrogen sulfide into solid lithium hydroxide monohydrate.

[0009]

[0010] When synthesizing in the presence of a solvent, impurities may be generated due to residual solvent, so recently, technologies utilizing dry methods that do not use solvents have been intensively studied. For dry synthesis, many technologies have been proposed, the first of which is a technology for producing lithium sulfide using a reactor equipped with a stirrer that mixes solid lithium hydroxide (PCT / JP2015 / 006273, JP2017-116114). In this case, the stirrer alone may not disperse the lithium hydroxide well inside the reactor, making it difficult to remove the moisture generated as a byproduct. The remaining moisture may react with the produced lithium sulfide and be converted back to lithium hydroxide, remaining as an impurity in the product, which may cause particle agglomeration. The second technology proposed is a technology that uses a Rotary Kiln reactor to react lithium hydroxide with hydrogen sulfide while allowing it to flow in the direction of gravity (JP2016-170516, JP2014-007648). However, the structure of this reactor for injecting hydrogen sulfide gas and discharging water as a byproduct is complicated, making it unsuitable for commercial production. Another technology proposed is a technology that produces hydrogen sulfide by reacting sulfur and hydrogen and then reacts it with lithium hydroxide monohydrate (JP2019-059723, JP2016-022946). However, this technology has a problem in that unreacted hydrogen is generated together with hydrogen sulfide due to the use of excessive hydrogen when producing hydrogen sulfide, and the two types of gases must be separated when processing the unreacted gas later. In addition, according to the patent, although the influence of the injected gas flow rate has not been confirmed, if the flow rate is not controlled, the reaction gas flows only to a certain part of the raw material due to the channeling phenomenon, which reduces the uniformity of the reaction, and as a result, an excessive amount of unreacted lithium hydroxide may remain in the lithium sulfide.In addition, the above literature describes the particle size range of the raw material lithium hydroxide as 100 to 1,500 ㎛, so lithium sulfide having a large particle size is synthesized, but this has limitations in that it is outside the range of the recent trend of lithium sulfide micronization.

[0011]

[0012] In general, little research has been conducted on the characteristics of lithium sulfide products. Typically, sulfide-based solid electrolytes are manufactured by mechanically milling lithium sulfide, phosphorus pentasulfide, and lithium chloride. The characteristics of lithium sulfide particles are crucial for the synthesis of high-performance solid electrolytes. Large lithium sulfide particles can exhibit reduced reactivity with other raw materials, potentially leaving unreacted lithium sulfide in the solid electrolyte. Furthermore, if the particles are too small, agglomeration of lithium sulfide particles can occur, resulting in residual moisture between the particles. This moisture can remain even after the surrounding lithium sulfide is converted to lithium hydroxide. Furthermore, using highly agglomerated lithium sulfide as a raw material for solid electrolytes can negatively impact solid electrolyte performance, as it reduces reactivity and leaves unreacted lithium sulfide behind. Therefore, research is needed to develop lithium sulfide with an appropriate particle size and uniform particle distribution.

[0013]

[0014] Meanwhile, residual lithium hydroxide within lithium sulfide can also be problematic. Because lithium hydroxide contains a significant amount of moisture, synthesis may not proceed properly when manufacturing sulfide-based solid electrolytes, which are vulnerable to moisture. Furthermore, residual lithium hydroxide can generate impurities such as Li3PO4.

[0015]

[0016] Accordingly, there is a need for research on the production of lithium sulfide having an appropriate particle size suitable for use as a high-performance solid electrolyte raw material to solve the above-described problems, a uniform particle distribution, and reduced residual impurities.

[0017]

[0018] The present invention relates to a method for producing high-purity lithium sulfide having a uniform particle distribution, no agglomeration, and excellent flowability, and to lithium sulfide produced thereby.

[0019]

[0020] The present invention comprises the steps of recrystallizing lithium hydroxide to obtain lithium hydroxide monohydrate having a uniform particle size; and

[0021] A step of producing lithium sulfide by reacting lithium hydroxide monohydrate and hydrogen sulfide;

[0022] The above recrystallized lithium hydroxide monohydrate has a SPANa value of 10 or less according to the following formula A,

[0023] The above lithium sulfide manufacturing step is carried out in a manner in which the reaction raw material is floated in the reactor by the injection gas containing hydrogen sulfide.

[0024] The flowability of the lithium sulfide measured using a powder characteristic analyzer is 20 mJ / kg or less, and the cohesion is 100 mJ / kg or less.

[0025] Provided is a method for producing lithium sulfide:

[0026] [Formula A]

[0027] SPANa = (D90a-D10a) / D50a

[0028] In the above formula A,

[0029] D90a, D10a and D50a represent the particle sizes at 90%, 10% and 50% points of the cumulative particle volume distribution according to particle size, respectively, when analyzing particle size distribution using laser diffraction for lithium hydroxide monohydrate particles.

[0030]

[0031] In addition, the present invention does not contain a solvent, and has a particle size D50b of 100 ㎛ or less,

[0032] The SPANb value according to the following formula B is 10 or less,

[0033] The content of residual lithium hydroxide (Residue LiOH) in lithium sulfide is 5,000 ppm or less.

[0034] Provides lithium sulfide:

[0035] [Formula B]

[0036] SPANb = (D90b-D10b) / D50b

[0037] In the above formula B,

[0038] D90b, D10b and D50b refer to the particle sizes at 90%, 10% and 50% points of the cumulative particle volume distribution according to particle size, respectively, when analyzing particle size distribution using laser diffraction for lithium sulfide particles.

[0039]

[0040] The method for producing lithium sulfide according to the present invention can block the introduction of additional impurities by not using a solvent, and can provide lithium sulfide having a uniform particle distribution, less agglomeration, and excellent flowability by carrying out the reaction in a floating form of raw lithium hydroxide by controlling the flow rate of the reaction gas and the concentration of hydrogen sulfide.

[0041]

[0042] In addition, the lithium sulfide according to the present invention is a high-purity lithium sulfide having excellent performance as a solid electrolyte raw material, with uniform particle distribution, little agglomeration, excellent flowability, and fundamentally reducing impurities by supplying lithium hydroxide having a uniform particle range and an appropriate particle size through recrystallization pretreatment of raw lithium hydroxide monohydrate, while at the same time having uniform particle distribution.

[0043]

[0044] Figure 1 is a graph showing the XRD analysis results of lithium sulfide of examples and comparative examples.

[0045] Figure 2 is a graph showing the correlation between the SPANb value of manufactured lithium sulfide particles and the content of lithium hydroxide remaining in lithium sulfide (Residue LiOH) through experimental values.

[0046] Figure 3 is a graph showing the contactability (C) of raw materials and the resulting particle homogeneity (H) during the production of lithium sulfide.

[0047]

[0048] In the present invention, terms such as first, second, etc. are used to describe various components, and the terms are used only for the purpose of distinguishing one component from another.

[0049] Additionally, the terms used herein are merely used to describe exemplary embodiments and are not intended to limit the present invention.

[0050] Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0051] In this specification, the terms “comprise,” “include,” or “have” are intended to describe a feature, number, step, component, or combination thereof implemented, but do not exclude the possibility of one or more other features, numbers, steps, components, combinations, or additions thereof.

[0052] Additionally, in this specification, when each layer or element is referred to as being formed “on” or “over” each layer or element, it means that each layer or element is formed directly on each layer or element, or that other layers or elements may be additionally formed between each layer, on the object, or on the substrate.

[0053] The present invention is susceptible to various modifications and takes various forms. Specific embodiments are illustrated and described in detail below. However, this does not limit the invention to a specific disclosed form, but rather encompasses all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0054]

[0055] The terms “D10,” “D50,” and “D90” used in this specification mean particle diameters at the 10%, 50%, and 90% points of the cumulative particle number distribution according to particle diameter, respectively. The D10, D50, and D90 can be measured using a laser diffraction scattering particle size distribution measuring device (PSA).

[0056] Additionally, the SPAN value is calculated using this value to determine particle uniformity. The SPAN value can be calculated as (D90-D10) / D50, with a smaller value indicating more uniform particles.

[0057]

[0058] Hereinafter, the present invention will be described in detail.

[0059]

[0060] (Method for producing lithium sulfide)

[0061] The present invention comprises the steps of recrystallizing lithium hydroxide to obtain lithium hydroxide monohydrate having a uniform particle size; and

[0062] A step of producing lithium sulfide by reacting lithium hydroxide monohydrate and hydrogen sulfide;

[0063] The above recrystallized lithium hydroxide monohydrate has a SPANa value of 10 or less according to the following formula A,

[0064] The above lithium sulfide manufacturing step is carried out in a manner in which the reaction raw material is floated in the reactor by the injection gas containing hydrogen sulfide.

[0065] The flowability of the lithium sulfide measured using a powder characteristic analyzer is 20 mJ / kg or less, and the cohesion is 100 mJ / kg or less.

[0066] Provided is a method for producing lithium sulfide:

[0067] [Formula A]

[0068] SPANa = (D90a-D10a) / D50a

[0069] In the above formula A,

[0070] D90a, D10a and D50a represent the particle sizes at 90%, 10% and 50% points of the cumulative particle volume distribution according to particle size, respectively, when analyzing particle size distribution using laser diffraction for lithium hydroxide monohydrate particles.

[0071]

[0072] Typically, lithium sulfide manufacturing technology involves introducing a lithium precursor, such as lithium hydroxide, into a reactor along with hydrogen sulfide, allowing the reaction to proceed for a set period of time before obtaining the product. Anhydrous lithium hydroxide is typically used to enhance the reactivity of the dried lithium hydroxide precursor. However, anhydrous lithium hydroxide is highly hygroscopic, making it highly susceptible to contamination when exposed to air.

[0073]

[0074] The inventors of the present invention have completed the present invention by confirming that when lithium hydroxide monohydrate, which is a lithium precursor, is recrystallized to remove impurities while producing lithium hydroxide monohydrate having a uniform particle size, and when the space velocity of the injected gas and the concentration of hydrogen sulfide in the injected gas are controlled to improve the reactivity of the raw material, and the reaction proceeds in a form in which the reaction raw material including lithium hydroxide monohydrate floats in the reactor by the injected gas, the particle size distribution of the produced lithium sulfide is uniform, and the flowability and cohesion are excellent, and at the same time, impurities can be reduced. Furthermore, the present invention was able to block the possibility of additional impurities being generated due to the use of a solvent by not using a solvent in the reaction of lithium hydroxide and hydrogen sulfide gas described above.

[0075]

[0076] First, the present invention includes a step of recrystallizing lithium hydroxide to obtain lithium hydroxide monohydrate having a uniform particle size. That is, this step involves recrystallizing a lithium raw material, thereby removing impurities from lithium hydroxide monohydrate, the lithium raw material, while simultaneously producing a uniform particle size for the raw material.

[0077]

[0078] Specifically, the lithium hydroxide recrystallization step may be performed using an aqueous solution of lithium hydroxide monohydrate dissolved in water. At this time, the dissolution temperature of the lithium hydroxide monohydrate may be 60 to 95°C. Preferably, the dissolution temperature may be 65 to 90°C, 70 to 85°C, or 75 to 80°C.

[0079] Next, the temperature of the dissolved lithium hydroxide monohydrate solution is lowered to recrystallize the lithium hydroxide. The recrystallization temperature may be 5 to 50°C. Preferably, it may be 8 to 40°C, or 10 to 35°C. In addition, the recrystallization may be performed for a minimum of 2 hours and a maximum of 10 hours.

[0080]

[0081] In addition, as described above, the particle distribution of the lithium hydroxide raw material can be made uniform through lithium hydroxide recrystallization, and further, the particle size (particle diameter) of lithium hydroxide monohydrate can be controlled by controlling the recrystallization time.

[0082] For example, the particle size D10a of lithium hydroxide monohydrate after recrystallization may be 1 um or more, 2 um or more, or 3 um or more, and 20 um or less, 19 um or less, or 18 um or less.

[0083] Additionally, the particle size D50a may be 3 um or more, 4 um or more, or 5 um or more, and may be 100 um or less, 99 um or less, or 98 um or less.

[0084] Additionally, the particle size D90a may be 20 um or more, 21 um or more, or 22 um or more, and 200 um or less, 199 um or less, or 198 um or less.

[0085]

[0086] In addition, in the method for producing lithium sulfide of the present invention, the recrystallized lithium hydroxide monohydrate has a SPANa value of 10 or less according to the following formula A.

[0087] [Formula A]

[0088] SPANa = (D90a-D10a) / D50a

[0089] In the above formula A,

[0090] D90a, D50a and D10a are as defined above.

[0091]

[0092] When the particle size of lithium hydroxide monohydrate is controlled by performing recrystallization so that the SPANa value defined according to the above formula A becomes 10 or less, and lithium hydroxide monohydrate having a uniform particle size distribution is used as a raw material, the reaction occurs uniformly on the surface of the raw material, and moisture generated as a byproduct can be effectively discharged, so that lithium sulfide having uniform particles can be obtained, and by controlling the reaction conditions in the lithium sulfide production step described below, lithium sulfide having a uniform particle distribution and excellent cohesiveness and flowability can be produced. Preferably, the SPANa value may be 10.0 or less, or 8.0 or less, or 5.0 or less.

[0093]

[0094] Next, the present invention includes a step of producing lithium sulfide by reacting lithium hydroxide monohydrate obtained through the recrystallization with hydrogen sulfide.

[0095]

[0096] Specifically, the step of producing lithium sulfide may first include a step of producing hydrogen sulfide. The hydrogen sulfide is produced by reacting solid sulfur with hydrogen gas in the presence of a catalyst, and the molar ratio of the hydrogen gas to the solid sulfur may be 1:1 to 1:10.

[0097]

[0098] More specifically, solid sulfur can be dissolved in a solvent and then reacted with hydrogen gas in the presence of a catalyst to produce hydrogen sulfide (H2S). At this time, the solvent that can be used is not particularly limited, but may be an aromatic solvent, and more specifically, metal naphthalene, toluene, xylene, etc. can be mentioned.

[0099]

[0100] In addition, the above hydrogen sulfide production is carried out under temperature conditions of 170 to 240 ℃ and 10 to 20 kg / cm 2It can be carried out under the pressure conditions of. When the reaction is carried out under the said temperature and pressure conditions, high purity hydrogen sulfide can be produced while reducing the amount of hydrogen gas used. More preferably, the hydrogen sulfide production can be carried out at a temperature of 170 ℃ or higher, 180 ℃ or higher, or 190 ℃ or higher, and 240 ℃ or lower, 230 ℃ or lower, or 220 ℃ or lower, and 11 to 17 kg / cm 2 , or 13 to 16 kg / cm 2 can proceed under the pressure of.

[0101]

[0102] Additionally, the molar ratio of the hydrogen gas to the solid sulfur may be 1:1 to 1:10, 1:2 to 1:9, or 1:2 to 1:8. If hydrogen gas is used in greater amounts than solid sulfur, hydrogen sulfide as a product and unreacted hydrogen gas may be generated together, and an additional process for separating the two gases may be required. Additionally, if excessive amounts of solid sulfur are used, the reactivity may be reduced, resulting in an excessively long hydrogen sulfide production time.

[0103]

[0104] In addition, the above hydrogen sulfide production is carried out in the presence of a catalyst. At this time, as catalysts that can be used, Ni-Mo catalyst, Co-Mo catalyst, Ni catalyst, Pd catalyst, Activated Alumina catalyst, Ag-Supported Active Carbon catalyst, etc. can be used.

[0105]

[0106] Through the above-described series of steps, it is possible to manufacture high-purity hydrogen sulfide and reduce the production of additional impurities.

[0107]

[0108] Next, the present invention produces lithium sulfide by reacting recrystallized lithium hydroxide monohydrate with hydrogen sulfide. The reaction between lithium hydroxide monohydrate and hydrogen sulfide is a dry reaction, which is a non-solvent reaction that does not use a separate solvent. In the present invention, the lithium sulfide production step is carried out in a form where the raw material floats in the reactor by an injection gas containing hydrogen sulfide.

[0109]

[0110] Meanwhile, if necessary, a step of drying lithium hydroxide monohydrate prior to the reaction may be further included. That is, in the presence of an inert gas, the recrystallized lithium hydroxide monohydrate may be dried at a temperature of 170 to 450°C for 4 to 10 hours to convert it to an anhydrous form and then used.

[0111]

[0112] According to one embodiment of the present invention, the reaction for producing lithium sulfide may be carried out at a temperature of 120°C to 450°C. Preferably, the reaction may be carried out at a temperature of 150 to 400°C, 170 to 350°C, or 180 to 300°C. If the reaction is carried out at a temperature lower than 120°C, moisture generated as a byproduct may not vaporize but remain in a liquid form inside the reactor, making it difficult to remove the moisture. In addition, if the reaction is carried out at a temperature exceeding 450°C, the process efficiency may be reduced. In addition, if the reaction temperature approaches the melting point (462°C) of lithium hydroxide, which is a raw material, the raw material may not float well due to the reaction gas, which may reduce the reactivity.

[0113]

[0114] Meanwhile, in the reaction of lithium hydroxide monohydrate and hydrogen sulfide, the molar ratio of lithium hydroxide monohydrate to hydrogen sulfide may be 1:1 or more and 1:15 or less, and preferably, 1:2 or more and 1:14 or less, or 1:4 or more and 1:12 or less. If the molar ratio of hydrogen sulfide to lithium hydroxide monohydrate is less than 1:1, the reactivity of hydrogen sulfide and lithium hydroxide raw materials is low, so the reaction time may be prolonged and the process efficiency may decrease. If it exceeds 1:15, the reaction may proceed rapidly due to the injection of excessive hydrogen sulfide, so that the discharge of moisture generated as a byproduct may not be smooth, and the residual moisture inside the reactor may convert lithium sulfide to lithium hydroxide, thereby increasing the impurity content, and the cohesiveness of lithium sulfide may increase, so that the flowability may decrease.

[0115]

[0116] Meanwhile, hydrogen sulfide is introduced into the reactor mixed with an inert gas, and the reaction proceeds by contacting the hydrogen sulfide gas with lithium hydroxide monohydrate, a reaction raw material in the reactor, in a floating form. At this time, the space velocity of the injected gas relative to the reactor size is 3.0 hr. -1 6.0 hr -1 It can be, and preferably 3.0 hr -1 5.5 hr -1 It could be.

[0117]

[0118] In addition, the concentration of hydrogen sulfide in the injected gas may be 2.0 vol.% to 30.0 vol.%, or 2.0 vol.% to 25.0 vol.%, and more preferably 2.5 vol.% to 20 vol.%. If the concentration of hydrogen sulfide in the entire injected gas is less than 2.0 vol.%, the reactivity is lowered, so that the content of lithium hydroxide remaining in the lithium sulfide increases, and if it exceeds 30.0 vol.%, the reaction occurs rapidly, making it difficult to discharge moisture generated as a by-product, so that agglomeration occurs between particles due to moisture remaining inside the reactor, and the residual moisture is converted into lithium hydroxide due to a reverse reaction between the residual moisture and the surrounding lithium sulfide, so that the content of lithium hydroxide in the lithium sulfide increases.

[0119]

[0120] Meanwhile, according to the lithium sulfide manufacturing method of the present invention described above, as the SPAN value (SPANb) of the manufactured lithium sulfide increases, the particles become non-uniform, and the residual lithium hydroxide content also increases. According to one embodiment of the present invention, the following equation 1 can be satisfied:

[0121] [Formula 1]

[0122] 702.81·(SPANb) 0.57 -1700 ≤ Residue LiOH ≤ 702.81·(SPANb) 0.57 +2600

[0123] In the above equation 1,

[0124] Residue LiOH is the content of lithium hydroxide remaining in lithium sulfide (ppm), which is less than 5,000 (ppm).

[0125] SPANb is the SPAN value of lithium sulfide, according to the following formula B, but is 10 or less,

[0126] [Formula B]

[0127] SPANb = (D90b-D10b) / D50b

[0128] In the above formula B,

[0129] D90b, D10b and D50b refer to the particle sizes at 90%, 10% and 50% points of the cumulative particle volume distribution according to particle size, respectively, when analyzing particle size distribution using laser diffraction for lithium sulfide particles.

[0130]

[0131] When the correlation between the SPAN value of lithium sulfide particles in the range of 10 or less and the content of lithium hydroxide (Redidue LiOH) remaining in lithium sulfide in the range of 5,000 ppm or less satisfies Equation 1, lithium sulfide having uniform particles, low cohesion, and excellent flowability can be synthesized. The relationship between the SPAN value of the lithium sulfide particles and the content of lithium hydroxide remaining in lithium sulfide is shown in Figure 2 below.

[0132]

[0133] Meanwhile, in the above formula 1, Residue LiOH is the content of lithium hydroxide remaining in lithium sulfide, which can be measured using IC (Ion Chromatography). When the content of unreacted lithium hydroxide in lithium sulfide is 5,000 ppm or less, more preferably 4,500 ppm or less, it can be determined that high-performance lithium sulfide has been produced.

[0134]

[0135] Figure 2 is a graph showing the results of an experiment conducted while changing the conditions for the reaction gas, and it was confirmed that the residual lithium hydroxide content tends to increase as SPANb increases in the range of 10 or less. If a trend line is drawn for this trend, (Residue LiOH) = 702.81·(SPANb) 0.57The formula for the form can be derived, and the section containing most of the lithium sulfide exhibiting excellent properties obtained through experiments is expressed as Equation 1. Through this, the inventors were able to determine that a causal relationship between the main particle characteristics of lithium sulfide and the conditional factors of the reaction gas in the manufacturing method of the present invention appears.

[0136]

[0137] In addition, according to one embodiment of the present invention, in the lithium sulfide production step, the lithium sulfide particle characteristic value H according to the following formula 2 may be 2.4 or less:

[0138] [Formula 2]

[0139] H =

[0140] In the above equation 2,

[0141] Residue LiOH is the content of lithium hydroxide remaining in lithium sulfide (ppm),

[0142] SPANb is the SPAN value of lithium sulfide, according to the following formula B, but is 10 or less,

[0143] [Formula B]

[0144] SPANb = (D90b-D10b) / D50b

[0145] In the above formula B,

[0146] D90b, D10b and D50b refer to the particle sizes at 90%, 10% and 50% points of the cumulative particle volume distribution according to particle size, respectively, when analyzing particle size distribution using laser diffraction for lithium sulfide particles.

[0147]

[0148] The lithium sulfide particle characteristic value H according to Equation 1 of the present invention is a measure representing the homogeneity of lithium sulfide particles, and is a formula that expresses the relationship between the particle size distribution (SPANb) of the manufactured lithium sulfide and the content of lithium hydroxide (Residue LiOH) remaining in the lithium sulfide. That is, the inventors of the present invention confirmed that lithium sulfide having excellent physical properties can be manufactured by controlling the content of lithium hydroxide and the particle size distribution of lithium sulfide so that the H value is 2.4 or less. When the H value exceeds 2.4, the amount of residual lithium hydroxide in the manufactured lithium sulfide excessively increases compared to the SPAN value of the manufactured lithium sulfide, which increases the impurity content, which may cause unreacted residues to be generated during the synthesis of a solid electrolyte, and the particle size distribution may become uneven due to the hygroscopicity and cohesiveness of lithium hydroxide itself. Meanwhile, there is no special limitation on the lower limit of the above H value, and when the content of lithium hydroxide remaining in lithium sulfide is 0, the H value according to the above formula 1 may be 0.

[0149]

[0150] Additionally, the D50 (D50b) of the manufactured lithium sulfide may be 1 um or more, 2 um or more, or 3 um or more, and may be 100 um or less, 99 um or less, or 98 um or less.

[0151]

[0152] In addition, in the lithium sulfide production reaction, the gas flow rate injected into the reactor along with the concentration of hydrogen sulfide may also affect the contact between lithium hydroxide and hydrogen sulfide. That is, the space velocity of the injected gas and the concentration of hydrogen sulfide in the injected gas may affect the content of lithium hydroxide remaining in the lithium sulfide, which may in turn affect the particle characteristics of the lithium sulfide.

[0153]

[0154] In addition, preferably, the method for producing lithium sulfide of the present invention can satisfy the following formula 3:

[0155] [Formula 3]

[0156] -1.57·C + 4.54 ≤ H ≤ -1.58·C + 8.8

[0157] In the above equation 3,

[0158] H is as defined above,

[0159] C is a value according to the following equation 4,

[0160] [Formula 4]

[0161] C = C H2S / Sv

[0162] C H2S is the concentration of hydrogen sulfide in the injected gas (vol.%),

[0163] Sv is the space velocity of the injected gas (h -1 )am.

[0164]

[0165] The inventors of the present invention defined the C value as a value of the concentration of hydrogen sulfide in the injected gas based on the space velocity of the injected gas described above, as in Equation 4. The C value according to Equation 4 is a parameter related to the injected gas conditions and can be interpreted as meaning the contactability of the raw material.

[0166]

[0167] The inventors of the present invention have conducted research on the correlation between the C value according to the above equation 4, which indicates the contactability of raw materials, and the H value according to the equation 2, which is related to the homogeneity of lithium sulfide particles, and the correlation of the H value according to the above C value is shown in Fig. 3. Based on Fig. 3, when the experimental values ​​were graphed for contactability (C) and homogeneity (H), it was possible to limit the section where the experimental results with excellent H values ​​were concentrated.

[0168] That is, when the space velocity of the injection gas and the concentration of hydrogen sulfide in the injection gas are controlled so as to satisfy the above equation 3 while the H value according to the above equation 2 is in the range of 2.4 or less, lithium sulfide having uniform particles, low cohesion, and excellent flowability can be produced.

[0169]

[0170] Based on the relationship between the H value and the C value defined by the above equation 3, when -1.57·C + 4.54 > H, the concentration of hydrogen sulfide becomes significantly smaller than the total flow rate, which may cause an excess of unreacted lithium hydroxide to remain, and may have a negative effect on the characteristics of lithium sulfide particles, such as increased cohesion. Based on the relationship between the H value and the C value defined by the above equation 3, when H > -1.58·C + 8.8, the concentration of hydrogen sulfide becomes excessively high compared to the total flow rate, which may cause insufficient time for the by-product moisture to escape to the outside of the reactor, which may increase the residual moisture content in the lithium sulfide. When the residual moisture content increases, lithium sulfide is converted to lithium hydroxide through a reverse reaction, which increases the content of residual lithium hydroxide and increases particle cohesion, which may have a negative effect on the characteristics of lithium sulfide. As a result of analyzing the experimental data due to this phenomenon, a graph of the form shown in Fig. 3 was drawn, and the above equation 3 was derived by considering the homogeneity, cohesion, and flowability of the lithium sulfide manufactured through this.

[0171]

[0172] Meanwhile, the lithium sulfide manufacturing method of the present invention can proceed while removing moisture during the lithium sulfide manufacturing step, and the reaction can proceed until moisture is no longer generated. As such, techniques widely known in the art can be utilized as a method for removing moisture during the reaction step, and specifically, removal can be achieved using a condenser or the like. If moisture is not removed effectively, residual moisture and lithium hydroxide will be generated within the lithium sulfide, which will adversely affect the cohesiveness and flowability of the lithium sulfide.

[0173]

[0174] Titration can be used to analyze the residual moisture in the lithium sulfide manufactured above, and the residual moisture content in the lithium sulfide can be 500 ppm or less, preferably 350 ppm or less.

[0175]

[0176] The lithium sulfide manufacturing method of the present invention described above has a flowability of 20 mJ / kg or less and a cohesiveness of 100 mJ / kg or less, as measured using a powder characteristic analyzer.

[0177] Flowability is a measurement of the potential energy of the powder when the powder rotates. A smaller value indicates higher flowability. Generally, flowability of 20 mJ / kg or less is considered to be very excellent. The lithium sulfide manufactured according to the manufacturing method of the present invention may have a flowability of 20 mJ / kg or less, preferably 19 mJ / kg or less, 18 mJ / kg or less, 17 mJ / kg or less, 16 mJ / kg or less, or 15 mJ / kg or less. The lower limit of the flowability is not particularly limited, but may be 1 mJ / kg or more, 3 mJ / kg or more, 5 mJ / kg or more, or 10 mJ / kg or more.

[0178] Cohesion is a numerical expression of the force of interaction between a flowing powder and a stationary powder during powder rotation, and a smaller numerical value indicates lower cohesion. Typically, cohesion is considered excellent when it is 100 mJ / kg or less. The lithium sulfide manufactured according to the manufacturing method of the present invention has a cohesion of 100 mJ / kg or less, and preferably, 90 mJ / kg or less, 80 mJ / kg or less, 70 mJ / kg or less, or 60 mJ / kg or less. The lower limit of the cohesion is not particularly limited, but may be 1 mJ / kg or more, 5 mJ / kg or more, 10 mJ / kg or more, or 15 mJ / kg or more.

[0179] The method for measuring cohesion and flowability using the above powder characteristic analyzer can be specified in the examples described below.

[0180]

[0181] Meanwhile, there is no particular limitation on the form of the reactor used in the production of lithium sulfide according to the present invention. A batch reactor, a semi-batch reactor, a flow reactor, a fluidized bed reactor, etc. may be used, as long as the reactor can continuously inject reaction gases and continuously discharge moisture-containing gases from the reactor after the reaction, and the raw materials can be evenly dispersed and floated to ensure a uniform reaction.

[0182]

[0183] (lithium sulfide)

[0184] In addition, the present invention provides lithium sulfide which does not contain a solvent, has a particle size D50b of 100 μm or less, a SPANb value according to the following formula B of 10 or less, and a lithium hydroxide content remaining in the lithium sulfide (Residue LiOH) of 5,000 ppm or less:

[0185] [Formula B]

[0186] SPANb = (D90b-D10b) / D50b

[0187] In the above formula B,

[0188] D90b, D10b and D50b refer to the particle sizes at 90%, 10% and 50% points of the cumulative particle volume distribution according to particle size, respectively, when analyzing particle size distribution using laser diffraction for lithium sulfide particles.

[0189]

[0190] In addition, the lithium sulfide of the present invention can satisfy the following equation 1:

[0191] [Formula 1]

[0192] 702.81·(SPANb) 0.57 -1700 ≤ Residue LiOH ≤ 702.81·(SPANb) 0.57 +2600

[0193] In the above equation 1,

[0194] Residue LiOH is the content of lithium hydroxide remaining in lithium sulfide (ppm),

[0195] SPANb is as defined above.

[0196]

[0197] In addition, the lithium sulfide of the present invention may have a lithium sulfide particle characteristic value H according to the following formula 2 of 2.4 or less:

[0198] [Formula 2]

[0199] H =

[0200] In the above equation 2,

[0201] Residue LiOH is the content of lithium hydroxide remaining in lithium sulfide (ppm),

[0202] SPANb is as defined above.

[0203]

[0204] The description of the particle size (D10, D50 and D90), SPAN value, residual lithium hydroxide content in lithium sulfide (Residue LiOH) and their correlations is given above.

[0205]

[0206] Additionally, the lithium sulfide of the present invention may have a residual moisture content of 500 ppm or less, or preferably 350 ppm or less.

[0207]

[0208] In addition, the lithium sulfide of the present invention may have a flowability of 20 mJ / kg or less and a cohesiveness of 100 mJ / kg or less as measured using a powder characteristic analyzer. Preferably, the flowability may be 19 mJ / kg or less, 18 mJ / kg or less, 17 mJ / kg or less, 16 mJ / kg or less, or 15 mJ / kg or less. The lower limit of the flowability is not particularly limited, but may be 1 mJ / kg or more, 3 mJ / kg or more, 5 mJ / kg or more, or 10 mJ / kg or more.

[0209] Also, preferably, the cohesiveness may be 90 mJ / kg or less, 80 mJ / kg or less, 70 mJ / kg or less, or 60 mJ / kg or less. The lower limit of the cohesiveness is not particularly limited, but may be 1 mJ / kg or more, 5 mJ / kg or more, 10 mJ / kg or more, or 15 mJ / kg or more.

[0210]

[0211] In addition, the lithium sulfide of the present invention has uniform particles and appropriate flowability and cohesion, so that it can achieve excellent performance when manufacturing a solid electrolyte material.

[0212] Specifically, the solid electrolyte material manufactured by mixing lithium sulfide, phosphorus pentasulfide, and lithium of the present invention has a high possibility of being used as an all-solid-state battery, as measured by an ionic conductivity of 1.0 mS / cm or more, 1.2 mS / cm or more, or 1.5 mS / cm or more.

[0213]

[0214] Hereinafter, the functions and effects of the invention will be described in more detail through specific examples. However, these examples are provided merely as examples of the invention and do not define the scope of the invention.

[0215]

[0216] [Example]

[0217] Manufacturing example

[0218] Production of hydrogen sulfide (H2S)

[0219] Solid sulfur was dissolved in methyl naphthalene solvent. After charging the Ni-Mo catalyst (90 mL), the reaction solution was pumped into the reactor heated to 200°C, and hydrogen gas was simultaneously injected so that the mole ratio of H2:S = 1:2. Afterwards, 15 kg / cm 2 The reaction was carried out under pressure for 1 hour to obtain 99.9% pure H2S gas.

[0220]

[0221] Example 1-1

[0222] Recrystallization of lithium hydroxide monohydrate

[0223] 254 g of lithium hydroxide monohydrate (LiOH·H2O, D50: 82.1 um, SPAN: 15.3) was placed in a recrystallization reactor, 1 L of water was added, and the temperature was raised to 80°C to completely dissolve. The temperature was lowered to 15°C to recrystallize the completely dissolved lithium hydroxide. After the reactor temperature reached 15°C, the temperature was maintained for 3 hours to grow lithium hydroxide crystals. Thereafter, the lithium hydroxide crystals and moisture were separated, and the crystals were dried to obtain purified lithium hydroxide monohydrate (LiOH·H2O).

[0224]

[0225] Production of lithium sulfide (Li2S)

[0226] After introducing the purified lithium hydroxide monohydrate (LiOH H2O) into the reactor, the temperature was raised to 200°C in a N2 atmosphere and dried for 6 hours to obtain lithium hydroxide anhydrous (LiOH). After that, the hydrogen sulfide (H2S) produced in the manufacturing example was introduced into the reactor containing the anhydrous lithium hydroxide by mixing it with an inert gas (N2). At this time, the molar ratio of lithium hydroxide and hydrogen sulfide was 1:4, and the space velocity of the total injected gas was 3.0 hr. -1 , the concentration of hydrogen sulfide in the total injected gas was 10.0 vol.%. Thereafter, the reaction was carried out at a reaction temperature of 230°C. The mixed gas of moisture and hydrogen sulfide coming out from the upper part of the reactor was separated through a condenser, and the hydrogen sulfide from which moisture had been removed was injected back into the reactor. The reaction was carried out until no more moisture was generated, thereby producing lithium sulfide.

[0227]

[0228] Example 1-2

[0229] When manufacturing lithium sulfide, the space velocity of the entire injected gas is 5.0 hr -1 Lithium sulfide was prepared in the same manner as in Example 1-1, except that the concentration of hydrogen sulfide in the entire injected gas was changed to 20.0 vol.%.

[0230]

[0231] Example 2-1

[0232] Lithium sulfide was prepared in the same manner as in Example 1-1, except that the recrystallization time was changed to 6 hours during the recrystallization of lithium hydroxide monohydrate.

[0233]

[0234] Example 2-2

[0235] When manufacturing lithium sulfide, the space velocity of the entire injected gas is 5.0 hr -1Lithium sulfide was prepared in the same manner as in Example 2-1, except that the concentration of hydrogen sulfide in the entire injected gas was changed to 20.0 vol.%.

[0236]

[0237] Example 3-1

[0238] Lithium sulfide was prepared in the same manner as in Example 1-1, except that the recrystallization time was changed to 9 hours during the recrystallization of lithium hydroxide monohydrate.

[0239]

[0240] Example 3-2

[0241] When manufacturing lithium sulfide, the space velocity of the entire injected gas is 5.0 hr -1 Lithium sulfide was prepared in the same manner as in Example 3-1, except that the concentration of hydrogen sulfide in the entire injected gas was changed to 20.0 vol.%.

[0242]

[0243] Example 4

[0244] When manufacturing lithium sulfide, the space velocity of the entire injection gas is 3.6 hr -1 Lithium sulfide was prepared in the same manner as in Example 2-1, except that the concentration of hydrogen sulfide in the entire injected gas was changed to 7.5 vol%.

[0245]

[0246] Example 5

[0247] When manufacturing lithium sulfide, the space velocity of the entire injection gas is 3.6 hr -1 Lithium sulfide was manufactured in the same manner as in Example 2-1, except that the concentration of hydrogen sulfide in the entire injected gas was changed to 8.6 vol%.

[0248]

[0249] Example 6

[0250] In the production of lithium sulfide, the space velocity of the entire injected gas is 5.7 hr -1Lithium sulfide was prepared in the same manner as in Example 3-1, except that the concentration of hydrogen sulfide in the total injected gas was changed to 21.0 vol.%.

[0251]

[0252] Example 7

[0253] In the production of lithium sulfide, the space velocity of the entire injected gas is 5.7 hr -1 Lithium sulfide was prepared in the same manner as in Example 3-1, except that the concentration of hydrogen sulfide in the entire injected gas was changed to 30.0 vol.%.

[0254]

[0255] Comparative Example 1

[0256] When manufacturing lithium sulfide, the space velocity of the entire injected gas is 5.0 hr -1 Lithium sulfide was prepared in the same manner as in Example 2-1, except that the concentration of hydrogen sulfide in the entire injected gas was changed to 1.0 vol.%.

[0257]

[0258] Comparative Example 2

[0259] When manufacturing lithium sulfide, the space velocity of the entire injected gas is 5.0 hr -1 Lithium sulfide was prepared in the same manner as in Example 2-1, except that the concentration of hydrogen sulfide in the entire injected gas was changed to 50.0 vol.%.

[0260]

[0261] Comparative Example 3

[0262] When manufacturing lithium sulfide, the space velocity of the entire injected gas is 8.0 hr -1 Lithium sulfide was prepared in the same manner as in Example 3-1, except that the concentration of hydrogen sulfide in the entire injected gas was changed to 28 vol.%.

[0263]

[0264] Comparative Example 4

[0265] In the production of lithium sulfide, the space velocity of the entire injected gas is 7.5 hr -1 Lithium sulfide was prepared in the same manner as in Example 3-1, except that the concentration of hydrogen sulfide in the total injected gas was changed to 26.5 vol.%.

[0266]

[0267] Comparative Example 5

[0268] Lithium hydroxide monohydrate (LiOH H2O) that had not undergone recrystallization was introduced into a reactor, heated to 200°C in a N2 atmosphere, and dried for 6 hours to obtain lithium hydroxide anhydrous (LiOH). After that, hydrogen sulfide (H2S) produced in the manufacturing example was introduced into the reactor containing anhydrous lithium hydroxide by mixing it with an inert gas (N2). At this time, the molar ratio of lithium hydroxide and hydrogen sulfide was 1:4, and the space velocity of the total injected gas was 5.0 hr. -1 , the concentration of hydrogen sulfide in the total injected gas was 20.0 vol.%. Thereafter, the reaction was carried out at a reaction temperature of 230°C. The mixed gas of moisture and hydrogen sulfide coming out from the upper part of the reactor was separated through a condenser, and the hydrogen sulfide from which moisture had been removed was injected back into the reactor. The reaction was carried out until moisture was no longer generated, thereby producing lithium sulfide.

[0269]

[0270] The manufacturing conditions of the above examples and comparative examples are summarized in Table 1 below.

[0271]

[0272] Recrystallization timeTotal injected gas space velocity (hr) -1) Concentration of hydrogen sulfide in the total injected gas (vol.%) Example 1-133.010.0 Example 1-235.020.0 Example 2-163.010.0 Example 2-265.020.0 Example 3-193.010.0 Example 3-295.020.0 Example 463.67.5 Example 563.68.6 Example 695.721.0 Example 795.730.0 Example 895.716.5 Comparative Example 165.01.0 Comparative Example 265.050.0 Comparative Example 398.028.0 Comparative Example 497.024.5 Comparative Example 5X5.020.0

[0273] [Experimental Example]

[0274] (1) X-ray diffraction analysis

[0275] Using XRD, an instrument that analyzes the diffraction phenomenon of X-rays passing through the crystal lattice of lithium sulfide manufactured in the examples and comparative examples, it was confirmed that lithium sulfide was produced. The results of the XRD analysis are shown in Fig. 1.

[0276]

[0277] (2) Particle size measurement

[0278] For lithium sulfide manufactured in the examples and comparative examples, a laser diffraction particle size analyzer was used to derive D10, D50 and D90 based on volume through particle size analysis after sample introduction, and the SPAN values ​​of lithium hydroxide and lithium sulfide were calculated according to the following equations A and B.

[0279] [Formula A]

[0280] SPANa = (D90a-D10a) / D50a

[0281] In the above formula A,

[0282] D90a, D10a and D50a represent the particle sizes at 90%, 10% and 50% of the cumulative particle volume distribution according to particle size, respectively, when analyzing particle size distribution using laser diffraction for lithium hydroxide monohydrate particles.

[0283] [Formula B]

[0284] SPANb = (D90b-D10b) / D50b

[0285] In the above formula B,

[0286] D90b, D10b and D50b refer to the particle sizes at 90%, 10% and 50% points of the cumulative particle volume distribution according to particle size, respectively, when analyzing particle size distribution using laser diffraction for lithium sulfide particles.

[0287]

[0288] (3) Measurement of impurity content

[0289] The residual moisture in the lithium sulfide manufactured in the above examples and comparative examples was measured using the Karl Fisher moisture titration method, which is a method of measuring the potential difference that changes according to the amount of residual moisture.

[0290] In addition, the content of residual lithium hydroxide (Residue LiOH) in the lithium sulfide manufactured in the above examples and comparative examples was measured based on the mass of lithium sulfide using ion chromatography, which can measure the content of a substance according to ion affinity.

[0291]

[0292] (4) Evaluation of H value (homogeneity), C value (contactability) and performance excellence

[0293] The H value for lithium sulfide manufactured in the examples and comparative examples was calculated according to the following equation 1.

[0294] [Formula 2]

[0295] H =

[0296] In the above equation 2,

[0297] Residue LiOH is the content of lithium hydroxide remaining in lithium sulfide (ppm),

[0298] SPANb is the SPAN value of lithium sulfide as previously defined.

[0299]

[0300] Additionally, the performance excellence was evaluated based on whether the following equation 3 was satisfied in the range of H values ​​of 2.4 or less.

[0301] [Formula 3]

[0302] -1.57·C + 4.54 ≤ H ≤ -1.58·C + 8.8

[0303] In the above equation 3,

[0304] H is as defined above,

[0305] C is a value according to the following equation 4,

[0306] [Formula 4]

[0307] C = C H2S / Sv

[0308] C H2S is the concentration of hydrogen sulfide in the injected gas (vol.%),

[0309] Sv is the space velocity of the injected gas (h -1 )am.

[0310]

[0311] (5) Flow and cohesion

[0312] The powder flow characteristics were measured using a powder characteristic analysis device capable of analyzing and quantifying the flow characteristics of powder in a fluid state and measuring in a sealed, moisture-proof environment. Powder was placed inside a rotating drum, and the powder simultaneously rose and fell along the drum surface. The difference in potential energy was measured to derive the flow characteristics. The cohesiveness was derived by measuring the interaction force between the powder when stationary and when flowing. After a total of 100 measurements, the standard deviations of the flow characteristics and cohesiveness were calculated.

[0313]

[0314] After recrystallization, lithium hydroxide monohydrate information product lithium sulfide information particle size (D50, um) SPAN a Residue LiOH (ppm) moisture content (ppm) particle size (D50, um) SPAN b Example 1-1 3.8 6.11, 96 2 3 0 4 3.5 5.9 Example 1-2 4.15 4 1, 8 1 2 2 8 14.25.2 Example 2-1 1 3.3 5.31, 6 1 2 2 7 8 12.25.1 Example 2-2 1 3.6 5.81, 6 8 9 2 5 3 13.15.5 Example 3-1 1 8.9 5 1, 7 5 8 2 1 2 1 8.24.7 Example 3-2 2 0.24.8 1, 8 2 0 2 0 8 19.14.6 Example 415.69.3312322114.59Example 514.86.9158721413.66.3Example 630.22.6223021722.12.1Example 722.57.698722521.57.2Example 823.25.7423120922.85.09Comparative Example 113.15.67,62488212.65.2Comparative Example 215.712.19,82199215.311.7Comparative Example 320.57.2687279820.16.83Comparative Example 419.79.2598278218.98.89Comparative Example 582.113.29,9918128013.2

[0315] Residue LiOH (ppm) Moisture content (ppm) Contact (C) Homogeneity (H) Performance excellence Flowability (mJ / kg) Cohesion (mJ / kg) Example 1-1 196 230 43.33 1.015 O 13.89 65.66 Example 1-2 18 12 2 8 14.00 1.007 O 13.2 15 8.47 Example 2-1 16 12 2 7 8 3.33 0.906 O 11.81 48.53 Example 2-2 16 8 9 2 5 34.00 0.909 O 12.35 52.27 Example 3-1 17 5 8 2 1 2 3.33 1.035 O 11.62 29.87 Example 3-218202084.001.085O10.8333.09Example 431232212.081.270O10.9835.21Example 515872142.390.791O11.3234.32Example 622302173.682.079O10.8234.82Example 79872255.260.456O11.5231.23Example 842312092.892.381O10.8832.56Comparative Example 175248820.204.183X22.3105.27Comparative Example 298219927.003.439X25.82106.18Comparative example 368727983.503.271X23.4103.13Comparative example 459827823.502.450X21.3103.25Comparative example 599918124.003.266X32.3112.02

[0316] (6) Solid electrolyte ionic conductivity

[0317] Solid electrolyte performance evaluation was conducted using lithium sulfide manufactured in the above examples and comparative examples.

[0318] Specifically, lithium sulfide (Li2S), phosphorus pentasulfide (P2S5, Sigma Aldrich), and lithium chloride (LiCl, Sigma Aldrich) manufactured in the examples and comparative examples were mixed in a molar ratio of 5:1:2, and milled at 400 rpm for 80 minutes. Thereafter, the mixed raw materials were pelletized using a hydraulic press and heat-treated at 550 ℃ for 6 hours. The heat-treated pellets were ground and then sieved (with a 53 μm sieving sieve) to obtain a solid electrolyte with a particle size of 50 μm or less, and the ionic conductivity was measured using a potentiostat device that can induce an electrochemical reaction by applying a constant voltage or current.

[0319]

[0320] Ionic Conductivity Example 1-11.76 Example 1-21.74 Example 2-11.79 Example 2-21.89 Example 3-11.68 Example 3-21.59 Example 41.58 Example 51.59 Example 61.61 Example 71.66 Example 81.69 Comparative Example 10.76 Comparative Example 20.92 Comparative Example 30.89 Comparative Example 40.95 Comparative Example 90.88

[0321] As can be confirmed from Tables 2 and 3 above, according to the method for producing lithium sulfide of the present invention, it was confirmed that by controlling the raw material recrystallization and reaction conditions, the SPAN value of lithium sulfide becomes smaller, the particles become uniform, and the particle size can be controlled according to the recrystallization time. In addition, when the H value according to Equation 1 of the present invention is 2.4 or less and the relationship of Equation 2 is satisfied, it was confirmed that lithium sulfide with excellent performance was produced, with flowability and cohesion of 20 mJ / kg or less and 80 mJ / kg or less, respectively, and a moisture content of 500 ppm or less. As can be confirmed from Table 4 above, it was confirmed that the solid electrolyte ionic conductivity also shows a range in which a battery can be operated, with 1.0 mS / cm or more.

[0322]

[0323] On the other hand, in the case of Comparative Example 1, the concentration of hydrogen sulfide in the reaction gas was too low, so the SPAN value was similar to that of the example, but the lithium hydroxide content was somewhat increased due to the unreacted raw material, so it was confirmed that the flowability and cohesion were high. In addition, in the case of Comparative Example 2, it was confirmed that the reaction occurred rapidly due to the excessive amount of hydrogen sulfide being added, so that moisture could not escape well, so that lithium sulfide was converted to lithium hydroxide, and the lithium hydroxide content increased, and accordingly, the moisture content increased. In addition, it was confirmed that as the moisture content increased, the cohesion phenomenon between particles occurred, so the SPAN value also increased somewhat.

[0324] In the case of Comparative Examples 3 and 4, it was confirmed that the overall gas injection speed was too fast, so the raw material could not be evenly suspended, and the gas was discharged out of the reactor before the reaction progressed sufficiently, resulting in an increase in the content of unreacted lithium hydroxide.

[0325] In addition, in the case of Comparative Example 5, since recrystallization was not performed, the particle size was large and uneven, which lowered the reactivity of the raw material, and moisture could not escape smoothly, so the lithium hydroxide content increased, and accordingly, the moisture content was confirmed to increase.

[0326] Accordingly, the lithium sulfides of Comparative Examples 1 to 5 did not satisfy the relationship between homogeneity (H value) and contactability (C value) according to Equation 2 of the present invention, and accordingly, particle aggregation and flow characteristics were deteriorated, and it was confirmed that a lithium hydroxide peak was observed in the XRD results of Fig. 1. In addition, it was confirmed that a low ionic conductivity of 1.0 mS / cm or less was observed when manufacturing a solid electrolyte.

Claims

1. A step of recrystallizing lithium hydroxide to obtain lithium hydroxide monohydrate having a uniform particle size; and A step of producing lithium sulfide by reacting lithium hydroxide monohydrate and hydrogen sulfide; The above recrystallized lithium hydroxide monohydrate has a SPANa value of 10 or less according to the following formula A, The above lithium sulfide manufacturing step is carried out in a manner in which the reaction raw material is floated in the reactor by the injection gas containing hydrogen sulfide. The flowability of the lithium sulfide measured using a powder characteristic analyzer is 20 mJ / kg or less, and the cohesion is 100 mJ / kg or less. Method for producing lithium sulfide: [Formula A] SPANa = (D90a-D10a) / D50a In the above formula A, D90a, D10a and D50a represent the particle sizes at 90%, 10% and 50% points of the cumulative particle volume distribution according to particle size, respectively, when analyzing particle size distribution using laser diffraction for lithium hydroxide monohydrate particles.

2. In paragraph 1, The D50a of the above lithium hydroxide monohydrate is 100 μm or less, Method for producing lithium sulfide.

3. In paragraph 1, The recrystallization temperature of the above lithium hydroxide is 5 to 50°C. Method for producing lithium sulfide.

4. In paragraph 1, The above hydrogen sulfide is produced by reacting solid sulfur with hydrogen gas in the presence of a catalyst. The molar ratio of the hydrogen gas and the solid sulfur is 1:1 to 1:10, Method for producing lithium sulfide.

5. In paragraph 1, The space velocity of the above injected gas is 3.0 to 6.0 hr -1 person, Method for producing lithium sulfide.

6. In paragraph 1, The concentration of hydrogen sulfide in the above-mentioned injected gas is 2.0 to 30.0 vol.%, Method for producing lithium sulfide.

7. In paragraph 1, Satisfying the following equation 1, Method for producing lithium sulfide: [Formula 1] 702.81·(SPANb) 0.57 -1700 ≤ Residue LiOH ≤ 702.81·(SPANb) 0.57 +2600 In the above equation 1, Residue LiOH is the content of lithium hydroxide remaining in lithium sulfide (ppm), which is less than 5,000 (ppm). SPANb is the SPAN value of lithium sulfide, according to the following formula B, but is 10 or less, [Formula B] SPANb = (D90b-D10b) / D50b In the above formula B, D90b, D10b and D50b refer to the particle sizes at 90%, 10% and 50% points of the cumulative particle volume distribution according to particle size, respectively, when analyzing particle size distribution using laser diffraction for lithium sulfide particles.

8. In paragraph 1, In the above lithium sulfide manufacturing step, Lithium sulfide particle characteristic value H according to the following formula 2 is 2.4 or less, Method for producing lithium sulfide: [Formula 2] H = In the above equation 2, Residue LiOH is the content of lithium hydroxide remaining in lithium sulfide (ppm), SPANb is the SPAN value of lithium sulfide, according to the following formula B, but is 10 or less, [Formula B] SPANb = (D90b-D10b) / D50b In the above formula B, D90b, D10b and D50b refer to the particle sizes at 90%, 10% and 50% points of the cumulative particle volume distribution according to particle size, respectively, when analyzing particle size distribution using laser diffraction for lithium sulfide particles.

9. In paragraph 8, Satisfying the following equation 3, Method for producing lithium sulfide: [Formula 3] -1.57·C + 4.54 ≤ H ≤ -1.58·C + 8.8 In the above equation 3, H is as defined in Article 8, C is a value according to the following equation 4, [Formula 3] C = C H2S / Sv C H2S is the concentration of hydrogen sulfide in the injected gas (vol.%), Sv is the space velocity of the injected gas (h -1 )am.

10. In paragraph 1, The residual moisture content in lithium sulfide is less than 500 ppm, Method for producing lithium sulfide.

11. Does not contain solvent, has a particle size D50b of 100 ㎛ or less, The SPANb value according to the following formula B is 10 or less, The content of residual lithium hydroxide (Residue LiOH) in lithium sulfide is 5,000 ppm or less. Lithium sulfide: [Formula B] SPANb = (D90b-D10b) / D50b In the above formula B, D90b, D10b and D50b refer to the particle sizes at 90%, 10% and 50% points of the cumulative particle volume distribution according to particle size, respectively, when analyzing particle size distribution using laser diffraction for lithium sulfide particles.

12. In paragraph 11, Satisfying the following equation 1, Lithium sulfide: [Formula 1] 702.81·(SPANb) 0.57 -1700 ≤ Residue LiOH ≤ 702.81·(SPANb) 0.57 +2600 In the above equation 1, Residue LiOH is the content of lithium hydroxide remaining in lithium sulfide (ppm), SPANb is as defined in Article 11.

13. In paragraph 11, H, which is a characteristic value of lithium sulfide particles according to the following formula 2, is 2.4 or less. Lithium sulfide: [Formula 2] H = In the above equation 2, Residue LiOH is the content of lithium hydroxide remaining in lithium sulfide (ppm), SPANb is as defined in Article 11.

14. In paragraph 11, With a residual moisture content of 500 ppm or less, Lithium sulfide.

15. In paragraph 11, Flowability measured using a powder characteristic analyzer is 20 mJ / kg or less, and cohesion is 100 mJ / kg or less. Lithium sulfide.

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