Method for producing sulfide solid electrolyte powder

Abstract

The present invention pertains to a method for producing sulfide solid electrolyte powder, including: mixing raw materials to obtain a raw material mixture; synthesizing at least one of a sulfide powder and a sulfide precursor powder from the raw material mixture; and performing heat treatment on the synthesized powder in a heating furnace, wherein the heat treatment is performed with inert gas circulating through the heating furnace, and when the volume of the heating furnace is defined as A (L) and the flow rate of the inert gas is defined as B (L / h), a substitution rate B / A is at least 0.3 / h.

Description

Method for producing sulfide solid electrolyte powder

[0001] This invention relates to a method for producing sulfide solid electrolyte powder.

[0002] Lithium-ion rechargeable batteries are widely used in portable electronic devices such as mobile phones and laptop computers. Traditionally, lithium-ion rechargeable batteries have used liquid electrolytes. However, in recent years, all-solid-state lithium-ion rechargeable batteries, which use solid electrolytes, have attracted attention due to the potential for improved safety, faster charging and discharging, and smaller case sizes.

[0003] Examples of solid electrolytes used in all-solid-state lithium-ion secondary batteries include sulfide solid electrolytes.

[0004] Methods for synthesizing sulfide solid electrolytes include a method in which the raw material mixture is mechanically milled and then calcined (solid-phase reaction method), and a method in which the raw material mixture is heated and melted to prepare a melt, which is then cooled and solidified (melting method).

[0005] As an example of a sulfide solid electrolyte, Patent Document 1 discloses a sulfide solid electrolyte containing an argyrodite-type crystal structure, and discloses a method for producing an argyrodite-type solid electrolyte with small particle size and high ionic conductivity, which involves heat-treating a solid electrolyte precursor at a predetermined temperature.

[0006] Furthermore, Patent Document 2 discloses a method for stabilizing the crystal structure of a sulfide solid electrolyte and removing impurities such as sulfur attached to the particle surface by heat-treating at least one of a sulfide powder and a sulfide precursor powder synthesized from a raw material mixture, and then cooling it under specific conditions.

[0007] Japanese Patent Publication No. 2019-36536 Japanese Patent No. 7420296

[0008] As described in Patent Document 2, it was known that when sulfide precursor powders in solid-phase reaction methods or sulfide powders in melting methods are subjected to heat treatment, the crystalline structure of the resulting sulfide solid electrolyte powder is stabilized, i.e., the quality is stabilized. Furthermore, as mentioned above, it was also known that in the case of sulfide precursor powders, heat treatment can cause the powder to be calcined to obtain sulfide solid electrolyte powder.

[0009] As a result of diligent research, the inventors have found that the above-described heat treatment not only stabilizes the quality of the sulfide solid electrolyte powder, but also removes excess sulfur contained in the sulfide powder or sulfide precursor powder before heat treatment, promoting the rearrangement of the crystal structure of the sulfide solid electrolyte powder and improving the lithium ion conductivity.

[0010] However, it was found that when the sulfur concentration in the heat treatment atmosphere is high, the above-mentioned excessive sulfur desorption is less likely to occur.

[0011] Therefore, the present invention aims to provide a method for producing a sulfide solid electrolyte powder that exhibits high lithium ion conductivity.

[0012] One aspect of the present invention relates to a method for producing a sulfide solid electrolyte powder, comprising: mixing raw materials to obtain a raw material mixture; synthesizing at least one of sulfide powder and sulfide precursor powder from the raw material mixture; and heat-treating the powder in a heating furnace, wherein the heat treatment is performed while flowing an inert gas through the heating furnace, and when the volume of the heating furnace is A (L) and the flow rate of the inert gas is B (L / h), the substitution rate expressed as B / A is 0.3 / h or more.

[0013] According to the manufacturing method of the present invention, a sulfide solid electrolyte powder exhibiting high lithium ion conductivity can be produced.

[0014] Figure 1 is a flow chart showing a method for producing sulfide solid electrolyte powder according to this embodiment. Figure 2 is a flow chart showing one aspect of the method for producing sulfide solid electrolyte powder according to this embodiment. Figure 3 is a flow chart showing another aspect of the method for producing sulfide solid electrolyte powder according to this embodiment. Figure 4 is a perspective view showing one aspect of an apparatus that can be used for producing sulfide solid electrolyte powder according to this embodiment.

[0015] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified and implemented as appropriate without departing from the spirit of the invention. Furthermore, the "~" indicating a numerical range is used to mean that the numbers written before and after it are included as the lower limit and upper limit.

[0016] [Method for producing sulfide solid electrolyte powder] The method for producing sulfide solid electrolyte powder according to this embodiment (hereinafter also referred to as "this production method") includes the following steps S1 to S3 in order, as shown in Figure 1. Step S1 is a step of mixing raw materials to obtain a raw material mixture. Step S2 is a step of synthesizing at least one of sulfide powder and sulfide precursor powder from the raw material mixture obtained in step S1. Step S3 is a step of heat-treating the powder obtained in step S2 in a heating furnace.

[0017] When the manufacturing method is a melting method, in step S2, it is preferable to obtain a powder containing sulfide powder by cooling the molten material obtained by heating the raw material mixture, and it is more preferable to obtain a powder containing sulfide powder by cooling and pulverizing the molten material. Specifically, it is even more preferable that step S2 includes steps S2a-1 to S2a-3, as shown in Figure 2.

[0018] Step S2a-1 is a step in which the raw material mixture obtained in step S1 is heated and melted to obtain a molten product. Step S2a-2 is a step in which the molten product obtained in step S2a-1 is cooled to obtain a solid sulfide. Step S2a-3 is a step in which the solid sulfide obtained in step S2a-2 is crushed to obtain sulfide powder.

[0019] In step S2a-2, the powder may be obtained while cooling the melt. In this case, since step S2a-2 also serves as the grinding step in S2a-3, the sulfide powder can be obtained without going through the grinding step in S2a-3 separately. Examples of methods for obtaining the powder while cooling the melt include spray cooling, dropping into a cooling medium, and gas atomization.

[0020] By performing the heat treatment in step S3 on the sulfide powder obtained in steps S2a-3 under predetermined conditions, excess sulfur is removed, promoting rearrangement of the crystal structure, and a sulfide solid electrolyte powder with stabilized quality is obtained. This rearrangement and stabilization increases the lithium ion conductivity of the sulfide solid electrolyte powder, improving battery performance when applied to lithium-ion secondary batteries.

[0021] When this manufacturing method is a solid-phase reaction method, in step S2, it is preferable to obtain a powder containing sulfide precursor powder by mechanical milling the raw material mixture. Specifically, it is preferable that step S2 includes step S2b, as shown in Figure 3.

[0022] Step S2b is a process in which the raw material mixture obtained in step S1 is mechanically milled to obtain sulfide precursor powder.

[0023] By subjecting the sulfide precursor powder obtained in step S2b to the heat treatment in step S3, a sintered body is formed from the calcined sulfide precursor powder, yielding sulfide solid electrolyte powder. Furthermore, by performing the heat treatment in step S3 under predetermined conditions, excess sulfur is removed, promoting the rearrangement of the crystal structure, and resulting in a sulfide solid electrolyte powder with stabilized quality. This rearrangement and stabilization enhances the lithium-ion conductivity of the sulfide solid electrolyte powder, improving battery performance when applied to lithium-ion secondary batteries.

[0024] Let's explain each step.

[0025] Step S1: In Step S1, raw materials are mixed to obtain a raw material mixture. Depending on the composition of the sulfide solid electrolyte powder to be obtained, for example, raw materials containing Li, raw materials containing P, and raw materials containing S are mixed to obtain a raw material mixture. When obtaining a sulfide solid electrolyte powder containing an argyrodite-type crystal structure, in addition to raw materials containing Li, raw materials containing P, and raw materials containing S, raw materials containing Ha are also used. In this specification, Ha (halogen element) is at least one element selected from the group consisting of F, Cl, Br, and I. When obtaining a sulfide solid electrolyte powder consisting of sulfide-based crystallized glass as described later, raw materials containing Li, raw materials containing P, and raw materials containing S are mixed, and each raw material is mixed to obtain a raw material mixture so that the composition of the resulting sulfide-based glass satisfies Li: 30-42% and P: 5-16% in atomic percent.

[0026] The raw materials may contain other elements to match the desired composition of the sulfide solid electrolyte powder. Matching the composition of the sulfide solid electrolyte powder means, for example, if some of the elements such as Li, P, and S are substituted with other elements, the raw materials may also contain the other elements that have been substituted. Examples of other elements include Si, Al, Sn, In, Cu, Sb, Ge, B, O, Ga, C, Mg, Ca, Sr, Ba, Se, and N.

[0027] As raw materials containing Li, P, and S, and optionally Ha, conventionally known raw materials can be used. Specifically, Li element or Li-containing compounds, P element or P-containing compounds, S element or S-containing compounds, and optionally Ha-containing compounds can be used in appropriate combinations. If the sulfide solid electrolyte powder contains O element, an oxide may be used as the above compound. Furthermore, the above compound may be a compound containing two or more of Li, P, and S, and optionally Ha. For example, as a compound that is both an S-containing compound and a P-containing compound, diphosphorus pentasulfide (P ２ S５ ), and the like. Further, as a compound that serves both as a Li-containing compound and a Ha-containing compound, lithium halide may be mentioned.

[0028] As raw materials containing Li element, in addition to metallic lithium, examples of Li-containing compounds include lithium sulfide (Li ２ S), lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２ O), and lithium compounds such as lithium hydroxide (LiOH), etc. may be mentioned. As the raw material containing Li element, lithium sulfide is preferable from the viewpoints of ease of handling and reactivity. On the other hand, since lithium sulfide is expensive, lithium compounds other than lithium sulfide, metallic lithium, etc. are preferable from the viewpoint of suppressing production costs. Specifically, it is preferable to use one or more selected from the group consisting of metallic lithium, lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２ O) and lithium hydroxide (LiOH). These may be used alone, or may be used in combination of two or more kinds.

[0029] As raw materials containing S element, in addition to elemental sulfur, examples of S-containing compounds include phosphorus trisulfide (P ２ S ３ ), phosphorus pentasulfide (P ２ S ５ ), other sulfur compounds containing phosphorus, and sulfur-containing compounds, etc. may be mentioned. Examples of sulfur-containing compounds include H ２ S, CS ２ , FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S and other iron sulfides, bismuth sulfide (Bi ２ S ３ ), CuS, Cu ２ S, Cu １－ｘExamples include copper sulfide such as S. From the viewpoint of reactivity and preventing the inclusion of elements other than those constituting the target sulfide solid electrolyte powder, phosphorus sulfide is preferred as the raw material containing element S, and diphosphorus pentasulfide (P) ２ S ５ ) is more preferable. These may be used individually or in combination of two or more. Note that phosphorus sulfide is a compound that contains both sulfur and phosphorus.

[0030] As raw materials containing element P, in addition to elemental phosphorus, as a compound containing P, for example, diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) such as phosphorus sulfide, sodium phosphate (Na ３ PO ４ ) and lithium thiophosphate (Li ３ PS ４－ｘ O ｘ Examples include phosphorus compounds such as ) and others. From the viewpoint of preventing the inclusion of elements other than those constituting the target sulfide solid electrolyte powder, phosphorus sulfide is preferred as the raw material containing element P, and diphosphorus pentasulfide (P ２ S ５ ) is more preferable. These may be used individually or in combination of two or more. Also, if the raw material containing element P contains an oxide, for example, P ２ O ５ Li ３ PO ４ Li ４ P ２ O ７ These are some examples. In particular, from the perspective of ease of manufacturing, P ２ O ５ This is preferable. These compounds may be used individually or in combination of two or more.

[0031] As optional components, examples of compounds containing Ha, which are raw materials containing the element Ha, include lithium halides such as lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), as well as phosphorus halides, phosphoryl halides, sulfur halides, sodium halides, and boron halides. From the viewpoint of preventing the inclusion of elements other than those constituting the target sulfide solid electrolyte powder, lithium halides are preferred as raw materials containing the element Ha, and LiCl, LiBr, and LiI are more preferred. These compounds may be used individually or in combination of two or more.

[0032] Furthermore, lithium halides are also compounds containing Li. When the raw materials contain lithium halides, some or all of the Li in the raw materials may be derived from lithium halides.

[0033] If the sulfide solid electrolyte powder contains elements other than Li, S, P, and Ha, the raw materials containing these other elements are also mixed to obtain the raw material mixture.

[0034] As an optional component, raw materials containing the element Si include, for example, SiO ２ SiS ２ These include SiO2, which is particularly important from the standpoint of lithium-ion conductivity and water resistance. ２ This is more preferable. These compounds may be used individually or in combination of two or more.

[0035] As an optional component, a raw material containing the element Al is, for example, Al ２ S ３ Al ２ O ３ AlCl ３ These include, in particular, Al ２ S ３ AlCl ３ Preferably, Al ２ S ３ This is more preferable. These compounds may be used individually or in combination of two or more.

[0036] As an optional component, examples of raw materials containing Sn element include SnS, SnS ２ , SnO, SnO ２ , SnCl ２ . Among these, from the perspective of lithium ion conductivity, SnS ２ , SnCl ２ are preferable, and SnS ２ is more preferable. These compounds may be used alone or in combination of two or more kinds.

[0037] As an optional component, examples of raw materials containing In element include In ２ O ３ , In ２ S ３ , InCl ３ . Among these, from the perspective of lithium ion conductivity, In ２ S ３ , InCl ３ are preferable, and In ２ S ３ is more preferable. These compounds may be used alone or in combination of two or more kinds.

[0038] As an optional component, examples of raw materials containing Cu element include Cu ２ O, CuO, Cu ２ S, CuS, CuCl ２ . Among these, from the perspective of lithium ion conductivity, CuS and CuCl ２ are preferable, and CuS is more preferable. These compounds may be used alone or in combination of two or more kinds.

[0039] As an optional component, examples of raw materials containing Sb element include Sb ２ O ３ , Sb ２ S ３ , SbCl ３ . Among these, from the perspective of lithium ion conductivity, Sb ２ S ３ , SbCl ３ are preferable, and Sb ２ S ３is more preferred. These compounds may be used alone or in combination of two or more kinds.

[0040] As an optional component, examples of raw materials containing a Ge element include GeO ２ , GeS, GeS ２ , GeCl ２ and the like. Among these, from the viewpoint of lithium ion conductivity, GeS ２ , GeCl ２ are preferred, and GeS ２ is more preferred. These compounds may be used alone or in combination of two or more kinds.

[0041] As an optional component, examples of raw materials containing a B element include B ２ S ３ , B ２ O ３ , BCl ３ and the like. Among these, from the viewpoint of lithium ion conductivity, B ２ S ３ , BCl ３ are preferred, and B ２ S ３ is more preferred. These compounds may be used alone or in combination of two or more kinds.

[0042] As an optional component, examples of raw materials containing a Ga element include Ga, Ga ２ O ３ , Ga ２ S ３ , GaCl ３ and the like. Among these, from the viewpoint of lithium ion conductivity, Ga ２ S ３ , GaCl ３ are preferred, and Ga ２ S ３ is more preferred. These compounds may be used alone or in combination of two or more kinds.

[0043] As an optional component, examples of raw materials containing a C element include Li ２ CO ３ , Li ２ C ２ , CaCO ３These are some examples. In particular, from the standpoint of availability and lithium-ion conductivity, Li ２ CO ３ This is preferable. These compounds may be used individually or in combination of two or more.

[0044] As an optional component, raw materials containing the element Mg include, for example, Mg, MgO, MgS, and MgBr. ２ MgI ２ These are some examples. In particular, from the viewpoint of ease of solubility, Mg and MgBr ２ Preferably, MgBr ２ This is more preferable. These compounds may be used individually or in combination of two or more.

[0045] As an optional component, raw materials containing the element Ca include, for example, Ca, CaO, CaS, and CaBr. ２ CaI ２ These are some examples. In particular, from the viewpoint of ease of solubility, CaBr ２ CaI ２ This is preferable. These compounds may be used individually or in combination of two or more.

[0046] As an optional component, raw materials containing the element Sr include, for example, Sr, SrO, SrS, and SrBr. ２ , SrI ２ These are some examples. In particular, from the viewpoint of ease of solubility, SrBr ２ , SrI ２ Preferably, SrI ２ This is more preferable. These compounds may be used individually or in combination of two or more.

[0047] As an optional component, raw materials containing the element Ba include, for example, Ba, BaO, BaS, and BaBr. ２ These are some examples. Among them, Ba is preferred from the viewpoint of ease of solubility. These compounds may be used individually or in combination of two or more.

[0048] As an optional component, raw materials containing element Se include, for example, Se, Li ２ Se, P ２ See ５These are some examples. Among them, Se is preferred from the viewpoint of availability. These compounds may be used individually or in combination of two or more.

[0049] As an optional component, a raw material containing element N is, for example, Li ３ N, LiNO ３ , P ３ N ５ These are some examples. In particular, from the perspective of procurement, Li ３ N, LiNO ３ Preferably, LiNO ３ This is more preferable. These compounds may be used individually or in combination of two or more.

[0050] Raw materials can be mixed by methods such as mortar and pestle, media-based mixing like a planetary ball mill, or media-less mixing like a pin mill, powder agitator, or airflow mixing.

[0051] However, when this manufacturing method is carried out by a solid-phase reaction method, in the subsequent step S2, mechanical milling in step S2b is performed to obtain either a sulfide precursor powder, which is a more homogeneous mixture of raw material components, or a sulfide precursor powder, which is an amorphous compound. In this mechanical milling process in step S2b, a chemical reaction occurs, and energy is applied to such an extent that the bonding state of the elements changes. When this manufacturing method is carried out by a solid-phase reaction method, the mixing in step S1 refers to a degree of mixing such as putting multiple raw materials into one container or mixing the raw materials in that container with a mortar and pestle or stirring blade, in preparation for step S2b.

[0052] Step S2: In Step S2, at least one of sulfide powder and sulfide precursor powder is synthesized from the raw material mixture obtained in Step S1. When sulfide solid electrolyte powder is produced by the melting method, a powder containing sulfide powder is obtained in Step S2. When sulfide solid electrolyte powder is produced by the solid-phase reaction method, a powder containing sulfide precursor powder is obtained in Step S2.

[0053] In the melting method, as mentioned above, steps S2a-1 to S2a-3 are performed. In step S2a-1, the raw material mixture obtained in step S1 is heated and melted to obtain a molten product.

[0054] The specific method for heating and melting the raw material mixture in step S2a-1 is not particularly limited; the raw materials may be placed in a heat-resistant container and heated in a heating furnace. The raw material mixture may also be sealed in a heat-resistant container. Alternatively, the melting may be carried out in an atmosphere containing sulfur elements. An atmosphere containing sulfur elements may include a mixed gas atmosphere of sulfur-containing gases such as sulfur gas, hydrogen sulfide gas, and sulfur dioxide gas, and an inert gas.

[0055] Examples of the above-mentioned inert gases include nitrogen gas, argon gas, and helium gas, and these may be used individually or in mixtures of two or more.

[0056] As heat-resistant containers, heat-resistant containers made of carbon, heat-resistant containers containing oxides such as quartz, quartz glass, borosilicate glass, aluminosilicate glass, alumina, zirconia, and mullite, heat-resistant containers containing nitrides such as silicon nitride and boron nitride, and heat-resistant containers containing carbides such as silicon carbide may be used. Furthermore, these heat-resistant containers may be formed in bulk from the above materials, or they may be containers with layers of carbon, oxides, nitrides, carbides, etc. formed on the surface, such as carbon-coated quartz tubes.

[0057] The heating temperature when heating and melting the raw material mixture varies depending on the raw materials used and the composition of the raw material mixture, but for example, 550 to 1000°C is preferred, 600 to 950°C is more preferred, 630 to 900°C is even more preferred, and 650 to 850°C is particularly preferred. Here, from the viewpoint of increasing the melting properties of the raw materials and homogenizing the melt in a short time, a heating temperature of 550°C or higher is preferred, 600°C or higher is more preferred, 630°C or higher is even more preferred, and 650°C or higher is particularly preferred. Furthermore, from the viewpoint of suppressing deterioration of components due to heating, suppressing compositional deviations due to volatilization of components, and suppressing decomposition, a heating temperature of 1000°C or lower is preferred, 950°C or lower is more preferred, 900°C or lower is even more preferred, and 850°C or lower is particularly preferred.

[0058] The heating and melting time varies depending on the scale, but is preferably 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, even more preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. From the viewpoint of ensuring the reaction proceeds well, the heating and melting time is preferably 10 minutes or more, more preferably 30 minutes or more, even more preferably 45 minutes or more, and particularly preferably 1 hour or more. Also, from the viewpoint of productivity, the heating and melting time is preferably 10 hours or less, more preferably 9.5 hours or less, and even more preferably 9 hours or less.

[0059] The pressure during heating and melting is not particularly limited, but atmospheric pressure or slight pressure is preferred, and atmospheric pressure is more preferred. In this specification, atmospheric pressure means a pressure range of approximately (gauge pressure ± 15 kPa). Gauge pressure means atmospheric pressure, and in this specification it is defined as 101.3 kPa.

[0060] The dew point during heating and melting is preferably -20°C or lower, and although there is no particular lower limit, it is usually around -80°C.

[0061] The oxygen concentration in the atmosphere during heating and melting is preferably 1000 ppm by volume or less.

[0062] In step S2a-1, complete dissolution of the molten material can be confirmed by the absence of crystal-derived peaks in high-temperature X-ray diffraction measurements.

[0063] In the subsequent step S2a-2, the molten material obtained in step S2a-1 is cooled to obtain a solid sulfide. The solid obtained here is a sulfide compound and may contain crystals, or it may consist of amorphous glass that does not contain a crystalline phase, for example. This sulfide can also function as a solid electrolyte, but it lacks homogeneity because it has not gone through the subsequent step S3.

[0064] Cooling can be carried out by known methods, and the method is not particularly limited. More specific cooling methods include, for example, pouring the molten material onto a plate-like body made of carbon or the like and cooling it; pouring it into a narrow gap and forming it into a thin layer, as exemplified by the twin-roll method; and spraying the molten material and cooling it in the air.

[0065] When obtaining sulfide solid electrolyte powder containing crystalline structures such as argyrodite, the cooling rate is preferably 0.1 to 10,000°C / second, more preferably 0.5 to 5,000°C / second, and even more preferably 1 to 1,000°C / second. From the viewpoint of improving compositional homogeneity and suppressing variations in quality, the cooling rate is preferably 0.1°C / second or higher, more preferably 0.5°C / second or higher, and even more preferably 1°C / second or higher. Furthermore, there is no particular upper limit to the cooling rate, but considering the cooling rate of twin rollers, which are generally said to have the fastest rapid cooling rate, the upper limit is 1,000,000°C / second or less. From the viewpoint of actual production, the cooling rate is more preferably 10,000°C / second or less, even more preferably 5,000°C / second or less, and even more preferably 1,000°C / second.

[0066] On the other hand, when obtaining a sulfide solid electrolyte powder made of sulfide-based crystallized glass as described later, the cooling rate is preferably 100 to 100,000°C / second, more preferably 200 to 50,000°C / second, and even more preferably 300 to 10,000°C / second. By using ultra-rapid cooling of 100°C / second or more, which is faster than conventional methods, even compositions that would conventionally result in crystal precipitation can be solidified as glass. This significantly increases the degree of freedom in composition, and allows for the selection of compositions that exhibit high lithium ion conductivity. Furthermore, by performing the above cooling and solidification process so that the molten material is cooled uniformly and there are no thermal inconsistencies, a higher lithium ion conductivity can be achieved compared to conventional glass. As a result, the lithium ion conductivity of the crystallized glass obtained by heat-treating the glass can also be increased. In addition, by performing the above cooling and solidification process under atmospheric pressure conditions, the compositional discrepancy between the composition of the raw material mixture and the composition of the resulting glass can be reduced. From the viewpoint of ease of glass formation, the above cooling rate is preferably 100°C / second or more, more preferably 200°C / second or more, and even more preferably 300°C / second or more. Furthermore, there is no particular upper limit to the cooling rate, but from the viewpoint of equipment capacity, it is preferably 100,000°C / second or less, more preferably 50,000°C / second or less, and even more preferably 10,000°C / second or less. Such ultra-rapid cooling can be achieved, for example, by using a rapid cooling twin roll.

[0067] The atmosphere during cooling is preferably a low-moisture, inert atmosphere, similar to the atmosphere during heating and melting in step S2a-1.

[0068] In the following step S2a-3, the solid sulfide obtained in step S2a-2 is pulverized to obtain sulfide powder. Here, either wet pulverization or dry pulverization may be used, but unlike the fine pulverization performed when using it as a solid electrolyte in lithium-ion secondary batteries, as will be described later, it is preferable to pulverize it until, for example, the average particle diameter is 5 to 300 μm. In this specification, the average particle diameter refers to the median diameter (D50), which means that 50% of the particles have a particle diameter of that value or less, and is determined from the volume-based particle size distribution chart obtained by measuring the particle size distribution using a particle size distribution analyzer using the laser diffraction method.

[0069] Step S2a-3 may be omitted if the sulfide obtained in step S2a-2 is a powder with an average particle size of about 1 to 100 μm.

[0070] In the solid-phase reaction method, as mentioned above, step S2b involves mechanically milling the raw material mixture obtained in step S1 to obtain a sulfide precursor powder, which is referred to as synthesis. The mechanical milling method is not particularly limited as long as it is a method of mixing multiple raw materials that will become the sulfide solid electrolyte powder while applying mechanical energy, but examples of mechanical milling include ball mills such as planetary ball mills, vibratory mills, turbo mills, mechanofusions, and disc mills.

[0071] When using a planetary ball mill, the rotational speed of the base plate is preferably, for example, 100 to 500 rpm, and the processing time is preferably, for example, 1 to 100 hours, and more preferably 1 to 50 hours.

[0072] The material and size of the container and grinding balls used in the planetary ball mill are not particularly limited, and conventionally known materials can be used. Examples of materials include alumina, zirconia, glass, and silicon nitride. The diameter of the grinding balls is, for example, 0.3 to 20 mm.

[0073] Mechanical milling can be performed dry or wet. When performing mechanical milling wet, it is preferable to use a dispersion medium that does not react with each raw material to generate hydrogen sulfide or the like.

[0074] When mechanical milling is performed using a wet method, it is preferable to dry the sulfide precursor powder before the subsequent step S3. The drying method is not particularly limited and can be, for example, an external heat drying oven or a hot air circulation drying oven.

[0075] Unlike sulfide powders obtained by melting, which contain crystals that function as solid electrolytes, sulfide precursor powders are powders of mixtures in which multiple raw materials are mixed very homogeneously, powders in which the chemical bonding state has changed from the starting materials through reaction, or powders of amorphous compounds.

[0076] For use in the subsequent step S3, the average particle size of the sulfide powder or sulfide precursor powder obtained in step S2 is preferably 0.3 to 5000 μm, more preferably 1.0 to 1000 μm, even more preferably 3.0 to 500 μm, and particularly preferably 5.0 to 300 μm. Here, from the viewpoint of suppressing scattering during the heat treatment, the average particle size of the powder is preferably 0.3 μm or more, more preferably 1.0 μm or more, even more preferably 3.0 μm or more, and particularly preferably 5.0 μm or more. Furthermore, from the viewpoint of making the effects of the subsequent heat treatment more readily apparent and making it easier to use for subsequent fine grinding, the average particle size of the powder is preferably 5000 μm or less, more preferably 1000 μm or less, even more preferably 500 μm or less, and particularly preferably 300 μm or less.

[0077] In the sulfide powder or sulfide precursor powder obtained in step S2, the excess percentage of sulfur S is compared to the stoichiometric composition of the raw material mixture. αIt is preferable that the sulfur content be 0.1% by mass or more. The excess sulfur content compared to the stoichiometric composition is determined by subtracting the proportion of sulfur (mass%) in the stoichiometric ratio (composition of the raw material mixture) from the measured proportion (mass%) of sulfur (S) contained in the sample. The proportion of sulfur (S) contained in the sample is quantified by combustion in an oxygen stream - infrared absorption method. Specifically, the sample is sealed in an Sn container in a glove box with a dew point of -50°C or lower, and the lid is closed. Then the container is set in the instrument (Horiba, Ltd., carbon-sulfur analyzer "EMIA-expert") and the analysis is performed.

[0078] From the viewpoint of lithium ion conductivity of sulfide solid electrolyte powder, the excess percentage of sulfur S in the powder obtained in step S2 compared to the stoichiometric composition of the raw material mixture α The excess amount of sulfur S is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1.0% by mass or more. Furthermore, from the viewpoint of reducing conductivity, the excess amount of sulfur S is also preferable. α The excess amount of sulfur S is preferably 15.0% by mass or less, more preferably 10.0% by mass or less, and even more preferably 5.0% by mass or less. α This may be, for example, 0.1 to 15.0 mass%.

[0079] Excess proportion S of sulfur mentioned above α This can be prepared, for example, by adding elemental sulfur or a sulfur-containing compound to the raw material mixture and performing the synthesis in step S2 above. In the melting method, in addition to the above, S can also be prepared by performing the heating and melting in step S2a-1 in an atmosphere containing sulfur elements. α It can be adjusted.

[0080] Step S3: In Step S3, the powder obtained in Step S2 is heat-treated. The sulfide powder obtained by the melting method becomes a sulfide solid electrolyte powder whose quality is stabilized and whose crystal structure is rearranged by the heat treatment in Step S3, as described above. Furthermore, if the sulfide powder consists of amorphous glass that does not contain a crystalline phase, the heat treatment in Step S3 causes crystals to precipitate, resulting in a sulfide solid electrolyte powder consisting of crystallized glass that contains a crystalline phase. The sulfide precursor powder obtained by the solid-phase reaction method becomes a sulfide solid electrolyte powder, which is the powder of a calcined sintered body, by the heat treatment in Step S3, and whose quality is stabilized and whose crystal structure is rearranged, as described above.

[0081] One embodiment of the heat treatment in step S3 will be described with reference to Figure 4. An example of a device that can be used for the heat treatment is a continuous heating furnace 100. The heating furnace 100 has a heating furnace body 10, an inert gas supply port 12, and an inert gas outlet 14. This allows the heat treatment to be carried out while circulating an inert gas within the heating space 11 of the heating furnace body 10. During the heat treatment, at least one of the sulfide powder and sulfide precursor powder 30 obtained in step S2 is placed into a container 20. As shown by the arrow in Figure 4, the container 20 moves from the heating furnace inlet 16, through the heating space 11 of the heating furnace body 10, to the heating furnace outlet 18. In this way, the powder obtained in step S2 is heat treated. Note that the inside of the heating furnace body 10 may be provided with an insulating material or the like (not shown).

[0082] Although a continuous heating furnace was used as an example above, the heating process in step S3 may also be carried out in a batch heating furnace.

[0083] The heat treatment is carried out in a heating furnace while an inert gas is circulated through the furnace. Examples of the inert gas include nitrogen gas, argon gas, and helium gas, and these may be used individually or in a mixture of two or more.

[0084] In the heat treatment step S3 of this manufacturing method, when the volume of the heating furnace is A (L) and the flow rate of the inert gas is B (L / h), the substitution rate expressed as B / A is 0.3 / h or more. According to the inventors' studies, it was found that when the sulfur concentration in the atmosphere during the heat treatment is high, the desorption of excess sulfur contained in the sulfide powder or sulfide precursor powder is difficult to occur from the viewpoint of chemical equilibrium. In contrast, it was found that by setting the ratio of the flow rate of the inert gas to the volume of the heating furnace, i.e., the substitution rate of the heating furnace by the inert gas to a predetermined value or higher, the sulfur concentration in the atmosphere during the heat treatment can be reduced and the desorption of excess sulfur can be promoted. It is presumed that this promotes the rearrangement of the crystal structure of the sulfide solid electrolyte powder and improves the lithium ion conductivity. The above "volume of the heating furnace" means the volume of the region heated during the heat treatment. Here, if the heating furnace has an insulating material or the like inside, the above "volume of the region heated during the heat treatment" also includes the volume occupied by the insulating material or the like.

[0085] From the viewpoint of sufficiently reducing the sulfur concentration in the heat treatment atmosphere, the substitution rate expressed as B / A is 0.3 / h or more, preferably 0.5 / h or more, more preferably 1.0 / h or more, and even more preferably 2.0 / h or more. The upper limit of the substitution rate B / A is not particularly limited, but it is usually 100 / h or less. The substitution rate B / A may be, for example, 0.3 to 100 / h.

[0086] In the sulfide powder or sulfide precursor powder obtained in step S2, the excess proportion of sulfur compared to the stoichiometric composition of the raw material mixture is S α (mass%), when the above substitution rate is B / A( / h), S α The value expressed as / (B / A) is preferably 20% by mass·h or less. From the viewpoint of promoting the desorption of excess sulfur contained in the powder, S α The value of / (B / A) is preferably 20% by mass·h or less, more preferably 18% by mass·h or less, and even more preferably 15% by mass·h or less. α The lower limit of the value of / (B / A) is not particularly limited, but it is usually 0.1 mass%·h or higher, and may also be 1 mass%·h or higher. αThe value of / (B / A) may be, for example, 0.1 to 20 mass%·h.

[0087] During heat treatment, the sulfide powder or sulfide precursor powder may be placed in a container and then placed in a heating furnace. While there are no particular restrictions on the container used for the sulfide powder or sulfide precursor powder, any heat-resistant container is preferable. However, from the viewpoint of preventing contamination, ceramic containers such as alumina, zirconia, and mullite are preferred. Furthermore, containers made of electronically conductive materials such as carbon or corrosion-resistant metals can be used in applications where electronic conductivity is acceptable.

[0088] The container capacity can be adjusted as appropriate depending on the amount processed by this manufacturing method.

[0089] The container should preferably have a low height and a wide base. This helps to suppress the powder from being compressed and agglomerating under its own weight.

[0090] Specifically, when a container is used to hold sulfide powder or sulfide precursor powder during heat treatment, it is preferable that the relationship 2a > b is satisfied, and more preferably that the relationship 1.5a > b is satisfied, where a is the longest side of the bottom and b is the height.

[0091] Examples of containers with base shapes other than rectangular include circles (including perfect circles and ellipses) and polygons. When the base shape is circular, the longest side of the base refers to the longest side of the square or rectangle in which the circle is inscribed. When the base shape is triangular, the longest side is defined as the longest side of the base. When the base shape is a polygon with five or more sides, the longest diagonal is defined as the longest side of the base.

[0092] The heating temperature in the heat treatment varies depending on the composition of the target sulfide solid electrolyte powder, but is preferably, for example, 150 to 500°C. Here, from the viewpoint of homogenizing the particles and stabilizing the quality, the heating temperature is preferably 150°C or higher, more preferably 170°C or higher, even more preferably 190°C or higher, and particularly preferably 200°C or higher. Furthermore, from the viewpoint of suppressing deterioration and decomposition of components in the powder due to heating, the heating temperature is preferably 500°C or lower, more preferably 480°C or lower, even more preferably 460°C or lower, and particularly preferably 450°C or lower.

[0093] In particular, when the obtained sulfide solid electrolyte powder has an argyrodite-type crystal structure, the heating temperature in the heat treatment is preferably 300 to 500°C. Here, from the viewpoint of homogenizing the particles and stabilizing the quality, the heating temperature is preferably 300°C or higher, more preferably 350°C or higher, and even more preferably 400°C or higher. Furthermore, from the viewpoint of suppressing deterioration and decomposition of components in the powder due to heating, the heating temperature is preferably 500°C or lower, more preferably 475°C or lower, and even more preferably 450°C or lower. Note that the above heating temperatures can be used not only when the sulfide solid electrolyte powder has an argyrodite-type crystal structure, but also when it has crystal structures such as an LGPS-type crystal structure or a thiolysicone-type crystal structure.

[0094] On the other hand, in particular, when the target sulfide solid electrolyte powder consists of sulfide-based crystallized glass as described later, the heating temperature in the heat treatment is preferably 150 to 300°C. Here, from the viewpoint of homogenizing the particles and stabilizing the quality, the heating temperature is preferably 150°C or higher, more preferably 170°C or higher, and even more preferably 190°C or higher. Furthermore, from the viewpoint of suppressing deterioration and decomposition of components in the powder due to heating, the heating temperature is preferably 300°C or lower, more preferably 270°C or lower, and even more preferably 240°C or lower.

[0095] The heating time in the heat treatment varies depending on the composition of the target sulfide solid electrolyte powder, but is preferably, for example, 1 minute to 10 hours. Here, from the viewpoint of particle homogenization and quality stabilization, the heating time is preferably 1 minute or more, more preferably 10 minutes or more, even more preferably 30 minutes or more, and particularly preferably 1 hour or more. Also, from the viewpoint of manufacturing cost, the heating time is preferably 10 hours or less, more preferably 8 hours or less, even more preferably 6 hours or less, and particularly preferably 4 hours or less.

[0096] The pressure during the heat treatment is not particularly limited, but atmospheric pressure or slight pressure is preferred, and atmospheric pressure is more preferred.

[0097] The dew point during the above heat treatment is preferably -20°C or lower, and although there is no particular lower limit, it is usually around -80°C.

[0098] The oxygen concentration in the atmosphere during heat treatment is preferably 1000 ppm by volume or less.

[0099] From the viewpoint of lithium ion conductivity of sulfide solid electrolyte powder, the excess percentage of sulfur S in the sulfide solid electrolyte powder obtained in step S3 compared to the stoichiometric composition of the raw material mixture. β The excess percentage of sulfur S is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and even more preferably 1.0% by mass or more. Furthermore, from the viewpoint of ionic conductivity, the excess percentage of sulfur S is also preferable. β The excess amount of sulfur S is preferably 5.0% by mass or less, more preferably 4.5% by mass or less, and even more preferably 4.0% by mass or less. β This may be, for example, 0.1 to 5.0 mass%.

[0100] [Sulfide Solid Electrolyte Powder] The sulfide solid electrolyte powder obtained by the method described above in the [Method for Producing Sulfide Solid Electrolyte Powder] is specifically Li ７ P ３ S １１ Sulfide solid electrolytes having a crystalline structure containing elements Li, P, and S, such as LPS systems; Li １０ GeP ２ S １２These may include sulfide solid electrolytes having a crystalline structure containing Li, Ge, P, and S elements, known as the LGPS system; sulfide solid electrolytes having an argyrodite-type crystalline structure containing Li, P, S, and Ha elements; sulfide solid electrolytes made of Li-P-S-Ha crystallized glass; and sulfide solid electrolytes having a thiolysicone-type crystalline structure. Furthermore, sulfide solid electrolytes may include a crystalline phase having the above-mentioned crystalline structure and an amorphous phase.

[0101] The above argyrodite-type crystal structure refers to the composition formula Ag ８ GeS ６ This is the crystalline structure of the group of compounds derived from the mineral represented by [the given formula]. Furthermore, the sulfide solid electrolyte powder obtained by this manufacturing method is not limited to having the above crystalline structure, and some of the elements in the above crystalline structure may be substituted with other elements.

[0102] When the sulfide solid electrolyte powder obtained by this manufacturing method has an argyrodite-type crystal structure, it is more preferable that the Ha element contains at least one element selected from the group consisting of Cl, Br, and I, and even more preferable that it contains two or more elements. Furthermore, the sulfide solid electrolyte obtained by this manufacturing method is more preferably to contain at least one of Cl and Br as the Ha element, and even more preferably to contain both Cl and Br.

[0103] The argyrodite type crystal structure is preferably the structure described above, but the compositional formula is Li α PS β Ha γIt is preferably expressed as such, satisfying the relationships 5≦α≦7, 4≦β≦6 and 1.3≦γ≦2. Such elemental ratios are more preferably satisfied with the relationships 5.1<α<6.3, 4<β<5.3 and 1.4≦γ≦1.9, and even more preferably satisfied with the relationships 5.2<α<6.2, 4.1<β<5.2 and 1.5≦γ≦1.8. That is, for α, it is preferably 5 or more, more preferably greater than 5.1, even more preferably greater than 5.2, and also preferably 7 or less, more preferably less than 6.3, and even more preferably less than 6.2. For β, it is preferably 4 or more, more preferably greater than 4, even more preferably greater than 4.1, and also preferably 6 or less, more preferably less than 5.3, and even more preferably less than 5.2. For γ, it is preferably 1.3 or more, more preferably 1.4 or more, even more preferably 1.5 or more, and also preferably 2 or less, more preferably 1.9 or less, and even more preferably 1.8 or less.

[0104] In the argyrodite crystal structure, some of the S elements are replaced by Ha elements, O elements, and also Se, Te, and BH. ４ It may be substituted with CN, etc. Also, some of the P element may be substituted with Si, Al, Sn, In, Cu, Sb, Ge, etc.

[0105] The sulfide solid electrolyte powder obtained by this manufacturing method may consist of sulfide-based crystallized glass containing a crystalline phase derived from sulfide-based glass that satisfies all of the following conditions (1) to (4): (1) The sulfide-based glass contains Li and P as elements constituting the cationic component, and S as an element constituting the anionic component. (2) The composition of the sulfide-based glass satisfies Li: 30 to 42% and P: 5 to 16% in atomic percent. (3) The glass transition temperature of the sulfide-based glass is 110 to 300°C. (4) The lithium ion conductivity of the sulfide-based glass at 25°C is 2 mS / cm or more.

[0106] The above-mentioned sulfide-based crystallized glass is a crystallized glass containing a crystalline phase, and includes a crystalline phase derived from a sulfide-based glass that satisfies all of the above conditions (1) to (4). It may also optionally contain an amorphous phase, in which case the amorphous phase includes a phase made of the above-mentioned sulfide-based glass.

[0107] Here, the crystalline phase derived from the above-mentioned sulfide-based glass refers to the crystalline phase obtained by heat treatment of such glass. Except in cases where the sulfide-based crystallized glass consists solely of a crystalline phase with 100% crystallinity, the glass from which the crystalline phase originates can be inferred from the crystal structure and mass ratio of the crystalline phase and the overall composition of the sulfide-based crystallized glass.

[0108] Specifically, the crystalline phase is analyzed using Rietveld analysis and other methods on the XRD patterns obtained by powder X-ray diffraction (XRD) measurements to calculate the crystalline structure and mass ratio of the crystalline phase. On the other hand, the overall composition of the crystallized glass is determined using methods such as ICP emission spectroscopy, atomic absorption spectroscopy, ion chromatography, and XPS, depending on the type of element, similar to how the constituent elements and their respective content (composition ratio) of sulfide-based glass are determined later.

[0109] Then, by subtracting the composition of the crystalline phase by its mass ratio from the overall composition of the crystallized glass, the composition and amount of the amorphous phase can be calculated. The composition of this amorphous phase is considered to be the composition of the glass before crystallization (also called the matrix composition). If this matrix composition corresponds to the composition of the sulfide-based glass described above, then the crystallized glass can be determined to be the sulfide-based crystallized glass described above.

[0110] Furthermore, the crystalline phase of sulfide-based crystallized glass can take on thiolysicon region II type or LGPS type crystalline structures.

[0111] The proportion of the crystalline phase (degree of crystallinity) in sulfide-based crystallized glass is preferably 10 to 100% by mass, more preferably 20 to 90% by mass, and even more preferably 30 to 80% by mass. From the viewpoint of lithium ion conductivity, the degree of crystallinity is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 30% by mass or more. From the viewpoint of productivity, the degree of crystallinity is preferably 100% by mass or less, more preferably 90% by mass or less, and even more preferably 80% by mass or less. Note that sulfide-based crystallized glass may have a degree of crystallinity of 100% by mass and consist only of the crystalline phase.

[0112] The above degree of crystallinity is determined by powder X-ray diffraction (XRD) measurement of sulfide-based crystallized glass together with an internal standard crystal powder, and then performing Rietveld analysis to determine the proportion of crystals, which is then subtracted from 100% by mass.

[0113] To obtain the sulfide solid electrolyte powder made of the above-mentioned sulfide-based crystallized glass, in step S1 described above, the raw materials are mixed to obtain a raw material mixture such that the sulfide-based glass contains Li and P as elements constituting the cation component and S as an element constituting the anion component, and its composition satisfies the requirements of Li: 30-42% and P: 5-16% in atomic percent.

[0114] The above sulfide-based glass contains Li and P as elements constituting the cation component, but may further contain at least one element selected from the group consisting of Sn, Sb, Si, Ge, Ga, Al, B, C, Mg, Ca, Sr, and Ba. In particular, from the viewpoint of water resistance, it is preferable to contain at least one element selected from the group consisting of Sb, Si, and Sn, and more preferably to contain Si. Furthermore, from the viewpoint of ionic conductivity, it is preferable to contain at least one of the elements Al and B.

[0115] The elements constituting the cationic components are described below. Note that the content of each element in the above sulfide-based glass is expressed as atomic percent relative to the total content of all elements in the glass.

[0116] Li is an essential element responsible for ion conduction as a solid electrolyte. The Li content in the above sulfide-based glass is 30-42%, preferably 33-41%. From the viewpoint of lithium ion conductivity, the above content is 30% or more, preferably 33% or more, and more preferably 35% or more. From the viewpoint of vitrification, the above content is 42% or less, preferably 41% or less, and more preferably 40% or less.

[0117] P is an essential element for forming the glass phase. The P-S bond is highly resistant to both oxidation and reduction in sulfides. Therefore, it has a wide potential window as a solid electrolyte and excellent electrochemical stability. The P content in the above sulfide-based glass is 5 to 16%, preferably 6 to 14%. Here, from the viewpoint of vitrification, the above content is 5% or more, preferably 6% or more, and more preferably 7% or more. Also, from the viewpoint of lithium ion conductivity, the above content is 16% or less, preferably 14% or less, and more preferably 12% or less.

[0118] When the above sulfide-based glass contains Si as an element constituting the cation component, Si has the effect of increasing the viscosity of the melt and promoting vitrification. The Si content in the above sulfide-based glass is preferably 0 to 10%, more preferably 0.5 to 10%, and even more preferably 2 to 9%. Here, from the viewpoint of suitably obtaining the effect of Si, the Si content when included is preferably 0.5% or more, and more preferably 2% or more. Furthermore, from the viewpoint of electrochemical stability, the Si content is preferably 10% or less, and more preferably 9% or less.

[0119] When the above sulfide-based glass contains Sn as an element constituting the cation component, Sn has the effect of increasing the viscosity of the melt and promoting vitrification. The Sn content in the above sulfide-based glass is preferably 0 to 10%, more preferably 0.1 to 10%, and even more preferably 0.5 to 8%. Here, from the viewpoint of suitably obtaining the effect of Sn, the Sn content when it is included is preferably 0.1% or more, and more preferably 0.5% or more. Furthermore, from the viewpoint of electrochemical stability, the Sn content is preferably 10% or less, and more preferably 8% or less.

[0120] When the above sulfide-based glass contains Sb as an element constituting the cation component, Sb has the effect of increasing the viscosity of the melt and promoting vitrification. The Sb content in the above sulfide-based glass is preferably 0 to 10%, more preferably 0.1 to 8%, and even more preferably 1 to 5%. Here, from the viewpoint of suitably obtaining the effect of Sb, the Sb content when present is preferably 0.1% or more, and more preferably 1% or more. Furthermore, from the viewpoint of lithium ion conductivity, the Sb content is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less.

[0121] When the above sulfide-based glass contains at least one of Ge and Ga as elements constituting the cation component, Ge and Ga have the effect of promoting improved lithium ion conductivity. The Ge and Ga content in the above sulfide-based glass is preferably 0 to 10%, and if at least one of Ge and Ga is included, it is more preferably 0.1 to 8%, and even more preferably 1 to 5%. Here, from the viewpoint of suitably obtaining the effects of Ge and Ga, if at least one of Ge and Ga is included, the content is preferably 0.1% or more, and more preferably 1% or more. Furthermore, from the viewpoint of glass formation, the Ge and Ga content is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less.

[0122] When the above sulfide-based glass contains Al as an element constituting the cation component, Al has the effect of increasing the viscosity of the melt and promoting vitrification. The Al content in the above sulfide-based glass is preferably 0 to 10%, more preferably 0.1 to 8%, and even more preferably 1 to 5%. Here, from the viewpoint of suitably obtaining the effect of Al, the Al content when Al is included is preferably 0.1% or more, and more preferably 1% or more. Furthermore, from the viewpoint of lithium ion conductivity, the Al content is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less.

[0123] When the above sulfide-based glass contains B as an element constituting the cation component, B has the effect of increasing the viscosity of the melt and promoting vitrification. The content of B in the above sulfide-based glass is preferably 0 to 10%, more preferably 0.1 to 8%, and even more preferably 1 to 5%. Here, from the viewpoint of suitably obtaining the effect of B, the content of B when included is preferably 0.1% or more, and more preferably 1% or more. Furthermore, from the viewpoint of lithium ion conductivity, the content of B is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less.

[0124] When the above sulfide-based glass contains carbon (C) as an element constituting the cation component, C has the effect of increasing the glass-forming ability. The C content in the above sulfide-based glass is preferably 0 to 10%, more preferably 0.1 to 8%, and even more preferably 1 to 5%. Here, from the viewpoint of suitably obtaining the effect of C, the C content when C is included is preferably 0.1% or more, and more preferably 1% or more. Furthermore, from the viewpoint of lithium ion conductivity, the C content is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less.

[0125] When the above sulfide-based glass contains alkaline earth metal elements as elements constituting the cation component, the alkaline earth metal elements have the effect of increasing the glass-forming ability. Examples of alkaline earth metal elements include one or more selected from the group consisting of Mg, Ca, Sr, and Ba. The content of each alkaline earth metal element in the above sulfide-based glass is preferably 0 to 10%, more preferably 0.1 to 8%, and even more preferably 1 to 5%. Here, from the viewpoint of suitably obtaining the effect of alkaline earth metal elements, the content of each alkaline earth metal element when it is included is preferably 0.1% or more, and more preferably 1% or more. Also, from the viewpoint of lithium ion conductivity, the content of each alkaline earth metal element is preferably 10% or less, more preferably 8% or less, and even more preferably 5% or less. Furthermore, the total content of alkaline earth metal elements in the above sulfide-based glass is preferably 0 to 20%, more preferably 0.2 to 18%, and even more preferably 1 to 15%. Here, the total content is preferably 0.2% or more, more preferably 1% or more, preferably 20% or less, more preferably 18% or less, and even more preferably 15% or less.

[0126] The above sulfide-based glass contains S as an element constituting the anionic component, but may further contain at least one element selected from the group consisting of F, Cl, Br, I, O, Se, N, and C. In particular, from the viewpoint of improving ionic conductivity, it is preferable to contain at least one element selected from the group consisting of F, Cl, Br, and I, more preferably at least one element selected from the group consisting of Cl, Br, and I, and even more preferably I. Furthermore, from the viewpoint of improving vitrification ability, it is preferable to contain at least one element selected from the group consisting of O, Se, N, and C.

[0127] The elements constituting the anionic components are described below. Note that the content of each element in the above sulfide-based glass is expressed as atomic percent relative to the total content of all elements in the glass.

[0128] S is an element that forms a P-S bond with P and is an essential element for forming the glass phase. The S content in the above sulfide-based glass is preferably 30 to 60%, more preferably 33 to 55%, and even more preferably 37 to 50%. Here, from the viewpoint of vitrification, the above content is preferably 30% or more, more preferably 33% or more, and even more preferably 37% or more. Furthermore, from the viewpoint of lithium ion conductivity, the above content is preferably 60% or less, more preferably 55% or less, and even more preferably 50% or less.

[0129] When the above sulfide-based glass contains a halogen element (Ha) as an element constituting the anionic component, Ha is an element that contributes to high lithium ion conductivity. The total Ha content in the above sulfide-based glass is preferably 0 to 20%, more preferably 1 to 20%, and may also be 1 to 12% or 2 to 10%. Here, from the viewpoint of suitably obtaining the effect of Ha, the total Ha content when Ha is included is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, and particularly preferably 6% or more. Furthermore, from the viewpoint of preventing the precipitation of lithium halide crystals, the total Ha content is preferably 20% or less, more preferably 19% or less, and even more preferably 17% or less. Furthermore, the total Ha content may also be 12% or less, or 10% or less.

[0130] In particular, of the total amount of Ha mentioned above, it is preferable that the combined content of Br and I accounts for 50% or more, more preferably 70% or more, and it may even account for 100%, i.e., consist only of Br and I. Furthermore, the content ratio expressed as Cl:Br is preferably 100:0 to 0:100, more preferably 80:20 to 0:100, and even more preferably 60:40 to 0:100. However, this does not preclude the inclusion of only Cl as Ha.

[0131] When the above sulfide-based glass contains F as an element constituting the anionic component, the F content in the sulfide-based glass is preferably 0.1 to 20%, may also be 0.1 to 10%, or 0.5 to 5%. Here, the F content is preferably 0.1% or more, more preferably 0.5% or more, even more preferably 3% or more, and particularly preferably 6% or more. Furthermore, the F content is preferably 20% or less, more preferably 19% or less, and even more preferably 17% or less. If lithium fluoride crystals are likely to precipitate, the F content may be 10% or less, or even 5% or less.

[0132] When the above sulfide-based glass contains Cl as an element constituting the anionic component, the Cl content in the sulfide-based glass is preferably 0.1 to 20%, may also be 0.1 to 10%, or 0.5 to 5%. Here, the Cl content is preferably 0.1% or more, more preferably 0.5% or more, even more preferably 3% or more, and particularly preferably 6% or more. Furthermore, the Cl content is preferably 20% or less, more preferably 19% or less, and even more preferably 17% or less. If lithium chloride crystals are likely to precipitate, the Cl content may be 10% or less, or even 5% or less.

[0133] When the above sulfide-based glass contains Br as an element constituting the anionic component, the Br content in the sulfide-based glass is preferably 0.1 to 20%, may be 0.1 to 10%, or 1 to 8%. Here, the Br content is preferably 0.1% or more, more preferably 1% or more, even more preferably 3% or more, and particularly preferably 6% or more. Furthermore, the Br content is preferably 20% or less, more preferably 19% or less, and even more preferably 17% or less. If lithium bromide crystals are likely to precipitate, the Br content may be 10% or less, or 8% or less.

[0134] When the above sulfide-based glass contains I as an element constituting the anionic component, I is particularly preferred because it contributes to improving ionic conductivity. The I content in the above sulfide-based glass is preferably 0.1 to 20%, may also be 0.1 to 10%, 1 to 8%, or 2 to 6%. Here, the I content is preferably 0.1% or more, more preferably 1% or more, even more preferably 2% or more, even more preferably 3% or more, and particularly preferably 6% or more. Furthermore, the I content is preferably 20% or less, more preferably 19% or less, and even more preferably 17% or less. In cases where lithium iodide crystals are likely to precipitate, or from the viewpoint of improving vitrification, the I content may be 10% or less, 8% or less, or 6% or less.

[0135] When the above sulfide-based glass contains at least one of O, Se, N, and C as elements constituting the anionic component, O, Se, N, and C have the effect of improving ionic conductivity. The content of O, Se, N, and C in the above sulfide-based glass is preferably 0 to 5%, and if at least one of O, Se, N, and C is included, it is more preferably 0.1 to 4%, and even more preferably 0.5 to 3%. Here, from the viewpoint of suitably obtaining the effects of O, Se, N, and C, the content when at least one of O, Se, N, and C is included is preferably 0.1% or more, and more preferably 0.5% or more. Furthermore, from the viewpoint of water resistance, the content of O, Se, N, and C is preferably 5% or less, more preferably 4% or less, and even more preferably 3% or less.

[0136] Note that carbon (C) can be an element that constitutes either a cationic component or an anionic component. Whether carbon is present in one of these states can be determined by measuring the glass using XPS (X-ray photoelectron spectroscopy), and carbon is never present in both states simultaneously.

[0137] The above-mentioned sulfide-based glass may contain other elements in addition to the elements constituting the above-mentioned cationic or anionic components, to the extent that it does not impair the effects of the present invention. Examples of other elements include Na, K, Y, Zr, Cr, Zn, Fe, Co, Ti, Mn, and the like.

[0138] The total content of the other elements in the above sulfide-based glass may be expressed in atomic percent as, for example, 0 to 5%, or if other elements are included, 0.1 to 4%, or 0.5 to 3%. Here, the total content may be 0.1% or more, 0.5% or more, 4% or less, or 3% or less.

[0139] The composition of the above sulfide-based glass should satisfy Li: 30-42% and P: 5-16% in atomic percent, but it is preferable that it also satisfies one or more of the following: S: 30-60%, Ha: 1-20%, Si: 1-10%, and Sn: 0.1-10%, preferably two or more, and more preferably three or more. Furthermore, if Ha: 1-20% is satisfied, it is even more preferable that at least one of Br: 0.1-19% and I: 0.1-19% is also satisfied. The composition of the above sulfide-based glass may also satisfy one or more of the following: S: 30-60%, Ha: 1-12%, Si: 1-10%, and Sn: 0.1-10%, preferably two or more, and may also satisfy three or more. Furthermore, if the above Ha: 1-12% is satisfied, at least one of Br: 0.1-10% and I: 0.1-10% may also be satisfied.

[0140] The method for determining the constituent elements and their respective content (composition ratio) of the above-mentioned sulfide-based glass varies depending on the element. For example, P, S, Sn, Sb, Si, Ge, Ga, Al, Mg, Ca, Sr, Ba, and Se are determined by ICP emission spectrometry, Li and B by atomic absorption spectrometry, Ha by ion chromatography, and C, O, and N by XPS (X-ray photoelectron spectroscopy).

[0141] The glass transition temperature of the above sulfide-based glass is 110 to 300°C, preferably 130 to 300°C, more preferably 140 to 290°C, and particularly preferably 150 to 280°C. By melting a glass raw material mixture and rapidly cooling it, a glass having a glass transition temperature can be obtained. From the viewpoint of improving the stability of the above sulfide-based glass, the above glass transition temperature is 110°C or higher, preferably 130°C or higher, more preferably 140°C or higher, and particularly preferably 150°C or higher. Furthermore, from the viewpoint of moldability, the above glass transition temperature is 300°C or lower, preferably 290°C or lower, and more preferably 280°C or lower. In this specification, the glass transition temperature is the temperature at the first inflection point of the DSC chart obtained by differential scanning calorimetry (DSC), and can be adjusted by the composition of the glass and the cooling rate from the melt.

[0142] The crystallization temperature of the above sulfide-based glass is not particularly limited, but is preferably 130 to 400°C, more preferably 140 to 400°C, and particularly preferably 150 to 370°C. Here, from the viewpoint of moldability, the crystallization temperature is preferably 130°C or higher, more preferably 140°C or higher, and particularly preferably 150°C or higher. Furthermore, from the viewpoint of the stability of the above sulfide-based glass, the crystallization temperature is preferably 400°C or lower, and more preferably 370°C or lower.

[0143] In this specification, the crystallization temperature refers to the temperature at the peak of the exothermic peak observed when glass is subjected to DSC and heated at a heating rate of 10°C / min.

[0144] When the glass transition temperature of the above sulfide-based glass is Tg and the crystallization temperature is Tc, the temperature difference expressed as (Tc - Tg) is preferably 10 to 200°C, and more preferably 20 to 180°C. Here, from the viewpoint of the stability of the above sulfide-based glass, the above difference is preferably 10°C or more, and more preferably 20°C or more. Also, from the viewpoint of productivity, the above difference is preferably 200°C or less, and more preferably 180°C or less.

[0145] The lithium ion conductivity of the above sulfide-based glass, when compacted at 380 MPa, at 25°C is 2 mS / cm or more, preferably 3 mS / cm or more, and higher is preferable. In this specification, lithium ion conductivity is determined by AC impedance measurement using a sample of powder compacted at 380 MPa as the measurement sample. Specifically, the AC impedance measurement of the measurement sample is performed with a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C, and the value obtained from the resulting Nyquist plot is defined as the lithium ion conductivity.

[0146] The lithium-ion conductivity can be adjusted by the composition of the sulfide-based glass, reducing thermal unevenness during rapid cooling of the molten raw material mixture, and controlling the cooling rate. In particular, the sulfide-based glass is obtained by a melting method rather than a solid-phase reaction method, specifically by melting and rapidly cooling the raw material mixture. This broadens the range in which vitrification is possible, making it easier to include desired anionic and cationic components, and as a result, enabling the adoption of a composition that achieves high lithium-ion conductivity.

[0147] The above sulfide-based glass was subjected to H2 when exposed to air with a dew point of -30°C for 1 hour. ２ The amount of hydrogen sulfide (S) generated is preferably 10 mL / g or less, more preferably 4 mL / g or less, even more preferably 1 mL / g or less, particularly preferably 0.1 mL / g or less, and the less the better. ２ The amount of S generated is an indicator of the water resistance of the glass. Note that the above H ２ The more specific measurement conditions for the amount of sulfur (H) generated are as follows: First, the sample is passed through a 100 μm mesh to obtain a powder with an average particle size of 10 to 20 μm. Then, 10 mg of this powder is exposed to air humidified to a dew point of -30°C for 1 hour, and the amount of hydrogen sulfide (H) measured is measured. ２ S) Monitor the amount generated and the total amount H ２ This is the amount of S produced.

[0148] The sulfide solid electrolyte powder obtained by this manufacturing method preferably has a lithium ion conductivity of 2 mS / cm or more at 25°C, more preferably 3 mS / cm or more, even more preferably 5 mS / cm or more, and particularly preferably 8 mS / cm or more; the higher the value, the better.

[0149] The sulfide solid electrolyte powder obtained by this manufacturing method is finely ground to an average particle size of about 0.1 to 2.0 μm using a conventionally known fine grinding process, and then used to form an electrode mixture by applying pressure together with a positive electrode active material or a negative electrode active material, or to form a solid electrolyte layer by applying pressure together with additives such as binders as needed, and is suitable for use in all-solid-state lithium secondary batteries.

[0150] As described above, the following configurations are disclosed in this specification: [1] A method for producing a sulfide solid electrolyte powder, comprising: mixing raw materials to obtain a raw material mixture; synthesizing at least one of sulfide powder and sulfide precursor powder from the raw material mixture; and heat-treating the powder in a heating furnace, wherein the heat treatment is carried out while an inert gas is flowed through the heating furnace, and when the volume of the heating furnace is A (L) and the flow rate of the inert gas is B (L / h), the substitution rate expressed as B / A is 0.3 / h or more. [2] An excess ratio S of sulfur in the powder compared with the stoichiometric composition of the raw material mixture. αThe method for producing sulfide solid electrolyte powder according to [1], wherein the amount is 0.1% by mass or more. [3] The method for producing sulfide solid electrolyte powder according to [1] or [2], wherein the average particle size of the powder is 0.3 to 5000 μm. [4] The method for producing sulfide solid electrolyte powder according to any one of [1] to [3], wherein the heat treatment is performed at a temperature of 150 to 500°C. [5] The method for producing sulfide solid electrolyte powder according to any one of [1] to [4], wherein the raw materials include Li, P, S and Ha, and the Ha element is at least one element selected from the group consisting of F, Cl, Br and I, and the obtained sulfide solid electrolyte powder has an argyrodite type crystal structure. [6] The method for producing sulfide solid electrolyte powder according to [5], wherein the heat treatment is performed at a temperature of 300 to 500°C. [7] The method for producing a sulfide solid electrolyte powder according to any one of [1] to [4], wherein the raw materials include elements Li, P and S, and the obtained sulfide solid electrolyte powder consists of sulfide crystallized glass containing a crystalline phase derived from sulfide glass that satisfies all of the following conditions (1) to (4): (1) The sulfide glass contains Li and P as elements constituting the cation component, and S as an element constituting the anion component. (2) The composition of the sulfide glass satisfies Li: 30 to 42% and P: 5 to 16% in atomic percent. (3) The glass transition point of the sulfide glass is 110 to 300°C. (4) The lithium ion conductivity of the sulfide glass at 25°C is 2 mS / cm or more. [8] The method for producing a sulfide solid electrolyte powder according to [7], wherein the heat treatment is performed at a temperature of 150 to 300°C. [9] A method for producing a sulfide solid electrolyte powder according to any one of [1] to [8], wherein the molten material obtained by heating the raw material mixture in the synthesis is cooled to obtain the powder containing the sulfide powder.

[0151] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these. Examples 1 to 4 are examples, and Examples 5 to 7 are comparative examples.

[0152] [Example 1] Under a dry nitrogen gas atmosphere, Li ５．４ PS ４．４ Cl０．８ Br ０．８ Lithium sulfide powder (Sigma, 99.98% purity), phosphorus pentasulfide powder (Sigma, 99% purity), lithium chloride powder (Sigma, 99.99% purity), and lithium bromide powder (Sigma, 99.995% purity) were weighed to achieve the specified composition ratio and mixed in a mortar to obtain a raw material mixture. The obtained raw material mixture was placed in a heat-resistant container, and 15% by mass of elemental sulfur was added per 100% by mass of the raw material mixture. This was heated at 750°C for 1 hour to obtain a molten product of the raw material mixture, which was the synthesized compound.

[0153] The obtained molten material was then cooled to room temperature at 5°C / second to obtain a solid sulfide. This sulfide was pulverized using a cutter mill to adjust the average particle size to 10-20 μm, and then passed through a 100 μm mesh to obtain sulfide powder. The excess sulfur content S of the obtained sulfide powder was compared with the stoichiometric composition of the raw material mixture. α The sulfur content was measured using the method described later and was found to be 5% by mass. One kilogram of the obtained sulfide powder was placed in a cylindrical container made of carbon with a base diameter of 150 mm and a height of 150 mm. Then, it was heated in an electric furnace at 400°C for one hour while dry nitrogen gas was flowing through it. The volume A of the electric furnace was 12 L, the flow rate B of the dry nitrogen gas was 120 L / h, and the substitution rate B / A was 10 / h. The mixture was then cooled again to room temperature at 1°C / second to obtain a sulfide solid electrolyte powder containing argyrodite-type crystals. The obtained sulfide solid electrolyte powder was confirmed to have almost the same composition as the target composition by X-ray diffraction measurement and Rietveld analysis. Furthermore, the excess sulfur content S of the obtained sulfide solid electrolyte powder was compared with the stoichiometric composition of the raw material mixture. β The lithium-ion conductivity was measured using the method described later.

[0154] [Example 2] A sulfide solid electrolyte powder was obtained in the same manner as in Example 1, except that the flow rate B of the dry nitrogen gas was 36 L / h and the substitution rate B / A was 3 / h during the heat treatment.

[0155] [Example 3] A sulfide solid electrolyte powder was obtained in the same manner as in Example 1, except that the flow rate B of the dry nitrogen gas was 6 L / h and the substitution rate B / A was 0.5 / h during the heat treatment.

[0156] [Example 4] A sulfide solid electrolyte powder was obtained in the same manner as in Example 3, except that 8% by mass of elemental sulfur was added per 100% by mass of the raw material mixture during the heating and melting of the raw material mixture.

[0157] [Example 5] A sulfide solid electrolyte powder was obtained in the same manner as in Example 1, except that the flow rate B of the dry nitrogen gas was 1.2 L / h and the substitution rate B / A was 0.1 / h during the heat treatment.

[0158] [Example 6] A sulfide solid electrolyte powder was obtained in the same manner as in Example 5, except that 8% by mass of elemental sulfur was added per 100% by mass of the raw material mixture during the heating and melting of the raw material mixture.

[0159] [Example 7] A sulfide solid electrolyte powder was obtained in the same manner as in Example 1, except that the flow rate B of the dry nitrogen gas was 0.36 L / h and the substitution rate B / A was 0.03 / h during the heat treatment.

[0160] (Sulfur excess ratio S) α S β In Examples 1 to 7, the excess sulfur ratio S of the sulfide powder and sulfide solid electrolyte powder compared to the stoichiometric composition of the raw material mixture. α and S β The following method was used to determine the sulfur content (S) in the powder sample. Sulfur (S) in the powder sample was quantified using the combustion-infrared absorption method in an oxygen stream (equipment: EMIA-expert carbon-sulfur analyzer, Horiba, Ltd.). Specifically, the powder sample was sealed in an Sn container in a glove box with a dew point of -50°C or lower, and the lid was closed. The container was then placed in the above-mentioned apparatus for analysis. The excess sulfur percentage (mass%) was calculated by subtracting the mass percentage of sulfur in the stoichiometric ratio (composition of the raw material mixture) from the measured sulfur content. The results are shown in Table 1. Furthermore, the S calculated above was also used. α And, from the substitution rate B / A in the production of sulfide solid electrolyte powder, S α The value of / (B / A) (mass %・h) was calculated. The results are shown in Table 1.

[0161] (Lithium-ion conductivity) The lithium-ion conductivity was measured using an AC impedance measuring device (potentiostat / galvanostat VSP, manufactured by Bio-Logic Sciences Instruments) with the sulfide solid electrolyte powders obtained in Examples 1 to 7 as samples. The measurement conditions were: measurement frequency: 100 Hz to 1 MHz, measurement voltage: 100 mV, and measurement temperature: 25°C. The results are shown in Table 1.

[0162]

[0163] Based on the above results, the sulfide solid electrolyte powders in Examples 1 to 4, which had a substitution rate B / A of 0.3 / h or higher during heat treatment in manufacturing, showed high lithium ion conductivity. On the other hand, the sulfide solid electrolyte powders in Examples 5 to 7, which had a substitution rate B / A of less than 0.3 / h during heat treatment in manufacturing, showed inferior lithium ion conductivity.

[0164] Although the present invention has been described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications are possible without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2025-048762, filed on 24 March 2025, which is incorporated herein by reference in its entirety.

[0165] 100 Heating furnace 10 Heating furnace body 11 Heating space 12 Inert gas supply port 14 Inert gas outlet 16 Heating furnace inlet 18 Heating furnace outlet 20 Container 30 Powder of at least one of sulfide powder and sulfide precursor powder

Claims

1. A method for producing a sulfide solid electrolyte powder, comprising: mixing raw materials to obtain a raw material mixture; synthesizing at least one of sulfide powder and sulfide precursor powder from the raw material mixture; and heat-treating the powder in a heating furnace, wherein the heat treatment is performed while flowing an inert gas through the heating furnace, and when the volume of the heating furnace is A (L) and the flow rate of the inert gas is B (L / h), the substitution rate expressed as B / A is 0.3 / h or more.

2. The excess percentage S of sulfur in the powder compared to the stoichiometric composition of the raw material mixture. α A method for producing sulfide solid electrolyte powder according to claim 1, wherein the amount is 0.1% by mass or more.

3. The method for producing a sulfide solid electrolyte powder according to claim 1 or 2, wherein the average particle size of the powder is 0.3 to 5000 μm.

4. The method for producing sulfide solid electrolyte powder according to claim 1 or 2, wherein the heat treatment is performed at a temperature of 150 to 500°C.

5. The method for producing a sulfide solid electrolyte powder according to claim 1 or 2, wherein the raw materials include Li, P, S and Ha, the Ha element being at least one element selected from the group consisting of F, Cl, Br and I, and the resulting sulfide solid electrolyte powder has an argyrodite-type crystal structure.

6. The method for producing sulfide solid electrolyte powder according to claim 5, wherein the heat treatment is performed at a temperature of 300 to 500°C.

7. A method for producing a sulfide solid electrolyte powder according to claim 1 or 2, wherein the raw materials include elements Li, P, and S, and the obtained sulfide solid electrolyte powder consists of sulfide crystallized glass containing a crystalline phase derived from sulfide glass that satisfies all of the following conditions (1) to (4): (1) The sulfide glass contains Li and P as elements constituting the cationic component, and S as an element constituting the anionic component. (2) The composition of the sulfide glass satisfies Li: 30 to 42% and P: 5 to 16% in atomic percent. (3) The glass transition temperature of the sulfide glass is 110 to 300°C. (4) The lithium ion conductivity of the sulfide glass at 25°C is 2 mS / cm or more.

8. The method for producing sulfide solid electrolyte powder according to claim 7, wherein the heat treatment is performed at a temperature of 150 to 300°C.

9. The method for producing a sulfide solid electrolyte powder according to claim 1 or 2, wherein in the synthesis, the molten material obtained by heating the raw material mixture is cooled to obtain the powder containing the sulfide powder.

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