Method for producing high purity alkali metal sulfide

Abstract

One embodiment of the present invention discloses a method for producing high purity alkali metal sulfide, comprising the steps of mixing an alkali metal sulfide salt precursor and a reducing agent to form a mixture, reducing the mixture to obtain an alkali metal sulfide, and purifying the resulting alkali metal sulfide.

Description

[Technical field]

[0001] The present invention relates to a method for producing high purity alkali metal sulfides. [Background technology]

[0002] The manufacturing method of lithium sulfide, an example of an alkali metal sulfide, is a chemical reaction using Li2CO3 and H2S, and the Li2S synthesis process is widely used, but there is a problem that an additional H2S gas storage device, which is a toxic substance, and an exhaust facility for control purposes are required.In addition, in the case of unreactive H2S, a process is required in which the substance must be completely burned using a burner, etc., neutralized with sodium hydroxide solution, and then treated with sodium sulfide.

[0003] In addition, the method requires additional equipment and processes for managing H2S gas in order to synthesize Li2S, which reduces productivity. In addition, since a large amount of H2S is used during mass production of Li2S, in addition to the basic material costs for the synthesis process, the cost of setting up and maintaining the equipment to maintain stability is increased, which may reduce the economic viability of the method as a mass production method.

[0004] LiOH (lithium hydroxide), which is used as a raw material in other conventional lithium sulfide manufacturing methods, is more expensive than Li2SO4 (lithium sulfate). In this technology, the synthesis is carried out using a dry ball milling process, so the process is simpler than other methods, but the basic raw material price issue makes it less economical when moving to the mass production stage. In addition, the purity of the powder synthesized by the milling process is relatively low, requiring an additional purification process.

[0005] Therefore, there is a need for an economical method for synthesizing high-purity alkali metal sulfides. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a new and economical method for producing high purity alkali metal sulfides. [Means for solving the problem]

[0007] One embodiment of the present invention discloses a method for producing high purity alkali metal sulfide, comprising the steps of mixing a precursor of an alkali metal sulfide salt with a reducing agent to form a mixture, reducing the mixture to obtain an alkali metal sulfide, and purifying the obtained alkali metal sulfide. Effect of the Invention

[0008] According to the present invention, an alkali metal sulfide having high purity can be synthesized economically. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a flow chart illustrating a method for producing high purity alkali metal sulfide according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a graph showing the results of Raman spectroscopy of lithium sulfide after the purification process. [Diagram 3] FIG. 3 is a graph showing the results of Raman spectroscopic analysis of lithium sulfide before the purification process. [Figure 4] FIG. 4 is a graph showing X-ray diffraction spectroscopy (XRD) results of lithium sulfide produced according to one embodiment compared to commercially available lithium sulfide. [Diagram 5] FIG. 5 is a graph showing the results of comparing the half-width of lithium sulfide produced according to one embodiment with commercially available lithium sulfide. [Figure 6] FIG. 6 is a graph showing the results of confirming peaks of lithium sulfide reduced depending on the heat treatment temperature during the production of lithium sulfide according to one embodiment. [Figure 7]FIG. 7 is a graph showing a change in Gibbs free energy depending on the heat treatment temperature and the amount of carbon input when lithium sulfide is produced according to one embodiment. [Figure 8] FIG. 8 is a graph showing the results of confirming peaks of lithium sulfide reduced depending on the amount of carbon input when lithium sulfide is produced according to an embodiment. [Figure 9] FIG. 9 is a photograph showing lithium sulfide separated from impurities after a purification process by centrifugation during the production of lithium sulfide according to an embodiment, and lithium sulfide finally obtained after the impurities are removed. BEST MODE FOR CARRYING OUT THEINVENTION

[0010] One embodiment of the present invention discloses a method for producing high purity alkali metal sulfide, comprising the steps of mixing a precursor of an alkali metal sulfide salt with a reducing agent to form a mixture, reducing the mixture to obtain an alkali metal sulfide, and purifying the obtained alkali metal sulfide.

[0011] In this embodiment, the mixing step may form the mixture in a non-polar solvent.

[0012] In this embodiment, the reducing step can reduce the mixture with a reducing gas.

[0013] In this embodiment, the reducing gas may include hydrogen and at least one selected from the group consisting of carbon monoxide, nitrogen, argon, helium, neon, methane, ethane, propane, and butane.

[0014] In this embodiment, the reducing step may include a heat treatment step.

[0015] In this embodiment, the heat treatment step can be performed at a temperature of 800°C to 1500°C.

[0016] In this embodiment, the purifying step may purify the obtained alkali metal sulfide using a polar solvent.

[0017] In this embodiment, the polarity index of the polar solvent may be 4.3 to 6.2.

[0018] In this embodiment, in the purification step, the obtained alkali metal sulfide may be dissolved in the polar solvent.

[0019] In this embodiment, after the purification step, a step of crystallizing the alkali metal sulfide may be further included.

[0020] In this embodiment, the crystallization step can be performed by performing a heat treatment at 300°C to 1000°C to cause crystallization. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The above objects, other objects, features and advantages of the present invention will be easily understood through the following preferred embodiments in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced in this specification are provided to make the disclosed content thorough and complete, and to fully convey the concept of the present invention to those skilled in the art.

[0022] While describing each drawing, similar reference numerals have been used for similar components. In the accompanying drawings, the dimensions of the structures are shown exaggerated for clarity of the present invention. Terms such as first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another component. For example, the first component can be named the second component, and the second component can be named the first component, without departing from the scope of the present invention. A singular expression includes a plural expression unless the context clearly indicates otherwise.

[0023] In this specification, the terms "comprise" or "have" are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described herein, and should be understood not to preclude the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof. In addition, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only when it is "directly on" the other part, but also when there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "under" another part, this includes not only when it is "directly under" the other part, but also when there is another part in between.

[0024] Unless otherwise indicated, all numbers, values ​​and / or expressions expressing amounts of ingredients, reaction conditions, polymer compositions and formulations used herein are approximations reflecting various uncertainties of measurement that arise in obtaining these values, while these numbers are inherently different, and therefore should be understood to be modified in all cases by the term "about". Furthermore, when a range of values ​​is disclosed herein, the range is continuous and includes all values ​​from the minimum value to said maximum value, including the maximum value, unless otherwise indicated. Furthermore, when such a range refers to integers, all integers from the minimum value to said maximum value, including the maximum value, are included, unless otherwise indicated.

[0025] FIG. 1 is a flow chart showing a method for producing high purity alkali metal sulfide according to one embodiment of the present invention.

[0026] Referring to FIG. 1, the method for producing high purity alkali metal sulfide according to the present embodiment may include step S100 of mixing a precursor and a reducing agent to form a mixture, step S200 of reducing the mixture to obtain an alkali metal sulfide, step S300 of purifying the obtained alkali metal sulfide, step S400 of drying the purified alkali metal sulfide, and step S500 of crystallizing the dried alkali metal sulfide.

[0027] The precursors may be compounds containing an alkali element and an element sulfur. For example, the precursors may be lithium sulfate, sodium sulfate, potassium sulfate, etc. These compounds may be hydrated or anhydrous.

[0028] The reducing agent may include carbon. The reducing agent is a carbon-based reducing agent, and the material is not particularly limited, and may have a gas, liquid, or solid phase. In addition, the reducing agent may include a non-carbon atom as long as it can be a source of carbon.

[0029] The reducing agent may include at least one of solid carbonaceous materials such as coal, coke, black smoke, carbon black, fullerenes, carbon tubes, charcoal, carbide, elemental carbon and its allotropes. A representative example of elemental carbon and its allotropes may be graphite. The reducing agent may also be a metal-based reducing agent such as LiBH4.

[0030] On the other hand, if the content of the reducing agent is too low, the reduction efficiency decreases, but conversely, if the content of the reducing agent is too high, impurities may be excessively generated, which may decrease the production efficiency. Therefore, the precursor and the reducing agent may be mixed at a molar ratio of about 1:1 to about 1:5. For example, they may be mixed at a molar ratio of 1:1 to 1:5, 1:1 to 1:4, 1:2 to 1:4, 1:3 to 1:6, or 1:3 to 1:5.

[0031] The precursor and the reducing agent may be mixed uniformly to form a mixture (S100).

[0032] The precursor and the reducing agent can be mixed by milling, stirring, a homogenizer, ultrasonic waves, etc. As an example, the precursor and the reducing agent can be mixed by a milling process. The milling process may be selected from the group consisting of a ball mill, an attrition mill, a vibration mill, a disk mill, a jet mill, a rotor mill, a pearl mill, and combinations thereof.

[0033] A solvent may be further included when mixing the precursor and the reducing agent. The solvent is not necessarily included, and may be omitted when mixing the precursor and the reducing agent.

[0034] The solvent used in mixing the precursor and the reducing agent may be a non-polar solvent, for example, selected from the group consisting of cyclohexane, hexane, n-heptane, and combinations thereof.

[0035] Meanwhile, when a solvent is used when mixing the precursor and the reducing agent, a drying step for removing the solvent may be further included. Drying may be performed by various methods such as vacuum drying, hot air drying, freeze drying, spray drying, etc.

[0036] After the mixture is formed, the mixture can be reduced to obtain an alkali metal sulfide (S200).

[0037] A reducing gas can be supplied when the mixture is reduced. The reducing gas can include hydrogen. In one example, the reducing gas can be hydrogen. The reducing gas can also be a mixture of hydrogen and at least one selected from the group consisting of carbon monoxide, nitrogen, argon, helium, neon, methane, ethane, propane, and butane. In this way, when a reducing gas containing hydrogen is supplied when the mixture is reduced, the reduction effect by the reducing agent containing carbon can be further improved.

[0038] On the other hand, the reduction can be carried out together with a heat treatment. The heat treatment temperature can be about 700 to 900° C. Furthermore, the heat treatment time can be about 1 to about 24 hours.

[0039] Step S300 of purifying the obtained alkali metal sulfide is a step for removing reducing agents and unreacted precursors mixed with the obtained alkali metal sulfide, in which the obtained alkali metal sulfide is mixed with an organic solvent and then only the purified solvent is extracted.

[0040] The solvent used during purification may be a polar solvent. Specifically, the polarity index of the polar solvent may be between 4.3 and 6.2. The polar solvent may be, for example, ethanol. Since only the obtained alkali metal sulfide is dissolved in such a solvent and the remaining impurities sink, the alkali metal sulfide and the impurities can be easily separated, and a high-purity alkali metal sulfide can be obtained.

[0041] The purification may include a centrifugation step. The centrifugation step may be performed at about 1000 to about 5000 rpm for about 5 to about 60 minutes. Specifically, for example, the centrifugation step may be performed at 1000 to 4000, 1000 to 3000, 2000 to 5000, 2000 to 4000, 2000 to 3000, 3000 to 5000, or 3000 to 4000 rpm for 5 to 50, 5 to 40, 5 to 30, 10 to 60, 10 to 50, 10 to 40, 10 to 30, 20 to 60, 20 to 50, 20 to 40, 30 to 60, or 30 to 50 minutes.

[0042] As another example, the resulting alkali metal sulfide can be separated from impurities by various methods such as filtering, pressure dewatering, and filter press.

[0043] Next, the solvent in which the refined alkali metal sulfide is dissolved can be separated and dried (S400), and the alkali metal sulfide can be crystallized by heat treatment (S500).

[0044] Drying may be performed by vacuum drying, hot air drying, freeze drying, spray drying, or the like, which allows the solvent to be removed.

[0045] The alkali metal sulfide from which the solvent has been removed can be crystallized by heat treatment, where the heat treatment temperature can be 300° C. to 930° C. Meanwhile, the purity of the alkali metal sulfide can be further improved by supplying at least one reducing gas selected from the group consisting of carbon monoxide, nitrogen, hydrogen, argon, helium, neon, methane, ethane, propane, and butane during the heat treatment for crystallization.

[0046] Meanwhile, a pre-crystallization step may be further included between the drying step S400 and the crystallization step S500. The pre-crystallization step is for preliminarily crystallizing the alkali metal sulfide before the crystallization step S500. By carrying out the pre-crystallization step followed by the crystallization step S500, a completely crystalline alkali metal sulfide required for lithium-sulfur batteries and the like can be produced.

[0047] However, when the alkali metal sulfide is used as a raw material for synthesis, such as a solid electrolyte, it is not necessary to carry out the pre-crystallization step because excellent reactivity is required, i.e., by making the alkali metal sulfide have a relatively low crystallinity, chemical reactions such as decomposition may become more active.

[0048] The preparation of the alkali metal sulfide according to the embodiment of the present invention may be carried out in a glove box or a dry room that is not exposed to moisture and oxygen.

[0049] Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention, however, these are presented as preferred examples of the present invention and should not be construed as limiting the present invention in any sense.

[0050] <Embodiment 1: Production of alkali metal sulfide (lithium sulfide)> Li2SO4 and carbon were milled and mixed in a molar ratio of 1:4 in heptane solvent. The mixture was heat-treated at 800°C for 12 hours in a 3% hydrogen and argon (Ar) gas atmosphere to synthesize Li2S.

[0051] The synthesized Li2S was dissolved in ethanol (polarity index = 5.2) and then centrifuged at 3000 RPM for 30 minutes in a centrifuge, whereby impurities other than Li2S dissolved in ethanol were sunk, and only Li2S dissolved in ethanol was separated.

[0052] The ethanol solvent in which the Li2S was dissolved was separated, extracted, and vacuum dried, and then heat-treated at 600°C for 5 hours, whereby the ethanol component of the solvent evaporated and high-purity Li2S was obtained.

[0053] <Experimental Example 1: Raman spectroscopy and XRD (X-ray diffraction spectroscopy) analysis> Fig. 2 is a graph showing the results of Raman spectroscopy analysis of lithium sulfide after the purification step, and Fig. 3 is a graph showing the results of Raman spectroscopy analysis of lithium sulfide before the purification step. Furthermore, Fig. 4 is a graph showing the results of X-ray diffraction analysis (XRD) of lithium sulfide produced according to one embodiment in comparison with commercially available lithium sulfide.

[0054] The lithium sulfide produced in the first embodiment was analyzed by Raman spectroscopy, and it was confirmed that the main bond in the sample after the purification process was Li2S, as shown in Figure 2. On the other hand, when the sample before the purification process was analyzed by Raman spectroscopy, it was confirmed that Li2S and carbon were mixed, as shown in Figure 3. That is, it can be seen that impurities in the sample were removed by the purification process according to the present invention.

[0055] In addition, when the XRD main peak of the lithium sulfide prepared in the embodiment 1 was confirmed, it was the same as that of commercially available Li2S as shown in FIG. 4, which shows that the purification process of the embodiment 1 is effective.

[0056] <Experimental Example 2 Size Analysis> FIG. 5 is a graph showing the results of comparing the half-width of lithium sulfide produced according to one embodiment with commercially available lithium sulfide.

[0057] Furthermore, when the XRD peak of the lithium sulfide produced in the first embodiment is confirmed, as shown in FIG. 5, the half-width appears to be at a level of about 92% on average compared to the peak morphology of commercially available lithium sulfide, and it is found that the lithium sulfide produced in the first embodiment exhibits excellent characteristics in terms of crystallinity.

[0058] In addition, when the particle size of the powder was measured, the lithium sulfide produced in the first embodiment had an average size of about 22.8 nm, while the commercially available lithium sulfide had an average size of about 19.4 nm, as shown in Table 1 below. These results are considered to be at the same level.

[0059] [Table 1]

[0060] <Experimental Example 3: XRD and Ellingham diagram analysis according to heat treatment temperature and carbon ratio> Fig. 6 is a graph showing the results of confirming the peak of lithium sulfide reduced according to the heat treatment temperature during the production of lithium sulfide according to an embodiment, Fig. 7 is a graph showing the change in Gibbs free energy according to the heat treatment temperature and the amount of carbon input during the production of lithium sulfide according to an embodiment, and Fig. 8 is a graph showing the results of confirming the peak of lithium sulfide reduced according to the amount of carbon input during the production of lithium sulfide according to an embodiment.

[0061] XRD peaks and Ellingham diagrams according to temperature were observed during the heat treatment for the synthesis of lithium sulfide in the same manner as in Example 1. As shown in Fig. 6, it was confirmed that the peak of Li2S reduced from Li2SO4 was clearly generated when the reaction temperature was 800°C.

[0062] In addition, the Ellingham diagram confirmed that the Gibbs free energy decrease increases with increasing heat treatment temperature and carbon input, as shown in Figure 7. When Li2SO4 and carbon were heat treated in a 1:4 ratio, a large Gibbs free energy change of approximately -250 kJ / mol was observed at approximately 800℃.

[0063] In addition, as shown in FIG. 8, it was confirmed that the greater the amount of carbon added, the clearer the peak of lithium sulfide reduced from Li2SO4 became.

[0064] <Experimental Example 4: Confirmation of lithium sulfide after purification and crystallization> As in the first embodiment, different solvents were used in the purification process. As a result, it was found that lithium sulfide dissolves in solvents within a specific polarity range as shown in Table 2 below.

[0065] [Table 2]

[0066] In addition, after the purification process using a centrifuge as in the first embodiment, it was confirmed that a layer of lithium sulfide dissolved in the solvent and a layer of impurities including carbon were separated as shown in the left photograph of Figure 9. Then, the solvent from which the impurity precipitate was removed was collected using a filter, and vacuum drying and additional heat treatment were performed, resulting in a high-purity final product as shown in the right photograph of Figure 9. In summary, it can be seen that the lithium sulfide produced in the first embodiment has improved purity compared to lithium sulfide produced by the conventional synthesis method.

[0067] Thus, the present invention has been described with reference to one embodiment shown in the drawings, but this is merely illustrative, and those skilled in the art will appreciate that various modifications and variations of the embodiment are possible. Therefore, the true technical scope of the present invention should be determined by the technical ideas of the appended claims.

Claims

1. mixing an alkali metal sulfide salt precursor and a reducing agent to form a mixture; reducing the mixture to obtain an alkali metal sulfide; and purifying the obtained alkali metal sulfide.

2. The method for producing high purity alkali metal sulfide according to claim 1 , wherein the step of mixing forms the mixture in a non-polar solvent.

3. The method for producing high purity alkali metal sulfide according to claim 1 , wherein the reducing step reduces the mixture with a reducing gas.

4. 4. The method for producing high purity alkali metal sulfide according to claim 3, wherein the reducing gas contains hydrogen and at least one selected from the group consisting of carbon monoxide, nitrogen, argon, helium, neon, methane, ethane, propane, and butane.

5. The method for producing high purity alkali metal sulfide according to claim 1 , wherein the reducing step includes a heat treatment step.

6. The method for producing high purity alkali metal sulfide according to claim 5, wherein the heat treatment step is carried out at 800°C to 1500°C.

7. The method for producing high purity alkali metal sulfide according to claim 1 , wherein the refining step purifies the obtained alkali metal sulfide using a polar solvent.

8. The method for producing high purity alkali metal sulfide according to claim 7, wherein the polarity index of the polar solvent is 4.3 to 6.

2.

9. The method for producing high purity alkali metal sulfide according to claim 7, wherein in the purification step, the obtained alkali metal sulfide is dissolved in the polar solvent.

10. The method for producing high purity alkali metal sulfide according to claim 1 , further comprising the step of crystallizing the alkali metal sulfide after the purification step.

11. The method for producing high purity alkali metal sulfide according to claim 10, wherein the crystallization step is performed by heat treatment at 300°C to 1000°C.

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