Method for producing sulfide-based solid electrolyte

Abstract

Provided is a method for producing a sulfide-based solid electrolyte, the method having: a raw material preparation step for preparing an electrolyte raw material containing an element other than sulfur among elements constituting the sulfide-based solid electrolyte, and elemental sulfur and forming a raw material aggregate; and a synthesis step for heating the raw material aggregate to synthesize the sulfide-based solid electrolyte, wherein in the raw material preparation step, a molar ratio of the elemental sulfur to a lithium element in the raw material aggregate is set to be 1.5 to 6.5.

Description

Method for producing sulfide-based solid electrolyte

[0001] This invention relates to a method for producing a sulfide-based solid electrolyte suitable for use in, for example, all-solid-state batteries. This application claims priority based on Japanese Patent Application No. 2024-072856, filed on April 26, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, sulfide-based solid electrolytes have attracted attention as electrolytes for lithium-ion secondary batteries because they have high ionic conductivity and are safer than liquid electrolytes. A widely used method for producing sulfide-based solid electrolytes involves first mechanically milling a mixture of raw materials to vitrify or amorphousize them, followed by heat treatment and a solid-state reaction to synthesize the sulfide-based solid electrolyte.

[0003] For example, Patent Document 1 describes a process for producing sulfide glass and glass ceramics, which are types of sulfide-based solid electrolytes, in which a mixture of metallic lithium, elemental sulfur, and elemental phosphorus is vitrified by mechanical milling and then heat-treated. Patent Documents 2 and 3 also describe a process for producing a sulfide-based solid electrolyte with an LGPS crystal structure in which a mixture of various sulfides is amorphized by mechanical milling, followed by heat treatment and crystallization by a solid-phase reaction. That is, a method in which a mixture of electrolyte raw materials is subjected to mechanical milling to diffuse and mix the contained elements and homogenize the chemical composition of the entire mixture before heat treatment has become a common method for producing a solid electrolyte with sufficient ionic conductivity.

[0004] Furthermore, Patent Document 4 discloses a method for producing a sulfide solid electrolyte, in which elemental sulfur or a sulfur compound is mixed with a raw material and the mixture is heat-treated. It is described that this production method can achieve ionic conductivity equivalent to that achieved when hydrogen sulfide gas is passed through the electrolyte, even without using hydrogen sulfide gas during the heat treatment.

[0005] Japanese Patent Publication No. 2003-208919 (A) Japanese Patent No. 5527673 (B) Japanese Patent No. 5888609 (B) Japanese Patent Publication No. 2020-027715 (A)

[0006] However, in general methods for producing sulfide-based solid electrolytes, mechanical milling is performed as described in Patent Documents 1 to 3. However, because mechanical milling requires a large amount of energy and a long time, it is not possible to efficiently produce sulfide-based solid electrolytes, and it is difficult to scale up the equipment. Furthermore, because the sulfide-based solid electrolyte is synthesized by a solid-state reaction, the chemical composition of the synthesized sulfide-based solid electrolyte becomes non-uniform, and there is a risk that the ionic conductivity of the sulfide-based solid electrolyte will not be sufficiently improved.

[0007] In Patent Document 4, a sulfide-based solid electrolyte is produced by mixing elemental sulfur or a sulfur compound with raw materials without performing mechanical milling, and then heat-treating the mixture. However, the raw materials or the raw materials and the elemental sulfur or the sulfur compound are not mixed uniformly, and the chemical composition of the synthesized sulfide-based solid electrolyte becomes non-uniform, which may result in an insufficient improvement in ionic conductivity of the sulfide-based solid electrolyte.

[0008] In all-solid-state batteries using a sulfide-based solid electrolyte, if the ionic conductivity of the sulfide-based solid electrolyte is low, the resistance increases. The sulfide-based solid electrolytes produced by the production methods described in Patent Documents 1 to 4 had insufficient ionic conductivity and could not be used as sulfide-based solid electrolytes for high-power batteries.

[0009] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method for producing a sulfide-based solid electrolyte that can efficiently produce a sulfide-based solid electrolyte that has excellent ionic conductivity and is particularly suitable for high-power solid-state batteries.

[0010] In order to solve the above problems, the present inventors have conducted extensive research and have found that the composition of the sulfide-based solid electrolyte synthesized by subjecting raw materials to a liquid-phase reaction can be made uniform, thereby significantly improving the combined ionic conductivity of the sulfide-based solid electrolyte.

[0011] The present invention has been made based on the above-mentioned findings, and a method for producing a sulfide-based solid electrolyte according to Aspect 1 of the present invention is a method for producing a sulfide-based solid electrolyte, comprising: a raw material preparation step of preparing an electrolyte raw material containing elements other than sulfur from among the elements constituting the sulfide-based solid electrolyte, and elemental sulfur, and forming a raw material assembly; and a synthesis step of heating the raw material assembly to synthesize the sulfide-based solid electrolyte, wherein in the raw material preparation step, a molar ratio of elemental sulfur to elemental lithium in the raw material assembly is set to 1.5 or more and 6.5 or less.

[0012] According to the method for producing a sulfide-based solid electrolyte of aspect 1 of the present invention, in the raw material preparation step, in which electrolyte raw materials containing elements other than sulfur and elemental sulfur are prepared to form a raw material assembly, the molar ratio of elemental sulfur to elemental lithium in the raw material assembly is set to 1.5 or more and 6.5 or less. Therefore, in the synthesis step, in which the raw material assembly is heated to synthesize the sulfide-based solid electrolyte, the elemental sulfur melts to ensure a sufficient amount of liquid phase, and the reaction between the electrolyte raw materials and elemental sulfur proceeds through this liquid phase of elemental sulfur. This results in a uniform composition of the synthesized sulfide-based solid electrolyte, significantly improving the ionic conductivity of the sulfide-based solid electrolyte. Furthermore, this method eliminates the need for processes that require large amounts of energy and long times, such as mechanical milling, allowing for efficient production of the sulfide-based solid electrolyte.

[0013] A method for producing a sulfide-based solid electrolyte according to Aspect 2 of the present invention is the method for producing a sulfide-based solid electrolyte according to Aspect 1 of the present invention, characterized in that in the raw material preparation step, the molar ratio of elemental sulfur to elemental lithium in the raw material assembly is 2.0 or more. According to the method for producing a sulfide-based solid electrolyte according to Aspect 2 of the present invention, since the molar ratio of elemental sulfur to elemental lithium in the raw material assembly is 2.0 or more, a more sufficient amount of liquid phase elemental sulfur is secured in the synthesis step, the composition of the synthesized sulfide-based solid electrolyte is further uniform, and the ionic conductivity of the sulfide-based solid electrolyte can be further improved.

[0014] A method for producing a sulfide-based solid electrolyte according to Aspect 3 of the present invention is the method for producing a sulfide-based solid electrolyte according to Aspect 1 or Aspect 2 of the present invention, characterized in that in the synthesis step, the raw material assembly is heated at a heating temperature of 400° C. or higher and 1000° C. or lower. According to the method for producing a sulfide-based solid electrolyte according to Aspect 3 of the present invention, the raw material assembly is heated at a heating temperature of 400° C. or higher and 1000° C. or lower in the synthesis step, which makes it possible to reliably generate a liquid phase of elemental sulfur and to promote the reaction between the electrolyte raw materials and elemental sulfur, thereby efficiently producing a sulfide-based solid electrolyte having a uniform composition and excellent ionic conductivity.

[0015] A method for producing a sulfide-based solid electrolyte according to Aspect 4 of the present invention is characterized in that, in the method for producing a sulfide-based solid electrolyte according to any one of Aspects 1 to 3 of the present invention, diffraction peaks due to crystalline substances contained in the electrolyte raw materials and elemental sulfur are detected when the raw material assembly is subjected to X-ray diffraction analysis. According to the method for producing a sulfide-based solid electrolyte according to Aspect 3 of the present invention, since diffraction peaks due to crystalline substances contained in the electrolyte raw materials and elemental sulfur are detected, a large amount of energy is not used when forming the raw material assembly, and a sulfide-based solid electrolyte can be produced more efficiently.

[0016] A method for producing a sulfide-based solid electrolyte according to aspect 5 of the present invention is the method for producing a sulfide-based solid electrolyte according to any one of aspects 1 to 4 of the present invention, wherein the sulfide-based solid electrolyte is a sulfide-based solid electrolyte having a space group P4 ２ / nmc belonging LGPS (Li １０ GeP ２ S １２The present invention is characterized in that the crystal structure has a crystalline structure of the formula (A1) type, and when measured by X-ray diffraction measurement using CuKα radiation, peaks of the following formulas (A1) to (A6) are detected as diffraction peaks, and when the diffraction intensity of the peak of formula (A6) is defined as IA and the diffraction intensity of the peak of formula (A7) is defined as IB, the peak intensity ratio of IB to IA 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)

[0017] According to the method for producing a sulfide-based solid electrolyte of the fifth aspect of the present invention, LGPS (Li １０ GeP ２ S １２ ) type crystal structure and can efficiently produce a sulfide-based solid electrolyte with excellent ionic conductivity.

[0018] A method for producing a sulfide-based solid electrolyte according to Aspect 6 of the present invention is characterized in that, in the method for producing a sulfide-based solid electrolyte according to any one of Aspects 1 to 4 of the present invention, the sulfide-based solid electrolyte contains an Argyrodite-type crystal structure. According to the method for producing a sulfide-based solid electrolyte according to Aspect 6 of the present invention, a sulfide-based solid electrolyte having an Argyrodite-type crystal structure and excellent ionic conductivity can be efficiently produced.

[0019] A method for producing a sulfide-based solid electrolyte according to Aspect 7 of the present invention is the method for producing a sulfide-based solid electrolyte according to any one of Aspects 1 to 4 of the present invention, wherein the sulfide-based solid electrolyte is Li ａ M ｂ S ｃand has a crystal structure of space group Pnma, and is characterized in that, when measured by X-ray diffraction using CuKα radiation, the following peaks of 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) where M is at least one element of Group 13, Group 14, and Group 15, and a, b, and c are numbers greater than 0.

[0020] According to the method for producing a sulfide-based solid electrolyte of the seventh aspect of the present invention, Li ａ M ｂ S ｃ and has a crystal structure of the space group Pnma, and a sulfide-based solid electrolyte with excellent ionic conductivity can be efficiently produced.

[0021] According to the present invention, it is possible to provide a method for producing a sulfide-based solid electrolyte that is excellent in ionic conductivity and is particularly suitable for high-power solid-state batteries, and that can efficiently produce such a sulfide-based solid electrolyte.

[0022] FIG. 1 is a flow chart showing an example of a method for producing a sulfide-based solid electrolyte according to an embodiment of the present invention.

[0023] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the following embodiments are specifically described to provide a better understanding of the gist of the invention, and do not limit the present invention unless otherwise specified.

[0024] The method for producing a sulfide solid electrolyte according to this embodiment is for producing a sulfide solid electrolyte to be used as a solid electrolyte constituting, for example, an all-solid-state battery. Sulfide solid electrolytes have relatively high ionic conductivity, are non-flammable, and are highly safe, and therefore are applied to electric vehicles and the like. Here, in order to construct a high-power solid-state battery, a sulfide-based solid electrolyte with even better ionic conductivity is required.

[0025] In addition, the sulfide-based solid electrolyte material produced in this embodiment is, for example, LGPS (Li １０ GeP２ S １２ Examples of such materials include an LGPS material having a crystalline structure of Argyrodite type, an Argyrodite material having a crystalline structure of Argyrodite type, and an LMS material having Li, S, and at least one element of Groups 13, 14, and 15.

[0026] Here, the method for producing a sulfide-based solid electrolyte according to this embodiment will be described with reference to the flow diagram of Fig. 1. As shown in Fig. 1, the method for producing a sulfide-based solid electrolyte according to this embodiment includes a raw material preparation step S01 in which electrolyte raw materials containing elements other than sulfur among the elements constituting the sulfide-based solid electrolyte and elemental sulfur are prepared to form a raw material assembly, and a synthesis step S02 in which the raw material assembly is heated to produce the sulfide-based solid electrolyte.

[0027] (Raw Material Preparation Step S01) First, an electrolyte raw material containing elements other than sulfur among the elements constituting the sulfide-based solid electrolyte and elemental sulfur are prepared to form a raw material assembly. That is, the raw material assembly is made to reliably contain elemental sulfur. The elemental sulfur may be α-sulfur (orthorhombic sulfur), β-sulfur (monoclinic sulfur), γ-sulfur (monoclinic sulfur), or any other sulfur isotope.

[0028] The electrolyte raw material may be a non-sulfide that does not contain sulfur (including one that contains sulfur as an unavoidable impurity), or a sulfide that contains sulfur, but is not elemental sulfur. More specifically, the electrolyte raw material is preferably at least one of an element other than sulfur that constitutes the sulfide-based solid electrolyte member, a compound of elements other than sulfur that constitute the sulfide-based solid electrolyte member, and a sulfide of an element other than sulfur that constitutes the sulfide-based solid electrolyte member. In this embodiment, the electrolyte raw material preferably does not contain any elements other than those that constitute the solid electrolyte member, except for unavoidable impurities.

[0029] For example, in the case of an LGPS material containing Li, Ge, P, and S, the raw material assembly is composed of the electrolyte raw material (Li ２ It may be a mixture of elemental sulfur (S, Ge, P (red phosphorus)) and elemental sulfur (S), or an electrolyte raw material (Li ３ P Ｓ4, G) and elemental sulfur S. If the argyrodite material contains Li, P, S, and Cl, the raw material assembly can be a mixture of the electrolyte raw material (Li, ２ The raw material assembly may be a mixture of the electrolyte raw material (LiS, P (red phosphorus)) and elemental sulfur S, as long as the LMS material contains Li, Sn, and S. The raw material assembly may be a mixture of the electrolyte raw material (LiS, P (red phosphorus)) and elemental sulfur S. Although not particularly limited, the Li content in the electrolyte raw material may be 8% by mass to 12% by mass, 11% by mass to 15% by mass, or 14% by mass to 18% by mass.

[0030] In the method for producing a sulfide-based solid electrolyte according to the present embodiment, the molar ratio of elemental sulfur to elemental lithium in the raw material assembly is set to 1.5 or more and 6.5 or less. That is, the number of moles M of elemental lithium in the raw material assembly is Ｌｉ and the number of moles of elemental sulfur M Ｓ Relative to M Ｓ / M Ｌｉ is set to 1.5 or more and 6.5 or less, so that the amount of elemental sulfur contained exceeds the stoichiometric ratio of the sulfide-based solid electrolyte to be synthesized. The molar ratio of elemental sulfur to elemental lithium in the raw material assembly is more preferably 2.0 or more, and even more preferably 2.2 or more. On the other hand, the upper limit of the molar ratio of elemental sulfur to elemental lithium in the raw material assembly is more preferably 5.0 or less, and even more preferably 4.6 or less.

[0031] Furthermore, in the raw material preparation step S01, there are no particular limitations on the method as long as it can uniformly mix the raw materials, and examples of various existing methods include a general mixer, blender, ball mill, bead mill, vibration mill, V-type mixer, etc. Furthermore, instead of a general mixing process, mixing may be performed using a planetary ball mill, vibration mill, ball mill, etc.

[0032] In this embodiment, the raw material aggregate is preferably mixed so that diffraction peaks due to the crystalline substances contained in the raw material for the electrolyte and the elemental sulfur are detected when the raw material aggregate is subjected to X-ray diffraction measurement. That is, it is preferable not to apply a method that applies a large amount of energy, such as mechanical milling, so that the crystalline substances contained in the raw material for the electrolyte and the elemental sulfur are not altered during mixing.

[0033] The mixing process in the raw material preparation step S01 is preferably carried out in an inert atmosphere such as nitrogen, argon, or other rare gases. Additionally, the atmospheric gas used preferably does not contain oxygen, and the oxygen concentration in the atmospheric gas is preferably 50 mass ppm or less, more preferably 30 mass ppm or less, and even more preferably 10 mass ppm or less. The dew point is preferably −50° C. or less, more preferably −60° C. or less, and even more preferably −70° C. or less.

[0034] (Synthesis Step S02) In this synthesis step S02, the raw material assembly is heated to produce a sulfide-based solid electrolyte material. At this time, elemental sulfur becomes a liquid phase. Here, in the method for producing a sulfide-based solid electrolyte material according to this embodiment, as described above, the molar ratio of elemental sulfur to elemental lithium in the raw material assembly is set to 1.5 or more, so that a sufficient liquid phase of elemental sulfur is produced. As a result, the reaction of the other electrolyte raw materials proceeds in the liquid phase of elemental sulfur, making it possible to synthesize a sulfide-based solid electrolyte material with a uniform composition. Meanwhile, the molar ratio of elemental sulfur to elemental lithium in the raw material assembly is set to 6.5 or less, so that excess sulfur can be prevented from remaining and being mixed in as an impurity, making it possible to synthesize a sulfide-based solid electrolyte material with high purity and high ionic conductivity.

[0035] In particular, in the synthesis step S02, lithium sulfide (Li ２ S) undergoes a polysulfide reaction with elemental sulfur to form Li ２ S ４It is believed that the progress of the synthesis reaction of the sulfide-based solid electrolyte is accelerated starting from the process in which the sulfide-based solid electrolyte is transformed into the elemental sulfur and melted. In the present embodiment, the molar ratio of elemental sulfur to lithium element in the raw material assembly is set to 1.5 or more, and therefore the above-mentioned polysulfuration reaction is accelerated, and the sulfide-based solid electrolyte can be efficiently synthesized.

[0036] The heating temperature in the synthesis step S02 is preferably 400° C. or higher, more preferably 450° C. or higher, and even more preferably 500° C. or higher. On the other hand, the heating temperature in the synthesis step S02 is preferably 1000° C. or lower, and more preferably 650° C. or lower.

[0037] The holding time at the heating temperature is preferably 0.5 hours or more, more preferably 1.0 hour or more, while the holding time at the heating temperature is preferably 72 hours or less, more preferably 24 hours or less, and even more preferably 12 hours or less.

[0038] The heat treatment in the synthesis step S02 is preferably carried out in an inert atmosphere such as nitrogen, argon, or other rare gases. In addition, the atmospheric gas used preferably does not contain oxygen, and the oxygen concentration in the atmospheric gas is preferably 50 mass ppm or less, more preferably 30 mass ppm or less, and even more preferably 10 mass ppm or less. In addition, the dew point is preferably -50°C or less, more preferably -60°C or less, and even more preferably -70°C or less.

[0039] The average rate of temperature rise from room temperature (25°C) to the heating temperature is preferably 0.1°C / min or more, more preferably 1°C / min or more, and even more preferably 5°C / min. On the other hand, the average rate of temperature rise from room temperature (25°C) to the heating temperature is preferably 20°C / min or less, more preferably 15°C / min or less, and even more preferably 10°C / min or less.

[0040] The average cooling rate from the heating temperature to room temperature (25°C) is preferably 0.1°C / min or more, more preferably 0.5°C / min or more, and even more preferably 2°C / min. On the other hand, the average cooling rate from the heating temperature to room temperature (25°C) is preferably 50°C / min or less, more preferably 40°C / min or less, and even more preferably 30°C / min or less.

[0041] The firing vessel into which the raw material assembly is charged during the heat treatment preferably has an inner wall made of a material that is not easily reactive with the liquid phase of elemental sulfur, in other words, a material that is not easily corroded by sulfurization. Specific examples of such materials include alumina, zirconia, carbon, and silicon.

[0042] Through the above steps, a sulfide-based solid electrolyte material is produced.

[0043] Here, the electrolyte raw material (Li ２ When a raw material assembly containing a mixture of elemental sulfur (S, Ge, P (red phosphorus)) and elemental sulfur (S) is used, the synthesis step S02 produces an LGPS material (Li １０ GeP ２ S １２ ) is produced. ２ S+Ge+2P+7S→Li １０ GeP ２ S １２

[0044] This LGPS material (Li １０ GeP ２ S １２ ) is in the space group P4 ２ / nmc belonging LGPS (Li １０ GeP ２ S １２When measured by X-ray diffraction using CuKα radiation, the diffraction peaks of the following formulas (A1) to (A6) are detected, and when the diffraction intensity of the peak of formula (A6) is defined as IA and the diffraction intensity of the peak of formula (A7) is defined as IB, the peak intensity ratio of IB to IA 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)

[0045] Since the peak of formula (A7) is due to an impurity and the peak of formula (A6) is due to the target substance, the peak intensity ratio IB / IA of the diffraction intensity IA of the peak of formula (A6) to the diffraction intensity IB of the peak of formula (A7) is less than 50%, and the proportion of the impurity phase is sufficiently reduced. Note that the peak intensity ratio IB / IA is preferably 10% or less, particularly preferably 1% or less, and most preferably 0.

[0046] Raw material for electrolyte (Li ２ S, LiCl, P ２ S ５ When a raw material aggregate obtained by mixing a raw material aggregate obtained by mixing elemental sulfur S with Argyrodite-type crystal structure (Li ５．５ P.S. ４．５ C ｌ１．５ ) is generated.

[0047] Raw material for electrolyte (Li ２ When a raw material aggregate containing a mixture of elemental sulfur (S, P (red phosphorus)) and elemental sulfur (S) is used, the LMS material (Li ４ MS ４This LMS material has a crystal structure of space group Pnma, and when measured by X-ray diffraction using CuKα radiation, 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)

[0048] According to the method for producing a sulfide solid electrolyte material of this embodiment configured as described above, in the raw material preparation step S01, the molar ratio of elemental sulfur to lithium in the raw material assembly is set to 1.5 or more and 6.5 or less. Therefore, in the synthesis step S02, the elemental sulfur is melted to ensure a sufficient amount of liquid phase, and the reaction between the electrolyte raw material and elemental sulfur proceeds through this liquid phase of elemental sulfur. This results in a uniform composition of the synthesized sulfide-based solid electrolyte, significantly improving the ionic conductivity of the sulfide-based solid electrolyte. Furthermore, this method eliminates the need for processes that require large amounts of energy and a long time, such as mechanical milling, allowing for efficient production of a sulfide-based solid electrolyte.

[0049] In the method for producing a sulfide solid electrolyte material according to the present embodiment, when the molar ratio of elemental sulfur to elemental lithium in the raw material aggregate is set to 2.0 or more, a more sufficient amount of liquid phase elemental sulfur is secured in the synthesis step S02, the composition of the synthesized sulfide-based solid electrolyte is further uniform, and the ionic conductivity of the sulfide-based solid electrolyte can be further improved.

[0050] In the method for producing a sulfide solid electrolyte material according to the present embodiment, when the heating temperature of the raw material assembly in the synthesis step S02 is set within a range of 400°C or higher and 1000°C or lower, a liquid phase of elemental sulfur can be reliably produced, and the reaction between the electrolyte raw materials and elemental sulfur can be advanced, thereby efficiently producing a sulfide-based solid electrolyte having a uniform composition and excellent ionic conductivity.

[0051] In the method for producing a sulfide solid electrolyte material according to the present embodiment, if a configuration is adopted in which diffraction peaks resulting from crystalline substances contained in the electrolyte raw material and elemental sulfur are detected when the raw material assembly is subjected to X-ray diffraction measurement, a large amount of energy is not used when forming the raw material assembly in the raw material preparation step S01, and a sulfide-based solid electrolyte can be produced more efficiently.

[0052] In the method for producing a sulfide solid electrolyte material according to the present embodiment, the electrolyte raw material (Li ２ When a raw material assembly containing a mixture of elemental sulfur (S, Ge, P (red phosphorus)) and elemental sulfur (S) is used, as described above, LGPS (Li １０ GeP ２ S １２ ) type crystal structure and can efficiently produce a sulfide-based solid electrolyte with excellent ionic conductivity.

[0053] In the method for producing a sulfide solid electrolyte material according to the present embodiment, the electrolyte raw material (Li ２ S, LiCl, P ２ S ５ When a raw material assembly in which sulfur dioxide is mixed with elemental sulfur S is used, a sulfide-based solid electrolyte having an argyrodite-type crystal structure and excellent ionic conductivity can be efficiently produced.

[0054] In the method for producing a sulfide solid electrolyte material according to the present embodiment, the electrolyte raw material (Li ２ When a raw material assembly containing a mixture of sulfur atoms (S, P (red phosphorus)) and elemental sulfur S is used, a sulfide-based solid electrolyte having a crystal structure represented by LiaMbSc and a space group Pnma and excellent ionic conductivity can be efficiently produced.

[0055] Although one embodiment of the present invention has been described above, the present invention is not limited to this and can be modified as appropriate within the scope of the technical idea of ​​the invention.

[0056] A confirmation experiment conducted to confirm the effectiveness of the present invention will be described.

[0057] As raw materials, the electrolyte raw materials and elemental sulfur shown in Tables 1 and 2 were prepared, and then weighed and mixed to obtain the blending ratios shown in Tables 1 and 2 to obtain a raw material assembly. The molar ratio of elemental sulfur to elemental lithium (S / Li) in the raw material assembly is shown in Tables 1 and 2. The electrolyte raw materials and elemental sulfur were weighed and mixed in an argon gas atmosphere in a glove box with a dew point of −70°C or less and an oxygen concentration of 10 mass ppm or less. Mixing was carried out for 24 hours using a planetary ball mill using zirconia balls.

[0058] The obtained raw material aggregate was placed in a firing container (made of alumina) and placed in a heating furnace, where it was heated from room temperature to a heating temperature shown in Table 1 at an average heating rate of 5°C / min and held at the heating temperature for 6 hours. Thereafter, it was cooled from the heating temperature to room temperature at an average cooling rate of 2°C / min to obtain a sulfide-based solid electrolyte.

[0059] The ionic conductivity of the obtained sulfide-based solid electrolyte was measured as follows. The measurement results are shown in Tables 1 and 2. The sulfide-based solid electrolyte was taken out of a glove box in an argon atmosphere and then crushed in an agate mortar. 0.3 g was weighed out and filled into a stainless steel ionic conductivity measurement cell (cylindrical with an inner diameter of 17 mm). The ionic conductivity (mS / cm) was then measured by an AC impedance method using a measuring device "Potentio / Galvanostat SP-300" manufactured by Biologic Corporation under the conditions of a measurement temperature of 25°C, a measurement frequency of 1 Hz to 1 MHz, and an applied pressure of 360 MPa to the measurement cell.

[0060] The obtained sulfide-based solid electrolyte was used as LGPS (Li １０ GeP ２ S １２ ) type crystal structure of LGPS material, and Li ａ M ｂ S ｃXRD measurement was carried out on an LMS material having a crystal structure of space group Pnma, expressed as follows. The XRD measurement was carried out using a Rigaku XRD device "Uitima IV" under the conditions of a step width of 0.01° and a scan rate of 2° / min in the range of 10°≦2θ≦50°. The measurement sample was prepared in a glove box under an argon atmosphere, and the solid electrolyte material was crushed in an agate mortar and sealed in a sealable measurement cell. Powder X-ray diffraction measurement was carried out without exposing the sample to the atmosphere.

[0061]

[0062]

[0063] Inventive Examples 1-1 to 1-7 and Comparative Examples 1-1 to 1-2 are electrolyte raw materials (Li ２ The LGPS-type sulfide-based solid electrolyte was manufactured using a raw material assembly containing a mixture of elemental sulfur (S, Ge, P (red phosphorus)) and elemental sulfur (S). In Comparative Example 1-1, the molar ratio of elemental sulfur to lithium element in the raw material assembly was set to 1.2, resulting in a low ionic conductivity of 2.2 mS / cm. This is presumably due to a lack of liquid phase of elemental sulfur during synthesis, resulting in a non-uniform composition. In Comparative Example 1-2, the molar ratio of elemental sulfur to lithium element in the raw material assembly was set to 7.5, resulting in a low ionic conductivity of 3.1 mS / cm. This is presumably due to the inclusion of excess elemental sulfur as an impurity.

[0064] In contrast, in Inventive Examples 1-1 to 1-7, in which the molar ratio of elemental sulfur to lithium in the raw material aggregate was set within the range of 1.5 to 6.5, the ionic conductivity was increased to 3.4 mS / cm or more. This is presumably because, during heating and synthesis, a liquid phase of elemental sulfur was sufficiently generated, resulting in a uniform composition and preventing excess elemental sulfur from being mixed in as an impurity. Furthermore, Inventive Examples 1-1 to 1-5, in which the heating temperature during synthesis was set to 400°C or more and 1000°C or less, the ionic conductivity was further increased to 4.1 mS / cm or more.

[0065] As a result of X-ray diffraction of the LGPS-type sulfide-based solid electrolytes of Invention Examples 1-1 to 1-7, peaks of the following formulas (A1) to (A6) were detected as diffraction peaks. When the diffraction intensity of the peak of formula (A6) is defined as IA and the diffraction intensity of the peak of formula (A7) is defined as IB, the peak intensity ratio of IB to IA was 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)

[0066] Inventive Examples 2-1 to 2-3 and Comparative Examples 2-1 to 2-2 are electrolyte raw materials (Li ２ The LMS-type sulfide-based solid electrolyte was manufactured using a raw material assembly that mixed elemental sulfur (S, P (red phosphorus)) and elemental sulfur S. In Comparative Example 2-1, the molar ratio of elemental sulfur to lithium element in the raw material assembly was set to 1.2, and the ionic conductivity was 6.7 × 10 －５ mS / cm. This is presumably because the liquid phase of elemental sulfur was insufficient during synthesis, resulting in a non-uniform composition. In Comparative Example 2-2, the molar ratio of elemental sulfur to lithium element in the raw material aggregate was set to 7.5, and the ionic conductivity was 5.5 × 10 －５ The conductivity was low at 1000 mS / cm. This is presumably due to the inclusion of excess elemental sulfur as an impurity.

[0067] In contrast, in Examples 2-1 to 2-3 of the present invention, in which the molar ratio of elemental sulfur to lithium element in the raw material aggregate was set within the range of 1.5 to 6.5, the ionic conductivity was 1.1 × 10 －４ This is presumably because, during the heating and synthesis, a sufficient liquid phase of elemental sulfur is produced, resulting in a uniform composition, and the incorporation of excess elemental sulfur as an impurity is suppressed.

[0068] As a result of X-ray diffraction analysis of the LMS-type sulfide-based solid electrolytes of Inventive Examples 2-1 to 2-3, the following diffraction peaks were 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).

[0069] Inventive Examples 3-1 to 3-3 and Comparative Examples 3-1 to 3-2 are electrolyte raw materials (Li ２ S, LiCl, P ２ S ５ A sulfide-based solid electrolyte (Li) having an Argyrodite-type crystal structure was produced using a raw material assembly in which elemental sulfur (S) was mixed. ５．５ P.S. ４．５ C ｌ１．５ ) In Comparative Example 3-1, the molar ratio of elemental sulfur to lithium element in the raw material aggregate was set to 1.2, and the ionic conductivity was low at 0.076 mS / cm. This is presumably because the liquid phase of elemental sulfur was insufficient during synthesis, resulting in a non-uniform composition. In Comparative Example 3-2, the molar ratio of elemental sulfur to lithium element in the raw material aggregate was set to 7.5, and the ionic conductivity was low at 0.091 mS / cm. This is presumably because excess elemental sulfur was mixed in as an impurity.

[0070] In contrast, in Inventive Examples 3-1 to 3-3, in which the molar ratio of elemental sulfur to lithium in the raw material aggregate was set within the range of 1.5 to 6.5, the ionic conductivity was high, at 0.390 or more. This is presumably because, during synthesis by heating, a liquid phase of elemental sulfur was sufficiently generated, resulting in a uniform composition and preventing excess elemental sulfur from being mixed in as an impurity.

[0071] Inventive Examples 4-1 to 4-3 and Comparative Examples 4-1 to 4-2 are electrolyte raw materials (Li ２ S, SnS ２ The sulfide-based solid electrolyte was manufactured using a raw material assembly in which elemental sulfur S was mixed with elemental lithium. In Comparative Example 4-1, the molar ratio of elemental sulfur to lithium in the raw material assembly was set to 1.2, and the ionic conductivity was 2.6 × 10 －４The ionic conductivity was as low as 3.1 × 10 mS / cm. This is presumably because the liquid phase of elemental sulfur was insufficient during synthesis, resulting in a non-uniform composition. In Comparative Example 4-2, the molar ratio of elemental sulfur to lithium element in the raw material aggregate was set to 7.5, and the ionic conductivity was 3.1 × 10 －４ The viscosity was low at 1000mS / cm. This is presumably due to the inclusion of excess elemental sulfur as an impurity.

[0072] In contrast, in Examples 4-1 to 4-3 of the present invention, in which the molar ratio of elemental sulfur to lithium element in the raw material aggregate was set within the range of 1.5 to 6.5, the ionic conductivity was 8.8 × 10 －４ This is presumably because, during the heating and synthesis, a sufficient liquid phase of elemental sulfur is produced, resulting in a uniform composition, and the incorporation of excess elemental sulfur as an impurity is suppressed.

[0073] As a result of the above confirmatory experiments, it was confirmed that the present invention can provide a method for producing a sulfide-based solid electrolyte that is excellent in ionic conductivity and is particularly suitable for high-power solid-state batteries, and that can efficiently produce such a sulfide-based solid electrolyte.

[0074] It is possible to provide a method for producing a sulfide-based solid electrolyte that is excellent in ionic conductivity and is particularly suitable for high-power solid-state batteries, and is capable of efficiently producing such a sulfide-based solid electrolyte.

Claims

1. A method for producing a sulfide-based solid electrolyte, comprising: a raw material preparation step of preparing electrolyte raw materials containing elements other than sulfur from among the elements constituting the sulfide-based solid electrolyte, and elemental sulfur, and forming a raw material assembly; and a synthesis step of heating the raw material assembly to synthesize the sulfide-based solid electrolyte, wherein in the raw material preparation step, the molar ratio of elemental sulfur to lithium in the raw material assembly is set to 1.5 or more and 6.5 or less.

2. The method for producing a sulfide-based solid electrolyte according to claim 1, characterized in that in the raw material preparation step, the molar ratio of elemental sulfur to elemental lithium in the raw material assembly is set to 2.0 or more.

3. The method for producing a sulfide-based solid electrolyte according to claim 1 or 2, characterized in that in the synthesis step, the raw material assembly is heated at a heating temperature of 400°C or higher and 1000°C or lower.

4. The method for producing a sulfide-based solid electrolyte according to claim 1 or 2, characterized in that, when the raw material assembly is subjected to X-ray diffraction measurement, diffraction peaks attributable to crystalline substances contained in the electrolyte raw material and the elemental sulfur are detected.

5. The sulfide-based solid electrolyte has space group P4. ２ / nmc belonging LGPS (Li １０ GeP ２ S １２ 2. The method for producing a sulfide-based solid electrolyte according to claim 1, wherein the sulfide-based solid electrolyte has a crystalline structure of formula (A1)-type, and when measured by X-ray diffraction measurement using CuKα radiation, peaks of the following formulas (A1) to (A6) are detected as diffraction peaks, and when the diffraction intensity of the peak of formula (A6) is defined as IA and the diffraction intensity of the peak of formula (A7) is defined as IB, the peak intensity ratio of IB to IA is less than 50%.

6. A method for producing a sulfide-based solid electrolyte according to claim 1 or 2, characterized in that the sulfide-based solid electrolyte contains an argyrodite-type crystal structure.

7. The sulfide-based solid electrolyte is Li ａ M ｂ S ｃ and has a crystal structure of space group Pnma, and when measured by X-ray diffraction using CuKα radiation, 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) where M is at least one element of Group 13, Group 14, and Group 15, and a, b, and c are numbers greater than 0.

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