JP2013075816A - Lithium sulfide, method for producing the lithium sulfide, and method for producing inorganic solid electrolyte - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing lithium sulfide of small particle diameter.SOLUTION: There is provided a method for producing lithium sulfide by: bringing lithium carbonate of ≤10 μm average particle diameter into contact with a gaseous sulfur compound in a fluidizing state from at a temperature of 450°C or higher to at a melting point of lithium carbonate or lower; and reacting lithium carbonate with the sulfur compound to obtain the lithium sulfide.

Description

  The present invention relates to a method for producing lithium sulfide. The present invention also relates to a method for producing an inorganic solid electrolyte using lithium sulfide obtained by the method for producing lithium sulfide.

  Lithium sulfide is useful as a positive electrode material for lithium secondary batteries and a raw material for inorganic solid electrolytes.

  As a method for producing this lithium sulfide, for example, in Patent Document 1, lithium hydroxide and hydrogen sulfide are reacted in an aprotic organic solvent to produce lithium hydrosulfide, and then this reaction solution is dehydrosulfurized. A method for producing lithium sulfide or a method for producing lithium sulfide directly by reacting lithium hydroxide and hydrogen sulfide in an aprotic organic solvent is disclosed. Patent Document 2 discloses a method for producing lithium sulfide by reacting sodium hydrosulfide and lithium chloride in an aprotic organic solvent and then dehydrosulfiding the produced lithium hydrosulfide. ing.

  However, Patent Document 1 and Patent Document 2 are methods for synthesizing lithium sulfide in an aprotic organic solvent. The use of an expensive organic solvent requires disposal or regeneration of the organic solvent after use. For this reason, there is a problem in that it is disadvantageous in terms of the production cost of lithium sulfide because the cost for that is expensive.

  On the other hand, a method for producing lithium sulfide that does not use an organic solvent has been proposed. For example, Patent Document 3 discloses a lithium sulfide in which metallic lithium and sulfur vapor or hydrogen sulfide are directly reacted in a low temperature range, and then replaced with an inert gas to generate unreacted metallic lithium in a high temperature range. A method is disclosed in which lithium sulfide is obtained by diffusing and permeating into a metal and repeating this cycle. However, in Patent Document 3, in the reaction between metallic lithium and hydrogen sulfide, there is a problem that the reaction in the low temperature region only reacts on the surface of the metallic lithium, and the reaction in the high temperature region is too intense. There was a problem that control was difficult.

  Patent Document 4 discloses a method of obtaining lithium sulfide by reacting lithium hydroxide having a particle diameter of 0.1 mm to 1.5 mm with hydrogen sulfide at a temperature of 130 ° C. or higher and lower than 445 ° C. Yes. In Patent Document 4, lithium hydroxide used as a raw material is usually supplied as a monohydrate, and a dehydration step is required for the reaction, which causes a problem that the process becomes complicated.

Japanese Patent Laid-Open No. 7-330312 Japanese Patent Laid-Open No. 10-130005 JP-A-9-110404 JP-A-9-278423

  Incombustible inorganic solid electrolytes are materials that are particularly attracting attention because they increase the safety of batteries. In producing this inorganic solid electrolyte, there is a demand for fine lithium sulfide that can be easily and uniformly mixed with other raw materials and has excellent reactivity.

  However, in Patent Document 4, only 0.1 to 1.5 mm of coarse-grained lithium sulfide can be obtained. Further, even in the methods using the solvents of Patent Document 1 and Patent Document 2, it is difficult to produce fine lithium sulfide having an average particle diameter of 10 μm or less.

  On the other hand, in order to obtain fine lithium sulfide, a method of pulverizing the obtained coarse lithium sulfide may be considered, but excessive pulverization is not desirable because lithium sulfide itself is an unstable substance. In addition, since there is a problem of gas generated by decomposition, the pulverization operation must be performed in a state where the outside air is shut off.

  Accordingly, an object of the present invention is to provide a method for producing lithium sulfide capable of obtaining lithium sulfide having a small particle size. Moreover, the objective of this invention is providing the lithium sulfide which can make manufacture of an inorganic solid electrolyte easy.

The object is achieved by the present invention described below.
That is, in the present invention (1), lithium carbonate having an average particle size of 10 μm or less is brought into contact with a gaseous sulfur compound at a temperature not lower than 450 ° C. and not higher than the melting point of lithium carbonate. The present invention provides a method for producing lithium sulfide, which is characterized in that lithium sulfide is obtained by performing a reaction with.

  Moreover, this invention (2) obtains lithium sulfide by the manufacturing method of lithium sulfide of this invention (1), and then obtained lithium sulfide, phosphorus sulfide, silicon sulfide, germanium sulfide, boron sulfide, aluminum sulfide And a method for producing an inorganic solid electrolyte, characterized by reacting with one or more sulfides selected from the group of gallium sulfide.

  Further, the present invention (3) has an average particle diameter of 5 to 10 μm and (b) a diffraction peak in the vicinity of 2θ = 27 ° (111 plane) derived from lithium sulfide (a) in X-ray diffraction analysis. The present invention provides lithium sulfide characterized in that the intensity ratio (b / a) of diffraction peaks around 2θ = 32 ° (002 plane) derived from lithium carbonate is 0.01 or less.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of lithium sulfide which can obtain lithium sulfide with a small particle diameter can be provided. Moreover, according to this invention, the lithium sulfide which can make manufacture of an inorganic solid electrolyte easy can be provided.

2 is an X-ray diffraction pattern of lithium sulfide obtained in Example 1. FIG. 2 is an X-ray diffraction pattern of lithium sulfide obtained in Example 2. FIG. 2 is an X-ray diffraction pattern of lithium sulfide obtained in Comparative Example 1. FIG. 5 is an X-ray diffraction pattern of lithium sulfide obtained in Comparative Example 2. FIG. 6 is an X-ray diffraction pattern of lithium sulfide obtained in Comparative Example 3. FIG. 4 is an X-ray diffraction pattern of lithium sulfide obtained in Example 3. FIG. 6 is an X-ray diffraction pattern of lithium sulfide obtained in Example 4. FIG. 6 is an X-ray diffraction pattern of lithium sulfide obtained in Comparative Example 4. FIG. 6 is an X-ray diffraction pattern of lithium sulfide obtained in Comparative Example 5. FIG.

  In the method for producing lithium sulfide of the present invention, lithium carbonate having an average particle diameter of 10 μm or less is brought into contact with a gaseous sulfur compound at a temperature not lower than 450 ° C. and not higher than the melting point of lithium carbonate. It is a method for producing lithium sulfide, characterized in that lithium sulfide is obtained by reacting with a compound.

  In the method for producing lithium sulfide of the present invention, lithium carbonate is used as the lithium source. Since lithium carbonate is an anhydrous salt, it can be finely pulverized. Therefore, finely divided lithium carbonate can be obtained by using finely pulverized lithium carbonate. On the other hand, since lithium hydroxide has deliquescence, even if it is finely pulverized, the pulverized particles are aggregated, so that fine lithium hydroxide cannot be obtained. In addition, since lithium carbonate is a neutral salt, it is also advantageous that the fine pulverization of lithium carbonate does not require measures against alkaline dust as in the case of pulverizing lithium hydroxide.

  The lithium carbonate used in the method for producing lithium sulfide of the present invention may be obtained by any production method or may be a commercial product. Lithium carbonate usually contains dissimilar metals and other impurities, but is preferably as pure as possible from the viewpoint of suppressing side reactions.

  The average particle size of lithium carbonate used in the method for producing lithium sulfide of the present invention is 10 μm or less, preferably 0.1 to 5 μm. When the average particle diameter of lithium carbonate is in the above range, the particle diameter of lithium sulfide can be reduced. Further, by bringing lithium carbonate having an average particle diameter in the above range into contact with a gaseous sulfur compound in a flowing state, lithium sulfide (a), which will be described later, is around 2θ = 27 ° (111 plane) derived from lithium sulfide. (B) The intensity ratio (b / a) of the diffraction peak in the vicinity of 2θ = 32 ° (002 plane) derived from lithium carbonate (b / a) (hereinafter also simply referred to as “b / a value”) is 0. 0.01 or less, preferably 0.001 or less, particularly preferably 0.00.

  The maximum particle size of lithium carbonate used in the method for producing lithium sulfide of the present invention is preferably 50 μm or less, particularly preferably 20 μm or less. When the maximum particle size of lithium carbonate is in the above range, the reaction efficiency can be increased. Further, by bringing lithium carbonate having a maximum particle size in the above range into contact with a gaseous sulfur compound in a flowing state, the b / a value is 0.01 or less, preferably 0.001 or less, particularly preferably 0. The effect that it can be set to 0.00 is increased.

  In the present invention, the average particle diameter is an integrated 50% (D50) particle diameter determined by volume frequency particle size distribution measurement by a laser diffraction / scattering method. Further, the maximum particle size is the maximum particle size of volume frequency particle size distribution measurement obtained by a laser diffraction / scattering method.

  As the lithium carbonate used in the method for producing lithium sulfide of the present invention, lithium carbonate having a large average particle diameter and a maximum particle diameter adjusted by pulverizing lithium carbonate having a large particle diameter as a pulverization raw material is used. The pulverization treatment is not particularly limited, but dry pulverization is preferable. Examples of the dry pulverization method include a method using a jet mill, a ball mill, or the like.

  In the method for producing lithium sulfide of the present invention, a gaseous sulfur compound is brought into contact with lithium carbonate to react the lithium carbonate with the gaseous sulfur compound.

  As the gaseous sulfur compound used in the method for producing lithium sulfide of the present invention, a gaseous sulfur compound is particularly suitable as long as it is gaseous and reacts with lithium carbonate at a reaction temperature at which lithium carbonate reacts with the gaseous sulfur compound. Without being limited, for example, hydrogen sulfide, carbon disulfide, elemental sulfur gas (boiling point 444 ° C.) and the like can be mentioned. Of these, hydrogen sulfide is preferred as the gaseous sulfur compound because it has excellent reactivity and is easily available industrially.

  When hydrogen sulfide is used as the gaseous sulfur compound, it is preferable that the hydrogen sulfide has as little impurity content as possible, for example, one having a purity of 99.9 vol% or more and a water content of 2 mg / L or less is preferable. .

  In addition, when hydrogen sulfide is used as a gaseous sulfur compound, hydrogen sulfide containing moisture is corrosive to metals, and corrosive substances generated during corrosion are mixed into the reaction system as impurities. Therefore, as a pipe for supplying hydrogen sulfide to the reaction system, it is preferable to use a pipe made of a material other than a metal such as glass or a metal pipe whose inner surface is mirror-polished.

  And in the manufacturing method of lithium sulfide of the present invention, while supplying gaseous sulfur compound in the reaction system in a state in which lithium carbonate is flowed, lithium carbonate and gaseous sulfur compound in the reaction system in a fluid state To make lithium carbonate and a gaseous sulfur compound react with each other.

  In the reaction system, the reaction temperature when the lithium carbonate and the gaseous sulfur compound are brought into contact with each other and reacted is 450 ° C. or higher and the melting point of the lithium carbonate (723 ° C.) or lower, preferably 450 to 700 ° C. When the reaction temperature is in the above range, the gaseous sulfur compound is activated, and the reaction with lithium carbonate is promoted.

  The time for contacting the gaseous sulfur compound with lithium carbonate is not particularly limited as long as no unreacted lithium carbonate remains.

  As a method for supplying the gaseous sulfur compound into the reaction system, only the gaseous sulfur compound may be supplied into the reaction system, or the gaseous sulfur compound may be replaced with nitrogen, argon, helium, or the like. It may be mixed with a diluent gas that does not react with a gaseous sulfur compound such as an inert gas, and the mixed gas may be supplied into the reaction system. When the gaseous sulfur compound is mixed with the diluent gas, the ratio of the gaseous sulfur compound in the mixed gas is not particularly limited, but is preferably 20 to 95 vol%, particularly preferably 40 to 90 vol, from the viewpoint of reactivity. %, More preferably 55 to 85 vol%.

  The contact method between the lithium carbonate in a fluid state and the gaseous sulfur compound is not particularly limited. For example, (i) lithium carbonate is flowed in the reaction system, and the gaseous sulfur compound is sprayed on the lithium carbonate. And (ii) a method in which lithium carbonate is allowed to flow in the reaction system, and a certain amount of gaseous sulfur compound is supplied into the reaction system while a certain amount of gas in the reaction system is discharged. It is done. Examples of a method for bringing a gaseous sulfur compound into contact with these fluidized lithium carbonates include a method in which lithium carbonate is fluidized in a rotary kiln and a gaseous sulfur compound is supplied into the rotary kiln.

  The supply amount of the gaseous sulfur compound to the lithium carbonate is not particularly limited as long as the lithium carbonate does not remain unreacted and the supply amount of the gaseous sulfur compound is not excessive. It is preferably 1.1 to 10 mol, particularly preferably 1.5 to 5 mol in terms of S atom with respect to 1 mol.

  When lithium carbonate is reacted with a sulfur compound, carbon dioxide is by-produced. When a large amount of carbon dioxide stays in the reaction system, the reaction between lithium sulfide and carbon dioxide occurs on the surface of the lithium sulfide particles once generated, and lithium carbonate is easily generated on the particle surface. Therefore, in the method for producing lithium sulfide of the present invention, the reaction is performed while supplying the gaseous sulfur compound into the reaction system and discharging the carbon dioxide in the reaction system together with the gas in the reaction system. This is preferable in that a side reaction between lithium and carbon dioxide is prevented, and lithium sulfide substantially free of carbonate radicals is obtained.

When hydrogen sulfide is used as the gaseous sulfur compound, the reaction between lithium carbonate and hydrogen sulfide is represented by the following formula:
Li ₂ CO ₃ + H ₂ S → Li ₂ S + CO ₂ + H ₂ O
In the reaction between lithium carbonate and hydrogen sulfide, carbon dioxide and water are by-produced. In this reaction, water produced as a by-product is water vapor, and since this water vapor efficiently absorbs carbon dioxide gas, in the method for producing lithium sulfide of the present invention, while supplying hydrogen sulfide into the reaction system, Performing the reaction while discharging the carbon dioxide and water in the reaction system together with the gas in the reaction system prevents side reaction between lithium sulfide and carbon dioxide, resulting in lithium sulfide substantially free of carbonate radicals. This is preferable because the effect is enhanced.

  Then, while supplying the gaseous sulfur compound into the reaction system at a supply amount of 0.0005 to 0.0040 mol (mol / min / 1 g of lithium carbonate) per minute with respect to 1 g of lithium carbonate, It is preferable to carry out the reaction between lithium carbonate and a sulfur compound while discharging the gas in the reaction system. The gaseous sulfur compound is introduced into the reaction system at a rate of 0.0005 to 0.005 per minute with respect to 1 g of lithium carbonate. It is particularly preferable to carry out the reaction between lithium carbonate and a sulfur compound while discharging the gas in the reaction system from the reaction system while supplying at a supply amount of 0025 mol (mol / min / lithium carbonate 1 g). Thus, when the lithium carbonate is brought into contact with the gaseous sulfur compound in a fluid state, the b / a value is 0.01 or less, preferably 0.001 or less, and particularly preferably 0.00. The effect of being able to do increases. The supply amount of gaseous sulfur compound per minute per 1 g of lithium carbonate is the reaction amount of gaseous sulfur compound supplied per minute (mol / min) into the reaction system in the reaction system. It is the value divided by the mass of lithium carbonate to be made.

  After carrying out the method for producing lithium sulfide of the present invention, it is cooled and, if necessary, further pulverized or crushed, classified, packaged, etc., to obtain lithium sulfide of the product. Since it is a stable compound, after completion of the reaction, it is preferable to carry out cooling and subsequent operations in an atmosphere of an inert gas such as nitrogen, argon or helium or in a vacuum. The inert gas used at this time is preferably as high as possible from the viewpoint of preventing contamination of impurities. Further, in order to avoid contact with moisture, the dew point of the inert gas is preferably −50 ° C. or less, and particularly preferably −60 ° C. or less.

  The average particle diameter of the lithium sulfide obtained by the method for producing lithium sulfide of the present invention is an integrated 50% (D50) particle diameter determined by volume frequency particle size distribution measurement by a laser diffraction / scattering method, and is 10 μm or less, preferably 5 10 μm, particularly preferably 0.1 to 5 μm. That is, in the method for producing lithium sulfide of the present invention, fine lithium sulfide having a small particle size can be obtained. The lithium sulfide obtained by the method for producing lithium sulfide of the present invention may be in the form of a block in which the particle powder is crumbly bonded after the reaction, but in this case, by appropriately crushing or crushing, Lithium sulfide having an average particle diameter of 10 μm or less, preferably 5 to 10 μm, particularly preferably 0.1 to 5 μm is obtained.

When lithium sulfide obtained by the method for producing lithium sulfide of the present invention is used as a raw material for an inorganic solid electrolyte, in addition to the above characteristics, the content of sulfur oxides is to prevent a decrease in ionic conductivity. It is preferably 1000 ppm or less, and particularly preferably 500 ppm or less. Note that the content of sulfur oxides in the present invention, showing the content of _SO ^{3 2-,} _SO ⁴ 2- and _S ² _O ^{3 2-} of the total amount as determined by ion chromatography.

  Furthermore, the lithium sulfide obtained by the method for producing lithium sulfide of the present invention, when used as a raw material for an inorganic solid electrolyte, substantially contains lithium carbonate in terms of preventing the decrease in ionic conductivity in addition to the above characteristics. It is preferable not to contain. In the present invention, lithium sulfide substantially does not contain lithium carbonate when lithium sulfide is subjected to X-ray diffraction analysis using Cu-Kα rays (a) around 2θ = 27 ° derived from lithium sulfide. The intensity ratio (b / a) of the diffraction peak in the vicinity of 2θ = 32 ° (002 plane) derived from lithium carbonate with respect to the diffraction peak of (111 plane) is 0.01 or less, preferably 0.001 or less. It shows that. In the present invention, the diffraction peak intensity ratio (b / a) is the ratio of the diffraction peak area of (b) to the diffraction peak area of (a).

  The lithium sulfide obtained by the method for producing lithium sulfide of the present invention is suitably used as a raw material for an inorganic solid electrolyte of a lithium ion secondary battery.

  The method for producing an inorganic solid electrolyte of the present invention is obtained by obtaining lithium sulfide by the method for producing lithium sulfide of the present invention, and then the obtained lithium sulfide, phosphorus sulfide, silicon sulfide, germanium sulfide, boron sulfide, aluminum sulfide and sulfide. An inorganic solid electrolyte production method comprising reacting one or more sulfides (A) selected from the group of gallium. Hereinafter, in the method for producing an inorganic solid electrolyte of the present invention, a sulfide to be reacted with lithium sulfide is referred to as sulfide (A) in order to distinguish it from lithium sulfide.

The inorganic solid electrolyte obtained by the method for producing lithium sulfide of the present invention is Li ₂ S—P ₂ S ₃ , Li ₂ S—SiS ₂ , Li ₂ S—GeS ₂ , Li ₂ S—Ga ₂ S ₃ , Li _2. etc. _{S-B 2 S 3, Li} 2 S-Al 2 S 3 and the like.

  The physical properties and the like of the sulfide (A) used in the method for producing an inorganic solid electrolyte of the present invention are not particularly limited, but the average particle diameter of the sulfide (A) is easy in that uniform mixing with lithium sulfide is facilitated. 20 μm or less is preferable, and 1 to 10 μm is particularly preferable.

  In the method for producing an inorganic solid electrolyte of the present invention, as a method of reacting lithium sulfide and sulfide (A), for example, (i) after lithium sulfide and sulfide (A) are vitrified by mechanical milling And (ii) mixing lithium sulfide and sulfide (A), heating and melting the resulting mixture in an inert gas atmosphere, and then quenching. And the like.

In the methods (i) and (ii), the blending ratio of lithium sulfide and sulfide (A) is appropriately selected according to the composition of the target inorganic solid electrolyte. For example, when an inorganic solid electrolyte having a composition of Li ₂ S—P ₂ S ₅ is obtained from lithium sulfide and phosphorus pentasulfide, the compounding amount of phosphorus pentasulfide with respect to 1 mol of lithium sulfide is 0.1 to 0. 0.7 mol, preferably 0.25 to 0.5 mol.

  In addition, in the methods (i) and (ii), in addition to lithium sulfide and sulfide (A), sulfur may be blended as necessary for the purpose of adjusting the composition.

  The method (i) includes a vitrification step in which lithium sulfide and sulfide (A) are vitrified by mechanical milling, and a heat treatment step in which the obtained glass is heat-treated at a glass transition or higher.

  In the vitrification step according to the method (i), a predetermined amount of lithium sulfide and a predetermined amount of sulfide (A) are inactivated by using a mechanical means such as a planetary ball mill or the like using nitrogen gas, argon gas, or the like. Mechanical milling in a gas atmosphere. Examples of the equipment for performing mechanical milling include pulverizing equipment such as a bead mill, a planetary ball mill, and a vibration mill, that is, equipment in which a granular medium is present in powder to be mixed and fluidized at high speed. . And by making them flow at high speed, mechanical energy is added to the powder to be mixed by the granular medium. By controlling the rotation speed and rotation time of mechanical milling, finer and more homogeneous glass powder can be prepared, but appropriate conditions can be selected appropriately according to the type of equipment, the type of raw material, and the intended use. It is preferable to perform mechanical milling. In addition, there exists a tendency for the conversion rate to glass to become high, so that the production | generation speed | rate of glass becomes quick, so that rotation speed is fast, and rotation time is long.

In the heat treatment step according to the method (i), the obtained glass is heat-treated at a glass transition temperature or higher. By this heat treatment, lithium ion conductivity can be improved as compared with the case where only the vitrification step is performed. The heating temperature in the heat treatment step according to the method (i) varies depending on the type and blending amount of raw materials used. For example, when obtaining an inorganic solid electrolyte having a composition of Li ₂ S—P ₂ S ₅ , 200 ° C. As mentioned above, Preferably it is 250-400 degreeC. The heating time is 1 hour or longer, preferably 3 to 12 hours. Moreover, it is preferable to heat in inert gas atmosphere or a vacuum from a viewpoint of suppressing the fall of lithium ion conductivity by the oxidation of a solid electrolyte.

  In the method (ii), lithium sulfide and sulfide (A) are mixed, a melting step of heating and melting the resulting mixture in an inert gas atmosphere, and a quenching step of quenching the melt. Have.

In the melting step according to the method (ii), a predetermined amount of lithium sulfide and a predetermined amount of sulfide (A) are mixed in an inert gas atmosphere such as nitrogen gas or argon gas using mechanical means. To obtain a homogeneous mixture. The mixing apparatus that can be used is not particularly limited as long as uniform mixing can be performed, and examples thereof include a bead mill, a ball mill, a paint shaker, an attritor, and a sand mill. Next, the mixture of raw materials is heated in an inert gas atmosphere such as nitrogen gas or argon gas to melt the mixture. The heating temperature varies depending on the composition of the mixture to be melted, but when obtaining a composition of Li ₂ S—P ₂ S ₅ , the heating temperature is 700 to 1000 ° C., preferably 800 to 950 ° C., and the heating time Is 1 hour or more, preferably 3 to 6 hours.

  In the rapid cooling process according to the method (ii), the melt obtained in the melting process is rapidly cooled to obtain an inorganic solid electrolyte. In the rapid cooling step, the melt is cooled to 10 ° C. or lower, preferably 0 ° C. or lower by rapid cooling. Moreover, the cooling rate at that time is 1-1000 degreeC / second, Preferably it is 100-1000 degreeC / second. Examples of the rapid cooling method include conventional methods such as water cooling, rapid cooling with liquid nitrogen, twin-roller rapid cooling, and splat rapid cooling method.

  After obtaining the inorganic solid electrolyte by the method for producing an inorganic solid electrolyte of the present invention, if necessary, the inorganic solid electrolyte is pulverized or formed into a sheet shape, for example, composed of at least a positive electrode, a negative electrode, and an inorganic solid electrolyte In a lithium secondary battery composed of an inorganic solid electrolyte of an all-solid-state lithium battery or a non-aqueous organic electrolyte containing a positive electrode, a negative electrode, a separator, and a lithium salt, lithium metal or lithium alloy used for the positive electrode material or the negative electrode Used as a covering material.

  The lithium sulfide of the present invention has an average particle diameter of 5 to 10 μm, and (b) lithium carbonate with respect to a diffraction peak in the vicinity of 2θ = 27 ° (111 plane) derived from (a) lithium sulfide in X-ray diffraction analysis Lithium sulfide is characterized in that the intensity ratio (b / a) of the diffraction peak in the vicinity of 2θ = 32 ° (002 plane) derived from is 0.01 or less.

  The average particle diameter of the lithium sulfide of the present invention is 5 to 10 μm, preferably 0.1 to 5 μm. When the average particle diameter of lithium sulfide is in the above range, the production thereof is facilitated when used for the production of an inorganic solid electrolyte. In particular, since the average particle diameter of lithium sulfide is in the above range, the amount of inorganic solid electrolyte that adheres to the reactor during the reaction in the production process of the inorganic solid electrolyte by the reaction between lithium sulfide and sulfide can be reduced. Can be reduced.

  In the X-ray diffraction analysis of lithium sulfide of the present invention, (a) the diffraction peak near 2θ = 27 ° (111 plane) derived from lithium sulfide (b) near 2θ = 32 ° (002 plane) derived from lithium carbonate. The intensity ratio (b / a) of the diffraction peak is 0.01 or less, preferably 0.001 or less, and particularly preferably 0.00. When the intensity ratio (b / a) of the diffraction peak of (b) to the diffraction peak of (a) of lithium sulfide is in the above range, the ionic conductivity of the inorganic solid electrolyte can be increased. In the present invention, the diffraction peak intensity ratio (b / a) is the ratio of the diffraction peak area of (b) to the diffraction peak area of (a).

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.
(1) Average particle diameter and maximum particle diameter Device name: Microtrac, manufacturer: Nikkiso Co., Ltd., model: HRA, volume particle size distribution measurement by laser diffraction / scattering method was used, and average particle diameter (D50) and The maximum particle size was determined.
(2) X-ray diffraction measurement Device name: D8 ADVANCE, manufacturer: Bruker AXS, measurement conditions: target Cu-Kα, tube voltage 40 kV, tube current 40 mA, scanning speed 0.1 ° / sec, X Line diffraction measurement was performed.
(3) Ionic conductivity measurement After sandwiching both sides of a solid electrolyte with 0.30 g of electrodes (composed of 95 wt% Ni and 5 wt% Sn), the structure is held at 20 MPa for 5 minutes to form a three-layer structure A molded body was created. The ion conductivity was measured by using an AC impedance measuring device (manufactured by Solartron) using the molded body as a measurement sample.

Example 1
An average particle size of 3 cm in a rotary kiln (manufactured by Takasago Industry Co., Ltd., batch type rotary kiln) having an inner diameter of 34 cm and a length of 66 cm provided with an inlet for supplying the raw material gas into the interior and an outlet for discharging the internal gas. 100 g of lithium carbonate (manufactured by Nippon Chemical Industry Co., Ltd., lithium carbonate S) having a maximum particle size of 12 μm was added. Next, while rotating the kiln at a rotation speed of 1 rpm, a raw material gas having a volume ratio of hydrogen sulfide of 75 vol% and supplying a mixed gas of hydrogen sulfide and nitrogen at a flow rate of 5 L / min from the inlet is 600 ° C. For 2 hours. During the reaction, the reaction was carried out while discharging the gas in the rotary kiln from the outlet.
After completion of the reaction, the raw material gas was switched to nitrogen gas and cooled to room temperature. The evaluation results of the obtained lithium sulfide are shown in Table 1. An X-ray diffraction diagram is shown in FIG. (A) The intensity ratio (b / a) of the diffraction peak near 2θ = 32 ° (002 plane) derived from lithium carbonate to the diffraction peak near 2θ = 27 ° (111 plane) derived from lithium sulfide is (b / a). 0.00.

(Example 2)
The raw material gas is changed to a hydrogen sulfide of 100 vol% instead of the mixed gas of hydrogen sulfide and nitrogen whose volume ratio of hydrogen sulfide is 75 vol%, and the supply amount of the raw material gas is changed to a flow rate of 5 L / min. The same method as in Example 1 was performed except that the flow rate was 2 L / min. The evaluation results of the obtained lithium sulfide are shown in Table 1. An X-ray diffraction diagram is shown in FIG. The intensity ratio (b / a) of the diffraction peak was 0.00.

(Comparative Example 1)
Instead of lithium carbonate having an average particle size of 3.0 μm and a maximum particle size of 12 μm (made by Nippon Chemical Industry Co., Ltd., lithium carbonate S), lithium carbonate having an average particle size of 60 μm and a maximum particle size of 400 μm (manufactured by Nippon Chemical Industry Co., Ltd., The same method as in Example 1 was performed except that lithium carbonate H) was used. The evaluation results of the obtained lithium sulfide are shown in Table 1. An X-ray diffraction diagram is shown in FIG. In addition, the intensity ratio (b / a) of the diffraction peak was 0.12.

(Comparative Example 2)
It replaced with making it react at 600 degreeC for 2 hours, and it carried out by the same method as Example 1 except making it react at 300 degreeC for 10 hours. The evaluation results of the obtained lithium sulfide are shown in Table 1. An X-ray diffraction diagram is shown in FIG. The intensity ratio (b / a) of the diffraction peak was 1.89.

(Comparative Example 3)
It replaced with making it react at 600 degreeC for 2 hours, and it carried out by the same method as Example 1 except making it react at 800 degreeC for 2 hours. The evaluation results of the obtained lithium sulfide are shown in Table 1. An X-ray diffraction diagram is shown in FIG. The intensity ratio (b / a) of the diffraction peak was 0.00.

(Example 3)
Lithium carbonate (Nippon Chemical Industry Co., Ltd.) with an average particle size of 3.0 μm and a maximum particle size of 12 μm was added to a horizontal tubular furnace equipped with an inlet for supplying the raw material gas and an exhaust port for discharging the internal gas. 100 g of lithium carbonate S) was added. Next, while supplying a mixed gas of hydrogen sulfide and nitrogen having a volume ratio of 75% by volume of hydrogen sulfide as a source gas into the reaction apparatus at a flow rate of 5 L / min from the inlet, the reaction is performed at 600 ° C. for 6 hours. It was. During the reaction, the reaction was carried out while discharging the gas in the reactor from the outlet.
After completion of the reaction, the raw material gas was switched to nitrogen gas and cooled to room temperature. The evaluation results of the obtained lithium sulfide are shown in Table 1. An X-ray diffraction diagram is shown in FIG. The intensity ratio (b / a) of the diffraction peak was 0.00.

Example 4
An average particle size of 3 cm in a rotary kiln (manufactured by Takasago Industry Co., Ltd., batch type rotary kiln) having an inner diameter of 34 cm and a length of 66 cm provided with an inlet for supplying the raw material gas into the interior and an outlet for discharging the internal gas. 100 g of lithium carbonate (manufactured by Nippon Chemical Industry Co., Ltd., lithium carbonate S) having a maximum particle size of 12 μm was added. Next, while rotating the kiln at a rotation speed of 1 rpm, while supplying a mixed gas of carbon disulfide and nitrogen having a volume ratio of carbon disulfide of 50 vol% as a source gas at a flow rate of 5 L / min, The reaction was carried out at 650 ° C. for 10 hours. During the reaction, the reaction was carried out while discharging the gas in the rotary kiln from the outlet.
After completion of the reaction, the raw material gas was switched to nitrogen gas and cooled to room temperature. The evaluation results of the obtained lithium sulfide are shown in Table 1. An X-ray diffraction diagram is shown in FIG. The intensity ratio (b / a) of the diffraction peak was 0.00.

(Comparative Example 4)
Lithium hydroxide (manufactured by Nippon Chemical Industry Co., Ltd.) having an average particle diameter of 1 mm was pulverized with a coffee mill. Observation of the pulverized lithium hydroxide confirmed that fine particles of lithium hydroxide were agglomerated.
Next, in place of lithium carbonate having an average particle size of 3.0 μm and a maximum particle size of 12 μm (made by Nippon Kagaku Kogyo Co., Ltd., lithium carbonate S) Performed in the same manner as Example 1. The evaluation results of the obtained lithium sulfide are shown in Table 1. The intensity ratio (b / a) of the diffraction peak was 0.00.

(Comparative Example 5)
Lithium carbonate having an average particle size of 3.0 μm and a maximum particle size of 12 μm (Nihon Kagaku Kogyo Co., Ltd.) in a heating furnace equipped with an introduction port for supplying the raw material gas and an exhaust port for discharging the internal gas. Manufactured, lithium carbonate S) 100 g. Next, while the lithium carbonate was left standing, a mixed gas of hydrogen sulfide and nitrogen having a volume ratio of 75% by volume of hydrogen sulfide was supplied as a raw material gas at a flow rate of 600 ° C. at a flow rate of 5 L / min. The reaction was performed for 2 hours. During the reaction, the reaction was carried out while discharging the gas in the heating furnace from the outlet.
After completion of the reaction, the raw material gas was switched to nitrogen gas and cooled to room temperature. The evaluation results of the obtained lithium sulfide are shown in Table 1. An X-ray diffraction diagram is shown in FIG. (A) The intensity ratio (b / a) of the diffraction peak near 2θ = 32 ° (002 plane) derived from lithium carbonate to the diffraction peak near 2θ = 27 ° (111 plane) derived from lithium sulfide is (b / a). 0.53.

1) Supply amount of sulfur compounds per minute per gram of lithium carbonate

(Example 5)
Using a planetary mill, weighed 0.651 g (70 mol%) of lithium sulfide produced in Example 1, and weighed and added 1.349 g (30 mol%) of phosphorus pentasulfide (manufactured by Aldrich). The solid electrolyte was manufactured by performing a process for 400 rotations for 20 hours.
Next, the solid electrolyte was recovered from the planetary mill. The weight of the collected solid electrolyte was weighed, and the difference from the total weight of the above-mentioned lithium sulfide and phosphorus pentasulfide was calculated, so that the solid electrolyte that could not be recovered because it was fixed on the planetary mill was And the ratio (henceforth "the container adhering rate") to the total weight of phosphorus pentadisulfide was calculated.
Table 2 shows the container adhesion rate and the ionic conductivity of the solid electrolyte.
Container fixing ratio (%) = ((total weight of lithium sulfide and phosphorus pentasulfide−weight of recovered solid electrolyte) / total weight of lithium sulfide and phosphorus pentasulfide) × 100

(Example 6)
A solid electrolyte was produced by using the same method as in Example 5 except that the lithium sulfide produced in Example 4 was used in place of the lithium sulfide produced in Example 1.
Table 2 shows the container adhesion rate and ionic conductivity of the solid electrolyte.

(Comparative Example 6)
A solid electrolyte was produced by using the same method as in Example 5, except that the lithium sulfide produced in Comparative Example 1 was used instead of the lithium sulfide produced in Example 1.
Table 2 shows the container adhesion rate and ionic conductivity of the solid electrolyte.

(Comparative Example 7)
A solid electrolyte was produced by using the same method as in Example 5 except that the lithium sulfide produced in Comparative Example 4 was used instead of the lithium sulfide produced in Example 1.
Table 2 shows the container adhesion rate and ionic conductivity of the solid electrolyte.

  From the results in Table 2, it was confirmed that the inorganic solid electrolyte prepared using the lithium sulfide of the present invention has both high ionic conductivity and reduced container fixing rate as compared with the comparative example.

Claims (9)

  By bringing lithium carbonate having an average particle size of 10 μm or less into contact with a gaseous sulfur compound at a temperature not lower than 450 ° C. and not higher than the melting point of lithium carbonate, the reaction between lithium carbonate and the sulfur compound is carried out. A method for producing lithium sulfide, comprising obtaining lithium.   The lithium carbonate has an average particle size of 10 μm or less and a maximum particle size of 50 μm or less. The gaseous sulfur compound is added to the reaction system in an amount of 0.0005 to 0.0040 per minute with respect to 1 g of lithium carbonate. The reaction of the lithium carbonate and the gaseous sulfur compound in the reaction system while discharging the gas in the reaction system from the reaction system while supplying at a supply amount of mol (mol / min / lithium carbonate 1 g) The method for producing lithium sulfide according to claim 1, wherein:   3. The method for producing lithium sulfide according to claim 1, wherein the lithium carbonate has an average particle size of 0.1 to 5 μm and a maximum particle size of 50 μm or less.   The method for producing lithium sulfide according to any one of claims 1 to 3, wherein the gaseous sulfur compound is hydrogen sulfide.   The reaction temperature of the said lithium carbonate and the said gaseous sulfur compound is 450-700 degreeC, The manufacturing method of the lithium sulfide of any one of Claims 1-4 characterized by the above-mentioned.   The gaseous sulfur compound is hydrogen sulfide, and while supplying hydrogen sulfide into the reaction system, while discharging carbon dioxide and water vapor generated in the reaction system to the outside of the reaction system, the lithium carbonate and the gaseous state The method for producing lithium sulfide according to any one of claims 1 to 5, wherein the reaction with a sulfur compound is performed.   The method for producing lithium sulfide according to any one of claims 1 to 6, wherein the generated lithium sulfide has an average particle size of 10 µm or less.   Lithium sulfide is obtained by the method for producing lithium sulfide according to any one of claims 1 to 7, and then the obtained lithium sulfide and phosphorus sulfide, silicon sulfide, germanium sulfide, boron sulfide, aluminum sulfide and gallium sulfide are obtained. A method for producing an inorganic solid electrolyte, comprising reacting one or more sulfides selected from the group.   (B) 2θ = 32 ° derived from lithium carbonate with respect to a diffraction peak in the vicinity of 2θ = 27 ° (111 plane) derived from lithium sulfide (a) in X-ray diffraction analysis in an average particle diameter of 5 to 10 μm. Lithium sulfide, wherein the intensity ratio (b / a) of the diffraction peak in the vicinity (002 plane) is 0.01 or less.