Methods for manufacturing high-purity lithium sulfide using wet and dry processes

Abstract

This invention relates to a method for manufacturing high-purity lithium sulfide using both wet and dry processes. In particular, it relates to a method for mass-producing high-purity lithium sulfide by a wet process of reacting lithium hydroxide (LiOH) with hydrogen sulfide (H2S) gas in an organic solvent and a dry process of reacting the obtained dried product with hydrogen sulfide (H2S) gas.

Description

Technical Field

[0001] This invention relates to a method for manufacturing high-purity lithium sulfide through wet and dry processes. Background Technology

[0002] The theoretical energy density of lithium-sulfur secondary batteries is 2,800 Wh / kg (1,675 mAh / g), which is much higher than that of currently commercially available lithium secondary batteries. Moreover, sulfur, which is used as an anode active material, is abundant in natural resources and inexpensive, and has attracted much attention as an environmentally friendly material.

[0003] In the lithium-sulfur secondary battery described above, the lithium metal used as the cathode may cause an internal short circuit during the process of lithium ions dissociating from the lithium metal and re-depositing due to the growth of the lithium metal into a dendrite phase. This is the main reason for the decrease in battery stability and thus becomes a major limiting factor in the commercialization of lithium-sulfur secondary batteries.

[0004] Furthermore, to activate sulfur in lithium-sulfur secondary batteries, a composite material with carbon needs to be formed. However, as mentioned above, because the sublimation temperature of sulfur is too low (~115°C), ampoules must always be used. Moreover, even when using ampoules as described above, the degree of adsorption with carbon is too low, requiring the same process to be repeated many times to obtain an appropriate level of sulfur loading density, thus incurring excessive engineering costs.

[0005] To fundamentally solve the problems of lithium-sulfur secondary batteries as described above, a method has been proposed that uses lithium sulfide (Li₂S) instead of sulfur as the anode. When lithium sulfide is used as the anode, there is no need to use lithium metal as the cathode, and because of the higher melting temperature (~1000°C), the anode fill rate can be adjusted to the desired level, allowing for simpler battery manufacturing. Furthermore, the higher melting temperature allows for various types of post-processing at higher temperatures, and through the post-processing described above, the activity of lithium sulfide can be maximized.

[0006] Furthermore, unlike existing lithium-ion batteries that use liquid electrolytes, all-solid-state batteries (ASSB) that use solid electrolytes do not suffer from problems such as flammability, corrosion, leakage, and evaporation that can occur with liquid electrolytes. Therefore, they are safer and can be used in a variety of temperature ranges compared to existing lithium-ion batteries.

[0007] All-solid-state lithium-ion batteries consist of an anode, a cathode, and a solid electrolyte. Solid electrolytes are broadly classified into polymer, oxide, and sulfide types. Among these, oxide and sulfide solid electrolytes exhibit high ionic conductivity, excellent mechanical properties, and flame retardancy, thus attracting active research.

[0008] Because lithium sulfide (Li2S), used as a material for sulfide-based solid electrolytes as described above, cannot be produced from natural minerals, it must be synthesized.

[0009] As one of the existing methods for synthesizing lithium sulfide, one option is to use the reaction between lithium hydroxide (LiOH) and a gaseous sulfur source, namely hydrogen sulfide. Japanese Patent Application Publication No. 09-278423 proposes a method to dry-produce lithium sulfide by pulverizing lithium hydroxide particles to a diameter of 0.1 to 1.5 mm and setting the heating temperature for the reaction of lithium hydroxide and hydrogen sulfide in an inactive gas environment to 80 to 445 °C.

[0010] However, in the dry lithium sulfide manufacturing method described above, it is difficult to process large quantities of lithium hydroxide due to its high hygroscopicity, and it is also difficult to pulverize the obtained lithium sulfide, which in turn makes it difficult to mass-produce lithium sulfide. Summary of the Invention

[0011] The purpose of this invention is to solve the problems described above by providing a method for manufacturing lithium sulfide that can achieve both mass production and the production of high-purity lithium sulfide.

[0012] However, the stated purpose is merely illustrative and the technical concept of the present invention is not limited thereto.

[0013] To achieve the aforementioned objective, one aspect of the present invention relates to a method for manufacturing lithium sulfide, comprising: step a) of reacting a reaction solution containing lithium hydroxide (LiOH) and an organic solvent at a pressure higher than atmospheric pressure by injecting hydrogen sulfide (H2S) gas after heating the reaction solution to above 100°C; step b) of repeating the process of injecting hydrogen sulfide (H2S) gas into the reaction solution again and reacting again once or more after step a); step c) of obtaining a first reactant by removing the organic solvent from the reaction solution after step b); step d) of reacting a first reactant at a pressure higher than ambient temperature by injecting hydrogen sulfide (H2S) gas after heating the first reactant to above 100°C; and step e) of removing the reaction byproduct, i.e., water, by using a vacuum pump after step d) and then repeating the process of injecting hydrogen sulfide (H2S) gas into the reaction solution again and reacting again once or more.

[0014] In one embodiment, steps a) and b) can each be performed independently at a reaction temperature of 100 to 150°C.

[0015] In one embodiment, the organic solvent may be a mixture of two or more selected from aromatic organic solvents, amide organic solvents, and sulfur-containing organic solvents. As a specific example, the aromatic organic solvent may be one or more selected from alkylbenzene, dialkylbenzene, alkylnaphthalene, dialkylnaphthalene, alkylbiphenyl, and dialkylbiphenyl; the amide organic solvent may be one or more selected from N-methyl-2-pyrrolidone (NMP), N,N'-dimethylacetamide (DMAc), hexamethylphosphoramide (HMPA), and N,N-dimethylformamide (DMF); and the sulfur-containing organic solvent may be one or more sulfite solvents selected from alkylene sulfite, dialkyl sulfite, diaryl sulfite, and alkylaryl sulfite.

[0016] In one embodiment, the volume ratio of aromatic organic solvent to sulfur-containing organic solvent in the mixed solvent can be from 1:0.1 to 10.

[0017] In one embodiment, the concentration of lithium hydroxide (LiOH) in the reaction solution can be from 0.1 to 10 M.

[0018] In the first embodiment, step b) can be repeated 10 to 100 times.

[0019] In one embodiment, steps d) and e) can each be performed independently at a reaction temperature of 100 to 150°C.

[0020] In the first embodiment, in steps d) and e), an inactive gas may be injected along with the hydrogen sulfide (H2S) gas. Specifically, the inactive gas may be one or more selected from argon (Ar), helium (He), and nitrogen (N2).

[0021] According to the lithium sulfide manufacturing method of the present invention, a reaction solution containing lithium hydroxide (LiOH) and an organic solvent is reacted with hydrogen sulfide in a wet process, and then the resulting first reactant is reacted with hydrogen sulfide again in a dry process to produce lithium sulfide. Therefore, both mass production and high-purity lithium sulfide can be obtained. Attached Figure Description

[0022] Figure 1 The results are X-ray diffraction (XRD) patterns of lithium sulfide (Li2S) manufactured by wet and dry processes according to Example 1.

[0023] Figure 2 The results are based on the X-ray diffraction (XRD) pattern analysis of lithium sulfide (Li2S) manufactured by wet process in Comparative Example 1. Detailed Implementation

[0024] Next, a detailed description will be given of the method for manufacturing high-purity lithium sulfide using both wet and dry processes according to the present invention. The accompanying drawings, which are provided below, are merely examples to fully convey the spirit of the invention to those skilled in the art. Therefore, the invention is not limited by the drawings described below, but can be implemented in other forms, and the drawings may be exaggerated to clearly illustrate the spirit of the invention. In this case, unless otherwise defined, the technical and scientific terms used have the same meaning as commonly understood by those skilled in the art to which this invention pertains. In the following description and drawings, descriptions related to well-known functions and structures that may obscure the essence of the invention will be omitted.

[0025] One aspect of the present invention relates to a method for manufacturing lithium sulfide, comprising: step a) of reacting a reaction solution containing lithium hydroxide (LiOH) and an organic solvent at a pressure higher than atmospheric pressure by injecting hydrogen sulfide (H2S) gas after heating the reaction solution to above 100°C; step b) of repeating the process of injecting hydrogen sulfide (H2S) gas into the reaction solution again after step a) when the pressure inside the reactor returns to atmospheric pressure; step c) of obtaining a first reactant by removing the organic solvent from the reaction solution after step b); step d) of reacting a reaction solution at a pressure higher than ambient temperature by injecting hydrogen sulfide (H2S) gas after heating the first reactant to above 100°C; and step e) of removing the reaction byproduct, i.e., water, by a vacuum pump after step d) and then repeating the process of injecting hydrogen sulfide (H2S) gas into the reaction solution again after step d) at a pressure higher than ambient pressure.

[0026] As described above, the lithium sulfide manufacturing method according to the present invention can be carried out by a wet process to react a reaction solution containing lithium hydroxide (LiOH) and an organic solvent with hydrogen sulfide for the first time, and then the obtained first reactant is reacted with hydrogen sulfide again by a dry process to produce lithium sulfide. Therefore, it can achieve mass production and obtain high-purity lithium sulfide.

[0027] Next, the various steps in the method for manufacturing lithium sulfide according to one embodiment of the present invention will be described in more detail.

[0028] First, step a) can be performed by heating the reaction solution containing lithium hydroxide (LiOH) and an organic solvent to above 100°C and then injecting hydrogen sulfide (H2S) gas to carry out the reaction at a pressure above atmospheric pressure.

[0029] In one embodiment of the present invention, the reaction solution is a product obtained by dissolving lithium hydroxide in an organic solvent. As a specific example, the organic solvent may be a mixture of two or more solvents selected from aromatic organic solvents, amide organic solvents, and sulfur-containing organic solvents. Preferably, when a mixture of aromatic organic solvents and sulfur-containing organic solvents is used as the reaction solvent, the reaction between lithium hydroxide and hydrogen sulfide can be further activated, thereby effectively synthesizing lithium sulfide and further improving its purity.

[0030] As a specific example, the aromatic organic solvent may be one or more selected from alkylbenzene, dialkylbenzene, alkylnaphthalene, dialkylnaphthalene, alkylbiphenyl, and dialkylbiphenyl, wherein the alkyl group may refer to an alkyl group having 1 to 6 carbon atoms, preferably an alkyl group having 1 to 3 carbon atoms. As a more specific example, the aromatic organic solvent may be one or more selected from toluene, ethylbenzene, cumene, xylene, diethylbenzene, diisopropylbenzene, methylnaphthalene, dimethylnaphthalene, ethylbiphenyl, and diethylbiphenyl. In the case of having two alkyl groups, the aromatic solvent may be in an ortho, meta, or para configuration.

[0031] The amide organic solvent may be one or more selected from N-methyl-2-pyrrolidone (NMP), N,N'-dimethylacetamide (DMAc), hexamethylphosphoramide (HMPA), and N,N-dimethylformamide (DMF).

[0032] Furthermore, the sulfur-containing organic solvent may be one or more sulfite solvents selected from alkylene sulfites, dialkyl sulfites, diaryl sulfites, and alkylaryl sulfites. In this case, the alkyl or alkylene group may refer to an alkyl or alkylene group having 1 to 6 carbon atoms, preferably an alkyl or alkylene group having 1 to 3 carbon atoms, while the aryl group may refer to an aryl group having 6 to 20 carbon atoms. As a more specific example, the sulfite solvent may be one or more selected from ethylene sulfite, propylene sulfite, butylene sulfite, dimethyl sulfite, diethyl sulfite, dipropyl sulfite, dibutyl sulfite, methyl phenyl sulfite, ethyl phenyl sulfite, methyl benzyl sulfite, and ethyl benzyl sulfite.

[0033] Furthermore, as mentioned above, when a mixed solvent of aromatic organic solvent and sulfur-containing organic solvent is used as the reaction solvent, the reaction of lithium hydroxide and hydrogen sulfide can be further activated, thereby effectively synthesizing lithium sulfide and further improving its purity. Therefore, it is preferable to use a mixed solvent of aromatic organic solvent and sulfur-containing organic solvent as the reaction solvent.

[0034] As a specific example, the volume ratio of aromatic organic solvent to sulfur-containing organic solvent in the mixed solvent can be from 1:0.1 to 10, preferably from 1:0.2 to 3, and more preferably from 1:0.3 to 1. Within the range described above, excellent reaction activation can be ensured.

[0035] Furthermore, the concentration of lithium hydroxide (LiOH) in the reaction solution can be from 0.1 to 10 M, preferably from 1 to 5 M. Within the range described above, lithium hydroxide can react effectively with hydrogen sulfide gas, thereby efficiently synthesizing lithium sulfide.

[0036] Furthermore, in one embodiment of the invention, step a) can be performed at a reaction temperature of 100 to 150°C, preferably at a reaction temperature of 110 to 130°C. Within the range described above, lithium hydroxide can react effectively with hydrogen sulfide gas, thereby efficiently synthesizing lithium sulfide.

[0037] Furthermore, atmospheric pressure can refer to 1 to 1.5 atmospheres, more preferably 1 to 1.2 atmospheres. Pressure above atmospheric pressure can refer to pressure above 1.5 atmospheres, for example, 2 to 10 atmospheres.

[0038] Next, when the pressure inside the reactor returns to atmospheric pressure after step a), step b) can be repeated more than once, after the hydrogen sulfide (H2S) gas is injected into the reaction liquid again.

[0039] That is, the process of injecting hydrogen sulfide gas in step a) and then reducing the internal pressure of the reactor back to atmospheric pressure (1 to 1.5 atmospheres) through lithium sulfide synthesis, followed by re-injection of hydrogen sulfide gas and subsequent reaction, can be repeated more than once. Preferably, this process can be repeated 10 to 100 times, and more preferably 30 to 50 times. By repeatedly performing the reaction process after injecting hydrogen sulfide gas as described above, most of the lithium hydroxide can be converted into lithium sulfide.

[0040] In this case, step b) can also be performed at a reaction temperature of 100 to 150°C, preferably at a reaction temperature of 110 to 130°C. Within the range described above, lithium hydroxide can react effectively with hydrogen sulfide gas, thereby efficiently synthesizing lithium sulfide.

[0041] Next, step c) can be performed after step b) to obtain the first reactant by removing the organic solvent from the reaction solution. The method of removing the organic solvent is not particularly limited; for example, the organic solvent can be removed by evaporation and drying.

[0042] Next, in order to completely convert the small amount of unreacted lithium hydroxide remaining in the first reactant into lithium sulfide, an additional dry process can be performed. Specifically, step d) can be performed by heating the first reactant to above 100°C and then injecting hydrogen sulfide (H2S) gas to carry out the reaction at a pressure above room temperature; and step e) after step d) removing the reaction byproduct, i.e., water, by vacuum pumping, and then repeating the process of re-injecting hydrogen sulfide (H2S) gas and carrying out the reaction again can be performed more than once.

[0043] At this point, steps d) and e) can be performed at a reaction temperature of 100 to 150°C, preferably at a reaction temperature of 120 to 140°C. Within the range described above, unreacted lithium hydroxide can react effectively with hydrogen sulfide gas to obtain high-purity lithium sulfide.

[0044] Furthermore, in one embodiment of the present invention, an inert gas may be injected along with hydrogen sulfide (H2S) gas in steps d) and e). In this case, the inert gas may be one or more selected from argon (Ar), helium (He), and nitrogen (N2).

[0045] Furthermore, the volume ratio of hydrogen sulfide (H2S) gas to inactive gas can be from 1:0.1 to 10, preferably from 1:0.5 to 3. Within the range described above, unreacted lithium hydroxide can react effectively with hydrogen sulfide gas to obtain high-purity lithium sulfide.

[0046] Furthermore, after the reaction process is repeated following the injection of hydrogen sulfide gas, a process to remove water generated as a reaction byproduct must be performed. Without water removal, unreacted lithium hydroxide may remain as an impurity. In this case, the water removal method is not specifically limited; for example, it can be removed using a vacuum pump.

[0047] Step e) can be repeated until no more moisture condenses when observed through a sight glass. It is advisable to obtain lithium sulfide from the glove box after the reaction is complete.

[0048] As described above, by performing the dry process steps d) to e) after the wet process in steps a) to c), high-purity lithium sulfide can be produced in large quantities. The purity of this high-purity lithium sulfide can be 99.9% or higher, preferably 99.93% or higher, and more preferably 99.95% or higher. Furthermore, the upper limit of purity can be 100%, and practically it can be 99.999%.

[0049] Next, the method for manufacturing high-purity lithium sulfide according to the present invention via wet and dry processes will be described in more detail through examples. However, the following examples are merely for reference in providing a detailed description of the present invention, and the present invention is not limited thereto, but can be implemented in various forms.

[0050] Furthermore, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in describing this application is for the purpose of effectively illustrating specific embodiments only and is not intended to limit the invention. Additionally, the unit for additives not explicitly stated in this specification may be weight%.

[0051]

Example 1

[0052] After adding 350 ml of p-xylene, 150 ml of vinyl sulfite, and 25 g of lithium hydroxide (LiOH) to a 2 L reactor, the temperature was raised to 110 °C. At 110 °C, 4 L of hydrogen sulfide (H₂S) was injected into the reactor, and 2 L of H₂S was added simultaneously while stirring at 50 rpm. This process was repeated 40 times, with continued stirring to reduce the pressure from excessive H₂S injection to atmospheric pressure (1 atm), followed by the addition of 2 L of H₂S.

[0053] Next, the mixed solvent was removed and dried using an evaporative drying method to obtain the first reactant. To remove unreacted LiOH from the dried first reactant, 5 L of argon (Ar) and 7 L of H₂S were injected into a 2 L reactor while stirring at 50 rpm at 130 °C. The reaction was allowed to proceed for 1 minute after injection, and then the reaction byproducts, namely water and residual gas, were removed under vacuum. This process was repeated until no more water condensed as observed through a sight glass. After the reaction was complete, lithium sulfide (Li₂S) was obtained from the glove box.

[0054]

Example 2

[0055] Except for the use of 500 ml of p-xylene as a solvent, the remaining process was performed in the same manner as in Example 1.

[0056]

Example 3

[0057] Except for the use of 400 ml of p-xylene and 100 ml of vinyl sulfite as solvents, the remaining process was performed in the same manner as in Example 1.

[0058]

Example 4

[0059] Except for the use of 250 ml of p-xylene and 250 ml of vinyl sulfite as solvents, the remaining process was performed in the same manner as in Example 1.

[0060]

Example 5

[0061] Except for the use of 150 ml of p-xylene and 350 ml of vinyl sulfite as solvents, the remaining process was performed in the same manner as in Example 1.

[0062]

Example 6

[0063] Except for using 500 ml of vinyl sulfite, the remaining process was performed in the same manner as in Example 1.

[0064]

Comparative Example 1

[0065] After adding 350 ml of p-xylene, 150 ml of vinyl sulfite, and 25 g of LiOH to a 2 L reactor, the temperature was raised to 110 °C. At 110 °C, 4 L of H2S was injected into the reactor, and an additional 2 L of H2S was added while stirring at 50 rpm. This process was repeated 40 times, with continued stirring to reduce the pressure (1 atmosphere) caused by excessive H2S injection, followed by the addition of 2 L of H2S.

[0066] Next, the mixed solvent is removed and dried using an evaporation-drying method to obtain lithium sulfide (Li2S).

[0067]

Comparative Example 2

[0068] After adding 25g of LiOH to a 2L reactor, 5L of Ar and 7L of H2S were injected while stirring at 50rpm. The reaction was allowed to proceed for 1 minute after injection, and then the reaction byproducts, namely water and residual gas, were removed by vacuum. The process was repeated until no more water condensed when observed through a sight glass. After the reaction was complete, lithium sulfide (Li2S) was obtained from the glove box.

[0069]

Feature Evaluation

[0070] The X-ray diffraction (XRD) patterns of lithium sulfide (Li2S) produced by Example 1 and Comparative Example 1 were analyzed, and the results are as follows: Figure 1 as well as Figure 2 As shown.

[0071] See Figure 1 It can be confirmed that in Example 1, which simultaneously implements wet and dry processes according to the present invention, high-purity lithium sulfide can be synthesized without impurities.

[0072] In addition, see Figure 2 It can be confirmed that the final product of Comparative Example 1, which was manufactured solely by wet process, contained a relatively large amount of unreacted lithium hydroxide (LiOH) residue, and peaks of other impurities besides lithium sulfide or lithium hydroxide were also detected, indicating a significant reduction in its purity.

[0073] The purity of lithium sulfide (Li2S) produced according to Examples 1 to 6 and Comparative Example 2 was analyzed by inductively coupled plasma optical emission spectrometry (ICP-OES) and energy dispersive analysis of X-rays (EDAX). The average value of the purity of the three analytical samples was taken and recorded in Table 1 below.

[0074] Table 1

[0075]

[0076] Referring to Table 1, it can be confirmed that the purity is better when p-xylene and vinyl sulfite are used in combination. In particular, it can be confirmed that high-purity lithium sulfide can be produced when the mixing ratio (volume ratio) of p-xylene:vinyl sulfite is 1:0.2 to 3.

[0077] The present invention has been described above through specific details and limited embodiments. However, these details are provided only to help to understand the present invention more completely. The present invention is not limited by the embodiments described. Those skilled in the art to which this invention pertains can make various modifications and variations based on the following description.

[0078] Therefore, the concept of the present invention is not limited by the illustrated embodiments, but should be included within the scope of the present invention as well as the appended claims and their equivalent or equivalent variations.

Claims

1. A method for producing lithium sulfide, comprising: a step a) of performing a reaction at a pressure higher than an atmospheric pressure by injecting hydrogen sulfide (H2S) gas after warming a reaction liquid containing lithium hydroxide (LiOH) and an organic solvent to 100°C or higher; a step b) of repeating a process of performing a reaction again after injecting hydrogen sulfide (H2S) gas again to the reaction liquid once or more when the pressure inside a reactor is returned to an atmospheric pressure after the step a); a step c) of obtaining a first reaction product by removing the organic solvent from the reaction liquid after the step b); a step d) of performing a reaction at a pressure higher than an atmospheric pressure by injecting hydrogen sulfide (H2S) gas after warming the first reaction product to 100°C or higher; and a step e) of removing a reaction by-product, i.e., water, by a vacuum pump after the step d) and then repeating a process of performing a reaction again after injecting hydrogen sulfide (H2S) gas again once or more, the organic solvent being a mixed solvent in which an aromatic organic solvent and a sulfur-containing organic solvent are mixed, a volume ratio of the aromatic organic solvent to the sulfur-containing organic solvent in the mixed solvent being 1:0.1 to 10, and the sulfur-containing organic solvent being one or more sulfite solvents selected from the group consisting of an alkylene sulfite, a dialkyl sulfite, a diaryl sulfite, and an alkyl aryl sulfite.

2. The method for producing lithium sulfide according to claim 1, wherein the step a) and the step b) are each independently performed at a reaction temperature of 100 to 150°C.

3. The method for producing lithium sulfide according to claim 1, wherein the aromatic organic solvent is one or more selected from the group consisting of an alkylbenzene, an alkylnaphthalene, and an alkylbiphenyl.

4. The method for producing lithium sulfide according to claim 1, wherein the aromatic organic solvent is one or more selected from the group consisting of a dialkylbenzene, a dialkylnaphthalene, and a dialkylbiphenyl.

5. The method for producing lithium sulfide according to claim 1, wherein a concentration of lithium hydroxide (LiOH) in the reaction liquid is 0.1 to 10 M.

6. The method for producing lithium sulfide according to claim 1, wherein the step b) is repeated 10 to 100 times.

7. The method for producing lithium sulfide according to claim 1, wherein the step d) and the step e) are each independently performed at a reaction temperature of 100 to 150°C.

8. The method for producing lithium sulfide according to claim 1, wherein a non-reactive gas is injected together with hydrogen sulfide (H2S) gas in the step d) and the step e).

9. The method for producing lithium sulfide according to claim 8, wherein the non-reactive gas is one or more selected from the group consisting of argon (Ar), helium (He), and nitrogen (N2). ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Images