JP6162981B2 - 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.

  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.

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

  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, 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.

  Moreover, in the method using a gaseous sulfur source like patent document 3, the problem of toxicity and corrosion of a gaseous sulfur source arises. Moreover, in order to handle sulfur vapor, hydrogen sulfide vapor, etc., the facilities are complicated. In addition, since the reaction in the high temperature region is too intense, it is difficult to control, and there is a problem that excessive cost is required for the control.

  Accordingly, an object of the present invention is to provide a method for producing lithium sulfide that does not use an organic solvent or a gaseous sulfur source, has a small number of steps, and has a low content of heterogeneous phases.

The object is achieved by the present invention described below.
That is, the present invention (1) is lithium hydroxide solid, and the solid sulfur, by mixing an organic compound having a plurality of hydroxyl groups, to give a firing mixture and then the calcination mixture for, not Calcining at 600 to 1200 ° C. in an active gas atmosphere or a reducing gas atmosphere to obtain lithium sulfide;
The organic compound having a plurality of hydroxyl groups is sucrose, fructose or polyvinyl alcohol,
The ratio of sulfur atoms to lithium atoms in the firing mixture is 0.5 to 3 in terms of atomic ratio (S / Li), and the ratio of carbon atoms to lithium atoms in the firing mixture Is a molar ratio (C / Li) in terms of atoms and is 0.05 to 0.5,
A method for producing lithium sulfide is provided.

  The present invention (2) also provides lithium sulfide obtained by the method for producing lithium sulfide of the present invention (1), and then obtained lithium sulfide, phosphorus sulfide, silicon sulfide, germanium sulfide, boron sulfide, aluminum sulfide and An object of the present invention is to provide a method for producing an inorganic solid electrolyte, characterized by reacting one or more sulfides selected from the group of gallium sulfide.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of lithium sulfide which does not use an organic solvent or a gaseous sulfur source, there are few processes, and there is little content of a different phase can be provided.

It is an X-ray diffraction pattern of lithium sulfide obtained in Examples and Comparative Examples.

  In the method for producing lithium sulfide of the present invention, solid lithium hydroxide, solid sulfur, and an organic compound having a plurality of hydroxyl groups are mixed to obtain a firing mixture, and then the firing mixture is converted to 600. It is a method for producing lithium sulfide characterized in that it is fired at ˜1200 ° C. to obtain lithium sulfide.

  The solid lithium hydroxide according to the method for producing lithium sulfide of the present invention may be obtained by any production method or may be a commercial product. In obtaining high-purity lithium sulfide, solid lithium hydroxide having a lower impurity content is more preferable. Solid lithium hydroxide may be a monohydrate or an anhydrous salt. The particle size of the solid lithium hydroxide is not particularly limited.

  The solid sulfur according to the method for producing lithium sulfide of the present invention is not particularly limited. In obtaining high-purity lithium sulfide, solid sulfur having a lower impurity content is preferred, and the purity is particularly preferably 99% by mass or more. The particle size of solid sulfur is not particularly limited.

  The organic compound having a plurality of hydroxyl groups according to the method for producing lithium sulfide of the present invention is a compound comprising a carbon atom, a hydrogen atom, and an oxygen atom and having two or more hydroxyl groups in the molecule. The compound having a plurality of hydroxyl groups may be solid or liquid. In addition, when a compound other than a carbon atom, a hydrogen atom, and an oxygen atom is present in a compound having a plurality of hydroxyl groups, it causes a decrease in the purity of lithium sulfide. A compound consisting only of a hydrogen atom and an oxygen atom is preferred.

  Examples of the organic compound having a plurality of hydroxyl groups include saccharides and polyhydric alcohols. Examples of sugars related to organic compounds having a plurality of hydroxyl groups 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, xylitol, Examples thereof include sugar alcohols such as sorbitol. Examples of polyhydric alcohols related to organic compounds having a plurality of hydroxyl groups include divalent alcohols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol, and trivalent alcohols such as glycerin and trimethylolpropane. And alcohols having four or more hydroxyl groups in the molecule, polymers having many hydroxyl groups such as polyvinyl alcohol, and the like. Among these, as an organic compound having a plurality of hydroxyl groups, monosaccharides or disaccharides are obtained in that the effect of obtaining lithium sulfide with a low content of heterogeneous phase is increased and the amount of carbon remaining in lithium sulfide is reduced. Are preferred, and sucrose is particularly preferred.

  In the method for producing lithium sulfide of the present invention, first, solid lithium hydroxide, solid sulfur, and an organic compound having a plurality of hydroxyl groups are mixed to obtain a firing mixture.

The ratio of sulfur atoms to lithium atoms in the firing mixture is preferably a molar ratio (S / Li) in terms of atoms, preferably 0.5 to 3, and particularly preferably 0.6 to 1.0. When the ratio of sulfur atoms to lithium atoms in the firing mixture is within the above range, the purity is high and the recovery rate is high. On the other hand, when the ratio of sulfur atoms to lithium atoms in the firing mixture is less than the above range, Li ₂ O tends to be generated as a heterogeneous phase, and when it exceeds the above range, the recovery rate tends to be low. The ratio of sulfur atoms to lithium atoms in the firing mixture is adjusted by adjusting the amount of solid lithium hydroxide and solid sulfur mixed.

  The ratio of carbon atoms to lithium atoms in the firing mixture is a molar ratio (C / Li) in terms of atoms, preferably 0.05 to 0.5, and particularly preferably 0.1 to 0.3. When the ratio of carbon atoms to lithium atoms in the firing mixture is within the above range, the remaining carbon in the lithium sulfide after firing is reduced. The ratio of carbon atoms to lithium atoms in the firing mixture is adjusted by adjusting the mixing amount of solid lithium hydroxide and an organic compound having a plurality of hydroxyl groups.

  The method of mixing solid lithium hydroxide, solid sulfur, and an organic compound having a plurality of hydroxyl groups is not particularly limited, and examples thereof include a method of mixing them using a paint shaker or the like. .

  In the method for producing lithium sulfide of the present invention, the firing mixture is then fired at 600 to 1200 ° C. to react lithium hydroxide and sulfur in the presence of an organic compound having a plurality of hydroxyl groups, thereby producing lithium sulfide. Get.

  The firing temperature when firing the firing mixture is 600 to 1200 ° C, preferably 800 to 1200 ° C, and particularly preferably 900 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 firing mixture is appropriately selected within a range where unreacted lithium hydroxide does not remain. The firing atmosphere when firing the firing mixture is an inert gas atmosphere such as nitrogen, argon or helium or a reducing gas atmosphere such as hydrogen gas.

  After the firing mixture is fired, the fired product, that is, the generated lithium sulfide is cooled in an inert gas atmosphere such as nitrogen, argon or helium, in a reducing gas atmosphere such as hydrogen gas, or in a vacuum, and cooled. Thereafter, if necessary, pulverization or crushing, classification, packaging, and the like are further 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.

  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 1 to 100 μm, particularly preferably 10 to 50 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.

When a mixture of only solid lithium hydroxide and solid sulfur is baked and lithium hydroxide and sulfur are reacted to obtain lithium sulfide, if sulfur is excessive with respect to lithium hydroxide, Li ₂ SO as a different phase ₄ is easy to generate. In contrast, in the method for producing lithium sulfide of the present invention, lithium hydroxide and sulfur are added at 600 to 1200 ° C. in the presence of an organic compound having a plurality of hydroxyl groups, preferably sugars or polyhydric alcohols, particularly preferably sucrose. Since Li ₂ SO ₄ produced as a different phase is reduced by a carbide of an organic compound having a plurality of hydroxyl groups by firing and reacting with, the lithium sulfide as the fired product does not contain Li ₂ SO ₄ Even if Li ₂ SO ₄ is contained, the content of lithium sulfide is very small.

  Further, in the method for producing lithium sulfide of the present invention, since solid lithium hydroxide and solid sulfur 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 gaseous sulfur source such as hydrogen sulfide. Further, in the method for producing lithium sulfide of the present invention, lithium sulfide is obtained by mixing solid lithium hydroxide, solid sulfur, and an organic compound having a plurality of hydroxyl groups, and then firing the mixture. 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 an inorganic solid electrolyte of a lithium ion secondary battery.

  The inorganic solid electrolyte production method of the present invention is obtained by obtaining lithium sulfide by the lithium sulfide production method 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 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 , 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) a method of vitrifying lithium sulfide and sulfide (A) by mechanical milling (Ii) A method in which lithium sulfide and sulfide (A) are mixed, the resulting mixture is heated and melted in an inert gas atmosphere, and then rapidly cooled. Moreover, the method of improving electroconductivity 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 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.

  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 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 is possible, 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.

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 the 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 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.

  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 in detail, 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 abundances of heterogeneous Li ₂ SO ₄ , Li ₂ O and LiCO _{3 in} the lithium sulfide crystal were determined as follows. The diffraction peak intensity ratio is the area ratio of diffraction peaks.
<Abundance of Li ₂ SO ₄ >
Diffraction peak intensity ratio (b / a) = (a) diffraction peak intensity around 2θ = 27 ° (111 plane) derived from lithium sulfide / (b) 2θ = around 22 ° (002 plane) derived from lithium sulfate Diffraction peak intensity <Li ₂ O abundance>
Diffraction peak intensity ratio (c / a) = (a) diffraction peak intensity around 2θ = 27 ° (111 plane) derived from lithium sulfide / (c) 2θ = about 33.6 ° derived from lithium oxide (111 Surface) diffraction peak intensity <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) Measurement of ionic conductivity of the solid electrolyte Both sides of the solid electrolyte are sandwiched by 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.

Example 1
Lithium hydroxide monohydrate (manufactured by Nippon Kagaku Kogyo Co., Ltd., BQ product) was pulverized with a mill (Wonder Blender) for 15 seconds, sieved with a 212 μm sieve, and then dried in a box furnace at 200 ° C. in a nitrogen gas atmosphere for 4 hours. As a result, a lithium hydroxide dehydrated product was obtained. Next, the obtained lithium hydroxide, sulfur, and sucrose were weighed so that the molar ratio in terms of atoms was Li atom: S atom: C atom = 1: 0.6: 0.2, and a paint shaker was used. Mix for 40 minutes.
Next, the obtained mixture was heated in a firing furnace in a nitrogen gas atmosphere at 5 ° C./min to 900 ° C. and then held at 900 ° C. for 6 hours for firing. After firing, the mixture was cooled to room temperature in a nitrogen gas atmosphere to obtain lithium sulfide. Table 1 shows the yield of the obtained lithium sulfide and the abundance of heterogeneous phases. An X-ray diffraction chart of the obtained lithium sulfide is shown in FIG.

(Example 2)
Instead of lithium hydroxide, sulfur and sucrose in terms of molar ratio in terms of atoms: Li atom: S atom: C atom = 1: 0.6: 0.2, lithium hydroxide, sulfur and sucrose The same operation as in Example 1 was conducted except that Li atom: S atom: C atom = 1: 2: 0.2 in terms of molar ratio. The results are shown in Table 1 and FIG.

(Example 3)
Lithium hydroxide not dehydrated is used, that is, lithium hydroxide monohydrate (manufactured by Nippon Kagaku Kogyo Co., Ltd., BQ product) is pulverized with a mill (Wonder Blender) for 15 seconds, sieved with a 212 μm sieve, and then box furnace In place of lithium hydroxide dehydrated product obtained by drying at 200 ° C. for 4 hours in a nitrogen gas atmosphere, lithium hydroxide monohydrate (manufactured by Nippon Chemical Industry Co., Ltd., BQ product) is milled (Wonder Blender). This was carried out in the same manner as in Example 1 except that lithium hydroxide was obtained by pulverizing for 15 seconds and then sieving with a 212 μm sieve. The results are shown in Table 1 and FIG.

(Comparative Example 1)
It replaced with baking at 900 degreeC, and performed by the method similar to Example 1 except baking at 500 degreeC. The results are shown in Table 1 and FIG.

Example 4
Instead of lithium hydroxide, sulfur and sucrose in terms of molar ratio in terms of atoms: Li atom: S atom: C atom = 1: 0.6: 0.2, lithium hydroxide, sulfur and sucrose The same operation as in Example 1 was conducted except that Li atom: S atom: C atom = 1: 4: 0.2 in terms of molar ratio. The results are shown in Table 1 and FIG.

(Comparative Example 2)
Instead of using sucrose, that is, replacing lithium hydroxide, sulfur, and sucrose with atomic molar ratio of Li atom: S atom: C atom = 1: 0.6: 0.2, The same procedure as in Example 1 was performed except that lithium and sulfur were weighed so that Li atom: S atom = 1: 0.6 (molar ratio of C atom was 0) in terms of molar ratio in terms of atoms. It was. The results are shown in Table 1 and FIG.

(Example 5)
It replaced with using sucrose and performed by the method similar to Example 1 except using fructose. The results are shown in Table 1 and FIG.

(Example 6)
It replaced with using sucrose, and performed by the method similar to Example 3 except using polyvinyl alcohol (PVA). The results are shown in Table 1 and FIG.

(Example 7)
0.383 g (75 mol%) of lithium sulfide obtained in Example 1 and 0.617 g (25 mol%) of phosphorus pentasulfide (manufactured by Aldrich) were weighed, and they were rotated 400 times on 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 2.

Claims (3)

Solid lithium hydroxide, solid sulfur, and an organic compound having a plurality of hydroxyl groups are mixed to obtain a firing mixture, and then the firing mixture is placed in an inert gas atmosphere or a reducing gas atmosphere. and then calcined at 600 to 1200 ° C., to obtain lithium sulfide,
The organic compound having a plurality of hydroxyl groups is sucrose, fructose or polyvinyl alcohol,
The ratio of sulfur atoms to lithium atoms in the firing mixture is 0.5 to 3 in terms of atomic ratio (S / Li), and the ratio of carbon atoms to lithium atoms in the firing mixture Is a molar ratio (C / Li) in terms of atoms and is 0.05 to 0.5,
A process for producing lithium sulfide characterized by the above. 請 Motomeko 1 method for producing lithium sulfide according you wherein the organic compound having a plurality of hydroxyl groups is sucrose. Lithium sulfide is obtained by the method for producing lithium sulfide according to claim 1 or 2 , 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.

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