Method for manufacturing sulfide solid electrolyte materials

Abstract

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. [Solution] A method for producing a sulfide solid electrolyte material, comprising: a raw material mixing step S01 of mixing raw materials containing each element constituting the sulfide solid electrolyte material to obtain a mixed raw material; and a production step S02 of heating the mixed raw material to produce the sulfide solid electrolyte material, wherein the production step S02 is characterized in that the heating atmosphere contains sulfur gas with controlled partial pressure.

Description

【Technical Field】 【0001】 This invention relates to a method for producing a sulfide solid electrolyte material, which is suitably used, for example, in all-solid-state batteries and the like. 【Background Art】 【0002】 In recent years, as an electrolyte for lithium-ion secondary batteries, sulfide-based solid electrolyte materials with high ionic conductivity and higher safety than electrolytic solutions have attracted attention. As a method for producing a sulfide solid electrolyte material, a process of heat-treating a mixture of raw materials to synthesize a sulfide solid electrolyte by a solid-phase reaction is generally adopted. 【0003】 For example, Patent Documents 1 to 3 describe methods for producing a sulfide solid electrolyte by heat-treating a mixture of raw materials in an inert gas atmosphere such as nitrogen or argon, or under vacuum (sealing). Also, Patent Documents 4 and 5 describe a sulfide solid electrolyte obtained by heating a mixture of raw materials under the flow of hydrogen sulfide gas, or a method for producing the same. 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2003-208919 【Patent Document 2】 U.S. Patent No. 5527673 【Patent Document 3】 U.S. Patent No. 5888609 【Patent Document 4】 Japanese Patent Application Laid-Open No. 2016-24874 【Patent Document 5】 Japanese Patent Application Laid-Open No. 2018-67552 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 Incidentally, as disclosed in Patent Documents 1 to 3, when manufacturing a sulfide solid electrolyte material, in order to prevent oxidation of the raw materials and the produced sulfide solid electrolyte material, a method of heat-treating the mixture in an inert gas atmosphere such as nitrogen or argon, or under vacuum, has become common. However, sulfur deficiency may occur due to evaporation of sulfur, causing a deterioration in the quality of the solid electrolyte material, and it has sometimes been impossible to easily manufacture a sulfide solid electrolyte material of sufficient quality. 【0006】 Also, in Patent Documents 4 and 5, a method of heat-treating in a hydrogen sulfide gas atmosphere has been proposed as a method for manufacturing a sulfide solid electrolyte material. Hydrogen sulfide gas can suppress the generation of sulfur deficiency due to evaporation of sulfur, but it is toxic and flammable and requires decontamination equipment and safety equipment, which has been an obstacle to reducing manufacturing costs. 【0007】 This invention has been made in view of the above-described circumstances, and an object thereof is to provide a method for manufacturing a sulfide solid electrolyte material capable of manufacturing a high-quality sulfide solid electrolyte material having sufficient ionic conductivity by suppressing evaporation of sulfur components during heat treatment without using hydrogen sulfide gas. 【Means for Solving the Problems】 【0008】 In order to solve the above problems, the method for manufacturing a sulfide solid electrolyte material according to Aspect 1 of the present invention is a method for manufacturing a sulfide solid electrolyte material, including 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 generating step of heating the mixed raw material to generate the sulfide solid electrolyte material, wherein in the generating step, the heating atmosphere 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, which is a mixture of raw materials 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. Therefore, it is possible to suppress the evaporation of sulfur from the mixed raw material and the produced sulfide solid electrolyte material during the heat treatment. Thus, it is possible to produce a high-quality sulfide solid electrolyte material having sufficient ionic conductivity. Furthermore, because sulfur gas is used, there is no need to install special pollution control equipment or safety equipment as is required when using hydrogen sulfide gas, allowing for the inexpensive and efficient production of sulfide solid electrolyte materials. 【0010】 A method for producing a sulfide solid electrolyte material according to aspect 2 of the present invention is characterized in that, in the method for producing a sulfide solid electrolyte material according to aspect 1 of the present invention, 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. According to the method for producing a sulfide solid electrolyte material of embodiment 2 of the present invention, the partial pressure of the sulfur gas in the production step is set to 45% or more of the saturated vapor pressure of sulfur at the heating temperature, so that the evaporation of sulfur can be sufficiently suppressed, and it is possible to produce a high-quality sulfide solid electrolyte material having sufficient ionic conductivity. 【0011】 A method for producing a sulfide solid electrolyte material according to aspect 3 of the present invention is characterized in that, in the method for producing a sulfide solid electrolyte material according to aspect 1 or aspect 2 of the present invention, the production step is heated until elemental sulfur evaporates. According to the method for producing a sulfide solid electrolyte material of aspect 3 of the present invention, in the production step, elemental sulfur molecules may be mixed into or remain in the produced sulfide solid electrolyte material due to condensation or solidification of sulfur gas in the atmosphere or unreacted elemental sulfur in the mixed raw materials, potentially becoming 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 produce a high-purity, 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 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 is LGPS (Li 10 GeP2S 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. 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 of I B with respect to I B / I A 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】 The manufacturing method of the sulfide solid electrolyte material according to Embodiment 5 of the present invention is the manufacturing method of the sulfide solid electrolyte material according to any one of Embodiments 1 to 3 of the present invention, characterized by containing an Argyrodite type crystal structure. 【0014】 The manufacturing method of the sulfide solid electrolyte material according to Embodiment 6 of the present invention is 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 is represented by Li a M b S c and has a crystal structure of the space group Pnma. When measured by X-ray diffraction using CuKα rays, the peaks of the following formulas (B1) to (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) However, M is at least one element from groups 13, 14, and 15, and a, b, and c are numbers greater than 0. [Effects of the Invention] 【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. [Brief explanation of the drawing] 【0016】 [Figure 1] This is a flow chart of a method for producing a sulfide solid electrolyte material, which is an embodiment of the present invention. [Modes for carrying out the 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 GeP2S 12) and Argyrodite materials (Li) that have an Argyrodite-type crystal structure, such as the Ag8GeS6 mineral. 7-x PS 6-x Ha x Examples include LMS materials containing [Ha=Cl,Br,I, x=0.0~1.8], 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. In this embodiment, the method for producing a sulfide solid electrolyte material includes a raw material mixing step S01 and a production step S02, as shown in Figure 1. 【0021】 The raw material mixing step S01 and the production step S02 are preferably carried out in a gaseous 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 them out 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, making it possible to produce high-quality sulfide solid electrolyte materials. 【0022】 (Raw material mixing process S01) First, raw materials containing each element constituting the sulfide solid electrolyte material are mixed to obtain a mixed raw material. The raw materials may be simple sulfides, complex sulfides such as Li3PS4, 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 raw materials containing each element 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 material. Elemental sulfur refers to sulfur that contains no elements other than sulfur, excluding unavoidable impurities. In other descriptions of this embodiment, unless otherwise specified, each raw material may contain unavoidable impurities. Furthermore, 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, each raw material and elemental sulfur are preferably 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, if the LGPS material contains Li, Ge, P, and S, then Li2S, GeS2, P2S5 may be mixed, or Li2S, Ge, P, S may be mixed, or Li4GeS4, Li3PS4 may be mixed, or Li3PS4, Ge, S may be mixed. If the Argyrodite material contains Li, P, S, and Cl, then Li2S, LiCl, P2S5 may be mixed, or Li2S, LiCl, P, S may be mixed. If the LMS material contains Li, Sn, and S, then Li2S, SnS2 may be mixed, or Li2S, P, 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. 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, or ball mills may be performed instead of a general mixing process. However, from the standpoint of economic rationality and mass production, general mixing methods using the aforementioned existing methods are more preferable. 【0025】 (Generation process S02) Next, the resulting mixed raw materials are placed in a firing container such as a crucible or saggar, and heated at a temperature T1 to react with the mixed raw materials and produce a sulfide solid electrolyte material. The materials used for the inner walls of the furnace and the firing container are preferably materials that are resistant to corrosion by sulfidation, as they come into contact with sulfur gas or elemental sulfur and sulfides in the heating atmosphere. 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 process S02 contains sulfur gas with controlled partial pressure. That is, sulfur gas is included in the heating atmosphere when the firing container into which the mixed raw materials are introduced is heated from room temperature, and the partial pressure of this sulfur gas is controlled. Furthermore, it is preferable that the partial pressure of sulfur gas in the atmosphere be 45% or more of the saturated vapor pressure of sulfur at the heating temperature at that time, both while the heating temperature is rising from room temperature to temperature T1 and while the heating temperature is maintained at temperature T1. By keeping the partial pressure of sulfur gas in the atmosphere within this range, the evaporation of sulfur from the mixed raw materials and the generated sulfide solid electrolyte material can be suppressed before the formation of the sulfide solid electrolyte material (at a temperature below the formation temperature during heating), during formation, and during crystal growth, thereby sufficiently suppressing 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. As a result, a sulfide solid electrolyte material with sufficient ionic conductivity can be easily manufactured. 【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 elemental sulfur identical to 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. Since sulfur gas at temperatures above 150°C usually contains multiple allotropes such as S3, S5, S6, S7, and S8, this method makes it possible to introduce sulfur gas into the heating atmosphere whose allotrope ratio is the same as the sulfur gas that can be generated 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 less, more preferably 650°C or less, and even more preferably 600°C or less. 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 solid electrolyte formation reaction, making it possible to easily produce 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 all the production reactions and crystal growth of the sulfide solid electrolyte material are complete and the stoichiometric amount of sulfur elements has 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 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 the remaining elemental sulfur to evaporate, or, if not (if the heat treatment conditions at temperature T1 are insufficient for all the remaining 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 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) necessary to completely evaporate elemental sulfur vary depending on factors such as 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 added to the calcination vessel, and the temperature T1. 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), is one possible solution. 【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 it 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, when Li2S, GeS2, and P2S5 are used as raw materials, in the production step S02, the following reaction occurs to produce LGPS material (Li 10 GeP2S 12 ) generates. 5Li2S + GeS2 + P2S5 → Li 10 GeP2S 12 Furthermore, when Li2S, Ge, P, S are used as raw materials, in the production step S02, the following reaction occurs to produce LGPS material (Li 10 GeP2S 12 ) generates. 5Li2S+Ge+2P+7S→Li 10 GeP2S 12 【0035】 This LGPS material (typical composition: Li 10 GeP2S 12 ) is LGPS (Li) belonging to the space group P42 / nmc. 10 GeP2S 12 It has a crystal structure of 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 from 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 will be 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) is from the impurity phase, and the peak in equation (A6) is from 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 said to be less than 50%, indicating that the proportion of the impurity phase has been sufficiently reduced. Note that the peak intensity ratio I B / I AIt is preferably 10% or less, more preferably 1% or less, and most preferably 0. 【0037】 Furthermore, when Li2S, LiCl, and P2S5 are used as raw materials, an Argyrodite material (typical composition: Li6PS5Cl) with an Argyrodite-type crystal structure is produced. 【0038】 Furthermore, when Li2S and SnS2 are used as raw materials, LMS material (Li4MS4) is produced. This LMS material has a crystal structure of space group Pnma, and when measured by X-ray diffraction using CuKα rays, the diffraction peaks shown in equations (B1) to (B4) below 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 producing 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 the evaporation of sulfur from the mixed raw materials and the produced sulfide solid electrolyte material during the heat treatment can be suppressed. Therefore, it is possible to produce 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 also thought that the suppression of sulfur evaporation contributes to the reduction of sulfur deficiency in the sulfide solid electrolyte material. Furthermore, because it uses sulfur gas instead of toxic hydrogen sulfide, there is no need to install special pollution control or safety equipment, allowing for the inexpensive and efficient production of sulfide solid electrolyte materials. 【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 can be evaporated by subsequent heating, thereby 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. [Examples] 【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 having a dew point temperature 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 a firing container of an alumina crucible and heated in an electric furnace at a rate of 3°C / min. After holding at 550°C for 6 hours and then allowing natural cooling until the firing container reached room temperature, the firing container was taken out of the electric furnace to produce a sulfide solid electrolyte material. Here, the partial pressure of sulfur gas in the atmosphere during the heat treatment (during the heating temperature increase and during the holding at 550°C) and while the firing container was being naturally cooled was adjusted to the values shown in Tables 1 and 2 as the ratio to the saturated vapor pressure of sulfur at the respective heating temperatures at that 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 rays. Also, the ionic conductivity was measured as the performance of the sulfide solid electrolyte material. The methods of XRD measurement and ionic conductivity measurement are shown below. 【0047】 <XRD Measurement> For 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. In addition, 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 The ratio I of 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> The sulfide solid electrolyte material was removed in a glove box under an argon atmosphere and then ground in an agate mortar. 0.3 g was weighed and packed into an insulating tube (cylindrical with an inner diameter of 17 mm), and sealed inside an ionic conductivity measurement cell. Subsequently, using a Biologic SP-300 potentiometer / galvanostat, the ionic conductivity (mS / cm) was measured by AC impedance method under the following conditions: measurement temperature of 25°C, measurement frequency of 1Hz to 1MHz, and applied pressure of 360MPa to the measurement cell. 【0049】 [Table 1] 【0050】 [Table 2] 【0051】 In Examples 1-5 of the present invention, where the sulfur partial pressure in the atmosphere during the heat treatment of the production process was 3% or more, the ionic conductivity was more than twice as high as in Comparative Example 1, where the sulfur partial pressure in the atmosphere during the heat treatment of the production process was 0%. Furthermore, the peak intensity ratio I B / I A It was confirmed that the amount was significantly smaller than in Comparative Example 1, indicating a reduction in the proportion of the impurity phase. Furthermore, comparing Examples 1-5 of the present invention, the ionic conductivity improves as the sulfur partial pressure increases, and the peak intensity ratio I B / I A It was confirmed that the value decreased. In particular, when comparing Examples 3 and 4 of the present invention, the ionic conductivity improved by more than 1.5 times, 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. 【0052】 In Examples 11-15 of the present invention, where the sulfur partial pressure in the atmosphere during the heat treatment of the production process was 3% or more, the ionic conductivity was more than 8 times higher compared to Comparative Example 11, where the sulfur partial pressure in the atmosphere during the heat treatment of the production process was 0%. Furthermore, the peak intensity ratio I B / I A It was confirmed that the amount was significantly smaller than in Comparative Example 1, indicating a reduction in the proportion of the impurity phase. Furthermore, comparing Examples 11-15 of the present invention, the ionic conductivity improves as the sulfur partial pressure increases, and the peak intensity ratio I B / I A It was confirmed that the size decreased. 【0053】 In Examples 21-25 of the present invention, where the sulfur partial pressure 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 21, where the sulfur partial pressure in the atmosphere during the heat treatment of the production process was 0%. Furthermore, the peak intensity ratio I B / I A It was confirmed that the amount was significantly smaller than in Comparative Example 1, indicating a reduction in the proportion of the impurity phase. Furthermore, comparing Examples 21-25 of the present invention, the ionic conductivity improves as the sulfur partial pressure increases, and the peak intensity ratio I B / I A It 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 sulfur partial pressure 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 sulfur partial pressure in the atmosphere during the heat treatment of the production process was 0%. Furthermore, a comparison of Examples 31-35 of the present invention revealed that ionic conductivity improved as the partial pressure of sulfur increased. In particular, a comparison of Examples 33 and 34 showed that ionic conductivity improved by more than 1.5 times, and the improvement 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 sulfur partial pressure in the atmosphere during the heat treatment of the production process was 3% or more, the ionic conductivity was more than seven times higher compared to Comparative Example 41, where the sulfur partial pressure in the atmosphere during the heat treatment of the production process was 0%. Furthermore, a comparison of Examples 41-45 of the present invention revealed that ionic conductivity improved as the sulfur partial pressure increased. In particular, a comparison of Examples 43 and 44 showed that the ionic conductivity more than doubled, and the improvement was even greater when the partial pressure of the sulfur gas was 45% or higher 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.

Claims

[Claim 1] A method for producing a sulfide solid electrolyte material, The process includes 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. A method for producing a sulfide solid electrolyte material, characterized in that the heating atmosphere in the production step contains sulfur gas with controlled partial pressure. [Claim 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. [Claim 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. [Claim 4] The sulfide solid electrolyte material is in space group P4 ２ LGPS (Li) belonging to / nmc １０ GeP ２ S １２ It contains 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. Let the diffraction intensity of the peak of formula (A6) be I Ａ and the diffraction intensity of the peak of formula (A7) be I Ｂ . When I Ａ is I Ｂ , the peak intensity ratio of I Ｂ to I Ａ (I Ｂ / 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) [Claim 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. [Claim 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 crystalline structure of space group Pnm, and when measured by X-ray diffraction using CuKα rays, the following peaks from formula (B1) to formula (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) However, 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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