WO2024151153A1 - Method for producing lithium sulfide - Google Patents

Abstract

The present invention relates to a method for producing lithium sulfide More specifically, the present invention relates to a method for producing lithium sulfate, of which the particle size is controlled using a polar and nonpolar solvent mixed system.

Description

Method for producing lithium sulfide

Cross-Citation with Related Application(s)

This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0004791, dated January 12, 2023, and all contents disclosed in the documents of the Korean Patent Applications are included as part of this specification.

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

With the recent development of the secondary battery industry, the possibility of using solid electrolyte materials is increasing. Among them, sulfide-based solid electrolytes have higher ionic conductivity compared to oxide-based solid electrolytes and are evaluated as being stable over a wide voltage range. 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.

Among these, the method of 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 then thermally decomposing LiSH, which is an intermediate product. The reaction of hydrogen persulfide generally proceeds in a single solvent, either a polar solvent or a non-polar solvent. However, when the above reaction is carried out in a single solvent such as a polar solvent or a non-polar solvent, there are problems such as a decrease in the reaction rate and difficulty in removing the solvent.

Meanwhile, as research on the synthesis and evaluation of solid electrolytes synthesized using lithium sulfide (Li ₂ S), lithium chloride (LiCl), and phosphorus pentasulfide (P ₂ S ₅ ) as raw materials is actively conducted, lithium sulfide as a raw material It has been found that the smaller the particle size, the easier it is to synthesize a solid electrolyte using it as a raw material, and it is possible to synthesize a solid electrolyte with higher purity and ionic conductivity. However, most of the conventional technologies for synthesizing lithium sulfide using lithium hydroxide (LiOH) and hydrogen sulfide (H ₂ S) as raw materials are limited to the synthesis of lithium sulfide (Li ₂ S) and synthesized lithium sulfide (Li ₂ S) A separate additional process is required to control the particle size.

Accordingly, there is a need for research on a method for producing lithium sulfide that can solve the problems in the reaction step as described above and control the particle size of the produced lithium sulfide.

The present invention relates to a method for producing lithium sulfide that can control the particle size of the produced lithium sulfide while increasing the reaction efficiency of each step in the method for producing lithium sulfide from lithium hydroxide.

The present invention includes the steps of preparing a mixture containing lithium hydroxide and a solvent (step 1); and reacting the mixture with hydrogen sulfide gas (step 2), wherein the solvent includes a polar solvent and a non-polar solvent.

The method for producing 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 through smooth removal of reaction water generated during the reaction. .

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

Additionally, the terminology used herein is only used to describe exemplary embodiments and is not intended to limit the invention.

Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, terms such as “comprise,” “comprise,” or “have” are used to describe implemented features, numbers, steps, components, or combinations thereof, and include one or more other features, numbers, or steps. , does not exclude the possibility of components, combinations or additions thereof.

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

Since the present invention can be subject to various changes and can take various forms, specific embodiments will be illustrated and described in detail below. However, this does not limit the present invention to the specific disclosed form, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention.

The present invention includes the steps of preparing a mixture containing lithium hydroxide and a solvent (step 1); and reacting the mixture with hydrogen sulfide gas (step 2), wherein the solvent includes a polar solvent and a non-polar solvent.

For example, the process of producing lithium sulfide from lithium hydroxide may proceed in a two-step reaction as follows.

Step 1 is a step in which the reaction between lithium hydroxide and hydrogen sulfide gas is carried out, and can be carried out in the presence or absence of a solvent. A process that does not use solvents has the advantage of requiring no solvent removal or recovery processes. However, there are disadvantages in that removal of reaction water generated from the acid-base reaction is difficult and the reaction temperature is high, so using a solvent is advantageous in terms of process economics. Meanwhile, when using a solvent, it was generally common to produce lithium sulfide using a single solvent.

Non-polar solvents or polar solvents were used as the single solvent, and among these, polar solvents with a high boiling point were mainly used. When using a high boiling point polar solvent, the reaction rate of Step 1 is fast, but the thermal decomposition rate of LiSH, the reaction product, is slow, a high thermal decomposition temperature is required, and the viscosity of the reactant increases significantly during the reaction, requiring stirring during the reaction. There is a difficult problem. In particular, when the thermal decomposition temperature and thermal decomposition time of LiSH are not sufficient, the remaining LiSH reduces the purity of lithium sulfide, and a lot of energy is required for removal due to the high boiling point characteristics of the polar solvent and excellent compatibility with water.

On the other hand, when using a non-polar aromatic or aliphatic solvent, 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, the reaction rate of Step 1 is relatively slow, so water produced by the acid and base neutralization reaction of lithium hydroxide, which is the starting material, and hydrogen sulfide, and lithium hydroxide and the final product, lithium sulfide, coexist, and sulfide produced by moisture The reverse reaction of lithium proceeds, causing problems with the final yield.

Accordingly, the inventors of the present invention, when proceeding with the reaction of Step 1, mixed lithium hydroxide with a polar and non-polar mixed solvent and then reacted with hydrogen sulfide gas, the reaction efficiency of Step 1 and Step 2 without the use of a catalyst. The present invention was completed by confirming that smooth removal of the solvent and reaction water used in the reaction was possible while increasing . Furthermore, when producing lithium sulfide using a polar and non-polar mixed solvent according to the present invention, the particle size (D ₅₀ ) of the produced lithium sulfide can be controlled to a certain level, and a separate device for additional particle size control of lithium sulfide can be used. It was confirmed that the process could be omitted.

Step 1 of the present invention is a step of preparing a mixture containing lithium hydroxide and a solvent. In the present invention, the solvent includes a polar solvent and a non-polar solvent.

The polar solvent is, for example, N-methylpyrrolidone (NMP), methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, diethyl ether, diisopropyl ether, t- Examples include butylmethyl ether, phenyl methyl ether, diethoxyethane, and tetrahydrofuran, and in the present invention, they can be used alone or in a mixture of two or more types.

In addition, the non-polar solvent includes, for example, aromatic hydrocarbon-based solvents such as toluene, xylene, ethylbenzene, decalin, and 1,2,3,4-tetrahydronaphthalene; Examples include aliphatic hydrocarbon solvents such as hexane, pentane, 2-ethyl hexane, heptane, octane, decane, cyclohexane, methyl cyclohexane, hexene, heptene, and cyclohexene, and in the present invention, these can be used alone or in a mixture of two or more. You can use it.

Preferably, the polar solvent usable in the present invention is a solvent that has excellent solubility in the raw material LiOH, the intermediate product LiSH, and water, and the non-polar solvent has no reactivity with raw materials such as LiOH and H ₂ S and is thermally stable. With this solvent, the particle size of the produced lithium sulfide can be controlled by improving reactivity by controlling the solubility of raw materials and intermediate products according to the solvent ratio when mixing a polar solvent and a non-polar solvent having the above characteristics. Preferably, the polar solvent may be at least one selected from aprotic polar solvents, and the non-polar solvent may be at least one selected from aromatic solvents. More preferably, the polar solvent may be N-methylpyrrolidone, and the non-polar solvent may be xylene.

Additionally, in the present invention, the solvent includes a non-polar solvent in an amount greater than that of the polar solvent. For example, the polar solvent may be included in an amount of 1 to 50 parts by weight based on a total of 100 parts by weight of the solvent. That is, it may contain 1 to 50 parts by weight of a polar solvent and 50 to 99 parts by weight of a nonpolar solvent. When the mixed solvent contains the polar solvent and the non-polar solvent within the above range, it is easy to remove water generated by the subsequent solvent removal process and neutralization reaction, and induces high dispersion of the reactive material, lithium hydroxide, in the solvent, thereby increasing the particle size. It is easy to control. More preferably, based on a total of 100 parts by weight of the solvent, the polar solvent is used 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 more. It may contain less than or equal to 40 parts by weight.

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

According to one embodiment of the present invention, step 1 may be heated to 70 to 200° C. and then step 2 may be performed. In step 1, lithium hydroxide and the 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 added in step 2 to proceed with the reaction. Preferably, in step 1, the temperature is raised from 80 ℃ or higher, 90 ℃ or higher, 100 ℃ or higher, or 110 ℃ to 180 ℃ or lower, 160 ℃ or lower, 150 ℃ or lower, or 140 ℃ or lower, and then proceed to step 2. You can.

According to one embodiment of the present invention, in step 2, hydrogen sulfide gas may be introduced at a rate of 0.1 L/min to 5 L/min. When hydrogen sulfide gas is used in the above range, an appropriate reaction rate can be maintained, the amount of unreacted lithium hydroxide can be reduced, and the reverse reaction can be suppressed by appropriately controlling the amount of water produced by the produced lithium sulfide and neutralization reaction. . Preferably, in step 2, the hydrogen sulfide gas is 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. It can be put into .

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

Meanwhile, according to the method for producing lithium sulfide of the present invention described above, based on the average particle size (D ₅₀ ) of lithium hydroxide, which is the raw material used, the average particle size (D ₅₀ ) of the manufactured lithium sulfide is 1% or more, 1.2% or more, or While it is 1.5% or more, it can be controlled to 20% or less, 15% or less, 12% or less, or 10% or less. This is because particle size control can be appropriately controlled by utilizing the dispersibility and solubility of lithium hydroxide, which is a reactant, and lithium sulfide, which is a product, in a mixed solvent atmosphere containing a polar solvent and a non-polar solvent of the present invention.

According to one embodiment of the present invention, the average particle diameter (D ₅₀ ) of the produced lithium sulfide is 10 μm to 650 μm. The definition of average particle diameter (D ₅₀ ) is as described above. When the average particle size of lithium sulfide is controlled within the above range, it is easy to synthesize a solid electrolyte made from lithium sulfide as a raw material, and purity and ionic conductivity can be increased. Preferably, the average particle diameter (D ₅₀ ) of the lithium sulfide may be 10 um or more, but may be 650 um or less, 500 um or less, 200 um or less, or 100 um or less.

Hereinafter, the operation and effects of the invention will be described in more detail through specific examples of the invention. However, these examples are merely presented as examples of the invention, and the scope of the invention is not determined by them.

[Example]

Example 1

A solvent containing LiOH (30 g) as a raw material with an average particle diameter (D ₅₀ ) of 650 um, a mixture of the non-polar solvent xylene, and the polar solvent N-methylpyrrolidone (NMP) was used. LiOH (30 g) as a starting material was added, mixed with a mixed solvent (250 g, 2% by weight of N-methylpyrrolidone (NMP), 98% by weight of Xylene), and stirred at 200 to 400 rpm. The synthesis temperature was carried out at 130°C, and when the temperature was raised to the corresponding temperature, hydrogen sulfide (H ₂ S) 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 and base neutralization reaction ended.

It was confirmed that the average particle size of the produced lithium sulfide was 11 um.

Example 2

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

Example 3

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

Example 4

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

Example 5

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

Comparative example

Raw materials LiOH (30 g) and Xylene (250 g) with an average particle diameter (D ₅₀ ) of 650 um were mixed and stirred at 200 to 400 rpm. The synthesis temperature was carried out at 130°C, and hydrogen sulfide (H ₂ S) with a purity of 98% or more was injected at a rate of 0.2 L/min to 1 L/min at that temperature. Lithium sulfide was produced by terminating the reaction based on the point at which water generation due to the acid and base neutralization reaction ended.

The average particle size of the produced lithium sulfide was confirmed to be around 650 um, similar to that of LiOH, the starting material.

[Experimental example]

(1) Measurement of lithium sulfide particle size

D ₅₀ of LiOH used in Examples and Comparative Examples and the produced lithium sulfide were measured using a laser diffraction particle size measuring device, and the results are listed in Table 1 below.

	Lithium hydroxide average particle size (um)	solvent used	Li 2 S 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

Referring to Table 1, in Examples 1 to 5 and Comparative Examples, the average particle size of lithium hydroxide is the same at 650 um, but when the mixed solvent of Examples 1 to 5 is used, sulfide has an average particle size of about 100 um or less. While lithium was produced, when the single solvent of the comparative example was used, it was confirmed that the average particle size of lithium hydroxide was 650 um, and from this, the method for producing lithium sulfide of the present invention produced sulfide at a level smaller than the average particle size of lithium hydroxide. It was confirmed that lithium production was possible.

Claims (10)

1. Preparing a mixture comprising lithium hydroxide and a solvent (step 1); and

   Reacting the mixture with hydrogen sulfide gas (step 2),

   The solvent includes polar solvents and non-polar solvents,

   Method for producing lithium sulfide.
2. According to paragraph 1,

   Polar solvents include N-methylpyrrolidone (NMP), methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-pentanol, diethyl ether, diisopropyl ether, t-butylmethyl ether, Containing at least one member selected from the group consisting of phenyl methyl ether, diethoxyethane, and tetrahydrofuran,

   Method for producing lithium sulfide.
3. According to paragraph 1,

   Non-polar solvents include toluene, xylene, ethylbenzene, decalin, 1,2,3,4-tetrahydronaphthalene, hexane, pentane, 2-ethyl hexane, heptane, octane, decane, cyclohexane, methyl cyclohexane, hexene, Containing at least one member selected from the group consisting of heptene and cyclohexene,

   Method for producing lithium sulfide.
4. According to paragraph 1,

   The solvent is a mixture of N-methylpyrrolidone and xylene,

   Method for producing lithium sulfide.
5. According to paragraph 1,

   Containing 1 to 50 parts by weight of a polar solvent based on a total of 100 parts by weight of the solvent,

   Method for producing lithium sulfide.
6. According to paragraph 1,

   Lithium hydroxide and solvent are used in a ratio of 1:5 to 1:10 by mass,

   Method for producing lithium sulfide.
7. According to paragraph 1,

   After raising the temperature in step 1 to 70 to 200 ° C, proceed to step 2,

   Method for producing lithium sulfide.
8. According to paragraph 1,

   In step 2, hydrogen sulfide gas is introduced at 0.1 L/min to 5 L/min,

   Method for producing lithium sulfide.
9. According to paragraph 1,

   The average particle diameter (D ₅₀ ) of lithium hydroxide is 600 um to 700 um,

   Method for producing lithium sulfide.
10. According to paragraph 1,

    The average particle diameter (D ₅₀ ) of lithium sulfide is 10 um to 650 um,

    Method for producing lithium sulfide.