Method for producing lithium sulfide

Abstract

The present invention relates to a method for manufacturing lithium sulfide. More specifically, it relates to a method for manufacturing lithium sulfide with controlled particle size using a polar and non-polar mixed solvent system.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing lithium sulfide. More specifically, it relates to a method for manufacturing lithium sulfide with controlled particle size using a polar and non-polar mixed solvent system. Background Technology

[0003] With the recent development of the secondary battery industry, the potential for using solid electrolyte materials is increasing. Among them, sulfide-based solid electrolytes are evaluated as having high ionic conductivity and stability over a wide voltage range compared to oxide-based solid electrolytes. Lithium sulfide, the main raw material for sulfide-based solid electrolytes, is generally manufactured by reacting a solid lithium precursor with a gaseous sulfur precursor.

[0005] Among these, a method for producing lithium sulfide through the reaction of lithium hydroxide and hydrogen sulfide relates to a method of producing lithium sulfide by reacting lithium hydroxide with hydrogen sulfide and subsequently thermally decomposing the intermediate product LiSH. The reaction between lithium hydroxide and hydrogen sulfide is generally carried out primarily in a single solvent, such as a polar solvent or a non-polar solvent. However, when the reaction is carried out in a single solvent, such as a polar solvent or a non-polar solvent, problems such as a decrease in reaction rate and difficulty in solvent removal arise.

[0007] Meanwhile, as research on the synthesis and evaluation of solid electrolytes using lithium sulfide (Li2S), lithium chloride (LiCl), and phosphorus pentasulfide (P2S5) as raw materials is actively underway, it has been revealed that as the particle size of the lithium sulfide raw material decreases, the synthesis of solid electrolytes using it becomes easier, and it is possible to synthesize solid electrolytes with higher purity and ionic conductivity. However, most conventional technologies for synthesizing lithium sulfide using lithium hydroxide (LiOH) and hydrogen sulfide (H2S) as raw materials are limited to the synthesis of lithium sulfide (Li2S), and thus require separate additional processes to control the particle size of the synthesized lithium sulfide (Li2S).

[0009] Accordingly, there is a need for research on a method for manufacturing lithium sulfide that can resolve the problems in the reaction step described above and control the particle size of the manufactured lithium sulfide. The problem to be solved

[0011] The present invention relates to a method for producing lithium sulfide from lithium hydroxide, wherein the particle size of the produced lithium sulfide can be controlled while increasing the reaction efficiency of each step. means of solving the problem

[0013] The present invention provides a method for producing lithium sulfide, comprising the steps of: preparing a mixture comprising lithium hydroxide and a solvent (Step 1); and reacting the mixture with hydrogen sulfide gas (Step 2), wherein the solvent comprises a polar solvent and a non-polar solvent. Effects of the invention

[0015] The method for manufacturing lithium sulfide according to the present invention has excellent reaction efficiency, enables efficient removal of the solvent used in the reaction, and can solve secondary problems such as environmental pollution by facilitating the smooth removal of reaction water generated during the reaction. Specific details for implementing the invention

[0017] In the present invention, terms such as first, second, etc. are used to describe various components, and these terms are used solely for the purpose of distinguishing one component from another component.

[0018] Furthermore, the terms used in this specification are used merely to describe exemplary embodiments and are not intended to limit the invention.

[0019] Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0020] In this specification, terms such as “comprising,” “comprising,” or “having” are used to describe features, numbers, steps, components, or combinations thereof that are implemented, and do not exclude one or more other features, numbers, steps, components, combinations thereof, or the possibility of addition.

[0021] Additionally, in this specification, where each layer or element is referred to as being formed "on" or "above" each layer or element, it means that each layer or element is formed directly on each layer or element, or that another layer or element may be additionally formed between each layer, on an object, or on a substrate.

[0022] The present invention is capable of various modifications and may take various forms, and specific embodiments are illustrated and described in detail below. However, this is not intended to limit the invention to the specific disclosed forms, and it should be understood that the invention includes all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0024] The present invention provides a method for manufacturing lithium sulfide, comprising the steps of: preparing a mixture comprising lithium hydroxide and a solvent (Step 1); and reacting the mixture with hydrogen sulfide gas (Step 2), wherein the solvent comprises a polar solvent and a non-polar solvent.

[0026] The process of producing lithium sulfide from lithium hydroxide can proceed as a two-step reaction, for example, as follows.

[0027]

[0029] Step 1 is a step for carrying out the reaction between lithium hydroxide and hydrogen sulfide gas, which can be performed in the presence or absence of a solvent. A process without a solvent has the advantage of eliminating the need for solvent removal or recovery steps. However, because removing the reaction water generated by the acid-base reaction is difficult and the reaction temperature is high, using a solvent is advantageous in terms of process economics. Meanwhile, when a solvent is used, it has generally been common to manufacture lithium sulfide using a single solvent.

[0031] As the single solvent mentioned above, either a non-polar or a polar solvent was used; among these, polar solvents with a high boiling point were mainly used. When using a high-boiling-point polar solvent, while the reaction rate of Step 1 is fast, the thermal decomposition rate of the reaction product LiSH is slow, a high thermal decomposition temperature is required, and the viscosity of the reactant increases significantly during the reaction, leading to problems such as difficulty in stirring during the reaction. In particular, if the thermal decomposition temperature and time of LiSH are insufficient, the remaining LiSH degrades the purity of lithium sulfide, and due to the high boiling point characteristics and excellent compatibility with water of polar solvents, a large amount of energy is required for its removal.

[0033] Meanwhile, when using non-polar solvents such as aromatic or aliphatic solvents, the thermal decomposition rate of LiSH, the reaction product of Step 1, is fast, and the thermal decomposition reaction proceeds at a relatively low temperature. However, because the reaction rate of Step 1 is relatively slow, water, lithium hydroxide, and the final product lithium sulfide coexist due to the acid-base neutralization reaction of the starting material lithium hydroxide and hydrogen sulfide, and the reverse reaction of lithium sulfide produced by the water proceeds, causing problems with the final yield.

[0035] Accordingly, the inventors of the present invention have completed the present invention by confirming that when lithium hydroxide is mixed with a polar and non-polar mixed solvent and then reacted with hydrogen sulfide gas during the reaction of Step 1, the reaction efficiency of Steps 1 and 2 can be increased without the use of a catalyst, while also enabling the smooth removal of the solvent and reaction water used in the reaction. Furthermore, when lithium sulfide is manufactured using a polar and non-polar mixed solvent according to the present invention, the particle size (D) of the manufactured lithium sulfide 50 It was confirmed that the particle size of lithium sulfide can be controlled to a certain level, thereby eliminating the need for a separate process for additional control of lithium sulfide particle size.

[0037] Step 1 of the present invention is a step of preparing a mixture comprising lithium hydroxide and a solvent, wherein the solvent in the present invention includes a polar solvent and a non-polar solvent.

[0039] Examples of the above polar solvents include N-methylpyrrolidone (NMP), methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, diethyl ether, diisopropyl ether, t-butylmethyl ether, phenylmethyl ether, diethoxyethane, tetrahydrofuran, etc., and in the present invention, these may be used alone or in a mixture of two or more.

[0041] In addition, the above-mentioned nonpolar solvents may include, for example, aromatic hydrocarbon solvents such as toluene, xylene, ethylbenzene, decarin, and 1,2,3,4-tetrahydronaphthalene; aliphatic hydrocarbon solvents such as hexane, pentane, 2-ethylhexane, heptane, octane, decane, cyclohexane, methylcyclohexane, hexene, heptene, and cyclohexene, and in the present invention, these may be used alone or in a mixture of two or more types.

[0043] Preferably, the polar solvent usable in the present invention is a solvent having excellent solubility for the raw material LiOH, the intermediate product LiSH, and water, and the non-polar solvent is a solvent having no reactivity with raw materials such as LiOH and H2S and having thermally stable properties. When the polar solvent and the non-polar solvent having the above properties are mixed, the particle size of the lithium sulfide produced can be controlled by improving reactivity through the property of controlling the solubility of the raw material and the intermediate product according to the solvent ratio. For example, N-methylpyrrolidone may be used as the polar solvent, and xylene may be used as the non-polar solvent.

[0045] In addition, in the present invention, the solvent comprises a non-polar solvent in an amount greater than or equal to that of the polar solvent. For example, the polar solvent may be included in an amount of 1 to 50 parts by weight per 100 parts by weight of the total solvent. That is, the polar solvent may be included in an amount of 1 to 50 parts by weight, and the non-polar solvent may be included in an amount of 50 to 99 parts by weight. When the polar solvent and the non-polar solvent are included in the above ranges in the mixed solvent, it is easy to remove water generated by the subsequent solvent removal process and neutralization reaction, and it is easy to control the particle size by inducing high dispersion of the reaction material, lithium hydroxide, in the solvent. More preferably, the polar solvent may be included in an amount of 1.5 parts by weight or more, 2 parts by weight or more, 3 parts by weight or more, 4 parts by weight or more, or 5 parts by weight or more, and 50 parts by weight or less, 45 parts by weight or less, or 40 parts by weight or less, per 100 parts by weight of the total solvent.

[0047] In addition, in the present invention, lithium hydroxide and the solvent may be used in a ratio of 1:5 to 1:10 by mass. When lithium hydroxide and the solvent are used in the above range, high dispersion of lithium hydroxide is induced, which is advantageous for controlling the particle size of the lithium sulfide produced. Preferably, lithium hydroxide and the solvent may be used in a ratio of 1:5.5 to 1:9.5, 1:6 to 1:9, or 1:7 to 1:8 by mass.

[0049] According to one embodiment of the present invention, Step 1 can be performed by raising the temperature to 70 to 200°C, and then proceeding to Step 2. In Step 1, lithium hydroxide and a solvent can be mixed by stirring, and the temperature of the mixture can be raised to the above range while stirring and mixing. After raising the temperature to the above range, hydrogen sulfide can be introduced in Step 2 to carry out the reaction. Preferably, Step 1 can be performed by raising the temperature to 80°C or higher, 90°C or higher, 100°C or higher, or 110°C or higher and 180°C or lower, 160°C or lower, 150°C or lower, or 140°C or lower, and then proceeding to Step 2.

[0051] According to one embodiment of the present invention, hydrogen sulfide gas may be introduced in step 2 at a rate of 0.1 L / min to 5 L / min. When hydrogen sulfide gas is used within this range, an appropriate reaction rate can be maintained, and while reducing the amount of unreacted lithium hydroxide, the amount of water produced by the neutralization reaction with the prepared lithium sulfide can be appropriately controlled to suppress the reverse reaction. Preferably, in step 2, hydrogen sulfide gas may be introduced at a rate of 0.15 L / min or more, or 0.2 L / min or more, and 4 L / min or less, 3 L / min or less, 2 L / min or less, or 1 L / min or less.

[0053] According to one embodiment of the present invention, the average particle size (D) of lithium hydroxide 50) is 600 µm to 700 µm. In this specification, the average particle size (D 50 ) refers to the particle diameter at the 50% point of the cumulative distribution of particle numbers according to particle size (particle diameter). The above average particle diameter (D 50 ) can be measured using a laser diffraction scattering particle size distribution measuring device, and the particle size at the point where the cumulative distribution of particle numbers according to particle diameter reaches 50% is calculated, and this is the average particle diameter (D 50 It is defined as ). Preferably, the average particle size (50) of the lithium hydroxide may be 600 µm or more or 650 µm or more, and 700 µm or less.

[0055] According to one embodiment of the present invention, the average particle size (D) of the manufactured lithium sulfide 50 The average particle size (D) is 10 µm to 650 µm. 50 The definition of ) is as described above. When the average particle size of lithium sulfide is controlled within the above range, it facilitates the synthesis of solid electrolytes manufactured using lithium sulfide as a raw material, while increasing purity and ionic conductivity. Preferably, the average particle size (D) of the lithium sulfide is 50 ) may be 10 µm or more, and 650 µm or less, 500 µm or less, 200 µm or less, or 100 µm or less.

[0057] The operation and effects of the invention will be described in more detail below through specific embodiments. However, these embodiments are merely examples of the invention and do not define the scope of the invention.

[0059] [Example]

[0060] Example 1

[0061] Average particle size (D 50A solvent was used in which raw material LiOH (30 g) of a 650 μm level was mixed with a non-polar solvent Xylene and a polar solvent N-methylpyrrolidone (NMP). The starting material LiOH (30 g) was added, and the mixed solvent (250 g, 2 wt% N-methylpyrrolidone (NMP), 98 wt% Xylene) was mixed and stirred at 200 to 400 rpm. The synthesis was carried out at a temperature of 130 ℃, and once the temperature was raised to this level, hydrogen sulfide (H2S) was injected at a rate of 0.2 L / min to 1 L / min. Lithium sulfide was produced by terminating the reaction at the point when water generation due to acid-base neutralization reaction ceased.

[0062] It was confirmed that the average particle size of the synthesized lithium sulfide was 11 μm.

[0064] Example 2

[0065] Lithium sulfide was prepared in the same manner as in Example 1, except that a mixed solvent of 5 wt% NMP and 95 wt% Xylene was used.

[0067] Example 3

[0068] Lithium sulfide was prepared in the same manner as in Example 1, except that a mixed solvent of 10 wt% NMP and 90 wt% Xylene was used.

[0070] Example 4

[0071] Lithium sulfide was prepared in the same manner as in Example 1, except that a mixed solvent of 30% NMP and 70% Xylene was used.

[0073] Example 5

[0074] Lithium sulfide was prepared in the same manner as in Example 1, except that a mixed solvent of 50 wt% NMP and 50 wt% Xylene was used.

[0076] Comparative example

[0077] Average particle size (D 50 ) mixed raw materials LiOH (30 g) and Xylene (250 g) of a 650 µm level and stirred at 200 to 400 rpm. The synthesis was carried out at a temperature of 130 ℃, and at that temperature, hydrogen sulfide (H2S) with a purity of 98% or higher was injected at a rate of 0.2 L / min to 1 L / min. Lithium sulfide was produced by terminating the reaction based on the point at which water generation due to the acid-base neutralization reaction ceased.

[0078] The average particle size of the manufactured lithium sulfide was confirmed to be around 650 μm, similar to that of the starting material, LiOH.

[0080] [Experimental Example]

[0081] (1) Measurement of lithium sulfide particle size

[0082] D of the LiOH used in the examples and comparative examples and the prepared lithium sulfide 50 The particle size was measured using a laser diffraction particle size measuring device, and the results are listed in Table 1 below.

[0084] Lithium hydroxide average particle size (um) Solvent used Li2S average particle size (D 50 , um) Example 1 650 NMP 2%, Xylene 98% 11 Example 2 650 NMP 5%, Xylene 95% 14 Example 3 650 NMP 10%, Xylene 90% 22 Example 4 650 NMP 30%, Xylene 70% 31 Example 5 650 NMP 50%, Xylene 50% 52 Comparative example 650 Xylene 650

[0085] Referring to Table 1, in Examples 1 to 5 and Comparative Example, the average particle size of lithium hydroxide is the same at the level of 650 μm; however, when the mixed solvent of Examples 1 to 5 is used, lithium sulfide having an average particle size of about 100 μm or less is produced, whereas when the single solvent of Comparative Example is used, it is confirmed that it is at the same level as the average particle size of lithium hydroxide of 650 μm. From this, it was confirmed that the method for producing lithium sulfide according to the present invention can produce lithium sulfide at a level smaller than the average particle size of lithium hydroxide.

Claims

Claim 1 A method for manufacturing lithium sulfide, comprising the steps of: preparing a mixture comprising lithium hydroxide and a solvent (Step 1); and reacting the mixture with hydrogen sulfide gas (Step 2), wherein the solvent comprises a polar solvent and a non-polar solvent, and the polar solvent comprises 1 to 50 parts by weight per 100 parts by weight of the total solvent. Claim 2 A method for producing lithium sulfide according to claim 1, wherein the polar solvent comprises one or more selected from the group consisting of N-methylpyrrolidone (NMP), methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, diethyl ether, diisopropyl ether, t-butylmethyl ether, phenylmethyl ether, diethoxyethane, and tetrahydrofuran. Claim 3 A method for producing lithium sulfide according to claim 1, wherein the non-polar solvent comprises one or more selected from the group consisting of toluene, xylene, ethylbenzene, decarin, 1,2,3,4-tetrahydronaphthalene, hexane, pentane, 2-ethylhexane, heptane, octane, decane, cyclohexane, methylcyclohexane, hexene, heptene, and cyclohexene. Claim 4 A method for producing lithium sulfide according to claim 1, wherein the solvent is a mixture of N-methylpyrrolidone and xylene. Claim 5 delete Claim 6 A method for manufacturing lithium sulfide according to claim 1, wherein lithium hydroxide and a solvent are used in a mass ratio of 1:5 to 1:

10. Claim 7 A method for manufacturing lithium sulfide according to claim 1, wherein the temperature of step 1 is raised to 70 to 200 ℃, and then step 2 is performed. Claim 8 A method for manufacturing lithium sulfide according to claim 1, wherein in step 2, hydrogen sulfide gas is introduced at a rate of 0.1 L / min to 5 L / min. Claim 9 In paragraph 1, the average particle size (D) of lithium hydroxide 50 A method for manufacturing lithium sulfide, wherein ) is 600 µm to 700 µm. Claim 10 In paragraph 1, the average particle size of lithium sulfide (D 50 A method for manufacturing lithium sulfide, wherein ) is 10 μm to 650 μm.

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