JP5303428B2 - Lithium sulfide and method for producing the same - Google Patents

Description

  The present invention relates to lithium sulfide and a method for producing the same. More specifically, the present invention relates to lithium sulfide particularly useful as a raw material for sulfide-based solid electrolytes used in lithium batteries, solid electrolytes using the same, lithium batteries using the same, and electronic devices equipped with the same.

Conventionally, in Patent Document 1 and Patent Document 2, as a method for producing lithium sulfide, hydrogen sulfide is blown into a slurry composed of lithium hydroxide and an aprotic organic solvent, and after lithium hydrosulfide is prepared, dehydration and dehydrogenation are performed. Discloses a method for producing anhydrous lithium sulfide and a method for producing anhydrous lithium sulfide directly by continuously blowing hydrogen sulfide.
Further, as a method for producing an alkali metal sulfide, Patent Document 3 discloses an anhydrous alkali metal sulfide obtained by reacting a hydrous alkali metal hydrosulfide and an aqueous alkali metal hydroxide solution with a water-insoluble dispersion medium. A manufacturing method characterized by contacting and dehydrating is disclosed.
On the other hand, in Patent Document 4, hydrogen gas and sulfur gas are simultaneously or hydrogen sulfide blown into solid lithium hydroxide whose particle size is controlled to 0.1 mm to 1.5 mm, and the temperature is 130 ° C. to 445 ° C. A method for producing lithium sulfide is disclosed.

In the method for producing lithium sulfide described in Patent Documents 1 to 3, since an organic solvent is used as a solvent, organic impurities are by-produced.
Moreover, in order to process the organic solvent used with the manufacturing method of patent documents 1-3, it had to finally incinerate, and the burden of solvent processing was large.
On the other hand, in Patent Document 4, lithium sulfide is produced without using an organic solvent. However, since lithium sulfide is produced by reacting solid lithium hydroxide with gaseous hydrogen sulfide, the dew point is − In addition to using a mixed gas of hydrogen and sulfur, which is a combustible gas, and hydrogen sulfide gas at high temperatures, special equipment was required from the viewpoint of preventing explosions.
There is also a technique for producing a sulfide-based solid electrolyte by reacting lithium sulfide particles and phosphorus sulfide particles in an organic solvent (Patent Document 5). However, the larger the surface area of the lithium sulfide particles, the more efficiently the solid electrolyte can be produced.

Japanese Patent Laid-Open No. 7-330312 JP 2006-016281 A WO2004 / 106232 JP-A-9-278423 WO2009 / 047977

  It is an object of the present invention to provide a method for producing lithium sulfide that does not require special equipment, can be easily treated with a solvent after use, and has few by-products of impurities such as organic substances.

According to the present invention, the following method for producing lithium sulfide and the like are provided.
1. A method for producing lithium sulfide, which comprises reacting lithium hydroxide and hydrogen sulfide in an aqueous solvent to produce lithium sulfide.
2. 2. The method for producing lithium sulfide according to 1, wherein gaseous hydrogen sulfide is introduced into the aqueous solvent containing lithium hydroxide.
3. 3. Lithium sulfide produced by the method for producing lithium sulfide as described in 1 or 2 above.
4). 4. A sulfide-based solid electrolyte synthesized from the lithium sulfide described in 3 above and a sulfide containing one or more elements selected from phosphorus, silicon, boron and germanium.
5. A lithium battery comprising at least one of a solid electrolyte layer produced from the solid electrolyte described in 4 above and a positive electrode produced from the solid electrolyte described in 4 and a negative electrode produced from the solid electrolyte described in 4.
6). 6. An apparatus comprising the lithium battery as described in 5 above.

  The present invention can provide a method for producing lithium sulfide that does not require special equipment, can be easily treated with a solvent after use, and has few by-products of impurities such as organic substances.

2 is a SEM photograph of lithium sulfide produced in Example 1. 4 is a SEM photograph of lithium sulfide produced in Comparative Example 1.

The method for producing lithium sulfide according to the present invention is characterized in that lithium sulfide is produced by reacting lithium hydroxide and hydrogen sulfide in an aqueous solvent. When lithium hydroxide and hydrogen sulfide are reacted in an aqueous solvent, the generated lithium sulfide is precipitated in the aqueous solvent.
In the present invention, for example, gaseous hydrogen sulfide is preferably introduced into an aqueous solvent added with lithium hydroxide (preferably an aqueous lithium hydroxide solution).

There is no restriction | limiting in particular as lithium hydroxide which is a raw material, What is marketed industrially can be used. Since high-purity lithium sulfide can be obtained, it is preferable to use lithium hydroxide having a low impurity content. Moreover, you may remove the insoluble matter in lithium hydroxide aqueous solution by filtration etc. as needed.
In the method for producing lithium sulfide according to the present invention, since lithium hydroxide dissolved in water is used, a special lithium hydroxide shape as in Patent Document 4 is not required.

The solvent is a water (H 2 _O), in particular, without limitation, distilled water and deionized water normally applied can be preferably used. This is because high-purity lithium sulfide can be obtained.
In the present invention, since water is used as a solvent, no by-product impurities are generated when an organic solvent is used. Moreover, since the impurity containing lithium (for example, N-methyl-aminobutyric acid lithium byproduced when NMP is used as a solvent) is not generated, the use efficiency of lithium can be improved. Moreover, water has low reactivity with the raw materials lithium hydroxide and hydrogen sulfide, and hardly produces impurities. This eliminates the need for a purification step for removing impurities and greatly simplifies the manufacturing process.

When mixing lithium hydroxide and water, the amount of lithium hydroxide charged is not particularly limited, and may be a slurry exceeding the saturation concentration. An appropriate concentration may be set in consideration of handling and transportation.
Therefore, in the present invention, the water solvent and lithium hydroxide mean a slurry that is a lithium hydroxide aqueous solution or a mixture of a lithium hydroxide aqueous solution and a lithium hydroxide powder (hereinafter referred to as “lithium hydroxide aqueous solution etc.”). .)

  The hydrogen sulfide used in the present invention is a gas. The purity of hydrogen sulfide is not particularly limited, but it is preferable to use hydrogen sulfide having a low impurity content such as carbon dioxide or ammonia gas. This is because high-purity lithium sulfide can be obtained when hydrogen sulfide containing few impurities is used.

In the production method of the present invention, for example, hydrogen sulfide is blown into a lithium hydroxide aqueous solution or the like, and the lithium hydroxide and hydrogen sulfide in the lithium hydroxide aqueous solution or the like are reacted.
The method of blowing hydrogen sulfide is not particularly limited, and a blow port for blowing hydrogen sulfide into a lithium hydroxide aqueous solution or the like may be inserted, and hydrogen sulfide is introduced from a blow port provided outside the lithium hydroxide aqueous solution or the like. May be blown.
The blowing speed of hydrogen sulfide may be appropriately adjusted depending on the scale of the reaction system, reaction conditions, and the like.
In the production method of the present invention, not only does lithium hydroxide and hydrogen sulfide dissolved in a lithium hydroxide aqueous solution react, but also lithium hydroxide and hydrogen sulfide in the slurry react.

The temperature during the reaction is not particularly limited, but it is preferably 100 ° C. or lower, which is the boiling point of water, under normal pressure. After the reaction, the temperature can be raised above the boiling point of water to remove water and water solvent generated by the reaction.
The reaction time is generally until the generation of water generated by the reaction between lithium hydroxide and hydrogen sulfide stops.

  Regarding the reaction pressure, when changing the reaction pressure, it is preferable to control the reaction temperature below the boiling point of water under the pressure. When the reaction pressure is increased, the solubility of hydrogen sulfide in the aqueous solvent can be adjusted, so that the reaction rate can be controlled.

The method for separating lithium sulfide and water produced by the above production method is not particularly limited. For example, since the produced lithium sulfide is in a mixed state (slurry) with water, the temperature can be raised above the boiling point of water, and the water and water solvent generated by the reaction can be removed.
In addition, the hydrolysis reaction by the produced | generated lithium sulfide and water can be suppressed by blowing hydrogen sulfide after completion of reaction.

  The production apparatus applied to the present invention is not particularly limited, but has a reaction vessel and a stirring blade, and is equipped with a hydrogen sulfide introduction / outflow mechanism, a moisture removal mechanism, a heating / cooling mechanism, and the like. Is preferred.

  In the production method of the present invention, hydrogen sulfide is introduced into a lithium hydroxide aqueous solution or the like, and lithium sulfide is generated until the amount of hydrogen sulfide introduced becomes ½ mol of lithium hydroxide in the lithium hydroxide aqueous solution or the like. When hydrogen sulfide is further introduced beyond the ½ molar amount of lithium hydroxide, lithium hydrosulfide is produced. Thereafter, when water is evaporated by heating or the like in the presence of hydrogen sulfide, dehydrosulfurization of lithium hydrosulfide proceeds to become lithium sulfide. Then, lithium sulfide exceeding the saturation solubility is precipitated. This reaction from lithium hydrosulfide to lithium sulfide proceeds during high-temperature drying after water is almost distilled off.

When the reaction proceeds and lithium hydroxide as a raw material disappears from the reaction system, generation of water due to the reaction stops. In the present invention, it is preferable to continue blowing hydrogen sulfide until water in the reaction system evaporates and becomes dry. If the blowing of hydrogen sulfide is stopped before the water is completely distilled off, the hydrolysis of lithium sulfide may proceed.
After the water is distilled off, an inert gas is blown to remove excess hydrogen sulfide outside the system.

Water can be removed from the system by condensing water vapor evaporated from the reaction system by heating or the like with a condenser or the like. As the moisture is removed, lithium sulfide is precipitated and the slurry concentration is increased, so that the viscosity is increased. Therefore, the stirring is stopped when an appropriate viscosity is reached, and the drying process is started. During this time, hydrogen sulfide is continuously blown to remove all moisture in the system, and the reaction is completed at the time of drying.
After drying, the lithium sulfide that has become a solid component is recovered.

  The reaction of the lithium sulfide according to the present invention proceeds in an aqueous solvent, and after production, lithium sulfide exceeding the saturation solubility is deposited on the vessel wall and the stirring blade. Therefore, the recovered lithium sulfide exhibits a scaly shape.

Since the lithium sulfide according to the present invention is scaly, the production time of the solid electrolyte can be shortened compared to the case of granular lithium sulfide. Therefore, it is suitable as a raw material for sulfide-based solid electrolytes.
Subsequently, the sulfide-based solid electrolyte of the present invention will be described.
The sulfide-based solid electrolyte of the present invention is synthesized from the above-described lithium sulfide (Li ₂ S) of the present invention and a sulfide containing one or more elements selected from phosphorus, silicon, boron, and germanium. .
Examples of the sulfide containing one or more elements selected from phosphorus, silicon, boron, and germanium include P ₂ S ₅ , SiS ₂ , GeS ₂ , P ₂ S ₅ , B ₂ S _{3 and the} like.

As a method for producing an inorganic solid electrolyte composed of Li ₂ S and the above sulfide, a mechanical milling method can be applied as a simple method. P ₂ S ₅ and the above sulfide are mixed in a predetermined amount in a mortar and reacted for a predetermined time by a mechanical milling method, whereby a sulfide-based solid electrolyte glass is obtained.

The mechanical milling method using the above raw materials can be reacted at room temperature. According to the MM method, since a glassy electrolyte can be produced at room temperature, there is an advantage that a raw material is not thermally decomposed and a glassy electrolyte having a charged composition can be obtained. Further, the MM method has an advantage that the glassy electrolyte can be made into fine powder simultaneously with the production of the glassy electrolyte.
Although various types of pulverization methods can be used for the MM method, it is particularly preferable to use a planetary ball mill. The planetary ball mill is suitable for manufacturing because the pot rotates around the pot and the base rotates around the pot and can generate very high impact energy efficiently.
The rotation speed and treatment time of the MM method are not particularly limited, but the faster the rotation speed, the faster the glassy electrolyte production rate, and the longer the treatment time, the higher the conversion rate of the raw material to the glassy electrolyte.
The electrolyte thus obtained is a glassy electrolyte. For example, when P ₂ S ₅ is used as the sulfide, the ionic conductivity is usually about 1.0 × 10 ^{−5 to} 8.0 × 10 ⁻⁴ (S / cm).
As conditions for the MM method, for example, when a planetary ball mill is used, the rotational speed may be set to several tens to several hundreds of revolutions / minute, and the treatment may be performed for 0.5 hours to 100 hours.
Although specific examples of sulfide glass by the MM method have been described above, manufacturing conditions such as temperature conditions and processing time can be appropriately adjusted according to the equipment used. Also, a sulfide glass can be similarly prepared by a melt quenching method in which the mixture is heated to the melting point of lithium sulfide and other sulfides or more, specifically about 1000 ° C. and then rapidly cooled.

Thereafter, the obtained sulfide-based solid electrolyte glass is heat-treated at a predetermined temperature, thereby producing a sulfide-based solid electrolyte glass ceramic containing a crystal component.
The heat treatment temperature for producing such a solid electrolyte is preferably 190 ° C to 340 ° C, more preferably 195 ° C to 335 ° C, and particularly preferably 200 ° C to 330 ° C. When the temperature is lower than 190 ° C., it may be difficult to obtain a crystal with high ion conductivity. When the temperature is higher than 340 ° C., a crystal with low ion conductivity may be generated.
The heat treatment time is preferably 3 to 240 hours, particularly preferably 4 to 230 hours, when the temperature is 190 ° C or higher and 220 ° C or lower. When the temperature is higher than 220 ° C and not higher than 340 ° C, 0.1 to 240 hours are preferable, 0.2 to 235 hours are particularly preferable, and 0.3 to 230 hours are more preferable. If the heat treatment time is shorter than 0.1 hour, it may be difficult to obtain a crystal with high ion conductivity. If the heat treatment time is longer than 240 hours, a crystal with low ion conductivity may be formed.

The thus obtained sulfide-based solid electrolyte glass ceramic lithium ion conductive inorganic solid electrolyte containing a crystal component has a normal ionic conductivity of 7.0 × 10 ^{−4 to} 5.0 × 10 ^{−. 3} (S / cm) or so.
This lithium ion conductive inorganic solid electrolyte has 2θ = 17.8 ± 0.3 deg, 18.2 ± 0.3 deg, 19.8 ± 0.3 deg, X-ray diffraction (CuKα: λ = 1.5418４), It has diffraction peaks at 21.8 ± 0.3 deg, 23.8 ± 0.3 deg, 25.9 ± 0.3 deg, 29.5 ± 0.3 deg, 30.0 ± 0.3 deg. A solid electrolyte having such a crystal structure has extremely high lithium ion conductivity.

The solid electrolyte produced by the above method has an indeterminate shape having an average particle diameter of several μm to several tens of μm, and is used in the form of dry powder or slurry.
The solid electrolyte of the present invention can be suitably used for a component of a lithium battery, for example, an electrolyte layer, a positive electrode layer, a negative electrode layer, and the like.

  The lithium battery according to the present invention has an electrolyte layer, a positive electrode, and a negative electrode, and at least one of them is manufactured from the above-described solid electrolyte of the present invention. In addition, the electrolyte layer, the positive electrode, and the negative electrode other than those manufactured from the solid electrolyte of the present invention are usually used in lithium batteries (for example, an electrolyte solution or a polymer electrolyte immersed in a separator, a polymer electrolyte Cured solid electrolyte).

The lithium battery of the present invention can be either a secondary battery or a primary battery, and can be used in devices such as watches, mobile phones, personal computers, automobiles, and generators.
Among the above-described devices, the automobile includes an electric automobile whose driving source is an electric motor, and a hybrid electric automobile using a combination of an electric motor and an internal combustion engine as a driving source, and these automobiles require a large current and a large voltage.
The lithium battery of this invention can take out bigger electric power by connecting in series and / or parallel and making it a battery cell. By connecting a plurality of battery cells in series and / or parallel to form a battery module (battery pack, battery unit), a battery that satisfies the large current and large voltage required by the automobile can be obtained.

Example 1
Under a nitrogen stream, 45 g of distilled water (Hiroshima Wako reagent) as a water solvent was added to a 200 ml separable flask, followed by charging with 5 g of lithium hydroxide (Honjo Chemical) and stirring at 25 ° C. with a full zone stirring blade at 300 rpm. Held on. Subsequently, heating was started while blowing hydrogen sulfide (manufactured by Sakai Shokai) into the liquid at a supply rate of 300 ml / min. In the presence of an aqueous solvent, when hydrogen sulfide is blown at 25 ° C., the reaction starts immediately. Further, when the inside of the system was heated to approximately 90 ° C. or more, water was evaporated with the reaction, and water was continuously discharged from the separable flask, so it was condensed by a condenser outside the system. As the reaction progressed and the water evaporated, the amount of water gradually decreased and the system became a paste. Distillation of water was not observed at 150 ° C. for 5 hours after the introduction of hydrogen sulfide (the total amount of water was 49 ml). Thereafter, the temperature was raised to 205 ° C. over 2 hours.
As moisture is removed, lithium sulfide is deposited on the vessel wall and the stirring blade, and the solution viscosity also increases. Therefore, stirring was stopped when the paste state was reached and the drying process was started. During this drying step, hydrogen sulfide was continuously blown to completely remove moisture from the system.
Thereafter, the hydrogen sulfide was switched to nitrogen and circulated at 300 ml / min for 2 hours.

When the white powder obtained by drying was analyzed by hydrochloric acid titration and silver nitrate titration, the purity of lithium sulfide was 99.6%. As a result of X-ray diffraction measurement, it was confirmed that no peaks other than the crystal pattern of lithium sulfide were detected.
FIG. 1 shows a scanning electron microscope (SEM) photograph of the lithium sulfide obtained. From the photograph, it was confirmed that lithium sulfide was obtained as a scaly powder.
As a result of ion chromatography analysis and titration analysis of this powder, all impurities were 500 ppm or less.

Comparative Example 1
Lithium sulfide was synthesized according to the method described in Japanese Patent No. 3528866, which has been conventionally known. First, as a first step, 270 g of N-methyl-2-pyrrolidone solvent (hereinafter referred to as NMP: Hiroshima Wako Reagent), which is a polar solvent, is added to a 600 ml separable flask, followed by 30 g of lithium hydroxide (Honjo Chemical). ) And maintained at 130 ° C. while stirring with a full zone stirring blade of 300 rpm. Here, hydrogen sulfide (manufactured by Sakai Shokai) was blown into the liquid at a supply rate of 300 ml / min for 2 hours. As a result, a water flow lithium (LiSH) solution was produced according to the LiOH + H ₂ S → LiSH + H ₂ O reaction. Subsequently, as a second step, the reaction solution was heated in a nitrogen stream (50 ml / min) to dehydrosulfide the hydrous lithium. Since water generated as a by-product due to the above reaction evaporates as the temperature rises, it was condensed outside the system by a condenser and distilled off. Although the temperature increased with the evaporation of water, the temperature was maintained at 200 ° C. The holding time was 2 hours when the dehydrosulfurization reaction was completed and lithium sulfide was present stably. After cooling, the solution was filtered under reduced pressure using a glass filter, and the solid content was washed twice with NMP solvent three times and further washed twice with a toluene solvent.

The white powder obtained by drying was subjected to X-ray diffraction measurement, and it was confirmed that no peaks other than the crystal pattern of lithium sulfide were detected.
FIG. 2 shows a scanning electron micrograph of the obtained lithium sulfide. From the photograph, it was confirmed that lithium sulfide was a powder containing a hexahedral structure. The average particle diameter of this lithium sulfide powder was 31.2 μm.
As a result of performing ion chromatographic analysis and titration analysis of the produced solid, Li ₂ SO ₃ was 0.31 wt%, Li ₂ SO ₄ was 0.14 wt%, and LMAB (lithium N-methylaminobutyrate) was 4.96 wt%. there were.

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

Evaluation Example 1 [Preparation Example of Solid Electrolyte]
Place 16.27 g of Li ₂ S produced in Example 1 and Comparative Example 1 above and 33.73 g of P ₂ S ₅ (manufactured by Aldrich) having an average particle size of about 50 μm in a 500 ml alumina container containing 175 10 mmφ alumina balls. Sealed. The above weighing and sealing operations were all carried out in a glove box, and all the equipment used was water removed beforehand by a dryer.
This sealed alumina container was subjected to mechanical milling treatment at room temperature for a predetermined time using a planetary ball mill (PM400 manufactured by Lecce), and X-ray diffraction measurement (CuKα: λ = 1) of the white yellow solid electrolyte glass particles obtained. 5418). In Li ₂ S of Comparative Example 1, it took 36 hours for the Li ₂ S crystal peak to disappear. In contrast, in Li ₂ S of Example 1, the Li ₂ S peak disappeared after 30 hours of treatment.

Evaluation Example 2 [Production Example of Lithium Battery]
A positive electrode mixture was laminated on an aluminum foil as a positive electrode current collector, and was pressed under pressure of 1 MPa to 68 MPa to form a positive electrode mixture layer. The positive electrode mixture was prepared by mixing 30 parts by weight of the solid electrolyte prepared using Li ₂ S of Example 1 and 70 parts by weight of the lithium cobaltate-based composite oxide as the positive electrode active material in Evaluation Example 1 described above. Produced.
Similarly, a negative electrode mixture layer was formed on an aluminum foil as a negative electrode current collector using a negative electrode mixture in which 60 parts by weight of carbon as a negative electrode active material was mixed with 40 parts by weight of a solid electrolyte.
A solid electrolyte layer was similarly formed on the positive electrode composite material layer using the solid electrolyte described above. As described above, a battery composed of three layers of a positive electrode mixture layer, a solid electrolyte layer, and a negative electrode mixture layer was produced by being sandwiched between positive and negative electrode current collectors. The laminate was further thinned by applying a pressure of 1 MPa to 300 MPa.
The laminate was sandwiched between aluminum laminate films and heat sealed under vacuum to produce a lithium battery (battery cell).

In addition, as a positive electrode active material, even when lithium nickelate, lithium manganate, these complex oxides, etc. other than lithium cobaltate were used, it confirmed that charging / discharging as a battery was possible.
Similarly, it was confirmed that the negative electrode active material can be charged and discharged as a battery even when carbon black such as graphite, a mixture thereof, or a metal powder such as tin or silicon is used.

  According to the method for producing lithium sulfide of the present invention, lithium sulfide suitable as a raw material for the solid electrolyte can be obtained.

Claims (6)

  A method for producing lithium sulfide, which comprises reacting lithium hydroxide and hydrogen sulfide in an aqueous solvent to produce lithium sulfide.   The method for producing lithium sulfide according to claim 1, wherein gaseous hydrogen sulfide is introduced into the aqueous solvent containing lithium hydroxide.   Lithium sulfide produced by the method for producing lithium sulfide according to claim 1 or 2. Lithium sulfide according to claim 3,
A sulfide-based solid electrolyte synthesized from a sulfide containing one or more elements selected from phosphorus, silicon, boron, and germanium.   At least one of the solid electrolyte layer manufactured from the solid electrolyte according to claim 4, the positive electrode manufactured from the solid electrolyte according to claim 4, and the negative electrode manufactured from the solid electrolyte according to claim 4. A lithium battery comprising:   An apparatus comprising the lithium battery according to claim 5.