Lithium sulfide manufacturing method

Abstract

To provide a method for producing lithium sulfide, which can produce high-purity lithium sulfide at a low cost through a simple process.SOLUTION: A lithium source containing a lithium compound, excluding lithium sulfide, is heated within a reaction vessel in an atmosphere containing sulfur gas, resulting in lithium sulfide.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing lithium sulfide suitable as a constituent material of a sulfide solid electrolyte material for an all-solid-state battery, for example. [Background technology]

[0002] Lithium-ion batteries are widely used as power sources in vehicles such as EVs (electric vehicles) and HEVs (hybrid electric vehicles), as well as electronic devices such as mobile phones and laptops. Conventional lithium-ion batteries use an organic electrolyte solution, in which a lithium salt such as lithium hexafluorophosphate (LiPF6) is dissolved in an organic solvent.

[0003] These organic electrolytes are flammable and can be damaged by excessive heating or impact. In addition, in lithium-ion batteries that use metallic lithium in the negative electrode, dendrites of metallic lithium grow on the surface of the negative electrode during charging, which can cause internal short circuits between the electrodes and lead to malfunctions.

[0004] To improve the safety and durability of conventional lithium-ion batteries that use organic electrolytes, all-solid-state lithium-ion batteries using sulfide-based solid electrolytes have been proposed. Examples of sulfide-based solid electrolytes currently proposed include Li2S-P2S5, Li2S-P2S3, Li2S-SiS2, Li2S-Ga2S2, and Li2S-GeS2.

[0005] In all of these sulfide-based solid electrolytes, high-purity lithium sulfide (Li2S) is used as a constituent material. As a method for producing high-purity lithium sulfide, for example, Patent Document 1 discloses a method in which lithium hydroxide is reacted with hydrogen sulfide in an aprotic organic solvent to produce lithium hydrosulfide, and lithium sulfide is obtained from the lithium hydrosulfide.

[0006] Furthermore, Patent Document 2 discloses a method for obtaining lithium sulfide by repeating a reaction cycle in which metallic lithium is reacted with sulfur gas or hydrogen sulfide to produce lithium sulfide on the surface of metallic lithium, and then unreacted metallic lithium is melted and diffused and penetrated into the lithium sulfide that has already been produced, and then the unreacted metallic lithium is reacted again with sulfur gas or hydrogen sulfide.

[0007] Furthermore, Patent Document 3 discloses a method for producing lithium sulfide by reacting lithium carbonate with a sulfur-containing gas such as hydrogen sulfide. Furthermore, Patent Document 4 discloses a method for obtaining lithium sulfide from a raw material in which lithium sulfate and carbon powder are mixed in the form of fine particles to increase the surface area (reaction area). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-151725 [Patent Document 2] Japanese Patent Application Publication No. 9-110404 [Patent Document 3] Patent No. 4948659 [Patent Document 4] Japanese Patent Application Laid-Open No. 2013-227180 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the invention disclosed in Patent Document 1 requires the use of an aprotic organic solvent, and the organic solvent used must be treated separately, resulting in problems such as a complicated production process and high production costs.

[0010] The invention disclosed in Patent Document 2 requires metallic lithium to be reacted with sulfur gas or hydrogen sulfide multiple times, which results in a long production time and low production efficiency. Furthermore, metallic lithium is highly reactive and prone to forming an oxide film on its surface, making it difficult to handle the raw material, such as by requiring it to be handled in an inert gas atmosphere.

[0011] The invention disclosed in Patent Document 3 requires the use of toxic hydrogen sulfide gas, which poses the problem of high equipment costs, such as the need to maintain the airtightness of the reaction apparatus and the need to treat unreacted hydrogen sulfide gas.

[0012] In the invention disclosed in Patent Document 4, lithium sulfate and carbon powder need to be made into fine particles to improve reactivity, which increases the number of processing steps and raises concerns that impurities may be mixed in during the fine particle formation process. Furthermore, depending on the reaction, by-products such as lithium carbonate and lithium oxide may be produced, which may reduce the purity of the lithium sulfide.

[0013] The present invention has been made in view of the above background, and an object of the present invention is to provide a method for producing lithium sulfide that can produce high-purity lithium sulfide at low cost using simple steps. [Means for solving the problem]

[0014] In order to achieve the above object, the present invention is configured as follows. That is, the method for producing lithium sulfide according to the present invention comprises heat-treating a lithium source containing a lithium compound other than lithium sulfide in a reaction vessel under an atmosphere containing sulfur gas to produce lithium sulfide. A method for producing lithium sulfide, wherein the lithium compound is a compound containing sulfur. Here, the atmosphere containing sulfur gas is characterized in that the partial pressure of sulfur gas is 1.0 × 10 ―6 It refers to an atmosphere that is better than an ATM.

[0015] According to the present invention, high-purity lithium sulfide can be produced by a simple process of heat-treating a lithium source containing a lithium compound in an atmosphere containing sulfur gas. Therefore, high-purity lithium sulfide can be produced easily at low cost without producing by-products.

[0016] In the present invention, the lithium compound may be a compound containing sulfur.

[0017] In the present invention, the lithium compound may be lithium sulfate.

[0018] In the present invention, the lithium source may be a mixture containing the lithium compound and a carbon material.

[0019] In the present invention, the sulfur gas partial pressure (Ps) in the reaction vessel is set to 10 -5 atm or more, 10 -1 It may be in the range below atm.

[0020] In the present invention, the reaction temperature in the reaction vessel may be set in the range of 700°C or higher and 950°C or lower. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a method for producing lithium sulfide that can produce high-purity lithium sulfide at low cost using simple steps. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, a method for producing lithium sulfide according to one embodiment of the present invention will be described. Note that each embodiment shown below is specifically described to provide a better understanding of the gist of the invention, and does not limit the present invention unless otherwise specified.

[0023] The method for producing lithium sulfide according to this embodiment is for producing lithium sulfide (LiS), which is a constituent material of a sulfide solid electrolyte used as a solid electrolyte in an all-solid-state battery. Sulfide solid electrolyte materials have high ionic conductivity, are non-flammable, and are highly safe, making them suitable as materials for on-board batteries of electric vehicles (EVs) and hybrid electric vehicles (HEVs).

[0024] When lithium sulfide is produced by the method for producing lithium sulfide according to this embodiment, sulfur and a lithium source are introduced into an airtight reaction vessel, and the vessel is heated to a predetermined reaction temperature. For example, β-sulfur (monoclinic sulfur) powder can be used as the sulfur. This sulfur powder can be vaporized by heating it in the reaction vessel, and the reaction vessel can be filled with an atmosphere containing sulfur gas. Note that the reaction vessel can also be configured such that sulfur gas vaporized from sulfur powder outside the reaction vessel is introduced into the reaction vessel.

[0025] The lithium source contains at least a lithium compound other than lithium sulfide. Examples of lithium compounds include lithium sulfate, lithium carbonate, lithium oxide, and lithium hydroxide. In this embodiment, among these compounds, lithium sulfate, which contains sulfur and serves as a sulfur source for producing lithium sulfide, is used.

[0026] The lithium source may further contain a carbon material, a solvent, a binder material, and the like in addition to the lithium compound. The carbon material may be, for example, activated carbon, carbon black, etc. In this embodiment, activated carbon powder is used as the carbon material.

[0027] The solvent may be, for example, pure water or an organic solvent, and in this embodiment, pure water is used as the solvent. The binder may be a synthetic resin, and in this embodiment, polyvinyl alcohol (PVA) is used as the binder.

[0028] The lithium source of this embodiment was a granulated powder obtained by kneading a mixed powder of lithium sulfate and activated carbon powder with pure water (solvent) and polyvinyl alcohol (binder). More specifically, lithium sulfate and activated carbon were mixed in a molar ratio of 1.0:2.0, and the mixture was kneaded in a kneader with pure water in which a certain amount of polyvinyl alcohol had been dissolved, followed by extrusion granulation in a granulator. The granulated powder had a particle size of about 0.5 to 3 mm and was used as the lithium source.

[0029] As the reaction vessel (reaction device), for example, a closed rotary kiln (rotary furnace) can be used.

[0030] When lithium sulfide is produced by this embodiment, the lithium source (granulated powder) and a raw material mixture with sulfur powder are stored in a hopper at the top of the rotary kiln. After the atmosphere in the hopper and the rotary kiln is replaced with an inert gas, the raw material in the hopper is fed at a constant speed using a screw feeder into the rotary kiln, which has been heated to a predetermined temperature, and reacted continuously.

[0031] The reaction temperature may be set in the range of 700°C or higher and 950°C or lower, preferably 750°C or higher and 850°C or lower. By setting the reaction temperature to 700°C or higher, the reaction rate can be maintained within a practical range, thereby increasing productivity. Furthermore, by setting the reaction temperature to 950°C or lower, melting of lithium sulfide can be prevented. In particular, if the reaction temperature is set to 850°C or lower, when lithium sulfate is used as the lithium compound, the lithium sulfate will not melt, and lithium sulfide can be produced while maintaining its particle shape.

[0032] In addition, the partial pressure of the vaporized sulfur gas in the reaction vessel is 10 -5 atm or more, 10 -1 The amount of sulfur powder mixed with the lithium source (granulated powder) should be set so that the partial pressure of sulfur gas is in the range of 10 atm or less. -5 By reducing the partial pressure of sulfur gas to 10 atm or more, it is possible to prevent the generation of by-products such as lithium oxide and lithium carbonate. -5By setting the pressure at or below 1000 kJ / cm 2 , it is possible to suppress the amount of sulfur deposits, which are solidified sulfur gas and tend to form in low temperature parts of the reaction vessel.

[0033] Even in a configuration in which sulfur gas is introduced into the reaction vessel from the outside without mixing sulfur powder with the lithium source (granulated powder), the flow rate of the sulfur gas may be adjusted so that the partial pressure falls within the above-mentioned range.

[0034] The holding time at the reaction temperature is preferably 0.5 hours or more, more preferably 1 hour or more, and the holding time at the heating temperature is preferably 10 hours or less, more preferably 5 hours or less. When a rotary kiln is used as the reaction vessel, the rotation speed of the kiln may be set to 0.1 rpm or more and 20 rpm or less.

[0035] In the method for producing lithium sulfide according to the present embodiment, lithium sulfide is produced by the reaction shown in formula 1 below. Li2SO4+2C→Li2S+2CO2···(1) As shown in Equation 1, in this embodiment, sulfur gas is not involved in the chemical reaction. However, by using an atmosphere containing sulfur gas as the reaction atmosphere, the desorption of sulfur from lithium sulfate is suppressed in terms of equilibrium, and the generation of by-products such as lithium oxide and lithium carbonate that accompany the desorption of sulfur is suppressed.

[0036] If the lithium compound contained in the lithium source does not contain sulfur in its composition, sulfur gas in the reaction vessel is involved in the chemical reaction, sulfurizing the lithium in the compound to produce lithium sulfide.

[0037] Through the above steps, lithium sulfide can be produced. According to this embodiment, high-purity lithium sulfide is produced by a simple process of heat-treating a lithium source containing a lithium compound in an atmosphere containing sulfur gas. Therefore, high-purity lithium sulfide can be produced easily at low cost without producing by-products.

[0038] Although one embodiment of the present invention has been described above, this embodiment is presented as an example and is not intended to limit the scope of the invention. This embodiment can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. This embodiment and its modifications are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as defined in the claims. [Example]

[0039] The method for producing lithium sulfide according to this embodiment was verified below. For the verification, lithium sulfate and activated carbon were mixed in a molar ratio of 1.0:2.0, water (solvent) and PVA (binder) were added, and the mixture was kneaded using a kneader (SPG-25, manufactured by Dalton Co., Ltd.) to obtain a kneaded mixture. This kneaded mixture was then extrusion-granulated using a granulator (Disc Pelletter F5, manufactured by Dalton Co., Ltd.) to produce granulated powder with a particle size of approximately 0.5 mm to 3 mm. This granulated powder was then thoroughly dried to remove the solvent and water of crystallization. In Examples 1 to 7, sulfur powder was mixed in a predetermined ratio to obtain sample powders for Examples 1 to 7 and Comparative Example 1.

[0040] Each sample powder was then heat-treated for 3 hours at a predetermined temperature in a rotary kiln equipped with an alumina furnace tube (reaction vessel) while argon gas was flowing through the furnace tube, and the heat-treated product was recovered. Each product was pulverized in an agate mortar and then phase-identified by powder X-ray diffraction measurement (D8 ADVANCE, manufactured by Bruker Corporation). The results are shown in Table 1.

[0041] Example 1: The reaction temperature was set to 780°C, and at this temperature, the sulfur gas partial pressure was 1.0 x 10 -2 Sulfur powder was added to the pressure so that the pressure became (atm). Example 2: The reaction temperature was set to 780°C, and the sulfur gas partial pressure was 1.0 x 10 -3 Sulfur powder was added to the pressure so that the pressure became (atm). Example 3: The reaction temperature was set to 780°C, and at this temperature, the sulfur gas partial pressure was 1.0 x 10 -4 Sulfur powder was added to the pressure so that the pressure became (atm). Example 4: The reaction temperature was set to 780°C, and the sulfur gas partial pressure was 1.0 x 10 -1 Sulfur powder was added to the pressure so that the pressure became (atm). Example 5: The reaction temperature was set to 780°C, and at this temperature, the sulfur gas partial pressure was 2.0 x 10 -1 Sulfur powder was added to the pressure so that the pressure became (atm). Example 6: The reaction temperature was set to 800°C, and at this temperature, the sulfur gas partial pressure was 1.0 x 10 -2 Sulfur powder was added to the pressure so that the pressure became (atm). Example 7: The reaction temperature was set to 830°C, and at this temperature, the sulfur gas partial pressure was 1.0 x 10 -2 Sulfur powder was added to the pressure so that the pressure became (atm). Comparative Example 1: The reaction temperature was set to 780° C., and no sulfur powder was added. The sulfur gas partial pressure (Ps / atm) was calculated from the flow rate of argon gas and the amount of sulfur powder introduced (the amount of sulfur powder introduced can be calculated from the set value of the sulfur gas partial pressure and the flow rate of argon gas).

[0042] [Table 1]

[0043] According to the results shown in Table 1, it was confirmed that none of the samples of Examples 1 to 7, in which sulfur powder was added and the reaction was carried out in an atmosphere containing sulfur gas, produced by-products and was capable of producing high-purity lithium sulfide.

[0044] On the other hand, in Comparative Example 1, in which the reaction was carried out in an argon gas atmosphere without adding sulfur powder, lithium carbonate and lithium oxide were produced as by-products in addition to lithium sulfide. The increase in the product weight in Comparative Example 1 compared to Examples 1 to 4 is presumed to be due to these by-products, and the lithium sulfide in Comparative Example 1 remained low in purity due to the mixture of these by-products. Therefore, it was confirmed that the present invention makes it possible to produce high-purity lithium sulfide at low cost using a simple process.

Claims

1. A method for producing lithium sulfide by heat-treating a lithium source containing a lithium compound other than lithium sulfide in a reaction vessel filled with an atmosphere containing sulfur gas, The method for producing lithium sulfide, wherein the lithium compound is a compound containing sulfur.

2. 2. The method for producing lithium sulfide according to claim 1, wherein the lithium compound is lithium sulfate.

3. 3. The method for producing lithium sulfide according to claim 1, wherein the lithium source is a mixture containing the lithium compound and a carbon material.

4. The sulfur gas partial pressure in the reaction vessel was set to 10 －５ ATM or higher, 10 －１ The method for producing lithium sulfide according to any one of claims 1 to 3, characterized in that the pressure is in the range of 1000 kJ / cm2 or less.

5. The method for producing lithium sulfide according to any one of claims 1 to 4, wherein the reaction temperature in the reaction vessel is set in a range of 700°C or higher and 950°C or lower.

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