Method for producing high purity lithium sulfide by wet and dry processes

Abstract

The present invention relates to a method for producing high-purity lithium sulfide by wet and dry processes, and more particularly, to a method for producing lithium sulfide capable of mass-producing high-purity lithium sulfide by a wet process in which lithium hydroxide (LiOH) is reacted with hydrogen sulfide (HS) gas in an organic solvent, and a dry process in which a dried product obtained therefrom is reacted with hydrogen sulfide (HS) gas.

Description

[Technical field]

[0001] The present invention relates to a method for producing high purity lithium sulfide by wet and dry processes. [Background technology]

[0002] Lithium-sulfur secondary batteries have a theoretical energy density of 2,800Wh / kg (1,675mAh / g), which is much higher than the theoretical energy density of currently commercially available lithium secondary batteries. In addition, the sulfur-based materials used as the positive electrode active material are abundant and therefore inexpensive, and are attracting attention as environmentally friendly materials.

[0003] In such lithium-sulfur secondary batteries, the lithium metal used in the negative electrode has a problem in that when lithium ions dissociate from the lithium metal and then re-deposit during the charge and discharge process of the battery, the lithium metal grows into a dendrite phase, causing a short circuit inside the battery. This reduces the stability of the battery and is pointed out as a major limitation to the commercialization of lithium-sulfur secondary batteries.

[0004] In addition, in order to activate sulfur in lithium-sulfur secondary batteries, a composite with carbon must be made, but in this case, an ampoule must always be used because the sublimation temperature of sulfur is too low (~115°C). Even if such an ampoule is used, the degree of adsorption with carbon is too low, so the same process can be repeated several times to obtain the appropriate loading density of sulfur, but the process costs are high.

[0005] In order to fundamentally solve these problems with lithium-sulfur secondary batteries, lithium sulfide (Li) was used instead of sulfur in the positive electrode. 2A method of using lithium sulfide (S) has been proposed. When lithium sulfide is used in the positive electrode, lithium metal does not need to be used in the negative electrode, and the high melting temperature (~1000°C) allows the filling rate of the positive electrode to be adjusted to a desired level, making it possible to realize a battery through a simpler process. In addition, the high melting temperature allows various types of post-treatment processes to be carried out at high temperatures, and there is an advantage in that the activity of lithium sulfide can be maximized through such post-treatment processes.

[0006] Meanwhile, unlike conventional lithium-ion batteries that use liquid electrolytes, all-solid-state batteries (ASSBs) that use solid electrolytes are safer than conventional lithium-ion batteries because they do not have problems such as flammability, corrosion, water leakage, and evaporation that occur with liquid electrolytes, and have the advantage of being usable in a wide range of temperatures.

[0007] All-solid-state lithium secondary batteries consist of a positive electrode, a negative electrode, and a solid electrolyte. Solid electrolytes can be broadly classified into polymer, oxide, and sulfide types. Among these, oxide-based solid electrolytes and sulfide-based solid electrolytes, which have relatively high ionic conductivity, excellent mechanical properties, and are non-flammable, have been actively researched. Lithium sulfide (Li) is used as a material for such sulfide-based solid electrolytes. 2 S) is not found as a natural mineral product and is therefore provided synthetically.

[0008] One of the conventional methods for synthesizing lithium sulfide is a method that utilizes a reaction between lithium hydroxide (LiOH) and hydrogen sulfide, which is a gaseous sulfur source. Japanese Patent Laid-Open Publication No. 09-278423 proposed a method for producing lithium sulfide in a dry manner by powdering lithium hydroxide particles to have a diameter of 0.1 to 1.5 mm, and setting the heating temperature during the reaction of lithium hydroxide with hydrogen sulfide in an inert gas atmosphere to 80 to 445°C.

[0009] However, in the above-mentioned dry method for producing lithium sulfide, lithium hydroxide has a problem that it is difficult to handle in large quantities because it is highly hygroscopic and therefore prone to agglomeration, and it is also difficult to finely pulverize the obtained lithium sulfide, making mass production of lithium sulfide difficult. Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention is made to solve the above problems, and an object of the present invention is to provide a method for producing lithium sulfide, which can obtain high-purity lithium sulfide that can be mass-produced. However, the above objects are merely illustrative and the technical idea of ​​the present invention is not limited thereto. [Means for solving the problem]

[0011] In one embodiment of the present invention to achieve the above object, a) a reaction solution containing lithium hydroxide (LiOH) and an organic solvent is heated to 100° C. or higher, and then hydrogen sulfide (H 2 S) gas is injected to react under a pressure higher than normal pressure, and b) after step a), when the internal pressure of the reactor returns to normal pressure, hydrogen sulfide (H 2 S) repeating the process of injecting a gas and reacting again at least once; c) removing the organic solvent from the reaction solution after step b) to obtain a primary reactant; d) heating the primary reactant to 100° C. or more and then injecting hydrogen sulfide (H 2 S) gas is injected to react under a pressure higher than normal pressure, and after steps e) and d), water, which is a reaction by-product, is removed using a vacuum pump, and hydrogen sulfide (H 2 S) repeating the process of injecting a gas and reacting again one or more times.

[0012] In one embodiment, the steps a) and b) may be carried out at a reaction temperature of 100 to 150° C., independently of each other. In the above embodiment, the organic solvent may be a mixed solvent of two or more selected from an aromatic organic solvent, an amide-based organic solvent, and a sulfur-containing organic solvent. Specifically, for example, the aromatic organic solvent may be one or more selected from an alkylbenzene, a dialkylbenzene, an alkylnaphthalene, a dialkylnaphthalene, an alkylbiphenyl, and a dialkylbiphenyl, the amide-based 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-based solvents selected from an alkylene sulfite, a dialkyl sulfite, a diaryl sulfite, and an alkylaryl sulfite.

[0013] In the embodiment, the mixed solvent may have a volume ratio of the aromatic organic solvent: the sulfur-containing organic solvent of 1:0.1-10. In the embodiment, the concentration of lithium hydroxide (LiOH) in the reaction solution may be 0.1 to 10M. In one embodiment, the step b) may be repeated 10 to 100 times. In the embodiment, the steps d) and e) may be carried out at a reaction temperature of 100 to 150° C., independently of each other. In one embodiment, steps d) and e) comprise hydrogen sulfide (H 2 An inert gas may be further injected together with the S gas. Specifically, the inert gas may be, for example, argon (Ar), helium (He), and nitrogen (N 2 ) may be one or more selected from the following. Effect of the Invention

[0014] The method for producing lithium sulfide according to the present invention has an advantage that it is possible to provide high-purity lithium sulfide that can be mass-produced by primarily reacting a reaction solution containing lithium hydroxide (LiOH) and an organic solvent with hydrogen sulfide in a wet process, and then secondary reacting the primary reactant obtained from the reaction with hydrogen sulfide again in a dry process to produce lithium sulfide. [Brief description of the drawings]

[0015] [Figure 1] 1 shows X-ray diffraction (XRD) pattern analysis results of lithium sulfide (LiS) prepared by wet and dry processes according to Example 1. [Diagram 2] 1 shows an X-ray diffraction (XRD) pattern analysis result of lithium sulfide (LiS) prepared by a wet process according to Comparative Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, a method for producing high purity lithium sulfide by wet and dry processes according to the present invention will be described in detail. The drawings introduced below are provided as examples to fully convey the concept of the present invention to those skilled in the art. Therefore, the present invention is not limited to the drawings presented below, and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the concept of the present invention. In this case, unless otherwise defined, the technical and scientific terms used have the meanings that are commonly understood by those having ordinary skill in the art to which the present invention belongs, and in the following description and the accompanying drawings, descriptions of known functions and configurations that may unnecessarily obscure the gist of the present invention are omitted.

[0017] One aspect of the present invention is to heat a reaction solution containing lithium hydroxide (LiOH) and an organic solvent to 100° C. or higher, and then add hydrogen sulfide (H 2 S) gas is injected to react under a pressure higher than normal pressure, and b) after step a), when the internal pressure of the reactor returns to normal pressure, hydrogen sulfide (H 2S) repeating the process of injecting a gas and reacting again at least once; c) removing the organic solvent from the reaction solution after step b) to obtain a primary reactant; d) heating the primary reactant to 100° C. or more and then injecting hydrogen sulfide (H 2 S) gas is injected to react under a pressure higher than normal pressure, and after steps e) and d), water as a reaction by-product is removed using a vacuum pump, and then hydrogen sulfide (H 2 S) repeating the process of injecting a gas and reacting again one or more times.

[0018] As described above, the method for producing lithium sulfide according to the present invention has an advantage that it is possible to provide high-purity lithium sulfide that can be mass-produced by primarily reacting a reaction solution containing lithium hydroxide (LiOH) and an organic solvent with hydrogen sulfide in a wet process, and then secondary reacting the primary reactant obtained from the reaction with hydrogen sulfide again in a dry process to produce lithium sulfide.

[0019] Each step of the method for producing lithium sulfide according to one embodiment of the present invention will now be described in more detail. First, a) a reaction solution containing lithium hydroxide (LiOH) and an organic solvent is heated to 100°C or higher, and then hydrogen sulfide (H 2 S) A step of injecting a gas to react under a pressure higher than normal pressure can be carried out.

[0020] In one embodiment of the present invention, the reaction solution is obtained by dissolving lithium hydroxide in an organic solvent, and as a specific example, the organic solvent may be a mixed solvent of two or more selected from an aromatic organic solvent, an amide organic solvent, and a sulfur-containing organic solvent. Preferably, when a mixed solvent of an aromatic organic solvent and a sulfur-containing organic solvent is used as a reaction solvent, the reaction between lithium hydroxide and hydrogen sulfide is more activated, and lithium sulfide can be effectively synthesized, and the purity can be further improved.

[0021] As a specific example, the aromatic organic solvent may be one or more selected from alkylbenzene, dialkylbenzene, alkylnaphthalene, dialkylnaphthalene, alkylbiphenyl, and dialkylbiphenyl, and in this case, the alkyl may mean an alkyl group having 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms. More specifically, for example, the aromatic organic solvent may be one or more selected from toluene, ethylbenzene, isopropylbenzene, xylene, diethylbenzene, diisopropylbenzene, methylnaphthalene, dimethylnaphthalene, ethylbiphenyl, and diethylbiphenyl. In this case, when there are two alkyl groups, the aromatic solvent may be any of ortho, meta, and para.

[0022] The amide-based organic solvent may be at least one selected from N-methyl-2-pyrrolidone (NMP), N,N'-dimethylacetamide (DMAc), hexamethylphosphoramide (HMPA), and N,N-dimethylformamide (DMF).

[0023] The sulfur-containing organic solvent may be one or more sulfite-based solvents selected from alkylene sulfite, dialkyl sulfite, diaryl sulfite, and alkylaryl sulfite. In this case, the alkyl or alkylene may mean an alkyl or alkylene group having 1 to 6 carbon atoms, preferably 1 to 3 carbon atoms, and the aryl may mean an aryl group having 6 to 20 carbon atoms. More specifically, for example, the sulfite-based solvent may be one or more solvents 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.

[0024] Moreover, as described above, when a mixed solvent obtained by mixing an aromatic organic solvent and a sulfur-containing organic solvent is used as a reaction solvent, the reaction between lithium hydroxide and hydrogen sulfide is more activated, lithium sulfide can be effectively synthesized, and the purity can be further improved. Therefore, it is preferable to use a mixed solvent obtained by mixing an aromatic organic solvent and a sulfur-containing organic solvent as a reaction solvent.

[0025] As a specific example, the mixed solvent may have a volume ratio of aromatic organic solvent:sulfur-containing organic solvent of 1:0.1 to 10, preferably 1:0.2 to 3, and more preferably 1:0.3 to 1. Within such a range, the reaction activation effect is excellent.

[0026] On the other hand, the concentration of lithium hydroxide (LiOH) in the reaction solution may be 0.1 to 10 M, and preferably 1 to 5 M. Within such a range, lithium hydroxide and hydrogen sulfide react well, and lithium sulfide can be synthesized well.

[0027] In addition, in one embodiment of the present invention, the step a) may be performed at a reaction temperature of 100 to 150° C., preferably 110 to 130° C. Within this range, lithium hydroxide and hydrogen sulfide react well, and lithium sulfide can be synthesized well.

[0028] The normal pressure may mean 1 to 1.5 atm, preferably 1 to 1.2 atm. A pressure higher than normal pressure may mean a pressure higher than 1.5 atm, for example, 2 to 10 atm.

[0029] Next, after step b)a), when the internal pressure of the reactor returns to normal pressure, hydrogen sulfide (H 2 S) The step of injecting gas and re-reacting the gas may be repeated one or more times.

[0030] That is, after injecting hydrogen sulfide gas in step a), when the internal pressure of the reactor is lowered again to the normal pressure level (1-1.5 atm) due to the synthesis of lithium sulfide, hydrogen sulfide (H 2 The process of injecting hydrogen sulfide gas and re-reacting the hydrogen sulfide gas can be repeated one or more times, preferably 10 to 100 times, more preferably 30 to 50 times. By repeating the process of injecting hydrogen sulfide gas and re-reacting the hydrogen sulfide gas several times in this manner, most of the lithium hydroxide can be converted to lithium sulfide.

[0031] In this case, step b) may also be carried out at a reaction temperature of 100 to 150° C., preferably 110 to 130° C. Within this range, lithium hydroxide and hydrogen sulfide react well, and lithium sulfide can be synthesized well.

[0032] Then, after step c) and step b), a step of removing the organic solvent from the reaction solution to obtain a primary reactant may be performed. The method of removing the organic solvent is not particularly limited, and for example, the organic solvent may be removed by evaporation drying.

[0033] Thereafter, in order to completely convert the small amount of unreacted lithium hydroxide remaining in the primary reactant into lithium sulfide, a dry process may be further carried out. Specifically, d) the primary reactant is heated to 100° C. or higher, and then hydrogen sulfide (H 2 S) gas is injected to react under a pressure higher than normal pressure, and after steps e) and d), water as a reaction by-product is removed using a vacuum pump, and then hydrogen sulfide (H 2 S) repeating the process of injecting gas and reacting again one or more times.

[0034] Here, the steps d) and e) may be carried out independently at a reaction temperature of 100 to 150° C., preferably 120 to 140° C. Within this range, unreacted lithium hydroxide and hydrogen sulfide react well to obtain high-purity lithium sulfide.

[0035] In one embodiment of the present invention, the steps d) and e) are carried out by using hydrogen sulfide (H 2 An inert gas may be further injected together with the S gas. In this case, the inert gas may be argon (Ar), helium (He), or nitrogen (N 2 ) may be one or more selected from the above.

[0036] In addition, the hydrogen sulfide (H 2 The volume ratio of hydrogen sulfide (H2S) gas to inert gas may be 1:0.1-10, and is preferably hydrogen sulfide (H2S) gas. 2 The volume ratio of S) gas:inert gas may be 1:0.5 to 3. Within such a range, unreacted lithium hydroxide and hydrogen sulfide react well to obtain high-purity lithium sulfide.

[0037] Meanwhile, after the process of injecting hydrogen sulfide gas and re-reacting it, a process of removing water generated as a reaction by-product must be performed, and if the water is not removed, unreacted lithium hydroxide may remain as an impurity. In this case, the method of removing water is not particularly limited, and it can be removed, for example, by using a vacuum pump.

[0038] Step e) may be repeated until no moisture is observed when observed through a sight glass. After completion of the reaction, lithium sulfide is preferably obtained in a glove box.

[0039] In this way, after the wet process of steps a) to c), the dry process of steps d) to e) is carried out, and thus high-purity lithium sulfide can be mass-produced. At this time, the purity of the high-purity lithium sulfide may be 99.9% or more, preferably 99.93% or more, and more preferably 99.95% or more. Furthermore, the upper limit of the purity may be 100, and practically may be 99.999%. EXAMPLES

[0040] Hereinafter, the method for producing high purity lithium sulfide by wet and dry processes according to the present invention will be described in more detail with reference to the following examples. However, the following examples are merely a reference for explaining the present invention in detail, and the present invention is not limited thereto, and may be realized in various forms.

[0041] In addition, 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 the present invention belongs. The terms used in the description in this specification are for the purpose of effectively describing a particular embodiment, and are not intended to limit the present invention. In addition, the unit of additives not specifically described in the specification may be weight percent.

[0042] [Example 1] Wet + dry 350 ml of p-xylene, 150 ml of ethylene sulfite, and 25 g of lithium hydroxide (LiOH) were added to a 2 L reactor, and the temperature was raised to 110° C. When the temperature reached 110° C., hydrogen sulfide (H 2 S) Pour in 4 L of water and add 2 L of H2O while stirring at 50 rpm. 2 S was injected. H was injected too much. 2 Continue stirring until the pressure increased by S reaches normal pressure (1 atm), and add 2 L of H 2 The process of injecting additional S was repeated 40 times.

[0043] Thereafter, the mixed solvent was removed and dried using an evaporation drying method to obtain a primary reactant. In order to remove unreacted LiOH from the dried primary reactant, the primary reactant was added to a 2 L reactor, and then stirred at 130° C. at 50 rpm with 5 L of argon (Ar) and 7 L of H. 2 After injecting S and reacting for 1 minute, the reaction by-product water and remaining gas were removed by vacuum. This process was repeated until no moisture was observed when observed through the sight glass. After the reaction was completed, lithium sulfide (Li 2 S) was obtained from the glove box.

[0044] [Example 2] The same procedure as in Example 1 was repeated except that 500 ml of p-xylene was used as the solvent. [Example 3] The procedure of Example 1 was repeated except that 400 ml of p-xylene and 100 ml of ethylene sulfite were used as the solvent. [Example 4] The same procedure as in Example 1 was repeated except that 250 ml of p-xylene and 250 ml of ethylene sulfite were used as the solvent. [Example 5] The procedure of Example 1 was repeated except that 150 ml of p-xylene and 350 ml of ethylene sulfite were used as the solvent. [Example 6] The same procedure as in Example 1 was repeated except that 500 ml of ethylene sulfite was used.

[0045] [Comparative Example 1] Wet 350 ml of p-xylene, 150 ml of ethylene sulfite, and 25 g of LiOH were added to a 2 L reactor, and the temperature was raised to 110° C. When the temperature reached 110° C., 4 L of H 2 Add S and 2 L of H while stirring at 50 rpm. 2 S was injected. H was injected too much. 2 Continue stirring until the pressure increased by S reaches normal pressure (1 atm), and add 2 L of H 2 The process of injecting additional S was repeated 40 times. Then, the mixed solvent was removed and dried using an evaporation drying method to obtain lithium sulfide (Li 2 S).

[0046] [Comparative Example 2] Dry type 25 g of LiOH was added to a 2 L reactor, and then 5 L of Ar and 7 L of H were added while stirring at 50 rpm. 2 After injecting S and reacting for 1 minute, the reaction by-product water and remaining gas were removed by vacuum. This process was repeated until no moisture was observed when observed through the sight glass. After the reaction was completed, lithium sulfide (Li 2 S) was obtained from the glove box.

[0047] [Characteristics evaluation] Lithium sulfide (Li 2 S) was analyzed for X-ray diffraction (XRD) patterns, and the results are shown in FIG. 1 and FIG. 2. Referring to FIG. 1, in the case of Example 1 in which both the wet process and the dry process were performed according to the present invention, it was confirmed that lithium sulfide was synthesized with high purity without impurities. Meanwhile, referring to FIG. 2, in the case of the final product of Comparative Example 1 produced only by the wet process, it was found that a somewhat large amount of unreacted lithium hydroxide (LiOH) remained, and peaks of impurities other than lithium sulfide and lithium hydroxide were also detected, confirming that the purity was significantly reduced.

[0048] Lithium sulfide (Li 2 The purity of each of the three samples was analyzed, and the average value was calculated, as shown in Table 1 below.

[0049] [Table 1]

[0050] Referring to Table 1, it can be seen that the purity is more excellent when p-xylene and ethylene sulfite are mixed and used. In particular, it can be seen that lithium sulfide with higher purity can be produced when the mixing ratio (volume ratio) of p-xylene:ethylene sulfite is 1:0.2-3.

[0051] Although the present invention has been described above using specific matters and limited examples, this is merely provided to assist in a more general understanding of the present invention, and the present invention is not limited to the above examples. Those having ordinary skill in the art to which the present invention pertains can make various modifications and variations from such descriptions.

[0052] Therefore, the spirit of the present invention should not be limited to the described embodiments, and all modifications equivalent to or equivalent to the scope of the claims, as well as the scope of the claims described below, should be considered to fall within the scope of the spirit of the present invention.

Claims

1. a) A reaction solution containing lithium hydroxide (LiOH) and an organic solvent is heated to 100° C. or higher, and then hydrogen sulfide (H ２ S) injecting a gas to react under a pressure higher than normal pressure, wherein the organic solvent is p-xylene, ethylene sulfite, or a mixture thereof; b) After step a), when the internal pressure of the reactor returns to normal pressure, hydrogen sulfide (H ２ S) repeating the process of injecting gas and reacting again one or more times; c) removing the organic solvent from the reaction solution after step b) to obtain a primary reactant; d) After the primary reactant is heated to 100° C. or higher, hydrogen sulfide (H ２ S) injecting gas and argon to react under a pressure higher than atmospheric pressure; e) After step d), water as a reaction by-product is removed using a vacuum pump, and hydrogen sulfide (H ２ S) repeating the process of injecting gas and reacting again one or more times.

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

3. 2. The method for producing lithium sulfide according to claim 1, wherein the mixed solvent has a volume ratio of p-xylene:ethylene sulfite of 1:0.1-10.

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

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

6. The method for producing lithium sulfide according to claim 1, wherein the steps d) and e) are independently carried out at a reaction temperature of 100 to 150° C.

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