JP5495472B2 - Lithium sulfide powder and inorganic solid electrolyte - Google Patents

Description

  The present invention relates to a raw material for producing a polysulfide polymer, an electronic material, particularly a lithium sulfide powder useful as a raw material for producing an inorganic solid electrolyte, a production method thereof, and an inorganic solid electrolyte using the lithium sulfide powder.

  At present, an organic electrolytic solution in which a lithium salt such as lithium hexafluoride is dissolved in an organic solvent is used as an electrolyte of a lithium ion battery that is used in large quantities as a power source for mobile phones and notebook computers. This organic electrolytic solution is flammable and has a risk of ignition, explosion, etc. due to temperature rise or impact due to some cause. In addition, in lithium ion secondary batteries containing organic electrolytes, dendritic lithium metal grows on the surface of the lithium metal during repeated charging and discharging, which can cause internal short circuit between the electrodes, causing explosion, etc. It has been pointed out.

Improvement of the safety of lithium ion batteries using such organic electrolytes is a long-awaited wish, and as a means to solve this problem, all solid-state lithium ion batteries using inorganic solid electrolytes have been proposed. Yes. As the inorganic solid electrolyte currently proposed, for example, Li ₂ S—P ₂ S ₅ system, Li ₂ S—P ₂ S ₃ system, Li ₂ S—SiS ₂ system, Li ₂ S—Ga ₂ S ₃ system, such as Li ₂ S-GeS ₂ systems have been proposed.
For these inorganic solid electrolytes, the most important quality characteristic is that the ionic conductivity as a solid electrolyte is required to be greater than 5 × 10 ⁻⁴ S / cm.

  As a conventional method for producing lithium sulfide, for example, lithium hydroxide and hydrogen sulfide are reacted in an aprotic organic solvent to produce lithium hydrosulfide, and then this reaction solution is dehydrosulfurized to obtain lithium sulfide. Or a method of directly producing lithium sulfide by reacting lithium hydroxide and hydrogen sulfide in an aprotic organic solvent (see Patent Document 1), lithium hydroxide, aprotic organic solvent, and necessary In response to this, hydrogen sulfide gas is blown into a solution consisting of an azeotropic compound, dehydrated and dehydrogenated with heating, and after the residual moisture in the system has substantially disappeared, the blowing of hydrogen sulfide gas is stopped and heated. In addition, an inert gas is further blown to desulfurize and hydrosulfide lithium sulfide (refer to Patent Document 2), including lithium hydroxide, hydrogen sulfide and hydrogen. When lithium sulfide is synthesized by reaction with sulfur vapor, a powder having a particle diameter of 0.1 mm to 1.5 mm is used as lithium hydroxide, and the heating temperature during the reaction is 130 or lower than the melting point of lithium hydroxide. A method for producing lithium sulfide at a temperature of from ° C to 445 ° C (see Patent Document 3) has been proposed.

However, lithium sulfide obtained by using lithium hydroxide as a raw material according to Patent Document 1 and Patent Document 2 mainly focuses on the use of polysulfide polymers and the like, and Patent Document 3 focuses on the use in inorganic solid electrolytes. However, even in this inorganic solid electrolyte using lithium sulfide, the ionic conductivity is insufficient, and problems such as electrochemical characteristics such as a decrease in decomposition voltage tend to occur.
Japanese Patent Laid-Open No. 7-330312 JP 2000-247609 A JP-A-9-278423

In view of the above circumstances, the present inventors have conducted extensive research on lithium sulfide that can also be used for applications of inorganic solid electrolytes. As a result, lithium hydroxide that has undergone a specific purification step is used as a raw material. The SiO ₂ content of lithium sulfide can be reduced to a specific value, and further, 150 to 190 ° C. in an inert gas atmosphere while distilling off the water produced in the reaction of lithium hydroxide and hydrogen sulfide in an aprotic solvent. The first reaction is carried out at 100 to 150 ° C. while distilling off the water that forms the lithium hydroxide and hydrogen sulfide in an aprotic solvent, and then an inert gas at 150 to 190 ° C. Lithium sulfide powder obtained by performing the second reaction in the atmosphere to obtain lithium sulfide and then performing the washing and drying steps in an inert gas atmosphere or in vacuum is an unreacted raw material. In addition to lithium hydroxide, lithium hydroxide produced as a by-product by washing and drying is reduced to a specific value or less. Further, the inorganic solid electrolyte using the lithium sulfide has electric conductivity such as ion conductivity and decomposition voltage. The inventors have found that the chemical characteristics are excellent and have completed the present invention.
That is, the object of the present invention is to provide lithium sulfide powder that can also be used for inorganic solid electrolyte applications, a method for producing the same, and an inorganic solid having excellent electrochemical properties such as ion conductivity and decomposition voltage using the powder. To provide an electrolyte.

The first invention provided by the present invention is the relative intensity of the diffraction peak (a) of lithium sulfide (111 plane) and the diffraction peak (b) of lithium hydroxide (101 plane) when X-ray diffraction analysis is performed. The lithium sulfide powder is characterized in that the ratio {(b / a) × 100} is 3 or less and the content of SiO ₂ is 50 ppm or less.
The lithium sulfide powder preferably has a (111) plane diffraction peak half-value width of 0.15 degrees or less determined by X-ray diffraction analysis, and an average particle diameter of 10 to 80 μm. Moreover, it is especially preferable that the content of the metal elements of Al and Ca is 50 ppm or less in total.

A second invention provided by the present invention is an inorganic solid electrolyte characterized by including the lithium sulfide powder of the first invention.

Hereinafter, the present invention will be described in detail based on preferred embodiments thereof.
The lithium sulfide powder of the present invention has a diffraction peak around 2θ = 26.98 ° (111 plane) of lithium sulfide when X-ray diffraction analysis is performed using Cu—Kα ray with the lithium sulfide powder as a radiation source. The relative intensity ratio {(b / a) × 100} of the diffraction peak (b) of (101 plane) near 2θ = 32.48 ° derived from (a) and lithium hydroxide is 3 or less, preferably 2 or less. In addition to the above characteristics, the lithium sulfide powder according to the present invention is characterized in that the content of SiO ₂ is 50 ppm or less, preferably 30 ppm or less.

Lithium hydroxide as an impurity contained in lithium sulfide lowers the ionic conductivity of the solid electrolyte, and further reduces the decomposition voltage of the solid electrolyte due to the hydroxyl group contained in lithium hydroxide. Further, when such a solid electrolyte containing lithium hydroxide is used, an exchange reaction between lithium ions and protons occurs between the electrode active materials, and thus desired battery performance cannot be obtained. On the other hand, SiO ₂ as an impurity contained in lithium sulfide enters the main skeleton of the glassy composition of the inorganic solid electrolyte, resulting in a decrease in ionic conductivity and an unnecessary electronic conductivity in the inorganic solid electrolyte. .

Since the lithium sulfide powder according to the present invention contains lithium hydroxide and SiO ₂ as impurities within the above range and does not substantially contain these impurities, it is excellent in an inorganic solid electrolyte using the lithium sulfide powder. Further, when the ion conductivity and the decomposition voltage are imparted and the inorganic solid electrolyte is used, the electron conductivity is suppressed to a low level, and excellent electrochemical characteristics can be imparted.
In the present invention, the content of SiO ₂ in the lithium sulfide powder is determined by ICP emission analysis.

  In addition to the above characteristics, the lithium sulfide powder according to the present invention has a (111 plane) of lithium sulfide around 2θ = 26.98 ° when X-ray diffraction analysis is performed using Cu—Kα ray as a radiation source. One of the characteristics is that the half-value width of the diffraction peak is 0.15 degrees or less, preferably 0.05 to 0.15 degrees, and the crystallinity is superior to that of commercially available lithium sulfide. By using lithium sulfide having excellent crystallinity, the ionic conductivity of the inorganic solid electrolyte containing lithium sulfide can be further improved.

  Further, the lithium sulfide powder of the present invention has an average particle size determined from a scanning electron micrograph (SEM) of 10 to 80 μm, preferably 20 to 60 μm, and is finer than industrially available lithium sulfide. One of the characteristics is that it is a crystal and has excellent reactivity.

  The lithium sulfide powder according to the present invention includes, for example, a large amount of oxides and hydroxides of Al and Ca as described later in the raw material lithium hydroxide, and these impurities include hydrogen sulfide and Since it remains as an electrically insulating impurity without reacting, in addition to the above characteristics, the total amount of electrically insulating Al and Ca compounds as Al and Ca metal is 50 ppm or less, preferably 30 ppm or less. This is particularly preferable because the ionic conductivity of the inorganic solid electrolyte containing lithium sulfide can be further improved.

Subsequently, the manufacturing method of the lithium sulfide powder of this invention is demonstrated.
The lithium sulfide powder of the present invention can be produced by the following two methods.
1. A first step of microfiltration of an aqueous solution containing lithium hydroxide to obtain purified lithium hydroxide, and then 150 to 190 while distilling off the water produced in the aprotic solvent to obtain the purified lithium hydroxide and hydrogen sulfide obtained. A second step of obtaining lithium sulfide by reacting at 2 ° C., then a third step of washing the lithium sulfide with an organic solvent, and then a fourth step of drying the washed lithium sulfide, wherein the step 2A is inactive A method of performing in a gas atmosphere, and performing the third to fourth steps in an inert gas atmosphere or in a vacuum.
2. One step to obtain purified lithium hydroxide by microfiltration of an aqueous solution containing lithium hydroxide, and then 100-150 ° C. while distilling off the water that forms the purified lithium hydroxide and hydrogen sulfide obtained in an aprotic solvent And then the second reaction at 150 to 190 ° C. to obtain lithium sulfide, the third step of washing the lithium sulfide with an organic solvent, and then the washed lithium sulfide. A method of performing at least the second reaction of the second B step in an inert gas atmosphere and performing the third step to the fourth step in an inert gas atmosphere or in a vacuum.

  In the above-mentioned two manufacturing methods, the first step, the third step to the fourth step are steps performed under the same conditions, so that the first step, the third step, and the fourth step are distinguished between the two manufacturing methods. This will be explained below.

(First step)
The first step is a step of obtaining purified lithium hydroxide in which the aqueous solution containing lithium hydroxide is subjected to microfiltration to mainly reduce the SiO ₂ content to 50 ppm or less, preferably 30 ppm or less.

Industrially available lithium hydroxide (hereinafter referred to as “crude lithium hydroxide”) is mainly obtained by carbonating lithium-containing ore into crude lithium carbonate, and obtained by reaction of this crude lithium carbonate with slaked lime. Therefore, in such lithium hydroxide, inevitably SiO ₂ is 100 ppm or more as an impurity, and further, an electrically insulating compound such as an oxide or hydroxide of Al and Ca is 100 ppm or more as Al metal and Ca. Containing 50 ppm or more as a metal.

Therefore, by carrying out the first step, the content of SiO ₂ can be within the above range, and the content of an electrically insulating Al compound such as an oxide or hydroxide of Al is 50 ppm or less as Al metal. , Preferably, it can be reduced to 30 ppm or less.

  Specifically, the microfiltration operation first prepares a lithium hydroxide solution in which the crude lithium hydroxide is dissolved in water. The concentration of the crude lithium hydroxide in the aqueous solution is not particularly limited as long as it is equal to or lower than the saturation solubility. However, since the solubility of lithium hydroxide strongly depends on the temperature at which it is dissolved, for example, to dissolve at a temperature of 80 ° C. LiOH is preferably 1 to 12% by weight, more preferably 9 to 12% by weight.

The water in which the crude lithium hydroxide is dissolved is passed through at least a reverse osmosis membrane, an ultrafiltration membrane, an ion exchange membrane, and the like to remove pure ionic impurities such as Na, K, Ca, Cl, and SO _4. The use of water is particularly preferable because it can prevent contamination of impurities derived from dissolved water. In addition, as the to-be-treated water passed through the reverse osmosis membrane, the ultrafiltration membrane, or the ion exchange resin, for example, a pretreatment device made of raw water such as industrial water, city water, river water, etc. is formed by a coagulation filtration device, activated carbon, etc. In this method, a material obtained by removing most of the suspended matter and organic matter in the raw water, or a material treated with a pure water apparatus using an ion exchange resin is used.

  As the reverse osmosis membrane, a commercially available membrane module can be used, and the operating conditions and the like are not particularly limited and may be in accordance with conventional methods. Specifically, the reverse molecular weight of the reverse osmosis membrane is 400 to 100,000, preferably 1000 to 10000. Examples of the material include cellulose acetate, polyamide, crosslinked polyamine, crosslinked polyether, polysulfone, and sulfone. Polysulfone, polyvinyl alcohol and the like are appropriately used. The shape of the membrane may be any of flat plate type, spiral type, hollow fiber type, tubular, brief type and the like.

  As the ultrafiltration membrane, a commercially available membrane module can be used, and operating conditions and the like are not particularly limited and may be in accordance with ordinary methods. Specifically, the molecular weight cut off of the ultrafiltration membrane is 400-100000, preferably 1000-10000, and the materials are regenerated cellulose, polyethersulfone, polysulfone, polyacrylonitrile, polyvinyl alcohol, sintered metal. Ceramic, carbon, etc. are used as appropriate. The shape of the membrane may be any of a flat plate type, a spiral type, a tubular type, a hollow fiber type, a breez type and the like.

Next, the aqueous solution containing the crude lithium hydroxide having a predetermined concentration prepared above is subjected to microfiltration, and an insoluble component containing impurity components of Al compounds such as SiO ₂ and further Al ₂ O ₃ and Al (OH) _{3 is} removed. Remove.

  The microfiltration can be performed using a filtering material such as a microfiltration membrane. Examples of the microfiltration membrane that can be used include a screen filter having a surface filtration action, a depth filter having an internal filtration action, and the like. In the present invention, a screen filter having a surface filtration action can efficiently remove insoluble matters. It is particularly preferable in that it can be performed. The nominal pore size of the microfiltration membrane is 1 μm or less, preferably 0.1 to 0.5 μm, and the material of the microfiltration membrane is not particularly limited. For example, collodion, cellophane, acetylcellulose, polyacrylonitrile, polysulfone And organic films such as polyolefin, polyamide, polyimide, and polyvinylidene fluoride, and inorganic films such as graphite, ceramics, and porous glass. Moreover, if it is a laboratory scale, filter media, such as a PTFE membrane filter, can be used. The type of the screen filter is not particularly limited, but the cartridge type is particularly preferable in terms of easy operability. These microfiltrations can be carried out using a commercially available microfiltration apparatus by introducing the above-prepared crude lithium hydroxide aqueous solution having a predetermined concentration into the microfiltration apparatus. This microfiltration operation can be carried out under reduced pressure or under pressure, but is not particularly limited. Usually, the crude lithium hydroxide aqueous solution having the predetermined concentration prepared above is fed at a temperature of 0 with a feed pump. It introduce | transduces into a microfiltration apparatus at the flow rate of 1-30 ml / min, preferably 5-15 ml / min at -100 degreeC, Preferably 20-80 degreeC, 0.1-0.5 Mpa, Preferably it is 0.2-0. It is preferable to process at a pressure of 3 MPa. The filtration operation by microfiltration is preferably performed at a temperature at which lithium hydroxide does not precipitate from the aqueous solution.

In many cases, the above-described microfiltration treatment provides purified lithium hydroxide in which the content of SiO ₂ is reduced to 50 ppm or less, preferably 30 ppm or less, and further the Al content is reduced to 50 ppm or less, preferably 30 ppm or less. However, in the present invention, it is preferable to perform a crystallization operation in order to further reduce the Al content, particularly the content of electrically insulating impurities such as Ca oxide and hydroxide.

  A specific crystallization operation is a method of precipitating lithium hydroxide by cooling from an aqueous solution containing lithium hydroxide subjected to the above-described microfiltration or an aqueous solution containing lithium hydroxide subjected to the above-described microfiltration. In the present invention, the latter method of precipitating lithium hydroxide by heating is advantageous in that the recovery efficiency of purified lithium hydroxide is good. Is particularly preferable.

  The crystallization operation for precipitating lithium hydroxide by heating is carried out by using an aqueous solution containing 1 to 12% by weight, preferably 9 to 12% by weight of the lithium hydroxide subjected to the above-described microfiltration as LiOH, at a temperature of 80 ° C. It is preferably performed by heating to 90 to 100 ° C. and evaporating and removing 10 to 70% by weight, preferably 30 to 60% by weight of water. In this crystallization operation, purified lithium hydroxide from which impurities are efficiently removed can be obtained by removing water within the range. The crystallization operation by heating may be performed under reduced pressure.

The purified lithium hydroxide thus crystallized has a SiO ₂ content of 50 ppm or less, preferably 30 ppm or less, and the content of Al compounds such as electrically insulating Al oxides and hydroxides as Al metal. 25 ppm or less, preferably 15 ppm or less, and the content of Ca compounds such as electrically insulating Ca oxide and hydroxide is 25 ppm or less, preferably 15 ppm or less as Ca metal, and the total amount of Al metal and Ca metal The lithium hydroxide is reduced to 50 ppm or less, preferably 30 ppm or less.

に従って、硫化リチウムの他、水および硫化水素を副生する。副生する水は生成する硫化リチウムを分解する一つの要因となり、また、上記した反応は平衡反応であることから本発明において水を反応系から除去することで、硫化リチウムの分解を抑制し、また、効率よく反応を行うことができる。(2A process and 2B process)
The reaction between lithium hydroxide and hydrogen sulfide is represented by the following reaction formulas (1) and (2)

Accordingly, water and hydrogen sulfide are by-produced in addition to lithium sulfide. By-product water is one factor that decomposes the generated lithium sulfide, and since the reaction described above is an equilibrium reaction, by removing water from the reaction system in the present invention, the decomposition of lithium sulfide is suppressed, Moreover, it can react efficiently.

  In step 2A, the purified lithium hydroxide and hydrogen sulfide obtained in step 1 are reacted at 150 to 200 ° C. in an inert gas atmosphere while distilling off the water produced in the aprotic solvent. It is a process of generating. In the present invention, by selecting the second step A, lithium sulfide can be produced at once from the purified lithium hydroxide and hydrogen sulfide obtained in the first step.

  On the other hand, in the second step B, the first reaction is carried out at 100 to 150 ° C. while distilling off the water produced from the purified lithium hydroxide and hydrogen sulfide obtained in the first step in an aprotic solvent. In this step, lithium sulfide is generated by performing the second reaction at 150 to 200 ° C. in an active gas atmosphere. By selecting the second step B, lithium hydrosulfide is obtained from the purified lithium hydroxide and hydrogen sulfide obtained in the first step according to the reaction formula (1), and then desulfurized according to the reaction formula (2). Lithium sulfide can be obtained stepwise by hydrogenation.

  The generated lithium sulfide itself is a very unstable compound, and when it comes into contact with air, it reacts with water in the air and hydrolyzes to produce lithium hydroxide and hydrogen sulfide. As described above, when the lithium sulfide is used as a raw material for producing the inorganic solid electrolyte, it becomes one factor that decreases the ionic conductivity. Therefore, in the present invention, it is one important requirement that the second reaction in the second step A and the second step B be performed at least in an inert gas atmosphere.

  Examples of the inert gas that can be used include argon gas, helium gas, and nitrogen gas. These inert gases are preferably high-purity products in order to prevent impurities from entering the product, and those having a dew point of −50 ° C. or less, preferably −60 ° C. or less are used to avoid contact with moisture. It is particularly preferred.

  In the first reaction of the second A step and the second B step, the reaction is performed while distilling at least water produced as a by-product out of the reaction system. As a method for distilling off the by-produced water out of the reaction system, the reaction may be carried out at a reaction temperature described later using a reaction apparatus provided with a condenser at the top of the reaction vessel. In this case, it is preferable that the inert gas is always in an inert gas atmosphere by always supplying the inert gas to the reaction vessel during the reaction.

  In the operations of Steps 2A and 2B, first, a predetermined amount of purified lithium hydroxide is added to an aprotic solvent to prepare a suspension of the aprotic solvent containing purified lithium hydroxide, and then hydrogen sulfide is added. Introduce into the reaction system.

  As an aprotic solvent that can be used, for example, an amide compound, a lactam compound, a urea compound, an organic sulfur compound, a cyclic organic phosphorus compound, or the like can be used as a single solvent or as a mixed solvent.

  Examples of the amide compound include N, N-dimethylformamide, N, N-diethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N, N-dipropylacetamide, N, N-dimethylbenzoate. Examples include acid amides. Examples of the lactam compound include caprolactam, N-methylcaprolactam, N-ethylcaprolactam, N-isopropylcaprolactam, N-isobutylcaprolactam, N-normalpropylcaprolactam, N-normalbutylcaprolactam, and N-cyclohexylcaprolactam. N-alkylcaprolactams, N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone, N-isopropyl-2-pyrrolidone, N-isobutyl-2-pyrrolidone, N-normalpropyl-2-pyrrolidone, N-normalbutyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, N-methyl-3-methyl-2-pyrrolidone, N-ethyl-3-methyl-2-pyrrolidone, N-methyl-34,5-trimethyl- 2- Loridone, N-methyl-2-piperidone, N-ethyl-2-piperidone, N-isopropyl-2-piperidone, N-methyl-6-methyl-2-piperidone, N-methyl-3-ethyl-2- And piperidone. Examples of the urea compound include tetramethylurea, N, N′-dimethylethyleneurea, N, N′-dimethylpropyleneurea, and the like. Examples of the organic sulfur compound include dimethyl sulfoxide, diethyl sulfoxide, diphenyl sulfone, 1-methyl-1-oxosulfolane, 1-ethyl-1-oxosulfolane, 1-phenyl-1-oxosulfolane, and the like. Examples of the cyclic organic phosphorus compound include 1-methyl-1-oxophosphorane, 1-normalpropyl-1-oxophosphorane, 1-phenyl-1-oxophosphorane, and the like.

  These various aprotic solvents can be used alone or in combination of two or more. Among these, N-methyl-2-pyrrolidone (NMP) has a high boiling point, and the intermediate product lithium hydrosulfide is used. It is particularly preferable in that it dissolves but does not dissolve lithium sulfide, so that the target product is free of lithium hydrosulfide and lithium sulfide can be easily recovered.

  The compounding amount of the purified lithium hydroxide with respect to the aprotic solvent is not particularly limited, but if it exceeds 10 moles with respect to 1 L of the aprotic solvent, the reaction with hydrogen sulfide decreases because a uniform reaction cannot be performed. Further, since a considerable amount of hydrogen sulfide is required, the amount is preferably 10 mol or less with respect to 1 L of the aprotic solvent.

  The other raw material, hydrogen sulfide, preferably has a high purity with a low impurity content, and particularly preferably has a purity of 99.9 Vol% or more and a water content of 2 mg / L or less. Normally, hydrogen sulfide itself is not corrosive to metal, but hydrogen sulfide containing moisture is corrosive to metal, and the generated corrosive substance may be mixed into the reaction system. Therefore, the hydrogen sulfide used has a low water content, and the reaction liquid caused by corrosion using a metal material other than metal such as glass or a metal material obtained by mirror polishing the inner surface of the pipe as a pipe material for supplying hydrogen sulfide to the reaction system. It is preferable to prevent contamination.

  One important requirement for the reaction conditions in the second step A is that the reaction temperature is 150 to 200 ° C, preferably 150 to 190 ° C. The reason for this is that lithium hydrosulfide is generated at a temperature lower than 150 ° C. and lithium sulfide cannot be obtained directly, whereas if it exceeds 200 ° C., the boiling point of the solvent may be exceeded. The amount of hydrogen sulfide introduced in step 2A may be 1 or more in terms of a molar ratio to lithium hydroxide (LiOH), but if it is 1.5 to 4, the residual amount of lithium hydroxide as a raw material is significantly reduced. It is particularly preferable because it can be made. The addition rate of hydrogen sulfide is not particularly limited, but it is preferable to gradually introduce it into the reaction system at a constant rate in order to obtain a stable quality. The temperature at the time of introduction of hydrogen sulfide into the reaction system may be room temperature, but introduction into the reaction system in a state heated to the above reaction temperature and the water hydrated with lithium hydroxide , Which is preferable in that water generated by the reaction can be quickly distilled out of the system. The reaction in the second step A needs to take a long time so that unreacted lithium hydroxide does not remain, and the reaction time varies depending on the reaction conditions such as raw material charge amount and concentration. In this case, it is desirable that the time be 1 hour or longer, preferably 2 hours or longer.

  On the other hand, in the second step B, it is one important that the first reaction is performed at 100 to 150 ° C., preferably 110 to 150 ° C., and then the second reaction is performed at 150 to 200 ° C., preferably 150 to 190 ° C. Requirements. The reason for setting the reaction temperature in the above range in the first reaction is that the reaction rate is remarkably reduced when the temperature is less than 100 ° C., and it is difficult to distill off the produced water from the reaction system. Is generated. In addition, the reason for setting the reaction temperature in the second reaction in the above range is that lithium sulfide is not generated when the temperature is lower than 150 ° C., whereas the boiling point of the solvent may be exceeded when the temperature exceeds 200 ° C. The amount of hydrogen sulfide introduced in step 2B may be 1 or more in terms of molar ratio to lithium hydroxide (LiOH), but if it is 1.5 to 4, the residual amount of lithium hydroxide as a raw material is significantly reduced. It is particularly preferable because it can be made. The addition rate of hydrogen sulfide is not particularly limited, but it is preferable to gradually introduce it into the reaction system at a constant rate in order to obtain a stable quality. The temperature at the time of introduction of hydrogen sulfide into the reaction system may be room temperature, but introduction into the reaction system in a state heated to the reaction temperature of the first reaction hydrates lithium hydroxide. It is preferable in that the water that is generated and the water generated by the reaction can be quickly distilled out of the system. The first reaction and the second reaction need to be performed with sufficient time so that unreacted lithium hydroxide and lithium hydrosulfide do not remain, and the reaction time depends on the amount of raw material charged, the concentration, etc. Although it depends on the conditions, in many cases it is desirable to set the time to 1 hour or longer, preferably 2 hours or longer.

  The atmosphere in the first reaction of step 2B is not particularly limited since lithium hydrosulfide is a relatively stable compound, but after the first reaction is completed, the second reaction is continued. Since it can be performed, an inert gas atmosphere is preferable. Further, after the completion of the first reaction, unreacted lithium hydroxide may be solid-liquid separated and removed from the reaction system, and then the second reaction may be continued.

  After completion of the reaction in the second A step or the second B step, the above inert gas is used to carry out solid-liquid separation by an ordinary method under an inert gas atmosphere, and then cleaning is performed in a third step described later, followed by a fourth step To dry the product.

  In addition, the filtrate after solid-liquid separation can be reused as an aprotic solvent for the reaction solvent used in Step 2A or Step 2B by applying purification means such as distillation.

(3rd and 4th steps)
In the third step, the lithium sulfide obtained in the second step A or step 2B is washed with an organic solvent to remove impurities such as lithium hydrosulfide, and then dried in the fourth step to obtain a product. .

In the present invention, it is one important requirement to perform the third and fourth steps in an inert gas atmosphere or in a vacuum to suppress the decomposition of lithium sulfide due to contact with moisture in the air. Accordingly, in the third step and the fourth step, the inside of the container used for the operation is sufficiently replaced with an inert gas, or cleaning and drying are performed under a vacuum.

  Examples of the inert gas used in the third step and the fourth step include argon gas, helium gas, nitrogen gas, and the like. These inert gases are preferably high-purity products in order to prevent impurities from entering the product, and those having a dew point of −50 ° C. or less, preferably −60 ° C. or less to avoid contact with moisture. Is particularly preferred.

  As the cleaning method in the third step, it is particularly preferable to use the repulping method because cleaning efficiency is high and cleaning can be performed effectively.

  As the organic solvent used for washing, an organic solvent which has affinity for the solvent used at the time of reaction and is inert to lithium sulfide may be used. In addition to the aprotic solvent described above, for example, one type such as acetone or the like Two or more types can be used. Further, the organic solvent is dehydrated until the water content is 1000 ppm or less, preferably 100 ppm or less, particularly preferably 50 ppm or less in order to avoid decomposition of lithium sulfide with water, or a commercially available water content is 1000 ppm or less, It is particularly preferable to use one having a concentration of 100 ppm or less, particularly preferably 50 ppm or less. The method for dehydrating the organic solvent is not particularly limited. For example, according to Japanese Patent Application Laid-Open No. 07-235309 or Japanese Patent Application Laid-Open No. 07-235310, it is easy to bring the organic solvent into contact with the zeolite layer. Can be dehydrated.

  After the completion of cleaning, in the fourth step, drying is performed to obtain a product. The drying method is a method that can remove the solvent, and is not particularly limited as long as it is performed in an inert gas atmosphere or in a vacuum, and the drying temperature is not less than the volatilization temperature of the solvent used during washing. That's fine.

  After completion of drying, the product is pulverized, classified, packaged, etc. as desired to obtain a product. The pulverization performed as necessary is appropriately performed when the lithium sulfide powder obtained by drying is in the form of a crumbly bonded block, but the lithium sulfide powder particles themselves are the above-mentioned specific average particles. It has a diameter. That is, the obtained lithium sulfide powder has an average particle diameter determined from a scanning electron micrograph (SEM) of 10 to 80 μm, preferably 20 to 60 μm.

  The series of steps 2A to 4 or 2B to 4 in the lithium sulfide powder of the present invention, and the operations of pulverization, classification and packaging performed as necessary were replaced with inert gas. Alternatively, it is particularly preferable to perform in a vacuum glove box or the like because a series of operations can be easily performed by effectively blocking contact with moisture in the air.

The lithium sulfide powder according to the present invention shows a single phase of lithium sulfide in terms of X-ray diffraction, and does not substantially contain lithium hydroxide and SiO ₂ as impurities. Further, the lithium sulfide powder obtained according to a preferred embodiment of the present invention is fine, excellent in crystallinity, and substantially free of electrically insulating impurities composed of Al and Ca in addition to the above characteristics. is there.

  Such lithium sulfide powder can be suitably used not only as a raw material for producing polysulfide polymers but also as a raw material for producing electronic materials, particularly inorganic solid electrolytes.

Next, the inorganic solid electrolyte of the present invention will be described.
The inorganic solid electrolyte of the present invention contains at least the lithium sulfide powder. The content of the lithium sulfide powder in the inorganic solid electrolyte is not particularly limited, but is preferably 20 mol% or more, preferably 40 mol% or more. The inorganic solid electrolyte of the present invention is crystalline or It may be amorphous.

Examples of other compounds constituting the inorganic solid electrolyte of the present invention include phosphorus sulfide (P ₂ S ₅ ), lithium iodide (LiI), boron sulfide (B ₂ S ₃ ), silicon sulfide (SiS ₂ ), sulfide Germanium (GeS ₂ ), gallium sulfide (Ga ₂ S ₃ ), aluminum sulfide (Al ₂ S ₃ ), lithium phosphate (Li ₃ PO ₄ ), lithium oxide (Li ₂ O), lithium sulfate (Li ₂ SO ₄ ) , Phosphorus oxide (P ₂ O ₅ ), lithium borate (Li ₃ BO ₃ ), Li ₃ PO _4-x N _{2x / 3} (x is 0 <x <4), Li ₄ SiO _4-x N _{2x / 3} ( x is selected from 0 <x <4), Li ₄ GeO _4-x N _{2x / 3} (x is 0 <x <4), Li ₃ BO _3-x N _{2x / 3} (x is 0 <x <3) Including at least one or two or more selected from Without being limited thereto, in the present invention, particularly preferably an example of an inorganic solid electrolyte, for _{example, Li 2 S, Li 2 S} -P 2 S 5, Li 2 S-P 2 S 5 -X ( wherein , X is _LiI, B 2 _{S 3,} or at least one element selected from _{Al 2 S 3), Li 2} S-P 2 S 3, Li 2 S-SiS 2, Li 2 S-GeS 2, Li 2 S _{-Ga 2 S 3, Li 2 S} -B 2 S 3 , and the like.

Furthermore, when the inorganic solid electrolyte of the present invention is amorphous (glass), lithium phosphate (Li ₃ PO ₄ ), lithium oxide (Li ₂ O), lithium sulfate (Li ₂ SO ₄ ), phosphorus oxide (P ₂ O ₅ ), oxygen-containing compounds such as lithium borate (Li ₃ BO ₃ ), Li ₃ PO _4-x N _{2x / 3} (x is 0 <x <4), Li ₄ SiO _4-x N _{2x / 3} (X is 0 <x <4), Li ₄ GeO _4-x N _{2x / 3} (x is 0 <x <4), Li ₃ BO _3-x N _{2x / 3} (x is 0 <x <3), etc. The nitrogen-containing compound can be contained in the inorganic solid electrolyte. By the addition of the compound containing oxygen or the compound containing nitrogen, the gap between the formed amorphous skeletons can be widened, the movement of lithium ions can be made smooth, and the ion conductivity can be further improved.

  The inorganic solid electrolyte according to the present invention can be produced by a widely known method. For example, lithium sulfide powder and other compounds constituting the inorganic solid electrolyte are mixed, and an inert gas such as argon is used. It can be produced by quenching after heating and melting in an atmosphere.

  As a method for quenching, a common method such as water cooling, liquid nitrogen quenching, twin-roller quenching, or splat quenching method can be used.

  The inorganic solid electrolyte according to the present invention is pulverized or formed into a sheet, for example, a solid electrolyte of an all-solid lithium battery composed of at least a positive electrode, a negative electrode, and a solid electrolyte, or a positive electrode, a negative electrode, a separator, and In a lithium secondary battery composed of a non-aqueous organic electrolyte containing a lithium salt, it can be used as a coating material for lithium metal or lithium alloy used for the negative electrode.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.
In the examples of the present invention, commercially available lithium hydroxide monohydrate was used as crude lithium hydroxide.
The impurity content in this lithium hydroxide sample is shown in Table 1.
The amount of impurities is a value determined by ICP emission spectrometry, ICP mass spectrometry, and turbidimetry.

(First step)
The above-mentioned crude lithium hydroxide monohydrate 1062 g was dissolved in pure water 5000 g at 50 ° C. to prepare an aqueous solution. Pure water was obtained by treating water treated with a pure water production apparatus equipped with an ion exchange resin with an ultrafiltration module (manufactured by Asahi Chemical Industry Co., Ltd., molecular weight cut off 6000), and was used in the following examples. Pure water is also subjected to the same treatment as the pure water.
Next, the aqueous solution in which the crude lithium hydroxide prepared above was dissolved was filtered at 40 ° C. using a PTFE membrane filter having a pore size of 0.5 μm.
Table 2 shows impurity contents in a lithium hydroxide sample obtained by partially collecting the filtrate after filtration and drying under reduced pressure.

Next, the mixture was heated to 95 ° C. and crystallized for 4 hours while retaining moisture under reduced pressure. The recovered water was 3300 g. After cooling, the lithium hydroxide deposited by solid-liquid separation by a conventional method was collected, and dried under reduced pressure to obtain purified lithium hydroxide.
Table 3 shows the impurity content in the obtained purified lithium hydroxide sample and the average particle diameter determined by the laser diffraction method.

<Second step, third step, fourth step>
A flask equipped with a stirrer and a condenser was installed, and charged with 167.9 g (4 mol) of purified lithium hydroxide monohydrate obtained in the first step and 1 L of N-methyl-2-pyrrolidone (NMP).
Next, the flask was heated to 175 ° C. under an argon gas stream. Next, using a stainless steel pipe whose inner surface was mirror-polished, hydrogen sulfide gas was blown into the reaction solution with stirring at a supply rate of 400 ml / min over 7 hours, and after completion of the blowing, Reaction was performed at 175 degreeC for 2 hours. Although water was by-produced during the reaction, it was condensed by the condenser and extracted from the system, and argon gas was continuously supplied to the flask of the reaction vessel during the reaction.
The argon gas used was made by Nippon Oxygen Co., Ltd. having a purity of 99.998% or more and a dew point of −60 ° C. or less, and the hydrogen sulfide gas was made by Japan Fine Products Co., Ltd. with a purity of 99.99%.
After completion of the reaction, filtration, washing and drying were performed in a glove box substituted with argon gas using the above-mentioned argon gas to obtain 83.6 g of lithium sulfide powder (yield 91%).
The washing was performed three times by the repulping method using 500 ml of acetone (moisture content of 50 ppm or less, manufactured by Kanto Chemical Co., Ltd.), and the drying was performed at 110 ° C. for 2 hours by installing a heater in a glove box.

<First step>
The first step was performed under the same operating conditions as in Example 1.
<Second step>
A flask equipped with a stirrer and a condenser was installed, and 210 g (5 mol) of purified lithium hydroxide monohydrate obtained in the first step and 1 L of N-methyl-2-pyrrolidone (NMP) were charged.
Next, the flask was replaced with argon gas, and the temperature was raised to 180 ° C. Next, using a stainless steel pipe whose inner surface was mirror-polished, hydrogen sulfide gas was blown into the reaction liquid at a supply rate of 400 L / min with stirring at a supply rate of 400 L / min over 8 hours. The reaction was performed at 180 ° C. for 2 hours. Although water was by-produced during the reaction, it was condensed by the condenser and extracted from the system, and argon gas was continuously supplied to the flask of the reaction vessel during the reaction.
The argon gas used was made by Japan Oxygen Corporation with a purity of 99.998% and a dew point of −60 ° C. or less, and the hydrogen sulfide gas used was made by Japan Fine Products with a purity of 99.99%.
After completion of the reaction, the above argon gas was used, followed by filtration, washing and drying in a glove box substituted with the argon gas, to obtain 102 g of lithium sulfide powder (yield 89%).
The washing was performed three times by the repulping method using 500 ml of acetone (moisture content of 50 ppm or less, manufactured by Kanto Chemical Co., Ltd.), and the drying was performed at 110 ° C. for 2 hours by installing a heater in a glove box.

<First step>
The first step was performed under the same operating conditions as in Example 1.
<Second step>
A flask equipped with a stirrer and a condenser was installed, and 84 g (2 mol) of purified lithium hydroxide monohydrate obtained in the first step and 0.5 L of N-methyl-2-pyrrolidone (NMP) were charged.
Next, the flask was replaced with argon gas, and the temperature was raised to 110 ° C. Next, 103 g (3 mol) was blown in over 4 hours while stirring hydrogen sulfide gas into the reaction solution using a stainless steel pipe at a supply rate of 300 L / min. The produced water was condensed by a condenser and extracted out of the system. After completion of the blowing, the temperature was raised to 170 ° C. and the reaction was performed for 6 hours. Argon gas is 99.998% pure and made by Nippon Oxygen Co., Ltd. with a dew point of −60 ° C. or less, and hydrogen sulfide gas is 99.99% pure by Japan Fine Products Co., Ltd. Was used.
After completion of the reaction, filtration, washing and drying were performed in a glove box substituted with argon gas to obtain 40 g of lithium sulfide (yield 87%).
In addition, washing | cleaning was performed by the repulp method using 400 ml of acetone, and drying was performed at 110 degreeC for 2 hours.

Comparative Example 1
Using crude lithium hydroxide before performing the first step as lithium hydroxide, 82.7 g of lithium sulfide powder (yield 90%) was synthesized in the same manner as in Example 1.

Comparative Example 2
The first to second steps are carried out in the same manner as in Example 1, the glove box is in an atmospheric atmosphere (humidity 52%), and the third step is washed and dried in the same manner as in Example 1 to obtain 82 g of lithium sulfide powder. (Yield 89%) was synthesized.

<Evaluation of physical properties of lithium sulfide>
About the lithium sulfide powder obtained in Examples 1 to 3 and Comparative Examples 1 and 2 and the commercially available lithium sulfide powder (Comparative Example 3), the molar ratio of Li and S in the lithium sulfide powder, the impurity content, The average particle size and X-ray diffraction analysis were performed, and the results are shown in Table 4.
The molar ratio of Li and S was determined from the value obtained by measuring Li by atomic absorption and S by iodine titration, and the impurity content was determined by ICP emission spectrometry, ICP mass spectrometry, and turbidimetry. It is. Moreover, the average particle diameter was calculated | required by the scanning electron micrograph (SEM).
X-ray diffraction analysis uses Cu-Kα rays as a radiation source, and 2θ = 32. 2 derived from lithium hydroxide with respect to the diffraction peak (a) in the vicinity of 2θ = 26.98 ° (111 plane) of the lithium sulfide powder. The relative intensity ratio {(b / a) × 100} of the diffraction peak (b) near 48 ° (101 plane) and the half width of the diffraction peak of the (111) plane of the lithium sulfide powder were determined from Scherrer's equation.
The X-ray diffraction pattern of the lithium sulfide powder obtained in Example 1 is shown in FIG. 1, the X-ray diffraction pattern of a commercially available lithium sulfide powder is shown in FIG. 2, and the lithium sulfide powder obtained in Example 1 A scanning electron micrograph (SEM) of the body is shown in FIG.
X-ray diffraction was measured in an argon atmosphere.

(Inorganic solid electrolyte)
Examples 4-6 and Comparative Examples 4-6
The lithium sulfide powders of Examples 1 to 3 and Comparative Examples 1 to 3 and silicon sulfide (manufactured by ABCR GmbH) were weighed and mixed so that the molar ratio was 60:40. This mixture was filled in a glassy carbon crucible and melted at 1000 ° C. for 2 hours in an argon gas stream. Thereafter, the melt was dropped into liquid nitrogen to obtain a solid electrolyte.
Argon gas having a purity of 99.998% or more and a dew point of −60 ° C. or less manufactured by Nippon Oxygen Co., Ltd. was used.
In order to evaluate the electrochemical characteristics of the solid electrolyte thus obtained, the following ionic conductivity measurements and potential-current characteristics were investigated to investigate the electrochemical stability. The ionic conductivity of the solid electrolyte was measured by an AC impedance method by applying carbon paste as electrodes to both ends of the obtained solid electrolyte having a ribbon-like form. In addition, a measurement cell for measuring the potential-current characteristics is obtained by pressing a powder obtained by pulverizing solid electrolyte glass at 3 ton / cm ² to form a pellet having a diameter of 10 mm and a thickness of 3 mm. A metal lithium foil was used as the reversible electrode, and a platinum plate was used as the ion blocking electrode on the opposite end face. Using this measurement cell, the potential was swept up to 8 V (vs. Li ⁺ / Li) at a sweep rate of 5 mV / sec, and the potential-current behavior was recorded.
As a result, the obtained ionic conductivity (25 ° C.) and the oxidation current value that flowed when the potential was swept to 8 V are shown in Table 5.

  From the results of Table 5, the inorganic solid electrolyte prepared using the lithium sulfide of the present invention showed higher ionic conductivity than that of the comparative example, and the comparative example was compared with the inorganic solid electrolyte of the present invention. A higher oxidation current value was indicated, suggesting that the electron conductivity or the oxide decomposition reaction of the solid electrolyte occurred.

Examples 7-9 and Comparative Examples 7-9
The lithium sulfide powders of Examples 1 to 3 and Comparative Examples 1 to 3, silicon sulfide (manufactured by ABCR GmbH) and lithium phosphate (manufactured by Nippon Kagaku Kogyo Co., Ltd.) are weighed so that the molar ratio is 63: 36: 1. And mixed. This mixture was filled in a glassy carbon crucible and melted at 1000 ° C. for 2 hours in an argon gas stream. Next, the melt was ultra-quenched with a twin roller to obtain a solid electrolyte.
In order to evaluate the electrochemical characteristics of the solid electrolyte thus obtained, ion conductivity and potential-current characteristics were measured in the same manner as in Examples 3-4.
As a result, the obtained ionic conductivity (25 ° C.) and the oxidation current value that flowed when the potential was swept to 8 V are shown in Table 6.

  The lithium sulfide powder of the present invention is a raw material for producing a polysulfide polymer, an electronic material, particularly an inorganic solid electrolyte using the lithium sulfide powder of the present invention has high ionic conductivity, and an oxidative decomposition reaction of the solid electrolyte occurs. The lithium sulfide powder of the present invention can be used as a raw material for producing an inorganic solid electrolyte because it is difficult and exhibits excellent electrochemical characteristics.

FIG. 1 is an X-ray diffraction pattern of the lithium sulfide powder obtained in Example 1.
FIG. 2 is an X-ray diffraction pattern of a commercially available lithium sulfide powder (Comparative Example 3).
[FIG. 3] Scanning electron micrograph (SEM) of lithium sulfide obtained in Example 1 (magnification: x300)

Explanation of symbols

(A) is a diffraction peak of (111) plane of lithium sulfide.
(B) is a diffraction peak of (101) plane of lithium hydroxide.

Claims (5)

When the X-ray diffraction analysis is performed, the relative intensity ratio {(b / a) × 100} of the diffraction peak (a) of lithium sulfide (111 plane) and the diffraction peak (b) of lithium hydroxide (101 plane) is 3. A lithium sulfide powder characterized by having 3 or less and a SiO ₂ content of 50 ppm or less.   2. The lithium sulfide powder according to claim 1, wherein a half width of a diffraction peak of (111 plane) obtained by X-ray diffraction analysis is 0.15 degrees or less.   The lithium sulfide powder according to claim 1 or 2, having an average particle size of 10 to 80 µm.   The lithium sulfide powder according to any one of claims 1 to 3, wherein the total content of metal elements of Al and Ca is 50 ppm or less.   An inorganic solid electrolyte comprising the lithium sulfide powder according to any one of claims 1 to 4.

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