JP6602258B2 - Method for producing lithium sulfide and method for producing inorganic solid electrolyte - Google Patents

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.

  Although the method of patent document 1 and 2 can obtain a thing with high ion conductivity, since an expensive organic solvent is used, it becomes expensive and is not industrially advantageous.

  On the other hand, as a method for producing lithium sulfide that does not use an organic solvent, for example, Patent Document 3 discloses that metal lithium and sulfur vapor or hydrogen sulfide are directly reacted in a low temperature range, and then replaced with an inert gas at a high temperature. A method for obtaining lithium sulfide by diffusing and infiltrating unreacted metallic lithium into already produced lithium sulfide and repeating this cycle is disclosed.

  In addition, a method for producing lithium sulfide by reducing lithium sulfate with a reducing agent has been proposed (see, for example, Patent Documents 4 to 5).

  In addition, a method of reacting in a solid phase using lithium carbonate or lithium hydroxide as a lithium source has been proposed (see, for example, Patent Documents 6 to 8).

  A method that does not use an organic solvent is advantageous in terms of cost, but tends to have low ionic conductivity when used as an inorganic solid electrolyte.

  In addition, in the method of reacting in a solid phase using lithium hydroxide and lithium carbonate as a lithium source and the method of using lithium sulfate, in addition to lowering the ionic conductivity, the baked product further reacts with the reaction vessel. There is also a problem that it is difficult to take out lithium sulfide as a fired product by firmly fixing to the container.

Japanese Patent Laid-Open No. 7-330312 Japanese Patent Laid-Open No. 10-130005 JP-A-9-110404 JP 2013-227180 A JP-A-9-283156 JP 2014-169196 A JP 2014-169197 A JP2013-75816A

  Accordingly, an object of the present invention is to provide an industrially advantageous method capable of obtaining lithium sulfide having high ionic conductivity when used as an inorganic solid electrolyte.

  As a result of intensive studies in view of the above circumstances, the inventors of the present invention have prepared an inorganic lithium sulfide obtained by charging a raw material mixture containing a lithium source and a sulfur source in a firing container pre-laid with a granular ceramic and firing the mixture. It has been found that when used as a solid electrolyte, the ion conductivity becomes high, and further, it is easy to take out lithium sulfide from the fired product from the fired container even after firing, and the present invention is completed. It was.

  That is, the method for producing lithium sulfide to be provided by the present invention is characterized in that a raw material mixture containing a lithium source and a sulfur source is charged into a firing container preliminarily coated with granular ceramic and fired.

  In addition, the method for producing an inorganic solid electrolyte to be provided by the present invention is to obtain lithium sulfide by the above-described lithium sulfide production method, and then obtain the obtained lithium sulfide, phosphorus sulfide, silicon sulfide, germanium sulfide, sulfide It is characterized by reacting with one or more compounds selected from the group consisting of boron, aluminum sulfide, gallium sulfide, lithium phosphate, lithium silicate and lithium iodide.

  According to the present invention, lithium sulfide having high ionic conductivity when used as an inorganic solid electrolyte can be provided in an industrially advantageous manner.

2 is an X-ray diffraction chart of lithium sulfide obtained in Example 1 and Comparative Example 1. FIG. The X-ray-diffraction chart of the lithium sulfide obtained in Example 11 and Comparative Example 3.

  Hereinafter, the present invention will be described based on preferred embodiments thereof.

  The method for producing lithium sulfide according to the present invention is characterized in that a raw material mixture containing a lithium source and a sulfur source is charged in a firing container in which granular ceramic is previously laid and fired.

That is, this production method includes a raw material mixing step for obtaining a raw material mixture containing a lithium source and a sulfur source, a firing step for firing the raw material mixture, and a separation step for separating the granular ceramic from the fired product as necessary.
(1) Raw material mixing step;
As the lithium source related to the raw material mixing step, lithium carbonate and lithium hydroxide are preferable, and lithium hydroxide is particularly preferable.

  As the sulfur source for the raw material mixing step, sulfur alone is preferable.

  Moreover, the lithium source and sulfur source which concern on a raw material mixing process may contain both lithium and sulfur. As the compound containing both lithium and sulfur, lithium sulfate is preferable.

  The lithium source or sulfur source involved in the raw material mixing step may be obtained by any production method or may be a commercially available product. In obtaining high-purity lithium sulfide, the lithium source and sulfur source are preferably as low as possible. The lithium source and sulfur source may be hydrated or anhydrous.

  Further, the particle sizes of the lithium source and sulfur source are not particularly limited.

  The ratio of sulfur atoms to lithium atoms in the raw material mixture of the lithium source and sulfur source, and the molar ratio (S / Li) in terms of atoms is preferably 0.2 to 3, and particularly preferably 0.3 to 1.

  In this production method, a reducing agent can be contained in the raw material mixture as necessary depending on the types of lithium source and sulfur source to be used.

  That is, when a lithium source such as lithium carbonate or lithium hydroxide is used and sulfur alone or the like is used as a sulfur source, a reducing agent is not necessarily required, but when lithium sulfate is used as a lithium source and a sulfur source, It is preferable to use a reducing agent.

  Examples of the reducing agent in the raw material mixing step include a carbon material and an organic compound having a plurality of hydroxyl groups.

  The carbon material is a material composed of only carbon atoms, and examples thereof include carbon black, carbon fiber, graphite, activated carbon and the like. Carbon black related to the carbon material is not limited by what production method it is obtained, for example, furnace black obtained by the furnace method, channel black obtained by the channel method, obtained by the acetylene method Examples thereof include acetylene black and thermal black obtained by a thermal method. Examples of the carbon fiber related to the carbon material include polyacrylonitrile-based carbon fiber and pitch-based carbon fiber.

  As the organic compound having a plurality of hydroxyl groups, saccharides and polyhydric alcohols are preferable from the viewpoint of excellent reactivity.

  Examples of the saccharide include monosaccharides such as fructose, disaccharides such as sucrose and lactose, oligosaccharides in which monosaccharides are bound by about 3 to 20 molecules, polysaccharides such as starch and cellulose, and sugar alcohols such as xylitol and sorbitol. Is mentioned.

  Examples of the polyhydric alcohols include divalent alcohols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol, trivalent alcohols such as glycerin and trimethylolpropane, and 4 in the molecule. Examples include tetravalent or higher-valent alcohols having the above hydroxyl groups, polymers having a large number of hydroxyl groups such as polyvinyl alcohol, and the like.

  In this production method, the reducing agent is preferably a saccharide, and a monosaccharide or a disaccharide is preferable in that the effect of obtaining lithium sulfide with a low content of heterogeneous phase is increased and the amount of carbon remaining in the lithium sulfide is reduced. Sucrose is particularly preferred.

The compounding amount of the reducing agent varies depending on the lithium source and sulfur source to be used. When lithium sulfate is used as the lithium source and sulfur source, reduction with respect to O _{2 in} lithium sulfate (Li ₂ SO ₄ ) in terms of anhydride is performed. The molar ratio (C / O ₂ ) of carbon atoms in the agent is 1.00 to 2.10, preferably 1.40 to 2.00. When the molar ratio of the carbon atom in the reducing agent to O _{2 in} lithium sulfate is in the above range, there is little residual carbon in the lithium sulfide after firing, and the ionic conductivity when used as an inorganic solid electrolyte Tend to be higher.

  In addition, when lithium carbonate and / or lithium hydroxide is used as the lithium source and sulfur alone is used as the sulfur source, the ratio of the carbon atom derived from the reducing agent to the lithium atom in the raw material mixture is an atomic conversion molar ratio ( C / Li), 0.05 to 0.5 is preferable, and 0.1 to 0.3 is particularly preferable. When the ratio of carbon atoms to lithium atoms in the raw material mixture is within the above range, there is little carbon remaining in the lithium sulfide after firing, and ion conductivity tends to be high when used as an inorganic solid electrolyte. is there.

Further, in this production method, when a firing reaction in the next step is performed using a reducing agent (1) selected from organic compounds having a plurality of hydroxyl groups, the fired product is scattered in the firing container due to a rapid reaction. Although it is easy, by using a reducing agent (1) selected from an organic compound having a plurality of hydroxyl groups and a reducing agent (2) selected from a carbon material, a reduction reaction can be performed while suppressing an abrupt reaction. In addition, even after firing, it is even easier to take out lithium sulfide as a fired product from the firing container. Also, the lithium sulfide obtained in this way can be obtained having high ionic conductivity when used as an inorganic solid electrolyte. The carbon material of the reducing agent (2) used in combination with the reducing agent (1) is a porous carbon material that takes a lithium source, a sulfur source, and a reducing agent (1) into its pores, forming a reaction field, From the viewpoint that the effect of suppressing scattering is high, activated carbon is particularly preferable from the viewpoint of obtaining a large amount of a low specific surface area that has a high effect of preventing scattering of the fired product. Further, the BET specific surface area of the porous carbon material to be used, preferably 500 meters ² / g or more, particularly preferably it is preferred from the viewpoint of the effect of suppressing the scattering prevention of the burned material is increased to 800~3000m ² / g.

  Hereinafter, “reducing agent (1)” and “reducing agent (2)” are collectively referred to simply as “reducing agent”.

  The weight ratio of the reducing agent (1) and the reducing agent (2) (reducing agent (1) / {reducing agent (1) + reducing agent (2)}) is 85 to 99% by mass, preferably It is preferable to set it as 88-96 mass% from a viewpoint of making a reduction reaction advance efficiently and obtaining the scattering prevention effect of a baked product.

  The means for mixing the lithium source, sulfur source and reducing agent added as necessary in the raw material mixing step is not particularly limited, and a wet method or a dry method is used so that the raw materials are uniformly dispersed. Done.

  The wet method can be carried out by an apparatus such as a ball mill, a disper mill, a homogenizer, a vibration mill, a sand grind mill, an attritor, and a powerful stirrer.

  On the other hand, in the dry method, apparatuses such as a high speed mixer, a super mixer, a turbo sphere mixer, a Henschel mixer, a Nauter mixer, a ribbon blender, and a V-type mixer can be used. These uniform mixing operations are not limited to the illustrated mechanical means. If desired, the particle size may be adjusted by pulverizing with a jet mill or the like. Also, at the laboratory level, home mixing or manual mixing is sufficient.

The raw material mixture that has been subjected to the uniform mixing treatment is put into a firing container on which granular ceramics have been laid in advance and subjected to a firing step.
(2) firing step;
In the firing step, the raw material mixture is added to the firing container under the condition that the granular ceramic is laid on the firing container.

  By carrying out a firing reaction in a state where a granular ceramic is laid on a firing container, a product having high ionic conductivity when used as an inorganic solid electrolyte is obtained.

  As for the reaction related to this production method, for example, the present inventors presume that the reaction of reducing lithium sulfate monohydrate with sucrose proceeds mainly according to the following reaction formula (1).

_{3Li 2 SO 4 · H 2 O} + C 12 H 22 O 11
→ 3Li ₂ S + 14H ₂ O + 12CO ↑ (1)
In the present invention, the reason why high ionic conductivity is obtained when used as an inorganic solid electrolyte by firing in a state in which the particulate ceramic is laid on the firing container is not clear, but the present inventors Since the reaction can be carried out while efficiently excluding gaseous substances such as CO and water vapor produced as a by-product in the reduction reaction, the granular ceramic becomes a medium, the reduction reaction is easily completed. The present inventors presume that when lithium sulfide produced is used as an inorganic solid electrolyte, the ionic conductivity is high.

  In addition, by adding the raw material mixture to the firing container with the granular ceramic laid on the firing container, the raw material mixture does not directly contact the bottom of the firing container. As a result, the reaction product, lithium sulfide, is prevented from sticking to the firing container and easily peeled from the firing container. In addition, there is an advantage that contamination with impurities is reduced.

  The kind of granular ceramic is preferably inert to the raw material mixture and lithium sulfide from the viewpoint of obtaining high-purity lithium sulfide. Specifically, alumina, magnesia, zirconia, silicon nitride, chrome steel, stainless steel, menor, tungsten carbide, etc. can be used, and alumina is preferred from the viewpoint of being inert, inexpensive and easily available in large quantities. .

  The shape of the granular ceramic is not particularly limited, and may be a spherical shape, a cubic shape, a rectangular shape, a conical shape, a plate shape, a rod shape, or the like.

  The size of the granular ceramic is such that the average particle diameter determined by a method of directly measuring the particle diameter with a caliper or the like is 0.5 mm or more, preferably 1 to 10 mm in terms of handling of the granular ceramic, It is preferable from the viewpoint of ease of separation.

  Depending on how the granular ceramic is laid, the peelability between the fired container and the fired product, the concentration of impurities in the fired product, and the reaction may vary, so the granular ceramic should be evenly distributed along the bottom of the fired container and, if possible, along the wall surface. It is preferable to lay.

  The material of the firing container is not particularly limited as long as it is a container with little impurities mixed in, but for example, metal aluminum, alumina, cordierite, dalmitite, mullite, or from a hollow glass such as a ceramic coated metal surface. And the like.

  The firing temperature when firing the raw material mixture is 750 to 1000 ° C, preferably 800 to 1000 ° C. When the firing temperature is in the above range, generation of heterogeneous phases can be suppressed and lithium sulfide can be obtained efficiently. The firing time when firing the raw material mixture is appropriately selected as long as no unreacted raw material remains. The firing atmosphere when firing the raw material mixture is an inert gas atmosphere such as nitrogen, argon or helium or a reducing gas atmosphere such as hydrogen gas.

  After firing the raw material mixture, the fired product, that is, the generated lithium sulfide is cooled in an inert gas atmosphere such as nitrogen, argon, helium, etc., in a reducing gas atmosphere such as hydrogen gas, or in a vacuum, and after cooling If necessary, further pulverization or crushing, classification, packaging, etc. are performed to obtain lithium sulfide as a product. The inert gas or reducing 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 or reducing gas is preferably −50 ° C. or lower, and particularly preferably −60 ° C. or lower.

  In addition, the granular ceramic may adhere to the lithium sulfide of the fired product to be produced and collected together with the fired product from the fired container, but the granular ceramic attached to the fired product is pulverized or crushed as it is, Next, by performing a separation step of classifying with a sieve having an opening smaller than the particle size of the used granular ceramic, the fired product and the granular ceramic are separated, and only the lithium sulfide of the target fired product is separated and recovered. I can do it.

  The average particle diameter of the lithium sulfide obtained by the method for producing lithium sulfide of the present invention is not particularly limited, but is preferably 10 to 500 μm, particularly preferably 30 to 300 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.

  Further, in the method for producing lithium sulfide of the present invention, since the lithium source, the sulfur source and, if necessary, a reducing agent are reacted, the method for producing lithium sulfide of the present invention is not a method using an organic solvent, and It is not a production method using a sulfur source of a toxic gas such as hydrogen sulfide. Further, in the method for producing lithium sulfide of the present invention, lithium sulfate is obtained by mixing lithium sulfate and a reducing agent, and then firing using a firing container in which granular ceramic is previously spread. The manufacturing method of lithium sulfide is a manufacturing method with a small number of steps.

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

  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, sulfide A method for producing an inorganic solid electrolyte, comprising reacting one or more compounds selected from the group consisting of gallium, lithium phosphate, lithium silicate and lithium iodide. Hereinafter, in the method for producing an inorganic solid electrolyte of the present invention, a compound to be reacted with lithium sulfide is referred to as a compound (A) in order to distinguish it from lithium sulfide.

The inorganic solid electrolyte obtained by the method for producing an inorganic solid electrolyte of the present invention includes Li ₂ S—P ₂ S ₅ , Li ₂ S—SiS ₂ , Li ₂ S—GeS ₂ , Li ₂ S—Ga ₂ S ₃ , Li ₂ S—B ₂ S ₃ , Li ₂ S—Al ₂ S ₃ , Li ₄ SiO ₄ —Li ₂ S—SiS ₂ , Li ₃ PO ₄ —Li ₂ S—SiS ₂ , LiI—Li ₂ S—P ₂ S ₅ etc. are mentioned.

  The physical properties and the like of the compound (A) used in the method for producing an inorganic solid electrolyte of the present invention are not particularly limited, but the average particle size of the compound (A) is 20 μm in that uniform mixing with lithium sulfide is easy. The following 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 compound (A), for example, (i) a method of vitrifying lithium sulfide and compound (A) by mechanical milling, ( ii) A method in which lithium sulfide and the compound (A) are mixed, and the resulting mixture is heated and melted in an inert gas atmosphere and then rapidly cooled. Moreover, the method of improving ion conductivity is mentioned by performing the heat processing process which heat-processes the vitrified material obtained by (i) and (ii) at the temperature more than a glass transition.

In the methods (i) and (ii), the mixing ratio of lithium sulfide and the compound (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.

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

  In the vitrification step according to the method (i), a predetermined amount of lithium sulfide and a predetermined amount of compound (A) are mixed with an inert gas such as nitrogen gas or argon gas using mechanical means such as a planetary ball mill. Perform mechanical milling in an 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.

  The method (ii) has a melting step of mixing lithium sulfide and the compound (A) and heating and melting the resulting mixture in an inert gas atmosphere, and a quenching step of quenching the melt. .

In the melting step according to the method (ii), a predetermined amount of lithium sulfide and a predetermined amount of the compound (A) are mixed using a mechanical means in an inert gas atmosphere such as nitrogen gas or argon gas. 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. However, when a Li ₂ S—P ₂ S ₅ composition is obtained, 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.

In the method of further heat-treating the vitrified product obtained by the method (i) or (ii), the obtained vitrified product is further heated at a temperature equal to or higher than the glass transition temperature, and heat-treated. A heat treatment process is performed. By this heat treatment step, 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 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 , it is 200 ° C. or higher, preferably 250 to 400. ° C. The heating time is 1 hour or longer, preferably 3 to 12 hours. Moreover, it is preferable to perform heating in an inert gas atmosphere or under vacuum from the viewpoint of suppressing a decrease in lithium ion conductivity due to oxidation of the inorganic solid electrolyte.

  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.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these.
(1) 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-ray Diffraction measurement was performed.

Further, the abundance of heterogeneous Li ₂ CO _{3 in} the lithium sulfide crystal was determined as follows. The diffraction peak intensity ratio is the area ratio of diffraction peaks.
<Abundance of Li ₂ CO ₃ >
Intensity ratio of diffraction peaks (d / a) = (a) diffraction peak intensity around 2θ = 27 ° (111 plane) derived from lithium sulfide / (d) around 2θ = 21 ° (110 plane) derived from lithium carbonate (2) Ionic conductivity measurement of the inorganic solid electrolyte The both sides of the inorganic solid electrolyte were sandwiched between 0.30 g of electrodes (composed of 95 wt% Ni and 5 wt% Sn) and then held at 20 MPa for 5 minutes. Thus, a molded body having a three-layer structure was prepared. The ion conductivity was measured by using an AC impedance measuring device (manufactured by Solartron) using the molded body as a measurement sample.
(3) Evaluation of the state of scattering of the fired product in the crucible The contents of the crucible were visually observed after firing,
“×” indicates that the entire inner wall other than the bottom surface of the crucible is attached to the fired product.
“△” indicates that the fired material is attached to the inner wall other than the bottom of the crucible.
“○” indicates that there is almost no adhesion of the fired product on the inner wall other than the bottom of the crucible.
As evaluated.
(4) Evaluation of the state of fixation of the fired product to the crucible After recovering the fired product by turning the crucible upside down, the state of the bottom surface of the inner wall of the crucible was visually observed,
“×” indicates that the adhesion of the fired product is generally observed on the bottom surface of the inner wall of the crucible,
“△” indicates that the fired product is attached to the bottom of the inner wall of the crucible.
The one with almost no adhesion of the fired product to the bottom of the inner wall of the crucible
As evaluated.
{Example 1}
(1) Raw material mixing step;
Lithium sulfate monohydrate (Li ₂ SO ₄ .H ₂ O, average particle size 30 μm) 10.83 g and sucrose (C ₁₂ H ₂₂ O ₁₁ ) 9.17 g were mixed in a dry coffee mill for 30 seconds to obtain a raw material mixture. Obtained.
(2) firing step;
The raw material mixture was put in an alumina crucible (size: 50 mmφ) with 10 g of alumina beads (diameter: 3 mmφ) evenly spread all over the bottom in advance, and the temperature was raised to 850 ° C in a nitrogen gas atmosphere at 5 ° C / min. Then, baking was performed at 850 ° C. for 6 hours.

  After the completion of firing, the product was cooled to 120 ° C., and the crucible containing the fired product was quickly moved to the glove box.

  Next, the state of scattering of the fired product in the crucible was observed, and the fired product was recovered together with the beads by inverting the crucible from the fired product, and the state of fixation of the fired product to the crucible was observed. Next, the collected fired product was lightly pulverized in a mortar, and then the beads and the fired product were separated through a sieve having an opening of 2 mm. Next, the separated fired product was ground again in a mortar, and 4 g of lithium sulfide was obtained through a sieve having an opening of 200 μm.

Moreover, when the XRD analysis was performed about the obtained lithium sulfide, the different phase was not observed but it was a lithium sulfide single phase. An X-ray diffraction chart is shown in FIG.
{Examples 2 to 5}
(1) Raw material mixing step;
Lithium sulfate monohydrate (Li ₂ SO ₄ .H ₂ O, average particle size 30 μm), sucrose (C ₁₂ H ₂₂ O ₁₁ ) and activated carbon (manufactured by Nippon Environ Chemicals; Shirataka A; BET specific surface area 1000 m ² / g) were weighed so as to have the blending ratio shown in Table 1, and mixed in a dry coffee mill for 30 seconds to obtain a raw material mixture.
(2) firing step;
The raw material mixture was put into an alumina crucible (size: 50 mmφ) in which 10 g of alumina beads (diameter: 3 mmφ) were spread all over the bottom in advance, and the firing reaction was carried out in the firing furnace at the firing temperature shown in Table 1 in a nitrogen gas atmosphere. went.

  After the completion of firing, the product was cooled to 120 ° C., and the crucible containing the fired product was quickly moved to the glove box.

  Then, the crucible was turned upside down from the fired product, and the fired product was collected together with the beads. After lightly pulverizing with a mortar, the beads and the fired product were separated through a sieve having an opening of 2 mm. Next, the separated fired product was ground again in a mortar, and lithium sulfide was obtained through a sieve having an opening of 200 μm.

  Further, when XRD analysis was performed on the obtained lithium sulfide, no heterogeneous phase was observed, and the lithium sulfide was a single phase of lithium sulfide.

{Comparative Example 1}
The raw material mixing step and the firing step were performed in the same manner as in Example 1 except that an alumina crucible (size: 50 mmφ) in which alumina beads were not previously placed was used.

  After the completion of firing, the product was cooled to 120 ° C., and the crucible containing the fired product was quickly moved to the glove box.

  Next, the fired product is recovered by turning the crucible upside down from the fired product or scraping off the material adhering to the crucible with a spoon, etc., pulverized in a mortar, and 4 g of lithium sulfide is passed through a sieve having an opening of 200 μm. Obtained.

  Further, in the same manner as in Example 1, the state of scattering of the fired product and the state of fixation of the fired product to the crucible were observed.

Further, when the obtained lithium sulfide was XRD analysis, the _{Li 2 SO 4, Li 2 CO} 3 as the hetero-phase was observed. The abundance of Li ₂ CO ₃ was also evaluated, and the results are shown in Table 2. An X-ray diffraction chart is shown in FIG.

表中の「還元剤（１）の配合割合（ｗｔ％）」は、還元剤（１）／｛（還元剤（１）＋還元剤（２）｝として表した。また、還元剤の添加量は、無水物換算の硫酸リチウム中のＯ₂と還元剤（還元剤（１）＋還元剤（２））中のＣ原子のモル比（Ｃ／Ｏ₂）で表した。

The “mixing ratio (wt%) of reducing agent (1)” in the table is expressed as reducing agent (1) / {(reducing agent (1) + reducing agent (2)}. It is expressed as O ₂ and a reducing agent in the lithium sulfate in dry solid basis (the reducing agent (1) + reducing agent (2)) molar ratio of C atoms in the (C / O _2).

表２の結果、実施例１と比較例１を比較すると、本製造方法により、坩堝への焼成物の固着が改良され、また、得られる硫化リチウムについても異相のないものが得られることが分かる。また、実施例１と実施例２を比較すると、還元剤（１）と還元剤（２）を併用することで、焼成物の飛散を抑制し、更に坩堝からの焼成物の硫化リチウムの取り出しがいっそう容易になることが分かる。
（実施例６〜１０及び比較例２）
実施例及び比較例で得られた硫化リチウム０．３８３ｇ（７５モル％）と、五二硫化リン（Ａｌｄｒｉｃｈ社製）０．６１７ｇ（２５モル％）を秤量し、それらを、遊星ミルにて、４００回転で２０時間処理して、無機固体電解質を得た。得られた無機固体電解質のイオン伝導度を測定した。その結果を表３に示す。

As a result of Table 2, when Example 1 and Comparative Example 1 are compared, it can be seen that the present manufacturing method improves the adhesion of the fired product to the crucible, and the obtained lithium sulfide has no different phase. . Moreover, when Example 1 and Example 2 are compared, by using a reducing agent (1) and a reducing agent (2) in combination, scattering of the fired product is suppressed, and further, lithium sulfide of the fired product is taken out from the crucible. It can be seen that it becomes easier.
(Examples 6 to 10 and Comparative Example 2)
0.383 g (75 mol%) of lithium sulfide obtained in Examples and Comparative Examples and 0.617 g (25 mol%) of phosphorus pentasulfide (manufactured by Aldrich) were weighed, and they were measured using a planetary mill. An inorganic solid electrolyte was obtained by treatment at 400 rpm for 20 hours. The ionic conductivity of the obtained inorganic solid electrolyte was measured. The results are shown in Table 3.

表３の結果より、実施例１及び比較例１を比較して分かるように、予め粒状セラミックを敷いた焼成容器で焼成を行った硫化リチウムを用いることにより、無機固体電解質のイオン伝導度が高くなることが分かる。

From the results of Table 3, as can be seen by comparing Example 1 and Comparative Example 1, the ionic conductivity of the inorganic solid electrolyte is high by using lithium sulfide that has been fired in a firing container in which granular ceramics have been laid in advance. I understand that

{Example 11}
(1) Raw material mixing step;
Lithium hydroxide monohydrate (LiOH.H ₂ O, manufactured by Nippon Kagaku Kogyo Co., Ltd., BQ product) was ground for 15 seconds with a wonder blender, then sieved with a 212 μm sieve, 20.00 g, sulfur (manufactured by Hosoi Chemical, Finely pulverized product) 8.79 g was mixed in a dry coffee mill for 30 seconds to obtain a raw material mixture.
(2) firing step;
5.00 g of the raw material mixture was put in an alumina crucible (size: 50 mmφ) in which 5 g of alumina beads (diameter: 3 mmφ) were spread evenly over the entire bottom surface, and 900 ° C at 100 ° C / hour in a nitrogen gas atmosphere in a firing furnace. The mixture was heated up to 900 ° C. for 3 hours.

  After the completion of firing, it was cooled to 120 ° C., and the crucible containing the fired product was quickly moved to the glove box.

  Next, the fired product was collected together with the beads by turning the crucible upside down from the fired product, and the fixed state of the fired product on the crucible was observed. Next, the collected fired product was lightly pulverized in a mortar, and then the beads and the fired product were separated through a sieve having an opening of 2 mm. Next, the separated fired product was ground again in a mortar, and 0.94 g of lithium sulfide was obtained through a sieve having an opening of 200 μm.

  Moreover, when the XRD analysis was performed about the obtained lithium sulfide, the different phase was not observed but it was a lithium sulfide single phase. An X-ray diffraction chart is shown in FIG.

{Comparative Example 3}
(1) Raw material mixing step The raw material mixing step was performed in the same manner as in Example 11.
(2) Firing step 5.00 g of the raw material mixture is directly charged into an alumina crucible (size: 50 mmφ) without placing alumina beads, and the temperature is raised to 900 ° C. at 100 ° C./hour in a nitrogen gas atmosphere. And calcination at 900 ° C. for 3 hours.

  After the completion of firing, the product was cooled to 120 ° C., and the crucible containing the fired product was quickly moved to the glove box.

  Next, the fired product is recovered by turning the crucible upside down from the fired product or scraping off the material adhering to the crucible with a spoon, etc., pulverized in a mortar, and passed through a sieve having an opening of 200 μm to obtain lithium sulfide. 41 g was obtained.

  Further, in the same manner as in Example 11, the state of fixation of the fired product to the crucible was observed.

Further, when the obtained lithium sulfide was XRD analysis, Li ₂ SO ₄ was observed as different phase. An X-ray diffraction chart is shown in FIG.

表４の結果、実施例１１と比較例３を比較すると、本製造方法により、坩堝への焼成物の固着が大幅に改良され、また、得られる硫化リチウムについても還元剤を用いなくとも異相のないものが得られることが分かる。
（実施例１２）
実施例１１で得られた硫化リチウム０．３８３ｇ（７５モル％）と、五二硫化リン（Ａｌｄｒｉｃｈ社製）０．６１７ｇ（２５モル％）を秤量し、それらを、遊星ミルにて、４００回転で２０時間処理して、固体電解質を得た。得られた固体電解質のイオン伝導度を測定した。その結果を表５に示す。

As a result of Table 4, when Example 11 and Comparative Example 3 are compared, adhesion of the fired product to the crucible is greatly improved by the present production method, and the obtained lithium sulfide is also in a different phase without using a reducing agent. It can be seen that there is nothing.
Example 12
0.383 g (75 mol%) of lithium sulfide obtained in Example 11 and 0.617 g (25 mol%) of phosphorus pentasulfide (manufactured by Aldrich) were weighed and they were rotated 400 times in a planetary mill. For 20 hours to obtain a solid electrolyte. The ionic conductivity of the obtained solid electrolyte was measured. The results are shown in Table 5.

実施例１２の結果から明らかなように、実施例１１で得られた硫化リチウムを用いた無機固体電解質はイオン伝導度が高いことが分かる。

As is apparent from the results of Example 12, it can be seen that the inorganic solid electrolyte using lithium sulfide obtained in Example 11 has high ionic conductivity.

Claims (13)

  A method for producing lithium sulfide, comprising charging a raw material mixture containing a lithium source and a sulfur source into a firing container in which granular ceramic is previously laid and firing the mixture.   2. The method for producing lithium sulfide according to claim 1, wherein the raw material mixture further contains a reducing agent.   3. The method for producing lithium sulfide according to claim 1, wherein the lithium source is lithium carbonate or lithium hydroxide, and the sulfur source is sulfur alone.   3. The method for producing lithium sulfide according to claim 2, wherein the lithium source and the sulfur source are lithium sulfate.   The method for producing lithium sulfide according to any one of claims 1 to 4, wherein the granular ceramic is inert to the raw material mixture and lithium sulfide.   6. The method for producing lithium sulfide according to claim 1, wherein the granular ceramic is alumina.   The method for producing lithium sulfide according to any one of claims 2 to 6, wherein the reducing agent is an organic compound having a plurality of hydroxyl groups.   The method for producing lithium sulfide according to claim 7, wherein the organic compound having a plurality of hydroxyl groups is a saccharide or a polyhydric alcohol.   The method for producing lithium sulfide according to claim 7, wherein the organic compound having a plurality of hydroxyl groups is sucrose.   The method for producing lithium sulfide according to any one of claims 2 to 9, wherein the reducing agent is a combination of an organic compound having a plurality of hydroxyl groups and a carbon material.   The method for producing lithium sulfide according to claim 10, wherein the carbon material is a porous carbon material.   The method for producing lithium sulfide according to claim 11, wherein the porous carbon material is activated carbon.   Lithium sulfide is obtained by the method for producing lithium sulfide according to any one of claims 1 to 12, and then obtained lithium sulfide, phosphorus sulfide, silicon sulfide, germanium sulfide, boron sulfide, aluminum sulfide, sulfide A method for producing an inorganic solid electrolyte, comprising reacting one or more compounds selected from the group consisting of gallium, lithium phosphate, lithium silicate and lithium iodide.

Images