Method for producing solid electrolyte

Description

[Technical Field]

[0001] The present invention relates to a method for producing a 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 their power sources has become increasingly important. Conventionally, batteries used for such applications have used electrolytes containing flammable organic solvents, but by making batteries all-solid-state, flammable organic solvents are not used in the battery, safety devices can be simplified, and manufacturing costs and productivity are excellent. Therefore, batteries in which the electrolyte is replaced with a solid electrolyte layer are being developed.

[0003] In terms of the performance and manufacturing of all-solid-state lithium batteries, a method for manufacturing a solid electrolyte used in a solid electrolyte layer requires a method with small particle size. In all-solid-state lithium batteries, the cathode material, anode material, and electrolyte are all solid, so a small particle size of the solid electrolyte has the advantage of facilitating the formation of a contact interface between the active material and the solid electrolyte, thereby improving the paths for ionic and electronic conduction. As a method for reducing particle size (also referred to as "microparticulation"), for example, a manufacturing method has been disclosed that includes a step of adding an ether compound to a coarse-grained sulfide solid electrolyte material and microparticulating it by a pulverization process (see, for example, Patent Document 1).

[0004] Furthermore, as a method for producing a solid electrolyte, a liquid phase method has attracted attention as a method that can easily synthesize a large amount of the solid electrolyte. However, since it is difficult to precipitate the solid electrolyte while maintaining the dispersed state of the atoms that constitute the solid electrolyte in the liquid phase method, a method has been disclosed in which a complexing agent is further used to produce a solid electrolyte via an electrolyte precursor (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-20894 [Patent Document 2] International Publication No. 2020 / 105737 Brochure Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and has an object to provide a method for producing a sulfide solid electrolyte having high ionic conductivity by atomizing the sulfide solid electrolyte without complicating the production process. [Means for solving the problem]

[0007] The method for producing a crystalline sulfide solid electrolyte according to the present invention includes: a raw material containing at least one selected from a lithium atom, a sulfur atom, and a phosphorus atom, and a complexing agent are mixed without using a mechanical treatment machine to obtain an electrolyte precursor; heating the electrolyte precursor to obtain a complex decomposition product; smoothing the decomposition product to obtain a smoothed decomposition product; and heating the smoothed complex decomposition product; A method for producing a crystalline sulfide solid electrolyte, comprising: Further, the method for producing a crystalline sulfide solid electrolyte according to the present invention includes the steps of: mixing a raw material containing at least one selected from lithium atoms, sulfur atoms, and phosphorus atoms with a complexing agent without using a mechanical treatment machine to obtain an electrolyte precursor; heating the electrolyte precursor to obtain a complex decomposition product; mechanically treating the decomposition product to obtain a modified decomposition product; and heating the modified complex decomposition product; The present invention relates to a method for producing a crystalline sulfide solid electrolyte, comprising the steps of: [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a method for producing a sulfide solid electrolyte having high ionic conductivity by atomizing the sulfide solid electrolyte without complicating the production process. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a flow chart illustrating an example of a preferred mode of the manufacturing method of the present embodiment. [Figure 2] FIG. 2 is a flow diagram illustrating an example of a preferred embodiment of a flow including a reaction vessel used in the production method of the present embodiment. [Figure 3] FIG. 4 is a flow chart illustrating another example of a preferred mode of the manufacturing method of the present embodiment. [Figure 4] FIG. 4 is a flow chart illustrating another example of a preferred mode of the manufacturing method of the present embodiment. [Figure 5] 1 shows X-ray diffraction spectra of the electrolyte precursor (1), amorphous complex decomposition product (1), and crystalline sulfide solid electrolyte (1) obtained in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] (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. In the production method described in Patent Document 1, ionic conductivity is not sufficiently improved even with atomization, and therefore the amount of energy input to improve the ionic conductivity of the solid electrolyte before the atomization step tends to increase, resulting in low production efficiency. Therefore, there has been a demand for a method for efficiently producing a crystalline sulfide solid electrolyte with even higher ionic conductivity.

[0012] It was confirmed that the solid electrolyte produced using a polar solvent (complexing agent) as in the production method described in Patent Document 2 has a characteristic surface shape. In addition, the average particle size (D 50 ) is large, and it was found that the particle size needs to be reduced. The present inventors have succeeded in reducing the average particle size (D 50 ) can be reduced while improving ionic conductivity.

[0013] In this embodiment, it has been found that a finely divided crystalline sulfide solid electrolyte having high ionic conductivity can be produced without significantly changing the conventional production process by heating the electrolyte precursor to form the complex decomposition product, and then smoothing the complex decomposition product to obtain a smoothed complex decomposition product, or mechanically treating the complex decomposition product to obtain a modified complex decomposition product, and then further heating the resulting mixture. In this embodiment, the term "mechanical treatment" refers to a treatment involving stirring, mixing, pulverization, or a combination thereof, and by performing the "mechanical treatment," a sulfide solid electrolyte having high ionic conductivity can be produced by atomizing the sulfide solid electrolyte without complicating the production process. In particular, the term "smoothing treatment" refers to a treatment that includes at least pulverization, and achieves a low specific surface area together with atomization, making it possible to produce a sulfide solid electrolyte having higher ionic conductivity.

[0014] This embodiment is an extremely excellent manufacturing method because the ionic conductivity of the sulfide solid electrolyte can be improved simply by subjecting the solid electrolyte to mechanical treatment, including the smoothing treatment described below. This embodiment differs from conventional manufacturing methods in that it focuses on the surface state of the primary particles. The reason why this is possible is unclear, but one hypothesis is that when ions move through a solid electrolyte, conduction is hindered at the interfaces between the particles of the solid electrolyte. However, when the particles are micronized by "mechanical processing" including "smoothing processing," the particle interfaces that hinder ion conduction are reduced, allowing ions to move more smoothly, resulting in improved ionic conductivity.

[0015] Hereinafter, methods for producing crystalline sulfide solid electrolytes according to the first to twelfth aspects of this embodiment will be described. A method for producing a crystalline sulfide solid electrolyte according to a first aspect of the present embodiment includes: a raw material containing at least one selected from a lithium atom, a sulfur atom, and a phosphorus atom, and a complexing agent are mixed without using a mechanical treatment machine to obtain an electrolyte precursor; heating the electrolyte precursor to obtain a complex decomposition product; smoothing the decomposition product to obtain a smoothed decomposition product; and heating the smoothed complex decomposition product; The present invention relates to a method for producing a crystalline sulfide solid electrolyte, comprising:

[0016] In Patent Document 1, the solid electrolyte is produced using a planetary ball mill, which is different from the solid electrolyte production method of the present invention that uses a polar solvent (complexing agent), and the ionic conductivity is not significantly improved after the atomization treatment. In addition, the process is complicated because the treatment using the planetary ball mill is performed multiple times. According to the method of Patent Document 2, it is possible to produce a solid electrolyte with high ionic conductivity, but it has been confirmed that a solid electrolyte produced using a polar solvent (complexing agent) has a characteristic surface shape. It has been found that by smoothing this surface shape, it is possible to produce a solid electrolyte with even higher ionic conductivity. In conventional manufacturing methods, it has been difficult to reduce the specific surface area while reducing the particle size by granulation or the like. In contrast, according to the first embodiment, the specific surface area of the primary particles can be reduced while reducing or maintaining the particle size of the crystalline sulfide solid electrolyte, thereby improving ionic conductivity. The specific surface area will be described later.

[0017] The smoothing treatment described below must be carried out before the complex decomposition product described below is heated (crystallized) to form a crystalline sulfide solid electrolyte. The smoothing treatment is carried out using specific raw materials and a manufacturing device commonly used in the field, making it an industrially advantageous manufacturing method.

[0018] As described in Patent Document 1, a solid-phase method for producing a solid electrolyte is known, in which raw materials such as lithium sulfide and diphosphorus pentasulfide are mixed using a pulverizer such as a mechanical mill, followed by heat treatment as needed. The pulverizers used in the solid-phase method require high pressure, making it difficult to increase production volume. In contrast, this embodiment is preferable because it can obtain an electrolyte precursor without using a mechanical processor such as a pulverizer for mixing, allowing production using a simple manufacturing device. Furthermore, compared to Patent Document 2, the effect of reducing particle size while improving ionic conductivity is thought to be due to the mixing method. Mixing the raw material ingredients and complexing agent without using a mechanical processor is preferable in terms of achieving both high ionic conductivity and fine particle size in the subsequent smoothing process.

[0019] A method for producing a crystalline sulfide solid electrolyte according to a second aspect of the present embodiment includes: The method for producing a crystalline sulfide solid electrolyte is characterized in that the raw material further contains a halogen atom.

[0020] As will be described later, it is preferable that the raw material ingredients further contain halogen atoms in order to improve the ionic conductivity of the solid electrolyte.

[0021] A method for producing a crystalline sulfide solid electrolyte according to a third aspect of the present embodiment includes: The method for producing a crystalline sulfide solid electrolyte includes the mixing including a first mixing using a first complexing agent and a second mixing using a second complexing agent different from the first complexing agent.

[0022] As described below, mixing the raw materials in the first and second mixtures using different complexing agents is preferable from the viewpoint of improving ionic conductivity because a more homogeneous solid electrolyte can be obtained. Furthermore, the use of a complexing agent is preferable because it makes it possible to more easily proceed with the reaction of the raw material components without using a pulverizer.

[0023] A method for producing a crystalline sulfide solid electrolyte according to a fourth aspect of the present embodiment includes: This is a method for producing a crystalline sulfide solid electrolyte, wherein the first complexing agent is a complexing agent capable of forming a complex containing Li3PS4 and a halogen atom, and the second complexing agent is a complexing agent capable of forming a complex containing Li3PS4.

[0024] As will be described later, by using a complexing agent having specific properties in the first mixture and the second mixture, the formation of Li3PS4, which stagnates when only the first complexing agent is used, progresses when the second complexing agent is used, and a homogeneous solid electrolyte can be obtained, which is preferable from the viewpoint of improving ionic conductivity.

[0025] A method for producing a crystalline sulfide solid electrolyte according to a fifth aspect of the present embodiment includes: In this method for producing a crystalline sulfide solid electrolyte, the smoothing treatment is carried out using at least one device selected from a grinder and a stirrer.

[0026] As will be described later, by carrying out the smoothing treatment using at least one device selected from a grinder and a stirrer, granulation of the solid electrolyte does not occur and the specific surface area can be reduced, which is preferable from the viewpoint of improving ionic conductivity.

[0027] A method for producing a crystalline sulfide solid electrolyte according to a sixth aspect of the present embodiment includes: The method for producing a crystalline sulfide solid electrolyte according to claim 1, wherein the smoothing treatment is carried out using a solvent.

[0028] As will be described later, by carrying out the smoothing treatment together with a solvent, granulation of the solid electrolyte does not occur and the specific surface area can be reduced, which is preferable from the viewpoint of improving ionic conductivity.

[0029] A method for producing a crystalline sulfide solid electrolyte according to a seventh aspect of the present embodiment includes: This is a method for producing a crystalline sulfide solid electrolyte, in which the smoothing treatment is carried out using at least one type of apparatus selected from a ball mill, a bead mill, a cutter mill, a hammer mill, a pin mill, a tower mill, an attritor, an aquamizer, a sand grinder, a viscomill, a pearl mill, a co-ball mill, and a dynamic type grinder.

[0030] As will be described later, by carrying out the smoothing treatment using at least one device selected from a ball mill, a bead mill, a cutter mill, a hammer mill, a pin mill, a tower mill, an attritor, an aquamizer, a sand grinder, a viscomill, a pearl mill, a co-ball mill, and a dynamic type grinder, granulation of the solid electrolyte does not occur and the specific surface area can be reduced, which is preferable from the viewpoint of improving ionic conductivity.

[0031] A method for producing a crystalline sulfide solid electrolyte according to an eighth aspect of the present embodiment includes: In the method for producing a crystalline sulfide solid electrolyte, the solvent used in the smoothing treatment is at least one selected from nonpolar solvents and aprotic polar solvents.

[0032] As will be described later, by using at least one solvent selected from a nonpolar solvent and an aprotic polar solvent in the smoothing treatment, granulation of the solid electrolyte does not occur and the specific surface area can be reduced, which is preferable from the viewpoint of improving ionic conductivity.

[0033] A method for producing a crystalline sulfide solid electrolyte according to a ninth aspect of this embodiment includes: In this method for producing a crystalline sulfide solid electrolyte, the ratio (Sb / Sa) of the specific surface area (Sb) of the complex decomposition product before the smoothing treatment to the specific surface area (Sa) of the smoothed complex decomposition product is 1.0 or more and 10.0 or less.

[0034] The smoothing treatment of this embodiment is preferable from the viewpoint of reducing the specific surface area of the particle surface of the solid electrolyte and improving the ionic conductivity of the solid electrolyte. However, from the viewpoint of simplicity of the process, of keeping the average particle size of the solid electrolyte within a certain range, and of improving the ionic conductivity of the solid electrolyte, as will be described later, it is preferable that the ratio (Sb / Sa) of the specific surface area (Sb) of the complex decomposition product before the smoothing treatment to the specific surface area (Sa) of the smoothed complex decomposition product is 1.0 or more and 10.0 or less.

[0035] A method for producing a crystalline sulfide solid electrolyte according to a tenth aspect of this embodiment includes: The average particle size (D 50 b) and the average particle size of the smoothed complex decomposition product (D 50 a) ratio (D 50 b / D 50 a) is a method for producing a crystalline sulfide solid electrolyte in which the value of a) is 1.0 or more and 100.0 or less.

[0036] The smoothing treatment of this embodiment is preferable from the viewpoint of reducing the specific surface area of the particle surface of the solid electrolyte and improving the ionic conductivity of the solid electrolyte. However, as will be described later, from the viewpoint of simplicity of the process, from the viewpoint of keeping the average particle diameter of the solid electrolyte within a certain range, and from the viewpoint of improving the ionic conductivity of the solid electrolyte, it is preferable to set the average particle diameter (D 50 b) and the average particle size of the smoothed complex decomposition product (D 50 a) ratio (D 50 b / D 50 a) is preferably 1.0 or more and 100.0 or less.

[0037] A method for producing a crystalline sulfide solid electrolyte according to an eleventh aspect of the present embodiment includes: The method for producing a crystalline sulfide solid electrolyte is such that the crystalline sulfide solid electrolyte contains a thiolicon region II crystal structure.

[0038] The production method of this embodiment is particularly suitable for producing a crystalline sulfide solid electrolyte containing a thiolicon region II crystal structure, and is preferable from the viewpoint of improving ionic conductivity.

[0039] A method for producing a crystalline sulfide solid electrolyte according to a twelfth aspect of the present embodiment includes: a raw material containing at least one selected from a lithium atom, a sulfur atom, and a phosphorus atom, and a complexing agent are mixed without using a mechanical treatment machine to obtain an electrolyte precursor; heating the electrolyte precursor to obtain a complex decomposition product; mechanically treating the decomposition product to obtain a modified decomposition product; and heating the modified complex decomposition product; The present invention relates to a method for producing a crystalline sulfide solid electrolyte, comprising the steps of:

[0040] The manufacturing method of this embodiment is preferable because the complex decomposition product is mechanically treated to obtain a modified complex decomposition product, which can improve the ionic conductivity while reducing the particle size of the crystalline sulfide solid electrolyte or while maintaining the particle size.

[0041] The manufacturing method of this embodiment will be described in more detail below in accordance with the above-described embodiment.

[0042] [Method for producing sulfide solid electrolyte] As shown in FIG. 1 or 4 , the method for producing the sulfide solid electrolyte of this embodiment includes mixing a raw material component containing at least one selected from lithium atoms, sulfur atoms, and phosphorus atoms with a complexing agent without using a mechanical processor to obtain an electrolyte precursor, heating the electrolyte precursor to obtain a complex decomposition product, smoothing the complex decomposition product to obtain a smoothed complex decomposition product, and heating the smoothed complex decomposition product.

[0043] <Obtaining the electrolyte precursor> In this embodiment, "obtaining an electrolyte precursor" requires mixing a raw material component described below with a complexing agent described below. By mixing the raw material component with a complexing agent and complexing the raw material component, a complex containing lithium atoms, phosphorus atoms, sulfur atoms, etc., such as Li3PS4 is formed, even in a liquid phase method or a heterogeneous method, and separation of specific components is suppressed, thereby obtaining a homogeneous solid electrolyte, which is preferable.

[0044] (solid electrolyte) In this specification, the term "solid electrolyte" refers to an electrolyte that remains solid at 25° C. under a nitrogen atmosphere. The solid electrolyte in this embodiment contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, and has ionic conductivity due to the lithium atoms. The term "solid electrolyte" includes both a crystalline sulfide solid electrolyte having a crystal structure obtained by the manufacturing method of this embodiment and an amorphous solid electrolyte.

[0045] In this specification, a crystalline sulfide solid electrolyte refers to a solid electrolyte in which a peak derived from the solid electrolyte is observed in an X-ray diffraction pattern in an X-ray diffraction measurement, regardless of whether or not a peak derived from the raw material of the solid electrolyte is present. That is, the crystalline sulfide solid electrolyte includes a crystalline structure derived from the solid electrolyte, and a portion of the crystalline structure may be derived from the solid electrolyte, or the entire crystalline structure may be 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 include an amorphous solid electrolyte in part. Therefore, the crystalline sulfide solid electrolyte includes so-called glass ceramics obtained by heating an amorphous solid electrolyte to a temperature equal to or higher than the crystallization temperature. In addition, in this specification, an amorphous solid electrolyte refers to an X-ray diffraction pattern obtained by X-ray diffraction measurement that shows a halo pattern in which peaks other than those derived from the material are not substantially observed, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present.

[0046] (mixture) The "mixing" in this embodiment must be performed without using a mechanical processor, which will be described later. This allows production using simple production equipment without using large-scale equipment for pulverization, thereby simplifying the production process and reducing the energy input during production. The mechanical processor refers to a pulverizer, which will be described later.

[0047] Examples of mixing that is performed without using a mechanical processor include mixing with a stirrer and a mixer. For example, a mechanical agitation mixer that is equipped with a stirring blade in a reaction vessel and can perform agitation (also referred to as mixing by agitation or agitation mixing) can be mentioned. Examples of mechanical agitation mixers include high-speed agitation mixers and double-arm mixers. Examples of high-speed agitation mixers include vertical-axis rotary mixers and horizontal-axis rotary mixers, and either type of mixer can be used.

[0048] Examples of the shape of the stirring blade used in a 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-shaft blade type, flat blade type, C-type blade type, etc. From the viewpoint of more efficiently promoting the reaction of the raw materials, the shovel type, flat blade type, C-type blade type, anchor type, paddle type, full zone type, etc. are preferred, and the anchor type, paddle type, and full zone type are more preferred. When performing on a small scale, it is also preferable to use a Schlenk bottle with a stirring bar or a separable flask equipped with a rotor blade.

[0049] 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 230 rpm or less.

[0050] The temperature conditions when mixing 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. Mixing without external temperature control is also preferred. The mixing time is usually 0.1 to 500 hours, and from the viewpoint of more uniform dispersion of the raw materials and accelerating the reaction, it is preferably 1 to 450 hours, more preferably 10 to 425 hours, even more preferably 20 to 400 hours, and even more preferably 30 to 300 hours.

[0051] Alternatively, the mixing may be performed by circulating agitation, in which a fluid within the reaction vessel is withdrawn from an outlet provided in the reaction vessel to the outside, and the withdrawn fluid is returned to the reaction vessel from a return port provided in the reaction vessel, thereby circulating the fluid, as shown in Fig. 2. Mixing by circulating agitation is preferred because it can promote the reaction of the raw materials without pulverization, and it prevents raw materials with a high specific gravity, such as lithium halide, from settling and stagnating at the bottom of the reaction vessel, particularly immediately below the rotating shaft of the stirring blades, without requiring strong agitation that would cause the fluid to splash and adhere to the inner wall of the reaction vessel, thereby suppressing compositional deviations in the sulfide solid electrolyte due to non-contribution to the reaction, efficiently promoting the reaction, and producing a sulfide solid electrolyte with high ionic conductivity.

[0052] The mixing in this embodiment may be a single operation, or two or more operations under different conditions. As one operation, it is preferable to mix using one or more complexing agents selected from the first complexing agent and the second complexing agent described below.

[0053] As for two or more operations, the first mixing and the second mixing may be carried out consecutively as shown in FIG. 3, or another operation may be interposed between the first mixing and the second mixing. The mixture shown in FIG. 3 may include a first mixture using a first complexing agent, as described below, and a second mixture using a second complexing agent, as described below, that is different from the first complexing agent. The second mixing is preferably carried out by adding a second complexing agent after the first mixing, from the viewpoint of simplifying the production process and producing a homogeneous solid electrolyte.

[0054] (Raw material content) The raw material ingredients used in this embodiment are required to contain at least one selected from lithium atoms, sulfur atoms, and phosphorus atoms. Furthermore, the raw material ingredients used in this embodiment may also contain halogen atoms as needed, which is preferable from the viewpoint of forming a solid electrolyte having a specific crystal system as described below and improving ionic conductivity. More specifically, lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5); phosphorus halides such as various phosphorus fluorides (PF3, PF5), various phosphorus chlorides (PCl3, PCl5, P2Cl4), various phosphorus bromides (PBr3, PBr5), and various phosphorus iodides (PI3, P2I4); thiophosphoryl fluoride (PSF3), thiophosphoryl chloride (P Representative examples include raw materials consisting of at least two atoms selected from the above four types of atoms, such as thiophosphoryl halides such as thiophosphoryl bromide (PSBr3), thiophosphoryl iodide (PSI3), thiophosphoryl fluoride dichloride (PSCl2F), and thiophosphoryl fluoride dibromide (PSBr2F); and elemental halogens such as fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2), with bromine (Br2) and iodine (I2) being preferred.

[0055] Examples of materials that can be used as raw materials other than those mentioned above include raw materials that contain at least one atom selected from the above four types of atoms and also contain atoms other than the four types of atoms, more specifically, lithium compounds such as lithium oxide, lithium hydroxide, and lithium carbonate; alkali metal sulfides such as sodium sulfide, potassium sulfide, rubidium sulfide, and cesium sulfide; 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; halides of alkali metals other than lithium, such as sodium iodide, sodium fluoride, sodium chloride, and sodium bromide; 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 (POCl) and phosphorus oxybromide (POBr).

[0056] Among the above, preferred are lithium sulfide, phosphorus sulfides such as diphosphorus trisulfide (PS) and diphosphorus pentasulfide (PS), halogen elements such as fluorine (F), chlorine (Cl), bromine (Br), and iodine (I), and lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide. Furthermore, when oxygen atoms are introduced into the solid electrolyte, preferred are phosphate compounds such as lithium oxide, lithium hydroxide, and lithium phosphate. Preferred combinations of raw materials include lithium sulfide, diphosphorus pentasulfide, and lithium halides, and lithium sulfide, diphosphorus pentasulfide, and halogen elements. Preferred lithium halides are lithium bromide and lithium iodide, and preferred halogen elements are bromine and iodine.

[0057] In this embodiment, Li3PS4 containing the PS4 structure can be used as part of the raw material. Specifically, Li3PS4 is prepared in advance by manufacturing or the like, and then used as the raw material. The content of Li3PS4 relative to the total of the raw materials is preferably 60 to 100 mol%, more preferably 65 to 90 mol%, and even more preferably 70 to 80 mol%.

[0058] When Li3PS4 and a simple halogen are used, the content of the simple halogen relative to Li3PS4 is preferably 1 to 50 mol %, more preferably 10 to 40 mol %, even more preferably 20 to 30 mol %, and even more preferably 22 to 28 mol %.

[0059] The lithium sulfide used in this embodiment 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.

[0060] 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 70 to 80 mol%, more preferably 72 to 78 mol%, and even more preferably 74 to 78 mol%, from the viewpoint of obtaining higher chemical stability and higher ionic conductivity. 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 to 100 mol%, more preferably 65 to 90 mol%, and even more preferably 70 to 80 mol%. Furthermore, when lithium bromide and lithium iodide are used in combination as the lithium halide, from the viewpoint of improving ionic conductivity, the proportion of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, still more preferably 40 to 80 mol%, and particularly preferably 50 to 70 mol%.

[0061] When a halogen element is used as a raw material, and lithium sulfide and diphosphorus pentasulfide are used, the ratio of the number of moles of lithium sulfide excluding the same number of moles of lithium sulfide as the halogen element to the total number of moles of lithium sulfide and diphosphorus pentasulfide excluding the same number of moles of lithium sulfide as the halogen element is preferably within the range of 60 to 90%, more preferably within the range of 65 to 85%, even more preferably within the range of 68 to 82%, even more preferably within the range of 72 to 78%, and particularly preferably within the range of 73 to 77%. This is because higher ionic conductivity can be obtained at these ratios. From the same viewpoint, when lithium sulfide, diphosphorus pentasulfide, and a halogen element are used, the content of the halogen element relative to the total amount of lithium sulfide, diphosphorus pentasulfide, and the halogen element 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%.

[0062] When lithium sulfide, diphosphorus pentasulfide, a halogen element, and a lithium halide are used, the content of the halogen element (α mol %) and the content of the lithium halide (β mol %) relative to the total amount thereof preferably satisfy the following formula (2), more preferably satisfy the following formula (3), even more preferably satisfy the following formula (4), and even more preferably satisfy the following formula (5).

[0063] 2≦2α+β≦100…(2) 4≦2α+β≦80 …(3) 6≦2α+β≦50 …(4) 6≦2α+β≦30 …(5)

[0064] When two types of halogens are used as simple substances, the molar number of one halogen atom in the substance is A1, and the molar number of the other halogen atom in the substance is A2. The ratio A1:A2 is preferably 1 to 99:99 to 1, more preferably 10:90 to 90:10, even more preferably 20:80 to 80:20, and even more preferably 30:70 to 70:30.

[0065] Furthermore, when the two types of halogen atoms are bromine and iodine, where the number of moles of bromine is B1 and the number of moles of iodine is B2, the ratio B1:B2 is preferably 1 to 99:99 to 1, more preferably 15:85 to 90:10, even more preferably 20:80 to 80:20, still more preferably 30:70 to 75:25, and particularly preferably 35:65 to 75:25.

[0066] When mixing the raw material ingredients with a complexing agent described below, it is preferable to mix the raw material mixture with a solvent described below to form a slurry, since this will result in the raw material mixture becoming a uniform complex.

[0067] (complexing agent) The complexing agent used in this embodiment may be a single type or two or more types. When two or more types are used, it is preferable to use the first complexing agent and the second complexing agent described above. The first complexing agent is a complexing agent capable of forming a complex containing Li3PS4 and a halogen atom, and the second complexing agent is a complexing agent capable of forming a complex containing Li3PS4. This is preferable from the viewpoint of improving ionic conductivity, because the formation of Li3PS4 stagnates when using only the first complexing agent, but the formation of Li3PS4 progresses when using the second complexing agent, allowing a homogeneous solid electrolyte to be obtained.

[0068] In order to efficiently form a complex, the molar ratio of the amount of complexing agent added to the total molar amount of Li atoms contained in the two or more raw material compounds in the case where the mixing of this embodiment is carried out as a single operation and the total amount of complexing agent added when the mixing is carried out as two or more operations is preferably 0.5 to 7.0, more preferably 0.6 to 5.5, and even more preferably 0.8 to 3.5. The amount of complexing agent used in each operation when the mixing is carried out as two or more operations will be described later.

[0069] (First complexing agent) In this specification, the first complexing agent is a complexing agent capable of forming a complex containing Li3PS4 and a halogen atom obtained from Li2S and P2S5, etc., which are preferably used as raw materials for solid electrolytes, preferably having the ability to form Li3PS4 and capable of forming a complex containing the formed Li3PS4 and a halogen atom, and is used in the first step.

[0070] The first complexing agent can be used without any particular limitation as long as it has the above-mentioned properties, and is preferably a compound containing an atom having a high affinity with lithium atoms, such as a heteroatom such as a nitrogen atom, an oxygen atom, or a chlorine atom, and more preferably a compound having a group containing such a heteroatom, because such a heteroatom or group containing such a heteroatom can coordinate (bond) with lithium.

[0071] The heteroatoms present in the molecules of the first complexing agent have a high affinity for lithium atoms and are believed to have the ability to easily form complexes by bonding with raw materials containing lithium atoms and halogen atoms, such as Li3PS4, which contains the PS4 structure that is the main skeleton of the solid electrolyte produced by this embodiment, and lithium halides. Therefore, by mixing the raw materials with the first complexing agent, the complex is formed, making it possible to precipitate various components while maintaining their dispersed state even in the precipitation process, and obtaining an electrolyte precursor in which halogen atoms are more uniformly dispersed and fixed (hereinafter, the substance obtained by mixing the raw material containing at least one selected from lithium atoms, sulfur atoms, and phosphorus atoms with the complexing agent is also referred to as the electrolyte precursor). As a result, it is believed that a solid electrolyte with high ionic conductivity is obtained.

[0072] Therefore, the first complexing agent preferably has at least two heteroatoms capable of coordinating (bonding) in the molecule, and more preferably has a group containing at least two heteroatoms in the molecule. By having a group containing at least two heteroatoms in the molecule, raw materials containing lithium and halogen, such as Li3PS4 and lithium halide, can be bound via at least two heteroatoms in the molecule. Furthermore, among heteroatoms, nitrogen atoms are preferred, and amino groups are preferred as groups containing nitrogen atoms. In other words, amine compounds are preferred as complexing agents.

[0073] The amine compound is not particularly limited as long as it has an amino group in the molecule, as long as it can promote the formation of a complex, but a compound having at least two amino groups in the molecule is preferred. By having such a structure, raw materials containing lithium and halogen, such as Li3PS4 and lithium halide, can be bonded via at least two nitrogen atoms in the molecule.

[0074] Examples of such amine compounds include aliphatic amines, alicyclic amines, heterocyclic amines, and aromatic amines, and these can be used alone or in combination.

[0075] More specifically, typical and preferred examples of the aliphatic amine include aliphatic primary diamines such as ethylenediamine, diaminopropane, and diaminobutane; aliphatic secondary diamines such as N,N'-dimethylethylenediamine, N,N'-diethylethylenediamine, N,N'-dimethyldiaminopropane, and N,N'-diethyldiaminopropane; and aliphatic tertiary diamines such as N,N,N',N'-tetramethyldiaminomethane, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetraethylethylenediamine, N,N,N',N'-tetramethyldiaminopropane, N,N,N',N'-tetraethyldiaminopropane, N,N,N',N'-tetramethyldiaminobutane, N,N,N',N'-tetramethyldiaminopentane, and N,N,N',N'-tetramethyldiaminohexane. In the examples given in this specification, for example, in the case of diaminobutane, unless otherwise specified, all isomers of butane, such as linear and branched isomers, are included, in addition to isomers relating to the position of the amino group, such as 1,2-diaminobutane, 1,3-diaminobutane, and 1,4-diaminobutane.

[0076] The number of carbon atoms in the aliphatic amine is preferably 2 or more, more preferably 4 or more, and even more preferably 6 or more, with the upper limit being preferably 10 or less, more preferably 8 or less, and even more preferably 7 or less. The number of carbon atoms in the aliphatic hydrocarbon group in the aliphatic amine is preferably 2 or more, and the upper limit being preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0077] Typical preferred examples of the alicyclic amine include alicyclic primary diamines such as cyclopropanediamine and cyclohexanediamine; alicyclic secondary diamines such as bisaminomethylcyclohexane; and alicyclic tertiary diamines such as N,N,N',N'-tetramethyl-cyclohexanediamine and bis(ethylmethylamino)cyclohexane. Typical preferred examples of the heterocyclic amine include heterocyclic primary diamines such as isophoronediamine; heterocyclic secondary diamines such as piperazine and dipiperidylpropane; and heterocyclic tertiary diamines such as N,N-dimethylpiperazine and bismethylpiperidylpropane. The number of carbon atoms in the alicyclic amine and heterocyclic amine is preferably 3 or more, more preferably 4 or more, and the upper limit is preferably 16 or less, more preferably 14 or less.

[0078] Representative preferred examples of the aromatic amine include aromatic primary diamines such as phenyldiamine, tolylenediamine, and naphthalenediamine; aromatic secondary diamines such as N-methylphenylenediamine, N,N'-dimethylphenylenediamine, N,N'-bismethylphenylphenylenediamine, N,N'-dimethylnaphthalenediamine, and N-naphthylethylenediamine; and aromatic tertiary diamines such as N,N-dimethylphenylenediamine, N,N,N',N'-tetramethylphenylenediamine, N,N,N',N'-tetramethyldiaminodiphenylmethane, and N,N,N',N'-tetramethylnaphthalenediamine. The aromatic amine preferably has 6 or more carbon atoms, more preferably 7 or more carbon atoms, and even more preferably 8 or more carbon atoms, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less carbon atoms.

[0079] The amine compound used in this embodiment may be substituted with a substituent such as an alkyl group, an alkenyl group, an alkoxyl group, a hydroxyl group, or a cyano group, or with a halogen atom. Although diamines have been given as specific examples, it goes without saying that the amine compounds that can be used in this embodiment are not limited to diamines, and examples thereof include aliphatic monoamines corresponding to various diamines such as trimethylamine, triethylamine, ethyldimethylamine, and the above-mentioned aliphatic diamines, piperidine compounds such as piperidine, methylpiperidine, and tetramethylpiperidine, pyridine compounds such as pyridine and picoline, morpholine compounds such as morpholine, methylmorpholine, and thiomorpholine, imidazole compounds such as imidazole and methylimidazole, and the above-mentioned alicyclic diamines. In addition to monoamines such as alicyclic monoamines such as the corresponding monoamines, heterocyclic monoamines corresponding to the above heterocyclic diamines, and aromatic monoamines corresponding to the above aromatic diamines, polyamines having three or more amino groups, such as diethylenetriamine, N,N',N''-trimethyldiethylenetriamine, N,N,N',N'',N''-pentamethyldiethylenetriamine, triethylenetetramine, N,N'-bis[(dimethylamino)ethyl]-N,N'-dimethylethylenediamine, hexamethylenetetramine, and tetraethylenepentamine, can also be used.

[0080] Among the above, from the viewpoint of obtaining higher ionic conductivity, a tertiary amine having a tertiary amino group as the amino group is preferred, a tertiary diamine having two tertiary amino groups is more preferred, a tertiary diamine having two tertiary amino groups at both ends is even more preferred, and an aliphatic tertiary diamine having tertiary amino groups at both ends is even more preferred. Among the above amine compounds, the aliphatic tertiary diamine having tertiary amino groups at both ends is preferably tetramethylethylenediamine, tetraethylethylenediamine, tetramethyldiaminopropane, or tetraethyldiaminopropane, and in consideration of ease of availability, etc., tetramethylethylenediamine or tetramethyldiaminopropane is preferred.

[0081] Furthermore, compounds having a nitrogen atom as a heteroatom and a group other than an amino group, such as a nitro group or an amide group, can also provide the same effect.

[0082] From the viewpoint of efficiently forming a complex, the molar ratio of the amount of the first complexing agent added to the total molar amount of Li atoms contained in the two or more raw material compounds is preferably 0.1 or more and 2.0 or less, more preferably 0.5 or more and 1.5 or less, even more preferably 0.8 or more and 1.2 or less, and most preferably 1.0.

[0083] (Second complexing agent) In this specification, the second complexing agent is preferably a complexing agent other than the first complexing agent that can form a complex containing Li3PS4 obtained from Li2S and P2S5, which are preferably used as raw materials for solid electrolytes, and in particular, a complexing agent that forms Li3PS4 at a faster rate than the first complexing agent. By mixing the first complexing agent and then the second complexing agent, the Li3PS4 formation reaction can proceed without stagnation, which would otherwise occur if only the first complexing agent was mixed.

[0084] The reason why this is possible is unclear, but the following hypothesis is conceivable. That is, although the first complexing agent has a good balance of the ability to form Li3PS4 and the ability to form a complex containing Li3PS4 and a halogen atom, its Li3PS4 formation ability is inferior to that of the second complexing agent. Therefore, the Li3PS4 formation reaction proceeds, and as the concentration of Li2S and other compounds present in the system decreases, the rate of the Li3PS4 formation reaction slows down and gradually stagnates. However, by further adding a second complexing agent, which has a better ability to form Li3PS4 than the first complexing agent, after mixing the first complexing agent, it is possible to again accelerate the Li3PS4 formation reaction even when the concentration of Li2S and other compounds present in the reaction field is low. In this case, because the first complexing agent has a better ability to form a complex containing Li3PS4 and a halogen atom than the second complexing agent, the characteristics of both the first and second complexing agents are utilized, and the Li3PS4 formation reaction proceeds, and the complex containing Li3PS4 and a halogen atom is formed without stagnation.

[0085] The second complexing agent can be used without any particular limitation as long as it has the above-mentioned properties, and is preferably a compound containing an atom having a high affinity with lithium atoms, such as a heteroatom such as a nitrogen atom, an oxygen atom, or a chlorine atom, and more preferably a compound having a group containing such a heteroatom, because such a heteroatom or group containing such a heteroatom can coordinate (bond) with lithium. The heteroatoms present in the molecules of the second complexing agent have a high affinity for lithium atoms and are thought to have the ability to easily bond with Li3PS4, which contains the PS4 structure that is the main skeleton of the solid electrolyte produced by this embodiment, to form a complex. Therefore, it is thought that mixing the above raw materials with the second complexing agent accelerates the formation of a complex containing Li3PS4.

[0086] Furthermore, among heteroatoms, oxygen atoms are preferred, and the group containing an oxygen atom preferably has one or more functional groups selected from ether groups and ester groups, with an ether group being particularly preferred. That is, ether compounds are particularly preferred as complexing agents. Furthermore, in relation to the first complexing agent, it is preferable that the second complexing agent does not contain a nitrogen atom as a heteroatom. Therefore, in this embodiment, it is preferable to use a first complexing agent containing a nitrogen atom as a heteroatom, and a second complexing agent containing an oxygen atom but not a nitrogen atom as a heteroatom. This allows the functions of the first complexing agent and the second complexing agent described above to be effectively utilized, thereby improving the ionic conductivity of the resulting solid electrolyte.

[0087] Examples of such ether compounds include aliphatic ethers, alicyclic ethers, heterocyclic ethers, and aromatic ethers, and these compounds may be used alone or in combination.

[0088] More specifically, examples of aliphatic ethers include monoethers such as dimethyl ether, diethyl ether, diisopropyl ether, dibutyl ether, and tert-butyl methyl ether; diethers such as dimethoxymethane, dimethoxyethane, diethoxymethane, and diethoxyethane; polyethers having three or more ether groups such as diethylene glycol dimethyl ether (diglyme) and triethylene oxide glycol dimethyl ether (triglyme); and ethers containing hydroxyl groups such as diethylene glycol and triethylene glycol. The aliphatic ether preferably has 2 or more carbon atoms, more preferably 3 or more carbon atoms, and even more preferably 4 or more carbon atoms, and the upper limit is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less carbon atoms. The number of carbon atoms in the aliphatic hydrocarbon group in the aliphatic ether is preferably 1 or more, and the upper limit is preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0089] Examples of alicyclic ethers include ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, dioxane, and dioxolane. Examples of heterocyclic ethers include furan, benzofuran, benzopyran, dioxene, dioxin, morpholine, methoxyindole, and hydroxymethyldimethoxypyridine. The number of carbon atoms in the alicyclic ether and heterocyclic ether is preferably 3 or more, more preferably 4 or more, and the upper limit is preferably 16 or less, more preferably 14 or less.

[0090] Examples of aromatic ethers include methyl phenyl ether (anisole), ethyl phenyl ether, dibenzyl ether, diphenyl ether, benzyl phenyl ether, and naphthyl ether. The aromatic ether preferably has 7 or more carbon atoms, more preferably 8 or more carbon atoms, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less carbon atoms.

[0091] The ether compound used in this embodiment may be substituted with a substituent such as an alkyl group, an alkenyl group, an alkoxyl group, a hydroxyl group, or a cyano group, or with a halogen atom.

[0092] The ether compound used in this embodiment is preferably an aliphatic ether, more preferably dimethoxyethane or tetrahydrofuran, from the viewpoint of obtaining higher ionic conductivity.

[0093] Examples of the ester compound include aliphatic esters, alicyclic esters, heterocyclic esters, and aromatic esters, and these compounds may be used alone or in combination.

[0094] More specifically, examples of aliphatic esters include formate esters such as methyl formate, ethyl formate, and triethyl formate; acetate esters such as methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, and isobutyl acetate; propionate esters such as methyl propionate, ethyl propionate, propyl propionate, and butyl propionate; oxalate esters such as dimethyl oxalate and diethyl oxalate; malonate esters such as dimethyl malonate and diethyl malonate; and succinate esters such as dimethyl succinate and diethyl succinate. The number of carbon atoms in the aliphatic ester is preferably 2 or more, more preferably 3 or more, and even more preferably 4 or more, with the upper limit being preferably 10 or less, more preferably 8 or less, and even more preferably 7 or less. The number of carbon atoms in the aliphatic hydrocarbon group in the aliphatic ester is preferably 1 or more, more preferably 2 or more, and the upper limit being preferably 6 or less, more preferably 4 or less, and even more preferably 3 or less.

[0095] Examples of alicyclic esters include methyl cyclohexanecarboxylate, ethyl cyclohexanecarboxylate, dimethyl cyclohexanedicarboxylate, dibutyl cyclohexanedicarboxylate, and dibutyl cyclohexenedicarboxylate. Examples of heterocyclic esters include methyl pyridinecarboxylate, ethyl pyridinecarboxylate, propyl pyridinecarboxylate, methyl pyrimidinecarboxylate, ethyl pyrimidinecarboxylate, and lactones such as acetolactone, propiolactone, butyrolactone, and valerolactone. The number of carbon atoms in the alicyclic ester and heterocyclic ester is preferably 3 or more, more preferably 4 or more, and the upper limit is preferably 16 or less, more preferably 14 or less.

[0096] Examples of aromatic esters include benzoic acid esters such as methyl benzoate, ethyl benzoate, propyl benzoate, and butyl benzoate; phthalic acid esters such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, butyl benzyl phthalate, and dicyclohexyl phthalate; and trimellitic acid esters such as trimethyl trimellitate, triethyl trimellitate, tripropyl trimellitate, tributyl trimellitate, and trioctyl trimellitate. The aromatic ester preferably has 8 or more carbon atoms, more preferably 9 or more carbon atoms, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less carbon atoms.

[0097] The ester compound used in this embodiment may be substituted with a substituent such as an alkyl group, an alkenyl group, an alkoxyl group, a hydroxyl group, or a cyano group, or with a halogen atom.

[0098] The ester compound used in this embodiment is preferably an aliphatic ester, more preferably an acetate ester, and particularly preferably ethyl acetate, from the viewpoint of obtaining higher ionic conductivity.

[0099] In this embodiment, it is preferable to mix the second complexing agent after the complex formation reaction by the first complexing agent has progressed to a certain extent. The method for determining the appropriate timing for adding the second complexing agent is not particularly limited. For example, when lithium sulfide is used as one of the raw materials, a greater effect can be achieved by adding the second complexing agent at a timing when the remaining amount of lithium sulfide present in the system has decreased to a certain value. Specifically, the complex formation reaction can be further accelerated by adding the second complexing agent after the amount of lithium sulfide remaining has fallen to preferably 35 mol % or less, more preferably 30 mol % or less, and even more preferably 25 mol % or less, relative to the amount of lithium sulfide added. The amount of lithium sulfide remaining in the system can be measured by the method described in the Examples.

[0100] From the viewpoint of efficiently forming a complex, the molar ratio of the amount of the second complexing agent to the total molar amount of Li3PS4 that can be produced from two or more of the raw material components is preferably 1.0 or more and 5.0 or less, more preferably 2.0 or more and 4.0 or less, and even more preferably 2.5 or more and 3.5 or less.

[0101] By mixing the raw materials with a complexing agent, a complex is obtained in which the lithium, sulfur, phosphorus, and halogen atoms contained in the raw materials are bonded directly to one another with or without the aid of a complexing agent due to the interaction of the complexing agent with the lithium, sulfur, phosphorus, and halogen atoms contained in the raw materials. That is, in the method for producing a solid electrolyte of this embodiment, the complex obtained by mixing the raw materials with a complexing agent is composed of the complexing agent, lithium, sulfur, phosphorus, and halogen atoms. The complex obtained in this embodiment is not completely soluble in the liquid complexing agent and is generally solid. Therefore, in this embodiment, a suspension in which the complex is suspended in the complex and a solvent added as needed is obtained. Therefore, the method for producing a solid electrolyte of this embodiment corresponds to a heterogeneous system in a so-called liquid phase method.

[0102] (solvent) In this embodiment, a solvent may be further added when the raw material and the complexing agent are mixed. When a solid complex is formed in a liquid complexing agent, if the complex is easily soluble in the complexing agent, separation of the components may occur. Therefore, by using a solvent in which the complex is insoluble, the elution of components in the electrolyte precursor can be suppressed. Furthermore, by mixing the raw material ingredients and the complexing agent using a solvent, complex formation is promoted, allowing each main component to be more evenly present, and an electrolyte precursor in which halogen atoms are more dispersed and fixed can be obtained, which makes it easier to achieve the effect of obtaining high ionic conductivity.

[0103] The method for producing a solid electrolyte according to the present embodiment is a so-called heterogeneous method, and it is preferable that the complex does not completely dissolve in the liquid complexing agent but precipitates. The solubility of the complex can be adjusted by adding a solvent. Halogen atoms, in particular, tend to dissolve from the complex, so adding a solvent suppresses the dissolution of halogen atoms to obtain the desired complex. As a result, a crystalline sulfide solid electrolyte with high ionic conductivity can be obtained via an electrolyte precursor in which components such as halogens are dispersed, which is preferable.

[0104] A preferred example of a solvent having such properties is a solvent having a solubility parameter of 10 or less. In this specification, the solubility parameter is a value δ ((cal / cm)) calculated by the following formula (1), which is described in various documents, such as "Chemical Handbook" (published in 2004, 5th revised edition, Maruzen Co., Ltd.). 3 ) 1 / 2 ) and is also called the Hildebrand parameter or SP value.

[0105]

number

[0106] By using a solvent with a solubility parameter of 10 or less, halogen atoms, halogen-containing raw materials such as lithium halide, and even halogen-containing components constituting the co-crystal contained in the complex (e.g., an aggregate formed by bonding lithium halide and the complexing agent) can be made relatively less soluble compared to the complexing agent. This facilitates the fixation of halogen atoms in the complex, resulting in well-dispersed halogen atoms in the resulting electrolyte precursor and solid electrolyte, making it easier to obtain a solid electrolyte with high ionic conductivity. In other words, the solvent used in this embodiment preferably has the property of not dissolving the complex. From the same perspective, the solubility parameter of the solvent is preferably 9.5 or less, more preferably 9.0 or less, and even more preferably 8.5 or less.

[0107] More specifically, the solvent used in this embodiment can be a wide variety of solvents that have conventionally been used in the production of solid electrolytes. The solvent is preferably at least one selected from nonpolar solvents and aprotic polar solvents. Among these, a solvent having a solubility parameter within the above-mentioned range may be appropriately selected and used. Examples of the solvent include hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents; solvents containing carbon atoms such as alcohol-based solvents, ester-based solvents, aldehyde-based solvents, ketone-based solvents, ether-based solvents having 4 or more carbon atoms on one side, and solvents containing carbon atoms and heteroatoms. Among these, a solvent having a solubility parameter within the above-mentioned range may be appropriately selected and used.

[0108] More specifically, aliphatic hydrocarbon solvents such as hexane (7.3), pentane (7.0), 2-ethylhexane, heptane (7.4), octane (7.5), decane, undecane, dodecane, and tridecane; alicyclic hydrocarbon solvents such as cyclohexane (8.2) and methylcyclohexane; benzene, toluene (8.8), xylene (8.8), mesitylene, ethylbenzene (8.8), tert-butylbenzene, trifluoromethylbenzene, nitrobenzene, chlorobenzene (9.5), chlorotoluene (8.8), and bromobenzene. Examples of the solvents include aromatic hydrocarbon solvents such as ethanol (12.7) and butanol (11.4); aldehyde solvents such as formaldehyde, acetaldehyde (10.3), and dimethylformamide (12.1); ketone solvents such as acetone (9.9) and methyl ethyl ketone; ether solvents such as dibutyl ether, cyclopentyl methyl ether (8.4), tert-butyl methyl ether, and anisole; and solvents containing carbon atoms and heteroatoms such as acetonitrile (11.9), dimethyl sulfoxide, and carbon disulfide. Note that the numbers in parentheses in the above examples are SP values.

[0109] Among these solvents, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, aromatic hydrocarbon solvents, and ether-based solvents are preferred, and from the viewpoint of obtaining more stable and high ionic conductivity, heptane, cyclohexane, toluene, ethylbenzene, diethyl ether, diisopropyl ether, dibutyl ether, dimethoxyethane, cyclopentyl methyl ether, tert-butyl methyl ether, and anisole are more preferred, diethyl ether, diisopropyl ether, and dibutyl ether are even more preferred, and diisopropyl ether and dibutyl ether are even more preferred, and cyclohexane is particularly preferred. The solvent used in this embodiment is preferably an organic solvent exemplified above, and is an organic solvent different from the complexing agent. In this embodiment, these solvents may be used alone or in combination.

[0110] (Dry) In this embodiment, since the electrolyte precursor is often a suspension, a drying step may be included. This results in a powder of the electrolyte precursor. Drying before heating, which will be described later, is preferable because it allows for efficient heating. Note that drying and subsequent heating may be performed in the same step.

[0111] Drying can be performed at a temperature depending on the type of complexing agent and solvent remaining in the electrolyte precursor. For example, drying can be performed at a temperature equal to or higher than the boiling point of the complexing agent or solvent. Drying can be performed 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 about room temperature (23°C) (for example, about room temperature ±5°C), to volatilize the complexing agent and solvent. Unlike the complexing agent, the solvent is not easily incorporated into the complex, and therefore the amount of the solvent that can be contained in the complex is usually 3% by mass or less, preferably 2% by mass or less, and more preferably 1% by mass or less.

[0112] The drying may be performed by filtration using a glass filter or the like, solid-liquid separation by decantation, or solid-liquid separation using a centrifuge, etc. In this embodiment, after the solid-liquid separation, drying may be performed under the above-mentioned temperature conditions. Specifically, solid-liquid separation can be easily performed by decantation, in which the suspension is transferred to a container, and after the solid has settled, the supernatant complexing agent and the solvent added as needed are 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.

[0113] The complex is composed of a complexing agent, lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, and is characterized in that, in X-ray diffraction measurement, peaks distinct from those derived from the raw materials are observed in the X-ray diffraction pattern. Preferably, the complex includes a cocrystal composed of a complexing agent, lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms. Simply mixing the raw materials results in the observation of peaks derived from the raw materials. However, mixing the raw materials with a complexing agent results in the observation of peaks distinct from those derived from the raw materials. Therefore, the complex clearly has a structure distinct from that of the raw materials themselves. This is specifically confirmed in the Examples. An example of the X-ray diffraction pattern of an electrolyte precursor (complex) is shown in Figure 5. The intensities in the figure refer to intensity. The X-ray diffraction pattern reveals that the complex has a predetermined crystalline structure.

[0114] The electrolyte precursor is also characterized by having a structure different from that of the crystalline solid electrolyte. This has also been specifically confirmed in the Examples. FIG. 5 also shows the X-ray diffraction pattern of the crystalline sulfide solid electrolyte (1) 102 of Example 1, which is different from the diffraction pattern of the electrolyte precursor (1) 100. The electrolyte precursor (1) 100 has a specific crystalline structure and is also different from the amorphous complex decomposition product (1) 101, which has a broad pattern as shown in FIG. 5.

[0115] The content of the complexing agent in the electrolyte precursor varies depending on the molecular weight of the complexing agent, but is usually about 10% by mass to 70% by mass, preferably 15% by mass to 65% by mass.

[0116] <Obtaining complex decomposition products> In this embodiment, the electrolyte precursor is heated to obtain a complex decomposition product. (heating) The method for producing the solid electrolyte of this embodiment is required to include heating an electrolyte precursor to obtain an (amorphous or crystalline) complex decomposition product, and heating a smoothed complex decomposition product or a modified complex decomposition product described below to obtain a crystalline sulfide solid electrolyte. By including a step of heating the electrolyte precursor, the complexing agent in the electrolyte precursor is removed, and a complex decomposition product containing lithium atoms, sulfur atoms, phosphorus atoms, and, if necessary, halogen atoms is obtained. Here, the removal of the complexing agent in the electrolyte precursor is supported by the fact that the results of X-ray diffraction patterns, gas chromatography analysis, etc. show that the complexing agent forms a co-crystal with the electrolyte precursor, and also by the fact that the solid electrolyte obtained by removing the complexing agent by heating the electrolyte precursor has the same X-ray diffraction pattern as a solid electrolyte obtained by a conventional method without using a complexing agent.

[0117] In this embodiment, the complex decomposition product is obtained by heating the electrolyte precursor to remove the complexing agent from the electrolyte precursor. The less complexing agent in the complex decomposition product, the better. However, the complexing agent may be present to an extent that does not impair the performance of the complex decomposition product. The content of the complexing agent in the complex decomposition product is usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0118] In this embodiment, the crystalline sulfide solid electrolyte is obtained by heating and crystallizing the smoothed complex decomposition product or the modified complex decomposition product. Conventionally, to obtain a crystalline sulfide solid electrolyte with high ionic conductivity, it has been necessary to prepare an amorphous solid electrolyte by mechanical pulverization such as mechanical milling, or other melt-quenching treatments, and then heat the amorphous solid electrolyte to obtain it. However, in the production method of the present embodiment, when obtaining an electrolyte precursor, mechanical pulverization, other melt-quenching treatments, etc. are not performed, and instead mechanical treatments including a smoothing treatment described below are performed, thereby obtaining a sulfide solid electrolyte with high ionic conductivity while atomizing the sulfide solid electrolyte, which can be said to be advantageous over conventional production methods using mechanical milling or the like.

[0119] The heating temperature of the electrolyte precursor, for example, when obtaining a complex decomposition product, can be determined depending on the structure of the complex decomposition product obtained by heating the electrolyte precursor. Specifically, the electrolyte precursor is subjected to differential thermal analysis (DTA) at a temperature increase rate of 10°C / min using a differential thermal analyzer (DTA). The heating temperature is preferably 5°C or lower, more preferably 10°C or lower, and even more preferably 20°C or lower, starting from the temperature of the lowest exothermic peak observed at the lowest temperature. The lower limit is not particularly limited, but may be approximately −40°C or higher than the temperature of the lowest exothermic peak observed at the lowest temperature. By setting the temperature within this range, the complex decomposition product can be obtained more efficiently and reliably. The heating temperature for obtaining a solid electrolyte cannot be generally defined because it varies depending on the structure of the complex decomposition product to be obtained. However, it is generally preferably 135°C or lower, more preferably 130°C or lower, and even more preferably 125°C or lower. The lower limit is not particularly limited, but is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 110°C or higher.

[0120] Furthermore, when an amorphous smoothed complex decomposition product or modified complex decomposition product is heated to obtain a crystalline sulfide solid electrolyte, the heating temperature can be determined depending on the structure of the crystalline sulfide solid electrolyte, and is preferably higher than the heating temperature for obtaining an amorphous complex decomposition product. Specifically, the smoothed complex decomposition product or modified complex decomposition product is subjected to differential thermal analysis (DTA) using a differential thermal analyzer (DTA) at a temperature increase of 10°C / min. The temperature is preferably set to 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 at the lowest temperature. There is no particular upper limit, but it should be about 40°C or lower. By setting the temperature range in this way, a crystalline sulfide solid electrolyte can be obtained more efficiently and reliably. The heating temperature for obtaining a crystalline sulfide solid electrolyte cannot be generally defined because it varies depending on the structure of the crystalline sulfide solid electrolyte to be obtained. However, it is generally 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 300°C or lower, more preferably 280°C or lower, and even more preferably 250°C or lower.

[0121] The heating time is not particularly limited as long as it is a time that allows the desired complex decomposition product and crystalline sulfide solid electrolyte 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.

[0122] 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). This is because deterioration (e.g., oxidation) of the complex decomposition product and the crystalline sulfide solid electrolyte can be prevented. The heating method is not particularly limited, and examples thereof include methods using a hot plate, a vacuum heating device, an argon gas atmosphere furnace, and a calcination furnace. Furthermore, industrially, a horizontal dryer or a horizontal vibration fluidized dryer having a heating means and a feeding mechanism can also be used, and the method may be selected depending on the amount of heat to be processed.

[0123] (complex decomposition product) The complex decomposition product obtained by this embodiment contains lithium atoms, sulfur atoms, phosphorus atoms, and, if necessary, halogen atoms. Representative examples include solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as LiS-PS-LiI, LiS-PS-LiCl, LiS-PS-LiBr, and LiS-PS-LiI-LiBr; and solid electrolytes further containing other atoms such as oxygen and silicon atoms, such as LiS-PS-LiO-LiI and LiS-SiS-PS-LiI. From the viewpoint of obtaining higher ionic conductivity, solid electrolytes composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as LiS-PS-LiI, LiS-PS-LiCl, LiS-PS-LiBr, and LiS-PS-LiI-LiBr, are preferred. The types of atoms constituting the complex decomposition product can be confirmed, for example, by an ICP emission spectrometer.

[0124] When the complex decomposition product obtained in this embodiment has at least Li2S-P2S5, the molar ratio of Li2S to P2S5 is preferably 65-85:15-35, more preferably 70-80:20-30, and even more preferably 72-78:22-28, from the viewpoint of obtaining higher ionic conductivity. When the complex decomposition product obtained in this embodiment is, for example, Li2S-P2S5-LiI-LiBr, the total content of lithium sulfide and diphosphorus pentasulfide is preferably 60 to 95 mol%, more preferably 65 to 90 mol%, and even more preferably 70 to 85 mol%. The ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 90 mol%, even more preferably 40 to 80 mol%, and particularly preferably 50 to 70 mol%.

[0125] In the complex decomposition product obtained in this embodiment, the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms is preferably 1.0-1.8:1.0-2.0:0.1-0.8:0.01-0.6, more preferably 1.1-1.7:1.2-1.8:0.2-0.6:0.05-0.5, and even more preferably 1.2-1.6:1.3-1.7:0.25-0.5:0.08-0.4. Furthermore, when bromine and iodine are used in combination as halogen atoms, the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, bromine, and iodine is preferably 1.0-1.8:1.0-2.0:0.1-0.8:0.01-0.3:0.01-0.3, more preferably 1.1-1.7:1.2-1.8:0.2-0.6:0.02-0.25:0.02-0.25, more preferably 1.2-1.6:1.3-1.7:0.25-0.5:0.03-0.2:0.03-0.2, and even more preferably 1.35-1.45:1.4-1.7:0.3-0.45:0.04-0.18:0.04-0.18. By setting the compounding ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range, it becomes easier to obtain a solid electrolyte having a thiolicon region II crystal structure described below and higher ionic conductivity.

[0126] In this specification, the average particle size (D 50 ) is a value measured by a laser diffraction particle size distribution measurement method, and can be measured, for example, by the method described in the Examples. The shape of the decomposition product is not particularly limited, but may be, for example, particulate. The average particle size (D 50 The thickness b) can be, for example, in the range of 0.01 μm to 500 μm, and further in the range of 0.1 to 200 μm.

[0127] In this specification, the specific surface area is a value measured by the BET method, and can be measured, for example, by the method described in the Examples. The specific surface area (Sb) of the decomposition product before smoothing or mechanical treatment is preferably 21 m 2 / g or more, more preferably 23m 2 / g or more, more preferably 25m 2 / g or more, and even more preferably 27m 2 / g or more, and the upper limit is preferably 70m 2 / g or less, more preferably 60m 2 / g or less, more preferably 50m 2 / g or less, even more preferably 35m 2 / g or less.

[0128] <Obtaining smoothed or modified complex decomposition products> In this embodiment, the complex decomposition product is subjected to a smoothing treatment to obtain a smoothed complex decomposition product, or to a mechanical treatment to obtain a modified complex decomposition product. As described above, a preferred embodiment of the mechanical treatment is the smoothing treatment. By performing the smoothing treatment or mechanical treatment, the specific surface area of the complex decomposition product is reduced, and by subsequently performing the heating as described above, a crystalline sulfide solid electrolyte is obtained, which is preferable because a finely divided solid electrolyte with high ionic conductivity can be obtained.

[0129] (mechanical treatment) The mechanical treatment is a treatment for converting the complex decomposition product into a modified complex decomposition product. The "mechanical treatment" is a treatment for atomizing the solid electrolyte, and among the "mechanical treatments," the treatment for reducing the specific surface area while atomizing the particles is called the "smoothing treatment." The method for mechanically treating the complex decomposition product is not particularly limited as long as it includes a crushing treatment, and examples thereof include methods using equipment such as a grinder or a stirrer. Examples of the agitator include the mechanical agitation mixer provided with agitating blades in a tank, which are exemplified above as devices that can be used in the method for producing a complex decomposition product. Examples of mechanical agitation mixers include high-speed agitation mixers and double-arm mixers, and any type can be used. However, from the viewpoint of more easily adjusting the desired average particle size, high-speed agitation mixers are preferred. More specifically, as already mentioned, high-speed agitation mixers include vertical-axis rotary mixers and horizontal-axis rotary mixers, as well as various devices such as high-speed swirling thin-film agitators and high-speed shear agitators. Among these, high-speed swirling thin-film agitators (also referred to as "thin-film swirling high-speed mixers") are preferred because they can more easily atomize the particles to obtain the desired average particle size.

[0130] The pulverizer that can be used in the method for treating a sulfide solid electrolyte of this embodiment is a pulverizer having a volume-based average particle size of at least 3 μm or more measured by a laser diffraction particle size distribution measurement method and a specific surface area of at least 20 m2 measured by a BET method. 2 The example includes a pulverizer having a rotor capable of stirring a sulfide solid electrolyte having a molecular weight of 1 / g or more, that is, a complex decomposition product. In the sulfide solid electrolyte treatment method of this embodiment, the crushing (atomization) and granulation (particle growth) of the complex decomposition product can be adjusted by adjusting the peripheral speed of the rotor of the pulverizer. That is, the average particle size can be reduced by crushing and increased by granulation, so the average particle size of the sulfide solid electrolyte can be easily adjusted freely. More specifically, crushing can be achieved by rotating the rotor at a low peripheral speed, and granulation can be achieved by rotating the rotor at a high peripheral speed. In this way, the average particle size of the sulfide solid electrolyte can be easily adjusted simply by adjusting the peripheral speed of the rotor.

[0131] Regarding the peripheral speed of the rotating body, low and high peripheral speeds cannot be generally defined because they can vary depending on, for example, the particle size, material, and amount of the media used in the mill. For example, in the case of a device that does not use ball or bead milling media, such as a high-speed rotating thin-film mixer, even at relatively high peripheral speeds, mainly crushing occurs and granulation is difficult to occur. On the other hand, in the case of a device that uses milling media, such as a ball mill or bead mill, crushing can be performed at low peripheral speeds and granulation can be performed at high peripheral speeds, as described above. Therefore, if the specified conditions of the milling device, milling media, etc. are the same, the peripheral speed at which crushing is possible is lower than the peripheral speed at which granulation is possible. Therefore, for example, in the conditions under which granulation is possible at a peripheral speed of 6 m / s, a low peripheral speed means less than 6 m / s, and a high peripheral speed means 6 m / s or more.

[0132] A more specific example of a grinder is a media-type grinder, which is broadly classified into a container-driven grinder and a media-agitation grinder. Examples of the container-driven grinding machine include a stirring tank, a grinding tank, or a combination of these, such as a ball mill or a bead mill. As the ball mill or bead mill, any of various types such as a rotary type, a rolling type, a vibrating type, or a planetary type can be used. Examples of media agitation type crushers include impact crushers such as cutter mills, hammer mills, and pin mills; tower-type crushers such as tower mills; agitation tank-type crushers such as attritors, aquamizers, and sand grinders; flow tank-type crushers such as Viscomill and pearl mills; flow pipe-type crushers; annular-type crushers such as Coball mills; and continuous dynamic crushers.

[0133] In the method for treating a sulfide solid electrolyte according to this embodiment, from the viewpoint of more easily adjusting the desired average particle size, a container-driven pulverizer is preferred, and a bead mill or a ball mill is particularly preferred. Container-driven pulverizers such as a bead mill or a ball mill are equipped with a container, such as a stirring tank or a pulverizing tank, that stores the complex decomposition product as a rotating body capable of stirring the complex decomposition product. Therefore, as described above, the average particle size of the sulfide solid electrolyte can be easily adjusted by adjusting the peripheral speed of the rotating body. Bead mills and ball mills can adjust the average particle size by adjusting the particle size, material, amount used, etc. of the beads and balls used, making it possible to adjust the average particle size to a finer degree and also to adjust the average particle size to a level not previously possible.For example, a centrifugal type bead mill that can use so-called microbeads with extremely fine particles (φ0.015 to 1 mm or so) (e.g., Ultra Apex Mill (UAM)) can be used.

[0134] Regarding the adjustment of the average particle size, the smaller the energy applied to the complex decomposition product, i.e., the lower the peripheral speed of the rotor, or the smaller the particle size of the beads, balls, etc., the smaller the average particle size (crushing) and the larger the specific surface area tends to be. On the other hand, the larger the energy, i.e., the higher the peripheral speed of the rotor, or the larger the particle size of the beads, balls, etc., the larger the average particle size (granulation) and the smaller the specific surface area tends to be. Furthermore, for example, the longer the time of mechanical treatment, the larger the average particle size tends to be (granulation).

[0135] The particle size of the media used in a bead mill, ball mill, etc. may be determined appropriately taking into consideration the desired average particle size as well as the type and scale of the equipment used, but is usually preferably 0.01 mm or more, more preferably 0.015 mm or more, even more preferably 0.02 mm or more, and still more preferably 0.04 mm or more, with the upper limit being preferably 3 mm or less, more preferably 2 mm or less, even more preferably 1 mm or less, and still more preferably 0.8 mm or less. Examples of the material of the medium include metals such as stainless steel, chrome steel, and tungsten carbide; ceramics such as zirconia and silicon nitride; and minerals such as agate.

[0136] The processing time for the mechanical treatment may be appropriately determined taking into consideration the desired average particle size as well as the type and scale of the equipment used, but is generally preferably 5 seconds or more, more preferably 30 seconds or more, even more preferably 3 minutes or more, and even more preferably 15 minutes or more, with the upper limit being preferably 5 hours or less, more preferably 3 hours or less, even more preferably 2 hours or less, and even more preferably 1.5 hours or less. The peripheral speed of the rotating body in the mechanical treatment (the rotational speed of an apparatus such as a bead mill or ball mill) may be appropriately determined taking into consideration the desired average particle size as well as the type and scale of the apparatus used, but is usually preferably 0.5 m / s or more, more preferably 1 m / s or more, even more preferably 2 m / s or more, and still more preferably 3 m / s or more, with the upper limit being preferably 55 m / s or less, more preferably 40 m / s or less, even more preferably 25 m / s or less, and still more preferably 15 m / s or less. The peripheral speed may be the same or may be changed during the treatment.

[0137] The mechanical treatment can be carried out in combination with a solvent. The solvent can be appropriately selected from those exemplified as solvents that can be used in the above-described embodiments C and D of the method for producing a complex decomposition product. From the viewpoint of obtaining a predetermined average particle size and specific surface area as well as a more stable and high ionic conductivity, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, aromatic hydrocarbon solvents, and ether-based solvents are preferred. Heptane, cyclohexane, toluene, ethylbenzene, diethyl ether, diisopropyl ether, dibutyl ether, dimethoxyethane, cyclopentyl methyl ether, tert-butyl methyl ether, and anisole are more preferred, heptane, toluene, and ethylbenzene are even more preferred, and heptane and toluene are even more preferred. In this embodiment, the powder can be easily atomized by crushing without using a dispersant. However, a dispersant may be used to further enhance dispersion and achieve more efficient atomization. Among the above-described solvents, for example, ether-based solvents can function as a dispersant.

[0138] The amount of solvent used may be such that the content of the complex decomposition product relative to the total amount of the complex decomposition product and the solvent is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, and the upper limit is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less. When the mechanical treatment is carried out using a solvent, the modified complex decomposition product may be dried as described above.

[0139] (Modified complex decomposition product) The modified complex decomposition product has chemical characteristics similar to those of the above-mentioned complex decomposition product, but differs from the complex decomposition product in its average particle size. The shape of the modified complex decomposition product after the mechanical treatment is not particularly limited, but may be, for example, particulate. The average particle size (D 50 It is preferable that c) is not granulated by mechanical treatment, and examples thereof include a range of 0.01 μm to 500 μm, and further 0.1 to 200 μm. In this embodiment, the average particle size (D 50 d) and the average particle size of the modified complex decomposition product (D 50 c) ratio (D 50 d / D 50 From the viewpoint of increasing the ionic conductivity of the crystalline sulfide solid electrolyte, c) is preferably 1.0 or more and 100.0 or less, more preferably 2.0 or more and 80.0 or less, and even more preferably 2.5 or more and 70.0 or less.

[0140] (Smoothing process) The smoothing treatment is a treatment for converting the decomposition product into a smoothed decomposition product. In this embodiment, the smoothing treatment is preferably carried out using a grinder. In conventional atomization treatments, atomization generally increases the specific surface area and reduces ionic conductivity. On the other hand, in this embodiment, a raw material containing at least one selected from lithium atoms, sulfur atoms, and phosphorus atoms is mixed with a complexing agent without using a mechanical treatment machine to obtain an electrolyte precursor, and the electrolyte precursor is heated to obtain a complex decomposition product, and then a "smoothing treatment" is performed, thereby achieving both atomization and a low specific surface area and improving ionic conductivity.

[0141] The smoothing treatment is a form of mechanical treatment and means a treatment that includes at least pulverization, and the Sb / Sa ratio described below is set to 1.0 or more and 10.0 or less, and D 50 b / D 50 a) is a process that can make the value of a) between 1.0 and 100.0. Furthermore, the smoothing treatment is preferably carried out using the above-mentioned solvent as needed, as this allows for efficient smoothing and is preferred from the viewpoint of exhibiting high ionic conductivity when made into a crystalline sulfide solid electrolyte.

[0142] The method of smoothing the surface using a grinder has been conventionally adopted as a mechanical milling method. As the grinder, for example, a media grinder using grinding 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-through tank mills such as Viscomill and pearl mills; flow-through pipe 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 mill or bead mill exemplified as a vessel-driven mill is preferred.

[0143] 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.

[0144] Furthermore, as will be described later, when the material is in a liquid state involving a liquid such as a solvent or in a slurry state during the smoothing treatment, 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, dry planetary ball mills, and dry vibration mills) and dry non-media mills (e.g., jet mills) can also be used.

[0145] 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.

[0146] 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 0.2 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 30.0 mm or less, preferably 20.0 mm or less, more preferably 15.0 mm or less.

[0147] The amount of beads or balls used varies depending on the scale of processing and cannot be generalized, but is usually 100 g or more, preferably 200 g or more, and more preferably 300 g or more, with the upper limit being 5.0 kg or less, more preferably 3.0 kg or less, and even more preferably 1.0 kg 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.

[0148] Regarding the peripheral speed of the rotating body, low and high peripheral speeds cannot be generally defined because they can vary depending on, for example, the particle size, material, and amount of the media used in the mill. For example, in the case of a device that does not use ball or bead milling media, such as a high-speed rotating thin-film mixer, even at relatively high peripheral speeds, mainly crushing occurs and granulation is difficult to occur. On the other hand, in the case of a device that uses milling media, such as a ball mill or bead mill, crushing can be performed at low peripheral speeds and granulation can be performed at high peripheral speeds, as described above. Therefore, if the specified conditions of the milling device, milling media, etc. are the same, the peripheral speed at which crushing is possible is lower than the peripheral speed at which granulation is possible. Therefore, for example, in the conditions under which granulation is possible at a peripheral speed of 6 m / s, a low peripheral speed means less than 6 m / s, and a high peripheral speed means 6 m / s or higher. The peripheral speed is preferably set to a high value, since smoothing the decomposition product at a high peripheral speed reduces the specific surface area of the solid electrolyte and increases the ionic conductivity. It is also preferable to subsequently grind the smoothed decomposition product to adjust its particle size.

[0149] The smoothing treatment time varies depending on the scale of the treatment and cannot be generalized, but is usually 10 minutes or more, preferably 20 minutes or more, more preferably 30 minutes or more, and even more preferably 45 minutes or more, with the upper limit being usually 72 hours or less, preferably 65 hours or less, and more preferably 52 hours or less. This range is preferable because granulation is suppressed and smoothing proceeds.

[0150] By selecting the size and material of the media (beads, balls) used, the rotor rotation speed, time, etc., mixing, stirring, crushing, and combinations of these processes can be performed, and the particle size, etc. of the resulting sulfide can be adjusted. In the above-mentioned smoothing treatment, the above-mentioned solvent can be added to the above-mentioned complex decomposition product and mixed. When the smoothing treatment is carried out using a solvent, the smoothed complex decomposition product may be dried as described above.

[0151] (Smooth complex decomposition product) The smoothed decomposition product has chemical characteristics similar to those of the above-mentioned decomposition product, but its specific surface area is different from that of the decomposition product. The specific surface area of the smoothed decomposition product after the smoothing treatment is smaller than that of the decomposition product before the smoothing treatment. However, since it is affected by the specific surface area of the decomposition product used in the smoothing treatment, it cannot be said in general, but the specific surface area (Sa) of the smoothed decomposition product is preferably 0.5 m as a lower limit. 2 / g or more, more preferably 1.0m 2 / g or more, more preferably 2.0m 2 / g or more, and the upper limit is preferably 30m 2 / g or less, more preferably 20m 2 / g or less, more preferably 15m 2 / g or less, even more preferably 12m 2 / g or less. In this embodiment, the ratio (Sb / Sa) of the specific surface area (Sa) of the smoothed complex decomposition product to the specific surface area (Sb) of the complex decomposition product before the smoothing treatment is preferably 1.0 or more and 10.0 or less, more preferably 2.0 or more and 8.0 or less, and even more preferably 3.0 or more and 7.0 or less, from the viewpoint of increasing the ionic conductivity of the crystalline sulfide solid electrolyte.

[0152] The shape of the smoothed complex decomposition product is not particularly limited, but may be, for example, particulate. The average particle size (D 50 It is preferable that a) is not granulated by smoothing treatment, and examples thereof include a range of 0.01 μm to 500 μm, and further 0.1 to 200 μm. In this embodiment, the average particle size (D 50 b) and the average particle size of the smoothed complex decomposition product (D 50 a) ratio (D 50 b / D 50 From the viewpoint of increasing the ionic conductivity of the crystalline sulfide solid electrolyte, a) is preferably 1.0 or more and 100.0 or less, more preferably 2.0 or more and 80.0 or less, and even more preferably 2.5 or more and 70.0 or less.

[0153] <Heating the modified complex decomposition product or smoothed complex decomposition product> In this embodiment, the modified complex decomposition product or the smoothed complex decomposition product needs to be heated. Heating is preferred because it crystallizes and a solid electrolyte with high ionic conductivity is obtained. (Crystalline sulfide solid electrolyte) The crystalline sulfide solid electrolyte obtained by this embodiment may be a so-called glass ceramic obtained by heating a modified complex decomposition product or a smoothed complex decomposition product 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).

[0154] Also, Li 4-x Ge 1-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 xExamples 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 this production method 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 this production method 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 this production method 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 this production method does not contain crystalline Li3PS4 (β-Li3PS4).

[0155] 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 11Diffraction 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°.

[0156] As described above, when a thiolisiconregion II crystal structure is obtained in this embodiment, it is preferable that it does not contain crystalline Li3PS4 (β-Li3PS4). Figure 5 shows an example of X-ray diffraction measurement of the crystalline sulfide solid electrolyte (1) 102 obtained by this production method. The sulfide solid electrolyte of this embodiment does not have diffraction peaks at 2θ = 17.5° and 26.1° seen in crystalline Li3PS4, or even if it does, the peaks detected are extremely small compared to the diffraction peaks of the thiolisiconregion II crystal structure.

[0157] 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 y The crystal structure represented by S6 (x is -0.6 to 0.6, y is 0.1 to 0.6) is a cubic or orthorhombic crystal, preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, it has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. 7-x-2y PS 6-x-y Cl xThe crystal structure represented by (0.8 ≦ x ≦ 1.7, 0 < y ≦ -0.25x + 0.5) is preferably cubic, and in the X-ray diffraction measurement using CuKα rays, it mainly has peaks appearing at the positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Also, for the above composition formula Li 7-x PS 6-x Ha x (where Ha is Cl or Br, and x is preferably 0.2 to 1.8), the crystal structure is preferably cubic, and in the X-ray diffraction measurement using CuKα rays, it mainly has peaks appearing at the positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Regarding these peak positions, they may shift within a range of ±0.5°.

[0158] Also, for the crystalline sulfide solid electrolyte obtained by this manufacturing method, the full width at half maximum of the maximum peak including the background of 2θ = 10 to 40° in the X-ray diffraction measurement using CuKα rays is preferably Δ2θ = 0.32 or less. By having such properties, higher ionic conductivity can be obtained and the battery performance is improved. From the same perspective, as the full width at half maximum of the maximum peak, more preferably Δ2θ = 0.30 or less, and even more preferably Δ2θ = 0.28 or less. Typical examples of the crystalline sulfide solid electrolyte having such properties include those having a thiolischicon region II-type crystal structure.

[0159] For example, FIG. 5 shows an example of X-ray diffraction measurement of the crystalline sulfide solid electrolyte having a thiolicon region II crystal structure obtained in Example 1. It can be seen that the maximum peak, including the background from 2θ = 10 to 40°, is at 20.1° and has a sharp half-width of Δ2θ = 0.25. Since the maximum peak has a sharp half-width of 0.32 or less, the crystalline sulfide solid electrolyte exhibits extremely high ionic conductivity and can improve battery performance. Such a half-width indicates good crystallinity. This allows for crushing with little energy, making it less likely to experience a decrease in ionic conductivity due to vitrification (amorphization). Furthermore, the modified complex decomposition product or smoothed complex decomposition product of this embodiment has a porous structure with a relatively large specific surface area and good crystallinity. Therefore, even if the modified complex decomposition product is partially or completely vitrified by crushing and granulation, changes in the average particle size and specific surface area during recrystallization are relatively small. Therefore, the average particle size can be easily adjusted by mechanical processing or smoothing processing.

[0160] The half width can be calculated as follows. Use a range of ±2° from the maximum peak. Let A be the Lorentzian function ratio (0≦A≦1), B be the peak intensity correction value, C be the 2θ maximum peak, D be the peak position in the range used for calculation (C±2°), E be the half-width, F be the background, and G be the intensity of each peak in the peak range used for calculation. When the variables are A, B, C, D, E, and F, calculate the following for each peak position. H=G-{B×{A / (1+(DC) 2 / E 2 )+(1-A)×exp(-1×(DC) 2 / E 2 )}+F} The half-width can be calculated by summing up H within the range of ±2° of the above peak C and minimizing the total value with GRG nonlinearity using the solver function of the spreadsheet software Excel (Microsoft).

[0161] The shape of the crystalline 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.

[0162] The volume-based average particle size of the crystalline sulfide solid electrolyte obtained by this production method is 3 μm or more, the same as the average particle size of the sulfide solid electrolyte of this embodiment described above. The specific surface area of the crystalline sulfide solid electrolyte obtained by this production method, as measured by the BET method, is 20 m, which is the same as the specific surface area of the sulfide solid electrolyte of the present embodiment. 2 / g or more.

[0163] (Applications of crystalline sulfide solid electrolytes) The crystalline sulfide solid electrolyte of the present embodiment has a predetermined average particle size and specific surface area, high ionic conductivity, and excellent battery performance. In addition, it is unlikely to generate hydrogen sulfide, and therefore is suitable for use in batteries. It is particularly suitable when lithium element is used as the conductive species. The crystalline sulfide solid electrolyte of this embodiment may be used in the positive electrode layer, the negative electrode layer, or the electrolyte layer. Each layer can be manufactured by a known method.

[0164] 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 Au or the like coated with a material that reacts with the crystalline sulfide solid electrolyte, such as Au, Pt, Al, Ti, or Cu, can be used. [Example]

[0165] 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.

[0166] (1) Describe the measurement method. (1-1) Volume-based average particle size (D 50 ) Measurements were made using a laser diffraction / scattering particle size distribution analyzer (Partica LA-950 (model number), manufactured by Horiba, Ltd.).

[0167] A mixture of dehydrated toluene (Wako Pure Chemical Industries, special grade) and tertiary butyl alcohol (Wako Pure Chemical Industries, special grade) in a weight ratio of 93.8:6.2 was used as the dispersion medium. 50 mL of the dispersion medium was injected into the flow cell of the instrument and circulated. After that, the target substance was added and ultrasonicated, and the particle size distribution was measured. The amount of target substance added was adjusted so that the red light transmittance (R) corresponding to the particle concentration was 80-90% and the blue light transmittance (B) was 70-90% on the measurement screen specified by the instrument. The refractive index of the target substance was 2.16, and the refractive index of the dispersion medium was 1.49. The number of iterations was fixed at 15 for the distribution configuration, and particle size calculations were performed.

[0168] (1-2) Specific surface area measurement The specific surface area was determined by the BET flow method (three-point method) using nitrogen gas as the adsorbate in accordance with JIS R 1626:1996.

[0169] (1-3) Ionic conductivity measurement In this example, the ionic conductivity was measured as follows. From the sulfide solid electrolyte, a 10 mm diameter (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

[0170] (1-4) X-ray diffraction (XRD) measurement The resulting crystalline product was determined by XRD measurement. The precursor or solid electrolyte powder produced in each example was filled into a groove 20 mm in diameter and 0.2 mm deep, and the groove was smoothed with glass to prepare a sample. This sample was sealed with Kapton film for XRD and measured without exposing it to air. The powder X-ray diffraction measurement was carried out using a D2 PHASER powder diffraction measurement device manufactured by BRUKER Corporation under the following conditions.

[0171] Tube voltage: 30kV Tube current: 10mA X-ray wavelength: Cu-Kα ray (1.5418Å) Optical system: Concentration method Slit configuration: 4°sollar slit (both incident and receiving sides), 1mm divergence slit, Kβ filter (0.5% Ni plate), 3mm air scatter screen) Detector: Semiconductor detector Measurement range: 2θ=10-60deg Step width, scan speed: 0.05deg, 0.05deg / sec

[0172] Example 1 15.87 g of lithium sulfide (LiS) was introduced into a Schlenk tube (volume: 500 mL) equipped with a stirrer bar under a nitrogen atmosphere. After rotating the stirrer, 300 mL of cyclohexane was added, followed by 6.26 g of iodine (I) and stirring at room temperature for 2 hours. 3.94 g of bromine (Br) was then added, and the mixture was stirred at room temperature for 12 hours, followed by further stirring at 50°C for 3 hours. The slurry was allowed to stand to allow the solids to settle, and 190 mL of the supernatant was removed, followed by the addition of 190 mL of cyclohexane. This decantation was repeated three times to obtain a cyclohexane slurry containing lithium sulfide, lithium iodide, and lithium bromide.

[0173] A cyclohexane slurry containing lithium sulfide, lithium iodide, and lithium bromide was mixed with 21.93 g of diphosphorus pentasulfide (PS5) and 100 mL of cyclohexane and transferred to a 500 mL separable flask equipped with a rotor blade and a circulation line (Figure 2). 103 mL of tetramethylethylenediamine (TMEDA) was added, and mixing was initiated by circulatory stirring at room temperature (25 °C) with the rotor blade rotation speed at 200 rpm and a pump flow rate of 550 mL / min. After 48 hours, 61 mL of 1,2-dimethoxyethane (DME) was added, and circulatory stirring was continued for another 24 hours. The resulting slurry was dried under reduced pressure at room temperature to obtain powdered electrolyte precursor (1). The mixture was then heated under reduced pressure at 110 °C for 2 hours to obtain amorphous decomposition product (1). The mixture was then heated under reduced pressure at 180 °C for 2 hours to obtain crystalline decomposition product (1). In addition, crystallization peaks were detected at 2θ=20.2° and 23.6° in the X-ray diffraction spectrum of the crystalline complex decomposition product (1), confirming that it had a thiolicon region II type crystal structure.

[0174] A 1-L reactor equipped with a stirring blade was charged with 35.0 g of crystalline decomposition product (1) and 547 g of toluene. After rotating the stirring blade, a circularly operable bead mill (product name: Star Mill LMZ015, manufactured by Ashizawa Finetech Co., Ltd.) was used for 1 hour to carry out a smoothing treatment, a form of mechanical treatment (bead material: zirconia, bead diameter: 0.3 mm, bead amount: 456 g, pump flow rate: 650 mL / min, peripheral speed: 12 m / s, mill jacket temperature: 10°C). The resulting slurry was dried under vacuum (room temperature: 23°C) to obtain a white powder of the smoothed decomposition product (1). The mixture was then heated under reduced pressure at 180°C for 2 hours to obtain a crystalline sulfide solid electrolyte (1). Its ionic conductivity was measured to be 4.7 mS / cm. Furthermore, the crystalline sulfide solid electrolyte (1) was confirmed to have a thiolicon region II type crystal structure by X-ray diffraction spectroscopy.

[0175] Example 2 To the cyclohexane slurry containing lithium sulfide, lithium iodide, and lithium bromide obtained in Example 1, 21.93 g of diphosphorus pentasulfide (PS5) and 100 mL of cyclohexane were added and transferred to a 500 mL separable flask equipped with a rotor blade and a circulation line (Figure 2). 103 mL of tetramethylethylenediamine (TMEDA) was added, and mixing by circulation stirring was initiated at 40 °C with a rotor blade rotation speed of 200 rpm and a pump flow rate of 550 mL / min. After 160 hours, the resulting slurry was dried under reduced pressure at room temperature to obtain powdered electrolyte precursor (2). The pressure was then reduced to 110 °C for 2 hours to obtain amorphous complex decomposition product (2). The mixture was then heated under reduced pressure at 180 °C for 2 hours to obtain crystalline complex decomposition product (2). Furthermore, the crystalline decomposition product (2) was confirmed to have a thiolicon region II type crystal structure by X-ray diffraction spectroscopy.

[0176] A 1-L reactor equipped with a stirring blade was charged with 35.0 g of crystalline decomposition product (2) and 547 g of toluene. After rotating the stirring blade, a circularly operable bead mill (product name: Star Mill LMZ015, manufactured by Ashizawa Finetech Co., Ltd.) was used for 1 hour to carry out a smoothing treatment, a type of mechanical treatment (bead material: zirconia, bead diameter: 0.3 mm, bead amount: 456 g, pump flow rate: 650 mL / min, peripheral speed: 12 m / s, mill jacket temperature: 10°C). The resulting slurry was dried under vacuum (room temperature: 23°C) to obtain a white powder of the smoothed decomposition product (2). The mixture was then heated under reduced pressure at 180°C for 2 hours to obtain a crystalline sulfide solid electrolyte (2). The ionic conductivity was measured and found to be 4.7 mS / cm. Furthermore, the crystalline sulfide solid electrolyte (2) was confirmed to have a thiolicon region II type crystal structure by X-ray diffraction spectroscopy.

[0177] (Comparative Examples 1 and 2) The crystalline complex decomposition product (1) produced in Example 1 before the smoothing treatment was designated as Comparative Example 1, and the crystalline complex decomposition product (2) produced in Example 1 was designated as Comparative Example 2. Table 1 shows the specific surface area and average particle size (D 50) and ionic conductivity are shown in Table 1.

[0178] [Table 1]

[0179] From the results of Example 1, Sa=8, D 50 a=2.9, and from the results of Comparative Example 1, Sa=33, D 50 a = 9.2. From this, Sb / Sa = 4.1, D 50 b / D 50 a = 6.1, and it was confirmed that smoothing was achieved while suppressing granulation.

[0180] It was found that the specific surface area of Example 1 was smaller than that of Comparative Example 1 due to the smoothing treatment, and the ionic conductivity was significantly improved. Similarly, in Example 2 and Comparative Example 2, the ionic conductivity was significantly improved, and the effect of the smoothing treatment, which is one form of mechanical treatment, was confirmed. [Industrial Applicability]

[0181] According to this embodiment, a crystalline sulfide solid electrolyte having high ionic conductivity and excellent battery performance can be produced. The crystalline sulfide solid electrolyte obtained by the production method of this embodiment 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. [Explanation of symbols]

[0182] 1. Reaction tank 2.Extraction port 3.Return port 4. Mixer 5. Mixing blade 11. Pump 12.Circulation Line 13. Valve 100. Electrolyte precursor (1) 101. Amorphous Complex Decomposition Products (1) 102.Crystalline sulfide solid electrolyte (1)

Claims

1. a raw material containing at least one selected from a lithium atom, a sulfur atom, and a phosphorus atom, and a complexing agent are mixed without using a pulverizer to obtain an electrolyte precursor; heating the electrolyte precursor to obtain a complex decomposition product; smoothing the decomposition product to obtain a smoothed decomposition product; and heating the smoothed complex decomposition product; A method for producing a crystalline sulfide solid electrolyte, comprising:

2. The method for producing a crystalline sulfide solid electrolyte according to claim 1 , wherein the raw material contains further a halogen atom.

3. 3. The method for producing a crystalline sulfide solid electrolyte according to claim 1 or 2, wherein the mixing includes first mixing using a first complexing agent and second mixing using a second complexing agent different from the first complexing agent.

4. The first complexing agent is Li ３ P.S. ４ and a complexing agent capable of forming a complex containing a halogen atom, and the second complexing agent is Li ３ P.S. ４ The method for producing a crystalline sulfide solid electrolyte according to claim 3, wherein the complexing agent is capable of forming a complex containing

5. The method for producing a crystalline sulfide solid electrolyte according to any one of claims 1 to 4, wherein the smoothing treatment is performed using at least one device selected from a grinder and a stirrer.

6. The method for producing a crystalline sulfide solid electrolyte according to any one of claims 1 to 5, wherein the smoothing treatment is performed using a solvent.

7. The smoothing treatment is performed using at least one device selected from a ball mill, a bead mill, a cutter mill, a hammer mill, a pin mill, a tower mill, an attritor, an aquamizer, a sand grinder, a visco mill, a pearl mill, a co-ball mill, and a dynamic type pulverizer. The method for producing a crystalline sulfide solid electrolyte according to any one of claims 1 to 6.

8. The method for producing a crystalline sulfide solid electrolyte according to claim 6, wherein the solvent is at least one selected from a nonpolar solvent and an aprotic polar solvent.

9. The ratio (Sb / Sa) of the specific surface area (Sb) of the complex decomposition product before the smoothing treatment to the specific surface area (Sa) of the smoothed complex decomposition product is 1.0 or more and 10.0 or less. The method for producing a crystalline sulfide solid electrolyte according to any one of claims 1 to 8.

10. The ratio (D50b / D50a) of the average particle size (D50b) of the complex decomposition product before the smoothing treatment to the average particle size (D50a) of the smoothed complex decomposition product is 1.0 or more and 100.0 or less. The method for producing a crystalline sulfide solid electrolyte according to any one of claims 1 to 9.

11. The method for producing a crystalline sulfide solid electrolyte according to any one of claims 1 to 10, wherein the crystalline sulfide solid electrolyte comprises a thiolicon region II crystal structure.

12. The method for producing a crystalline sulfide solid electrolyte according to any one of claims 1 to 11, wherein a raw material containing at least one selected from a lithium atom, a sulfur atom, and a phosphorus atom and a complexing agent are mixed using one selected from a stirrer and a mixer to obtain an electrolyte precursor.

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