Method for producing modified sulfide solid electrolyte

Abstract

To efficiently provide a modified sulfide solid electrolyte which is excellent in coating suitability when applied as a paste and is suitable for use in a lithium ion battery.SOLUTION: A method for producing the modified sulfide solid electrolyte includes: mixing a raw material-containing product containing lithium atoms, sulfur atoms, and phosphorus atoms with a complexing agent to obtain an electrolyte precursor; heating the electrolyte precursor to obtain a sulfide solid electrolyte; and kneading the sulfide solid electrolyte by using a kneader including a casing and at least one rotating shaft which is arranged so as to penetrate the casing in a longitudinal direction and is provided with a paddle along an axial direction.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] In recent years, with the rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as power sources for these devices has become important. Conventionally, electrolytes containing flammable organic solvents have been used in batteries used for such purposes, but by making the battery all-solid-state, flammable organic solvents are not used in the battery, safety devices can be simplified, and manufacturing costs and productivity are excellent, so that all-solid-state batteries in which the electrolyte is replaced with a solid electrolyte layer are being developed.

[0003] The manufacturing method of the solid electrolyte used in the solid electrolyte layer is roughly divided into a solid phase method and a liquid phase method, and the liquid phase method is further divided into a homogeneous method in which the solid electrolyte material is completely dissolved in a solvent, and a heterogeneous method in which the solid electrolyte material is not completely dissolved and a solid-liquid coexisting suspension is formed. For example, among the liquid phase methods, a homogeneous method is known in which the solid electrolyte is dissolved in a solvent and reprecipitated (see, for example, Patent Document 1), and a heterogeneous method is known in which a solid electrolyte raw material such as lithium sulfide is reacted in a solvent containing a polar aprotic solvent (see, for example, Patent Documents 2 and 3, Non-Patent Document 1), and a manufacturing method of a solid electrolyte including mixing the raw material with a specific compound having an amino group (see, for example, Patent Document 4).

[0004] Patent Document 5 discloses a sulfide solid electrolyte and a processing method thereof, which focus on adjusting morphology such as particle size to a desired value when the sulfide solid electrolyte is used as a positive electrode material, a negative electrode material, and an electrolyte, and which is easily adjusted in morphology by performing at least one mechanical treatment selected from crushing and granulation. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-191899 A [Patent Document 2] International Publication No. 2014 / 192309 Brochure [Patent Document 3] International Publication No. 2018 / 054709 Brochure [Patent Document 4] International Publication No. 2020 / 105737 Brochure [Patent Document 5] International Publication No. 2020 / 105736 Brochure [Non-patent literature]

[0006] [Non-Patent Document 1] “CHEMISTRY OF MATERIALS”, 2017, No. 29, pp. 1830-1835 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and has an object to efficiently provide a modified sulfide solid electrolyte that has excellent applicability when applied as a paste and is suitable for use in lithium ion batteries. [Means for solving the problem]

[0008] The method for producing a sulfide solid electrolyte according to the present invention includes the steps of: Mixing a raw material containing lithium atoms, sulfur atoms, and phosphorus atoms with a complexing agent to obtain an electrolyte precursor; Heating the electrolyte precursor to obtain a sulfide solid electrolyte; and kneading the sulfide solid electrolyte using a kneader including a casing and at least one rotating shaft arranged to penetrate the casing in a longitudinal direction and having a paddle provided along an axial direction; A method for producing a modified sulfide solid electrolyte, comprising: It is. Effect of the Invention

[0009] According to the present invention, it is possible to efficiently provide a modified sulfide solid electrolyte that has excellent applicability when applied as a paste and is suitable for use in lithium ion batteries. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a schematic cross-sectional view of a multi-shaft kneader used in the production method of the present embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view of a multi-shaft kneader used in the production method of the present embodiment. [Diagram 3] 1 is a graph showing the relationship between integrated power and specific surface area in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention (hereinafter, sometimes referred to as "the present embodiment") will be described. In this specification, the upper and lower limit values ​​of the numerical ranges of "greater than or equal to", "less than or equal to", and "to" are values ​​that can be combined arbitrarily, and the numerical values ​​of the examples can also be used as the upper and lower limit values. Furthermore, provisions that are considered to be preferable can be adopted arbitrarily. In other words, one provision that is considered to be preferable can be adopted in combination with one or more other provisions that are considered to be preferable. It can be said that a combination of preferable things is more preferable.

[0012] (Findings Obtained by the Inventors to Achieve the Present Invention) As a result of intensive research aimed at solving the above problems, the present inventors have discovered the following and completed the present invention.

[0013] Until now, development has focused on improving the performance of the solid electrolyte itself. However, in recent years, as mass production of all-solid-state batteries progresses toward practical use, attention has been focused on the ease with which solid electrolytes can exhibit their performance when used in all-solid-state batteries. Solid electrolytes are used in the positive and negative electrodes and electrolyte layers of lithium-ion batteries, and attention has been focused on controlling the morphology, such as the particle size and specific surface area, to suit these applications.

[0014] The positive electrode, negative electrode, and electrolyte layer of a lithium-ion battery are generally formed by applying a solid electrolyte in a paste form. Therefore, if the specific surface area of ​​the solid electrolyte is large, the viscosity of the paste increases, and manufacturing problems such as a significant decrease in applicability are likely to occur. In this case, it is possible to improve the applicability of the paste by using a large amount of solvent to reduce the viscosity of the paste, but problems such as a longer drying time and a decrease in the density of the solid electrolyte constituting the layer, resulting in a decrease in battery performance. Thus, even if the performance of the solid electrolyte itself, such as ionic conductivity, is excellent, the battery performance may be deteriorated when used in an all-solid-state battery. Therefore, there is a demand for solid electrolytes that not only have excellent performance but also have a morphology controlled to be optimal for each application.

[0015] As seen in Patent Documents 1 to 4, a great deal of research has been done on solid electrolytes aimed at improving ion conductivity and battery performance. However, in these documents, in a situation where the practical application of lithium ion batteries is rapidly progressing, no consideration is given at all to methods for improving performance during the manufacturing process, such as paste coating suitability, with a focus on mass production. Furthermore, Patent Document 5 studies the adjustment of optimal morphology depending on the application. However, the method described in Patent Document 5 has room for improvement in terms of reducing energy consumption (which may also be referred to as "power consumption") when dealing with applications requiring a small specific surface area, for example.

[0016] Therefore, the present inventors have focused on a kneader (hereinafter, also simply referred to as a "kneader") that has a casing and at least one rotating shaft arranged to penetrate the casing in the longitudinal direction and with a paddle provided along the axial direction, as a device used for controlling morphology. A kneader is a device that is usually used to make a uniformly mixed material by simultaneously performing mechanical processes such as mixing, kneading, crushing, and pounding on different materials. The fact that a kneader is usually used for different materials can be seen from its use in, for example, reactions by kneading solid electrolyte raw materials together (see, for example, JP 2018-101593 A, etc.), and in mixing an electronic conductive material (corresponding to a solid electrolyte) with an active material, etc. (see, for example, JP 2016-213184 A, etc.).

[0017] In response to this, the present inventors found that when a single material, a solid electrolyte, was supplied to a kneader, the morphology could be controlled with less energy than when the morphology was controlled using a grinder such as a bead mill, and that the effect of reducing energy consumption was particularly noticeable when the specific surface area was reduced.

[0018] Meanwhile, in recent years, in order to put all-solid-state batteries into practical use, the liquid phase method has been attracting attention as a method that can be easily and mass-produced in addition to its versatility and applicability. Among the liquid phase methods, it has been found that the sulfide solid electrolyte obtained by the method for producing a sulfide solid electrolyte by the liquid phase method (heterogeneous method) in which a complexing agent and a solid electrolyte raw material are reacted, which is currently being developed, tends to have a large specific surface area. Therefore, the present inventors thought that controlling the morphology using a kneader, especially using a kneader to reduce the specific surface area, would be extremely effective in providing a more efficient sulfide solid electrolyte by the method for producing a sulfide solid electrolyte by the liquid phase method (heterogeneous method) in which a complexing agent and a solid electrolyte raw material are reacted.

[0019] Based on the above findings, it has been discovered that by kneading a sulfide solid electrolyte obtained by a liquid phase method (heterogeneous method) in which a complexing agent is reacted with a solid electrolyte raw material using a kneading machine, a modified sulfide solid electrolyte that has excellent applicability when applied as a paste and is suitable for use in lithium ion batteries can be efficiently obtained while still employing the liquid phase method.

[0020] (Various aspects of the present embodiment) A method for producing a modified sulfide solid electrolyte according to a first embodiment of the present invention includes the steps of: Mixing a raw material containing lithium atoms, sulfur atoms, and phosphorus atoms with a complexing agent to obtain an electrolyte precursor; Heating the electrolyte precursor to obtain a sulfide solid electrolyte; and kneading the sulfide solid electrolyte using a kneader including a casing and at least one rotating shaft arranged to penetrate the casing in a longitudinal direction and having a paddle provided along an axial direction; A method for producing a modified sulfide solid electrolyte, comprising: It is.

[0021] The sulfide solid electrolyte used in the method for producing a modified sulfide solid electrolyte of this embodiment is obtained by a liquid phase method (heterogeneous method) in which a complexing agent is reacted with a solid electrolyte raw material. The electrolyte precursor is obtained by mixing the complexing agent and the solid electrolyte raw material. The electrolyte precursor is a precursor of the sulfide solid electrolyte obtained by the manufacturing method of this embodiment, and can become a sulfide solid electrolyte by removing the complexing agent. Here, the complexing agent is a complexing agent, that is, an agent that can form a complex, and means a compound that is likely to form a complex with the solid electrolyte raw material contained in the raw material content. Therefore, since the electrolyte precursor is obtained by mixing the raw material content and the complexing agent, it can be said that it is a complex formed by the solid electrolyte raw material via the complexing agent.

[0022] The sulfide solid electrolyte used in the manufacturing method of this embodiment has a large specific surface area as described above, since a liquid phase method (heterogeneous method) is adopted in which a complexing agent and a solid electrolyte raw material are reacted. By kneading this with a kneader, the specific surface area can be reduced, and when applied as a paste, the increase in thixotropy as a viscous behavior of the paste is suppressed. Therefore, the modified sulfide solid electrolyte obtained by the manufacturing method of this embodiment has excellent applicability when applied as a paste, and is suitable for use in lithium ion batteries.

[0023] It is unclear why the use of a kneader in reducing the specific surface area results in a significant reduction in energy consumption compared to the use of a pulverizer such as a ball mill or a bead mill, but the following is thought to be the reason. In a grinding machine such as a ball mill or a bead mill, the specific surface area is thought to decrease due to repeated collisions between the medium such as balls or beads and the sulfide solid electrolyte powder, which causes the granulation of the sulfide solid electrolyte powder. In this case, the medium such as balls or beads is usually filled at 50 to 80% by volume of the capacity of the grinding chamber, resulting in a space of 20 to 50% by volume. Therefore, it cannot be said that the frequency of collisions between the medium and the sulfide solid electrolyte powder is high.

[0024] On the other hand, in the case of a kneader, only the sulfide solid electrolyte powder is densely packed inside the casing, so there is almost no space. As a result, the sulfide solid electrolyte powder collides (contacts) with itself extremely efficiently, which is thought to facilitate granulation of the sulfide solid electrolyte powder and thus efficiently reduce the specific surface area. Thus, according to the manufacturing method of the modified sulfide solid electrolyte of the present embodiment, it is believed that it is possible to efficiently provide a modified sulfide solid electrolyte that is suitable for use in lithium ion batteries, while adopting a liquid phase method and having excellent coatability when applied as a paste.

[0025] A method for producing a modified sulfide solid electrolyte according to a second aspect of the present embodiment includes the steps of: The kneader has two or more of the rotating shafts. That is it.

[0026] In the production method of this embodiment, the kneader can be any kneader having at least one rotating shaft without any particular limitation, that is, a single-shaft kneader having one rotating shaft can be used, or a multi-shaft kneader having two or more rotating shafts can be used. From the viewpoint of providing a modified sulfide solid electrolyte more efficiently, it is specified that a multi-shaft kneader is preferable.

[0027] A method for producing a modified sulfide solid electrolyte according to a third aspect of the present embodiment is the same as the first or second aspect, except that The kneader has a reverse screw. That is it.

[0028] At least one rotating shaft preferably has a forward section having a forward screw that exerts a force to send the sulfide solid electrolyte supplied from the supply port into the casing to the discharge port. In contrast, it is preferable to have a reverse section having a reverse screw that exerts a force to return the sulfide solid electrolyte from the discharge port to the supply port. When the reverse screw is provided, the sulfide solid electrolyte in the casing can be filled by returning the sulfide solid electrolyte near the discharge port of the kneader to the supply port side, and the retention of the sulfide solid electrolyte in the casing can also be suppressed. As a result, a modified sulfide solid electrolyte that is excellent in coatability and suitable for use in lithium ion batteries can be obtained more efficiently.

[0029] A method for producing a modified sulfide solid electrolyte according to a fourth aspect of the present embodiment includes the steps of: The raw material contains lithium sulfide and phosphorus sulfide. That is it. By employing a raw material content that includes such a solid electrolyte raw material, it becomes possible to more efficiently produce a modified sulfide solid electrolyte.

[0030] A method for producing a modified sulfide solid electrolyte according to a fifth aspect of the present embodiment includes the steps of: The raw material further contains a halogen atom. A sixth aspect of the present embodiment provides a method for producing a modified sulfide solid electrolyte in the fifth aspect, further comprising the steps of: The raw material contains at least one selected from lithium halide and a halogen element. That is it.

[0031] By including halogen atoms in the raw material ingredients, the resulting modified sulfide solid electrolyte will include halogen atoms. The sulfide solid electrolyte including halogen atoms has higher ionic conductivity than the sulfide solid electrolyte not including halogen atoms. Therefore, by including halogen atoms, it is possible to produce a modified sulfide solid electrolyte having higher ionic conductivity. Furthermore, as a solid electrolyte raw material containing halogen atoms, lithium halide is easy to handle.

[0032] A method for producing a modified sulfide solid electrolyte according to a seventh aspect of the present embodiment is the same as the fifth or sixth aspect, except that The halogen atom is at least one atom selected from a chlorine atom, a bromine atom, and an iodine atom. That is it. Among halogen atoms, chlorine atoms, bromine atoms and iodine atoms are effective in improving ionic conductivity.

[0033] The method for producing a modified sulfide solid electrolyte according to an eighth aspect of the present embodiment is the same as the first to seventh aspects, except that: The complexing agent is a compound containing a heteroatom. The method for producing a modified sulfide solid electrolyte according to a ninth aspect of the present embodiment is the same as the eighth aspect, except that: The heteroatom is at least one atom selected from a nitrogen atom and an oxygen atom. The method for producing a modified sulfide solid electrolyte according to a tenth aspect of the present embodiment is the same as the first to ninth aspects, except that: The compound is an aliphatic amine. That is it.

[0034] In addition, a method for producing a modified sulfide solid electrolyte according to an eleventh aspect of the present embodiment is the same as the tenth aspect, except that The complexing agent is a compound having at least two tertiary amino groups in the molecule. A method for producing a modified sulfide solid electrolyte according to a twelfth aspect of the present embodiment is the same as the eleventh aspect, except that The aliphatic amine is at least one selected from tetramethylethylenediamine and tetramethyldiaminopropane. That is it.

[0035] The complexing agent is a solvent that has the property of forming a complex with the solid electrolyte raw material contained in the raw material content as described above. As described later, the complexing agent is a compound having a heteroatom that is likely to form a complex with the solid electrolyte raw material, and is a preferred compound as the complexing agent. Among them, a compound containing a nitrogen atom or an oxygen atom as a heteroatom is not only more likely to form a complex, but also more likely to incorporate halogen atoms that are difficult to incorporate in the formation of a complex, making it easier to maintain the dispersion state of the solid electrolyte raw material uniform. Therefore, it is easier to obtain a higher ion conductivity.

[0036] The effect of using this complexing agent can be easily obtained by using an amine compound having a nitrogen atom as an amino group, particularly an aliphatic amine, particularly tetramethylethylenediamine and tetramethyldiaminopropane, as the compound containing a nitrogen atom as a heteroatom. The compound containing a nitrogen atom as a heteroatom also has the property of being easily separated and removed from the electrolyte precursor. Therefore, it becomes possible to more easily produce a sulfide solid electrolyte with high ionic conductivity.

[0037] A method for producing a sulfide solid electrolyte according to a thirteenth aspect of the present embodiment is the same as the first to twelfth aspects, except that The modified sulfide solid electrolyte has a thiolithium region II crystal structure; That is it.

[0038] In the manufacturing method of this embodiment, it is possible to manufacture a desired sulfide solid electrolyte by changing the type and compounding ratio of the solid electrolyte raw material contained in the raw material content. The sulfide solid electrolyte having the thiolicon region II type crystal structure is known as a sulfide solid electrolyte with extremely high ionic conductivity, and is preferable as the modified sulfide solid electrolyte to be obtained by the manufacturing method of this embodiment.

[0039] (solid electrolyte) In this specification, the term "solid electrolyte" refers to an electrolyte that maintains a solid state under a nitrogen atmosphere at 25° C. The solid electrolyte in this embodiment is a solid electrolyte that contains lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms and has ionic conductivity due to the lithium atoms.

[0040] The term "solid electrolyte" includes both amorphous solid electrolytes and crystalline solid electrolytes. In this specification, the crystalline solid electrolyte is a solid electrolyte in which a peak derived from the solid electrolyte is observed in the X-ray diffraction pattern in the X-ray diffraction measurement, and it does not matter whether or not there is a peak derived from the raw material of the solid electrolyte. That is, the crystalline solid electrolyte includes a crystal structure derived from the solid electrolyte, and a part of the crystal structure may be derived from the solid electrolyte, or the whole of the crystal structure may be derived from the solid electrolyte. And, as long as the crystalline solid electrolyte has the above-mentioned X-ray diffraction pattern, a part of the crystalline solid electrolyte may include an amorphous solid electrolyte. Therefore, the crystalline solid electrolyte includes so-called glass ceramics obtained by heating an amorphous solid electrolyte to a crystallization temperature or higher. In this specification, the term "amorphous solid electrolyte" refers to an amorphous solid electrolyte that has a halo pattern in which no peaks other than those derived from the material are substantially observed in an X-ray diffraction pattern obtained by X-ray diffraction measurement, regardless of whether or not there are peaks derived from the raw materials of the solid electrolyte.

[0041] [Method of manufacturing sulfide solid electrolyte] The method for producing the sulfide solid electrolyte of the present embodiment includes the steps of: Mixing a raw material containing lithium atoms, sulfur atoms, and phosphorus atoms with a complexing agent to obtain an electrolyte precursor; Heating the electrolyte precursor to obtain a sulfide solid electrolyte; and kneading the sulfide solid electrolyte using a kneader including a casing and at least one rotating shaft arranged to penetrate the casing in a longitudinal direction and having a paddle provided along an axial direction; A method for producing a modified sulfide solid electrolyte, comprising: It is.

[0042] [Obtaining the electrolyte precursor] The manufacturing method of this embodiment includes mixing a raw material content including lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms with a complexing agent to obtain an electrolyte precursor. In the manufacturing method of this embodiment, the ingredients will first be described.

[0043] (Raw material content) The raw material content used in this embodiment contains lithium atoms, sulfur atoms, and phosphorus atoms, and preferably also contains halogen atoms, and more specifically, is a compound containing one or more selected from the group consisting of these atoms (hereinafter, also referred to as "solid electrolyte raw material"). The raw material content used in this embodiment preferably contains two or more solid electrolyte raw materials.

[0044] Examples of solid electrolyte raw materials contained in the raw material content include 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), chloride Representative examples of the raw material include thiophosphoryl halides such as thiophosphoryl (PSCl3), 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), preferably bromine (Br2) and iodine (I2).

[0045] Examples of usable solid electrolyte raw materials other than those mentioned above include solid electrolyte raw materials containing at least one atom selected from the above four types of atoms and containing 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, SnS2), 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 (POCl3) and phosphorus oxybromide (POBr3).

[0046] Among the above, as the solid electrolyte raw material containing lithium atoms, sulfur atoms, and phosphorus atoms, phosphorus sulfides such as lithium sulfide, diphosphorus trisulfide (P2S3), diphosphorus pentasulfide (P2S5) are preferred, and among the phosphorus sulfides, diphosphorus pentasulfide is preferred. In addition, when oxygen atoms are introduced into the solid electrolyte, phosphate compounds such as lithium oxide, lithium hydroxide, and lithium phosphate are preferred.

[0047] In addition, the halogen atom is preferably a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, more preferably a chlorine atom, a bromine atom, or an iodine atom, and the solid electrolyte raw material may include those containing these halogen atoms. As the halogen atom, these halogen atoms may be used alone or in combination of multiple types, and it is preferable to use multiple types in combination. Preferred examples of solid electrolyte raw materials containing halogen atoms include simple halogens such as fluorine (F2), chlorine (Cl2), bromine (Br2), and iodine (I2), and lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide.

[0048] Preferred combinations of solid electrolyte raw materials include, for example, a combination of lithium sulfide, diphosphorus pentasulfide, and a lithium halide, and a combination of lithium sulfide, diphosphorus pentasulfide, and a halogen element. Preferred lithium halides include lithium enka, lithium bromide, and lithium iodide, and preferred halogen elements include chlorine, bromine, and iodine.

[0049] In this embodiment, Li3PS4 containing the PS4 structure can be used as a part of the raw material. Specifically, Li3PS4 is prepared in advance by manufacturing or the like, and used as the raw material. The content of Li3PS4 in the total of the raw materials is preferably 60 to 100 mol%, more preferably 65 to 90 mol%, and further preferably 70 to 80 mol%.

[0050] In addition, 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 %.

[0051] The lithium sulfide used in this embodiment is preferably in the form of particles. The average particle size of lithium sulfide particles (D 50 In this specification, the average particle size (D 50 ) is the particle size at which the particle size distribution cumulative curve is accumulated from the smallest particle size to 50% (volume basis) of the total, and the volume distribution is the average particle size that can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device. In addition, 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, that is, within the same range as the average particle size of the lithium sulfide particles.

[0052] When lithium sulfide, diphosphorus pentasulfide, and lithium halide are used as the solid electrolyte 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 solid electrolyte raw materials used as necessary are used, the content of lithium sulfide and diphosphorus pentasulfide relative to the total is preferably 50 to 100 mol%, more preferably 55 to 85 mol%, and even more preferably 60 to 80 mol%. Furthermore, when lithium bromide and lithium iodide are used in combination as the lithium halide, from the viewpoint of improving ion conductivity, the ratio of lithium bromide to the total of lithium bromide and lithium iodide is preferably 1 to 99 mol%, more preferably 20 to 80 mol%, even more preferably 30 to 70 mol%, and particularly preferably 40 to 60 mol%.

[0053] In the case where a halogen element is used as a solid electrolyte raw material, and lithium sulfide or diphosphorus pentasulfide is 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 ion 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%.

[0054] 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). 2≦2α+β≦100…(2) 4≦2α+β≦80 …(3) 6≦2α+β≦50 …(4) 6≦2α+β≦30 …(5)

[0055] 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, and 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.

[0056] Furthermore, when the two types of halogen elements are bromine and iodine, the molar number of bromine is B1 and the molar number of iodine is B2, then 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, even more preferably 30:70 to 75:25, and particularly preferably 35:65 to 75:25.

[0057] (Complexing Agent) As described above, the complexing agent is a compound that easily forms a complex with the solid electrolyte raw material contained in the raw material content, and is, for example, a compound that can form a complex with lithium sulfide and diphosphorus pentasulfide, which are preferably used as solid electrolyte raw materials, Li3PS4 obtained when these are used, and solid electrolyte raw materials containing halogen atoms (hereinafter, these are collectively referred to as "solid electrolyte raw materials, etc.").

[0058] The 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 nitrogen atom, an oxygen atom, a chlorine atom, or other heteroatom, and more preferably a compound having a group containing such a heteroatom, because such a heteroatom or group containing such a heteroatom can be coordinated (bonded) with lithium.

[0059] It is considered that the heteroatoms present in the molecules of the complexing agent have a high affinity with lithium atoms and have a property of easily forming a complex (hereinafter, also simply referred to as a "complex") by bonding with the solid electrolyte raw material, etc. Therefore, it is considered that a complex is formed by mixing the above-mentioned solid electrolyte raw material with the complexing agent, and the dispersion state of the solid electrolyte raw material, particularly the dispersion state of the halogen atoms, is easily maintained uniformly, and as a result, a sulfide solid electrolyte with high ionic conductivity is obtained.

[0060] Whether the complexing agent is capable of forming a complex with the solid electrolyte raw material or the like can be directly confirmed by an infrared absorption spectrum measured by, for example, FT-IR analysis (diffuse reflectance method). When the powder obtained by stirring tetramethylethylenediamine (hereinafter, simply referred to as “TMEDA”), which is one of the preferred complexing agents, and lithium iodide (LiI) and the complexing agent itself were analyzed by FT-IR analysis (diffuse reflectance method), the spectrum of TMEDA itself and the spectrum of the complexing agent itself, especially the spectrum of 1000 to 1250 cm -1 In addition, it is known that LiI-TMEDA complex is formed by stirring and mixing TMEDA and lithium iodide (for example, Aust. J. Chem., 1988, 41, 1925-34, especially Fig. 2, etc.), so it is reasonable to consider that LiI-TMEDA complex is formed.

[0061] In addition, for example, when the powder obtained by stirring the complexing agent (TMEDA) and Li3PS4 was analyzed by FT-IR analysis (diffuse reflectance method) in the same manner as above, the spectrum of TMEDA itself was different from that of the powder obtained by mixing the complexing agent (TMEDA) and Li3PS4 in the 1000-1250 cm -1 It can be seen that the peaks due to CN stretching vibrations in the spectrum are different, but that the spectrum is similar to that of the LiI-TMEDA complex. From this, it can be considered that the Li3PS4-TMEDA complex is formed. In the manufacturing method of the present embodiment, the raw material ingredients and the complexing agent are mixed to obtain a complex, which is used as an electrolyte precursor, and the complexing agent is removed from the electrolyte precursor powder by heating the electrolyte precursor powder, thereby producing a sulfide solid electrolyte.

[0062] The 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, the solid electrolyte raw material and the like can be bonded via at least two heteroatoms in the molecule.

[0063] Among the heteroatoms, oxygen atom and nitrogen atom are preferred, and it is more preferred that the heteroatom contains a nitrogen atom. The group containing a nitrogen atom is preferably an amino group, that is, the complexing agent is preferably an amine compound.

[0064] The amine compound is not particularly limited as long as it has an amino group in the molecule and 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, the solid electrolyte raw material and the like can be bonded via at least two nitrogen atoms in the molecule to form a complex.

[0065] Examples of such amine compounds include aliphatic amines, alicyclic amines, heterocyclic amines, and aromatic amines, and these can be used alone or in combination of two or more kinds.

[0066] More specifically, representative and preferred examples of the aliphatic amine include aliphatic primary diamines such as ethylenediamine, diaminopropane, and diaminobutane; aliphatic secondary diamines such as N,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 are included, such as isomers relating to the position of the amino group, such as 1,2-diaminobutane, 1,3-diaminobutane, and 1,4-diaminobutane, as well as linear and branched isomers for butane.

[0067] 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.

[0068] Representative and 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. Representative and 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.

[0069] Representative and 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 has preferably 6 or more, more preferably 7 or more, and even more preferably 8 or more, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less.

[0070] The amine compound used in the present 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.

[0071] Among the above, as the complexing agent containing a nitrogen atom, an aliphatic amine is preferable from the viewpoint of obtaining higher ionic conductivity. In addition, the amine compound is preferably a tertiary amine having a tertiary amino group as an amino group, more preferably a tertiary diamine having two tertiary amino groups, even more preferably a tertiary diamine having two tertiary amino groups at both ends, and even more preferably an aliphatic tertiary diamine having a tertiary amino group at both ends. In the above amine compound, the aliphatic tertiary diamine having a tertiary amino group at both ends is preferably tetramethylethylenediamine, tetraethylethylenediamine, tetramethyldiaminopropane, or tetraethyldiaminopropane, and considering the ease of availability, etc., tetramethylethylenediamine or tetramethyldiaminopropane is preferable.

[0072] In addition, a compound having a group other than an amino group, such as a nitro group or an amide group, that contains a nitrogen atom as a heteroatom can also provide the same effect.

[0073] In the production method of this embodiment, the complexing agent is preferably a compound containing an oxygen atom as a heteroatom in addition to the above-mentioned compound containing a nitrogen atom. The compound containing an oxygen atom is preferably a compound having one or more functional groups selected from an ether group and an ester group as a group containing an oxygen atom, and among these, a compound having an ether group is particularly preferred. That is, as a complexing agent containing an oxygen atom, an ether compound is particularly preferred.

[0074] Examples of the ether compound include ether compounds such as aliphatic ethers, alicyclic ethers, heterocyclic ethers, and aromatic ethers, and these can be used alone or in combination of two or more kinds.

[0075] 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, 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. 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.

[0076] 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.

[0077] 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, more preferably 8 or more, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less.

[0078] The ether compound used in the present 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.

[0079] Among the above ether compounds, from the viewpoint of obtaining higher ionic conductivity, aliphatic ethers are preferred, and dimethoxyethane and tetrahydrofuran are more preferred.

[0080] Examples of the ester compound include ester compounds such as aliphatic esters, alicyclic esters, heterocyclic esters, and aromatic esters, and these can be used alone or in combination of two or more kinds.

[0081] More specifically, examples of aliphatic esters include formic acid esters such as methyl formate, ethyl formate, triethyl formate, etc.; acetate esters such as methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, etc.; propionate esters such as methyl propionate, ethyl propionate, propyl propionate, butyl propionate, etc.; oxalate esters such as dimethyl oxalate, diethyl oxalate, etc.; malonate esters such as dimethyl malonate, diethyl malonate, etc.; and succinate esters such as dimethyl succinate, diethyl succinate, etc.

[0082] 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.

[0083] Examples of the alicyclic esters include methyl cyclohexanecarboxylate, ethyl cyclohexanecarboxylate, dimethyl cyclohexanedicarboxylate, dibutyl cyclohexanedicarboxylate, and dibutyl cyclohexenedicarboxylate. Examples of the heterocyclic esters include methyl pyridinecarboxylate, ethyl pyridinecarboxylate, propyl pyridinecarboxylate, methyl pyrimidinecarboxylate, ethyl pyrimidinecarboxylate, and lactones such as acetolactone, propiolactone, butyrolactone, and valerolactone.

[0084] The alicyclic ester and heterocyclic ester each preferably have 3 or more, more preferably 4 or more, and the upper limit thereof is preferably 16 or less, more preferably 14 or less.

[0085] 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.

[0086] The aromatic ester preferably has 8 or more, more preferably 9 or more, and the upper limit is preferably 16 or less, more preferably 14 or less, and even more preferably 12 or less.

[0087] The ester compound used in the present 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.

[0088] Among the above ester compounds, from the viewpoint of obtaining higher ionic conductivity, aliphatic esters are preferred, acetate esters are more preferred, and ethyl acetate is particularly preferred.

[0089] From the viewpoint of efficiently forming a complex, the molar ratio of the amount of complexing agent added to the total molar amount of lithium atoms contained in the raw material contents 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.

[0090] (mixture) In the manufacturing method of this embodiment, the above-mentioned solid electrolyte raw material and a complexing agent are mixed. In this embodiment, the solid electrolyte raw material and the complexing agent may be mixed in either a solid or liquid form, but since the solid electrolyte raw material contains a solid and the complexing agent is liquid, they are usually mixed in a form in which the solid electrolyte raw material is present in the liquid complexing agent. In addition, when mixing the raw material and the complexing agent, a solvent may be further mixed as necessary. Hereinafter, in the description of the mixing of the raw material and the complexing agent, unless otherwise specified, the complexing agent also includes the solvent used as necessary.

[0091] There is no particular limitation on the method for mixing the solid electrolyte raw material and the complexing agent, and the solid electrolyte raw material and the complexing agent may be mixed in a device capable of mixing the solid electrolyte raw material and the complexing agent. For example, it is preferable to supply the complexing agent into a tank, operate the stirring blade, and then gradually add the solid electrolyte raw material, since this provides a good mixed state of the solid electrolyte raw material and improves the dispersibility of the raw material. However, when a halogen element is used as the solid electrolyte raw material, the solid electrolyte raw material may not be solid, specifically, fluorine and chlorine are gaseous, and bromine is liquid, at room temperature and normal pressure. In such a case, for example, when the solid electrolyte raw material is liquid, it may be supplied into the tank together with a complexing agent separately from other solid solid electrolyte raw materials, and when the solid electrolyte raw material is gas, it may be supplied by blowing into the mixture of the solid solid electrolyte raw material and the complexing agent.

[0092] The manufacturing method of this embodiment is characterized by including mixing the solid electrolyte raw material and the complexing agent. That is, since it is sufficient to mix the solid electrolyte raw material and the complexing agent, and grinding is not required, the solid electrolyte raw material can be manufactured by a method that does not use equipment generally called a grinder, such as a media-type grinder such as a ball mill or a bead mill, which is used for the purpose of grinding the solid electrolyte raw material. In the manufacturing method of this embodiment, the solid electrolyte raw material and the complexing agent contained in the raw material content are mixed by simply mixing the solid electrolyte raw material and the complexing agent, and a complex, i.e., an electrolyte precursor, can be formed. In addition, in order to shorten the mixing time to obtain the complex or to pulverize it, the mixture of the raw material and the complexing agent may be ground by a grinder, but as already described, it is preferable not to use a grinder.

[0093] An example of an apparatus for mixing the solid electrolyte raw material and the complexing agent is a mechanical stirring mixer equipped with stirring blades in a tank. Examples of mechanical stirring mixers include high-speed stirring mixers and double-arm mixers, and the high-speed stirring mixer is preferably used from the viewpoint of increasing the uniformity of the solid electrolyte raw material in the mixture of the solid electrolyte raw material and the complexing agent and obtaining higher ion conductivity. Examples of the high-speed stirring mixer include a vertical shaft rotary mixer and a horizontal shaft rotary mixer, and either type of mixer may be used.

[0094] The shape of the impeller used in the mechanical stirring mixer includes anchor type, blade type, arm type, ribbon type, multi-stage blade type, double arm type, shovel type, double-shaft blade type, flat blade type, C-type blade type, etc., and from the viewpoint of improving the uniformity of the solid electrolyte raw material and obtaining a higher ion conductivity, the shovel type, flat blade type, C-type blade type, etc. are preferred. In addition, in the mechanical stirring mixer, it is preferable to install a circulation line that discharges the stirring target outside the mixer and then returns it to the inside of the mixer. This allows the raw material with a high specific gravity, such as lithium halide, to be stirred without settling or stagnating, making it possible to mix more uniformly.

[0095] The location of the circulation line is not particularly limited, but it is preferable to install it at a location where it can be discharged from the bottom of the mixer and returned to the top of the mixer. This makes it easier to uniformly mix the solid electrolyte raw material, which tends to settle, by carrying it on the convection caused by the circulation. Furthermore, it is preferable that the return port is located below the liquid surface of the object to be mixed. This can prevent the object to be mixed from splashing and adhering to the wall surface inside the mixer.

[0096] The temperature conditions when mixing the solid electrolyte raw material and the complexing agent are not particularly limited, and are, for example, −30 to 100° C., preferably −10 to 50° C., and more preferably about room temperature (23° C.) (for example, about room temperature ±5° C.) The mixing time is about 0.1 to 150 hours, and from the viewpoint of more uniform mixing and obtaining higher ionic conductivity, is preferably 1 to 120 hours, more preferably 4 to 100 hours, and even more preferably 8 to 80 hours.

[0097] In the process of obtaining an electrolyte precursor by mixing the raw material ingredients with a complexing agent, the raw material ingredients and the complexing agent may be mixed by adding the raw material ingredients in stages, or the complexing agent may be added in stages and mixed. For example, when a halogen element is used as the solid electrolyte raw material, it is preferable to mix the raw material ingredients stepwise, such as by premixing lithium sulfide and an elemental halogen, converting at least a part of the elemental halogen into lithium halide, and then adding diphosphorus pentasulfide and mixing. By doing so, it is possible to suppress side reactions, and it is expected that the reaction rate will not decrease and the ion conductivity will be improved. In this case, it is preferable to add the complexing agent when adding diphosphorus pentasulfide, from the same viewpoint as above.

[0098] By mixing the solid electrolyte raw material and the complexing agent, a complex is formed by the solid electrolyte raw material and the complexing agent. More specifically, the complex is considered to be formed by the action of the lithium atom, sulfur atom, phosphorus atom, or preferably used halogen atom contained in the solid electrolyte raw material and the complexing agent, and these atoms are directly bonded to each other with and / or without the intervention of the complexing agent. That is, in the production method of this embodiment, the complex obtained by mixing the solid electrolyte raw material and the complexing agent can be said to be composed of the complexing agent, lithium atom, sulfur atom, phosphorus atom, or preferably used halogen atom. The complex obtained in this embodiment is not completely dissolved in the complexing agent, which is a liquid, but is usually a solid, so that a suspension in which the complex is suspended in the complexing agent and a solvent used as necessary is obtained. Therefore, the method for producing a solid electrolyte in this embodiment corresponds to a heterogeneous system in a so-called liquid phase method.

[0099] (solvent) In this embodiment, when the solid electrolyte raw material and the complexing agent are mixed, a solvent may be further added. When a solid complex is formed in a liquid complexing agent, if the complex is easily dissolved in the complexing agent, separation of the components may occur. Therefore, by using a solvent in which the complex is not dissolved, the dissolution of the components in the electrolyte precursor can be suppressed. In addition, by mixing the solid electrolyte raw material and the complexing agent using a solvent, the complex formation is promoted, and each main component can be more evenly present, and an electrolyte precursor in which the dispersion state of the solid electrolyte raw material, especially the dispersion state of the halogen atoms, is uniformly maintained is obtained, so that the effect of obtaining high ion conductivity is easily achieved.

[0100] 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. In particular, halogen atoms are easily eluted from the complex, so that the desired complex can be obtained by adding a solvent to suppress the elution of halogen atoms. As a result, a sulfide solid electrolyte having high ionic conductivity can be easily obtained through an electrolyte precursor in which components such as solid electrolyte raw materials, particularly solid electrolyte raw materials containing halogen atoms, are uniformly dispersed.

[0101] Preferred examples of solvents having such properties include solvents 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) as described in various documents, such as "Chemical Handbook" (published in 2004, revised 5th edition, Maruzen Co., Ltd.). 3 ) 1 / 2 ) and is also called the Hildebrand parameter or SP value.

[0102]

number

[0103] By using a solvent with a solubility parameter of 10 or less, it is possible to make it difficult to dissolve the solid electrolyte raw material, especially halogen atoms, raw materials containing halogen atoms such as lithium halide, and further components containing halogen atoms constituting a complex (for example, an aggregate in which lithium halide and a complexing agent are bonded), etc., compared to the above complexing agent. Therefore, it is easy to fix the halogen atoms in particular in the complex, and the halogen atoms are present in a well-dispersed state in the obtained electrolyte precursor and further in the solid electrolyte, making it easy to obtain a solid electrolyte having high ionic conductivity. That is, it is preferable that the solvent used in this embodiment has a property in which the complex does not dissolve. From the same viewpoint, 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.

[0104] More specifically, the solvent used in the present embodiment can be a wide variety of solvents that have been conventionally used in the production of solid electrolytes. 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; and the like. Among these, a solvent having a solubility parameter within the above-mentioned range may be appropriately selected and used.

[0105] More specifically, aliphatic hydrocarbon solvents such as hexane (7.3), pentane (7.0), 2-ethylhexane, heptane (7.4), octane (7.5), decane, undecane, dodecane, tridecane, etc.; alicyclic hydrocarbon solvents such as cyclohexane (8.2) and methylcyclohexane, etc.; benzene, toluene (8.8), xylene (8.8), mesitylene, ethylbenzene (8.8), tert-butylbenzene, trifluoromethylbenzene, nitrobenzene, chlorobenzene (9.5), chlorotoluene (8.8), bromobenzene, etc. Examples of aromatic hydrocarbon solvents include: alcohol 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. The numbers in parentheses in the above examples are SP values. The above examples are merely examples, and for example, those having isomers may include all isomers. In addition, those substituted with halogen atoms, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents may also include those substituted with aliphatic groups such as alkyl groups.

[0106] Among these solvents, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, aromatic hydrocarbon solvents, and ether-based solvents are preferred, and from the viewpoint of obtaining a more stable and high ion 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 the 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.

[0107] [Obtaining a sulfide solid electrolyte by heating] The manufacturing method of this embodiment includes obtaining the above-mentioned electrolyte precursor, and then heating the electrolyte precursor to obtain a sulfide solid electrolyte. The electrolyte precursor is a precursor of a sulfide solid electrolyte, and can become a sulfide solid electrolyte by removing a complexing agent. The complexing agent is removed by heating the electrolyte precursor. In the manufacturing method of the present embodiment, the heating temperature can be adjusted during heating to allow crystallization, and the sulfide solid electrolyte can be made into a crystalline sulfide solid electrolyte.

[0108] As described above, there are two types of heating: heating for removing the complexing agent from the electrolyte precursor, and heating for crystallization. The manufacturing method of the present embodiment must include heating for removing the complexing agent from the electrolyte precursor, because a sulfide solid electrolyte is not obtained. On the other hand, heating for crystallization is a type of heating that may be performed when a crystalline sulfide solid electrolyte is desired.

[0109] When both of these heating processes are performed, they may be performed separately or simultaneously. In order to more stably produce a modified sulfide solid electrolyte that is excellent in coatability and suitable for use in lithium ion batteries, it is preferable to heat them separately. Here, performing the heating simultaneously means performing heating for crystallization. This is because the heating temperature for crystallization is higher than the heating temperature for removing the complexing agent, and therefore the complexing agent is also removed at the same time by heating at the heating temperature for crystallization. First, the heating for removing the complexing agent will be described.

[0110] (Heating to remove complexing agent) In the manufacturing method of the present embodiment, the heating of the electrolyte precursor requires at least heating for removing the complexing agent. By removing the complexing agent from the electrolyte precursor, a sulfide solid electrolyte is obtained.

[0111] The heating temperature for removing the complexing agent is not particularly limited as long as the complexing agent can be removed, and may be a temperature at which an amorphous sulfide solid electrolyte is obtained. The temperature at which an amorphous sulfide solid electrolyte is obtained may be determined according to the structure of the crystalline sulfide solid electrolyte obtained by heating the amorphous sulfide solid electrolyte (or electrolyte precursor). Specifically, the amorphous sulfide solid electrolyte (or electrolyte precursor) is subjected to differential thermal analysis (DTA) at a temperature rise rate of 10 ° C. / min using a differential thermal analyzer (DTA device), and the temperature is preferably set to 5 ° C. or less, more preferably 10 ° C. or less, and even more preferably 20 ° C. or less, starting from the temperature of the top of the exothermic peak observed on the lowest temperature side. The lower limit is not particularly limited as long as it is equal to or higher than the boiling point of the complexing agent, and may be set to about −40 ° C. or more, which is the temperature of the top of the exothermic peak observed on the lowest temperature side. By setting the temperature range, the complexing agent is more efficiently and reliably removed from the electrolyte precursor, and an amorphous sulfide solid electrolyte is obtained.

[0112] The heating temperature for removing the complexing agent cannot be generally defined because it varies depending on the structure of the crystalline sulfide solid electrolyte to be obtained. However, it is usually preferably 135°C or lower, more preferably 130°C or lower, and even more preferably 125°C or lower. There is no particular restriction on the lower limit as long as it is equal to or higher than the boiling point of the complexing agent, and it is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 110°C or higher.

[0113] The heating for removing the complexing agent can be carried out at normal pressure, but can also be carried out under a reduced pressure atmosphere or even under a vacuum atmosphere in order to reduce the heating temperature. Regarding the pressure conditions, when heating is performed under a reduced pressure atmosphere, the pressure is preferably 85 kPa or less, more preferably 80 kPa or less, and even more preferably 70 kPa or less, and the lower limit may be a vacuum (0 kPa), and considering ease of pressure adjustment, the pressure is preferably 1 kPa or more, more preferably 2 kPa or more, and even more preferably 3 kPa or more. When the pressure conditions are within the above range, the heating conditions can be made mild, and the size of the apparatus can be suppressed.

[0114] The heating time for removing the complexing agent is not particularly limited as long as the complexing agent can be removed, but is 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.

[0115] Moreover, the heating for removing the complexing agent is preferably carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere or an argon atmosphere), because this can prevent deterioration of the sulfide solid electrolyte (e.g., deterioration due to oxidation).

[0116] The heating method for removing the complexing agent is not particularly limited, and examples thereof include a method using a hot plate, a vacuum heating device, an argon gas atmosphere furnace, a calcination furnace, etc. Also, for industrial purposes, a horizontal dryer having a heating means and a feeding mechanism, a horizontal vibration fluidized dryer, etc. may be used, and may be selected according to the amount of processing to be heated. In addition to the above-mentioned devices, it is also possible to use other types of dryers, such as an airflow dryer, a medium flow dryer equipped with a mechanism for flowing a medium such as media particles by gas, a spray dryer, etc. If such a dryer with airflow is used, a sulfide solid electrolyte having a small average particle size can be efficiently obtained.

[0117] By the above heating, the complexing agent can be removed from the electrolyte precursor, and the electrolyte precursor becomes an amorphous sulfide solid electrolyte, but not all of the complexing agent is removed from the electrolyte precursor, and as a result, the complexing agent may remain in the amorphous sulfide solid electrolyte. In this case, the content of the complexing agent contained in the sulfide solid electrolyte is preferably 0 mass%, that is, no complexing agent is contained at all, but from the viewpoint of efficiently obtaining a sulfide solid electrolyte with high ion conductivity, the content is usually 50 mass% or less, further 45 mass% or less, 40 mass% or less, 35 mass% or less, or 25 mass% or less, and the lower limit is about 0.1 mass% or more.

[0118] In addition, similarly to the complexing agent, when a solvent is used, the solvent may remain. In this case, the content of the solvent is also in the same range as the content of the complexing agent. In this specification, the contents of the complexing agent and the solvent used as necessary contained in the sulfide solid electrolyte were measured by dissolving the powder obtained in the examples etc. in a mixed liquid of water and pentanol, using a gas chromatography (GC) device, and the contents of the complexing agent and the high boiling point solvent were quantified using an absolute calibration curve (GC calibration curve method).

[0119] (Heating for crystallization) In the manufacturing method of the present embodiment, heating for crystallization may be performed as desired following the heating for removing the complexing agent. An amorphous sulfide solid electrolyte is obtained by the heating for removing the complexing agent. By heating this for crystallization, a crystalline sulfide solid electrolyte can be obtained.

[0120] In addition, the complexing agent and the solvent used as necessary may remain in the amorphous sulfide solid electrolyte obtained by heating for removing the complexing agent. Furthermore, by performing heating for crystallization, the content of the complexing agent and the solvent remaining in the amorphous sulfide solid electrolyte is reduced, so that the quality of the sulfide solid electrolyte is improved and high ionic conductivity is easily obtained. In addition, even if the heating for removing the complexing agent is performed, the electrolyte precursor may remain without becoming an amorphous sulfide solid electrolyte. In this case, the complexing agent can be removed from the electrolyte precursor by heating for crystallization, and a crystalline sulfide solid electrolyte is obtained via the amorphous sulfide solid electrolyte.

[0121] The heating temperature for the crystallization is not particularly limited as long as it is a temperature higher than the heating temperature for removing the complexing agent described above. For example, the heating temperature may be determined depending on the structure of the crystalline sulfide solid electrolyte obtained by heating the amorphous sulfide solid electrolyte obtained by removing the complexing agent from the electrolyte precursor. Heating for crystallization may be performed successively after heating for the complexing agent, or heating for the complexing agent may be performed and then heating for crystallization may be performed separately. In the case of successive heating, for example, heating for the complexing agent may be performed, and then the heating temperature may be increased to the heating temperature required for heating for crystallization.

[0122] More specifically, the heating temperature for crystallization is preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 20°C or higher, starting from the temperature of the peak top of the exothermic peak observed on the lowest temperature side, obtained by removing the complexing agent from the electrolyte precursor using a differential thermal analyzer (DTA device) at a temperature rise of 10°C / min. The upper limit is not particularly limited, but it may be about 40°C or lower. By setting the temperature range as above, not only can a crystalline sulfide solid electrolyte be obtained more efficiently and reliably, but the content of the complexing agent remaining in the sulfide solid electrolyte and the solvent used as necessary can be reduced, and the purity of the sulfide solid electrolyte can be improved by reducing the content of the electrolyte precursor.

[0123] The heating temperature for crystallization cannot be generally defined because it varies depending on the structure of the crystalline sulfide solid electrolyte to be obtained. Generally, however, it is preferably 130°C or higher, more preferably 140°C or higher, and even more preferably 150°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.

[0124] The heating time, pressure conditions, carrying out the heating under an inert gas atmosphere, and heating method for the crystallization can be the same as those described for the heating for removing the complexing agent.

[0125] (Drying) The manufacturing method of the present embodiment may include drying the electrolyte precursor after obtaining the electrolyte precursor in the heating. The electrolyte precursor obtained by obtaining the electrolyte precursor may become a fluid (usually in a slurry state) containing a complexing agent that does not contribute to the formation of the electrolyte precursor and a solvent used as needed. In this case, the remaining complexing agent and the solvent used as needed can be removed by drying before heating. Drying is preferably performed before heating for removing the complexing agent. By drying in advance, the complexing agent can be removed from the electrolyte precursor more quickly, so that the content of the complexing agent in the obtained sulfide solid electrolyte can be further reduced, and the ion conductivity can be improved.

[0126] Examples of the drying method include filtration using a glass filter or the like, solid-liquid separation by decantation, and solid-liquid separation using a centrifuge, etc. Specifically, solid-liquid separation can be easily performed by decantation, in which a fluid (usually in a slurry state) containing the electrolyte precursor, the remaining complexing agent, and the solvent used as needed is transferred to a container, and after the solid has precipitated, the complexing agent and the solvent used as needed are removed as a supernatant, or by filtration using a glass filter having a pore size of about 10 to 200 μm, preferably 20 to 150 μm.

[0127] Also, drying can be performed by heating using a dryer or the like. The electrolyte precursor-containing material may be dried under any pressure condition, such as under pressure, normal pressure, or reduced pressure, and is preferably dried under normal pressure or reduced pressure. In particular, when drying at a lower temperature is considered, it is preferable to dry under reduced pressure, or even under vacuum, using a vacuum pump or the like. The temperature conditions for drying may be a temperature equal to or higher than the boiling point of the remaining complexing agent or the solvent used as necessary. Since the temperature conditions may vary depending on the type of complexing agent and solvent used, the specific temperature conditions cannot be generally stated, but the temperature is preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 15°C or higher, and the upper limit is preferably 110°C or lower, more preferably 85°C or lower, and even more preferably 70°C or lower.

[0128] As for the pressure conditions, as described above, normal pressure or reduced pressure is preferable. In the case of reduced pressure, specifically, the pressure is preferably 85 kPa or less, more preferably 80 kPa or less, and even more preferably 70 kPa or less. The lower limit may be a vacuum (0 Kpa). Considering the ease of adjusting the pressure, the pressure is preferably 1 kPa or more, more preferably 2 kPa or more, and even more preferably 3 kPa or more.

[0129] In the production method of this embodiment, when drying is performed, drying may be performed while heating after the solid-liquid separation. In the manufacturing method of this embodiment, drying may or may not be performed. That is, in the manufacturing method of this embodiment, the object to be heated may be a fluid (in a slurry state) containing the electrolyte precursor, the remaining complexing agent, and the solvent used as needed, or may be an electrolyte precursor (in a powder state) obtained by removing the remaining complexing agent and the solvent used as needed from the fluid by drying.

[0130] (Amorphous sulfide solid electrolyte) The sulfide solid electrolyte obtained by the above heating can be either an amorphous sulfide solid electrolyte or a crystalline sulfide solid electrolyte, as desired. That is, if heating for crystallization is not performed, an amorphous sulfide solid electrolyte is obtained, and if heating for crystallization is performed, a crystalline sulfide solid electrolyte is obtained.

[0131] The amorphous sulfide solid electrolyte obtained by the above heating contains lithium atoms, sulfur atoms, and phosphorus atoms, and preferably halogen atoms. Representative examples include solid electrolytes composed of lithium sulfide and phosphorus sulfide, lithium sulfide, phosphorus sulfide, and lithium halide, such as Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-LiCl-LiBr, and Li2S-P2S5-LiI-LiBr; and solid electrolytes further containing other atoms such as oxygen atoms and silicon atoms, such as Li2S-P2S5-Li2O-LiI and Li2S-SiS2-P2S5-LiI. From the viewpoint of obtaining higher ionic conductivity, a solid electrolyte composed of lithium sulfide, phosphorus sulfide, and lithium halide, such as Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, or Li2S-P2S5-LiI-LiBr, is preferred. The types of atoms constituting the amorphous sulfide solid electrolyte can be confirmed, for example, by an ICP emission spectroscopic analyzer.

[0132] When the amorphous sulfide solid electrolyte obtained by the heating 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.

[0133] When the amorphous sulfide solid electrolyte obtained by the heating 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%, more preferably 40 to 80 mol%, and particularly preferably 50 to 70 mol%.

[0134] In the amorphous sulfide solid electrolyte obtained by the heating, 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 further 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 thiolithiregion II type crystal structure described below and having higher ion conductivity.

[0135] The shape of the amorphous sulfide solid electrolyte is not particularly limited, but may be, for example, a particulate shape. The average particle size (D 50 ) is, for example, 0.01 μm or more, further 0.03 μm or more, 0.05 μm or more, or 0.1 μm or more, and the upper limit is 5 μm or less, further 3.0 μm or less, 1.5 μm or less, 1.0 μm or less, or 0.5 μm or less.

[0136] (Crystalline sulfide solid electrolyte) The crystalline sulfide solid electrolyte obtained by the above heating may be a so-called glass ceramic obtained by heating an amorphous sulfide solid electrolyte to a crystallization temperature or higher. The crystal structure of the glass ceramic may be Li3PS4 crystal structure, Li4P2S6 crystal structure, Li7PS6 crystal structure, Li7P3S 11Examples of such structures include a crystal structure having peaks at 2θ=approximately 20.2° and 23.6° (for example, JP 2013-16423 A).

[0137] Li 4-x Ge 1-x P x S4 thio-LISICON Region II crystal structure (Kanno et al., Journal of The Electrochemical Society, 148(7)A742-746(2001)), Li 4-x Ge 1-x P x Examples of the crystal structure include a crystal structure similar to the S4-based thio-LISICON Region II type (see Solid State Ionics, 177 (2006), 2721-2725). The crystal structure of the crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment is preferably the thio-LISICON Region II type crystal structure among the above, since it has a higher ionic conductivity. Here, the "thio-LISICON Region II type crystal structure" refers to a Li 4-x Ge 1-x P x S4 thio-LISICON Region II crystal structure, Li 4-x Ge 1-x P x This indicates that the crystal structure is similar to that of the S4 thio-LISICON Region II type.

[0138] The crystalline sulfide solid electrolyte obtained by the heating may contain the thio-licon region II type crystal structure or may contain it as the main crystal, but from the viewpoint of obtaining higher ionic conductivity, it is preferable that it contains it as the main crystal. In this specification, "containing it as the main crystal" means that the ratio of the target crystal structure among the crystal structures is 80% or more, preferably 90% or more, and more preferably 95% or more. In addition, from the viewpoint of obtaining higher ionic conductivity, it is preferable that the crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment does not contain crystalline Li3PS4 (β-Li3PS4).

[0139] 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°, the diffraction peaks of the Li7PS6 crystal structure appear, for example, at 2θ = 15.3°, 25.2°, 29.6°, and 31.0°, and the diffraction peaks of the Li7P3S 11 Diffraction peaks of the crystal structure appear, for example, at 2θ = 17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°. 4-x Ge 1-x P x The diffraction peaks of the S4 thio-LISICON Region II crystal structure appear, for example, at 2θ = 20.1°, 23.9°, and 29.5°, and Li 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°.

[0140] Also preferred is a crystalline sulfide solid electrolyte having the above-described Li7PS6 structural skeleton and an alluaudite-type crystal structure in which part of P is replaced by Si. Examples of the composition formula of the alluaudite-type crystal structure include the composition formula Li 7-x P 1-y Si y S6 and Li 7+x P 1-y Si y S6 (where x is -0.6 to 0.6 and y is 0.1 to 0.6). The alluaudite-type crystal structure represented by this composition formula is cubic or orthorhombic, preferably cubic, and in X-ray diffraction measurement using CuKα rays, it mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°.

[0141] Examples of the composition formula of the alluaudite-type crystal structure include the composition formula Li 7-x-2y PS 6-x-y Cl x (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5). The alluaudite-type crystal structure represented by this composition formula is preferably cubic, and in X-ray diffraction measurement using CuKα rays, it mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. In addition, examples of the composition formula of the alluaudite-type crystal structure include the 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 alluaudite-type crystal structure represented by this composition formula is preferably cubic, and in X-ray diffraction measurement using CuKα rays, it mainly has peaks appearing at positions of 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Note that the peak positions may shift within a range of ±0.5°.

[0142] The content of the complexing agent contained in the crystalline sulfide solid electrolyte obtained by the heating is less than the content of the complexing agent contained in the amorphous sulfide solid electrolyte. The content of the complexing agent in the crystalline sulfide solid electrolyte is preferably 0% by mass, i.e., no complexing agent is contained at all. From the viewpoint of efficiently obtaining a sulfide solid electrolyte with high ionic conductivity, however, the content is usually 10% by mass or less, further 8% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less, with the lower limit being approximately 0.01% by mass or more.

[0143] In addition, similarly to the complexing agent, when a solvent is used, the solvent may remain. In this case, the content of the solvent is also in the same range as the content of the complexing agent.

[0144] The shape of the crystalline sulfide solid electrolyte is not particularly limited, but may be, for example, a particulate shape. The average particle size (D 50 ) is, for example, 0.01 μm or more, further 0.03 μm or more, 0.05 μm or more, or 0.1 μm or more, and the upper limit is 15 μm or less, further 12 μm or less, or 10 μm or less.

[0145] The specific surface area of ​​the crystalline sulfide solid electrolyte obtained by the above heating is usually 10 m 2 / g or more, even 15m 2 / g or more, 20m 2 / g or more, 25m 2 / g or more, 30m 2 / g or more. There is no particular upper limit. For example, 50m 2 In this specification, the specific surface area is Based on the "Method of measurement of specific surface area of ​​fine ceramic powder by gas adsorption BET method" specified in JIS R1626:1996, this value is measured by a multipoint method using a flow method device as the measuring device. Either nitrogen (nitrogen method) or krypton (krypton method) may be used as the adsorbate, and the method is selected appropriately depending on the size of the specific surface area.

[0146] [Kneading] The manufacturing method of this embodiment includes obtaining the sulfide solid electrolyte, and then kneading the obtained sulfide solid electrolyte using a kneader including a casing and at least one rotating shaft arranged to penetrate the casing in the longitudinal direction and having a paddle provided along the axial direction. By kneading using a kneader, the specific surface area of ​​the sulfide solid electrolyte can be reduced while suppressing power consumption, and therefore a modified sulfide solid electrolyte that is excellent in coatability and suitable for use in lithium ion batteries can be efficiently obtained.

[0147] (Kneading machine) The kneader used in the manufacturing method of this embodiment includes a casing and at least one rotating shaft arranged to penetrate the casing in the longitudinal direction and having a paddle provided along the axial direction. As the kneader, either a single-shaft kneader having at least one rotating shaft or a multi-shaft kneader having two or more rotating shafts may be used, and from the viewpoint of more efficiently providing a modified sulfide solid electrolyte, a multi-shaft kneader is preferred.

[0148] Fig. 1 shows a plan view of a typical multi-shaft kneader used in the manufacturing method of this embodiment, broken at the center of the rotating shaft. Fig. 2 shows a plan view of a portion of the rotating shaft where the paddles are provided, broken perpendicularly to the rotating shaft. The kneader will be described below with reference to Figs. 1 and 2.

[0149] 1 is a twin-shaft kneader including a casing 1 with a supply port 2 at one end and a discharge port 3 at the other end, and two rotating shafts 4a and 4b that penetrate the casing 1 in the longitudinal direction. Paddles 5a and 5b are provided on the rotating shafts 4a and 4b, respectively. The sulfide solid electrolyte enters the casing 1 from the supply port 2, and shear stress is applied by the paddles 5a and 5b, resulting in a modified sulfide solid electrolyte with a small specific surface area and excellent coating suitability being discharged from the discharge port 3.

[0150] There are no particular limitations on the number of rotating shafts 4 (4a, 4b) as long as there are two or more, and in consideration of versatility, it is preferable that there are two to four, and more preferably two. The rotating shafts 4 may be parallel shafts that are parallel to each other or may be oblique, and the rotating directions of the rotating shafts may be the same or different. The different rotating directions may be selected when it is desired to reduce the specific surface area by the effect of kneading, and the same rotating direction may be selected when it is desired to prioritize the self-cleaning effect of sweeping out the sulfide solid electrolyte inside the casing and suppressing its retention inside the casing.

[0151] The paddles 5 (5a, 5b) are provided on the rotating shaft to knead the sulfide solid electrolyte, and are also called "forward screws" or "screw blades" because they exert a sending force that sends the sulfide solid electrolyte supplied from the supply port to the discharge port. The part of the rotating shaft where the paddles 5 are provided is called the forward section, and the sulfide solid electrolyte moves from the supply port toward the discharge port while being kneaded. The cross-sectional shape of the paddle 5 is not particularly limited, and examples thereof include a substantially triangular shape in which each side of an equilateral triangle has a uniform convex arc shape as shown in FIG. 2, a circular shape, an elliptical shape, a substantially rectangular shape, and the like. It may also be a shape based on these shapes and having a cutout portion in part.

[0152] When multiple paddles are provided, each paddle may be provided at a different angle to the rotation shaft as shown in Figure 2. In addition, the paddles may be of either intermeshing or non-intermeshing type, and when it is desired to reduce the specific surface area by the effect of kneading, the intermeshing type should be selected.

[0153] The multi-shaft kneader may be provided with screws 6 (6a, 6b) on the supply port 2 side as shown in FIG. 1 in order to smoothly supply the sulfide solid electrolyte into the kneader, and may be provided with reverse screws 7 (7a, 7b) on the discharge port 3 side as shown in FIG. 1 in order to prevent the modified sulfide solid electrolyte obtained through kneading with the paddles 5 from remaining in the casing.

[0154] As described above, the reverse screw not only suppresses retention in the casing, but also exerts a force to return the sulfide solid electrolyte near the discharge port of the kneader to the supply port side. By having a reverse section where the reverse screw 7 is provided, in contrast to the forward section where the paddle 5 is provided, the sulfide solid electrolyte moving toward the discharge port by the forward section and the sulfide solid electrolyte and modified sulfide solid electrolyte near the discharge port moving toward the supply port by the reverse section collide with each other and fill the casing. Therefore, the specific surface area is more efficiently reduced, and a modified sulfide solid electrolyte that is excellent in coatability and suitable for use in lithium ion batteries is obtained.

[0155] The amount (kg) of the sulfide solid electrolyte fed to the kneader per hour relative to the capacity (L) of the kneader casing is preferably 0.1 kg or more, more preferably 0.5 kg or more, even more preferably 1.0 kg or more, and even more preferably 3.0 kg or more, with the upper limit being preferably 10.0 kg or less, more preferably 9.0 kg or less, even more preferably 8.0 kg or less, and even more preferably 7.5 kg or less. Within the above ranges, a modified sulfide solid electrolyte that is excellent in coatability and suitable for use in lithium ion batteries can be obtained more reliably and efficiently.

[0156] (Properties of modified sulfide solid electrolyte) The shape of the modified sulfide solid electrolyte thus obtained is not particularly limited, but may be, for example, in the form of particles. The average particle size (D 50 ) is, for example, 0.01 μm or more, further 0.03 μm or more, 0.05 μm or more, or 0.1 μm or more, and the upper limit is 7.0 μm or less, further 5.0 μm or less, 4.0 μm or less, 3.0 μm or less, 2.5 μm or less, or 2.0 μm or less.

[0157] In addition, the specific surface area of ​​the modified sulfide solid electrolyte is smaller than that of the crystalline sulfide solid electrolyte, and is usually 25 m 2 / g or less, even 20m 2 / g or less, 15m 2 / g or less, 10m 2 / g or less, 5m 2 / g or less. There is no particular lower limit. For example, 2 / g or more.

[0158] The composition of the modified sulfide solid electrolyte obtained by the manufacturing method of this embodiment when it is an amorphous sulfide solid electrolyte, and the composition and crystal structure when it is a crystalline sulfide solid electrolyte are the same as those of the sulfide solid electrolyte obtained by the heating described above.

[0159] (Application) The modified sulfide solid electrolyte obtained by the manufacturing method of the present embodiment has excellent suitability for application as a paste, high ionic conductivity, and excellent battery performance, and is therefore suitable for use in lithium ion batteries. The modified sulfide solid electrolyte obtained by the manufacturing method of the present embodiment may be used in the positive electrode layer, the negative electrode layer, or the electrolyte layer. Each layer may be manufactured by a known method.

[0160] In addition, the battery preferably uses a current collector in addition to the positive electrode layer, electrolyte layer, and negative electrode layer, and a known current collector can be used. For example, a layer of a material that reacts with the solid electrolyte, such as Au, Pt, Al, Ti, or Cu, coated with Au or the like can be used. EXAMPLES

[0161] 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.

[0162] (Measurement of specific surface area) Based on the "Method of measuring the specific surface area of ​​fine ceramic powder by the gas adsorption BET method" specified in JIS R1626:1996, the specific surface area was measured by the multipoint method using a flow method device as the measuring device and nitrogen gas (purity: 99.9% or more) as the adsorbate.

[0163] (Measurement of average particle size) Measurements were made using a laser diffraction / scattering particle size distribution analyzer (Partica LA-950 (model number), manufactured by Horiba, Ltd.). Specifically, a mixture of dehydrated toluene (manufactured by Wako Pure Chemical Industries, special grade) and tertiary butyl alcohol (manufactured by Wako Pure Chemical Industries, special grade) in a mass 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 device and circulated, after which the powder to be measured was added and ultrasonicated, after which the particle size distribution was measured. In addition, the average particle size (D 50 ) was determined as the particle size that reached 50% (volume basis) of the total when the integral curve of the particle size distribution was drawn, starting from the smallest particle.

[0164] (Powder XRD diffraction measurement) Powder X-ray diffraction (XRD) measurements were carried out as follows. The sulfide solid electrolyte powder obtained in the examples and comparative examples was filled into a groove with a diameter of 20 mm and a depth of 0.2 mm, and smoothed with glass to prepare a sample. This sample was sealed with Kapton film for XRD and measured under the following conditions without exposing it to air. Measurement equipment: D2 PHASER, manufactured by Bruker Corporation Tube voltage: 30kV Tube current: 10mA X-ray wavelength: Cu-Kα ray (1.5418Å) Optical system: Concentration method Slit configuration: Solar slit 4°, divergence slit 1mm, Kβ filter (Ni plate) Detector: Semiconductor detector Measurement range: 2θ=10-60deg Step width, scan speed: 0.05deg, 0.05deg / sec

[0165] (Preparation example: Preparation of sulfide solid electrolyte) The sulfide solid electrolytes used in the examples and comparative examples were prepared by the following method, in which the amounts of the solid electrolyte raw materials, complexing agent, etc. used were adjusted to the amounts required for each example and comparative example while maintaining the same ratios of the amounts used as described in the following methods.

[0166] In a Schlenk flask (volume: 500 mL) containing a stirrer, 15.87 g of lithium sulfide (Li2S) was introduced under a nitrogen atmosphere. After rotating the stirrer, 300 mL of cyclohexane was added, followed by 6.26 g of iodine (I2), and the mixture was stirred at room temperature for 2 hours. Then, 3.94 g of bromine (Br2) was added, and the mixture was stirred at room temperature for 12 hours, and then the mixture was stirred at 50°C for another 3 hours. The obtained slurry was left to stand to allow the solids to settle, and 190 mL of the supernatant was removed, and decantation was performed three times to add 190 mL of cyclohexane, to obtain a cyclohexane slurry containing lithium sulfide, lithium iodide, and lithium bromide. To the obtained cyclohexane slurry, 21.93 g of phosphorus pentasulfide (P2S5) and 100 mL of cyclohexane were added, and the mixture was transferred to a separable flask (volume: 500 mL) equipped with a rotor blade and a circulation line. To this, 103 mL of tetramethylethylenediamine (TMEDA) was added as a complexing agent, and mixing by circulation stirring was started at room temperature with the rotor blade rotation speed: 200 rpm and pump flow rate: 550 mL / min. After 48 hours, 61 mL of dimethoxyethane (DME) was added, and circulation stirring was continued for another 24 hours. The obtained slurry was dried under reduced pressure at room temperature to obtain a powdered electrolyte precursor. The obtained electrolyte precursor was heated at a heating temperature of 110°C under reduced pressure for 2 hours to remove the complexing agent, and an amorphous sulfide solid electrolyte was obtained. The obtained amorphous sulfide solid electrolyte was further heated at a heating temperature of 160°C under reduced pressure for 2 hours to obtain a crystalline sulfide solid electrolyte.

[0167] The obtained crystalline sulfide solid electrolyte was subjected to powder XRD diffraction measurement, and crystallization peaks were detected at 2θ = 20.2° and 23.6°, confirming that the electrolyte had a thiolicon region II type crystal structure that exhibited high ionic conductivity. In addition, the specific surface area of ​​the obtained crystalline sulfide solid electrolyte was measured and found to be 33 m 2 / g.

[0168] Comparative Example 1 In a reaction vessel equipped with an impeller, 90 parts by mass of the crystalline sulfide solid electrolyte produced in the above production example, 657 parts by mass of toluene, and 0.9 parts by mass of dibutyl ether were put in, and the impeller was rotated to start stirring. 456 g of zirconia balls (diameter: 0.5 mmφ) (bead filling rate in the grinding chamber: 80%) were charged in a bead mill ("Labostar Mini LMZ015 (trade name)" manufactured by Ashizawa Finetech Co., Ltd.) that was connected to the reaction vessel and capable of circulating operation, and grinding was performed for 10 minutes while circulating between the reaction vessel and the grinding chamber under the conditions of pump flow rate: 550 mL / min, peripheral speed: 8 m / s, and mill jacket temperature: 20 °C. The slurry obtained by pulverization was dried under reduced pressure at room temperature. The specific surface area of ​​the obtained powder was measured and found to be 26 m 2 / g. The average particle size (D 50 ) was measured and found to be 0.2 μm. These results are shown in Table 1.

[0169] (Comparative Examples 2 to 4) In Comparative Example 1, the grinding time was changed to 20 minutes, 30 minutes, and 60 minutes to obtain slurries. The specific surface area of ​​the obtained slurries was measured and found to be 16 m 2 / g, 9m 2 / g and 7m 2 / g. The average particle size (D 50 The results are shown in Table 1.

[0170] Example 1 A commercially available small continuous twin-screw kneader was placed in a glove box filled with nitrogen. Five parts by mass of the crystalline sulfide solid electrolyte produced in the above manufacturing example was supplied from the supply port of the twin-screw kneader, and after 13 minutes, kneaded material A was discharged from the discharge port (5 parts by mass of the crystalline sulfide solid electrolyte were supplied from the supply port over 13 minutes). 3.6 parts by mass of the discharged kneaded material A was again supplied from the supply port of the twin-screw kneader, and after 13 minutes, kneaded material B was discharged from the discharge port (3.6 parts by mass of the crystalline sulfide solid electrolyte were supplied from the supply port over 13 minutes). Next, 3 parts by mass of the discharged kneaded material B was again supplied from the supply port of the twin-screw kneader, and after 14 minutes, kneaded material C was discharged from the discharge port (3 parts by mass of the crystalline sulfide solid electrolyte were supplied from the supply port over 14 minutes). The specific surface area of ​​these kneaded materials A to C was measured, and each was found to be 20 m 2 / g, 9m 2 / g and 5m 2 / g. Furthermore, when the average particle sizes of the kneaded materials A to C were measured, they were 1.9 μm, 3.6 μm and 5.0 μm, respectively. These results are shown in Table 1. In addition, when obtaining the kneaded material A, the amount of the sulfide solid electrolyte supplied per hour to the kneader (kg) relative to the capacity (L) of the kneader casing was 6.5 kg.

[0171] (About cumulative power) In the above Comparative Examples 1 to 4, a graph was created with the cumulative power required for pulverization (kWh / kg) on ​​the horizontal axis and the specific surface area on the vertical axis. 2 When the integrated power (kWh / kg) at which the kneading rate reached 1.0 / g was taken as the standard (1.0), the integrated power required to obtain the kneaded products A to C in Example 1 above was expressed as an index, and was 0.1, 0.3, and 0.5, respectively. The results are shown in Table 1. Fig. 3 shows a graph of Example 1 and Comparative Examples 1 to 4, with the horizontal axis representing the index of integrated power and the vertical axis representing the specific surface area.

[0172] [Table 1]

[0173] From the results shown in FIG. 3, the specific surface area of ​​the powder was increased to 10 m using a kneader according to the manufacturing method of the present embodiment. 2 The cumulative power required to achieve a specific surface area of ​​10 m / g is 0.25 (exponent). 2 It was confirmed that the integrated power required to achieve a rated current of 1000 W / s was only 25% of that required for achieving a rated current of 1000 W / s. Therefore, according to the manufacturing method of this embodiment, it is possible to efficiently provide a modified sulfide solid electrolyte that has excellent applicability when applied as a paste and is suitable for use in lithium ion batteries. [Industrial Applicability]

[0174] According to the method for producing the sulfide solid electrolyte of the present embodiment, it is possible to efficiently provide a modified sulfide solid electrolyte that has excellent applicability when applied as a paste and is suitable for use in lithium ion batteries. The modified sulfide solid electrolyte obtained by the production method of this embodiment is suitable for use in batteries, particularly lithium ion batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones.

Claims

1. Mixing a raw material inclusion containing lithium atoms, sulfur atoms, and phosphorus atoms with a complexing agent to obtain a precursor electrolyte; heating the precursor electrolyte to obtain a sulfide solid electrolyte; and kneading the sulfide solid electrolyte using a kneader including a casing and at least one rotating shaft arranged to penetrate the casing in the longitudinal direction and provided with paddles along the axial direction. A method for producing a modified sulfide solid electrolyte including these steps.

2. The method for producing a modified sulfide solid electrolyte according to Claim 1, wherein the kneader includes two or more of the rotating shafts.

3. The method for producing a modified sulfide solid electrolyte according to Claim 1 or 2, wherein the kneader has a reverse screw.

4. The method for producing a modified sulfide solid electrolyte according to Claim 1 or 2, wherein the raw material inclusion contains lithium sulfide and phosphorus sulfide.

5. The method for producing a modified sulfide solid electrolyte according to Claim 1 or 2, wherein the raw material inclusion further contains a halogen atom.

6. The method for producing a modified sulfide solid electrolyte according to Claim 5, wherein the raw material inclusion contains at least one selected from lithium halide and a halogen simple substance.

7. The method for producing a modified sulfide solid electrolyte according to Claim 5, wherein the halogen atom is at least one atom selected from a chlorine atom, a bromine atom, and an iodine atom.

8. The method for producing a modified sulfide solid electrolyte according to Claim 1 or 2, wherein the complexing agent is a compound containing a heteroatom.

9. The method for producing a modified sulfide solid electrolyte according to Claim 8, wherein the heteroatom is at least one atom selected from a nitrogen atom and an oxygen atom.

10. The method for producing a modified sulfide solid electrolyte according to Claim 1 or 2, wherein the complexing agent is a compound having at least two tertiary amino groups in the molecule.

11. The method for producing a modified sulfide solid electrolyte according to Claim 10, wherein the compound is an aliphatic amine.

12. The method for producing a modified sulfide solid electrolyte according to Claim 11, wherein the aliphatic amine is at least one selected from tetramethylethylenediamine and tetramethyldiaminopropane.

13. The method for producing a modified sulfide solid electrolyte according to Claim 1 or 2, wherein the modified sulfide solid electrolyte has a thio-Li2S-P2S5 region II type crystal structure.

Images