JP2010163356A - Method for producing lithium sulfide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing lithium sulfide, by which lithium sulfide having a large specific surface area can be efficiently produced. <P>SOLUTION: The method for producing lithium sulfide comprises: blowing hydrogen sulfide gas into slurry comprising lithium hydroxide and a hydrocarbon-based organic solvent, so as to allow lithium hydroxide to react with hydrogen sulfide; continuing the reaction while eliminating water produced by the reaction from the slurry; stopping blowing of the hydrogen sulfide after the water content in the system is substantially zero; and blowing an inert gas. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to lithium sulfide, a method for producing the same, and a sulfide-based solid electrolyte.

Conventionally, as a method for producing lithium sulfide, Patent Document 1 discloses anhydrous lithium sulfide by blowing hydrogen sulfide into a slurry composed of lithium hydroxide and an aprotic organic solvent, producing lithium hydrosulfide, and then dehydrating and desulfurizing it. A first invention for producing a lithium sulfide and a second invention for producing anhydrous lithium sulfide directly by continuously blowing hydrogen sulfide are disclosed.
In Patent Document 2, hydrogen gas and sulfur gas are simultaneously or hydrogen sulfide blown into solid lithium hydroxide whose particle size is controlled to 0.1 mm to 1.5 mm, and the temperature is 130 ° C. to 445 ° C. A method for producing lithium sulfide is disclosed.

  Further, as a method for producing an alkali metal sulfide, Patent Document 3 discloses that an alkali metal sulfide aqueous solution obtained by reacting a hydrated alkali hydrosulfide with an alkali metal hydroxide aqueous solution is brought into contact with a water-insoluble dispersion medium. And a production method characterized by dehydration.

  Lithium sulfide produced by using the above production method is known as a raw material for polyarylene sulfide, but in recent years, it has been increasingly used as a raw material for sulfide-based solid electrolytes for lithium batteries.

Regarding the sulfide-based solid electrolyte, Patent Document 4 discloses a solid electrolyte having ion conductivity of the order of 10 ⁻⁴ S / cm. Similarly, Patent Document 5 discloses a solid electrolyte synthesized from Li ₂ S and P ₂ S ₅ and having ion conductivity on the order of 10 ⁻⁴ / cm.

Patent Document 6 discloses sulfide-based crystallized glass obtained by synthesizing Li ₂ S and P ₂ S ₅ in a ratio of 68 to 74 mol%: 26 to 32 mol%. This solid electrolyte achieves ion conductivity on the order of 10 ⁻³ S / cm.

By the way, in the method for producing lithium sulfide described in Patent Document 1 and Patent Document 7, a polar solvent typified by N-methyl-2-pyrrolidone (NMP) is usually used as a solvent. However, when NMP is used, lithium N-methylaminobutyrate (LMAB) in which NMP and lithium hydroxide are reacted is generated as an impurity. In addition, for example, when dimethylformamide (DMF), which is a common polar solvent, or 1-octyl alcohol, which is an alcohol, is used as a solvent, it reacts with lithium hydroxide or hydrogen sulfide to produce impurities, resulting in a high reaction solution. Viscosity.
As described above, when a polar solvent is used to produce lithium sulfide from lithium hydroxide and hydrogen sulfide, there is a problem in that some impurities are generated and the loss of raw materials and the progress of the reaction are hindered.

In addition, in the conventional lithium sulfide production method using a polar solvent, a high temperature of 150 ° C. or higher is necessary in order to promote dehydrogenation of lithium hydrosulfide, which is a reaction intermediate.
In addition, since lithium hydrosulfide is usually dissolved in a polar solvent, increasing the preparation of lithium hydroxide as a raw material causes the viscosity of the lithium hydrosulfide solution to increase rapidly, resulting in a decrease in reaction rate and lithium hydroxide remaining. There was a bug.
Moreover, in order to make reaction temperature 150 degreeC or more, the polar solvent which has a high boiling point of 150 degreeC or more is desirable. However, in order to use the obtained lithium sulfide as an electrolyte raw material, it is necessary to remove polar solvents and impurities, and a drying step for removing high boiling point solvents is essential.
In addition, the reaction temperature is raised and the reaction product water is distilled off after lithium hydrosulfide production or during lithium sulfide production. At this time, since lithium sulfide crystals grow in the presence of moisture, the inside is clogged. Cubic Li ₂ S was obtained. Since this Li ₂ S has a structure in which the inside is clogged, the actual situation is that the specific surface area is less than 1.0 m ² / g.

Japanese Patent Laid-Open No. 7-330312 JP-A-9-278423 JP 2006-16281 A JP-A-4-202024 JP 2002-109955 A JP 2005-228570 A International Publication No. 04/106232 Pamphlet

The present inventors have found that in producing a solid electrolyte for a lithium battery, the solid electrolyte can be synthesized by stirring in a hydrocarbon-based organic solvent in addition to the conventional melting method and mechanical milling method. However, when lithium sulfide having a specific surface area of less than 1.0 m ² / g produced by a conventional method is used as a raw material, the synthesis time becomes very long as 40 hours or more, and unreacted lithium sulfide remains. There was a problem.
On the other hand, the synthesis by the mechanical milling method also differs depending on the pulverizer and conditions, but when the specific surface area of the raw material lithium sulfide is small, a reaction time of 30 hours or more is required.

  An object of the present invention is to provide a method for producing lithium sulfide capable of efficiently producing lithium sulfide having a large specific surface area.

According to the present invention, the following method for producing lithium sulfide and the like are provided.
1. Hydrogen sulfide gas is blown into a slurry composed of lithium hydroxide and a hydrocarbon-based organic solvent, the lithium hydroxide and hydrogen sulfide are reacted, and the reaction is continued while removing water generated by the reaction from the slurry. A method for producing lithium sulfide, characterized in that after water in the system is substantially exhausted, blowing of hydrogen sulfide is stopped and inert gas is blown.
2. 2. The method for producing lithium sulfide according to 1, wherein the hydrocarbon-based organic solvent comprises one or more solvents that form an azeotropic composition with water.
3. 3. The method for producing lithium sulfide according to 1 or 2, wherein the hydrocarbon-based organic solvent comprises one or more solvents selected from benzene, toluene, xylene, ethylbenzene and dodecane.

  ADVANTAGE OF THE INVENTION According to this invention, the method which can manufacture lithium sulfide with a large specific surface area efficiently can be provided. In addition, the production method of the present invention does not generate impurities and does not lose lithium as a raw material, compared to a production method using a polar solvent. Furthermore, since it can manufacture at a relatively low temperature, manufacturing costs can be reduced.

It is a schematic flowchart for demonstrating the manufacturing process of sulfide type solid electrolyte. 7 is a schematic view of a solid electrolyte production apparatus used in Example 7. FIG.

In the method for producing lithium sulfide of the present invention, hydrogen sulfide gas is blown into a slurry composed of lithium hydroxide and a hydrocarbon-based organic solvent, and the lithium hydroxide and hydrogen sulfide are reacted. And it is characterized by continuing reaction, removing the water which arises by reaction from a slurry.
In the present invention, a hydrocarbon organic solvent is used. Thereby, it is not necessary to consider the loss of raw materials due to impurities generated when a polar solvent typified by NMP is used. Hydrocarbon organic solvents have low reactivity with lithium hydroxide, which is a strong alkali, and hydrogen sulfide, which is an acid, and hardly produce impurities. This eliminates the need for a purification step for removing impurities and greatly simplifies the manufacturing process.

  Moreover, in this invention, a raw material is made to react, removing the water which arises by reaction from a slurry. For this reason, since there is substantially no water in the reaction system, lithium sulfide crystal growth does not proceed and lithium sulfide having a large specific surface area can be obtained. This lithium sulfide is suitable as a raw material for producing a solid electrolyte.

  There is no restriction | limiting in particular in the lithium hydroxide used with the manufacturing method of this invention, What is marketed industrially can be used. Since high-purity lithium sulfide can be obtained, it is preferable to use lithium hydroxide having a low impurity content.

  The hydrocarbon organic solvent used in the present invention is not particularly limited, but a solvent that forms an azeotropic composition with water is preferable. A hydrocarbon type organic solvent may be used by 1 type, and may be used by 2 or more types of mixed solvents. Specifically, benzene (boiling point 80 ° C.), toluene (boiling point 111 ° C.), xylene (boiling point: p-form, 138 ° C., m-form, 139 ° C., o-form, 144 ° C.), ethylbenzene (boiling point 136 ° C.) ) And dodecane (boiling point 215 ° C.) or a mixture thereof is preferably used.

  Lithium hydroxide and hydrocarbon organic solvent are mixed to form a slurry. At this time, the amount of lithium hydroxide charged is not particularly limited, and may be set to an appropriate concentration in consideration of handling and transfer. For example, the amount of lithium hydroxide in the slurry is desirably 30% by weight or less.

Hydrogen sulfide gas is blown into a slurry composed of lithium hydroxide and a hydrocarbon-based organic solvent to cause lithium hydroxide and hydrogen sulfide to react.
Although there is no restriction | limiting in particular also in the hydrogen sulfide to be used, Since high purity lithium sulfide can be obtained, it is preferable to use hydrogen sulfide with few impurity contents, such as a carbon dioxide and ammonia gas.
The blowing speed of hydrogen sulfide may be appropriately adjusted depending on the scale of the reaction system, reaction conditions, and the like.

  The pressure during the reaction may be normal pressure or increased pressure. By applying pressure, the reaction rate can be increased and the amount of hydrogen sulfide used can be reduced. The pressure for pressurization is preferably 0.2 to 3.0 MPa.

The temperature during the reaction varies depending on the boiling point of the hydrocarbon organic solvent used, the solubility of hydrogen sulfide, and the pressure during the reaction, but it is above the temperature at which the hydrocarbon organic solvent azeotropes with water, and carbonization under the pressure during the reaction. The boiling point of the hydrogen-based organic solvent is preferred.
As reaction temperature, 70 to 300 degreeC is preferable, for example. By reacting under heating, water generated by the reaction can be removed from the slurry. In particular, by using a solvent that forms an azeotropic composition with water, the water can be efficiently removed from the slurry. By quickly removing moisture from the reaction system, it is possible to make the reaction system substantially free of moisture, so that lithium sulfide crystal growth does not proceed and lithium sulfide having a large specific surface area can be obtained. .
Water can be removed from the system by condensing the azeotropic gas evaporated from the reaction system with a condenser or the like. At this time, the hydrocarbon-based organic solvent is also removed, but the removed amount may be newly added to the reaction system. Thereby, slurry concentration etc. can be adjusted.

  When the reaction proceeds and lithium hydroxide as a raw material disappears from the reaction system, the generation of water stops. In the present application, after the water in the system has substantially disappeared, it means a state in which water evaporated from the reaction system is no longer observed. After the generation of water stops, stop blowing hydrogen sulfide and blow inert gas. Residual hydrogen sulfide in the system can be removed by blowing the inert gas.

  After desulfurization, lithium sulfide can be recovered by separating and drying the solid component of the slurry and the organic solvent. As will be described later, it may be used in the production process of the solid electrolyte in a slurry state.

The lithium sulfide obtained by the production method of the present invention has a large specific surface area. Specifically, the specific surface area can be 1.0 m ² / g or more. When the specific surface area is less than 1.0 m ² / g, the effect of shortening the treatment time may not be obtained as compared with lithium sulfide synthesized by the conventional method.
The specific surface area of lithium sulfide is preferably 1.5 m ² / g or more, more preferably 10 m ² / g or more, and 100 m ² / g or more.

The specific surface area is measured by, for example, AUTOSORB 6 by the BET method. Since the measurement lower limit of the nitrogen method using nitrogen gas is 1.0 m ² / g, the measurement can be performed using krypton gas when it is equal to or lower than the measurement lower limit of the nitrogen method.

A sulfide-based solid electrolyte used for a lithium secondary battery or the like can be produced using lithium sulfide obtained by the above-described method of the present invention. By using Li ₂ S of the present invention, the solid electrolyte can be synthesized in a short time, so that productivity is increased. Moreover, a sulfide-based solid electrolyte can be synthesized at a desired composition ratio.
Hereinafter, an example of the production process of the sulfide-based solid electrolyte will be described with reference to the drawings. In addition, the manufacturing process of a sulfide type solid electrolyte is not limited to this example.

FIG. 1 is a schematic flow diagram for explaining a production process of a sulfide-based solid electrolyte.
The manufacturing process of the sulfide-based solid electrolyte shown in FIG. 1 mainly includes a lithium sulfide (Li ₂ S) manufacturing process 1 and a solid electrolyte manufacturing process 2.
In the lithium sulfide (Li ₂ S) production process 1, Li ₂ S is produced by the production method of the present invention described above. Specifically, lithium hydroxide (LiOH) and a water-insoluble organic solvent are charged into the reaction tank 11 to form a slurry. While heating and stirring the inside of the reaction vessel 11, hydrogen sulfide (H ₂ S) is supplied to obtain Li ₂ S. At this time, water generated during the reaction is removed outside the reaction tank 11.
After completion of the reaction, that is, generation of water stops, the supply of H ₂ S is stopped and desulfurized with an inert gas.

Li ₂ S obtained in the production process 1 is supplied to the solid electrolyte production process 2. At this time, Li ₂ S may be supplied from the reaction tank 11 in a slurry state, or Li ₂ S separated from the slurry may be supplied.
In the solid electrolyte production process 2, Li ₂ S obtained in the production process 1 is reacted with other sulfides. Specifically, Li ₂ S and other sulfides (for example, P ₂ S ₅ ) are charged into the electrolyte reaction tank 21, mixed, and then charged into the bead mill 22. The raw materials are reacted by mixing in the electrolyte reaction vessel 21 and mixing and pulverization in the bead mill 22 to obtain a solid electrolyte.

As the sulfide mixed with Li ₂ S, one or more sulfides selected from silicon sulfide, boron sulfide, and germanium sulfide can be preferably used in addition to the above-described phosphorus sulfide (P ₂ S ₅ ). P ₂ S ₅ is particularly preferable.
About said sulfide, there is no limitation in particular and what is marketed can be used.

  The above raw materials (including lithium sulfide and other sulfides) are reacted with an organic solvent added. By making it react in the state which added the organic solvent, the granulation effect at the time of a process can be suppressed and a synthetic reaction can be accelerated | stimulated efficiently. Thereby, the solid electrolyte which is excellent in uniformity and has a low content of unreacted raw materials can be obtained. Further, it is possible to prevent the raw materials and reactants from sticking to the vessel wall and the like, and to improve the product yield.

As the solvent, hydrocarbon solvents such as saturated hydrocarbons, unsaturated hydrocarbons, and aromatic hydrocarbons can be used.
Examples of the saturated hydrocarbon include hexane, pentane, 2-ethylhexane, heptane, decane, and cyclohexane.
Examples of the unsaturated hydrocarbon include hexene, heptene, cyclohexene and the like.
Aromatic hydrocarbons include toluene, xylene, decalin, 1,2,3,4-tetrahydronaphthalene and the like.
Of these, toluene and xylene are particularly preferable.

Moreover, it is also preferable to use the same solvent as the hydrocarbon-based organic solvent used in Li ₂ S production step 1. Since the lithium sulfide of the present invention generates less impurities than that produced by the conventional method, the slurry obtained in the production process 1 is charged into the electrolyte reaction vessel 21 without washing and refining lithium sulfide. can do. Moreover, since it is not necessary to use a high boiling point solvent, drying is also unnecessary. Thus, it is possible to commonly solvating between manufacturing and manufacturing the electrolyte of Li 2 _S, solid-liquid separation of lithium sulfide, washing, purification, drying can be reduced.

  The amount of water in the organic solvent is preferably 50 ppm (weight) or less in consideration of the reaction with the raw material sulfide and the synthesized sulfide solid electrolyte. Moisture causes the modification of the sulfide-based solid electrolyte due to the reaction, and deteriorates the performance of the solid electrolyte. Therefore, the lower the moisture content, the better, more preferably 30 ppm or less, and even more preferably 20 ppm or less.

  The amount of lithium sulfide charged during the reaction is preferably 30 to 95 mol%, more preferably 40 to 85 mol%, particularly 50 to 75 mol%, based on the total of lithium sulfide and other sulfides. It is preferable.

  The amount of the organic solvent is preferably such that the raw material lithium sulfide and other sulfides become a solution or slurry by the addition of the solvent. Usually, the amount of raw material (total amount) added to 1 kg of solvent is about 0.03 to 1 kg. Preferably it is 0.05-0.5Kg, Most preferably, it is 0.1-0.3Kg.

The temperature of the electrolyte reaction tank 21 is 60 ° C to 300 ° C, and preferably 80 ° C to 200 ° C. If it is less than 60 degreeC, it takes time for vitrification reaction and production efficiency is not enough. If it exceeds 300 ° C., undesirable crystals may be precipitated.
Moreover, the temperature of the bead mill 22 is 20 degreeC or more and 80 degrees C or less, Preferably they are 20 degreeC or more and 60 degrees C or less. If the treatment temperature is less than 20 ° C, the reaction time required for the production of the solid electrolyte may be long. If the treatment temperature exceeds 80 ° C, the strength of the zirconia, reinforced alumina, and alumina, which are the materials of the container and the ball, will significantly decrease. Containers and balls may be worn and deteriorated, and electrolyte contamination may occur.

The slurry taken out from the bead mill 22 consists of an organic solvent and a solid electrolyte (sulfide glass), and is transported to the crystallization heating tank 23 as it is.
If necessary, the solid electrolyte is crystallized in the crystallization heating tank 23 to obtain sulfide crystallized glass. Thereby, the ionic conductivity of the sulfide-based solid electrolyte can be improved.
The heating temperature in crystallization is 200 ° C. or more and 400 ° C. or less, more preferably 250 to 320 ° C. The heating time is preferably 1 to 5 hours, particularly preferably 1.5 to 3 hours. In addition, since it heats, stirring in a slurry state, it will be in a pressurized state with the vapor pressure of a hydrocarbon type organic solvent. Therefore, a pressure resistant reactor such as an autoclave is used for the crystallization heating tank.

After the reaction or crystallization treatment, the sulfide-based solid electrolyte can be dried with a dryer 24 if necessary. In a preferred embodiment, heating in the drying step and heating in the crystallization step can be made into one heating step. In this case, the slurry may be solid-liquid separated by a centrifugal separation process or the like and then dried by the dryer 24.
A solid electrolyte may be produced by charging Li ₂ S and other sulfides (for example, P ₂ S ₅ ) into the electrolyte reaction tank 21 and mixing and synthesizing (without using the bead mill 22). The solid electrolyte may be produced by reacting the raw materials by mixing and pulverization (without using the electrolyte reaction tank 21).

As mentioned above, although the manufacturing method of sulfide type solid electrolyte was demonstrated with reference to FIG. 1, the manufacturing method of this solid electrolyte is not limited to the above-mentioned method.
For example, production of a solid electrolyte in which a raw material containing at least lithium sulfide produced by the production method of the present invention and another sulfide is reacted in a pulverizer while being pulverized in a hydrocarbon solvent. It may be a method (Japanese Patent Application No. 2008-079753).
Further, it is a method for producing a solid electrolyte in which a raw material containing at least lithium sulfide produced by the production method of the present invention and another sulfide is reacted in a hydrocarbon solvent to produce a solid electrolyte. (PCT / JP2008 / 0667126).

  Further, in the pulverizer, a raw material containing at least lithium sulfide produced by the production method of the present invention and other sulfides is reacted while being pulverized in a hydrocarbon solvent to synthesize a solid electrolyte, and further reacted. In a tank, a raw material containing at least lithium sulfide produced by the production method of the present invention and another sulfide is reacted in a hydrocarbon solvent to synthesize a solid electrolyte, and the raw material in the reaction is crushed by the pulverizer. And a method for producing a solid electrolyte that circulates between the reaction tank (Japanese Patent Application No. 2008-292967).

The sulfide-based solid electrolyte can also be used as a solid electrolyte layer of an all-solid lithium secondary battery, a solid electrolyte mixed with a positive electrode or a negative electrode mixture, or the like.
For example, an all-solid lithium secondary battery is formed by forming a positive electrode, a negative electrode, and a layer made of a solid electrolyte between the positive electrode and the negative electrode.

[Production of lithium sulfide]
Example 1
270 g of paraxylene (Hiroshima Wako reagent) as a water-insoluble medium under a nitrogen stream was added to a 600 ml separable flask, followed by charging with 30 g of lithium hydroxide (Honjo Chemical) and stirring with a full zone stirring blade at 300 rpm. Maintained at 110 ° C.
The temperature was raised to 120 ° C. while hydrogen sulfide (manufactured by Sakai Shokai) was blown into the slurry at a supply rate of 300 ml / min. From the separable flask, an azeotropic gas of water and para-xylene was continuously discharged. This azeotropic gas was dehydrated by condensing with a condenser outside the system. During this time, the same amount of paraxylene as the distilled paraxylene was continuously supplied to keep the reaction liquid level constant.
The amount of water in the condensate gradually decreased, and no distillation of water was observed 6 hours after the introduction of hydrogen sulfide (the total amount of water was 22 ml). During the reaction, the solid was dispersed and stirred in paraxylene, and there was no moisture separated from paraxylene.
Thereafter, the hydrogen sulfide was switched to nitrogen and circulated at 300 ml / min for 1 hour.

The solid content was filtered and dried to obtain white powder of lithium sulfide. When this powder was analyzed (hydrochloric acid titration and silver nitrate titration), the purity of lithium sulfide was 99.6%. X-ray diffraction measurement confirmed that no peaks other than the lithium sulfide crystal pattern were detected.
It was 14.8 m < ² > / g as a result of measuring the specific surface area of the obtained lithium sulfide by BET method by nitrogen gas using AUTOSORB6.
Moreover, although ion chromatography analysis of the produced solid and gas chromatography analysis of para-xylene after the reaction were performed, no impurities were confirmed.

Example 2
In Example 1, lithium sulfide was obtained in the same manner except that 270 g of toluene (a reagent manufactured by Hiroshima Wako) was used as a water-insoluble medium, the temperature before blowing hydrogen sulfide was 95 ° C., and the temperature during and after blowing was changed to 104 ° C.
When the white powder obtained by filtering and drying the solid content was analyzed (hydrochloric acid titration and silver nitrate titration), the purity of lithium sulfide was 99.2%. X-ray diffraction measurement confirmed that no peaks other than the lithium sulfide crystal pattern were detected. It was 12.6 m < ² > / g as a result of measuring the specific surface area of the obtained lithium sulfide by BET method by nitrogen gas using AUTOSORB6.

Example 3
In Example 1, lithium sulfide was obtained in the same manner except that 235.5 g of dodecane (a reagent manufactured by Hiroshima Wako) was used as the water-insoluble medium, the temperature before blowing hydrogen sulfide was changed to 130 ° C., and the temperature during and after blowing was changed to 140 ° C. .
When the white powder obtained by filtering and drying the solid content was analyzed (hydrochloric acid titration and silver nitrate titration), the purity of lithium sulfide was 98.8%. X-ray diffraction measurement confirmed that no peaks other than the lithium sulfide crystal pattern were detected. It was 10.5 m < ² > / g as a result of measuring the specific surface area of the obtained lithium sulfide by BET method by nitrogen gas using AUTOSORB6.

Example 4
In Example 1, an autoclave was used instead of the separable flask, and the reaction was carried out while maintaining the system in a pressurized state by a pressure control valve.
Under a nitrogen stream, 270 g of paraxylene (Hiroshima Wako reagent) as a water-insoluble medium was added to a 600 ml autoclave, and then 30 g of lithium hydroxide (Honjo Chemical) was added. The pressure was increased to 0.85 MPa with nitrogen gas, and this pressure was maintained. While stirring at 300 rpm with a full zone stirring blade, the temperature was maintained at 200 ° C.

  The temperature was raised to 210 ° C. while hydrogen sulfide (manufactured by Sakai Shokai) was blown into the slurry at a supply rate of 300 ml / min. From the autoclave, an azeotropic gas of water and paraxylene was continuously discharged. This azeotropic gas was dehydrated by condensing with a condenser outside the system. During this time, the same amount of paraxylene as the distilled paraxylene was continuously supplied.

The amount of water in the condensate gradually decreased, and water distillation was not observed 3 hours after the introduction of hydrogen sulfide (the total amount of water was 22 ml). During the reaction, the solid was dispersed and stirred in paraxylene, and there was no moisture separated from paraxylene.
Thereafter, the supply of hydrogen sulfide was stopped, the autoclave was depressurized, and nitrogen gas was circulated at 300 ml / min for 1 hour.

The solid content was filtered and dried to obtain white powder of lithium sulfide. When this powder was analyzed (hydrochloric acid titration and silver nitrate titration), the purity of lithium sulfide was 99.4%. X-ray diffraction measurement confirmed that no peaks other than the lithium sulfide crystal pattern were detected.
It was 16.2 m < ² > / g as a result of measuring the specific surface area of the obtained lithium sulfide by BET method by nitrogen gas using AUTOSORB6.
Moreover, although ion chromatography analysis of the produced solid and gas chromatography analysis of para-xylene after the reaction were performed, no impurities were confirmed.

Example 5
In Example 4, lithium sulfide was obtained in the same manner except that paraxylene was replaced with 270 g of toluene (a reagent manufactured by Hiroshima Wako) as the water-insoluble medium.
When the white powder obtained by filtering and drying the solid content was analyzed (hydrochloric acid titration and silver nitrate titration), the purity of lithium sulfide was 99.0%. X-ray diffraction measurement confirmed that no peaks other than the lithium sulfide crystal pattern were detected.
It was 11.2 m < ² > / g as a result of measuring the specific surface area of the obtained lithium sulfide by BET method by nitrogen gas using AUTOSORB6.

Comparative Example 1
Lithium sulfide was synthesized according to the method described in Japanese Patent No. 3528866, which has been conventionally known. First, as a first step, 270 g of N-methyl-2-pyrrolidone solvent (hereinafter referred to as NMP: Hiroshima Wako Reagent), which is a polar solvent, is added to a 600 ml separable flask, followed by 30 g of lithium hydroxide (Honjo Chemical). ) And maintained at 130 ° C. while stirring with a full zone stirring blade of 300 rpm. Here, hydrogen sulfide (manufactured by Sakai Shokai) was blown into the liquid at a supply rate of 300 ml / min for 2 hours. As a result, a water flow lithium (LiSH) solution was produced according to the LiOH + H ₂ S → LiSH + H ₂ O reaction.

Subsequently, as a second step, the reaction solution was heated in a nitrogen stream (50 ml / min) to dehydrosulfide the hydrous lithium. Since water generated as a by-product due to the above reaction evaporates as the temperature rises, it was condensed outside the system by a condenser and distilled off. The temperature rises as the water is distilled off, but when the temperature reaches 205 ° C., the temperature is maintained. The holding time was 2 hours (desulfurization reaction was completed and lithium sulfide was present stably).
After cooling, the solution was filtered under reduced pressure using a glass filter, and the solid content was washed twice with NMP solvent three times and further washed twice with a toluene solvent.
It was confirmed by X-ray diffraction measurement that the white powder obtained after drying did not detect any peaks other than the lithium sulfide crystal pattern.
The specific surface area of the obtained lithium sulfide was measured by AETOSORB6 by the BET method using nitrogen gas, and as a result, it was less than 1.0 m ² / g which is the measurement limit. Therefore, nitrogen gas was changed to krypton gas and measured. The specific surface area was 0.04 m ² / g.

Comparative Example 2
As in Comparative Example 1, as a first step, 270 g of a polar solvent N, N-dimethylformamide solvent (hereinafter referred to as DMF: Hiroshima Wako Reagent) was added to a 600 ml separable flask, followed by 30 g of lithium hydroxide. (Honjo Chemical Co., Ltd.) was added and kept at 100 ° C. while stirring with a full zone stirring blade of 300 rpm.
Here, when hydrogen sulfide (manufactured by Keishokai Co., Ltd.) was blown into the liquid at a supply rate of 300 ml / min, the formation of hydrous lithium was confirmed, but the gas phase wall of the separable flask and the external condenser A large amount of white solid adhered to the upper pipe. An increase in the viscosity of the reaction solution was also observed.
This white solid is presumed to be a product derived from the decomposition of lithium hydroxide, which is a strong alkali, and the polar solvent DMF in the presence of water produced in the water flow reaction due to the amine odor.
Since there was a risk of clogging of the upper pipe with a white solid, the desulfurization reaction that was the second step could not be performed.

[Preparation of solid electrolyte]
Example 6
16.27 g of Li ₂ S prepared in Example 1 above and 33.73 g of P ₂ S ₅ (manufactured by Aldrich) having an average particle size of about 50 μm were placed in a 500 ml alumina container containing 175 10 mmφ alumina balls and sealed. The above weighing and sealing operations were all carried out in a glove box, and all the equipment used was water removed beforehand by a dryer.
This sealed alumina container was subjected to mechanical milling treatment at room temperature for a predetermined time using a planetary ball mill (PM400 manufactured by Lecce), and X-ray diffraction measurement (CuKα: λ = 1) of the white yellow solid electrolyte glass particles obtained. 5418) and the presence or absence of a Li ₂ S crystal peak was observed. It can be determined that the solid electrolyte glass was formed with the disappearance of the Li ₂ S crystal peak.
As a result, the time for the Li ₂ S crystal peak to disappear was 14 hours.

Comparative Example 3
Except for using Li ₂ S produced in Comparative Example 1, the presence or absence of a Li ₂ S crystal peak was observed in the same manner as in Example 6.
As a result, it took 36 hours for the Li ₂ S crystal peak to disappear.

From the comparison between Example 6 and Comparative Example 3, it was confirmed that the production time of the solid electrolyte could be shortened to half or less by using Li ₂ S of the present invention.

Example 7
A solid electrolyte was produced with a bead mill. Specifically, 35.2 g of Li ₂ S produced in Example 1 and 73.1 g of P ₂ S ₅ (manufactured by Aldrich) were pulverized and synthesized by a batch-type ready mill (RMB-08) manufactured by Imex. Ground synthetic conditions, 0.5MmfaiZrO ₂ beads 1271g to 800MlZrO ₂ pot was charged anhydrous toluene solvent _252.7g, Li 2 S _35.2g, the P ₂ S 5 73.1g, 1.5 hours at a rotation speed 2000rpm Thus, a solid electrolyte glass particle slurry was obtained. This solid electrolyte glass particle slurry was subjected to Nutsche-type vacuum filtration using a mesh sheet having a mesh size of 25 μm to separate and remove 0.5 mmφZrO ₂ beads to obtain a solid electrolyte glass toluene mixed solution having a solid content concentration of 30%.
As a result of X-ray diffraction measurement (CuKα: λ = 1.5418４) of the particles obtained after drying, the peak of the raw material Li ₂ S disappeared, and it was almost a halo pattern due to the solid electrolyte glass. The recovery rate of dry particles was 98%.
The solid electrolyte particles were sealed in a SUS tube under an Ar atmosphere in a glove box, and subjected to heat treatment at 300 ° C. for 2 hours to obtain electrolyte glass ceramic particles. In the X-ray diffraction measurement of this glass ceramic particle, peaks were observed at 2θ = 17.8, 18.2, 19.8, 21.8, 23.8, 25.9, 29.5, 30.0 deg. .

Comparative Example 4
In Example 5, a solid electrolyte was produced by a bead mill using Li ₂ S produced in Comparative Example 1. Specifically, 35.2 g of Li ₂ S and 73.1 g of P ₂ S ₅ (manufactured by Aldrich) manufactured in Comparative Example 1 were pulverized and synthesized by a batch-type ready mill (RMB-08) manufactured by IMEX. The pulverization and synthesis conditions were as follows: an 800 ml ZrO ₂ pot with 1271 g of 0.5 mmφZrO ₂ beads, 252.7 g of anhydrous toluene solvent, 35.2 g of Li ₂ S, and 73.1 g of P ₂ S ₅ , 1.5 hours at a rotational speed of 2000 rpm, It was treated for 3.5 hours to obtain solid electrolyte glass particle slurries. This solid electrolyte glass particle slurry was subjected to Nutsche-type vacuum filtration using a mesh sheet having a mesh size of 25 μm to separate and remove 0.5 mmφZrO ₂ beads to obtain a solid electrolyte glass toluene mixed solution having a solid content concentration of 30%.
As a result of X-ray diffraction measurement (CuKα: λ = 1.5418４) of the particles obtained after drying, in the solid electrolyte glass treated for 1.5 hours, the peak due to the raw material Li ₂ S is 2θ = 26.8, Observed at 31.0, 44.6, 52.8 deg,
In the particles treated for 3.5 hours, the peak of the raw material Li ₂ S disappeared, and the halo pattern was almost due to the solid electrolyte glass. The recovery rate of dry particles was 98%.
The solid electrolyte particles treated for 1.5 hours were sealed in a SUS tube in an Ar atmosphere in a glove box, and the electrolyte glass ceramic particles subjected to heat treatment at 300 ° C. for 2 hours were converted to Li ₂ S by X-ray diffraction measurement. A peak due to Li ₄ P ₂ S ₆ was observed while a peak due to it was still present. On the other hand, in the X-ray diffraction measurement of the electrolyte glass ceramic particles treated for 3.5 hours and heat-treated, 2θ = 17.8, 18.2, 19.8, 21.8, 23.8, 25. Peaks were observed at 9, 29.5 and 30.0 deg.
From the above, it was confirmed that the production time could be reduced to less than half even by synthesis with a bead mill.

Example 8
1.63 g of Li ₂ S prepared in Example 1 above and 3.37 g of P ₂ S ₅ (manufactured by Aldrich) having an average particle size of about 50 μm were charged into a 500 ml Schlenk bottle, and a xylene solvent (dehydrated p-xylene: Wako Pure) (Manufactured by Yakuhin Co., Ltd.) was added so that the solid concentration was 30%, and the temperature was raised to 140 ° C. while stirring with a stirrer, and reacted for a predetermined time.
5 ml of a slurry sample for each reaction time is extracted with a syringe and dried to obtain white-yellow solid electrolyte glass particles, which are subjected to X-ray diffraction measurement (CuKα: λ = 1.5418 mm) and observed for the presence of a Li ₂ S crystal peak. did.
As a result, it took 22 hours for the Li ₂ S crystal peak to disappear.

Comparative Example 5
Except for using Li ₂ S produced in Comparative Example 1, the presence or absence of a Li ₂ S crystal peak was observed in the same manner as in Example 8.
As a result, it took 48 hours for the Li ₂ S crystal peak to disappear.

From the comparison between Example 8 and Comparative Example 5, it was confirmed that the production time of the solid electrolyte could be shortened to half or less by using Li ₂ S of the present invention.

Example 9
A solid electrolyte was manufactured using the solid electrolyte manufacturing apparatus shown in FIG. In this apparatus 3, there are a reaction in the bead mill 30 and a reaction in the reaction tank 40 with stirring.
The solid electrolyte manufacturing apparatus 3 includes a bead mill 30 that synthesizes a solid electrolyte by reacting while pulverizing the raw material, and a stirred reaction tank 40 that synthesizes the solid electrolyte by reacting the raw material. The reaction tank 40 includes a container 42 and a stirring blade 44. The stirring blade 44 is driven by a motor (M).
The bead mill 30 is provided with a heater 50 through which hot water can be passed around the bead mill 30 in order to keep the inside of the bead mill 30 at 20 ° C. to 80 ° C. The reaction tank 40 is in an oil bath 60 in order to keep the inside of the reaction tank 40 at 60 ° C. to 300 ° C. The oil bath 60 heats the raw material and solvent in the container 42 to a predetermined temperature. The reaction tank 40 is provided with a cooling pipe 46 that cools and vaporizes the evaporated solvent.
The bead mill 30 and the reaction vessel 40 are connected by a first connection pipe 70 and a second connection pipe 72 (connection means). The first connection pipe 70 moves the raw material and the solvent in the bead mill 30 to the reaction tank 40, and the second connection part 72 moves the raw material and the solvent in the reaction tank 40 into the bead mill 30. A pump 74 is provided in the second connection pipe 52 in order to circulate the raw materials and the like through the connection pipes 50 and 52.
A star mill mini-zea (0.15 L) manufactured by Ashizawa Finetech Co., Ltd. was used as the bead mill 30, and 0.5 mmφ zirconia balls were charged and used.
As the reaction tank 40, a 1.5 L glass reactor equipped with a stirrer was used.

A reaction tank was prepared by adding 39.05 g (70 mol%) of Li ₂ S produced in Example 1, 80.95 g (30 mol%) of P ₂ S ₅ (30 mol%) manufactured by Aldrich, and 1080 g of dehydrated toluene manufactured by Hiroshima Wako Pure Chemical Industries, Ltd. 40 and bead mill 30 were filled.
The contents were circulated by the pump 74 at a flow rate of 400 mL / min, and the temperature of the reaction vessel 40 was increased to 80 ° C.
The main body of the bead mill 30 was operated at a peripheral speed of 8 m / s by passing warm water by external circulation so that the liquid temperature could be maintained at 70 ° C. After 6 hours, the slurry was extracted and dried at 150 ° C. to obtain a white powder.
As a result of measuring the XRD of the obtained powder, it was found that the peak of Li ₂ S as a raw material disappeared to become a solid electrolyte glass.

Comparative Example 6
A solid electrolyte was produced in the same manner as in Example 9 except that Li ₂ S produced in Comparative Example 1 was used. In this case, as a result of measuring the XRD of the powder obtained from the slurry after 6 hours, the peak of the raw material Li ₂ S did not disappear, and the treatment was insufficient. Further, the XRD of the powder obtained after the reaction was continued for 12 hours, and as a result, it was found that the peak of Li ₂ S as a raw material disappeared to become a solid electrolyte glass.

From comparison between Example 9 and Comparative Example 6, it was confirmed that the production time of the solid electrolyte could be shortened to about half by using Li ₂ S of the present invention.

Production example [Production of battery cells]
A positive electrode mixture was laminated on an aluminum foil, which was a positive electrode current collector, and pressed at 1 MPa to 68 MPa to form a positive electrode mixture layer. The positive electrode mixture was prepared by adding 70 parts by weight of the composite oxide to 30 parts by weight of the solid electrolyte and the solid electrolyte produced in Example 4 or 6 and the lithium cobaltate composite oxide as the positive electrode active material. Made.
Similarly, a negative electrode mixture layer was formed on an aluminum foil as a negative electrode current collector using a negative electrode mixture in which 60 parts by weight of carbon as a negative electrode active material was mixed with 40 parts by weight of a solid electrolyte.
A solid electrolyte layer is similarly formed on the positive electrode mixture layer described above using the solid electrolyte described above, and is sandwiched between positive and negative electrode current collectors. The positive electrode mixture layer, the solid electrolyte layer, and the negative electrode mixture layer are three layers. A battery constituted by was produced. The laminate was further thinned by applying a pressure of 1 MPa to 300 MPa.
The laminate was sandwiched between aluminum laminate films and heat-sealed under vacuum to produce a battery cell.
As the positive electrode active material used here, lithium nickelate, lithium manganate, a composite oxide thereof, and the like were implemented in addition to lithium cobaltate, and it was confirmed that the battery could be charged and discharged.
Similarly, as the negative electrode active material, carbon blacks such as graphite, mixtures thereof, and metal powders such as tin and silicon were implemented, and it was confirmed that the battery can be charged and discharged.

  According to the method for producing lithium sulfide of the present invention, lithium sulfide having a minute particle size can be produced efficiently. The lithium sulfide of the present invention is suitable as a raw material for sulfide-based solid electrolytes.

DESCRIPTION OF SYMBOLS 1 Lithium sulfide manufacturing process 11 Reaction tank 2 Solid electrolyte manufacturing process 21 Electrolyte reaction tank 22 Bead mill 23 Crystallization heating tank 24 Dryer 3 Solid electrolyte manufacturing apparatus 30 Bead mill 40 Reaction tank 42 with stirring Container 44 Stirring blade 46 Cooling pipe 50 Heater 60 Oil bath 70 First connecting pipe 72 Second connecting pipe 74 Pump

Claims (3)

Into a slurry composed of lithium hydroxide and a hydrocarbon organic solvent, hydrogen sulfide gas is blown to react the lithium hydroxide with hydrogen sulfide.
The reaction is continued while removing water generated by the reaction from the slurry,
A method for producing lithium sulfide, characterized in that after water in the system is substantially exhausted, blowing of hydrogen sulfide is stopped and inert gas is blown.   The method for producing lithium sulfide according to claim 1, wherein the hydrocarbon-based organic solvent is composed of one or more solvents that form an azeotropic composition with water.   The method for producing lithium sulfide according to claim 1 or 2, wherein the hydrocarbon-based organic solvent is composed of one or more solvents selected from benzene, toluene, xylene, ethylbenzene, and dodecane.

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