Inorganic sulfide having glass phase

Abstract

Disclosed is an inorganic sulfide which contains an Na2S component, an SiS2 component and an SiO2 component, wherein: the content of the Na2S component is 47.0 mol% to 67.0 mol% if the total amount of the inorganic sulfide is taken as 100 mol%; and the glass phase is the main phase. This inorganic sulfide is glass that can be easily produced and has a large amount of sodium.

Description

Inorganic sulfides with glassy phase

[0001] The present invention relates to an inorganic sulfide having a glass phase and a method for producing the same.

[0002] Lithium-ion secondary batteries have a high energy density and are therefore being used in practical applications as small power sources for devices such as mobile phones and laptops, as well as large power sources for devices such as electric vehicles, and demand for these batteries is expected to continue to grow.

[0003] In lithium-ion secondary batteries, lithium is used as a charge carrier, and lithium and cobalt are combined to form lithium cobalt oxide (LiCoO), which is commonly used as a positive electrode material. ２ Lithium and cobalt are rare metals whose resources are concentrated in South America, China, etc., and the raw material prices are high, raising concerns about the stable supply of raw materials.

[0004] To solve this problem, sodium-ion secondary batteries are being studied as next-generation secondary batteries that can reduce the amount of rare metals used, such as lithium and cobalt. Because sodium, the charge carrier in sodium secondary batteries, is an abundant and inexpensive material, there has been great expectation in recent years for the practical application of sodium-ion secondary batteries as secondary batteries with fewer resource constraints.

[0005] Sodium-ion secondary batteries typically use organic electrolytes, which contain large amounts of flammable, low-boiling-point solvents (dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc.) that are classified as Class 4 Hazardous Materials under the Fire Service Act and are classified as Class 2 Petroleum, raising concerns about battery fire and smoke. While companies are making efforts to improve safety, if the components could be changed, i.e., the electrolyte could be replaced with a less flammable solid electrolyte, and a dramatic improvement in safety could be achieved through material composition, which would reduce costs for safety considerations and be extremely useful from an industrial perspective.

[0006] Such a solid electrolyte is Na ２ S-MS ｙ (M=B, Al, Si, P, Ge, etc.; y=1.5 to 2.5)-based glasses are widely known as typical sodium ion-conducting sulfide-based glass electrolytes.２ It is known that increasing the amount of S increases the content of sodium ions, which act as carriers, and thus can achieve high electrical conductivity, but at the same time, it is known that glass formation becomes difficult. Conventionally, experts have recognized that vitrification by melting and quenching is difficult.

[0007] For this reason, it has been thought that the production of sulfide glass with a high sodium content requires methods such as mechanochemical methods, which have issues with mass production.

[0008] In response to this, the present inventors have invented a method for producing sodium-containing sulfides at atmospheric pressure via sodium polysulfide (see, for example, Patent Document 1). ３ B.S. ３ and Na ４ SiS ４ It is also described that it is possible to prepare glass containing Na ３ B.S. ３ It is also described that adding oxygen to the glass facilitates glass formation.

[0009] International Publication No. 2023 / 095890

[0010] However, in Patent Document 1, Na ４ SiS ４ It is unclear from the composition whether adding oxygen makes glass formation easier. Moreover, the method of Patent Document 1 requires rapid cooling after heating at a high temperature, which is not necessarily a simple method.

[0011] The present invention has been made in view of the above-mentioned current state of the prior art, and a main object of the present invention is to provide a glass with a high sodium content that can be easily produced.

[0012] The present inventors have conducted extensive research to achieve the above object. ４ SiS ４ When a trace amount of oxygen is added to the composition, Na ４ SiS ４In comparison with the composition, it is possible to heat at a lower temperature, and glass can be obtained not only by rapid cooling but also by air cooling, and depending on the composition, glass can also be obtained by slow cooling. ２ S component, SiS ２ Components and SiO ２ It has been found that an inorganic sulfide containing the above components and having a glass phase as the main phase can be obtained. The present invention has been completed based on this finding and further research. That is, the present invention includes the following features.

[0013] Item 1. Na ２ S component, SiS ２ Components and SiO ２ component, and the total amount of the inorganic sulfides is taken as 100 mol %. ２ An inorganic sulfide having an S component content of 47.0 to 67.0 mol % and a glass phase as a main phase.

[0014] Item 2. The total amount of the inorganic sulfide is 100 mol %, and the SiS ２ Item 2. The inorganic sulfide according to Item 1, wherein the content of the component is 23.0 to 33.0 mol%.

[0015] Item 3. The total amount of the inorganic sulfide is 100 mol %, and the SiO ２ Item 3. The inorganic sulfide according to Item 1 or 2, wherein the content of the component is 2.0 to 27.0 mol%.

[0016] Item 4. The inorganic sulfide according to any one of Items 1 to 3, wherein the content of the glass phase is 80 to 100% by weight, with the total amount of the inorganic sulfide being 100% by weight.

[0017] Item 5. General formula (1): Na ｘ１ SiS ｘ２－ｘ O ｘ (1) [wherein 3.8≦x1≦4.2, 3.8≦x2≦4.2, 0.05≦x≦0.65], or general formula (2): Na ｙ１ SiS ｙ２ ySiO ２ (2) The inorganic sulfide according to any one of items 1 to 4, having a composition represented by the formula: [wherein 3.8≦y1≦4.2, 3.8≦y2≦4.2, 0.010≦y≦1.500].

[0018] Item 6. ２９ Si magic angle spinning nuclear magnetic resonance spectrum ( ２９ In the Si MAS-NMR spectrum, SiS ４ ４－ The intensity of the peaks assigned to the SiS units ３ ２－ Unit or SiS ３ The ratio of the intensity of the peak assigned to the SiS ４ ４－ Unit peak intensity / SiS ３ ２－ Unit or SiS ３ Item 6. The inorganic sulfide according to any one of items 1 to 5, wherein the peak intensity of the O unit is 1.8 to 5.0.

[0019] Item 7. The inorganic sulfide according to any one of Items 1 to 6, wherein the difference between the glass transition temperature Tg and the crystallization temperature Tc is 65°C or more.

[0020] Item 8. A sodium ion conductive solid electrolyte containing the inorganic sulfide according to any one of Items 1 to 7.

[0021] Item 9. A solid electrolyte for a sodium ion secondary battery, comprising the sodium ion conductive solid electrolyte according to Item 8.

[0022] Item 10. A sodium ion secondary battery containing the solid electrolyte for sodium ion secondary batteries according to Item 9.

[0023] Item 11. The sodium ion secondary battery according to Item 10, which is an all-solid-state sodium ion secondary battery.

[0024] Item 12. A method for producing an inorganic sulfide according to any one of Items 1 to 7, comprising: (1) Na ２ S, Si, S and SiO ２ (2) a step of heating the mixture obtained in step (1); and (3) a step of cooling the heat-treated product obtained in step (2), wherein in step (1), a compound represented by general formula (1A): Na ｘ１ SiS ｘ２－ｘ O ｘ(1A) [wherein 3.8≦x1≦4.2, 3.8≦x2≦4.2, 0.05≦x≦0.30], and in the step (1), a compound represented by the general formula (2A): Na ｙ１ SiS ｙ２ ySiO ２ (2A) A production method, wherein, when mixing is performed to have a composition represented by the formula: [wherein 3.8≦y1≦4.2, 3.8≦y2≦4.2, 0.010≦y≦0.150], the cooling is rapid cooling or air cooling.

[0025] Item 13. The method according to Item 12, wherein the heating temperature in step (2) is 400 to 1000°C.

[0026] Item 14. The method according to Item 12 or 13, wherein the rapid cooling in step (3) is a cooling treatment at a cooling rate of 100° C. / second or more.

[0027] According to the present invention, a glass having a high sodium content can be easily produced.

[0028] The results of AC impedance measurement (Nyquist plot) of the inorganic sulfide obtained in Example 6 are shown. The X-ray diffraction patterns of the inorganic sulfides obtained in Examples 2, 4, and 6 and Comparative Example 4 are shown. The Raman spectra of the inorganic sulfides obtained in Examples 2, 4, and 6 and Comparative Example 4 are shown. The X-ray diffraction patterns of the inorganic sulfides obtained in Example 5 and Comparative Examples 1, 7, and 9 are shown. The Raman spectra of the inorganic sulfides obtained in Comparative Examples 1 and 9 are shown. The relationship between ionic conductivity and temperature of the inorganic sulfides obtained in the Examples and Comparative Examples is shown. The results of Examples 8 to 17 and Comparative Examples 1, 4, 10, and 11 are shown. The X-ray diffraction patterns of the inorganic sulfides obtained in Comparative Examples 1, 4, 10, and 11 and Examples 8 and 9 are shown. The appearance photographs of the inorganic sulfides obtained in Comparative Examples 1, 10, and 11 are shown. The X-ray diffraction patterns of the inorganic sulfides obtained in Examples 10 to 14 are shown. The Raman spectra of the inorganic sulfides obtained in Examples 8 to 14 and Comparative Example 4 are shown. The Raman spectra of the inorganic sulfides obtained in Examples 8 to 14 and Comparative Example 4 are shown. ２９1 shows the Si MAS-NMR spectrum. 2 shows the results of differential scanning calorimetry (DSC) of the inorganic sulfides obtained in Examples 8 to 10 and Comparative Example 4. 3 shows the difference between the glass transition temperature Tg and the crystallization temperature Tc of the inorganic sulfides obtained in Examples 8 to 14 and Comparative Example 4.

[0029] Hereinafter, one embodiment of the present invention will be described in detail, but the scope of the present invention is not limited to the embodiment described here, and various modifications can be made without departing from the spirit of the present invention. Furthermore, when multiple upper and lower limit values ​​are specified for a specific parameter, any upper and lower limit values ​​can be combined to form a suitable numerical range.

[0030] In this specification, the term "containing" is a concept that encompasses all of "comprise," "consist essentially of," and "consist only of."

[0031] In addition, in this specification, when a numerical range is expressed as "A to B," it means A or more and B or less.

[0032] 1. Inorganic sulfide The inorganic sulfide of the present invention is Na ２ S component, SiS ２ Components and SiO ２ The total amount of the inorganic sulfides is 100 mol %, and the Na ２ The content of the S component is 64.0 to 67.0 mol %, and the glass phase is the main phase. ４ SiS ４ Compared with the composition, oxygen, i.e., SiO ２ Since the glass contains the components, it can be heated at a lower temperature, and the glass can be obtained not only by rapid cooling but also by air cooling, and depending on the composition, the glass can also be obtained by slow cooling.

[0033] According to the present invention, glass with a high sodium content can be easily produced, and the content of sodium ions acting as carriers is increased, so that Na ２ The amount of S component is large. Specifically, when the total amount of inorganic sulfides is 100 mol%, Na２ The content of the S component is 47.0 to 67.0 mol%, preferably 48.0 to 66.7 mol%. When an inorganic sulfide having a composition in which the amount of silicon is partially deficient relative to the amount of sodium is used (for example, in the case of the general formula (1) described later), the total amount of the inorganic sulfide is taken as 100 mol%, and the amount of Na is ２ The content of the S component can be 64.0 to 67.0 mol%, preferably 65.0 to 66.7 mol%. When an inorganic sulfide having a composition in which silica is partially added to sodium silicon sulfide is used (for example, in the case of the general formula (2) described later), the total amount of the inorganic sulfide is taken as 100 mol%, and the content of Na ２ The content of the S component can be set to 47.0 to 66.0 mol %, preferably 48.0 to 65.0 mol %.

[0034] According to the present invention, glass with a high sodium content can be easily produced, and the content of sodium ions acting as carriers is increased, so that SiS ２ It is preferable that the amount of the component is not too large. Specifically, when the total amount of inorganic sulfides is 100 mol%, SiS ２ The content of the component is preferably 23.0 to 33.0 mol %, more preferably 24.0 to 32.5 mol %. ２ It is preferable that the amount of the component is not too large, but depending on the ionic conductivity, the total amount of inorganic sulfides is taken as 100 mol %, and SiS ２ The content of the component may be 27.0 to 33.0 mol %, preferably 28.0 to 32.5 mol %.

[0035] According to the present invention, oxygen, i.e., SiO ２ Since the glass contains SiO , it can be heated at a lower temperature, and can be obtained by air cooling as well as rapid cooling, and depending on the composition, it can also be obtained by slow cooling. From this viewpoint, the total amount of inorganic sulfides is taken as 100 mol %, and the amount of SiO ２The content of the component is preferably 2.0 to 27.0 mol%, more preferably 2.2 to 26.0 mol%. When an inorganic sulfide having a composition in which the amount of silicon is partially deficient relative to the amount of sodium is used (for example, in the case of the general formula (1) described later), the total amount of inorganic sulfides is taken as 100 mol%, and the content of SiO ２ The content of the component can be 2.0 to 10.0 mol%, preferably 2.2 to 9.0 mol%. When an inorganic sulfide having a composition in which silica is partially added to sodium silicon sulfide is used (for example, in the case of general formula (2) described later), the total amount of inorganic sulfides is taken as 100 mol%, and the content of SiO ２ The content of the component may be 2.0 to 27.0 mol %, preferably 2.2 to 26.0 mol %.

[0036] The inorganic sulfide of the present invention includes Na ２ S component, SiS ２ Components and SiO ２ In addition to the ingredients, there are also impurities that may be mixed into the raw materials (Na ２ O ２ Ingredients: Na ２ SO ４ Ingredients: Na ２ SO ３ component, NaOH component, NaSH component, Na ２ CO ３ components, etc.), crucibles and grinding media used in manufacturing (Al ２ O ３ Component: ZrO ２ The inorganic sulfide may contain 3.5 mol % or less, particularly 0.1 to 3.0 mol %, of inorganic sulfides as a dispersing agent for grinding, based on 100 mol % of the total amount of inorganic sulfides.

[0037] The composition of the inorganic sulfide of the present invention containing the above-mentioned components is not particularly limited, but from the viewpoints that it can be heated at a lower temperature, and that glass can be obtained not only by rapid cooling but also by air cooling, and that glass can also be obtained by slow cooling depending on the composition, it is preferable to use, for example, an inorganic sulfide containing a compound represented by the general formula (1): Na ｘ１ SiS ｘ２－ｘ O ｘ (1) [wherein 3.8≦x1≦4.2, 3.8≦x2≦4.2, 0.05≦x≦0.65], or general formula (2): Naｙ１ SiS ｙ２ ySiO ２ (2) [wherein 3.8≦y1≦4.2, 3.8≦y2≦4.2, 0.010≦y≦1.500].

[0038] In the general formula (1), x1 corresponds to the amount of sodium in the inorganic sulfide of the present invention. From the viewpoints of easy synthesis at low cost and easy improvement of ionic conductivity, 3.8≦x1≦4.2 is preferable, and 3.9≦x1≦4.1 is more preferable.

[0039] In the general formula (1), x2 corresponds to the amount of sulfur in the inorganic sulfide of the present invention. From the viewpoints of easy synthesis at low cost and easy improvement of ionic conductivity, 3.8≦x2≦4.2 is preferable, and 3.9≦x2≦4.1 is more preferable.

[0040] In the general formula (1), x corresponds to the amount of oxygen in the inorganic sulfide of the present invention. From the viewpoints of easy synthesis at low cost and easy improvement of ionic conductivity, 0.05≦x≦0.65 is preferable, and 0.10≦x≦0.55 is more preferable.

[0041] In the general formula (2), y1 corresponds to the amount of sodium in the inorganic sulfide of the present invention. From the viewpoints of easy synthesis at low cost and easy improvement of ionic conductivity, 3.8≦y1≦4.2 is preferable, and 3.9≦y1≦4.1 is more preferable.

[0042] In the general formula (2), y2 corresponds to the amount of sulfur in the inorganic sulfide of the present invention. From the viewpoints of easy synthesis at low cost and easy improvement of ionic conductivity, 3.8≦y2≦4.2 is preferable, and 3.9≦y2≦4.1 is more preferable.

[0043] In the general formula (2), y corresponds to the amount of oxygen in the inorganic sulfide of the present invention. From the viewpoint of easy synthesis at low cost and easy improvement of ionic conductivity, 0.010≦y≦1.500 is preferable, 0.050≦y≦0.800 is more preferable, and 0.180≦y≦0.390 is even more preferable.

[0044] As described above, the inorganic sulfide of the present invention is Na ２ S component, SiS ２ Components and SiO ２ The inorganic sulfide of the present invention contains not only the glass phase but also a crystalline phase (Na ４ SiS ４ Phase, Na ６ Si ２ S ７ Phase, Na ２ S phase, Na ２ SO ４ phase, SiO ２ Although the present invention does not completely exclude the inclusion of conventional Na ４ SiS ４ Compared with the composition, oxygen, i.e., SiO ２ Because it contains components, it can be heated at a lower temperature, and glass can be obtained not only by rapid cooling but also by air cooling, and depending on the composition, glass can also be obtained by slow cooling, so the glass phase is the main phase.

[0045] In the present invention, the glass phase being the main phase means that the content of the glass phase is 50% by weight or more, with the total amount of inorganic sulfides being 100% by weight. ２ S-MS ｙ Since sulfide-based glasses are widely known as typical sodium ion conductive sulfide-based glass electrolytes, a larger glass phase content is preferable in the inorganic sulfide of the present invention. Therefore, the glass phase content is preferably 80 to 100 wt %, and more preferably 90 to 100 wt %, based on 100 wt % of the total amount of inorganic sulfide. It is particularly preferable that the inorganic sulfide of the present invention has 100 mol % of glass phase, i.e., that it does not have a clear diffraction peak in an X-ray diffraction diagram using CuKα radiation.

[0046] The inorganic sulfide of the present invention is ２９ Si magic angle spinning nuclear magnetic resonance spectrum ( ２９ In the Si MAS-NMR spectrum, SiS ４ ４－ The peak attributable to the unit (δ = 9 ppm) and the peak attributable to the SiS ３ ２－Unit or SiS ３ In the inorganic sulfide of the present invention, a peak (δ=-5 ppm) attributable to the SiS ４ ４－ The intensity of the peaks assigned to the SiS unit is strong. ３ ２－ Unit or SiS ３ Although the peaks attributable to the O unit tend to be weak, the vitrification region tends to expand as the oxygen content increases, due to the formation of oxysulfide units and crosslinking units. ４ SiS ４ In comparison with the composition, SiS ４ ４－ The intensity of the peaks assigned to the SiS units ３ ２－ Unit or SiS ３ The ratio of the intensity of the peak assigned to the SiS ４ ４－ Unit peak intensity / SiS ３ ２－ Unit or SiS ３ Therefore, in the inorganic sulfide of the present invention, the peak intensity of SiS ４ ４－ The intensity of the peaks assigned to the SiS units ３ ２－ Unit or SiS ３ The ratio of the intensity of the peak assigned to the SiS ４ ４－ Unit peak intensity / SiS ３ ２－ Unit or SiS ３ The peak intensity of the O unit is preferably from 1.8 to 5.0, more preferably from 1.9 to 3.6.

[0047] In the inorganic sulfide of the present invention, conventional Na ４ SiS ４In comparison with the composition, the difference between the glass transition temperature Tg and the crystallization temperature Tc tends to be larger. The difference between the glass transition temperature Tg and the crystallization temperature Tc indicates the stability of the supercooled liquid, and it is suggested that the larger this difference, the easier it is to vitrify. For this reason, in the inorganic sulfide of the present invention, the difference between the glass transition temperature Tg and the crystallization temperature Tc is preferably 65°C or more, more preferably 70 to 120°C.

[0048] The inorganic sulfide of the present invention satisfies the above-mentioned conditions, but may contain other impurities as long as the impurities do not impair the performance of the inorganic sulfide. Examples of such impurities include metals such as sodium that may be mixed into the raw materials; oxygen that may be mixed into the raw materials or during production; and the like. Furthermore, residual materials (Na ２ S, Si, S, SiO ２ The amount of these impurities may be within a range that does not impair the performance of the inorganic sulfide of the present invention, and is usually preferably 5% by weight or less, more preferably 3% by weight or less, and even more preferably 2% by weight or less, based on 100% by weight of the total amount of inorganic sulfides that satisfy the above conditions.

[0049] When these impurities are present, diffraction peaks corresponding to the impurities may be present in the X-ray diffraction pattern.

[0050] As described above, the inorganic sulfide of the present invention can be heated at a lower temperature, and glass can be obtained not only by rapid cooling but also by air cooling. Depending on the composition, glass can also be obtained by slow cooling. The inorganic sulfide of the present invention also has excellent ionic conductivity (particularly sodium ionic conductivity). Therefore, the inorganic sulfide of the present invention can be used as a sodium ion conductive solid electrolyte. Furthermore, the inorganic sulfide of the present invention is useful as a solid electrolyte for sodium ion secondary batteries, and is particularly preferably used as a solid electrolyte for all-solid-state sodium ion secondary batteries.

[0051] 2. Sodium-ion secondary battery When the inorganic sulfide of the present invention is used as a solid electrolyte for a sodium-ion secondary battery, the structure of the sodium-ion secondary battery of the present invention (particularly, an all-solid-state sodium-ion secondary battery) can be the same as that of a known sodium-ion secondary battery, except that the inorganic sulfide of the present invention is used as the solid electrolyte.

[0052] For example, sodium cobaltate (LiCoO ２ ), sodium nickelate (LiNiO ２ ), sodium manganate (NaMn ２ O ４ ), sodium iron phosphate (NaFePO ４ A known positive electrode active material, such as a vanadium oxide-based material or a sulfur-based material, can be used. A positive electrode mixture containing this positive electrode active material, the inorganic sulfide of the present invention, and, if necessary, a conductive agent and a binder can be supported on a positive electrode current collector made of Al, Ni, stainless steel, carbon cloth, or the like. Examples of conductive agents that can be used include carbon materials such as graphite, coke, carbon black, and acicular carbon. Examples of binders that can be used include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, polyacrylic, styrene butadiene rubber (SBR), styrene-ethylene-butylene-styrene copolymer (SEBS), and carboxymethyl cellulose (CMC). These materials can be used alone or in combination of two or more. Conventional electrolytes can also be used as the electrolyte.

[0053] The negative electrode may be made of a known negative electrode active material such as metallic sodium, a carbon-based material (activated carbon, graphite, etc.), silicon, silicon oxide, a Si—SiO-based material, or sodium titanium oxide. A positive electrode mixture containing this negative electrode active material, the inorganic sulfide of the present invention, and, if necessary, a conductive agent and a binder may be supported on a negative electrode current collector such as Al, Ni, stainless steel, or carbon cloth. Examples of conductive agents that can be used include carbon materials such as graphite, coke, carbon black, and acicular carbon. Examples of binders that can be used include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, polyacrylic, styrene butadiene rubber (SBR), styrene-ethylene-butylene-styrene copolymer (SEBS), and carboxymethyl cellulose (CMC). These materials may be used alone or in combination of two or more. Conventional electrolytes may also be used as the electrolyte.

[0054] Furthermore, the inorganic sulfide of the present invention can be formed into a layer by a conventional method using a known binder as needed, and used as the electrolyte layer. Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, polyacrylic, styrene butadiene rubber (SBR), styrene-ethylene-butylene-styrene copolymer (SEBS), and carboxymethyl cellulose (CMC). These materials can be used alone or in combination of two or more. Conventionally used electrolytes can also be used in combination as the electrolyte constituting the electrolyte layer.

[0055] The separator may be made of a material such as a polyolefin resin, such as polyethylene or polypropylene, a fluororesin, nylon, aromatic aramid, or inorganic glass, and may be in the form of a porous film, nonwoven fabric, or woven fabric.

[0056] Furthermore, a sodium ion secondary battery can be assembled in accordance with a conventional method using other known battery components. In the present invention, the term "sodium ion secondary battery" is a concept that also encompasses "sodium secondary batteries" that use metallic sodium as the negative electrode material.

[0057] The shape of the sodium ion secondary battery is not particularly limited, and may be cylindrical, prismatic, or the like.

[0058] 3. Method for Producing Inorganic Sulfide The method for producing an inorganic sulfide of the present invention is not particularly limited, but may include the following: (1) Na ２ S, Si, S and SiO ２ (2) a step of heating the mixture obtained in step (1); and (3) a step of cooling the heat-treated product obtained in step (2), wherein in step (1), a compound represented by the general formula (1): Na ｘ１ SiS ｘ２－ｘ O ｘ (1) [wherein 3.8≦x1≦4.2, 3.8≦x2≦4.2, 0.05≦x≦0.30], and in the step (1), when mixing to have a composition represented by the general formula (2A): Na ｙ１ SiS ｙ２ ySiO ２ (2A) [wherein 3.8≦y1≦4.2, 3.8≦y2≦4.2, 0.010≦y≦0.150], the cooling is rapid cooling or air cooling.

[0059] (3-1) Step (1) In step (1), Na ２ S, Si, S and SiO ２ The mixing ratio of each raw material is not particularly limited, and they can be mixed so as to obtain the composition of the inorganic sulfide of the present invention described above.

[0060] The mixing method is not particularly limited, and any method that can uniformly mix the raw materials can be used, such as mortar mixing, mechanical milling, coprecipitation, a method in which the raw materials are dispersed in a solvent and then mixed, or a method in which the raw materials are dispersed in a solvent at once and then mixed.

[0061] (3-2) Step (2) In step (2), the atmosphere during heating is not particularly limited, but can be an inert gas atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere.

[0062] The heating temperature in step (2) is not particularly limited, but can be, for example, 400 to 1000° C. According to the present invention, the conventional Na ４ SiS ４ Compared with the composition, oxygen, i.e., SiO ２ Since the glass contains the components, it can be heated at a lower temperature, and glass can be obtained not only by rapid cooling but also by air cooling, and depending on the composition, glass can also be obtained by slow cooling. Therefore, even if the heating temperature in step (2) is slightly lower, vitrification can be achieved in step (3), making this a simple and economical method. From this perspective, the heating temperature is preferably 600 to 850°C, and more preferably 650 to 800°C.

[0063] The heating time in step (2) is not particularly limited, but is preferably 0.1 to 12.0 hours, more preferably 0.5 to 6.0 hours, from the viewpoint that glass can be obtained in step (3) not only by rapid cooling but also by air cooling, and that glass can also be obtained by slow cooling depending on the composition. In the present invention, the heating time means the time during which the glass is maintained at the maximum temperature.

[0064] (3-3) Step (3) In step (3), the heat-treated product obtained in step (2) is cooled. The cooling method used here includes rapid cooling, air cooling, slow cooling, and the like.

[0065] However, in step (1), the general formula (1A): Na ｘ１ SiS ｘ２－ｘ O ｘ (1A) [wherein 3.8≦x1≦4.2, 3.8≦x2≦4.2, 0.05≦x≦0.30], and in step (1), a compound represented by the general formula (2A): Na ｙ１ SiS ｙ２ ySiO ２When the mixture is mixed to have a composition represented by the formula (2A) [wherein 3.8≦y1≦4.2, 3.8≦y2≦4.2, 0.010≦y≦0.150], vitrification cannot be achieved by slow cooling. Therefore, in this case, cooling is performed by rapid cooling or air cooling.

[0066] On the other hand, in other cases, that is, in step (1), the general formula (1B): Na ｘ１ SiS ｘ２－ｘ O ｘ (1) [wherein 3.8≦x1≦4.2, 3.8≦x2≦4.2, 0.30<x≦0.65], and in step (1), when mixing to have a composition represented by the general formula (2B): Na ｙ１ SiS ｙ２ ySiO ２ (2B) [wherein 3.8≦y1≦4.2, 3.8≦y2≦4.2, 0.150<y≦1.500], vitrification can also be achieved by slow cooling. In this case, any of rapid cooling, air cooling, and slow cooling can be employed in this step.

[0067] In the step (3), when cooling by quenching is performed, this can be performed by iron pressing (pressing with a cooling plate), pouring the melt into a cooling medium such as twin-roller quenching or single-roller method, spraying the melt, etc., and from the viewpoint of facilitating vitrification, the cooling rate is preferably 100°C / hour or more, more preferably 100°C / second or more, even more preferably 200°C / second or more, and even more preferably 500°C / second or more. Furthermore, in the step (3), when cooling by quenching, the upper limit of the cooling rate is not particularly limited, and can be, for example, 100,000°C / second.

[0068] When cooling by air in step (3), the heat-treated product can usually be cooled by contacting it with air at room temperature (around 25°C), and the cooling rate can be, for example, 20 to 80°C / sec, particularly 30 to 70°C / sec.

[0069] In the step (3), when cooling is performed by slow cooling, the cooling can be performed by temperature control according to a program of an electric furnace, natural heat dissipation including air cooling, or the like. From the viewpoints of ease of vitrification and production efficiency, the cooling rate is preferably 0.005 to 10°C / second, more preferably 0.010 to 5°C / second, and even more preferably 0.020 to 1°C / second.

[0070] The cooling rate is particularly important near the melting point, so it is preferable that the cooling rate satisfies the above range particularly near the melting point.

[0071] Furthermore, the shorter the residence time in the temperature range in the supercooled liquid state between the melting point and the glass transition temperature Tg, the easier it is to obtain a glass. Therefore, if the difference between the melting point and the glass transition temperature Tg is small, a slow cooling rate is acceptable, whereas if the difference between the melting point and the glass transition temperature Tg is large, a fast cooling rate is preferred.

[0072] The present invention will be described in more detail below with reference to examples, but it goes without saying that the present invention is not limited to the following examples.

[0073] Test Example 1: Observation of Appearance (Vitrification) In order to simply evaluate whether or not the inorganic sulfides obtained in the following Examples and Comparative Examples were vitrified, the transparency of their appearance was evaluated visually.

[0074] Test Example 2: X-ray diffraction measurement The inorganic sulfides obtained in the following Examples and Comparative Examples were subjected to X-ray diffraction measurement to identify the crystalline phase or glass phase. The scanning speed was set to 10° / min.

[0075] Test Example 3: Raman Spectroscopic Analysis The inorganic sulfides obtained in the following Examples and Comparative Examples were subjected to Raman spectroscopic analysis to identify the crystalline phase or glass phase. The wavelength was set to 532 nm.

[0076] Test Example 4: ２９ Si MAS-NMR Measurement In order to identify the crystalline phase or glass phase of the inorganic sulfides obtained in the following Examples and Comparative Examples, ２９ Si MAS-NMR measurement was carried out, with calibration performed using polydimethylsiloxane (PDMS) as -34.1 ppm.

[0077] Test Example 5: Measurement of ionic conductivity For the inorganic sulfides obtained in the following Examples and Comparative Examples, the obtained powders were uniaxially pelletized at room temperature (25°C ± 3°C) and 360 MPa, and gold current collecting films were formed on both sides of the pellets by sputtering. The pellets were subjected to AC impedance measurements at various temperatures to measure the ionic conductivity σ at room temperature (25°C). ２５ The viscosity (S / cm) and activation energy Ea (kJ / mol) were measured.

[0078] Test Example 6: Differential scanning calorimetry (DSC measurement) Differential scanning calorimetry (DSC measurement) was carried out on the inorganic sulfides obtained in the following Examples and Comparative Examples. The measurement was carried out by sealing the sample in an aluminum sample pan under a nitrogen gas atmosphere at a heating rate of 10°C / min.

[0079] Comparative Example 1: Na ４ SiS ４ (Slow cooling) In a glove box under an argon atmosphere (not exposed to the atmosphere), sodium sulfide (Na ２ S) powder (manufactured by Nagao Corporation; 99.1%), silicon (Si) powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.; 99.9%), sulfur (S) powder (manufactured by Kojundo Chemical Laboratory Co., Ltd.; 99.99%), and silica (SiO ２ ) powder (manufactured by Kojundo Chemical Laboratory Co., Ltd.; 99.9%) was weighed and mixed in a molar ratio of 2:1:2:0. ８ A molecular crystal was used, but for convenience it will be referred to as S.

[0080] The obtained mixture was heated to 700°C over 4 hours at a temperature increase rate of 3°C / min using an electric furnace and maintained at this temperature for 12 hours. Thereafter, using the temperature control program of the electric furnace, the mixture was gradually cooled to room temperature at a cooling rate of 100°C / hour (0.028°C / sec) to obtain the inorganic sulfide (Na ４ SiS ４ ) was obtained.

[0081] The inorganic sulfide obtained was opaque and devitrified, possibly due to the progress of crystallization. ４ SiS ４Diffraction peaks attributable to crystalline phases were observed, and it was understood that almost no glass phase was formed. In addition, the electrical conductivity of the obtained inorganic sulfide at 25°C was 1.7 × 10 －７ The viscosity was insufficient at 5 S / cm.

[0082] Comparative Example 2: Na ４ SiS ４ (Air cooling) After the heat treatment, the inorganic sulfide (Na ４ SiS ４ ) was obtained.

[0083] The inorganic sulfide obtained was opaque and devitrified, possibly due to the progress of crystallization. ４ SiS ４ Diffraction peaks attributed to crystalline phases were observed, and it was understood that almost no glass phase was formed.

[0084] Comparative Example 3: Na ４ SiS ４ (Quenching) After the heat treatment, the inorganic sulfide (Na ４ SiS ４ ) was obtained.

[0085] The inorganic sulfide obtained was opaque and devitrified, possibly due to the progress of crystallization. ４ SiS ４ Diffraction peaks attributed to crystalline phases were observed, and it was understood that almost no glass phase was formed.

[0086] Comparative Example 4: Na ４ SiS ４ (Rapid cooling from 810°C) The inorganic sulfide (Na) of Comparative Example 4 was prepared in the same manner as Comparative Example 1, except that the heating temperature was 810°C instead of 700°C, and after the heat treatment, it was rapidly cooled to room temperature at a cooling rate of about 1000°C / second using an iron press. ４ SiS ４ ) was obtained.

[0087] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, which indicates that the inorganic sulfide was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 3.1 × 10 －５ S / cm.

[0088] Considering the results of Comparative Example 3 together, Na ４ SiS ４ It can be seen that in the case of inorganic sulfides of this composition, unless they are heated at a high temperature of 810°C, they are difficult to vitrify even if they are subsequently rapidly cooled.

[0089] Comparative Example 5: Na ４ SiS ３．８５ O ０．１５ (Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ The same procedure as in Comparative Example 1 was repeated except that the inorganic sulfide (Na) powders of Comparative Example 5 were weighed and mixed so that the molar ratio was 2:0.925:1.85:0.075 instead of 2:1:2:0. ４ SiS ３．８５ O ０．１５ ) was obtained.

[0090] The inorganic sulfide obtained was opaque and devitrified, possibly due to the progress of crystallization. ４ SiS ４ Diffraction peaks attributed to crystalline phases were observed, and it was understood that no glass phase was formed.

[0091] Example 1: Na ４ SiS ３．８５ O ０．１５ (Air-cooled) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ The inorganic sulfide (Na) powders of Example 1 were weighed and mixed so that the molar ratio was 2:0.925:1.85:0.075 instead of 2:1:2:0, and after the heat treatment, the mixture was air-cooled to room temperature at a cooling rate of about 50°C / sec by contacting with air at room temperature. ４ SiS ３．８５O ０．１５ ) was obtained.

[0092] The resulting inorganic sulfide was transparent and vitrified.

[0093] Example 2: Na ４ SiS ３．８５ O ０．１５ (Quenched) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ The inorganic sulfide (Na) powders of Example 2 were weighed and mixed in a molar ratio of 2:0.925:1.85:0.075 instead of 2:1:2:0, and after heat treatment, the mixture was rapidly cooled to room temperature at a cooling rate of about 1000°C / sec using an iron press. ４ SiS ３．８５ O ０．１５ ) was obtained.

[0094] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, which indicates that the inorganic sulfide was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 3.2 × 10 －５ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0095] Comparative Example 6: Na ４ SiS ３．８ O ０．２ (Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ ) powders of Comparative Example 6 were weighed and mixed in a molar ratio of 2:0.9:1.8:0.1 instead of 2:1:2:0. ４ SiS ３．８ O ０．２ ) was obtained.

[0096] The obtained inorganic sulfide was opaque, powdery, and devitrified, probably due to the progress of crystallization. ４ SiS ４ Diffraction peaks attributed to crystalline phases were observed, and it was understood that a glass phase was not formed as the main phase.

[0097] Example 3: Na ４ SiS ３．８ O ０．２ (Air-cooled) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ The inorganic sulfide (Na) powders of Example 3 were weighed and mixed so that the molar ratio was 2:0.9:1.8:0.1 instead of 2:1:2:0, and after the heat treatment, the mixture was air-cooled to room temperature at a cooling rate of about 50°C / sec by contacting with air at room temperature. ４ SiS ３．８ O ０．２ ) was obtained.

[0098] The resulting inorganic sulfide was transparent and vitrified.

[0099] Example 4: Na ４ SiS ３．８ O ０．２ (Quenched) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ The inorganic sulfide (Na) powders of Example 4 were weighed and mixed in a molar ratio of 2:0.9:1.8:0.1 instead of 2:1:2:0, and after heat treatment, the mixture was rapidly cooled to room temperature at a cooling rate of about 1000°C / sec using an iron press. ４ SiS ３．８ O ０．２ ) was obtained.

[0100] The obtained inorganic sulfide was plate-like, transparent, and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, indicating that it was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 3.1 × 10 －５ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0101] Comparative Example 7: Na ４ SiS ３．７ O ０．３ (Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO２ ) powders of Comparative Example 7 were weighed and mixed in a molar ratio of 2:0.85:1.7:0.15 instead of 2:1:2:0. ４ SiS ３．７ O ０．３ ) was obtained.

[0102] The obtained inorganic sulfide was opaque, powdery, and devitrified, probably due to the progress of crystallization. ４ SiS ４ Diffraction peaks attributable to crystalline phases were observed, and it was understood that almost no glass phase was formed. The electrical conductivity of the obtained inorganic sulfide at 25°C was 6.1 × 10 －７ The viscosity was insufficient at S / cm.

[0103] Example 5: Na ４ SiS ３．７ O ０．３ (Air-cooled) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ The inorganic sulfide (Na) powders of Example 5 were weighed and mixed so that the molar ratio was 2:0.85:1.7:0.15 instead of 2:1:2:0, and after the heat treatment, the mixture was air-cooled to room temperature at a cooling rate of about 50°C / sec by contacting with air at room temperature. ４ SiS ３．７ O ０．３ ) was obtained.

[0104] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, which indicates that the inorganic sulfide was composed of a glass phase.

[0105] Example 6: Na ４ SiS ３．７ O ０．３ (Quenched) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２The inorganic sulfide (Na) powders of Example 6 were weighed and mixed in a molar ratio of 2:0.85:1.7:0.15 instead of 2:1:2:0, and after heat treatment, the mixture was rapidly cooled to room temperature at a cooling rate of about 1000°C / sec using an iron press. ４ SiS ３．７ O ０．３ ) was obtained.

[0106] The obtained inorganic sulfide was plate-like, transparent, and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, indicating that it was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 2.8 × 10 －５ The inorganic sulfide obtained in Example 6 had a sufficient conductivity of 0.25 S / cm even when oxygen atoms were contained. As support for the measured ionic conductivity, the results of AC impedance measurement (Nyquist plot) of the inorganic sulfide obtained in Example 6 are shown in Figure 1.

[0107] Example 7: Na ４ SiS ３．５ O ０．５ (Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ ) powders were weighed and mixed in a molar ratio of 2:0.75:1.5:0.25 instead of 2:1:2:0, in the same manner as in Comparative Example 1, except that the inorganic sulfide (Na ４ SiS ３．５ O ０．５ ) was obtained.

[0108] The obtained inorganic sulfide was plate-like, transparent, and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, indicating that it was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 2.8 × 10 －５ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0109] Comparative Example 8: Na ４ SiS ３．３ O ０．７ (Slow cooling) Sodium sulfide (Na ２S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ The same procedure as in Comparative Example 1 was repeated except that the inorganic sulfide (Na) powders of Comparative Example 8 were weighed and mixed so that the molar ratio was 2:0.65:1.3:0.35 instead of 2:1:2:0. ４ SiS ３．３ O ０．７ ) was obtained.

[0110] The inorganic sulfide obtained was opaque and devitrified, possibly due to the progress of crystallization. ２ Diffraction peaks attributable to the S crystalline phase and a glass phase indicated by a halo pattern were observed. ２ Since S is segregated, it is possible to distinguish between a glass phase with a lower Na content than the starting composition and a Na ２ As a result, the electrical conductivity of the obtained inorganic sulfide at 25°C was 2.0 × 10 －６ S / cm, which was not sufficient.

[0111] Comparative Example 9: Na ４ SiS ３ O (slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ ) powders of Comparative Example 9 were weighed and mixed in a molar ratio of 2:0.5:1:0.5 instead of 2:1:2:0. ４ SiS ３ O) was obtained.

[0112] The inorganic sulfide obtained was opaque and devitrified, possibly due to the progress of crystallization. ２ Diffraction peaks attributable to the S crystalline phase and a glass phase indicated by a halo pattern were observed. ２ Since S is segregated, it is possible to distinguish between a glass phase with a lower Na content than the starting composition and a Na ２ As a result, the electrical conductivity of the obtained inorganic sulfide at 25°C was 3.2 × 10 －６ S / cm, which was not sufficient.

[0113] The results are shown in Table 1.

[0114]

[0115] Next, the X-ray diffraction patterns of the inorganic sulfides obtained in Examples 2, 4, and 6 and Comparative Example 4 are shown in Figure 2. As a result, a halo pattern was observed in each sample, and Na ４ SiS ４ It was shown that by incorporating oxygen into the composition, it was possible to vitrify the composition by subsequent cooling even when firing at a lower temperature than in Comparative Example 4.

[0116] The Raman spectra of the inorganic sulfides obtained in Examples 2, 4, and 6 and Comparative Example 4 are shown in Figure 3. As a result, in all samples, SiS ４ A peak attributable to the Na unit was observed. ４ SiS ４ Even if oxygen is added to SiS ４ ４－ This suggests that it is possible to produce glass that mainly contains units.

[0117] Next, the X-ray diffraction patterns of the inorganic sulfides obtained in Example 5 and Comparative Examples 1, 7 and 9 are shown in FIG. ４ SiS ４ It has been shown that when the composition is subjected to slow cooling, it crystallizes and glass cannot be produced. ４ SiS ４ It has also been shown that even if oxygen is added to Na, crystallization occurs in many compositions when the glass is cooled slowly, and it is not easy to manufacture the glass. ４ SiS ４ It is suggested that adding oxygen to SiO2 and cooling it in air suppresses crystallization and enables vitrification. In this regard, it is suggested that the vitrification region is expanded by substituting O for S.

[0118] On the other hand, in Comparative Examples 8 and 9, which contained a large amount of oxygen, some of the glass was vitrified, but Na ２The glass was separated into an S crystalline phase and a Na-Si-S-O glass phase, and it was not possible to produce a glass with a high sodium content. Considering the results of Example 7 and Comparative Example 8 together, a boundary for vitrification exists between x = 0.5 and x = 0.7, and in Example 7 in particular, vitrification was possible even with slow cooling, and the electrical conductivity was also high.

[0119] The Raman spectra of the inorganic sulfides obtained in Comparative Examples 1 and 9 are shown in FIG. 5. As a result, in all samples, SiS ４ While peaks attributable to the Na unit were observed, in Comparative Example 9, which contained a large amount of oxygen, ２ S unit and Si ４ S １０ Peaks attributable to Na units were also observed. ２ This suggests that the crystals are separated into an S crystal phase and an Na--Si--S--O glass phase.

[0120] The ionic conductivity and activation energy of the inorganic sulfides obtained as a result of the above are shown in FIG. 6 and Table 2. In Table 2, "MC method" means the mechanochemical method, and "MQ method" means the melt quench method. ４ SiS ４ In terms of composition, firing at 700°C does not allow vitrification even after subsequent cooling, resulting in a decrease in ionic conductivity. However, by substituting the sulfur element with the oxygen element, vitrification becomes possible. ４ SiS ４ The ionic conductivity was comparable to that of the comparative examples 10 and 11. In this case, the activation energy was slightly reduced by substituting a small amount of oxygen, suggesting that a local structure suitable for ionic conduction was formed. On the other hand, when a large amount of oxygen was contained, as in comparative examples 8 and 9, the ionic conductivity was reduced.

[0121]

[0122] Example 8: Na ４ SiS ４ 0.083SiO ２ (Quenched) Sodium sulfide (Na ２S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ The inorganic sulfide (Na) powders of Example 8 were weighed and mixed so that the molar ratio was 2:1:2:0.083 instead of 2:1:2:0, and after the heat treatment, the mixture was rapidly cooled to room temperature at a cooling rate of about 1000°C / sec using an iron press. ４ SiS ４ 0.083SiO ２ ) was obtained.

[0123] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, which indicates that the inorganic sulfide was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 3.4 × 10 －５ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0124] Example 9: Na ４ SiS ４ 0.124SiO ２ (Quenched) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ The inorganic sulfide (Na) powders of Example 9 were weighed and mixed so that the molar ratio was 2:1:2:0.124 instead of 2:1:2:0, and after the heat treatment, the mixture was rapidly cooled to room temperature at a cooling rate of about 1000°C / sec using an iron press. ４ SiS ４ 0.124SiO ２ ) was obtained.

[0125] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, which indicates that the inorganic sulfide was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 3.6 × 10 －５ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0126] Example 10: Na ４ SiS ４ 0.165SiO ２ (Slow cooling) Sodium sulfide (Na ２S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ ) powders were weighed and mixed in a molar ratio of 2:1:2:0.165 instead of 2:1:2:0, in the same manner as in Comparative Example 1, except that the inorganic sulfide (Na ４ SiS ４ 0.165SiO ２ ) was obtained.

[0127] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, a trace amount of crystals (Na ４ SiS ４ Although a crystalline phase (3.0 wt%) was observed, it can be seen that the majority (97 wt%) was composed of a glass phase. The weight percentage of the crystalline phase was measured by the RIR method using alumina standard crystal powder. The electrical conductivity of the obtained inorganic sulfide at 25°C was 4.2 × 10 －５ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0128] Example 11: Na ４ SiS ４ 0.200SiO ２ (Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ ) powders were weighed and mixed in a molar ratio of 2:1:2:0.200 instead of 2:1:2:0, in the same manner as in Comparative Example 1, except that the inorganic sulfide (Na ４ SiS ４ 0.200SiO ２ ) was obtained.

[0129] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, which indicates that the inorganic sulfide was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 4.1 × 10 －５ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0130] Example 12: Na ４ SiS ４ 0.250SiO ２(Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ ) powders were weighed and mixed in a molar ratio of 2:1:2:0.250 instead of 2:1:2:0, and the inorganic sulfide (Na ４ SiS ４ 0.250SiO ２ ) was obtained.

[0131] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, which indicates that the inorganic sulfide was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 4.1 × 10 －５ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0132] Example 13: Na ４ SiS ４ 0.330SiO ２ (Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ ) powders were weighed and mixed in a molar ratio of 2:1:2:0.330 instead of 2:1:2:0, in the same manner as in Comparative Example 1, except that the inorganic sulfide (Na ４ SiS ４ 0.330SiO ２ ) was obtained.

[0133] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, which indicates that the inorganic sulfide was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 4.1 × 10 －５ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0134] Comparative Example 10: Na ４ SiS ４ 0.083SiO ２ (Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２) powders of Comparative Example 10 were weighed and mixed in a molar ratio of 2:1:2:0.083 instead of 2:1:2:0. ４ SiS ４ 0.083SiO ２ ) was obtained.

[0135] The inorganic sulfide obtained was opaque and devitrified, possibly due to the progress of crystallization. ４ SiS ４ Diffraction peaks attributable to crystalline phases were observed, and it was understood that almost no glass phase was formed. The electrical conductivity of the obtained inorganic sulfide at 25°C was 2.7 × 10 －７ The viscosity was insufficient at S / cm.

[0136] Comparative Example 11: Na ４ SiS ４ 0.124SiO ２ (Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ ) powders of Comparative Example 11 were weighed and mixed in a molar ratio of 2:1:2:0.124 instead of 2:1:2:0. ４ SiS ４ 0.124SiO ２ ) was obtained.

[0137] The inorganic sulfide obtained was opaque and devitrified, possibly due to the progress of crystallization. ４ SiS ４ Diffraction peaks attributable to crystalline phases were observed, and it was understood that no glass phase was formed. In addition, the electrical conductivity of the obtained inorganic sulfide at 25°C was 1.9 × 10 －７ The viscosity was insufficient at S / cm.

[0138] Example 14: Na ４ SiS ４ 0.400SiO ２ (Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２) powders were weighed and mixed in a molar ratio of 2:1:2:0.400 instead of 2:1:2:0, and the inorganic sulfide (Na ４ SiS ４ 0.400SiO ２ ) was obtained.

[0139] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, which indicates that the inorganic sulfide was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 2.8 × 10 －５ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0140] Example 15: Na ４ SiS ４ 0.500SiO ２ (Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ ) powders were weighed and mixed in a molar ratio of 2:1:2:0.500 instead of 2:1:2:0, in the same manner as in Comparative Example 1, except that the inorganic sulfide (Na ４ SiS ４ 0.500SiO ２ ) was obtained.

[0141] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, which indicates that the inorganic sulfide was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 2.3 × 10 －５ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0142] Example 16: Na ４ SiS ４ 0.700SiO ２ (Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ ) powders of Example 16 were weighed and mixed in a molar ratio of 2:1:2:0.700 instead of 2:1:2:0.４ SiS ４ 0.700SiO ２ ) was obtained.

[0143] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, which indicates that the inorganic sulfide was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 1.9 × 10 －５ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0144] Example 17: Na ４ SiS ４ 1.000SiO ２ (Slow cooling) Sodium sulfide (Na ２ S) powder, silicon (Si) powder, sulfur (S) powder, and silica (SiO ２ The inorganic sulfide (Na) powder of Example 17 was weighed and mixed in a molar ratio of 2:1:2:1.000 instead of 2:1:2:0 in the same manner as in Comparative Example 1. ４ SiS ４ 1.000SiO ２ ) was obtained.

[0145] The obtained inorganic sulfide was transparent and vitrified. Furthermore, as a result of X-ray diffraction measurement, no clear diffraction peaks were observed, which indicates that the inorganic sulfide was composed of a glass phase. Furthermore, the electrical conductivity of the obtained inorganic sulfide at 25°C was 6.5 × 10 －６ Even though oxygen atoms were contained, the film had a sufficient conductivity of 0.25 S / cm.

[0146] The results are shown in Table 3 and FIG.

[0147]

[0148] Next, the X-ray diffraction patterns of the inorganic sulfides obtained in Comparative Examples 1, 4, 10 and 11 and Examples 8 and 9 are shown in FIG. ４ SiS ４ The X-ray diffraction pattern of the crystal is also shown. Also, photographs of the appearance of the inorganic sulfides obtained in Comparative Examples 1, 10, and 11 are shown in FIG. 9. As a result, when cooling was performed slowly, SiO ２ If the content is low, Na ４ SiS４ While crystals are formed, SiO ２ On the other hand, when the cooling is rapid, the SiO ２ Even if the content is small, SiO ２ All the samples were vitrified except for Comparative Example 4, which was not composited at all.

[0149] Next, the X-ray diffraction patterns of the inorganic sulfides obtained in Examples 10 to 14 are shown in FIG. ４ SiS ４ The X-ray diffraction pattern of the crystal is also shown. ２ In Example 10, where the molar number of Na is 0.165, most of the Na is vitrified, and some of the Na is vitrified. ４ SiS ４ Although crystals remain, SiO ２ When the number of moles of sodium was further increased, glass formation occurred even when the cooling was slow. In other words, it was possible to produce glass with a high sodium content even when the cooling was slow.

[0150] The Raman spectra of the inorganic sulfides obtained in Examples 8 to 14 and Comparative Example 4 are shown in Figure 11. As a result, in all samples, SiS ４ A peak attributable to the Na unit was observed. ４ SiS ４ It is suggested that a glass having the same structure can be produced even if oxygen is added to SiS. ４－ｘ O ｘ Peaks attributable to SiO units were also observed. ２ As the amount added increases, oxysulfide units are formed, and SiO ２ It has been suggested that it is combined with

[0151] The inorganic sulfides obtained in Examples 8 to 14 and Comparative Example 4 ２９ The Si MAS-NMR spectrum is shown in Figure 12. In all samples, SiS ４ Peaks attributable to units, as well as SiS ３ ２－ Unit or SiS ３ A peak attributable to the O unit was observed, and a peak attributable to the Na ４SiS ４ It is suggested that glass with the same structure can be produced even if oxygen is added to SiS. ４ ４－ The intensity of the peaks assigned to the SiS units ３ ２－ Unit or SiS ３ The ratio of the intensity of the peak assigned to the SiS ４ ４－ Unit peak intensity / SiS ３ ２－ Unit or SiS ３ O unit) is the peak intensity of SiO ２ As the content increases, the vitrification region expands with the generation of oxysulfide units and crosslinking units, and therefore becomes smaller. Specifically, SiS ４ ４－ The intensity of the peaks assigned to the SiS units ３ ２－ Unit or SiS ３ The ratio of the intensity of the peak assigned to the SiS ４ ４－ Unit peak intensity / SiS ３ ２－ Unit or SiS ３ The peak intensity of the SiS unit was 6.62 in Comparative Example 4, 4.50 in Example 8, 3.61 in Example 9, 2.62 in Example 10, 2.65 in Example 11, 2.11 in Example 12, 1.96 in Example 13, and 2.08 in Example 14. In Examples 13 and 14, SiS was present at around -27 ppm. ２ O ２ Peaks attributed to have also been confirmed.

[0152] The results of differential scanning calorimetry (DSC) of the inorganic sulfides obtained in Examples 8 to 14 and Comparative Example 4 are shown in Figure 13. The differences between the glass transition temperature Tg and the crystallization temperature Tc of the inorganic sulfides obtained in Examples 8 to 14 and Comparative Example 4 are also shown in Figure 14. As a result, it was found that the difference between the glass transition temperature Tg and the crystallization temperature Tc was due to the presence of SiO ２As the content increases, the difference becomes larger due to the generation of oxysulfide units and crosslinking units. Specifically, the difference between the glass transition temperature Tg and the crystallization temperature Tc was 40.3°C in Comparative Example 4, 69.7°C in Example 8, 65.2°C in Example 9, 70.0°C in Example 10, 74.9°C in Example 11, 83.8°C in Example 12, 117.8°C in Example 13, and 134.2°C in Example 14.

Claims

1. Na ２ S component, SiS ２ Components and SiO ２ The total amount of the inorganic sulfides is taken as 100 mol %, and the Na ２ An inorganic sulfide having an S component content of 47.0 to 67.0 mol % and a glass phase being a main phase.

2. The total amount of the inorganic sulfides is taken as 100 mol %, and the SiS ２ The inorganic sulfide according to claim 1, wherein the content of the component is 23.0 to 33.0 mol%.

3. The total amount of the inorganic sulfides is taken as 100 mol %, and the SiO ２ The inorganic sulfide according to claim 1, wherein the content of the component is 2.0 to 27.0 mol%.

4. The inorganic sulfide according to claim 1, wherein the content of the glass phase is 80 to 100% by weight, with the total amount of the inorganic sulfide being 100% by weight.

5. General formula (1): Na ｘ１ SiS ｘ２－ｘ O ｘ (1) [wherein, 3.8≦x1≦4.2, 3.8≦x2≦4.2, and 0.05≦x≦0.65 are satisfied.], or general formula (2): Na ｙ１ SiS ｙ２ ySiO ２ (2) The inorganic sulfide according to claim 1, having a composition represented by the formula: [wherein, 3.8≦y1≦4.2, 3.8≦y2≦4.2, 0.010≦y≦1.500].

6. ２９ Si magic angle spinning nuclear magnetic resonance spectrum ( ２９ In the Si MAS-NMR spectrum, ４ ４－ The intensity of the peaks assigned to the SiS units ３ ２－ Unit or SiS ３ Ratio of the intensity of the peak assigned to the SiS ４ ４－ Unit peak intensity / SiS ３ ２－ Unit or SiS ３ The inorganic sulfide according to claim 1, wherein the peak intensity of the O unit is 1.8 to 5.

0.

7. The inorganic sulfide according to claim 1, wherein the difference between the glass transition temperature Tg and the crystallization temperature Tc is 65° C. or more.

8. A sodium ion conductive solid electrolyte containing the inorganic sulfide according to any one of claims 1 to 7.

9. A solid electrolyte for a sodium ion secondary battery, comprising the sodium ion conductive solid electrolyte according to claim 8.

10. A sodium ion secondary battery comprising the solid electrolyte for sodium ion secondary batteries according to claim 9.

11. The sodium ion secondary battery according to claim 10, which is an all-solid-state sodium ion secondary battery.

12. A method for producing an inorganic sulfide according to any one of claims 1 to 7, comprising: (1) Na ２ S, Si, S and SiO ２ (2) a step of heating the mixture obtained in step (1); and (3) a step of cooling the heat-treated product obtained in step (2). ｘ１ SiS ｘ２－ｘ O ｘ (1A) [wherein 3.8≦x1≦4.2, 3.8≦x2≦4.2, and 0.05≦x≦0.30], and in the step (1), a compound represented by the general formula (2A): Na ｙ１ SiS ｙ２ ySiO ２ (2A) A production method, in which, when mixing is performed so as to have a composition represented by the formula: [wherein, 3.8≦y1≦4.2, 3.8≦y2≦4.2, 0.010≦y≦0.150], the cooling is rapid cooling or air cooling.

13. The method according to claim 12, wherein the heating temperature in step (2) is 400 to 1000°C.

14. The method according to claim 12, wherein the rapid cooling in the step (3) is a cooling treatment at a cooling rate of 100° C. / sec or more.

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