Method for producing sulfide solid electrolyte

Abstract

To provide a method for producing a sulfide solid electrolyte that can easily produce a sulfide solid electrolyte having a high PS4 fraction.SOLUTION: A method for producing a sulfide solid electrolyte, which comprises an airflow treatment in which a sulfide containing at least an alkali metal element, a phosphorus element and a sulfur element is treated with at least one type of gas selected from an inert gas and hydrogen gas.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a sulfide solid electrolyte. [Background technology]

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as power sources for these devices has become increasingly important. Among these, lithium-ion batteries have attracted attention due to their high energy density. Conventionally, batteries used for such applications have used electrolytes containing flammable organic solvents, which necessitates the installation of safety devices to suppress temperature rises during short circuits, as well as improvements in the structure and materials to prevent short circuits.In response to this, development is underway to replace the electrolyte with a solid electrolyte and make the battery all-solid, which eliminates the use of flammable organic solvents in the battery, simplifies the safety devices, and is superior in terms of manufacturing cost and productivity.

[0003] Methods for producing solid electrolytes used in solid electrolyte layers are broadly divided into solid-phase methods and liquid-phase methods. Liquid-phase methods include homogeneous methods, in which the solid electrolyte material is completely dissolved in a solvent, and heterogeneous methods, in which the solid electrolyte material is not completely dissolved but is instead a solid-liquid coexistence suspension. For example, a known solid-phase method involves mechanically milling raw materials such as lithium sulfide and diphosphorus pentasulfide using a device such as a ball mill or a bead mill, followed by heat treatment as needed to produce an amorphous or crystalline solid electrolyte (see, for example, Patent Document 1). According to this method, a solid electrolyte is obtained by applying mechanical stress to raw materials such as lithium sulfide to promote solid-solid reactions.

[0004] On the other hand, among the liquid phase methods, a known homogeneous method is one in which a solid electrolyte is dissolved in a solvent and reprecipitated (see, for example, Patent Document 2), and a known heterogeneous method is one in which solid electrolyte raw materials such as lithium sulfide and diphosphorus pentasulfide are reacted in a solvent, such as a hydrocarbon solvent such as toluene, using a stirrer or a grinder such as a rotary mill, a rocking mill, a vibration mill, or a bead mill (see Patent Document 3). Patent Document 4 also discloses a solid electrolyte production apparatus that combines a grinding synthesis means (specifically, a grinder) that grinds and reacts raw materials such as lithium sulfide in a solvent, and a synthesis means (specifically, a reaction vessel equipped with a stirring blade) that reacts raw materials such as lithium sulfide in a solvent, and a method for producing a solid electrolyte using the apparatus.

[0005] Patent Document 3 discloses that a sulfide solid electrolyte with relatively high lithium ion conductivity can be obtained by reacting solid raw materials such as lithium sulfide and diphosphorus pentasulfide using a mixer, a grinder such as a bead mill, or the like. The method of reacting solid raw materials while stirring and grinding them using a grinder such as a mixer or a bead mill is usually referred to as a solid-phase method or mechanical milling method, and is a method of progressing the reaction by causing collisions between media such as beads and the solid raw materials, or between the solid raw materials themselves, and further exposing new surfaces of the solid raw materials by repeated collisions, thereby further promoting the reaction between the solid raw materials. Patent Document 3 discloses that a solid electrolyte obtained by a method using a stirrer, a grinder, or the like may contain P2S6 units and P2S7 units in addition to PS4 units. It also discloses that increasing the proportion of PS4 units (also referred to as the "PS4 fraction") in a solid electrolyte leads to improved ionic conductivity. It is also known that glass with a low content of P2S7 units generates a low amount of hydrogen sulfide. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2017 / 159667 Brochure [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-191899 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-155087 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-207521 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a production method by which a sulfide solid electrolyte having a high PS4 fraction can be easily produced. [Means for solving the problem]

[0008] The method for producing a sulfide solid electrolyte according to the present invention includes the steps of: a method for producing a sulfide solid electrolyte, the method comprising subjecting a sulfide containing at least an alkali metal element, a phosphorus element, and a sulfur element to a gas flow treatment with at least one gas selected from an inert gas and a hydrogen gas; is. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a production method that can easily produce a sulfide solid electrolyte having a high PS4 fraction. [Brief explanation of the drawings]

[0010] [Figure 1] 3 shows 31P MAS NMR spectra of the sulfide solid electrolytes obtained in Examples 1 to 3 and Comparative Example 1. [Figure 2] 1 is an X-ray diffraction spectrum of the amorphous sulfide solid electrolyte obtained in Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, the upper and lower limit values ​​of a range of values ​​expressed as "greater than or equal to," "less than or equal to," and "to" can be arbitrarily combined, and the numerical values ​​in the examples can also be used as the upper and lower limit values.

[0012] (Findings gained by the inventors to arrive at the present invention) As a result of extensive research aimed at solving the above problems, the present inventors have discovered the following and have completed the present invention. As described in Patent Document 3, when conventional production methods such as the solid-phase method (mechanical milling method) are used to obtain sulfides such as sulfide solid electrolytes using solid raw materials such as lithium sulfide and diphosphorus pentasulfide, the resulting sulfides may contain not only PS4 units but also units such as P2S7 units and P2S6 units due to localized high temperatures caused by collisions between media such as beads and the solid raw materials, or between the solid raw materials themselves. It is also known that the higher the PS4 unit fraction (PS4 fraction), the higher the ionic conductivity. It is also disclosed that the PS4 fraction is affected by various reaction conditions, such as the particle size and other properties of the raw materials used, the equipment used in the reaction (i.e., agitators, grinders, etc.), and operating conditions.

[0013] The inventors noticed that while various reaction conditions have been investigated for conventional manufacturing methods such as the solid-phase method (mechanical milling), no studies have been conducted on methods for improving the PS4 fraction through subsequent treatment. They then conducted extensive research to determine whether the PS4 fraction could be improved by reducing the fractions of P2S7 and P2S6 units contained in sulfides, such as sulfide solid electrolytes, other than the PS4 units. They discovered that gas flow treatment with at least one gas selected from an inert gas and hydrogen gas reduces the proportion of P2S7 units (P2S7 fraction) and improves the PS4 fraction instead. Gas flow treatment of sulfides, particularly with a gas containing hydrogen gas, is expected to increase the generation of hydrogen sulfide, so gas flow treatment with a gas containing hydrogen gas has not typically been performed. However, when gas flow treatment with at least one gas selected from an inert gas and hydrogen gas was employed, the surprising effect of improving the PS4 fraction was discovered. As mentioned above, it is known that the PS4 fraction is affected by various reaction conditions. However, it has not been recognized until now that the PS4 fraction can be improved by subjecting sulfides to a post-treatment, i.e., a gas stream treatment using at least one gas selected from an inert gas and hydrogen gas.

[0014] In this specification, the term "solid electrolyte" refers to an electrolyte that remains solid at 25°C under a nitrogen atmosphere. The "sulfide solid electrolyte" obtained by the manufacturing method of this embodiment is a solid electrolyte containing an alkali metal element, sulfur, and phosphorus, preferably a halogen, and having ionic conductivity due to an alkali metal element such as lithium, and is obtained by subjecting a "sulfide" containing lithium, sulfur, and phosphorus, preferably a halogen, to an airflow treatment. The above-mentioned "sulfide solid electrolyte" and "sulfide" may also contain metal elements such as Ge, Na, K, Mg, Ca, Al, Si, Sb, Ti, and Zr.

[0015] The term "sulfide solid electrolyte" includes both a crystalline sulfide solid electrolyte having a crystalline structure obtained by the manufacturing method of this embodiment and an amorphous sulfide solid electrolyte. In this specification, a crystalline sulfide solid electrolyte is a solid electrolyte in which a peak derived from the solid electrolyte is observed in the X-ray diffraction pattern in X-ray diffraction measurement, regardless of whether or not a peak derived from the raw material of the solid electrolyte is present. That is, a crystalline sulfide solid electrolyte includes a crystalline structure derived from the solid electrolyte, and the crystalline structure may be partially or entirely derived from the solid electrolyte. Furthermore, as long as the crystalline sulfide solid electrolyte has the X-ray diffraction pattern described above, it may also partially contain an amorphous sulfide solid electrolyte (also referred to as a "glass component"). Therefore, the crystalline sulfide solid electrolyte includes so-called glass ceramics obtained by heating an amorphous solid electrolyte (glass component) above its crystallization temperature.

[0016] In this specification, the amorphous sulfide solid electrolyte (glass component) refers to a solid electrolyte in which the X-ray diffraction pattern is a halo pattern in which no peaks other than those derived from the material are observed in X-ray diffraction measurement, and it does not matter whether or not there are peaks derived from the raw materials of the solid electrolyte. The above distinction between crystalline and amorphous also applies to sulfides that are the target of the airflow treatment in this embodiment.

[0017] In addition, in this specification, the proportion of PS4 units (PS4 fraction), the proportion of P2S7 units (P2S7 fraction), and the proportion of P2S6 units (P2S6 fraction) are 31 P MAS NMR spectrum (solid 31 P NMR spectrum) and waveform separation are performed. The area of ​​each unit is the ratio of the area of ​​the peaks of the PS4 unit, P2S7 unit, and P2S6 unit to the total area of ​​the peaks of the PS4 unit, P2S7 unit, and P2S6 unit. 31 There are no particular limitations on the detailed conditions for measuring the P NMR spectrum, and the measurement may be carried out, for example, under the conditions described in the Examples.

[0018] [Method for producing sulfide solid electrolyte] A method for producing a sulfide solid electrolyte according to a first aspect of the present embodiment includes the steps of: a method for producing a sulfide solid electrolyte, the method comprising: subjecting a sulfide containing at least an alkali metal element, a phosphorus element, and a sulfur element to a gas flow treatment with at least one gas selected from an inert gas and a hydrogen gas; is.

[0019] A sulfide containing an alkali metal element, phosphorus element, and sulfur element is typically a sulfide solid electrolyte containing these elements, which can be said to correspond to a sulfide solid electrolyte obtained by a conventional method. Therefore, in light of conventional methods, the airflow treatment using at least one gas selected from an inert gas and hydrogen gas in the production method of this embodiment (hereinafter simply referred to as "airflow treatment") is positioned as a post-treatment performed after the production of a sulfide solid electrolyte, and it can be said that the production method of this embodiment makes it possible to improve the PS4 fraction by performing the post-treatment called airflow treatment.

[0020] As will be shown in the Examples described later, sulfides contain P2S7 and P2S6 units in addition to PS4 units, and it has been confirmed that by subjecting these sulfides to airflow treatment, the fraction of units other than PS4 units, i.e., at least one of the P2S7 and P2S6 fractions, decreases, the PS4 fraction increases accordingly, and high ionic conductivity is obtained. The reason why the airflow treatment of sulfides reduces at least one of the P2S7 fraction and the P2S6 fraction and increases the PS4 fraction accordingly is unknown. However, the present inventors speculated that the airflow treatment may be effective and arrived at the present invention.

[0021] Sulfides contain PS4, P2S7, and P2S6 units, but it is difficult to imagine that all of the atoms derived from the raw materials used to create sulfides, including sulfur atoms and phosphorus atoms, contribute to the formation of PS4, P2S7, and P2S6 units. Therefore, although it is difficult to detect their presence by measurement, it is thought that a certain amount of sulfur atoms are not incorporated into these units and exist in an isolated form.

[0022] Considering that isolated sulfur atoms are thought to contribute little to improving ionic conductivity and that increasing the PS4 fraction leads to improved ionic conductivity, we predicted that high ionic conductivity could be achieved by reducing the isolated sulfur atoms while increasing the PS4 fraction. To reduce the isolated sulfur atoms, we considered increasing the reactivity of the isolated sulfur atoms. Therefore, we considered converting the isolated sulfur atoms into more reactive hydrogen sulfide by gas flow treatment of the sulfide. By converting the isolated sulfur atoms into hydrogen sulfide by flowing at least one gas selected from an inert gas and hydrogen gas, particularly hydrogen gas, the hydrogen sulfide reacts with at least one of the P2S7 and P2S6 units, reducing the isolated sulfur atoms and at least one of the P2S7 and P2S6 units, while generating PS4 units, thereby improving the PS4 fraction.

[0023] Furthermore, exposing sulfides to a gas stream is also considered to have the effect of improving the PS4 fraction. Exposing sulfides to a gas stream improves the reactivity of isolated sulfur atoms and can also produce products by reaction with solvents or moisture remaining after volatilization in the gas stream, thereby significantly reducing the number of isolated sulfur atoms. Furthermore, it is conceivable that the isolated sulfur atoms react with at least one of the P2S7 and P2S6 units through the action of the reactants generated by the reaction. Therefore, exposing sulfides to a stream of an inert gas alone can also reduce at least one of the P2S7 and P2S6 units, generate PS4 units, and improve the PS4 fraction. Furthermore, when the gas contains hydrogen gas, the above-mentioned effect of hydrogen gas is considered to enhance the PS4 fraction improvement. Considering this, it is preferable that the gas used for the gas stream treatment contains hydrogen gas, as will be described in detail below. Thus, it is believed that by performing gas flow treatment with at least one gas selected from an inert gas and hydrogen gas, i.e., an inert gas alone, hydrogen gas alone, or a mixed gas of an inert gas and hydrogen gas, the PS4 fraction becomes high and high ionic conductivity can be obtained.

[0024] As mentioned above, it is difficult to specifically confirm the existence of sulfur atoms in an isolated form. However, it is difficult to imagine that all of the atoms derived from the raw materials used to prepare the sulfide, i.e., all of the sulfur atoms, contribute to the formation of PS4 units, P2S7 units, and P2S6 units, so it is reasonable to assume that a certain number of sulfur atoms exist in an isolated form.

[0025] The manufacturing method of this embodiment is an innovative manufacturing method in that it is possible to improve the PS4 fraction and obtain high ionic conductivity by any method for producing the sulfide or by finally performing airflow treatment after processing the sulfide, such as pulverization.

[0026] A method for producing a sulfide solid electrolyte according to a second aspect of the present embodiment includes the steps of: a method for producing a sulfide solid electrolyte, wherein the gas flow treatment is carried out under a hydrogen gas atmosphere; is. In the second embodiment, the gas flow treatment of the first embodiment is performed under a hydrogen gas atmosphere. As described above, the inclusion of hydrogen gas in the gas used in the gas flow treatment facilitates the conversion of isolated sulfur atoms to hydrogen sulfide. The hydrogen sulfide then reacts with at least one of the P2S7 and P2S6 units, reducing the isolated sulfur atoms and at least one of the P2S7 and P2S6 units, while generating PS4 units, which is believed to facilitate an improvement in the PS4 fraction. Therefore, it is preferable that the gas used in the gas flow treatment contains hydrogen gas. Exposing the sulfide to a hydrogen gas atmosphere allows the sulfide to come into contact with hydrogen gas evenly, thereby efficiently improving the PS4 fraction and achieving high ionic conductivity.

[0027] A method for producing a sulfide solid electrolyte according to a third aspect of the present embodiment includes the steps of: a method for producing a sulfide solid electrolyte, wherein the gas flow treatment is carried out while supplying a gas having a hydrogen gas content of 0.5% by volume or more and 100% by volume or less; is. In the third aspect, by supplying a gas containing a predetermined amount of hydrogen gas, the sulfide is brought into contact with hydrogen and the sulfide is exposed to a hydrogen gas atmosphere, thereby efficiently improving the PS4 fraction and achieving high ionic conductivity.

[0028] A method for producing a sulfide solid electrolyte according to a fourth aspect of the present embodiment includes: a method for producing a sulfide solid electrolyte, wherein the gas flow treatment is performed while pulverizing the sulfide; is. According to the fourth aspect, the pulverization process exposes new sulfide surfaces one after another, and the newly exposed surfaces can be sequentially subjected to airflow treatment, thereby more efficiently improving the PS4 fraction and achieving high ionic conductivity.

[0029] A method for producing a sulfide solid electrolyte according to a fifth aspect of the present embodiment includes: a method for producing a sulfide solid electrolyte, in which the pulverization is carried out by a mechanical milling method; is. In the fifth aspect, the pulverization in the fourth embodiment is carried out by a mechanical milling method (solid-phase method), which clarifies that the pulverization is carried out using a conventionally used pulverizer such as a bead mill, a ball mill, etc. The mechanical milling method, also known as a solid-liquid method, is a method in which a normally solid raw material is pulverized and reacted, but as will be described later, in this embodiment, the method may also include pulverization while forming a slurry using an appropriate solvent.

[0030] A method for producing a sulfide solid electrolyte according to a sixth aspect of the present embodiment includes: a method for producing a sulfide solid electrolyte, wherein the gas flow treatment is further performed by adding an alkali metal halide; is. The sixth aspect is an effective means for producing a sulfide solid electrolyte containing a halogen element, for example, when a sulfide not containing a halogen element is used. The inclusion of a halogen element in the sulfide solid electrolyte is expected to improve ionic conductivity. Furthermore, by employing an alkali metal halide as a means for supplying a halogen element, an alkali metal element that exhibits ionic conductivity can be supplied together with the halogen element, thereby making it possible to more efficiently improve ionic conductivity. Note that when a sulfide containing a halogen element in addition to an alkali metal element, phosphorus element, and sulfur element is used, an alkali metal halide need not be added, but may be added as needed.

[0031] A method for producing a sulfide solid electrolyte according to a seventh aspect of the present embodiment includes: a method for producing a sulfide solid electrolyte, wherein the alkali metal halide is at least one selected from the group consisting of lithium halide and sodium halide; is. By adopting at least one of lithium halide and sodium halide as the alkali metal halide, it is possible to supply lithium element and sodium element, which are more effective among alkali metal elements in expressing ionic conductivity, and therefore it is possible to improve ionic conductivity.

[0032] A method for producing a sulfide solid electrolyte according to an eighth aspect of the present embodiment includes: a method for producing a sulfide solid electrolyte, wherein the air flow treatment is carried out for 0.1 hours or more and 100 hours or less; is. By setting the time for the airflow treatment to between 0.1 hours and 100 hours, the airflow treatment can be carried out efficiently, the PS4 fraction can be improved, and high ionic conductivity can be obtained.

[0033] A method for producing a sulfide solid electrolyte according to a ninth aspect of the present embodiment includes: a method for producing a sulfide solid electrolyte, wherein the gas is supplied at a rate of 0.1 L / min or more and 20 L / min or less per 100 g of the sulfide; is. When airflow treatment is performed while supplying a gas containing hydrogen gas, supplying hydrogen gas at a flow rate within a predetermined range to the sulfide that is the target of airflow treatment enables efficient airflow treatment, improves the PS4 fraction, and also makes it possible to obtain high ionic conductivity.

[0034] A method for producing a sulfide solid electrolyte according to a tenth aspect of the present embodiment includes: a method for producing a sulfide solid electrolyte, which further comprises mixing two or more raw materials selected from compounds containing at least one element selected from an alkali metal element, a sulfur element, and a phosphorus element; is. The sulfide used in the production method of this embodiment is obtained by mixing two or more raw materials selected from compounds containing at least one element of an alkali metal element, a sulfur element, and a phosphorus element. It is specified that it is obtained by mixing two or more raw materials selected from compounds containing at least one element of an alkali metal element, a sulfur element, and a phosphorus element.

[0035] A method for producing a sulfide solid electrolyte according to an eleventh aspect of this embodiment includes: a method for producing a sulfide solid electrolyte, which further comprises mixing two or more raw materials selected from compounds containing at least one element selected from an alkali metal element, a sulfur element, a phosphorus element, and a halogen element; is. The eleventh aspect specifies that, in addition to the raw materials used in the tenth aspect, compounds containing halogen elements can also be used as raw materials. As a result, the sulfide solid electrolyte contains halogen elements, and further improvement in ionic conductivity is expected.

[0036] A method for producing a sulfide solid electrolyte according to a twelfth aspect of this embodiment includes: a method for producing a sulfide solid electrolyte, wherein the alkali metal element is at least one selected from lithium element and sodium element; is. As in the seventh embodiment, by employing at least one of lithium element and sodium element as the alkali metal element, it is possible to supply lithium element and sodium element, which are more effective among alkali metal elements in exhibiting ionic conductivity, and therefore it is possible to improve ionic conductivity.

[0037] A method for producing a sulfide solid electrolyte according to a thirteenth aspect of the present embodiment includes: a method for producing a sulfide solid electrolyte, wherein the compound contains lithium sulfide and diphosphorus pentasulfide; is. The "compound" in the tenth and eleventh embodiments is specified to contain lithium sulfide and diphosphorus pentasulfide. By using a raw material containing lithium sulfide and diphosphorus pentasulfide, it becomes easier to increase the PS4 fraction and obtain high ionic conductivity.

[0038] A method for producing a sulfide solid electrolyte according to a fourteenth aspect of the present embodiment includes: A method for producing a sulfide solid electrolyte, wherein the compound contains lithium sulfide, diphosphorus pentasulfide, and lithium halide; is. In a tenth embodiment, a raw material selected from compounds containing at least one element selected from lithium, sulfur, phosphorus, and a halogen is employed, and lithium halide is employed as the halogen-containing compound. By using a halogen-containing compound as a raw material, the resulting sulfide solid electrolyte contains a halogen element, and further improvement in ionic conductivity is expected. Furthermore, lithium, which is more effective among alkali metal elements in exhibiting ionic conductivity, can be supplied together with the halogen element, thereby enabling improvement in ionic conductivity.

[0039] A method for producing a sulfide solid electrolyte according to a fifteenth aspect of the present embodiment includes: a method for producing a sulfide solid electrolyte, wherein the sulfide is a sulfide containing an amorphous component; is. The sulfide used in the manufacturing method of this embodiment is preferably the tenth and eleventh forms, which can be obtained by mixing raw materials containing an alkali metal element, a sulfur element, a phosphorus element, and a compound containing a halogen element, and the sulfide obtained by this mixing is specified to be one containing an amorphous component, for example, an amorphous sulfide.

[0040] A method for producing a sulfide solid electrolyte according to a sixteenth aspect of the present embodiment includes: a method for producing a sulfide solid electrolyte, wherein the sulfide is a sulfide containing a P2S7 unit; is. The sulfide can be preferably obtained by mixing raw materials. The sulfide obtained by this mixing contains not only PS4 units but also P2S7 units and P2S6 units. When the mixing is performed using a grinder, as described above, collisions between media such as beads and solid raw materials, as well as between solid raw materials themselves, can cause localized high temperatures, making it easier to produce P2S7 units and P2S6 units. Even in such cases, the production method of this embodiment can reduce the proportion of at least one of the P2S7 units and P2S6 units, particularly the proportion of P2S7 units (P2S7 fraction), thereby improving the PS4 fraction and achieving high ionic conductivity. As shown in the examples, the proportion of P2S7 units (P2S7 fraction) tends to decrease more as the airflow treatment time increases.

[0041] [Sulfide] The sulfide used in the production method of this embodiment will be described. The sulfide used in the production method of this embodiment contains lithium, sulfur, and phosphorus, preferably a halogen, and is preferably obtained by a production method including mixing two or more raw materials selected from compounds containing at least one of these elements.

[0042] (raw materials) The raw materials are two or more selected from compounds containing at least one element selected from an alkali metal element, sulfur element, and phosphorus element, preferably a halogen element. That is, in this embodiment, two or more compounds containing at least one element selected from an alkali metal element, sulfur element, and phosphorus element, preferably a halogen element, are used as raw materials. As described above, the solid electrolyte in this embodiment contains an alkali metal element, sulfur element, and phosphorus element, preferably a halogen element, and therefore, raw materials for which two or more compounds are used include an alkali metal element, sulfur element, and phosphorus element, preferably a halogen element.

[0043] Compounds that can be used as raw materials include at least one element selected from alkali metal elements, sulfur elements, and phosphorus elements, and preferably halogen elements. More specifically, alkali metal sulfides such as lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; alkali metal halides such as lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide, and sodium halides such as sodium iodide, sodium fluoride, sodium chloride, and sodium bromide; phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5); various phosphorus fluorides (PF3, PF5), various phosphorus chlorides (PCl3, PC Representative examples of the starting material include phosphorus halides such as thiophosphoryl fluoride (PSF3), thiophosphoryl chloride (PSCl3), thiophosphoryl bromide (PSBr3), thiophosphoryl iodide (PSI3), thiophosphoryl fluoride dichloride (PSCl2F), and thiophosphoryl fluoride dibromide (PSBr2F); and starting materials composed of at least two elements selected from the above four elements, such as fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2), with bromine (Br2) and iodine (I2) being preferred.

[0044] Examples of compounds that can be used as raw materials other than those mentioned above include compounds that contain at least one element selected from the above four elements and also contain an element other than the four elements, more specifically lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; metal sulfides such as silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, tin sulfide (SnS, SnS), aluminum sulfide, and zinc sulfide; phosphate compounds such as sodium phosphate and lithium phosphate; metal halides such as aluminum halides, silicon halides, germanium halides, arsenic halides, selenium halides, tin halides, antimony halides, tellurium halides, and bismuth halides; and phosphorus oxyhalides such as phosphorus oxychloride (POCl3) and phosphorus oxybromide (POBr3).

[0045] In this embodiment, from the viewpoint of more easily obtaining a sulfide solid electrolyte having high ionic conductivity, among alkali metal elements, lithium element and sodium element are preferred, and lithium element is more preferred, and among halogen elements, chlorine element, bromine element and iodine element are preferred, and bromine element and iodine element are more preferred. Furthermore, these elements may be used alone or in combination of two or more kinds. From the same viewpoint, preferred compounds that can be used as raw materials include, among the above, alkali metal sulfides such as lithium sulfide and sodium sulfide; phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5); elemental halogens such as fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2); and lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; among alkali metal sulfides, lithium sulfide is preferred; among phosphorus sulfides, diphosphorus pentasulfide is preferred; among elemental halogens, chlorine (Cl2), bromine (Br2), and iodine (I2) are preferred, with bromine (Br2) and iodine (I2) being more preferred; and among lithium halides, lithium chloride, lithium bromide, and lithium iodide are preferred, with lithium bromide and lithium iodide being more preferred.

[0046] Preferred examples of combinations of compounds that can be used as raw materials include a combination of lithium sulfide and diphosphorus pentasulfide, and when a compound containing a halogen element is used, a combination of lithium sulfide, diphosphorus pentasulfide, and a lithium halide, and a combination of lithium sulfide, diphosphorus pentasulfide, and a simple halogen. Preferred lithium halides include lithium bromide, lithium iodide, and lithium chloride, and preferred simple halogens are bromine and iodine. In this embodiment, the alkali metal sulfides, alkali metal halides, halogen elements, and other compounds may be used alone or in combination of two or more of the above-mentioned examples.

[0047] In this embodiment, examples of compounds that can be used as raw materials include solid electrolytes such as Li3PS4 that contain PS4 units, etc. By using, as a raw material, a structure containing lithium such as Li3PS4 that exists as a main structure in the sulfide solid electrolyte obtained by the production method of this embodiment, the constituent ratio of the structure can be increased, i.e., the PS4 fraction can be improved, and high ionic conductivity can be obtained, compared to when a sulfide solid electrolyte is formed by synthesizing the structure through a reaction between compounds using a compound such as lithium sulfide as a raw material.

[0048] In this embodiment, examples of solid electrolytes that can be used as raw material compounds include amorphous sulfide solid electrolytes having a Li3PS4 molecular structure (also referred to as "amorphous Li3PS4") and crystalline sulfide solid electrolytes (also referred to as "crystalline Li3PS4"). Considering the need to increase the PS4 fraction and obtain high ionic conductivity, amorphous sulfide solid electrolytes or crystalline sulfide solid electrolytes that do not contain the Li4P2S7 structure are preferred. These solid electrolytes can be produced by conventional production methods such as mechanical milling, slurry production, and melt quenching, or commercially available products can also be used. In addition, the sulfide solid electrolyte used as a raw material is preferably amorphous. When a compound containing a halogen element is used as a raw material, the dispersibility of the halogen atoms is improved, and bonding between the halogen atoms and lithium atoms, sulfur atoms, and phosphorus atoms in the solid electrolyte is facilitated, resulting in a sulfide solid electrolyte having higher ionic conductivity.

[0049] When the above solid electrolyte is used as the compound, the content of the amorphous sulfide solid electrolyte having a Li3PS4 structure relative to the total amount of raw materials is preferably 60 to 100 mol%, more preferably 65 to 90 mol%, and even more preferably 70 to 80 mol%. When a solid electrolyte having a Li3PS4 structure or the like and a halogen element are used, the content of the halogen element relative to the amorphous sulfide solid electrolyte having a Li3PS4 structure or the like is preferably 1 to 50 mol%, more preferably 2 to 40 mol%, even more preferably 3 to 25 mol%, and even more preferably 3 to 15 mol%.

[0050] In the present embodiment, when lithium sulfide is used as the compound containing an alkali metal, the lithium sulfide is preferably in the form of particles. The average particle size of lithium sulfide particles (D 50 ) is preferably 10 μm or more and 2000 μm or less, more preferably 30 μm or more and 1500 μm or less, and even more preferably 50 μm or more and 1000 μm or less. 50 ) is the particle size at which 50% of the total particle size is obtained by accumulating the particle size distribution curve from the smallest particle size, and the volume distribution is the average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution analyzer. Furthermore, among the above-mentioned examples of raw materials, solid raw materials preferably have an average particle size similar to that of the lithium sulfide particles, i.e., within the same range as that of the lithium sulfide particles.

[0051] When lithium sulfide, diphosphorus pentasulfide, and lithium halide are used as raw materials, the ratio of lithium sulfide to the total of lithium sulfide and diphosphorus pentasulfide is preferably 60 mol% or more, more preferably 65 mol% or more, and even more preferably 68 mol% or more, from the viewpoint of obtaining higher chemical stability, improving the PS4 fraction, and obtaining high ionic conductivity, and the upper limit is preferably 80 mol% or less, more preferably 78 mol% or less, and even more preferably 76 mol% or less.

[0052] When lithium sulfide, diphosphorus pentasulfide, lithium halide, and other raw materials used as needed are used, the content of lithium sulfide and diphosphorus pentasulfide relative to the total of these is preferably 60 mol% or more, more preferably 65 mol% or more, and even more preferably 70 mol% or more, and the upper limit is preferably 100 mol% or less, more preferably 90 mol% or less, and even more preferably 80 mol% or less. Furthermore, when lithium bromide and lithium iodide are used in combination as the lithium halide, from the viewpoint of improving the PS4 fraction and obtaining high ionic conductivity, the proportion of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 mol% or more, more preferably 20 mol% or more, even more preferably 40 mol% or more, still more preferably 50 mol% or more, with the upper limit being preferably 99 mol% or less, more preferably 90 mol% or less, even more preferably 80 mol% or less, and still more preferably 70 mol% or less.

[0053] (mixture) Mixing of two or more raw materials selected from compounds containing at least one element selected from lithium, sulfur, and phosphorus, preferably halogen elements, can be carried out, for example, by using a mixer. It can also be carried out using a stirrer, a pulverizer, or the like. Mixing of raw materials can occur using a stirrer, and pulverization of raw materials occurs using a pulverizer, but mixing also occurs at the same time. In other words, it can be said that sulfides can be produced by stirring, mixing, pulverizing, or a combination of these processes of two or more raw materials selected from compounds containing at least one element selected from lithium, sulfur, and phosphorus, preferably halogen elements.

[0054] Examples of the stirrer or mixer include a mechanical stirring mixer that is equipped with stirring blades in a reaction vessel and can stir (also referred to as mixing by stirring or stirring mixing). Examples of the mechanical stirring mixer include a high-speed stirring mixer and a double-arm mixer. Examples of the high-speed stirring mixer include a vertical-axis rotary mixer and a horizontal-axis rotary mixer, and either type of mixer may be used.

[0055] Examples of the shape of the stirring blade used in the mechanical stirring mixer include blade type, arm type, anchor type, paddle type, full zone type, ribbon type, multi-stage blade type, double arm type, shovel type, double blade type, flat blade type, C-type blade type, etc., and from the viewpoint of promoting the reaction of the raw materials more efficiently, the shovel type, flat blade type, C-type blade type, anchor type, paddle type, full zone type, etc. are preferred, with the anchor type, paddle type, and full zone type being more preferred.

[0056] When a mechanically agitated mixer is used, the rotation speed of the agitator blades can be adjusted appropriately depending on the volume of the fluid in the reaction tank, the temperature, the shape of the agitator blades, etc., and is not particularly limited. However, it is usually set to about 5 rpm or more and 400 rpm or less. From the viewpoint of more efficiently promoting the reaction of the raw materials, the rotation speed is preferably 10 rpm or more and 300 rpm or less, more preferably 15 rpm or more and 250 rpm or less, and even more preferably 20 rpm or more and 200 rpm or less.

[0057] The temperature conditions when mixing is performed using a mixer are not particularly limited, and are, for example, usually −30 to 120° C., preferably −10 to 100° C., more preferably 0 to 80° C., and even more preferably 10 to 60° C. The mixing time is usually 0.1 to 500 hours, and from the viewpoint of dispersing the raw materials more uniformly and promoting the reaction, is preferably 1 to 450 hours, more preferably 10 to 425 hours, even more preferably 20 to 400 hours, and still more preferably 40 to 375 hours.

[0058] The method of mixing with pulverization using a pulverizer has been conventionally adopted as a solid-phase method (mechanical milling method). As the pulverizer, for example, a media-type pulverizer using pulverization media can be used. Media-type mills are broadly classified into vessel-driven mills and media-agitation mills. Examples of vessel-driven mills include agitation tanks, grinding tanks, and combinations thereof, such as ball mills and bead mills. Examples of media-agitation mills include impact mills such as cutter mills, hammer mills, and pin mills; tower mills and other tower-type mills; agitation tank mills such as attritors, aquamizers, and sand grinders; flow-tank mills such as Viscomill and pearl mills; flow-tube mills; annular mills such as Coball mills; continuous dynamic mills; and single- or multi-shaft kneaders. Among these, considering the ease of adjusting the particle size of the resulting sulfide, the ball mills and bead mills exemplified as vessel-driven mills are preferred, and planetary mills are particularly preferred.

[0059] These pulverizers can be appropriately selected depending on the desired scale, etc. For relatively small scales, container-driven pulverizers such as ball mills and bead mills can be used, while for large scales or mass production, other types of pulverizers may be used.

[0060] Furthermore, as will be described later, when the materials are in a liquid state involving a liquid such as a solvent or in a slurry state during mixing, it is preferable to use a wet mill that can handle wet milling. Representative examples of wet mills include wet bead mills, wet ball mills, and wet vibration mills, with wet bead mills using beads as milling media being preferred because they allow for flexible adjustment of milling conditions and are suitable for smaller particle sizes. Alternatively, dry mills such as dry media mills (e.g., dry bead mills, dry ball mills, and dry vibration mills) and dry non-media mills (e.g., jet mills) can also be used.

[0061] Furthermore, when the material to be mixed is in a liquid or slurry state, a flow-through mill that can be operated to circulate as needed can also be used. Specifically, a mill that circulates the material between a mill (milling mixer) that pulverizes the slurry and a temperature holding tank (reaction vessel) can be used.

[0062] The size of the beads or balls used in the ball mill or bead mill may be appropriately selected depending on the desired particle size, processing amount, etc. For example, the diameter of the beads is usually 0.05 mm or more, preferably 0.1 mm or more, more preferably 0.3 mm or more, with the upper limit being usually 5.0 mm or less, preferably 3.0 mm or less, more preferably 2.0 mm or less. The diameter of the balls is usually 2.0 mm or more, preferably 2.5 mm or more, more preferably 3.0 mm or more, with the upper limit being usually 20.0 mm or less, preferably 15.0 mm or less, more preferably 10.0 mm or less. Examples of materials include metals such as stainless steel, chrome steel, and tungsten carbide; ceramics such as zirconia and silicon nitride; and minerals such as agate.

[0063] Furthermore, when a ball mill or bead mill is used, the rotation speed varies depending on the scale of the treatment and cannot be generalized, but is usually 10 rpm or more, preferably 20 rpm or more, and more preferably 50 rpm or more, with the upper limit being usually 1,000 rpm or less, preferably 900 rpm or less, more preferably 800 rpm or less, and even more preferably 700 rpm or less. The grinding time in this case varies depending on the scale of the treatment and cannot be generalized, but is usually 0.5 hours or more, preferably 1 hour or more, more preferably 5 hours or more, and even more preferably 10 hours or more, with the upper limit being usually 100 hours or less, preferably 72 hours or less, more preferably 48 hours or less, and even more preferably 36 hours or less.

[0064] By selecting the size and material of the medium (beads, balls) used, the rotor rotation speed, time, etc., it is possible to perform mixing, stirring, pulverization, or a combination of these processes, and it is possible to adjust the particle size, etc. of the resulting sulfide.

[0065] (solvent) In the above mixing, a solvent may be added to the raw materials and mixed in. As the solvent, various solvents widely known as organic solvents may be used.

[0066] As the solvent, a wide variety of solvents that have conventionally been used in the production of solid electrolytes can be used, and examples thereof include hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents.

[0067] Examples of aliphatic hydrocarbons include hexane, pentane, 2-ethylhexane, heptane, octane, decane, undecane, dodecane, and tridecane. Examples of alicyclic hydrocarbons include cyclohexane and methylcyclohexane. Examples of aromatic hydrocarbon solvents include benzene, toluene, xylene, mesitylene, ethylbenzene, tert-butylbenzene, trifluoromethylbenzene, and nitrobenzene.

[0068] In addition to the above hydrocarbon solvents, examples of the solvent include solvents containing hetero elements such as elements other than carbon and hydrogen, such as nitrogen, oxygen, sulfur, and halogen elements. Preferred examples of the solvents containing oxygen as a hetero element include ether solvents, ester solvents, alcohol solvents, aldehyde solvents, and ketone solvents.

[0069] Preferred examples of the ether solvent include aliphatic ethers such as dimethyl ether, diethyl ether, tert-butyl methyl ether, dimethoxymethane, dimethoxyethane, diethylene glycol dimethyl ether (diglyme), triethylene oxide glycol dimethyl ether (triglyme), diethylene glycol, and triethylene glycol; alicyclic ethers such as ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, and dioxane; heterocyclic ethers such as furan, benzofuran, and benzopyran; and aromatic ethers such as methyl phenyl ether (anisole), ethyl phenyl ether, dibenzyl ether, and diphenyl ether.

[0070] Preferred examples of the ester solvent include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, and isopropyl acetate; aliphatic esters such as methyl propionate, ethyl propionate, dimethyl oxalate, diethyl oxalate, dimethyl malonate, diethyl malonate, dimethyl succinate, and diethyl succinate; alicyclic esters such as methyl cyclohexanecarboxylate, ethyl cyclohexanecarboxylate, and dimethyl cyclohexanedicarboxylate; heterocyclic esters such as methyl pyridinecarboxylate, methyl pyrimidinecarboxylate, acetolactone, propiolactone, butyrolactone, and valerolactone; and aromatic esters such as methyl benzoate, ethyl benzoate, dimethyl phthalate, diethyl phthalate, butyl benzyl phthalate, dicyclohexyl phthalate, trimethyl trimellitate, and triethyl trimellitate.

[0071] Preferred examples of the solvent include alcohol solvents such as ethanol and butanol; aldehyde solvents such as formaldehyde, acetaldehyde and dimethylformamide; and ketone solvents such as acetone and methyl ethyl ketone.

[0072] Examples of solvents containing a nitrogen element as a hetero element include solvents having a group containing a nitrogen element, such as an amino group, an amide group, a nitro group, or a nitrile group. Preferred examples of solvents having an amino group include aliphatic amines such as ethylenediamine, diaminopropane, dimethylethylenediamine, diethylethylenediamine, dimethyldiaminopropane, tetramethyldiaminomethane, tetramethylethylenediamine (TMEDA), and tetramethyldiaminopropane (TMPDA); alicyclic amines such as cyclopropanediamine, cyclohexanediamine, and bisaminomethylcyclohexane; heterocyclic amines such as isophoronediamine, piperazine, dipiperidylpropane, and dimethylpiperazine; and aromatic amines such as phenyldiamine, tolylenediamine, naphthalenediamine, methylphenylenediamine, dimethylnaphthalenediamine, dimethylphenylenediamine, tetramethylphenylenediamine, and tetramethylnaphthalenediamine. Preferred examples of the solvent include nitrogen-containing solvents such as dimethylformamide, acetonitrile, acrylonitrile, and nitrobenzene.

[0073] Preferred examples of the solvent containing a halogen element as a hetero element include dichloromethane, chlorobenzene, trifluoromethylbenzene, chlorobenzene, chlorotoluene, and bromobenzene. Preferred examples of the solvent containing elemental sulfur include dimethyl sulfoxide and carbon disulfide.

[0074] When a solvent is used, the amount of solvent used is preferably 100 mL or more, more preferably 200 mL or more, even more preferably 250 mL or more, and even more preferably 300 mL or more per kg of the total amount of raw materials, and the upper limit is preferably 3000 mL or less, more preferably 2500 mL or less, even more preferably 2000 mL or less, and even more preferably 1550 mL or less. When the amount of solvent used is within the above range, the raw materials can be reacted efficiently.

[0075] (Dry) If a solvent is used for mixing, the process may include drying the resulting fluid (usually a slurry) after mixing. Removal of the solvent yields a sulfide. The resulting sulfide has the structure of a solid electrolyte such as a PS4 unit, and exhibits ionic conductivity due to alkali metal elements such as lithium and sodium.

[0076] The fluid obtained by mixing can be dried at a temperature that depends on the type of solvent. Alternatively, the solvent can be evaporated by drying under reduced pressure (vacuum drying) using a vacuum pump or the like at typically 5 to 100°C, preferably 10 to 85°C, more preferably 15 to 70°C, and even more preferably at about room temperature (23°C) (for example, about room temperature ±5°C).

[0077] Drying may be performed by filtering the fluid using a glass filter or the like, by solid-liquid separation by decantation, or by solid-liquid separation using a centrifuge, etc. When a solvent is used, the sulfide is obtained by solid-liquid separation. Specifically, solid-liquid separation can be easily performed by decantation, in which the fluid is transferred to a container, the sulfide is precipitated, and then the supernatant solvent is removed, or by filtration using, for example, a glass filter with a pore size of about 10 to 200 μm, preferably 20 to 150 μm.

[0078] Drying may be carried out after mixing and before the air flow treatment described below, or may be carried out after the air flow treatment.

[0079] (sulfide) The sulfide obtained by the above mixing, or, if a solvent is used, the sulfide obtained by removing the solvent by drying, contains units possessed by solid electrolytes, such as P2S7 units and P2S6 units, in addition to the PS4 units, as described above, and exhibits ionic conductivity due to alkali metal elements such as lithium and sodium, and therefore has properties that can generally be called a sulfide solid electrolyte. In the production method of this embodiment, the sulfide obtained by the above mixing is subjected to an air flow treatment, thereby obtaining a sulfide solid electrolyte.

[0080] The proportions of PS4 units (PS4 fraction), P2S7 units (P2S7 fraction), and P2S6 units (P2S6 fraction) contained in sulfides vary depending on the types and blending ratios of compounds used as raw materials in the production of the sulfides, so cannot be generalized, but are usually as follows: The PS4 fraction is usually 10.0% or more, preferably 15.0% or more, more preferably 20.0% or more, even more preferably 40.0% or more, even more preferably 60.0% or more, and particularly preferably 80.0% or more, with a higher upper limit being preferable, and is usually 95.0% or less. The P2S7 fraction is usually 70.0% or less, preferably 65.0% or less, more preferably 50.0% or less, even more preferably 25.0% or less, still more preferably 10.0% or less, and particularly preferably 7.5% or less, with a lower limit of usually 1.0% or more. The P2S6 fraction is usually 20.0% or less, preferably 15.0% or less, with a lower limit of usually 5.0% or more.

[0081] The sulfide obtained by the above mixing basically becomes an amorphous sulfide (glass component) unless it is mixed by pulverizing it using a pulverizer to the extent that it crystallizes.

[0082] The sulfide obtained by the above mixing may be an amorphous sulfide (glass component) or a crystalline sulfide, and can be appropriately selected as desired. When a crystalline sulfide is used, the sulfide obtained by the above mixing can be converted into a crystalline sulfide by heating it. The sulfide may also include crystalline sulfides in which an amorphous component (glass component) is formed on the surface as a result of processing such as grinding described below to adjust the particle size of the crystalline sulfide powder. Therefore, sulfides containing an amorphous component include amorphous sulfides and crystalline sulfides in which an amorphous component is formed on the surface.

[0083] (heating) When a crystalline sulfide is used as the sulfide, heating may be further performed to obtain the sulfide. If an amorphous sulfide (glass component) is obtained by the above mixing, a crystalline sulfide can be obtained by heating, and if a crystalline sulfide is obtained, a crystalline sulfide with an improved crystallinity can be obtained. In addition, when a solvent is used during mixing, the solvent can be removed by heating without performing the above-mentioned drying, and a sulfide can be obtained. Depending on the heating conditions, either an amorphous sulfide or a crystalline sulfide can be obtained.

[0084] For example, when obtaining an amorphous sulfide, the heating temperature may be determined depending on the structure of the crystalline sulfide obtained by heating the amorphous sulfide. Specifically, the amorphous sulfide is subjected to differential thermal analysis (DTA) using a differential thermal analyzer (DTA) at a temperature increase rate of 10 ° C. / min. The heating temperature is preferably set to 5 ° C. or less, more preferably 10 ° C. or less, and even more preferably 20 ° C. or less, starting from the temperature of the exothermic peak observed at the lowest temperature. There is no particular limit to the lower limit, but it may be set to about -40 ° C. or more, which is the temperature at the top of the exothermic peak observed at the lowest temperature. By setting the temperature range, amorphous sulfides can be obtained more efficiently and reliably. The heating temperature for obtaining an amorphous sulfide cannot be generally defined because it varies depending on the structure of the crystalline sulfide to be obtained. However, it is usually preferably 135°C or lower, more preferably 130°C or lower, and even more preferably 125°C or lower. There is no particular lower limit, but it is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 105°C or higher.

[0085] Further, when an amorphous sulfide is heated to obtain a crystalline sulfide, the heating temperature may be determined according to the structure of the crystalline sulfide, and is preferably higher than the heating temperature for obtaining an amorphous sulfide. Specifically, the amorphous sulfide is subjected to differential thermal analysis (DTA) using a differential thermal analyzer (DTA) at a temperature increase rate of 10 ° C. / min. The temperature is preferably 5 ° C. or higher, more preferably 10 ° C. or higher, and even more preferably 20 ° C. or higher, starting from the peak top temperature of the exothermic peak observed on the lowest temperature side. There is no particular upper limit, but it should be about 40 ° C. or lower. By using such a temperature range, crystalline sulfide can be obtained more efficiently and reliably. The heating temperature for obtaining a crystalline sulfide cannot be generally defined because it varies depending on the composition and structure of the resulting crystalline sulfide. However, it is usually preferably 130°C or higher, more preferably 135°C or higher, and even more preferably 140°C or higher. There is no particular upper limit, but it is preferably 600°C or lower, more preferably 550°C or lower, and even more preferably 500°C or lower.

[0086] The heating time is not particularly limited as long as it is a time that allows the desired amorphous sulfide or crystalline sulfide to be obtained, but is, for example, preferably 1 minute or more, more preferably 10 minutes or more, even more preferably 30 minutes or more, and even more preferably 1 hour or more. The upper limit of the heating time is not particularly limited, but is preferably 24 hours or less, more preferably 10 hours or less, even more preferably 5 hours or less, and even more preferably 3 hours or less.

[0087] Furthermore, heating is preferably carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere or an argon atmosphere) or a reduced pressure atmosphere (particularly in a vacuum). An inert gas atmosphere containing hydrogen gas at a certain concentration, for example, the concentration of hydrogen gas in the gas flow treatment described below, may also be used. This is because deterioration (e.g., oxidation) of the crystalline sulfide can be prevented. The heating method is not particularly limited, and examples include methods using a hot plate, a vacuum heating device, an argon gas atmosphere furnace, and a calcination furnace. Furthermore, industrially, horizontal dryers and horizontal vibration fluidized dryers having a heating means and a feed mechanism can also be used, and the method can be selected depending on the amount of heat to be processed.

[0088] [Airflow processing] The manufacturing method of this embodiment includes subjecting the sulfide to an airflow treatment with at least one gas selected from an inert gas and hydrogen gas. The airflow treatment reduces the proportion of P2S7 units (P2S7 fraction) in the sulfide, thereby increasing the proportion of PS4 units (PS4 fraction), resulting in a sulfide solid electrolyte with high ionic conductivity. The gas used for the airflow treatment is preferably a gas containing at least hydrogen gas. This is because it facilitates a reduction in the proportion of P2S7 units (P2S7 fraction) in the sulfide, thereby increasing the proportion of PS4 units (PS4 fraction), thereby improving the ionic conductivity of the resulting sulfide solid electrolyte. As previously mentioned, airflow treatment reduces units other than PS4 units, i.e., P2S7 units and / or P2S6 units. However, examples have shown that the longer the airflow treatment time, the greater the reduction in P2S7 units. Therefore, it is believed that the effect of airflow treatment is more effective in reducing the proportion of P2S7 units (P2S7 fraction).

[0089] The gas flow treatment method is not particularly limited as long as it exposes the sulfide to an atmosphere of at least one gas selected from an inert gas and hydrogen gas, and for example, a method can be employed in which the sulfide is placed in a tank equipped with piping for supplying and exhausting a gas containing preferably hydrogen gas, and a gas containing preferably hydrogen gas is supplied into the tank. Furthermore, when the sulfide is in a slurry state or liquid state containing a solvent, a method can also be employed in which a gas containing preferably hydrogen gas is supplied by bubbling.

[0090] An example of the airflow treatment method is to pulverize the sulfide in an atmosphere of at least one gas selected from an inert gas and hydrogen gas, preferably hydrogen gas. As described above, by performing the pulverization while pulverizing, new surfaces of the sulfide are successively exposed, and the new surfaces can be sequentially subjected to the airflow treatment. This makes it possible to more efficiently improve the PS4 fraction and obtain high ionic conductivity. Furthermore, when a solid electrolyte with a small particle size is desired, the particle size of the sulfide solid electrolyte can be adjusted by pulverization. When the sulfide is a crystalline sulfide solid electrolyte, such as a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure, pulverization may result in the formation of P2S7 units as amorphous components on the surface. In such cases, performing airflow treatment after pulverization, or performing pulverization while performing airflow treatment, can improve the PS4 fraction and provide high ionic conductivity. It goes without saying that, not limited to such cases, employing a sulfide containing at least one of a P2S7 unit and a P2S6 unit, particularly a sulfide containing a P2S7 unit, as the sulfide is preferable from the viewpoint of improving the PS4 fraction and providing high ionic conductivity.

[0091] Examples of methods for pulverizing sulfides include the mechanical milling method (solid-phase method) described as a method for mixing raw materials in the sulfide production method, i.e., a method using a pulverizer such as a bead mill or a ball mill. The pulverization conditions may be appropriately selected depending on the average particle size of the desired sulfide solid electrolyte, and may be appropriately selected from the conditions described as a method for mixing raw materials.

[0092] Unlike the mixing of raw materials, the grinding of sulfides does not require thorough mixing, and therefore grinders of a different type than the grinders already mentioned, such as bead mills and ball mills, can be used. Such grinders include machines that can grind objects using ultrasound, such as ultrasonic grinders, ultrasonic homogenizers, and probe ultrasonic grinders. Needless to say, these grinders can also be used for mixing, since mixing occurs.

[0093] In this case, various conditions such as the frequency of the ultrasonic waves may be appropriately selected depending on the average particle size of the desired sulfide solid electrolyte, and the frequency may be, for example, about 1 kHz or more and 100 kHz or less, and from the viewpoint of more efficiently pulverizing the sulfide, the frequency is preferably 3 kHz or more and 50 kHz or less, more preferably 5 kHz or more and 40 kHz or less, and even more preferably 10 kHz or more and 30 kHz or less. The output of the ultrasonic crusher is usually about 500 to 16,000W, preferably 600 to 10,000W, more preferably 750 to 5,000W, and even more preferably 900 to 1,500W.

[0094] The average particle size (D 50 ) is determined appropriately as desired, but is usually 0.01 μm to 50 μm, preferably 0.03 μm to 5 μm, and more preferably 0.05 μm to 3 μm. By pulverizing the sulfide in a hydrogen atmosphere to set the average particle size within the above range, the PS4 fraction is improved, high ionic conductivity is obtained, and it is possible to meet the demand for sulfide solid electrolytes with small particle sizes, such as an average particle size of 1 μm or less.

[0095] The pulverization time is not particularly limited as long as it is a time that allows the sulfide solid electrolyte to have a desired average particle size, and is usually from 0.1 hours to 100 hours. From the viewpoint of efficiently achieving a desired particle size, the pulverization time is preferably from 0.3 hours to 72 hours, more preferably from 0.5 hours to 48 hours, and even more preferably from 1 hour to 24 hours.

[0096] Alternatively, the sulfide may be dried and powdered before being pulverized. In this case, it is preferable to use any of the dry grinders among the grinders exemplified above as grinders that can be used in the method for producing a sulfide.

[0097] The airflow treatment may be carried out by further adding an alkali metal halide to the sulfide. In this case, it is preferable to carry out the above-mentioned pulverization from the viewpoint of facilitating incorporation of the alkali metal halide into the structure of the sulfide. As the alkali metal halide, those exemplified as alkali metal halides that can be used as the raw material can be preferably used. The alkali metal element contained in the alkali metal halide to be added is preferably lithium or sodium, more preferably lithium, as in the alkali metal halide used as the raw material, and may be the same as or different from the alkali metal element contained in the alkali metal halide used as the raw material, but is preferably the same.

[0098] By performing the airflow treatment with the addition of an alkali metal halide, for example, when a sulfide not containing a halogen element is used, the halogen element can be incorporated into the structure, resulting in a sulfide solid electrolyte containing a halogen element, which is expected to improve ionic conductivity. Furthermore, even when a sulfide containing a halogen element is used, it is known that the halogen element easily escapes from the sulfide structure during the sulfide production process. Therefore, adding an alkali metal halide during the airflow treatment can replenish the escaped halogen element, which can be expected to improve the ionic conductivity of the sulfide solid electrolyte. Furthermore, adding an alkali metal halide can supply not only the halogen element but also the alkali metal element that exhibits ionic conductivity, making it possible to more efficiently improve ionic conductivity.

[0099] When an alkali metal halide is added, the amount to be added varies depending on whether the sulfide contains or does not contain a halogen element, and therefore cannot be generalized. However, the amount is usually about 1 g or more and 80 g or less per 100 g of sulfide, preferably 5 g or more, more preferably 10 g or more, and the upper limit is preferably 70 g or less, more preferably 50 g or less, and even more preferably 35 g or less.

[0100] The gas flow treatment can be carried out using at least one gas selected from an inert gas and hydrogen gas, i.e., an inert gas alone, hydrogen gas alone, or a gas containing an inert gas and hydrogen gas. As described above, it is preferable to supply a gas containing at least hydrogen gas (hydrogen gas alone, or a mixed gas containing an inert gas and hydrogen gas). Thus, hydrogen gas may be supplied as hydrogen gas alone (a gas containing 100% by volume of hydrogen) or together with an inert gas such as nitrogen or argon. From the viewpoint of more efficient gas flow treatment, the content of hydrogen gas in the hydrogen-containing gas is preferably 0.5% by volume or more, preferably 1% by volume or more, more preferably 3% by volume or more, with the upper limit being 100% by volume or less, preferably 80% by volume or less, more preferably 60% by volume or less, even more preferably 30% by volume or less, and even more preferably 15% by volume or less. When the gas flow treatment is performed in a hydrogen gas atmosphere, the concentration of the hydrogen gas in the atmosphere can be appropriately selected from the range of 1% by volume to 100% by volume, and may be in the same range as the content of the hydrogen gas in the hydrogen-containing gas. The hydrogen gas atmosphere may be created by supplying the hydrogen-containing gas.

[0101] The amount of gas supplied in the gas flow treatment, i.e., the amount of gas containing hydrogen gas or the amount of gas containing an inert gas alone, is adjusted appropriately depending on the hydrogen gas content in the hydrogen-containing gas, the capacity of the container in which the gas flow treatment is performed, etc., and although it is not possible to generalize, it is usually about 0.1 L / min to 20 L / min per 100 g of sulfide.From the viewpoint of performing the gas flow treatment more efficiently, it is preferably 0.5 L / min or more, more preferably 1.0 L / min or more, and even more preferably 3.0 L / min or more, and the upper limit is preferably 15 L / min or less, more preferably 10 L / min or less, and even more preferably 7.5 L / min or less.

[0102] When the gas used for the airflow treatment contains hydrogen gas, the supply rate of the hydrogen gas is usually about 0.01 L / min or more and 5.0 L / min or less per 100 g of sulfide. From the viewpoint of performing the airflow treatment more efficiently, the supply rate of the hydrogen gas is preferably 0.03 L / min or more, more preferably 0.05 L / min or more, and even more preferably 0.1 L / min or more, with the upper limit being preferably 3.0 L / min or less, more preferably 1.0 L / min or less, and even more preferably 0.5 L / min or less.

[0103] The temperature conditions for the airflow treatment are not particularly limited and may be appropriately selected within the range of usually 0°C or higher and 600°C or lower. From the viewpoint of more efficient airflow treatment, the temperature is preferably 5°C or higher, more preferably 10°C or higher, even more preferably 15°C or higher, with the upper limit being preferably 500°C or lower, more preferably 300°C or lower, even more preferably 200°C or lower, still more preferably 100°C or lower, and particularly preferably about ±5°C around room temperature (23°C). The time condition for performing the airflow treatment is not particularly limited as long as it is a time that allows the sulfide solid electrolyte to have the desired PS4 fraction, and is usually 0.1 hours or more and 100 hours or less. From the viewpoint of efficiently improving the PS4 fraction, the time is preferably 1 hour or more, more preferably 4 hours or more, even more preferably 10 hours or more, and still more preferably 14 hours or more, with the upper limit being preferably 72 hours or less, more preferably 48 hours or less.

[0104] The gas flow treatment of sulfides also includes gas flow treatment when mixing two or more raw materials selected from compounds containing lithium, sulfur, and phosphorus, or at least one element selected from lithium, sulfur, phosphorus, and a halogen. This is because a mixture of at least two solid raw materials containing any of these elements is also included in the sulfides because sulfides (mainly sulfide solid electrolytes) are produced by the reaction of the solid raw materials. Therefore, in producing the sulfide, mixing of two or more raw materials selected from compounds containing at least one element selected from lithium, sulfur, and phosphorus, preferably halogen, can be performed, for example, in a hydrogen gas atmosphere or while supplying hydrogen gas, preferably while undergoing gas flow treatment with a gas containing hydrogen gas. The sulfide obtained in this manner can also be subjected to gas flow treatment to produce a sulfide solid electrolyte.

[0105] (Drying and heating) The manufacturing method of this embodiment may include drying and heating following the airflow treatment. When the sulfide to be subjected to the airflow treatment is a fluid containing a sulfide solid electrolyte in a slurry state or liquid state with a solvent, this method is effective when the sulfide solid electrolyte obtained by the airflow treatment is used as a powder. The sulfide solid electrolyte obtained by treating the sulfide with an air stream can be dried and heated in the same manner as the drying and heating of the sulfide described above.

[0106] (Sulfide solid electrolyte) The sulfide solid electrolyte obtained by the above-described manufacturing method is an amorphous sulfide solid electrolyte (glass component) or a crystalline sulfide solid electrolyte.

[0107] (Amorphous sulfide solid electrolyte) The amorphous sulfide solid electrolyte obtained by the production method of this embodiment contains lithium, sulfur, and phosphorus, and preferably further contains a halogen element. Representative examples include solid electrolytes composed of lithium sulfide and phosphorus sulfide, more preferably lithium halide, such as LiS-P2S5, LiS-P2S5-LiI, LiS-P2S5-LiCl, LiS-P2S5-LiBr, and LiS-P2S5-LiI-LiBr; and solid electrolytes containing other elements such as oxygen and silicon, such as LiS-P2S5-Li2O-LiI and LiS-SiS2-P2S5-LiI. From the viewpoint of obtaining higher ionic conductivity, preferred examples of solid electrolytes include Li2S-P2S5, which is composed of lithium sulfide and phosphorus sulfide, and solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, and Li2S-P2S5-LiI-LiBr. The types of elements constituting the amorphous sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectrometer.

[0108] The shape of the amorphous sulfide solid electrolyte is not particularly limited, but may be, for example, particulate. The average particle diameter (D 50 ) can be, for example, in the range of 0.01 μm to 500 μm, or 0.1 to 200 μm.

[0109] (Crystalline sulfide solid electrolyte) The crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment may be a so-called glass ceramic obtained by heating an amorphous solid electrolyte to a crystallization temperature or higher, and its crystal structure may be Li3PS4 crystal structure, Li4P2S6 crystal structure, Li7PS6 crystal structure, Li7P3S 11 Examples of such a crystal structure include a crystal structure having peaks at 2θ=approximately 20.2° and 23.6° (for example, JP 2013-16423 A).

[0110] Also, Li 4-x Ge1-x P x S4-type thio-LISICON Region II crystal structure (Kanno et al., Journal of the Electrochemical Society, 148(7)A742-746(2001)), Li 4-x Ge 1-x P x Examples of such a crystal structure include a crystal structure similar to the S4-based thio-LISICON Region II type (see Solid State Ionics, 177 (2006), 2721-2725). The crystal structure of the crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment is preferably the thio-LISICON Region II type crystal structure among the above, since it can provide higher ionic conductivity. Here, the "thio-LISICON Region II type crystal structure" refers to a structure in which Li 4-x Ge 1-x P x S4-type thio-LISICON Region II crystal structure, Li 4-x Ge 1-x P x This indicates that the crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment has either the thio-LISICON Region II type or a crystal structure similar to that of the S4-based thio-LISICON Region II type. The crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment may have the thio-LISICON Region II type crystal structure or may have it as the main crystal. However, from the viewpoint of obtaining higher ionic conductivity, it is preferable that it has it as the main crystal. In this specification, "having it as the main crystal" means that the proportion of the target crystal structure in the crystal structure is 80% or more, preferably 90% or more, and more preferably 95% or more. Furthermore, from the viewpoint of obtaining higher ionic conductivity, it is preferable that the crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment does not contain crystalline Li3PS4 (β-Li3PS4).

[0111] In X-ray diffraction measurements using CuKα radiation, the diffraction peaks of the Li3PS4 crystal structure appear, for example, at 2θ = 17.5°, 18.3°, 26.1°, 27.3°, and 30.0°, the diffraction peaks of the Li4P2S6 crystal structure appear, for example, at 2θ = 16.9°, 27.1°, and 32.5°, and the diffraction peaks of the Li7PS6 crystal structure appear, for example, at 2θ = 15.3°, 25.2°, 29.6°, and 31.0°, and the diffraction peaks of the Li7P3S 11 Diffraction peaks of the crystal structure appear, for example, at 2θ = 17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°. 4-x Ge 1-x P x The diffraction peaks of the S4 thio-LISICON Region II crystal structure appear, for example, at 2θ = 20.1°, 23.9°, and 29.5°. 4-x Ge 1-x P x Diffraction peaks of a crystal structure similar to the S4 thio-LISICON Region II type appear, for example, at 2θ = 20.2 and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0112] As described above, when a thiolisiconregion II crystal structure is obtained in this embodiment, it is preferable that the thiolisiconregion II crystal structure does not contain crystalline Li3PS4 (β-Li3PS4). The sulfide solid electrolyte obtained by the production method of this embodiment does not have diffraction peaks at 2θ = 17.5° and 26.1° seen in crystalline Li3PS4, or even if it does have such peaks, the detected peaks are extremely small compared to the diffraction peaks of the thiolisiconregion II crystal structure.

[0113] The compound has the structural skeleton of Li7PS6 and has the composition formula Li in which part of the P is replaced with Si. 7-x P 1-y Si y S6 and Li 7+x P 1-y Si yThe crystal structure represented by S6 (where x ranges from -0.6 to 0.6 and y ranges from 0.1 to 0.6) is cubic or orthorhombic, preferably cubic, and in X-ray diffraction measurement using CuKα radiation, it mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. The above composition formula Li 7-x-2y PS 6-x-y Cl x (where 0.8 ≤ x ≤ 1.7 and 0 < y ≤ -0.25x + 0.5) is preferably cubic, and in X-ray diffraction measurement using CuKα radiation, it mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Also, the above composition formula Li 7-x PS 6-x Ha x (where Ha is Cl or Br and x is preferably from 0.2 to 1.8) is preferably cubic, and in X-ray diffraction measurement using CuKα radiation, it mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. The crystal structures basically having the structural framework of these Li7PS6 are also referred to as the argyrodite-type crystal structure. Note that regarding these peak positions, they may shift within a range of ±°0.5.

[0114] The shape of the crystalline sulfide solid electrolyte is not particularly limited, and for example, particulate form can be mentioned. The average particle size (D 50 ) of the particulate crystalline sulfide solid electrolyte can be exemplified within a range of, for example, 0.01 μm to 500 μm, 0.1 to 200 μm.

[0115] (Other properties of the sulfide solid electrolyte) The ionic conductivity of the sulfide solid electrolyte obtained by the manufacturing method of this embodiment is extremely high because of the high PS4 fraction, usually 1.0×10 -5 S / cm or more, and further, 1.5×10 -5 S / cm or more, 2.0×10 -5 S / cm or more, 2.5×10-5 S / cm or more, 3.0×10 -5 It can be more than S / cm.

[0116] Furthermore, the improvement rate of the PS4 fraction due to the airflow treatment (the ratio of the PS4 fraction in the sulfide solid electrolyte after the airflow treatment to the PS4 fraction in the sulfide before the airflow treatment) cannot be generalized because it varies depending on the PS4 fraction in the sulfide, but is usually 5% or more, and can be 10% or more, 30% or more, 40% or more, 50% or more, or 60% or more.

[0117] As described above, the method for producing a sulfide solid electrolyte of this embodiment is a production method that exhibits the effect of improving the PS4 fraction and obtaining high ionic conductivity through a simple post-treatment, namely, gas flow treatment with at least one gas selected from an inert gas and hydrogen gas, preferably a gas containing hydrogen gas.

[0118] The sulfide solid electrolyte obtained by the manufacturing method of this embodiment has high ionic conductivity and excellent battery performance, and is therefore suitable for use in batteries. It is particularly suitable when lithium element is used as the conductive species. The sulfide solid electrolyte obtained by the manufacturing method of this embodiment may be used in a positive electrode layer, a negative electrode layer, or an electrolyte layer. Each layer can be manufactured by a known method.

[0119] The battery preferably includes a current collector in addition to the positive electrode layer, electrolyte layer, and negative electrode layer, and a known current collector can be used. For example, a layer of a material that reacts with the solid electrolyte, such as Au, Pt, Al, Ti, or Cu, coated with Au or the like can be used. [Example]

[0120] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples in any way.

[0121] Example 1 Specifically, 1.30 g of lithium sulfide (LiS) and 2.70 g of diphosphorus pentasulfide (P2S5) were mixed in a 45 mL zirconia pot for a planetary ball mill (Classic Line P-7, Fritsch Japan Co., Ltd.) with 70 g of zirconia balls (5 mm diameter) in a molar ratio (LiS:P2S5) of 70.0:30.0. The pot was sealed under an argon atmosphere. The zirconia pot was attached to the planetary ball mill and mixed and milled at a table rotation speed of 600 rpm for a total of 20 hours (20 minutes on, 5 minutes off, repeated 60 times) to obtain powdered amorphous sulfide.

[0122] The obtained amorphous sulfide was then placed in a reaction vessel (volume: 45 mL) equipped with pipes for supplying and exhausting hydrogen gas, and a mixed gas of hydrogen gas and argon gas (hydrogen gas content: 5% by volume) was supplied at a flow rate of 100 mL / min for 24 hours to perform an airflow treatment, thereby obtaining an amorphous sulfide solid electrolyte. The airflow treatment was performed at room temperature (23°C). The PS4 fraction, P2S7 fraction, and P2S6 fraction of the obtained amorphous sulfide and amorphous sulfide solid electrolyte were measured by the following method. 31 P MAS NMR(solid state) 31 The P NMR spectrum is shown in Figure 1, and the measurement results of the fraction of each unit are shown in Table 1. In addition, the ionic conductivity of the obtained crystalline sulfide solid electrolyte was measured and found to be 3.2 × 10 -5 (S / cm), confirming that the material has high ionic conductivity.

[0123] (Measurement of PS4 fraction, P2S7 fraction and P2S6 fraction) 100 mg of the solid electrolyte obtained in each of the examples and comparative examples was filled into an NMR sample tube and analyzed using the following equipment and conditions. 31 P MAS NMR(solid state) 31P NMR spectrum was obtained. From this spectrum, the peaks of the PS4 unit (80-85 ppm), the P2S7 unit (85-95 ppm), and the P2S6 unit (105-110 ppm) were separated into waveforms, and the ratio of the area of ​​each unit to the total area was calculated to represent the PS4 fraction, the P2S7 fraction, and the P2S6 fraction, respectively. Nuclear magnetic resonance apparatus (NMR apparatus): JNM-ECX400 (model number, manufactured by JEOL Ltd.) Observation kernel: 31 P Resonance frequency: 400MHz Magnetic field: 9.4T Probe: 4mm Mas probe MAS speed: 15kMz Measurement temperature: room temperature (23℃) n / 2 pulse width: 3.11 μs Accumulation count: 32 times Measurement range: 350 ppm to -250 ppm Reference: 85% H3PO4

[0124] (Measurement of ionic conductivity) In this example, the ionic conductivity was measured as follows. From sulfide and sulfide solid electrolyte, a diameter of 10 mm (cross-sectional area S: 0.785 cm 2 ) and a height (L) of 0.1 to 0.3 cm were molded into circular pellets to serve as samples. Electrode terminals were attached to the top and bottom of the samples, and measurements were made at 25°C using the AC impedance method (frequency range: 1 MHz to 100 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. The real part Z' (Ω) at the point where -Z'' (Ω) is minimum near the right end of the arc observed in the high-frequency region was taken as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (S / cm) was calculated according to the following equation: R=ρ(L / S) σ=1 / ρ

[0125] Example 2 An amorphous sulfide solid electrolyte was obtained in the same manner as in Example 1, except that the airflow treatment time was changed to 4 hours. Powder X-ray diffraction (XRD) measurement was performed on the obtained amorphous sulfide solid electrolyte by the following method. The results of the XRD measurement are shown in FIG. 2. Furthermore, the PS4 fraction, P2S7 fraction, and P2S6 fraction were measured on the obtained amorphous sulfide and amorphous sulfide solid electrolyte in the same manner as in Example 1. 31 P MAS NMR(solid state) 31 The P NMR spectrum is shown in Figure 1, and the measurement results of the fraction of each unit are shown in Table 1.

[0126] (Powder X-ray diffraction (XRD) measurement) In this specification, powder X-ray diffraction (XRD) measurements were carried out as follows. The powders obtained in the examples and comparative examples were filled into a groove 20 mm in diameter and 0.2 mm deep, and leveled with glass to prepare a sample. This sample was sealed with Kapton film for XRD and measured under the following conditions without exposing it to air. Measuring device: M03xhf (model number, manufactured by Mac Science Co., Ltd.) Tube voltage: 40kV Tube current: 40mA X-ray wavelength: Cu-Kα ray (1.5418Å) Optical system: Concentration method Slit configuration: Divergence slit 0.5°, scattering slit 0.5°, receiving slit 0.3 mm, monochromator used Detector: Semiconductor detector Measurement range: 2θ=10-60deg Step width, scan speed: 0.05deg, 10 seconds / step

[0127] Examples 3 and 4 An amorphous sulfide solid electrolyte was obtained in the same manner as in Example 1, except that the treatment time and temperature conditions for the air flow treatment shown in Table 1 were used. The PS4 fraction, P2S7 fraction, and P2S6 fraction of the obtained amorphous sulfide solid electrolyte were measured in the same manner as in Example 1. The measurement results of the fractions of each unit are shown in Table 1. In addition, for the amorphous sulfide solid electrolyte of Example 3, 31 P MAS NMR(solid state) 31 The P NMR spectrum is shown in Figure 1.

[0128] (Comparative Example 1) An amorphous sulfide was obtained in the same manner as in Example 1, except that the airflow treatment was not carried out. The PS4 fraction, P2S7 fraction, and P2S6 fraction of the obtained amorphous sulfide were measured in the same manner as in Example 1. The measurement results of the fractions of each unit are shown in Table 1. 31 P MAS NMR(solid state) 31 The P NMR spectrum is shown in Figure 1.

[0129] [Table 1]

[0130] From the results of the above Examples and Comparative Examples, it was confirmed that the airflow treatment reduced the P2S7 fraction while improving the PS4 fraction, resulting in high ionic conductivity. Furthermore, the improvement rates of the PS4 fraction of the sulfide solid electrolytes treated with airflow treatment in Examples 1 to 4 from the PS4 fraction of the sulfide not treated with airflow treatment in Comparative Example 1 ranged from 33.2% (Example 2) to 66.4% (Example 4), demonstrating that the airflow treatment resulted in a high PS4 fraction.

[0131] Example 5 An amorphous sulfide solid electrolyte was obtained in the same manner as in Example 1, except that the amounts and molar ratio (LiS:P2S5) of lithium sulfide (LiS) and diphosphorus pentasulfide (P2S5) used as raw materials were changed to those shown in Table 2. The PS4 fraction, P2S7 fraction, and P2S6 fraction of the obtained amorphous sulfide solid electrolyte were measured in the same manner as in Example 1. The measurement results of the fractions of each unit are shown in Table 2.

[0132] (Comparative Example 2) An amorphous sulfide was obtained in the same manner as in Example 5, except that the airflow treatment was not performed. The PS4 fraction, P2S7 fraction, and P2S6 fraction of the obtained amorphous sulfide were measured in the same manner as in Example 1. The measurement results of the fractions of each unit are shown in Table 2.

[0133] [Table 2]

[0134] The results of Example 5 and Comparative Example 2 above confirmed that the airflow treatment reduced the P2S7 fraction while improving the PS4 fraction. Furthermore, the improvement in PS4 fraction was 12.8%, a significant improvement over the already high PS4 fraction of Comparative Example 2. Furthermore, the P2S7 fraction was 0.0%, demonstrating that the sulfide solid electrolyte of Example 5 can exhibit high ionic conductivity.

[0135] Example 6 Specifically, 1.30 g of lithium sulfide (LiS) and 2.70 g of diphosphorus pentasulfide (P2S5) were mixed in a 45 mL zirconia pot for a planetary ball mill (Classic Line P-7, Fritsch Japan Co., Ltd.) with 70 g of zirconia balls (5 mm diameter) in a molar ratio (LiS:P2S5) of 70.0:30.0. The pot was sealed under an argon atmosphere. The zirconia pot was attached to the planetary ball mill and mixed and milled at a table rotation speed of 600 rpm for a total of 20 hours (20 minutes on, 5 minutes off, repeated 60 times) to obtain powdered amorphous sulfide.

[0136] The obtained amorphous sulfide was then placed in a reaction vessel (volume: 45 mL) equipped with gas supply and exhaust pipes for gas flow treatment, and a mixed gas of hydrogen gas and argon gas (hydrogen gas content: 5% by volume) was supplied at a flow rate of 500 mL / min for 12 hours to perform gas flow treatment, thereby obtaining an amorphous sulfide solid electrolyte. The gas flow treatment was performed at room temperature (23°C). The PS4 fraction, P2S7 fraction, and P2S6 fraction of the obtained amorphous sulfide solid electrolyte were measured in the same manner as in Example 1. The measurement results of the fractions of each unit are shown in Table 3. In addition, the ionic conductivity of the obtained crystalline sulfide solid electrolyte was measured, and it was found to be 8.5 × 10 -5 (S / cm), confirming that the material has high ionic conductivity.

[0137] Examples 7 and 8 Amorphous sulfide solid electrolytes of Examples 7 and 8 were obtained in the same manner as in Example 6, except that the airflow treatment time was changed from 12 hours to 24 hours and 48 hours, respectively. The PS4 fraction, P2S7 fraction, and P2S6 fraction of the obtained amorphous sulfide solid electrolyte were measured in the same manner as in Example 1. The measurement results for the fractions of each unit are shown in Table 3. Furthermore, the ionic conductivity of the obtained crystalline sulfide solid electrolyte was measured, and was found to be 11×10 -5 (S / cm) and 9.8×10 -5 (S / cm), and it was confirmed that the sulfide solid electrolytes obtained in Examples 7 and 8 had high ionic conductivity.

[0138] [Table 3]

[0139] The results of Examples 6 to 8, compared with Comparative Example 1 in which no airflow treatment was performed, confirmed that performing airflow treatment with a gas containing hydrogen gas reduced at least one of the P2S7 fraction and the P2S6 fraction, while improving the PS4 fraction, resulting in high ionic conductivity. The improvement rates of the PS4 fraction of the sulfide solid electrolytes that were subjected to airflow treatment in Examples 6 to 8 from the PS4 fraction of the sulfide not subjected to airflow treatment in Comparative Example 1 were 1.9% (Example 6), 23.4% (Example 7), and 24.8% (Example 8), indicating that performing airflow treatment resulted in a high PS4 fraction. Furthermore, it was confirmed from the results of Examples 1 to 4 and Examples 6 to 8 that the longer the airflow treatment time, the more pronounced the tendency for the P2S7 fraction to decrease compared to the P2S6 fraction.

[0140] Example 9 An amorphous sulfide solid electrolyte was obtained in the same manner as in Example 6, except that the mixed gas was changed to argon gas alone and the treatment time was changed from 12 hours to 24 hours. The PS4 fraction, P2S7 fraction, and P2S6 fraction of the obtained amorphous sulfide solid electrolyte were measured. The measurement results for the fractions of each unit are shown in Table 4. The ionic conductivity of the obtained crystalline sulfide solid electrolyte was also measured, and was found to be 7.9 x 10 -5 (S / cm), and it was confirmed that the sulfide solid electrolyte obtained in Example 9 had high ionic conductivity.

[0141] [Table 4]

[0142] The results of Example 9 confirmed that the PS4 fraction was improved when the airflow treatment was performed using only an inert gas (argon gas alone), similar to the examples in which the airflow treatment was performed using other hydrogen-containing gases. More specifically, compared with Comparative Example 1, in which the airflow treatment was not performed, it was confirmed that the airflow treatment using a hydrogen-containing gas reduced the P2S7 fraction and P2S6 fraction, while improving the PS4 fraction, resulting in high ionic conductivity. Furthermore, the improvement in the PS4 fraction of the sulfide solid electrolyte in Example 9 that was subjected to the airflow treatment from the sulfide not subjected to the airflow treatment in Comparative Example 1 was 20.6%, demonstrating that the airflow treatment resulted in a high PS4 fraction. [Industrial Applicability]

[0143] According to the production method of this embodiment, a sulfide solid electrolyte having a high PS4 fraction can be easily produced. The sulfide solid electrolyte obtained by the production method of this embodiment has high ionic conductivity and is suitable for use in batteries, particularly batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones.

Claims

1. Mixing two or more raw materials selected from compounds containing at least one element selected from alkali metal elements, sulfur elements, and phosphorus elements; a sulfide obtained by the mixing, the sulfide containing at least an alkali metal element, phosphorus element, and sulfur element, is subjected to a gas flow treatment with at least one gas selected from an inert gas and a hydrogen gas, the gas flow treatment being carried out at a temperature of 5°C or higher and 100°C or lower, and the gas being supplied at a rate of 0.1 L / min or higher and 20 L / min or lower relative to 100 g of the sulfide.

2. The method for producing a sulfide solid electrolyte according to claim 1 , wherein the gas flow treatment is carried out in a hydrogen gas atmosphere.

3. 3. The method for producing a sulfide solid electrolyte according to claim 1, wherein the gas flow treatment is carried out while supplying a gas having a hydrogen gas content of 0.5% by volume or more and 100% by volume or less.

4. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 3, wherein the airflow treatment is carried out while pulverizing the sulfide.

5. The method for producing a sulfide solid electrolyte according to claim 4, wherein the pulverization is carried out by a mechanical milling method.

6. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 5, wherein the gas flow treatment is further carried out by adding an alkali metal halide.

7. 7. The method for producing a sulfide solid electrolyte according to claim 6, wherein the alkali metal halide is at least one selected from the group consisting of lithium halide and sodium halide.

8. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 7, wherein the air flow treatment is carried out for 0.1 hours or more and 100 hours or less.

9. A method for producing a sulfide solid electrolyte described in any one of claims 1 to 8, wherein the raw materials are two or more raw materials selected from compounds containing at least one element selected from alkali metal elements, sulfur elements, phosphorus elements, and halogen elements.

10. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 9, wherein the compound contains lithium sulfide and diphosphorus pentasulfide.

11. The method for producing a sulfide solid electrolyte according to claim 9, wherein the compound contains lithium sulfide, diphosphorus pentasulfide, and lithium halide.

12. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 11, wherein the alkali metal element is at least one selected from lithium element and sodium element.

13. The method for producing a sulfide solid electrolyte according to any one of claims 1 to 12, wherein the sulfide is a sulfide containing an amorphous component.

14. The sulfide is P ２ S ７ The method for producing a sulfide solid electrolyte according to any one of claims 1 to 13, wherein the sulfide contains a sulfide unit.

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