Lithium sulfide and production method therefor, and production method for sulfide solid electrolyte

Abstract

This lithium sulfide has a mass-specific unpaired electron quantity of 1.0×10–8 mol / g or less. The lithium sulfide preferably has a mass-specific unpaired electron quantity of 1.7×10–24 mol / g or greater. The lithium sulfide is preferably produced according to a method having: a hydration water removal step in which a lithium hydroxide hydrate is heated to obtain lithium hydroxide from which at least a portion of the hydration water has been removed; a sulfidation step in which the lithium hydroxide and a sulfur-including compound are reacted to perform sulfidation; and a cooling step in which the product of the sulfidation step is cooled. The cooling speed during the cooling step is set to 1.0°C / min or greater.

Description

Lithium sulfide and its manufacturing method, and method for producing a sulfide solid electrolyte

[0001] This invention relates to lithium sulfide powder and a method for producing the same. Furthermore, this invention relates to a method for producing a sulfide solid electrolyte.

[0002] In recent years, secondary batteries have attracted attention as an effort to prevent global warming by reducing carbon dioxide emissions. Among these, solid-state batteries are expected to be put into practical use as batteries that combine safety and high energy density. One of the solid electrolytes used in solid-state batteries is sulfide solid electrolyte. Sulfide solid electrolyte is manufactured using lithium sulfide as a raw material, for example. Lithium sulfide has generally been manufactured by reacting a lithium source compound with hydrogen sulfide. For example, Patent Document 1 describes a method for producing lithium sulfide by reacting lithium hydroxide, a lithium source, with hydrogen sulfide in a disc dryer without using a solvent. The same document states that this method can produce lithium sulfide with suppressed crystallization.

[0003] Patent Document 2 describes a method for producing a sulfide solid electrolyte using lithium sulfide as a raw material, in which lithium sulfide, phosphorus pentasulfide, lithium chloride, and lithium bromide are mixed, and the mixture obtained by the mixing is heated in a mixed gas atmosphere of sulfur gas and nitrogen gas, and lithium sulfide that has lost sulfur atoms due to long-term storage is used as the lithium sulfide.

[0004] Japanese Patent Publication No. 2017-222567, International Publication No. 2024 / 101110, Pamphlet

[0005] When lithium sulfide, such as that described in Patent Document 2, i.e., lithium sulfide lacking sulfur atoms, is used as a raw material for sulfide solid electrolytes, the quality of the sulfide solid electrolyte obtained through manufacturing tends to deteriorate. Sulfide solid electrolytes of deteriorated quality tend to have reduced performance. Therefore, in the same document, the concentration of the sulfur-containing atmosphere introduced during the manufacture of sulfide solid electrolytes is adjusted with the aim of preventing deterioration in the quality of sulfide solid electrolytes manufactured using sulfur-lacking lithium sulfide as a raw material. However, such concentration adjustment is time-consuming and not industrially advantageous.

[0006] The object of the present invention is to provide high-quality lithium sulfide powder and a method for producing the same. Another object of the present invention is to provide a method for producing high-quality sulfide solid electrolytes.

[0007] This invention provides an unpaired electron quantity of 1.0 × 10⁻¹⁶ per unit mass. －８ This invention provides lithium sulfide in a concentration of mol / g or less.

[0008] The present invention also provides a method for producing a sulfide solid electrolyte, comprising the steps of mixing lithium sulfide, diphosphorus pentasulfide, and lithium halide to obtain a mixture, and then calcining the mixture.

[0009] Furthermore, the present invention provides a method for producing lithium sulfide, comprising: a water hydration removal step of heating lithium hydroxide hydrate to obtain lithium hydroxide from which at least some of the water hydration has been removed; a sulfurization step of reacting the lithium hydroxide with a sulfur-containing compound to produce sulfurized lithium sulfide; and a cooling step of cooling the product from the sulfurization step, wherein the cooling rate in the cooling step is set to 1.0°C / min or higher.

[0010] Figure 1 shows the electron spin resonance spectrum of lithium sulfide obtained in Example 1. Figure 2 shows the electron spin resonance spectrum of lithium sulfide used in Comparative Example 1.

[0011] The present invention will be described below based on its preferred embodiments. The present invention relates to lithium sulfide. The lithium sulfide according to the present invention is characterized by a low amount of unpaired electrons. The amount of unpaired electrons is a measure of the quality of lithium sulfide; the lower the amount of unpaired electrons, the higher the quality of the lithium sulfide can be considered. Lithium sulfide with a low amount of unpaired electrons can be said to be lithium sulfide with less deviation in composition due to sulfur deficiency or the presence of impurities. The amount of unpaired electrons in lithium sulfide varies depending on the manufacturing method and storage method of lithium sulfide.

[0012] The inventors' research has revealed that using lithium sulfide with a low unpaired electron content as a raw material for manufacturing sulfide solid electrolytes improves the quality and performance of the sulfide solid electrolytes, and also reduces the amount of sulfur added during the manufacturing process.

[0013] In this invention, the amount of unpaired electrons in lithium sulfide can be measured by electron spin resonance (ESR) spectroscopy (hereinafter also referred to as "ESR method"). According to the ESR method, the number of unpaired electrons and the state of the unpaired electrons can be directly measured. Therefore, in this invention, the quality of lithium sulfide is evaluated by observing the unpaired electrons present in lithium sulfide using the ESR method.

[0014] From the viewpoint of producing high-quality sulfide solid electrolytes, the lithium sulfide of the present invention has an unpaired electron content of 1.0 × 10⁻¹⁶ per unit mass. －８ It is preferable that the concentration be mol / g or less, and 1.0 × 10 －９ It is even more preferable that the concentration be mol / g or less, and 1.0 × 10 －１０ It is even more preferable that the amount is mol / g or less. The amount of unpaired electrons is desirable because the smaller the value, the higher the quality of lithium sulfide, and it may be zero, but as a result of the inventors' research, the amount of unpaired electrons per unit mass is, for example, 1.7 × 10⁻⁶. －２４ It was found that a sufficiently high-performance sulfide solid electrolyte can be manufactured at a concentration of approximately mol / g. The lithium sulfide of the present invention has an unpaired electron content of, for example, 1.7 × 10⁻⁶ per unit mass. －２４ It may be mol / g or more, 1.7 × 10 －２３may be mol / g or more, 1.7×10 －２２ may be mol / g or more.

[0015] A method for measuring the amount of unpaired electrons in lithium sulfide will be described in Examples mentioned later.

[0016] It is preferable that the lithium sulfide of the present invention contains as few impurities as possible, from the viewpoint of improving the performance of a sulfide solid electrolyte produced using the lithium sulfide of the present invention as a raw material, for example, lithium ion conductivity. In the production of lithium sulfide, lithium sulfate, lithium thiosulfate and lithium oxide are generally produced as by-products, or lithium hydroxide as a starting material may remain in some cases. In the present invention, it is desirable that these compounds are not present in lithium sulfide as much as possible. However, the content of the above-mentioned compounds contained as impurities in the lithium sulfide of the present invention only needs to be within a range that does not adversely affect the performance of the sulfide solid electrolyte produced using the lithium sulfide of the present invention. Specifically, the amount of impurities contained in the lithium sulfide of the present invention is preferably 3.0% by mass or less, more preferably 1.0% by mass or less, and still more preferably 0.1% by mass or less.

[0017] There is no particular limitation on the particle size of the lithium sulfide of the present invention. From the viewpoint of successfully obtaining a sulfide solid electrolyte by a solid-phase reaction using the lithium sulfide of the present invention as a raw material, the volume cumulative particle diameter D of lithium sulfide at a cumulative volume of 50% by volume measured by a laser diffraction scattering particle size distribution measurement method ５０ is, for example, preferably 1 μm or more, more preferably 10 μm or more, and still more preferably 100 μm or more. On the other hand, the volume cumulative particle diameter D of lithium sulfide ５０ is, for example, preferably 1000 μm or less, more preferably 800 μm or less, and still more preferably 600 μm or less.

[0018] Lithium sulfide, which has a low amount of unpaired electrons and is of high quality, can preferably be produced by a method comprising the steps (a) to (c) described below. Each step will be described in detail below. (a) Hydration water removal step: Lithium hydroxide hydrate is heated to obtain lithium hydroxide from which at least some of the hydration water has been removed. (b) Sulfidation step: The lithium hydroxide is reacted with a sulfur-containing compound to perform sulfidation. (c) Cooling step: The product from the sulfidation step is cooled.

[0019] (a) Hydration Water Removal Process In this process, first, lithium hydroxide hydrate is prepared as the lithium source. Lithium hydroxide hydrate is generally monohydrate. Although lithium carbonate and lithium sulfate are also known as lithium sources for producing lithium sulfide, lithium hydroxide hydrate can be mainly used as the lithium source in this production method, and it is particularly preferable to use only lithium hydroxide hydrate. Furthermore, the lithium hydroxide hydrate used in this production method is solid. "Solid lithium hydroxide hydrate" means that lithium hydroxide in the state of aqueous solution is to be excluded. Therefore, lithium hydroxide that has absorbed water contained in the air is included in the category of solid lithium hydroxide.

[0020] There are no particular restrictions on the particle size of lithium hydroxide hydrate. In this process, since hydration water is removed from solid lithium hydroxide hydrate, it is desirable to have a particle size that allows for efficient removal of hydration water. From this viewpoint, the volume cumulative particle size D of lithium hydroxide hydrate at a cumulative volume of 50% by laser diffraction scattering particle size distribution measurement method is considered. ５０ For example, the particle size is preferably 1 μm or larger, more preferably 10 μm or larger, and even more preferably 100 μm or larger. On the other hand, the volume cumulative particle size D of lithium hydroxide hydrate ５０ For example, it is preferably 1000 μm or less, more preferably 800 μm or less, and even more preferably 600 μm or less.

[0021] To remove at least part of the water of hydration from lithium hydroxide hydrate, for example, lithium hydroxide hydrate may be heated in an air atmosphere. The heating temperature is preferably a temperature at which the lithium hydroxide hydrate does not melt. Heating of lithium hydroxide hydrate can be performed in a state where the lithium hydroxide hydrate is allowed to stand still, or can be performed in a state where it is fluidized. In any case, from the viewpoint of removing an appropriate amount of water of hydration, the heating temperature of lithium hydroxide hydrate is preferably 100°C or higher and 450°C or lower. From this viewpoint, the heating temperature of lithium hydroxide hydrate is more preferably 120°C or higher and 400°C or lower, and still more preferably 150°C or higher and 350°C or lower. When the heating temperature is within the above range, the heating time for lithium hydroxide hydrate is preferably 1 hour or more and 24 hours or less from the viewpoint of removing an appropriate amount of water of hydration. From this viewpoint, the heating time for lithium hydroxide hydrate is more preferably 3 hours or more and 20 hours or less, and still more preferably 5 hours or more and 16 hours or less.

[0022] In the present step, from the viewpoint of obtaining lithium sulfide with a small amount of unpaired electrons, it is preferable to remove water of hydration such that the content of water of hydration in the lithium hydroxide obtained in the present step is 10000 ppm by mass or less. From this viewpoint, the content of water of hydration in the lithium hydroxide obtained in the present step is more preferably 5000 ppm by mass or less, and still more preferably 1000 ppm by mass or less. The content of water of hydration in the lithium hydroxide obtained in the present step may be zero, but it is not required to be zero; for example, it may be 10 ppm by mass or more, 50 ppm by mass or more, or further 80 ppm by mass or more. The term "ppm" herein means a value based on mass.

[0023] The content of water of hydration in the lithium hydroxide obtained in the present step can be measured, for example, by a Karl Fischer moisture meter.

[0024] In the present production method, anhydrous lithium hydroxide may be used instead of lithium hydroxide obtained by removing water of hydration from lithium hydroxide hydrate.

[0025] (b) Sulfurization Step In this step, lithium hydroxide obtained in the water of hydration removal step, that is, lithium hydroxide from which at least a portion of water of hydration has been removed, is reacted with a sulfur-containing compound. Thereby, the lithium hydroxide obtained in the water of hydration removal step is sulfurized to obtain lithium sulfide. In the following description, for the purpose of distinguishing from lithium hydroxide hydrate subjected to the water of hydration removal step, the lithium hydroxide obtained in the water of hydration removal step is referred to as "water-of-hydration-removed lithium hydroxide".

[0026] As the sulfur-containing compound, any substance capable of reacting with water-of-hydration-removed lithium hydroxide to produce lithium sulfide can be used without particular limitation. Examples of such sulfur-containing compounds include hydrogen sulfide (H ２ S), carbon disulfide (CS ２ ), sulfur oxide (SO Ｘ ), and sulfur gas obtained by heating solid sulfur (S) to a temperature equal to or higher than its boiling point to vaporize the same.

[0027] It is preferable that the supply amount of the sulfur-containing compound is an excess amount relative to the water-of-hydration-removed lithium hydroxide, from the viewpoint of successfully obtaining lithium sulfide with a small amount of unpaired electrons. From this viewpoint, for example, it is preferable to cause the reaction between water-of-hydration-removed lithium hydroxide and the sulfur-containing compound while allowing a gas of the sulfur-containing compound to flow through the water-of-hydration-removed lithium hydroxide in a stationary state or a fluidized state.

[0028] The reaction between water-of-hydration-removed lithium hydroxide and the sulfur-containing compound is carried out by heating the reaction system preferably to 100°C or higher, more preferably 150°C or higher, still more preferably 200°C or higher, which is advantageous from the viewpoint of efficient sulfurization of the water-of-hydration-removed lithium hydroxide. Further, the reaction between water-of-hydration-removed lithium hydroxide and the sulfur-containing compound is carried out by heating the reaction system preferably to 450°C or lower, more preferably 400°C or lower, still more preferably 300°C or lower, which is advantageous from the viewpoint of preventing melting of the water-of-hydration-removed lithium hydroxide.

[0029] (c) Cooling Step In this step, the lithium sulfide produced in the sulfidation step is cooled. As a result of the inventors' research, it has been found that performing a cooling step successfully yields high-quality lithium sulfide with a low amount of unpaired electrons. In this specification, "performing a cooling step" means performing some treatment on the lithium sulfide produced in the sulfidation step in order to cool the lithium sulfide, for example, by controlling the cooling rate. Specifically, it is preferable to set the cooling rate in this step to 1°C / min or more, more preferably to 10°C / min or more, and even more preferably to 50°C / min or more. There is no particular upper limit to the cooling rate in this step, but from an industrial standpoint, the cooling rate may be 1000°C / min or less, 500°C / min or less, and even 300°C / min or less. The cooling rate may be constant within the above range. Alternatively, the cooling rate may change within the above range during cooling. In this specification, the cooling rate refers to the cooling rate of the lithium sulfide itself when the temperature of the lithium sulfide can be measured. If the temperature of lithium sulfide cannot be measured, it refers to the cooling rate of the reaction apparatus.

[0030] Cooling methods in this process include, for example, spraying a cooling gas or cooling liquid into the reactor, circulating a cooling liquid through a jacket provided in the reactor, and removing lithium sulfide from the reactor and moving it to a pre-cooled space.

[0031] Temperature T at the end of the cooling process in this step Ｃ The temperature is preferably 150°C or lower, more preferably 130°C or lower, and even more preferably 100°C or lower. The cooling rate mentioned above refers to the temperature of the reaction system in the sulfurization step. Ｂ In that case, (T Ｂ -T Ｃ ) / t (t is T from the start of cooling) Ｃ This represents the time it takes to first reach a certain point. It is defined as the time it takes for the reaction system to reach a certain point. Ｂ From T ＣWhile the reaction system is being cooled to T, it is preferable that the temperature of the reaction system gradually decreases. Specifically, the temperature of the reaction system can be continuously decreased or decreased in a stepwise manner. Ｂ From T Ｃ It is preferable that the temperature of the reaction system does not rise even temporarily while it is being cooled to that point.

[0032] During the cooling process in this step, it is preferable to maintain an atmosphere in the reaction system with a hydrogen sulfide concentration of 0.1 vol% or higher, from the viewpoint of successfully obtaining high-quality lithium sulfide with a low amount of unpaired electrons. From this viewpoint, it is even more preferable that the atmosphere in the cooling step has a hydrogen sulfide concentration of 1 vol% or higher, and even more preferable that it is 10 vol% or higher. On the other hand, the atmosphere in the cooling step may have a hydrogen sulfide concentration of 100 vol% or less, 80 vol% or less, or even 60 vol% or less.

[0033] The atmosphere during the cooling process is preferably a mixed atmosphere containing hydrogen sulfide and an inert gas. Examples of inert gases include noble gases such as helium, argon, and neon, as well as nitrogen gas.

[0034] By the above method, lithium sulfide of the present invention, i.e., lithium sulfide in which the amount of unpaired electrons per unit mass is below a specific value, can be successfully obtained. This lithium sulfide is useful, for example, as a raw material for sulfide solid electrolytes in lithium-ion batteries. For example, lithium sulfide of the present invention and phosphorus pentasulfide (P ２ S ５ ) or other sulfides are subjected to a mechanical milling reaction, for example Li ７ P ３ S １１ LiPS ４Solid electrolytes such as the above can be synthesized. Alternatively, a mixture (raw material composition) can be obtained by mixing lithium sulfide of the present invention, diphosphorus pentasulfide, and lithium halides such as lithium chloride (LiCl) and / or lithium bromide (LiBr), and by calcining the mixture under an inert gas atmosphere or a hydrogen sulfide atmosphere, a crystalline solid electrolyte, for example, a solid electrolyte having a crystalline phase of an argyrodite type crystal structure, can be synthesized. In this case, since the amount of unpaired electrons in lithium sulfide is small, the quality of the sulfide solid electrolyte obtained by production is high. As a result, this sulfide solid electrolyte has high performance such as lithium ion conductivity. Also, since the amount of unpaired electrons in lithium sulfide is small, unlike the technology described in Patent Document 2 above, it is not necessary to increase the amount of sulfur atoms contained in the calcination atmosphere during the production of the sulfide solid electrolyte. Therefore, it becomes possible to produce sulfide solid electrolytes economically. Note that the substance reacted with lithium sulfide to synthesize the solid electrolyte is not particularly limited. For example, in addition to the above-mentioned diphosphorus pentasulfide, silicon sulfide (SiS) can also be used. ２ ), germanium sulfide (GeS ２ Examples include:

[0035] With respect to the embodiments described above, the present invention further discloses the following lithium sulfide, a method for producing a sulfide solid electrolyte, and a method for producing lithium sulfide. [1] The amount of unpaired electrons per unit mass is 1.0 × 10 －８ Lithium sulfide with a concentration of mol / g or less. [2] Unpaired electrons per unit mass of 1.7 × 10 －２４[1] Lithium sulfide as described in [1], wherein the concentration is mol / g or more. [3] A method for producing a sulfide solid electrolyte, comprising the steps of mixing lithium sulfide as described in [1] or [2], phosphorus pentasulfide, and lithium halide to obtain a mixture, and calcining the mixture. [4] A method for producing lithium sulfide, comprising: a water hydration removal step of heating lithium hydroxide hydrate to obtain lithium hydroxide from which at least some of the water hydration has been removed; a sulfurization step of reacting the lithium hydroxide with a sulfur-containing compound to sulfurize it; and a cooling step of cooling the product from the sulfurization step, wherein the cooling rate in the cooling step is set to 1.0°C / min or more. [5] The method for producing lithium sulfide as described in [4], wherein the atmosphere in the cooling step is an atmosphere with a hydrogen sulfide concentration of 0.1 vol% or more. [6] The manufacturing method according to [4] or [5], wherein the hydrated water is removed in the hydrated water removal step so that the content of the hydrated water in the lithium hydroxide obtained in the hydrated water removal step is 10,000 ppm or less.

[0036] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples.

[0037] [Example 1] (1) Hydration water removal step particle size D ５０ Lithium hydroxide monohydrate (LiOH·H) has a diameter of 423.8 μm. ２ The lithium hydroxide monohydrate (O) was placed in a heating furnace, and the furnace was heated to 200°C. This temperature was maintained for 16 hours, and some of the water of hydration was removed from the lithium hydroxide monohydrate. The amount of water of hydration contained in the lithium hydroxide monohydrate after heating was calculated from the mass of the lithium hydroxide monohydrate before and after heating to be 153.9 ppm.

[0038] (2) Sulfidation process The hydrated water-removed lithium hydroxide obtained in the hydrated water removal process of (1) above was placed in a tubular reactor and heated while an atmosphere containing hydrogen sulfide was circulated in the reactor. The atmosphere composition was 100 vol% hydrogen sulfide. The heating temperature was 200°C. Lithium sulfide was produced by heating.

[0039] (3) Cooling process After the completion of the sulfidation process in (2) above, the heating of the tubular reactor was stopped. The temperature inside the tubular reactor decreased at a rate of 1.2°C / min (200°C to 130°C). At 130°C, the atmospheric composition inside the tubular reactor was 1 vol% hydrogen sulfide and 99 vol% argon. In this way, the target lithium sulfide was obtained. Particle size D of the obtained lithium sulfide ５０ The particle size was 458.2 μm. Furthermore, when the obtained lithium sulfide was subjected to Rietveld analysis using XRD, the purity of the lithium sulfide was found to be 99.6%.

[0040] [Comparative Example 1] As Comparative Example 1, commercially available lithium sulfide manufactured by Sigma Aldrich was used as is.

[0041] [Evaluation 1] The amount of unpaired electrons in lithium sulfide obtained in the examples and comparative examples was measured by the ESR method using the following procedure. The results are shown in Table 1 below. (1) Apparatus and conditions ・Apparatus: Electron spin resonance spectrometer (JES-X330 manufactured by JEOL) ・Microwave output: 0.25 mW ・Magnetic field sweep width: 322.5 ± 10 mT ・Modulated magnetic field: 0.1 ・Sensitivity: 50 ・Time constant: 0.03 s ・Measurement time: 2 minutes ・Measurement temperature: Room temperature (295 K) ・Reference material for amount of unpaired electrons: 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (hereinafter referred to as "TEMPOL") ・Others: Measured using a manganese marker (hereinafter referred to as "Mn marker"). The ESR spectra of lithium sulfide obtained in Example 1 and Comparative Example 1 are shown in Figures 1 and 2, respectively. As is clear from these figures, no peak was observed in the ESR spectrum of the lithium sulfide obtained in Example 1, whereas a peak was observed in the ESR spectrum of the lithium sulfide obtained in Comparative Example 1 (the peak indicated by the arrow in Figure 2).

[0042] (2) Acquisition of the calculated spectrum The measured ESR spectrum obtained in (1) above was reproduced with the following calculated spectrum. Specifically, peak position: X ０The signal intensity Y for X was calculated by substituting three constants—mT, full width at half maximum (WmT), and scaling constant (A)—and one variable, magnetic field (XmT), into the differential form of the Lorentz function. For X, 4096 equally spaced points from 312.5 mT to 332.5 mT were selected, and the calculated Y for each X was obtained to acquire the computational spectrum.

[0043] (3) Differential form of the Lorentz function The differential form of the Lorentz function was calculated using the three constants and the variable X described in the previous section (2) using the following formula.

[0044]

[0045] (4) Calibration curve acquisition A calibration curve using the reference substance TEMPOL was obtained as follows. TEMPOL toluene solutions were prepared at concentrations of 4 μM, 10 μM, 40 μM, and 400 μM. 100 μL of each solution was placed in a sample tube for ESR and measured under the conditions of item (1) above. The ESR spectrum obtained from the measurement showed two peaks for the Mn marker and three peaks for TEMPOL. Therefore, using five calculated spectra obtained by the methods of items (2) and (3) above, the variables of item (2) above were determined so that the sum of the five calculated spectra and the measured ESR spectrum fit as closely as possible visually. After visually adjusting the sum of the calculated spectra to approximate the measured ESR spectra as closely as possible, the variables were more precisely fitted using the solver function in Microsoft Excel (Microsoft Excel for Microsoft 365 MSO (version 2408 build 16.0.17928.20336) 32-bit). The fit accuracy was such that, after running the solver function in Excel, the mean squared error for all points from 312.5 mT to 332.5 mT was less than 2% of the difference between the maximum and minimum values ​​of the measured ESR spectra. A graph was created in Excel with the sum of the double integrals of the three calculated spectra of TEMPOL obtained through the above fitting plotted on the x-axis and the concentration of TEMPOL plotted on the y-axis, and a calibration curve was created on this graph using Excel's linear fit function.

[0046] (5) Calculation of unpaired electron reference value The unpaired electron reference value using the Mn marker was calculated using the following procedure. For each concentration of TEMPOL, the double integral values ​​of two of the five calculation spectra fitted in the previous section (4) were calculated. The sum of the absolute values ​​was input into the calibration curve formula obtained in the previous section (4) to calculate the unpaired electron amount corresponding to the double integral values ​​of the two peaks of the Mn marker. This was used as the unpaired electron reference value using the Mn marker.

[0047] (6) Calculation of the amount of unpaired electrons in the target sample The amount of unpaired electrons in the target sample was obtained by the following procedure. The target sample was measured under the conditions of item (1) above. If a signal was obtained for the target sample, the calculated spectra from items (2) and (3) above were used to fit the sample with a total of three calculated spectra: one calculated spectrum of the target sample and two calculated spectra of the Mn marker, in the same manner as in item (4) above. The double integral values ​​of the three calculated spectra were calculated for each, and the sum of the absolute values ​​of the double integral values ​​of the two calculated spectra of the Mn marker was calculated. １ and the double integral value B of the calculated spectrum of the target sample. ２ , and the unpaired electron quantity reference value B calculated by the Mn marker using the method in item (5) above. ０ Using this method, the unpaired electron quantity B of the target sample is determined. ３ The amount of unpaired electrons B was calculated using the following formula. ３ The amount of unpaired electrons per unit mass was calculated by dividing the amount in (mol) by the mass (g) of the target sample.

[0048]

[0049]

[0050] As is clear from the results shown in Table 1, the lithium sulfide obtained in the examples has a lower amount of unpaired electrons than the lithium sulfide obtained in the comparative example.

[0051] As described in detail above, the present invention provides high-quality lithium sulfide powder. By using the lithium sulfide powder of the present invention, high-quality sulfide solid electrolytes can be obtained.

Claims

1. The amount of unpaired electrons per unit mass is 1.0 × 10⁻⁶. －８ Lithium sulfide in a quantity of mol / g or less.

2. The amount of unpaired electrons per unit mass is 1.7 × 10⁻⁶ －２４ Lithium sulfide according to claim 1, wherein the concentration is mol / g or more.

3. A method for producing a sulfide solid electrolyte, comprising the steps of mixing lithium sulfide according to claim 1 or 2, phosphorus pentasulfide, and lithium halide to obtain a mixture, and calcining the mixture.

4. A method for producing lithium sulfide, comprising: a water hydration removal step of heating lithium hydroxide hydrate to obtain lithium hydroxide from which at least some of the water hydration has been removed; a sulfurization step of reacting the lithium hydroxide with a sulfur-containing compound to produce sulfurized lithium sulfide; and a cooling step of cooling the product produced in the sulfurization step, wherein the cooling rate in the cooling step is set to 1.0°C / min or higher.

5. The manufacturing method according to claim 4, wherein the atmosphere in the cooling step is an atmosphere with a hydrogen sulfide concentration of 0.1 vol% or more.

6. The manufacturing method according to claim 4 or 5, wherein the hydrated water is removed in the hydrated water removal step so that the content of the hydrated water in the lithium hydroxide obtained in the hydrated water removal step is 10,000 ppm or less.

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