Method for manufacturing sulfide solid electrolyte material

Abstract

This method for manufacturing a sulfide solid electrolyte material is characterized by including a starting material mixing step S01 for mixing starting materials, which respectively contain elements that constitute the sulfide solid electrolyte material, so as to obtain a mixed starting material and a generation step S02 for heating the mixed starting material so as to generate the sulfide solid electrolyte material, wherein, in the generation step S02, the heating atmosphere contains a sulfur gas with a controlled partial pressure.

Description

Method for manufacturing sulfide solid electrolyte materials 【0001】 This invention relates to a method for producing a sulfide solid electrolyte material suitable for use in, for example, all-solid-state batteries. This application claims priority based on Japanese Patent Application No. 2024-210022, filed in Japan on December 3, 2024, the contents of which are incorporated herein by reference. 【0002】 In recent years, sulfide-based solid electrolyte materials have attracted attention as electrolytes for lithium-ion secondary batteries because they have high ionic conductivity and are safer than liquid electrolytes. The generally accepted method for manufacturing sulfide solid electrolyte materials involves heat-treating a mixture of raw materials to synthesize the sulfide solid electrolyte through a solid-phase reaction. 【0003】 For example, Patent Documents 1-3 describe a method for producing a sulfide solid electrolyte by heat-treating a mixture of raw materials under an inert gas atmosphere such as nitrogen or argon, or under vacuum (sealed) conditions. Patent Documents 4 and 5 also describe a sulfide solid electrolyte obtained by heating a mixture of raw materials under a flow of hydrogen sulfide gas, or a method for producing the same. 【0004】 Japanese Patent Publication No. 2003-208919 (A) Japanese Patent Publication No. 5527673 (B) Japanese Patent Publication No. 5888609 (B) Japanese Patent Publication No. 2016-24874 (A) Japanese Patent Publication No. 2018-67552 (A) 【0005】 Incidentally, as disclosed in Patent Documents 1-3, when manufacturing sulfide solid electrolyte materials, it is common practice to heat-treat the mixture under an inert gas atmosphere such as nitrogen or argon, or under vacuum, in order to prevent oxidation of the raw materials and the resulting sulfide solid electrolyte material. However, sulfur evaporation can cause sulfur deficiency, leading to a decrease in the quality of the solid electrolyte material, and it has been difficult to easily manufacture sulfide solid electrolyte materials of sufficient quality. 【0006】Furthermore, Patent Documents 4 and 5 propose a method for manufacturing sulfide solid electrolyte materials that involves heat treatment under a hydrogen sulfide gas atmosphere. While hydrogen sulfide gas can suppress the formation of sulfur deficiencies due to sulfur evaporation, it is toxic and flammable, requiring pollution control and safety equipment, which hinders the reduction of manufacturing costs. 【0007】 This invention has been made in view of the circumstances described above, and aims to provide a method for producing a sulfide solid electrolyte material that has sufficient ionic conductivity by suppressing the evaporation of sulfur during heat treatment without using hydrogen sulfide gas. 【0008】 To solve the above problems, the method for producing a sulfide solid electrolyte material according to Embodiment 1 of the present invention is a method for producing a sulfide solid electrolyte material, comprising: a raw material mixing step of mixing raw materials containing each element constituting the sulfide solid electrolyte material to obtain a mixed raw material; and a production step of heating the mixed raw material to produce the sulfide solid electrolyte material, wherein the heating atmosphere in the production step contains sulfur gas with controlled partial pressure. 【0009】 According to the method for producing a sulfide solid electrolyte material of embodiment 1 of the present invention, in the production step in which a mixed raw material containing each element constituting the sulfide solid electrolyte material is heated to produce the sulfide solid electrolyte material, the heating atmosphere contains sulfur gas with controlled partial pressure, which suppresses the evaporation of sulfur from the mixed raw material and the produced sulfide solid electrolyte material during the heat treatment. Therefore, it is possible to produce a high-quality sulfide solid electrolyte material with sufficient ionic conductivity. Furthermore, because sulfur gas is used, there is no need to install special pollution control equipment or safety equipment as when hydrogen sulfide gas is used, and the sulfide solid electrolyte material can be produced inexpensively and efficiently. 【0010】The manufacturing method of the sulfide solid electrolyte material according to Embodiment 2 of the present invention is characterized in that, in the manufacturing method of the sulfide solid electrolyte material according to Embodiment 1 of the present invention, the partial pressure of the sulfur gas in the generation step is 45% or more of the saturated vapor pressure of sulfur at the heating temperature. According to the manufacturing method of the sulfide solid electrolyte material according to Embodiment 2 of the present invention, since the partial pressure of the sulfur gas in the generation step is 45% or more of the saturated vapor pressure of sulfur at the heating temperature, the evaporation of sulfur components can be sufficiently suppressed, and it becomes possible to manufacture a high-quality sulfide solid electrolyte material having sufficient ionic conductivity. 【0011】 The manufacturing method of the sulfide solid electrolyte material according to Embodiment 3 of the present invention is characterized in that, in the manufacturing method of the sulfide solid electrolyte material according to Embodiment 1 or Embodiment 2 of the present invention, in the generation step, heating is performed until elemental sulfur evaporates. According to the manufacturing method of the sulfide solid electrolyte material according to Embodiment 3 of the present invention, in the generation step, due to the condensation or solidification of sulfur gas in the atmosphere or the unreacted elemental sulfur in the mixed raw materials, elemental sulfur molecules may be mixed or remain in the generated sulfide solid electrolyte material, which may become impurities. However, as in the present invention, by evaporating the mixed or remaining elemental sulfur and removing it from the sulfide solid electrolyte material, it becomes possible to stably manufacture a high-purity and high-quality sulfide solid electrolyte material. 【0012】 The manufacturing method of the sulfide solid electrolyte material according to Embodiment 4 of the present invention is in the manufacturing method of the sulfide solid electrolyte material according to any one of Embodiments 1 to 3 of the present invention, wherein the sulfide solid electrolyte material belongs to the space group P42 / nmc and contains an LGPS (Li １０ GeP ２ S １２ )-type crystal structure. When measured by X-ray diffraction measurement using CuKα rays, the peaks of the following formulas (A1) to (A6) are detected as diffraction peaks. Taking the diffraction intensity of the peak of formula (A6) as I Ａ and the diffraction intensity of the peak of formula (A7) as I Ｂ , when I Ａ is compared with I Ｂ , the peak intensity ratio I Ｂ / I ＡThe characteristic is that the ratio is less than 50%. 2θ = 17.38° ± 1.0° ... (A1) 2θ = 20.18° ± 1.0° ... (A2) 2θ = 20.44° ± 1.0° ... (A3) 2θ = 23.96° ± 1.0° ... (A4) 2θ = 26.96° ± 1.0° ... (A5) 2θ = 29.58° ± 1.0° ... (A6) 2θ = 27.33° ± 1.0° ... (A7) 【0013】 A method for producing a sulfide solid electrolyte material according to aspect 5 of the present invention is characterized in that, in the method for producing a sulfide solid electrolyte material according to any one of aspects 1 to 3 of the present invention, it contains an argyrodite-type crystal structure. 【0014】 A method for producing a sulfide solid electrolyte material according to embodiment 6 of the present invention is a method for producing a sulfide solid electrolyte material according to any one of embodiments 1 to 3 of the present invention, wherein the sulfide solid electrolyte material is Li ａ M ｂ S ｃ It is represented by the following equations, has a crystal structure of space group Pnm, and when measured by X-ray diffraction using CuKα rays, the following diffraction peaks are detected: 2θ = 17.01 ± 0.50 ... (B1) 2θ = 18.50 ± 0.50 ... (B2) 2θ = 25.31 ± 0.50 ... (B3) 2θ = 26.23 ± 0.50 ... (B4) where M is at least one element from groups 13, 14, and 15, and a, b, and c are numbers greater than 0. 【0015】 According to the present invention, it is possible to provide a method for producing a high-quality sulfide solid electrolyte material having sufficient ionic conductivity by suppressing the evaporation of sulfur during heat treatment without using hydrogen sulfide gas. 【0016】 This is a flow chart of a method for producing a sulfide solid electrolyte material, which is an embodiment of the present invention. 【0017】Embodiments of the present invention will be described below with reference to the attached drawings. The embodiments described below are provided specifically to better illustrate the spirit of the invention and do not limit the present invention unless otherwise specified. 【0018】 The method for producing a sulfide solid electrolyte material according to this embodiment is for producing a sulfide solid electrolyte material that can be used, for example, as a solid electrolyte in an all-solid-state battery. Sulfide solid electrolyte materials have high ionic conductivity and are non-flammable, making them highly safe, and are therefore applied to electric vehicles and the like. 【0019】 The sulfide solid electrolyte material produced in this embodiment is, for example, an LGPS material having an LGPS-type crystal structure (typical composition: Li １０ GeP ２ S １２ ) and Ag ８ GeS ６ Argyrodite materials (Li) have an argyrodite-type crystal structure, which is represented by minerals. ７－ｘ PS ６－ｘ Ha ｘ Examples include LMS materials having [Ha = Cl, Br, I, x = 0.0 to 1.8], or Li, S, and at least one element from groups 13, 14, or 15. 【0020】 Next, the method for producing the sulfide solid electrolyte material according to this embodiment will be explained using the flow chart in Figure 1. As shown in Figure 1, the method for producing the sulfide solid electrolyte material according to this embodiment includes a raw material mixing step S01 and a production step S02. 【0021】The raw material mixing step S01 and the production step S02 are preferably carried out in a gas atmosphere that does not react with the raw materials, especially when the raw materials contain sulfides or the like. Therefore, it is preferable to carry out these steps in an inert atmosphere such as nitrogen, argon, or other noble gases. In addition, it is preferable that the atmospheric gas used does not contain water or oxygen gas. In particular, the amount of water in the atmospheric gas is preferably 1000 vol ppm or less, more preferably 500 vol ppm or less, even more preferably 100 vol ppm or less, and especially preferably 10 vol ppm or less. By keeping the amount of water in the atmospheric gas within this range, oxidation due to water is suppressed, and it is possible to produce high-quality sulfide solid electrolyte materials. 【0022】 (Raw material mixing process S01) First, raw materials containing each element that constitutes the sulfide solid electrolyte material are mixed to obtain a mixed raw material. The raw material may be a simple sulfide or Li ３ PS ４ The sulfides may be complex sulfides, non-sulfides (which may contain sulfur as an unavoidable impurity), or elemental sulfur. The non-sulfides may be individual elements or alloys of multiple elemental elements. Furthermore, in order to utilize the solid-liquid reaction between the elemental raw materials and liquid sulfur for the production of the sulfide solid electrolyte material, an excess of elemental sulfur exceeding the stoichiometric ratio composition of the sulfide solid electrolyte material may be added to the mixed raw materials. Elemental sulfur refers to sulfur that does not contain any elements other than sulfur, excluding unavoidable impurities. In other descriptions of this embodiment, unless otherwise specified, each raw material may contain unavoidable impurities. The elemental sulfur added may be any of the sulfur allotropes such as α-sulfur (orthorhombic sulfur), β-sulfur (monoclinic sulfur), γ-sulfur (monoclinic sulfur), or rubbery sulfur, or it may contain multiple allotropes. Furthermore, in order to promote elemental diffusion and chemical reactions in the subsequent production process S02, or to improve mass productivity, it is preferable that each raw material and elemental sulfur be in powder or granular form (powdered powder, particulate granules, or aggregates of powder and granules), and among these, powder form is more preferable. Therefore, the following description will focus on cases where each raw material and elemental sulfur are used in powder form. 【0023】 For example, in the case of an LGPS material containing Li, Ge, P, and S, Li ２ S, GeS ２ , P ２ S ５ You may mix them, or Li ２ You may mix S, Ge, P, and S, or Li4GeS ４ Li ３ PS ４ You may mix them, or Li ３ PS ４ Ge and S may be mixed. If the Argyrodite material contains Li, P, S and Cl, then Li ２ S, LiCl, P ２ S ５ You may mix them, or Li ２ S, LiCl, P, and S may be mixed. If the LMS material contains Li, Sn, and S, then Li ２ S, SnS ２ You may mix them, or Li ２ S, P, and S may be mixed. 【0024】 The mixing method in the raw material mixing process S01 is not particularly limited as long as it can uniformly mix each raw material, but various existing methods include general mixers, blenders, ball mills, bead mills, vibratory mills, and V-type mixers. Alternatively, mechanical milling using planetary ball mills, vibratory mills, ball mills, etc. may be performed instead of a general mixing process, but from the viewpoint of economic rationality and mass production, general mixing methods using the aforementioned existing methods are more preferable. 【0025】 (Production process S02) Next, the obtained mixed raw materials are placed in a firing container such as a crucible or saggar and heated at a temperature T1 to react the mixed raw materials and produce a sulfide solid electrolyte material. The material of the inner wall of the furnace and the firing container that are subjected to the heat treatment comes into contact with sulfur gas or elemental sulfur and sulfides in the heating atmosphere, so it is preferable to use a material that is resistant to corrosion by sulfidation. Examples include ceramics such as alumina and zirconia, metals with corrosion-resistant treatment on the surface, carbon, and silicon carbide. 【0026】In this embodiment, the heating atmosphere in the production step S02 contains sulfur gas with controlled partial pressure. That is, sulfur gas is contained in the heating atmosphere when the firing container into which the mixed raw materials are placed is heated from room temperature, and the partial pressure of this sulfur gas is controlled. Preferably, the partial pressure of sulfur gas in the atmosphere is 45% or more of the saturated vapor pressure of sulfur at the heating temperature at that time, from the time the heating temperature is raised from room temperature to temperature T1, and while the heating temperature is maintained at temperature T1. By setting the partial pressure of sulfur gas in the atmosphere within this range, the evaporation of sulfur from the mixed raw materials and the produced sulfide solid electrolyte material can be suppressed before the production of the sulfide solid electrolyte material (at a temperature below the production temperature during heating), during production, and during crystal growth, and the formation of impurity phases can be sufficiently suppressed. In addition, it is thought that the suppression of sulfur evaporation contributes to the reduction of sulfur deficiency in the sulfide solid electrolyte material. As a result, a sulfide solid electrolyte material with sufficient ionic conductivity can be easily produced. 【0027】 Furthermore, regarding the method of introducing sulfur gas into the heating atmosphere, if the mixed raw materials contain elemental sulfur, for example, one method is to use the same elemental sulfur as the elemental sulfur in the mixed raw materials as the sulfur gas source and introduce it into the heating furnace on an inert carrier gas such as nitrogen or argon. Sulfur gas at temperatures of 150°C or higher usually contains S ３ S ５ S ６ S ７ S ８ Because it contains multiple allotropes, this method makes it possible to introduce a sulfur gas into the heating atmosphere in which the ratio of allotropes is the same as that of the sulfur gas that can be produced by the evaporation of elemental sulfur in the mixed raw materials, thereby effectively suppressing the evaporation of sulfur in the mixed raw materials. 【0028】The heat treatment temperature T1 is preferably 350°C or higher, more preferably 400°C or higher, even more preferably 450°C or higher, and particularly preferably 500°C or higher. By setting the heating temperature within this range, the residue of intermediate products and impurity phases is suppressed, making it possible to produce high-quality sulfide solid electrolyte materials. In addition, in the case of crystalline sulfide solid electrolyte materials, it is possible to produce sulfide solid electrolyte materials with high crystallinity. Furthermore, the upper limit of the heat treatment temperature T1 is preferably 1000°C or lower, more preferably 650°C or lower, and even more preferably 600°C or lower. Furthermore, the holding time at this heating temperature is preferably 30 minutes or more, more preferably 1 hour or more, and even more preferably 6 hours or more. 【0029】 The heating rate from room temperature during the heat treatment is preferably 0.5°C / min to 20°C / min, more preferably 1°C / min to 15°C / min, and even more preferably 2°C / min to 10°C / min. In particular, when elemental sulfur is included in the mixed raw materials, setting the heating rate within this range allows the electrolyte raw materials to be quickly heated to temperature T1 while preventing the rapid evaporation of elemental sulfur. As a result, sufficient time is ensured for the high-temperature liquid sulfur to be in contact with the solid electrolyte raw materials at temperature T1. This promotes the formation reaction of the solid electrolyte, and allows for the easy production of a sulfide solid electrolyte material with sufficient ionic conductivity. 【0030】Furthermore, in the production process S02, there is a risk that sulfur molecules may be mixed into the firing container due to the condensation or solidification of sulfur gas in the atmosphere, or that elemental sulfur in the mixed raw materials may remain unreacted in the firing container. In either case, since the sulfur element does not form bonds with other elements and is not incorporated into the sulfide solid electrolyte compound, sulfur molecules will be present in the firing container after the completion of the production process S02, leading to the contamination of the sulfide solid electrolyte material with impurities after production. To prevent this contamination with impurities, it is preferable to evaporate and remove all excess elemental sulfur after the production reaction and crystal growth of the sulfide solid electrolyte material are completed and the stoichiometric amount of sulfur elements have formed bonds in the sulfide solid electrolyte material. In particular, if an excess of elemental sulfur exceeding the stoichiometric composition of the sulfide solid electrolyte material is added to the mixed raw materials, this prevents the contamination of the sulfide solid electrolyte material with sulfur molecules, and allows for the stable production of a high-quality sulfide solid electrolyte material with fewer impurities. 【0031】 Therefore, it is preferable to set the heat treatment conditions at temperature T1 to a thermal history (temperature, time) sufficient for all excess elemental sulfur to evaporate, or, if not (if the heat treatment conditions at temperature T1 are insufficient for all excess elemental sulfur to evaporate), to heat to a sufficient temperature and time after the heat treatment at temperature T1. In addition, after all the formation reactions and crystal growth of the sulfide solid electrolyte material are completed and the required amount of sulfur elements in terms of stoichiometric ratio have formed bonds in the sulfide solid electrolyte material, it is preferable that the partial pressure of sulfur gas in the atmosphere is lower than the saturated vapor pressure (100%) of sulfur at that temperature. The heat treatment conditions (thermal history) sufficient for all elemental sulfur to evaporate will vary depending on the value of the partial pressure of sulfur gas in the heating atmosphere, the proportion of elemental sulfur in the mixed raw materials, the amount of raw materials put into the calcination container, and the value of temperature T1, but for example, a thermal history of 1 to several hours at 400°C or higher, which is close to the boiling point of elemental sulfur (445°C), can be cited. 【0032】Furthermore, when removing the firing container from the furnace after the heat treatment is complete, it is common practice to wait until the firing container cools to around room temperature to 100°C by natural cooling or air cooling before removing it. It is preferable that the partial pressure of sulfur gas in the atmosphere while the firing container is cooling is lower than the saturated vapor pressure (100%) of sulfur at that temperature. This prevents sulfur gas in the atmosphere from condensing or solidifying and mixing into the firing container as the temperature cools, thus preventing it from becoming an impurity in the sulfide solid electrolyte material and enabling the stable production of high-quality sulfide solid electrolyte material. 【0033】 The sulfide solid electrolyte material is manufactured through the process described above. 【0034】 Here, Li is used as a raw material. ２ S, GeS ２ , P ２ S ５ When using this method, in the production step S02, the following reaction occurs to produce LGPS material (Li １０ GeP ２ S １２ ) generates. 5Li ２ S+GeS ２ +P ２ S ５ →Li １０ GeP ２ S １２ Also, Li as a raw material ２ When S, Ge, P, and S are used, in the production step S02, the following reaction occurs to produce LGPS material (Li １０ GeP ２ S １２ ) generates. 5Li ２ S+Ge+2P+7S→Li １０ GeP ２ S １２ 【0035】 This LGPS material (typical composition: Li １０ GeP ２ S １２ ) is LGPS (Li) belonging to the space group P42 / nmc １０ GeP ２ S １２It has a crystal structure of the type ), and when measured by X-ray diffraction using CuKα rays, the following peaks from equation (A1) to equation (A6) are detected as diffraction peaks, and the diffraction intensity of the peak of equation (A6) is I Ａ Let the diffraction intensity of the peak in equation (A7) be I Ｂ In that case, I Ａ I Ｂ Peak intensity ratio I Ｂ / I Ａ The percentage is less than 50%. 2θ = 17.38° ± 1.0° ... (A1) 2θ = 20.18° ± 1.0° ... (A2) 2θ = 20.44° ± 1.0° ... (A3) 2θ = 23.96° ± 1.0° ... (A4) 2θ = 26.96° ± 1.0° ... (A5) 2θ = 29.58° ± 1.0° ... (A6) 2θ = 27.33° ± 1.0° ... (A7) 【0036】 The peak in equation (A7) represents the impurity phase, and the peak in equation (A6) represents the target product. Therefore, the diffraction intensity of the peak in equation (A6) is I Ａ And the diffraction intensity of the peak in equation (A7) I Ｂ Peak intensity ratio I Ｂ / I Ａ The proportion is less than 50%, indicating that the proportion of the impurity phase has been sufficiently reduced. Furthermore, the peak intensity ratio I Ｂ / I Ａ It is preferably 10% or less, more preferably 1% or less, and most preferably 0%. 【0037】 Also, Li as a raw material ２ S, LiCl, P ２ S ５ When used, an Argyrodite material (typical composition: Li6PS5Cl) having an Argyrodite-type crystal structure is produced. 【0038】 Also, Li as a raw material ２ S, SnS ２When this is used, LMS material (Li4MS4) is produced. This LMS material has a crystal structure of space group Pnm, and when measured by X-ray diffraction using CuKα rays, the following diffraction peaks are detected: 2θ = 17.01 ± 0.50 ... (B1) 2θ = 18.50 ± 0.50 ... (B2) 2θ = 25.31 ± 0.50 ... (B3) 2θ = 26.23 ± 0.50 ... (B4) 【0039】 The method for manufacturing a sulfide solid electrolyte material according to this embodiment, which has the above configuration, comprises a raw material mixing step S01 in which raw materials containing each element constituting the sulfide solid electrolyte material are mixed to obtain a mixed raw material, and a production step S02 in which the mixed raw materials are heated to produce a sulfide solid electrolyte material. In the production step S02, the heating atmosphere is configured to contain sulfur gas with controlled partial pressure, so that evaporation of sulfur from the mixed raw materials and the produced sulfide solid electrolyte material can be suppressed during the heat treatment. Therefore, it is possible to manufacture a high-quality sulfide solid electrolyte material with sufficient ionic conductivity. One reason for this is that the suppression of sulfur evaporation suppresses the formation of impurity phases. In addition, it is thought that the suppression of sulfur evaporation contributes to the reduction of sulfur deficiency in the sulfide solid electrolyte material. Furthermore, since sulfur gas is used instead of toxic hydrogen sulfide, there is no need to install special pollution control equipment or safety equipment, and sulfide solid electrolyte materials can be manufactured inexpensively and efficiently. 【0040】 In the method for producing a sulfide solid electrolyte material according to this embodiment, if the partial pressure of sulfur gas in the production step S02 is set to 45% or more of the saturated vapor pressure of sulfur at the heating temperature, it is possible to sufficiently suppress the evaporation of sulfur from the mixed raw materials and the produced sulfide solid electrolyte material during the heat treatment, and it becomes possible to produce a high-quality sulfide solid electrolyte material with sufficient ionic conductivity. 【0041】Furthermore, in the method for producing a sulfide solid electrolyte material according to this embodiment, if the production step S02 is configured to heat until elemental sulfur evaporates, even if sulfur gas in the atmosphere condenses or solidifies and elemental sulfur is mixed in, or if elemental sulfur mixed as a raw material remains, the elemental sulfur is evaporated by subsequent heating, preventing the presence of elemental sulfur in the produced sulfide solid electrolyte material. This makes it possible to stably produce a high-quality sulfide solid electrolyte material with few impurities. 【0042】 Furthermore, in the method for producing sulfide solid electrolyte materials according to this embodiment, as described above, LGPS materials having an LGPS-type crystal structure, Argyrodite materials having an Argyrodite-type crystal structure, or LMS materials having Li, S, and at least one element from groups 13, 14, or 15 can be suitably produced. 【0043】 Although one embodiment of the present invention has been described above, the present invention is not limited thereto and can be modified as appropriate without departing from the technical spirit of the invention. 【0044】 The verification experiments conducted to confirm the effectiveness of the present invention will be described. 【0045】 In a glove box with an argon atmosphere and a dew point of -70°C or lower, powders of various raw materials shown in Tables 1 and 2 were prepared, and these raw materials were mixed in an agate mortar to obtain a mixed raw material. Next, the obtained mixed raw material was placed in an alumina crucible firing container and heated in an electric furnace at a rate of 3°C / min, held at 550°C for 6 hours, and then, after the firing container had cooled to room temperature by natural cooling, it was removed from the electric furnace to produce a sulfide solid electrolyte material. Here, during the heat treatment (during heating and holding at 550°C) and while the firing container was naturally cooling, the partial pressure of sulfur gas in the atmosphere was adjusted to the values ​​shown in Tables 1 and 2, as the ratio to the saturated vapor pressure of sulfur at the heating temperature at each time. 【0046】The obtained sulfide solid electrolyte material was taken out in a glove box with an argon atmosphere having a dew point temperature of -70°C or lower, pulverized in an agate mortar, and then the crystal structure was confirmed by X-ray diffraction measurement (XRD measurement) using CuKα radiation. Also, the ionic conductivity was measured as the performance of the sulfide solid electrolyte material. The methods for XRD measurement and ionic conductivity measurement are shown below. 【0047】 <XRD Measurement> For the XRD measurement, using an XRD device "D8 ADVANCE" manufactured by Bruker, θ-2θ measurement was performed in the range of 10° ≤ 2θ ≤ 55° under the conditions of a step width of 0.01° and an integration time of 1.2 seconds / step. The measurement sample was prepared in a glove box with an argon atmosphere, and the sulfide solid electrolyte material pulverized in an agate mortar was sealed in a sealable measurement cell, and powder X-ray diffraction measurement was performed while maintaining a state not exposed to the atmosphere. For the LGPS materials (Examples 1-5, 11-15, 21-25 of the present invention and Comparative Examples 1, 11, 21), the diffraction intensity I of the peak of formula (A6) Ａ and the diffraction intensity I of the peak of formula (A7) Ｂ of the ratio I Ｂ / I Ａ was calculated. The results are shown in Table 1. 2θ = 29.58° ± 1.0°... (A6) 2θ = 27.33° ± 1.0°... (A7) 【0048】 <Ionic Conductivity Measurement> After taking out the sulfide solid electrolyte material in a glove box in an argon atmosphere, it was pulverized in an agate mortar. 0.3 g was weighed and filled into an insulating tube (cylindrical with an inner diameter of 17 mm), and sealed in an ionic conductivity measurement cell. Then, using a measurement device "Potentiostat / Galvanostat SP-300" manufactured by Biologic, under the conditions of a measurement temperature of 25°C, a measurement frequency of 1 Hz to 1 MHz, and an applied pressure to the measurement cell of 360 MPa, the ionic conductivity (mS / cm) was measured by the alternating current impedance method. 【0049】 【0050】 【0051】In Invention Examples 1-5 of the present invention where the sulfur partial pressure in the atmosphere during the heat treatment in the production process is 3% or more, the ionic conductivity became 2 times or more higher than that in Comparative Example 1 where the sulfur partial pressure in the atmosphere during the heat treatment in the production process was 0%. Also, the peak intensity ratio I Ｂ / I Ａ was confirmed to be sufficiently smaller than that in Comparative Example 1, and the proportion of the impurity phase was reduced. When comparing Invention Examples 1-5 of the present invention, as the sulfur partial pressure increases, the ionic conductivity improves, and the peak intensity ratio I Ｂ / I Ａ was confirmed to become smaller. In particular, when comparing Invention Examples 3 and 4, the ionic conductivity has improved by 1.5 times or more, and when the partial pressure of sulfur gas is 45% or more of the saturated vapor pressure of sulfur at the heating temperature, the ionic conductivity improves more significantly. 【0052】 In Invention Examples 11-15 of the present invention where the sulfur partial pressure in the atmosphere during the heat treatment in the production process is 3% or more, the ionic conductivity became 8 times or more higher than that in Comparative Example 11 where the sulfur partial pressure in the atmosphere during the heat treatment in the production process was 0%. Also, the peak intensity ratio I Ｂ / I Ａ was confirmed to be sufficiently smaller than that in Comparative Example 1, and the proportion of the impurity phase was reduced. When comparing Invention Examples 11-15 of the present invention, as the sulfur partial pressure increases, the ionic conductivity improves, and the peak intensity ratio I Ｂ / I Ａ was confirmed to become smaller. 【0053】 In Invention Examples 21-25 of the present invention where the sulfur partial pressure in the atmosphere during the heat treatment in the production process is 3% or more, the ionic conductivity became 3 times or more higher than that in Comparative Example 21 where the sulfur partial pressure in the atmosphere during the heat treatment in the production process was 0%. Also, the peak intensity ratio I Ｂ / I Ａ was confirmed to be sufficiently smaller than that in Comparative Example 1, and the proportion of the impurity phase was reduced. When comparing Invention Examples 21-25 of the present invention, as the sulfur partial pressure increases, the ionic conductivity improves, and the peak intensity ratio I Ｂ / I ＡIt was confirmed that the value decreased. In particular, when comparing examples 23 and 24 of the present invention, the ionic conductivity improved by more than double, and the ionic conductivity improved even more significantly when the partial pressure of sulfur gas was 45% or more of the saturated vapor pressure of sulfur at the heating temperature. 【0054】 In Examples 31-35 of the present invention, where the partial pressure of sulfur in the atmosphere during the heat treatment of the production process was 3% or more, the ionic conductivity was more than three times higher compared to Comparative Example 31, where the partial pressure of sulfur in the atmosphere during the heat treatment of the production process was 0%. Furthermore, comparing Examples 31-35 of the present invention, it was confirmed that the ionic conductivity improved as the partial pressure of sulfur increased. In particular, comparing Examples 33 and 34 of the present invention, the ionic conductivity improved by more than 1.5 times, and the improvement in ionic conductivity was even greater when the partial pressure of sulfur gas was 45% or more of the saturated vapor pressure of sulfur at the heating temperature. 【0055】 In Examples 41-45 of the present invention, where the partial pressure of sulfur in the atmosphere during the heat treatment of the production process was 3% or more, the ionic conductivity was more than seven times higher than in Comparative Example 41, where the partial pressure of sulfur in the atmosphere during the heat treatment of the production process was 0%. Furthermore, comparing Examples 41-45 of the present invention, it was confirmed that the ionic conductivity improved as the partial pressure of sulfur increased. In particular, comparing Examples 43 and 44 of the present invention, the ionic conductivity improved by more than twofold, and the improvement in ionic conductivity was even greater when the partial pressure of sulfur gas was 45% or more of the saturated vapor pressure of sulfur at the heating temperature. 【0056】 In Example 51 of the present invention, where the partial pressure of sulfur in the atmosphere during the heat treatment of the production process was 3% or more, the ionic conductivity was more than three times higher compared to Comparative Example 51, where the partial pressure of sulfur in the atmosphere during the heat treatment of the production process was 0%. 【0057】 As described above, it has been confirmed that the present invention provides a method for producing a high-quality sulfide solid electrolyte material having sufficient ionic conductivity by suppressing the evaporation of sulfur during heat treatment without using hydrogen sulfide gas. 【0058】This invention provides a method for producing a high-quality sulfide solid electrolyte material with sufficient ionic conductivity by suppressing the evaporation of sulfur during heat treatment without using hydrogen sulfide gas.

Claims

1. A method for producing a sulfide solid electrolyte material, comprising: a raw material mixing step of mixing raw materials containing each element constituting the sulfide solid electrolyte material to obtain a mixed raw material; and a production step of heating the mixed raw material to produce the sulfide solid electrolyte material, wherein the production step is characterized in that the heating atmosphere contains sulfur gas with controlled partial pressure.

2. The method for producing a sulfide solid electrolyte material according to claim 1, characterized in that the partial pressure of the sulfur gas in the production step is 45% or more of the saturated vapor pressure of sulfur at the heating temperature.

3. A method for producing a sulfide solid electrolyte material according to claim 1 or 2, characterized in that the production step involves heating until elemental sulfur evaporates.

4. The sulfide solid electrolyte material contains an LGPS (Li １０ GeP ２ S １２ )-type crystal structure. When measured by X-ray diffraction measurement using CuKα radiation, the peaks of the following formulas (A1) to (A6) are detected as diffraction peaks. When the diffraction intensity of the peak of formula (A6) is I Ａ and the diffraction intensity of the peak of formula (A7) is I Ｂ , the peak intensity ratio (I Ａ / I Ｂ ) of I Ｂ with respect to I Ａ is less than 50%. The method for producing a sulfide solid electrolyte material according to claim 1 or claim 2, characterized in that: 2θ = 17.38° ± 1.0°... (A1) 2θ = 20.18° ± 1.0°... (A2) 2θ = 20.44° ± 1.0°... (A3) 2θ = 23.96° ± 1.0°... (A4) 2θ = 26.96° ± 1.0°... (A5) 2θ = 29.58° ± 1.0°... (A6) 2θ = 27.33° ± 1.0°... (A7) 5. A method for producing a sulfide solid electrolyte material according to claim 1 or 2, characterized in that the sulfide solid electrolyte material contains an argyrodite-type crystal structure.

6. The sulfide solid electrolyte material is Li ａ M ｂ S ｃ A method for producing a sulfide solid electrolyte material according to claim 1 or 2, characterized in that it is represented by, contains a crystal structure of space group Pnm, and when measured by X-ray diffraction using CuKα rays, the following peaks from equation (B1) to equation (B4) are detected as diffraction peaks: 2θ = 17.01 ± 0.50 ... (B1) 2θ = 18.50 ± 0.50 ... (B2) 2θ = 25.31 ± 0.50 ... (B3) 2θ = 26.23 ± 0.50 ... (B4) where M is at least one element from groups 13, 14, and 15, and a, b, and c are numbers greater than 0.

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