Solid electrolyte, electrode mixture and lithium-ion battery using same, and method for manufacturing modified solid electrolyte

Abstract

Provided are: a solid electrolyte having high ion conductivity and filling properties, and having a crystallite diameter of more than 180 Å and less than 477 Å as measured by X-ray diffraction measurement using a CuKα ray of a test piece formed to have a thickness of 1.0-2.0 mm by performing uniaxial compression molding treatment at a molding pressure of 1000 MPa and a molding time of 5 minutes; an electrode mixture and a lithium-ion battery using the same; and a method for manufacturing a modified solid electrolyte.

Description

Solid electrolyte, electrode mixture and lithium ion battery using the same, and method for manufacturing modified solid electrolyte

[0001] The present invention relates to a solid electrolyte, an electrode mixture and a lithium ion battery using the same, and a method for producing a modified solid electrolyte.

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries for use as their power sources has become increasingly important. Traditionally, batteries used for such applications have used electrolytes containing flammable organic solvents. However, because the electrolytes are liquid and flammable, safety concerns regarding leakage, fire, and the like have arisen when used in batteries. In particular, for automotive applications, high capacity and high output are required, and safety concerns regarding batteries using conventional electrolytes are becoming increasingly serious. Therefore, development of batteries in which the electrolyte is replaced with a solid electrolyte layer is underway, as solid-state batteries eliminate the use of flammable organic solvents, simplify safety devices, and offer superior manufacturing costs and productivity.

[0003] Various types of solid electrolytes have been developed for use in solid electrolyte layers. For example, Patent Document 1 discloses a crystalline sulfide solid electrolyte containing lithium atoms, phosphorus atoms, sulfur atoms, and at least one halogen atom selected from bromine and iodine atoms, exhibiting a predetermined diffraction peak in X-ray diffraction measurement and having a thiolicon region II crystal structure as its basic structure. Patent Document 2 also discloses a sulfide-based compound for a solid electrolyte of a lithium secondary battery having a cubic argyrodite-type crystal structure and represented by a predetermined composition formula, a solid electrolyte for a lithium secondary battery containing the compound, and a method for producing a solid electrolyte by mixing a lithium-containing compound, a phosphorus-containing compound, a sulfur-containing compound, a chlorine-containing compound, and a bromine-containing compound and firing the mixture at 450 to 600 °C under a hydrogen sulfide gas flow. Thus, development of sulfide solid electrolytes having various crystal structures and methods for producing them is currently underway.

[0004] International Publication No. 2023-167237 Pamphlet International Publication No. 2019-009228 Pamphlet

[0005] The present invention has been made in view of the above circumstances, and aims to provide a solid electrolyte having high ionic conductivity and packing ability, an electrode composite and a lithium ion battery using the same, and a method for producing the modified solid electrolyte.

[0006] The solid electrolyte according to the present invention is a solid electrolyte, wherein a test piece is subjected to uniaxial compression molding at a molding pressure of 1000 MPa for a molding time of 5 minutes to be molded to a thickness of 1.0 to 2.0 mm, and the crystallite diameter measured by X-ray diffraction using CuKα radiation is more than 180 Å and less than 477 Å.

[0007] The electrode mixture according to the present invention is an electrode mixture containing the above solid electrolyte and an electrode active material, and the lithium ion battery according to the present invention is a lithium ion battery containing at least one of the above solid electrolyte and the electrode mixture.

[0008] The present invention also provides a method for producing a modified solid electrolyte, which comprises subjecting a solid electrolyte to uniaxial compression molding at a molding pressure of 1000 MPa or more for a molding time of 5 minutes or more.

[0009] According to the present invention, it is possible to provide a solid electrolyte having high ionic conductivity and packing property, an electrode mixture and a lithium ion battery using the same, and a method for producing a modified solid electrolyte.

[0010] 1 shows X-ray diffraction spectra of solid electrolytes (test pieces) obtained in Examples and Comparative Examples.

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

[0012] (Findings Obtained by the Inventors to Achieve the Present Invention) The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found the following, which has led to the completion of the present invention.

[0013] To improve the battery performance of lithium-ion batteries using solid electrolytes, especially all-solid-state batteries, it is important that the solid electrolyte itself has high ionic conductivity. However, it is also important to pay attention to the state of the solid electrolyte when used in the solid electrolyte layer, positive electrode, and negative electrode. In the solid electrolyte layer, the particles of the solid electrolyte and the electrode active material are closely attached to each other, and in the positive electrode and negative electrode, the particles of the solid electrolyte and the electrode active material are closely attached to each other, thereby providing many junctions and interfaces between the particles, thereby ensuring ion conduction paths and achieving excellent battery performance. In other words, to achieve excellent battery performance, it is important that the solid electrolyte not only has high ionic conductivity, but also that it has packing properties that ensure ion conduction paths by providing many junctions and interfaces between the particles through close contact between the particles.

[0014] The inventions described in Patent Documents 1 and 2 focus on the types of crystal structures, such as the thiolicon region II crystal structure and the argyrodite crystal structure, to improve ionic conductivity. However, no attention is paid to properties such as packing ability, which are required when solid electrolytes are used in lithium ion batteries and even all-solid-state batteries. Therefore, developments that focus on improving properties such as packing ability when used in batteries are desired.

[0015] The inventors have been developing solid electrolytes, focusing not only on ionic conductivity but also on packing properties. They have discovered that solid electrolytes with crystallite diameters within a predetermined range after compression molding can achieve both high ionic conductivity and packing properties. While the reason for this is unclear, it is believed that such solid electrolytes have crystallite diameters large enough for ion conduction, and that the crystallites are prone to fracture or amorphization upon compression molding. Furthermore, the adhesion between solid electrolyte particles and between the solid electrolyte and the electrode active material is improved, increasing the number of junctions and surfaces between particles, thereby ensuring ion conduction paths. Furthermore, the improved packing properties allow the solid electrolyte to be effectively utilized when used in lithium-ion batteries, resulting in excellent battery performance. Furthermore, the crystallite diameter and improved packing properties adjusted by compression molding are uniquely maintained even after the solid electrolyte is subsequently returned to a powder form.

[0016] The fact that the crystallite size can be adjusted by compression molding and that this phenomenon is maintained regardless of the subsequent form of the solid electrolyte is not only not disclosed in Patent Documents 1 and 2, but is also not a phenomenon that has been discovered so far, and is therefore a surprising effect.

[0017] (Regarding Various Forms of the Present Embodiment) A solid electrolyte according to a first embodiment of the present embodiment is a solid electrolyte in which a test piece is subjected to uniaxial compression molding at a molding pressure of 1000 MPa for a molding time of 5 minutes to be molded to a thickness of 1.0 to 2.0 mm, and the crystallite diameter measured by X-ray diffraction using CuKα radiation is more than 180 Å and less than 477 Å.

[0018] The solid electrolyte of this embodiment has the property that the crystallite diameter of a test piece obtained by uniaxial compression molding at a molding pressure of 1000 MPa and a molding time of 5 minutes to a thickness of 1.0 to 2.0 mm is greater than 180 Å and less than 477 Å. The crystallite diameter refers to the diameter of the crystallites constituting the solid electrolyte particles and is an indicator of the degree of presence of grain boundaries, which are the interfaces between crystallites present in the solid electrolyte particles. As the crystallite diameter increases, the number of grain boundaries decreases, making it easier for lithium ions to move within the solid electrolyte particles, but the solid electrolyte becomes harder, making it easier for the adhesion between the solid electrolyte particles and between the solid electrolyte and the electrode active material to decrease. On the other hand, as the crystallite diameter decreases, the number of grain boundaries increases, improving the adhesion between the solid electrolyte particles and between the solid electrolyte and the electrode active material, but making it more difficult for lithium ions to move within the solid electrolyte particles.

[0019] The solid electrolyte of this embodiment, by setting the crystallite diameter of the molded test piece within the above range, aims to achieve both ease of lithium ion mobility and securing ion conduction paths by increasing the number of junctions and junction surfaces between particles due to improved adhesion. By doing so, it is possible to achieve both high levels of ionic conductivity and packing ability, and it is thought that the solid electrolyte of this embodiment will have high ionic conductivity and high packing ability.

[0020] A solid electrolyte according to a second aspect of the present embodiment is the solid electrolyte according to the first aspect, wherein a powder obtained by pulverizing the test piece has a crystallite diameter of more than 180 Å and less than 477 Å, as measured by X-ray diffraction measurement using CuKα radiation.

[0021] The solid electrolyte of this embodiment preferably has the property that the crystallite size of a test piece that has been compression-molded is maintained even after the test piece is pulverized. Because the solid electrolyte of this embodiment has such a property, it can be used as a molded product obtained by compression molding, or as a powder obtained by pulverizing this. In either form, it can be a solid electrolyte having high ionic conductivity and packing ability.

[0022] A solid electrolyte according to a third aspect of the present embodiment is the solid electrolyte according to the first or second aspect, wherein the solid electrolyte contains a lithium atom, a phosphorus atom, a sulfur atom, and a halogen atom. A solid electrolyte according to a fourth aspect is the solid electrolyte according to the third aspect, wherein the halogen atom contains at least one atom selected from a chlorine atom, a bromine atom, and an iodine atom.

[0023] The solid electrolyte of this embodiment is composed of lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms, i.e., a sulfide solid electrolyte, and is therefore likely to have the above-mentioned crystallite size, thereby improving ionic conductivity and packing properties. By including halogen atoms, and by using at least one atom selected from chlorine atoms, bromine atoms, and iodine atoms as the halogen atoms, the ionic conductivity in particular is likely to be improved.

[0024] The solid electrolyte according to a fifth aspect of the present embodiment is any one of the first to fourth aspects described above, in that it is a molded article, and the solid electrolyte according to a sixth aspect is any one of the first to fourth aspects described above, in that it is a powder.

[0025] The solid electrolyte of this embodiment may be a molded product obtained by compression molding as described above, or may be a powder obtained by pulverizing the molded product. Once a test piece, i.e., a molded product, has been obtained by compression molding, the subsequent form of the solid electrolyte may be either a molded product or a powder. The form of the solid electrolyte can be appropriately selected depending on the subsequent use.

[0026] The solid electrolyte according to a seventh aspect of the present embodiment is any one of the first to sixth aspects, wherein the solid electrolyte has an argyrodite-type crystal structure.

[0027] Among crystalline sulfide solid electrolytes, sulfide solid electrolytes having an argyrodite-type crystal structure, i.e., crystalline, are known to have high ionic conductivity and hard properties. Even if the solid electrolyte of this embodiment has such a hard crystal structure, if it has a predetermined crystallite size after compression molding, the adhesion between the solid electrolytes and between the solid electrolyte and the electrode active material is improved. Therefore, the solid electrolyte of this embodiment has high ionic conductivity and high packing ability.

[0028] An electrode mixture according to an eighth aspect of the present embodiment is an electrode mixture containing the solid electrolyte according to any one of the first to seventh aspects and an electrode active material.

[0029] The solid electrolyte of the present embodiment has high packing properties, and therefore improves adhesion with the electrode active material, thereby increasing the number of junctions and junction surfaces between particles, making it easier to ensure ion conduction paths. Furthermore, because the solid electrolyte of the present embodiment has high ionic conductivity, an electrode composite containing the solid electrolyte also exhibits high ionic conductivity. As a result, excellent battery performance can be obtained by using the electrode composite of the present embodiment in a lithium-ion battery.

[0030] A lithium ion battery according to a ninth aspect of the present embodiment is a lithium ion battery including at least one of the solid electrolyte according to any one of the first to seventh aspects and the electrode mixture according to the eighth aspect.

[0031] The solid electrolyte of the present embodiment has high packing properties, which improves not only the adhesion between the solid electrolyte and the electrode active material, but also the adhesion between the solid electrolytes themselves. Furthermore, because the solid electrolyte of the present embodiment has high ionic conductivity, the solid electrolyte and the electrode composite also exhibit high ionic conductivity. Therefore, by using the solid electrolyte and the electrode composite of the present embodiment in a lithium-ion battery, the lithium-ion battery of the present embodiment exhibits excellent battery performance.

[0032] A method for producing a modified solid electrolyte according to a tenth aspect of the present embodiment is a production method including subjecting a solid electrolyte to uniaxial compression molding at a molding pressure of 1000 MPa or more for a molding time of 5 minutes or more.

[0033] By subjecting a solid electrolyte to compression molding using the above method, the crystallite diameter of the solid electrolyte becomes greater than 180 Å and less than 477 Å, which is different from the crystallite diameter of the solid electrolyte before compression molding. A solid electrolyte having such a crystallite diameter has a high packing ratio and therefore excellent packing properties, and also has high ionic conductivity. Therefore, by subjecting a solid electrolyte to compression molding using the above method, the solid electrolyte is modified to become a modified solid electrolyte.

[0034] The solid electrolyte of this embodiment will be described in more detail below in accordance with the above embodiment.

[0035] In this specification, the term "solid electrolyte" refers to an electrolyte that maintains a solid state at 25°C under a nitrogen atmosphere. The solid electrolyte in this embodiment preferably contains lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms, uses lithium atoms as conductive species, and has ionic conductivity due to the lithium atoms. Here, those containing sulfur atoms are also called "sulfide solid electrolytes."

[0036] The term "solid electrolyte" includes both crystalline solid electrolytes and amorphous solid electrolytes. In this specification, a crystalline solid electrolyte is a solid electrolyte in which peaks derived from the solid electrolyte are observed in an X-ray diffraction pattern in X-ray diffraction measurement, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present. That is, a crystalline solid electrolyte includes a crystalline structure derived from the solid electrolyte, and a portion of the crystalline structure may be derived from the solid electrolyte, or the entire crystalline structure may be derived from the solid electrolyte. Furthermore, as long as a crystalline solid electrolyte has the X-ray diffraction pattern described above, it may also contain an amorphous solid electrolyte in part. Therefore, crystalline solid electrolytes include so-called glass ceramics obtained by heating an amorphous solid electrolyte to a temperature equal to or higher than its crystallization temperature. Furthermore, in this specification, an amorphous solid electrolyte is an electrolyte in which a halo pattern in X-ray diffraction measurement shows substantially no peaks other than those derived from the material, regardless of whether or not peaks derived from the raw materials of the solid electrolyte are present.

[0037] [Solid Electrolyte] The solid electrolyte of the present embodiment is a solid electrolyte in which a test piece is subjected to uniaxial compression molding at a molding pressure of 1000 MPa for a molding time of 5 minutes to be molded to a thickness of 1.0 to 2.0 mm, and the crystallite diameter measured by X-ray diffraction using CuKα radiation is more than 180 Å and less than 477 Å.

[0038] (Crystallite diameter) The test piece to be measured for crystallite diameter can be produced by uniaxial compression molding at a molding pressure of 1000 MPa and a molding time of 5 minutes, and any equipment can be used without any particular limitations as long as it can perform compression molding at a molding pressure of 1000 MPa and a molding time of 5 minutes. For example, a commercially available compression molding equipment such as a uniaxial compressor (manual, electric, pneumatic, hydraulic, screw jack, etc.) can be used.

[0039] The molding pressure is 1000 MPa. When performing the compression molding process, the molding pressure may be 1000 MPa and a single process may be performed, or it may be performed in multiple steps. When performing the compression molding process in multiple steps, at least one preliminary molding may be performed at a molding pressure of less than 1000 MPa, for example, 10 MPa or more, 30 MPa or more, 50 MPa or more, 75 MPa or more, with an upper limit of 900 MPa or less, and even 600 MPa or less, 300 MPa or less, and then molding may be performed at 1000 MPa. When the molding pressure exceeds 1000 MPa or more, almost no change in the crystallite diameter of the solid electrolyte is observed. Therefore, as already mentioned, even if the compression molding process is performed multiple times at a molding pressure of less than 1000 MPa, there is no effect on the crystallite diameter when the test piece is obtained.

[0040] The molding pressure of the compression molding process for obtaining the test piece of 1000 MPa does not necessarily mean strictly 1000 MPa, but also includes a molding pressure in the vicinity thereof. In this case, the vicinity includes a molding pressure of 1000 MPa or less and a molding pressure of 1000 MPa or more. When the molding pressure is 1000 MPa or less, it includes 900 MPa or more, 950 MPa or more, 970 MPa or more, and 990 MPa or more. When the molding pressure is 1000 MPa or more, it includes 1200 MPa or less, 1100 MPa or less, and 1050 MPa or less.

[0041] Furthermore, the term "5 minutes" used in the compression molding process to obtain the test specimens does not necessarily mean exactly 5 minutes, but also includes a time in the vicinity of 5 minutes. In this case, "nearby" includes a molding time of 5 minutes or less and a molding time of 5 minutes or more, and when the molding time is 5 minutes or less, it includes 4 minutes or more, further 4 minutes 15 seconds or more, 4 minutes 30 seconds or more, 4 minutes 45 seconds or more, and 4 minutes 55 seconds or more, and when the molding time is 5 minutes or more, it includes 8 minutes or less, further 7 minutes or less, 6 minutes or less, and 5 minutes 30 seconds or less.

[0042] In the compression molding process, the larger the molding pressure, the smaller the crystallite diameter, and in the vicinity of 1000 MPa, the crystallite diameter tends to approach a certain value. In addition, the molding time is within the above range, and in the vicinity of 1000 MPa, the crystallite diameter tends to approach a certain value. Therefore, even if the molding pressure and molding time of the compression molding process have the above-mentioned range, the measured crystallite diameter can be treated as the crystallite diameter of the test piece obtained by the above-mentioned predetermined method.

[0043] By setting the thickness of the test piece to 1.0 to 2.0 mm, uniform molding pressure is applied across the entire surface of the test piece, resulting in a uniform molded product. Therefore, measurement errors in the crystallite diameter of the test piece can be reduced. There are no particular restrictions on the size (diameter) of the test piece, and it is sufficient to set the size according to the equipment used for compression molding.

[0044] The crystallite size measured by X-ray diffraction measurement using CuKα rays can be determined by calculation using the measurement results of (powder X-ray diffraction (XRD) measurement) in the examples described below, according to the method of (measurement of crystallite size).

[0045] For the solid electrolyte of this embodiment, the crystallite diameter of the test piece measured by the above method is more than 180 Å and less than 477 Å. The crystallite diameter of the test piece is preferably 200 Å or more, more preferably 250 Å or more, even more preferably 275 Å or more, and even more preferably 300 Å or more, with the upper limit being preferably 470 Å or less, more preferably 460 Å or less, even more preferably 450 Å or less, and even more preferably 435 Å or less. Within the above numerical range, it is possible to achieve both high levels of ionic conductivity and packing ability.

[0046] In the solid electrolyte of this embodiment, the powder obtained by pulverizing the test piece obtained by the above method preferably has a crystallite diameter measured by the above method of more than 180 Å and less than 477 Å. The crystallite diameter of the powder obtained by pulverization is more preferably 200 Å or more, even more preferably 250 Å or more, still more preferably 275 Å or more, and particularly preferably 300 Å or more, with the upper limit being more preferably 470 Å or less, even more preferably 460 Å or less, still more preferably 450 Å or less, and particularly preferably 435 Å or less.

[0047] Here, the pulverization may be carried out using a pulverizer. The pulverizer may be appropriately selected from various pulverizers, such as container-driven pulverizers such as bead mills and ball mills, impact pulverizers such as hammer mills and pin mills, and other pulverizers exemplified below as pulverizers that can be used to pulverize raw materials. Depending on the scale, a mortar may also be used. As a pulverization method, for example, it is preferable to perform coarse pulverization using an impact pulverizer (especially a hammer mill) or a mortar, and then fine pulverization using a container-driven pulverizer (bead mill) or an impact pulverizer (especially a pin mill).

[0048] The average particle size of the solid electrolyte after the pulverization treatment may be adjusted appropriately depending on the application, for example, to 0.1 μm or more, 1 μm or more, 10 μm or more, or 100 μm or less. In this specification, the average particle size can be measured using, for example, a laser diffraction / scattering particle size distribution measuring device, and is the particle size (D) at which the particle size distribution is accumulated from the smallest particle size to 50% (volume basis) of the total when an accumulated particle size distribution curve is drawn. ５０ )

[0049] (Form of solid electrolyte) The solid electrolyte of this embodiment may be any solid electrolyte as long as a test piece compression-molded by the above-mentioned predetermined method has a predetermined crystallite diameter. The form of the solid electrolyte of this embodiment may be a powder or a test piece, i.e., a molded product, as long as the test piece has the predetermined crystallite diameter.

[0050] In the case of a powder, it may be a powder before being compression-molded into a test piece by the above-mentioned predetermined method, or a powder obtained by pulverizing a test piece, and from the viewpoint of obtaining higher ionic conductivity and packing property, it is preferable that it is a powder obtained by pulverizing a test piece.

[0051] The powder obtained by pulverizing the test piece may be a powder obtained by pulverizing a test piece obtained by a single compression molding process using the above-mentioned specified method, or may be a powder obtained after repeating compression molding and pulverization multiple times. If the test piece compression molded using the above-mentioned specified method has a specified crystallite size, it will have high ionic conductivity and high packing ability, whether it is in the form of a powder or a molded product.

[0052] In the case of a molded product, it may be a molded product obtained by compression molding using the above-mentioned predetermined method, or may be a molded product obtained by compression molding using a method other than the above-mentioned predetermined method. Furthermore, like the powder, it may be a test piece obtained by a single compression molding process, or may be a molded product obtained after repeating pulverization and compression molding multiple times.

[0053] The solid electrolyte of this embodiment has the property that it has the above-mentioned crystallite diameter when compression molded into a test piece by the above-mentioned predetermined method, and that the crystallite diameter is easily maintained even after subsequent pulverization. The solid electrolyte of this embodiment has the above-mentioned predetermined crystallite diameter as a test piece obtained by compression molding by the above-mentioned predetermined method. Therefore, the compression molding performed by the above-mentioned predetermined method can also be said to be a process for modifying the solid electrolyte. In other words, the compression molding performed by the above-mentioned predetermined method can be called a method for modifying the solid electrolyte, and the solid electrolyte of this embodiment can be called a modified solid electrolyte.

[0054] (Constituent Atoms) The solid electrolyte of this embodiment preferably contains lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms. By containing halogen atoms, the ionic conductivity is improved compared to sulfide solid electrolytes containing lithium atoms, phosphorus atoms, and sulfur atoms. Preferred examples of halogen atoms include fluorine atoms, chlorine atoms, bromine atoms, and iodine atoms, and among these, chlorine atoms, bromine atoms, and iodine atoms are preferred. In the solid electrolyte of this embodiment, the halogen atoms may be contained alone or in combination of two or more of the above halogen atoms.

[0055] The halogen atoms can be adopted depending on the crystal structure to be obtained. For example, when a crystalline sulfide solid electrolyte having a thiolicon region II crystal structure described later is to be obtained, the halogen atoms preferably contain at least one of a bromine atom and an iodine atom, more preferably a bromine atom and an iodine atom. When a crystalline sulfide solid electrolyte having an argyrodite crystal structure is to be obtained, the halogen atoms preferably contain at least one of a chlorine atom and a bromine atom, more preferably a chlorine atom and a bromine atom.

[0056] In the solid electrolyte of this embodiment, the composition ratio (molar ratio) of lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms is preferably 1.0 to 1.8:0.1 to 0.8:1.0 to 2.0:0.01 to 0.6, more preferably 1.1 to 1.7:0.2 to 0.6:1.2 to 1.8:0.05 to 0.5, and even more preferably 1.2 to 1.6:0.25 to 0.5:1.3 to 1.7:0.08 to 0.4.

[0057] When bromine and iodine, or bromine and chlorine are used in combination as halogen atoms, the composition ratio (molar ratio) of lithium atoms, phosphorus atoms, sulfur atoms, bromine, and iodine (or chlorine) is preferably 1.0 to 1.8: 0.1 to 0.8: 1.0 to 2.0: 0.01 to 0.3: 0.01 to 0.3, more preferably 1.1 to 1.7: 0.2 to 0.6: 1.2 to 1.8: 0.02 to 0.25: 0.02 to 0.25, even more preferably 1.2 to 1.6: 0.25 to 0.5: 1.3 to 1.7: 0.03 to 0.2: 0.03 to 0.2, and still more preferably 1.35 to 1.45: 0.3 to 0.45: 1.4 to 1.7: 0.04 to 0.18: 0.04 to 0.18.

[0058] By setting the composition ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms in the solid electrolyte of this embodiment within the above range, it becomes easier to obtain a solid electrolyte with higher ionic conductivity having a crystal structure described below, particularly a thiolicon region II crystal structure or an argyrodite crystal structure. Whether the solid electrolyte of this embodiment is an amorphous solid electrolyte or a crystalline solid electrolyte, it is preferable that the composition ratio (molar ratio) of each atom be within the above range. Furthermore, the type and composition ratio (molar ratio) of the atoms constituting the solid electrolyte of this embodiment can be confirmed, for example, using an ICP atomic emission spectrometer.

[0059] (Crystal Structure) The crystal structure of the solid electrolyte of this embodiment is not particularly limited as long as it is a crystal structure composed of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms. Preferred examples include an argyrodite-type crystal structure and a thiolisic region II-type crystal structure. Among the above, the solid electrolyte of this embodiment preferably has an argyrodite-type crystal structure. As described above, the argyrodite-type crystal structure is known to have high ionic conductivity among crystalline sulfide solid electrolytes. On the other hand, the argyrodite-type crystal structure is known to have hard properties and generally exhibits low adhesion between solid electrolytes and between the solid electrolyte and the electrode active material. Because the solid electrolyte of this embodiment has the above-mentioned specified crystallite size, even if it has an argyrodite-type crystal structure, the adhesion between solid electrolytes and between the solid electrolyte and the electrode active material is improved, resulting in high packing properties while maintaining the inherently high ionic conductivity.

[0060] The argyrodite crystal structure is ７ P.S. ６ The argyrodite-type crystal structure has a structural skeleton basically as shown in the figure, with some of the P substituted with Si. The composition formula of the argyrodite-type crystal structure is, for example, Li ７－ｘ P １－ｙ Si ｙ S ６ , Li ７＋ｘ P １－ｙ Si ｙ S ６ (x is -0.6 to 0.6, y is 0.1 to 0.6). The argyrodite-type crystal structure represented by these composition formulas is a cubic or orthorhombic crystal, preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, it has peaks that appear mainly at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Note that these peak positions may vary within a range of ±0.5°. The same applies to the diffraction peaks described below.

[0061] The composition formula of the argyrodite crystal structure is Li ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ(0.8≦x≦1.7, 0<y≦−0.25x+0.5). The argyrodite-type crystal structure represented by this composition formula is preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, it has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. The composition formula of the argyrodite-type crystal structure is preferably Li ７－ｘ P.S. ６－ｘ Ha ｘ (Ha is Cl or Br, and x is preferably 0.2 to 1.8) The argyrodite-type crystal structure represented by this composition formula is preferably a cubic crystal, and in X-ray diffraction measurement using CuKα radiation, it has peaks that appear mainly at 2θ=15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°.

[0062] Here, the solid electrolyte obtained by the production method of this embodiment preferably contains lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms. ７－ｘ P １－ｙ Si ｙ S ６ , Li ７＋ｘ P １－ｙ Si ｙ S ６ (x is -0.6 to 0.6, y is 0.1 to 0.6)" and when an atom other than a chlorine atom is used as a halogen atom, "Li ７－ｘ－２ｙ P.S. ６－ｘ－ｙ Cl ｘ (0.8≦x≦1.7, 0<y≦−0.25x+0.5)". However, when the sulfide solid electrolyte obtained by the production method of this embodiment has the same diffraction peaks as those described as the diffraction peaks possessed by the "argyrodite-type crystal structure" above, it can be said that the sulfide solid electrolyte obtained by the production method of this embodiment preferably has an argyrodite-type crystal structure formed by lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms. The same applies to the thiolicon region II crystal structure described below.

[0063] The thiolicon region II crystal structure is Li ４－ｘ Ge１－ｘ P ｘ S ４ 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 S ４ Representative examples include crystal structures similar to the thio-LISICON Region II type (see Solid State Ionics, 177 (2006), 2721-2725).

[0064] The above Li ４－ｘ Ge １－ｘ P ｘ S ４ The diffraction peaks of the thio-LISICON Region II crystal structure appear, for example, at 2θ=20.1°, 23.9°, and 29.5°. ４－ｘ Ge １－ｘ P ｘ S ４ The diffraction peaks of a crystal structure similar to thio-lisicon region II (thio-lisicon region II) type appear, for example, at 2θ = 20.2° and 23.6°. The thio-lisicon region II type crystal structure and the similar crystal structure have similar diffraction peaks, and are therefore very similar structures. Therefore, it is technically reasonable to treat the "thio-lisicon region II type crystal structure" as including both the thio-lisicon region II type crystal structure and the similar crystal structure.

[0065] (Properties of Solid Electrolyte) The pellet density (g / cm) of the test piece obtained by the compression molding treatment according to the above-mentioned predetermined method was ３ ) is preferably 1.50 g / cm ３ More preferably, 1.75 g / cm ３ More preferably, 2.00 g / cm ３ More preferably, 2.01 g / cm ３The upper limit is preferably 3.00 g / cm ３ or less, more preferably 2.50 g / cm ３ More preferably, 2.25 g / cm ３ More preferably, 2.10 g / cm or less ３ The following is the result.

[0066] The packing ratio of the solid electrolyte of this embodiment is preferably more than 2.1, more preferably 2.2 or more, even more preferably 2.4 or more, and still more preferably 2.6 or more, and the upper limit is preferably less than 3.2, more preferably 3.1 or less, and even more preferably 3.0 or less. Here, the packing ratio is a value calculated by the following formula.

[0067] Filling rate = pellet density (g / cm) of the solid electrolyte (test piece) after compression molding ３ ) / density of solid electrolyte before compression molding (g / cm ３ )

[0068] The packing ratio calculated by the above formula is a value obtained by dividing the pellet density of the solid electrolyte (test piece) after compression molding by the density of the solid electrolyte before compression molding, and indicates the degree to which the solid electrolyte before compression molding was compressed when it was made into a test piece. Thus, it is an index for determining packing property.

[0069] The crystallite size retention rate of the solid electrolyte of this embodiment is less than 33.4%, further 33.0% or less, 30.0% or less, 25.0% or less, 20.0% or less, 15.0% or less, or 10.0% or less, and the lower limit is preferably as small as possible, but is usually 1.0% or more. Here, the crystallite size retention rate is a value calculated by the following formula.

[0070] Crystallite diameter retention rate (%)=crystallite diameter (Å) of solid electrolyte (test piece) after compression molding / crystallite diameter (Å) of solid electrolyte before compression molding×100

[0071] The smaller the crystallite size retention rate calculated by the above formula, the greater the fluctuation range of the crystallite size, i.e., the more easily the crystallites break, which means that the adhesion between the solid electrolytes and between the solid electrolyte and the electrode active material is more likely to be improved. Since the solid electrolyte of this embodiment has a small crystallite size retention rate as described above, the adhesion between the solid electrolytes and between the solid electrolyte and the electrode active material is improved, resulting in high packing properties.

[0072] The ionic conductivity of the solid electrolyte of the present embodiment cannot be generally determined because it varies depending on the composition ratio (molar ratio) of the atoms constituting the solid electrolyte, the type of crystalline structure of the solid electrolyte, and the like, but is typically greater than 5.5 mS / cm, furthermore, 5.6 mS / cm or more, 5.8 mS / cm or more, 6.0 mS / cm or more, or 6.2 mS / cm or more, with the upper limit typically being 12.5 mS / cm or less, furthermore, 12.0 mS / cm or less, 11.5 mS / cm or less, or 11.0 mS / cm or less.

[0073] [Method for Producing Solid Electrolyte] The method for producing the solid electrolyte of this embodiment is not particularly limited as long as a solid electrolyte having the predetermined crystallite size can be obtained by performing compression molding by the above-mentioned predetermined method, but preferred examples include a production method (hereinafter also referred to as "production method 1") comprising: heat-treating a raw material content in a solvent using a pressure-resistant container or under reflux, removing the solvent, and firing the heat-treated product obtained by the heat treatment, and a production method (hereinafter also referred to as "production method 2") comprising: mixing the raw material content. This makes it possible to produce the solid electrolyte of this embodiment more efficiently.

[0074] [Production Method 1] (Heat Treatment) Production Method 1 includes heat treating a raw material-containing material in a solvent using a pressure-resistant container or under reflux. The raw material-containing material may contain a solid electrolyte raw material selected depending on the solid electrolyte to be obtained, and preferably includes a material containing multiple solid electrolyte raw materials containing at least one atom selected from a lithium atom, a phosphorus atom, a sulfur atom, and a halogen atom.

[0075] Examples of the solid electrolyte raw material contained in the raw material content include lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides; raw materials containing at least two atoms selected from the above-mentioned atoms, and fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ Representative examples of the raw material include a halogen element such as halogen, phosphorus, sulfur, and the like; and a raw material consisting of one atom selected from the above-mentioned elements.

[0076] Among the above, examples of the solid electrolyte raw material containing lithium atoms, sulfur atoms, and phosphorus atoms include lithium sulfide; diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ Among the phosphorus sulfides, diphosphorus pentasulfide is preferred.

[0077] Among the above, lithium sulfide, diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides, fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ and lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide are preferred. When oxygen atoms are introduced into the solid electrolyte, lithium oxide, lithium hydroxide, and phosphate compounds such as lithium phosphate are preferred.

[0078] Among the above, either a simple halogen or a lithium halide can be preferably used as the solid electrolyte raw material containing a halogen atom. The halogen atoms contained in the raw material inclusions are as described above as the halogen atoms that can be contained in the solid electrolyte of the present embodiment, and it is preferable to use a solid electrolyte raw material containing such halogen atoms.

[0079] As the lithium halide, lithium chloride, lithium bromide, and lithium iodide are more preferred. When attempting to obtain a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure, it is preferable to use at least one of lithium chloride and lithium bromide, and it is more preferable to use lithium chloride and lithium bromide in combination. Furthermore, when attempting to obtain a crystalline sulfide solid electrolyte having a thiolicon region II-type crystal structure, it is preferable to use at least one of lithium bromide and lithium iodide, and it is more preferable to use lithium bromide and lithium iodide in combination.

[0080] The halogen element is chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ ) is more preferred. When attempting to obtain a crystalline sulfide solid electrolyte having an argyrodite-type crystal structure, it is preferable to use at least one of chlorine and bromine, and it is more preferred to use chlorine and bromine in combination. When attempting to obtain a crystalline sulfide solid electrolyte having a thiolicon region II-type crystal structure, it is preferable to use at least one of bromine and iodine, and it is more preferred to use bromine and iodine in combination.

[0081] Preferred examples of the combination of solid electrolyte raw materials contained in the raw material inclusions include a combination of lithium sulfide, phosphorus sulfide, and lithium halide, a combination of lithium sulfide, phosphorus sulfide, and a simple halogen, and a combination of lithium sulfide, phosphorus sulfide, lithium halide, and a simple halogen. More preferred examples include a combination of lithium sulfide, phosphorus pentasulfide, and a lithium halide, and a combination of lithium sulfide, phosphorus pentasulfide, and a simple halogen. Among the above combinations, preferred lithium halides are lithium chloride, lithium bromide, and lithium iodide, and preferred simple halogens are chlorine, bromine, and iodine. As mentioned above, the solid electrolyte raw materials containing halogen atoms can be selected depending on the type of solid electrolyte to be obtained.

[0082] The raw material contains a solid electrolyte raw material containing at least two kinds of atoms selected from the above-mentioned atoms. Examples of solid electrolyte raw materials other than the above include various phosphorus fluorides (PF ３ , P.F. ５ ), various phosphorus chlorides (PCl ３ , PCl ５ , P ２ Cl ４ ), various phosphorus bromides (PBr ３ , PBr ５ ), various phosphorus iodides (PI ３ , P ２ I ４ ) and the like; phosphorus halides such as thiophosphoryl fluoride (PSF ３ ), thiophosphoryl chloride (PSCl ３ ), thiophosphoryl bromide (PSBr ３ ), thiophosphoryl iodide (PSI ３ ), thiophosphoryl fluoride dichloride (PSCl ２ F), thiophosphoryl fluoride dibromide (PSBr ２ F) and the like.

[0083] Examples of solid electrolyte raw materials other than those mentioned above that are contained in the raw material inclusion include solid electrolyte raw materials that contain at least one atom selected from the above atoms and also contain atoms other than the atoms mentioned above, 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; silicon sulfide, germanium sulfide, boron sulfide, gallium sulfide, and tin sulfide (SnS, SnS ２ metal sulfides such as aluminum sulfide and zinc sulfide; phosphate compounds such as sodium phosphate and lithium phosphate; halides of alkali metals other than lithium such as sodium halides 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; phosphorus oxychloride (POCl ３ ), phosphorus oxybromide (POBr ３When oxygen atoms are introduced into the solid electrolyte, phosphoric acid compounds such as lithium oxide, lithium hydroxide and lithium phosphate are preferred.

[0084] In this embodiment, PS ４ Li containing structure ３ P.S. ４ can also be used as a solid electrolyte raw material. ３ P.S. ４ In this case, the combination of the solid electrolyte raw materials contained in the raw material contents may be Li ３ P.S. ４ and the lithium halide, Li ３ P.S. ４ and the above-mentioned elemental halogens, Li ３ P.S. ４ and the lithium halide and the elemental halogen.

[0085] In Production Method 1, when lithium sulfide, diphosphorus pentasulfide, and lithium halide are used as the solid electrolyte raw materials, the compounding ratio (molar ratio) of these compounds is preferably 30 to 60:10 to 25:15 to 50, more preferably 45 to 55:10 to 15:30 to 50, even more preferably 45 to 50:11 to 14:35 to 45, and still more preferably 46 to 49:11 to 13:38 to 42.

[0086] In Production Method 1, the raw material content is preferably pulverized to an average particle size of 20 μm or less, more preferably 15 μm or less, and even more preferably 12 μm or less. A pulverizer can be used to pulverize the raw material. Examples of pulverizers include media-type pulverizers such as container-driven pulverizers and media-agitated pulverizers. Examples of container-driven pulverizers include agitated tanks, grinding tanks, or combinations thereof, such as ball mills and bead mills. Examples of media-agitated pulverizers include impact pulverizers such as cutter mills, hammer mills, and pin mills; tower-type pulverizers such as tower mills; agitated tank-type pulverizers such as attritors, aquamizers, and sand grinders; flow-through tank-type pulverizers such as Viscomills and pearl mills; flow-through pipe-type pulverizers; annular-type pulverizers such as Coball mills; continuous dynamic pulverizers; and single- or multi-axis kneaders. Pin mills are also preferred because of their short processing time and the ability to perform continuous pulverization.

[0087] It is preferable to roughly mix the raw material components in advance. Examples of mixers that can be used for rough mixing include mechanical agitation mixers that are equipped with agitation blades in a reaction vessel and can perform agitation (also referred to as agitation mixing). Examples of mechanical agitation mixers include high-speed agitation mixers and double-arm mixers. Examples of high-speed agitation mixers include vertical-axis rotary mixers and horizontal-axis rotary mixers, and either type of mixer may be used. Other preferred mixers include, for example, container-rotating mixers and fixed-container mixers, as well as Nauta mixers, which are conical screw mixers, and FM mixers, which are high-speed agitation mixers.

[0088] In the production method 1, it is preferable to heat-treat the product obtained by mixing and grinding the raw material components in a solvent. As the solvent used in the mixing and grinding, for example, a non-polar solvent such as a hydrocarbon solvent or a polar solvent such as a solvent containing a heteroatom is preferably used, and it is preferable to use a combination of a non-polar solvent and a polar solvent.

[0089] Examples of hydrocarbon solvents include saturated or unsaturated aliphatic hydrocarbons such as hexane, hexene, pentane, 2-ethylhexane, heptane, heptene, octane, decane, undecane, dodecane, and tridecane; saturated or unsaturated alicyclic hydrocarbons such as cyclohexane, methylcyclohexane, and cyclohexene; and aromatic hydrocarbon solvents such as benzene, toluene, xylene, mesitylene, ethylbenzene, and tert-butylbenzene. Among these, aromatic hydrocarbon solvents are preferred, and toluene and xylene are more preferably used.

[0090] Furthermore, as the solvent containing a heteroatom, an ether solvent or a nitrile solvent is preferably used. Preferred examples of the ether solvent include ether compounds such as aliphatic ethers, alicyclic ethers, heterocyclic ethers, and aromatic ethers, with aliphatic ethers and alicyclic ethers being preferred. Preferred examples of the aliphatic ether 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; and polyethers having three or more ether groups such as diethylene glycol dimethyl ether (diglyme) and triethylene oxide glycol dimethyl ether (triglyme). Among these, monoethers are preferred.

[0091] Examples of the alicyclic ether include ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, dimethoxytetrahydrofuran, cyclopentyl methyl ether, dioxane, dioxolane, etc. Among the above aliphatic ethers and alicyclic ethers, diethyl ether and tetrahydrofuran are preferred.

[0092] Preferred examples of nitrile solvents include aliphatic nitrile solvents such as acetonitrile, acrylonitrile, propionitrile, chloropropionitrile, isobutyronitrile, tert-butyronitrile, capronitrile, isocapronitrile, malononitrile, and fumaronitrile; alicyclic nitrile solvents such as cyclohexylnitrile; and aromatic nitrile solvents such as benzonitrile and fluorobenzonitrile. Among these, aliphatic nitrile solvents are preferred, with propionitrile, isobutyronitrile, and isocapronitrile being more preferred.

[0093] When a non-polar solvent and a polar solvent are used in combination, aromatic hydrocarbon solvents, particularly toluene and ethylbenzene, are preferred as non-polar solvents, and nitrile solvents, which have the property of forming an azeotrope with aromatic hydrocarbon solvents such as toluene and are easily removed together with aromatic hydrocarbon solvents such as toluene, are preferred as polar solvents.

[0094] The content of the nonpolar solvent in the solvent is preferably 95% by mass or more, and when a nonpolar solvent and a polar solvent are used in combination, the content of the polar solvent in the solvent is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.3% by mass or more, with the upper limit being preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 1% by mass or less.

[0095] The equipment used for mixing and grinding the raw material components includes the grinders exemplified above as grinders that can be used for grinding the raw materials, and particularly, grinders such as planetary ball mills, vibration mills, tumbling mills, and bead mills. As the grinder, a grinder that circulates the slurry between a grinder (grinding mixer) that grinds the slurry and a temperature holding tank (reaction vessel) can also be used. Kneaders such as single-shaft kneaders and multi-shaft kneaders can also be used.

[0096] When the raw material content is mixed and pulverized, the raw material content obtained by the mixed and pulverized process forms a slurry together with the solvent, and the solvent can be removed by drying. The drying method is not particularly limited as long as the solvent can be removed. For example, it can be performed by reduced pressure drying (vacuum drying) using a vacuum pump or the like, usually at 5 to 100°C, preferably 10 to 85°C, more preferably 15 to 70°C, and even more preferably at about room temperature (e.g., 23°C) (e.g., about room temperature ± 5°C). The slurry can be filtered using a glass filter or the like, solid-liquid separation by decantation, or solid-liquid separation using a centrifuge or the like, or solid-liquid separation can be performed first, followed by the drying. Furthermore, it is preferable to use the same solvent as that used in the heat treatment as the solvent used in the mixed and pulverized raw material content. This is because drying of the solvent is not necessary.

[0097] The heat treatment in a solvent in Production Method 1 is carried out using a pressure vessel or under reflux. By carrying out the heat treatment in a solvent, i.e., without distilling off the solvent, it is possible to prevent aggregation of the treated materials and reduce the size of secondary particles of the solid electrolyte.

[0098] The solvent used in the heat treatment can be appropriately selected from the non-polar solvents and polar solvents described above as the solvent used in the mixed grinding. Therefore, the same solvent as that used in the mixed grinding may be used, or a different solvent may be used. Using the same solvent is preferable because, as mentioned above, drying is not required. Among the above solvents, aromatic hydrocarbon solvents are preferred.

[0099] The heating temperature in the heat treatment may be appropriately selected depending on the type of solid electrolyte raw material used, and is, for example, preferably 150°C or higher, more preferably 160°C or higher, even more preferably 170°C or higher, and even more preferably 180°C or higher, with the upper limit being preferably 300°C or lower, more preferably 280°C or lower, even more preferably 270°C or lower, and even more preferably 260°C or lower. The heating time is preferably 10 minutes to 6 hours, more preferably 10 minutes to 3 hours, and even more preferably 30 minutes to 2 hours. By setting the above conditions, it is possible to obtain a PS ４The resulting structure allows halogens to be easily incorporated into the crystals, improving ionic conductivity. ４ It becomes easier to form a crystal structure containing the structure.

[0100] When the heat treatment is carried out using a pressure-resistant vessel, it is preferable to use an autoclave if the heating temperature exceeds the boiling point of the solvent used. When the heat treatment is carried out while refluxing the solvent, the method is not particularly limited, and for example, a cooler (e.g., a Dimroth cooler) that cools the vapor and returns it to the solvent can be used.

[0101] (Removing the Solvent) The above-mentioned production method 1 includes removing the solvent after the heat treatment in the solvent. The heat-treated product is obtained by removing the solvent from the slurry containing the solvent and the heat-treated product obtained by the heat treatment.

[0102] The method for removing the solvent from the slurry is not particularly limited as long as it can remove the solvent. For example, the slurry may be dried using a method similar to the drying method used to remove the solvent used during the mixed grinding.

[0103] (Caking) The above-mentioned production method 1 includes calcining the heat-treated product obtained by removing the solvent. This allows for the production of a solid electrolyte, preferably a crystalline solid electrolyte. The heating temperature in the calcination of the heat-treated product may be appropriately selected depending on the composition of the solid electrolyte to be obtained, and is, for example, preferably 300°C or higher, more preferably more than 300°C, even more preferably 320°C or higher, still more preferably 350°C or higher, and particularly preferably 380°C or higher, with the upper limit being preferably 470°C or lower, more preferably 460°C or lower, even more preferably 450°C or lower, still more preferably 440°C or lower, and particularly preferably 430°C or lower. The heating time is preferably 1 minute to 6 hours, more preferably 1 minute to 2 hours, and even more preferably 5 minutes to 1 hour.

[0104] The firing is preferably carried out in an inert gas atmosphere (e.g., a nitrogen atmosphere or an argon atmosphere) or a reduced pressure atmosphere (particularly in a vacuum). The firing can be carried out using a firing furnace such as a stationary hearth kiln or a rotary kiln.

[0105] (Pulverization) The above-mentioned production method 1 may further include pulverizing the fired product obtained by the above-mentioned firing. By pulverizing, it is possible to adjust the average particle size according to the application.

[0106] The calcined product can be pulverized using a pulverizer. The pulverizer can be appropriately selected from the pulverizers exemplified as those that can be used to pulverize the raw materials, and a container-driven pulverizer such as a ball mill or a bead mill is preferably used. The pulverization energy is preferably 0.05 kWh / kg or more, more preferably 0.1 kWh / kg or more, and even more preferably 0.15 kWh / kg or more, with the upper limit being preferably 1.5 kWh / kg or less, more preferably 1.25 kWh / kg or less, and even more preferably 1.0 kWh / kg or less. When the pulverization energy is within the above range, the crystallite diameter is easily maintained within a range of more than 180 Å and less than 477 Å, and the average particle size can be easily adjusted according to the desired application.

[0107] The solid electrolyte obtained by firing and further pulverization in Production Method 1 is a crystalline solid electrolyte, and examples of the crystalline solid electrolyte include solid electrolytes having the crystal structure described above as a possible crystal structure for the solid electrolyte of this embodiment. Production Method 1 is particularly suitable for producing a solid electrolyte having an argyrodite-type crystal structure.

[0108] (Compression molding and pulverization) Manufacturing method 1 may include uniaxial compression molding at a molding pressure of 1000 MPa for a molding time of 5 minutes. The specific molding method is as described above.

[0109] The molding pressure of 1000 MPa may be strictly 1000 MPa as described above, but may also be near 1000 MPa or greater. As described above, the crystallite diameter approaches a constant value near 1000 MPa, and the crystallite diameter does not change even at pressures above 1000 MPa. For the same reason, the molding time may be 5 minutes or thereabouts, or may be 5 minutes or greater. The thickness of the pellets during compression molding may be 1.0 to 2.0 mm, similar to the test specimens, or may be greater than 2.0 mm in consideration of manufacturing efficiency.

[0110] The manufacturing method 1 may also include pulverizing the molded product obtained by the compression molding process. The pulverization process can be carried out by the method described above for pulverizing the test piece of the solid electrolyte of this embodiment.

[0111] [Production Method 2] (Mixing) The solid electrolyte raw materials contained in the raw material inclusions used in Production Method 2 are as described in Production Method 1 above. The method for mixing the raw material inclusions in Production Method 2 is not particularly limited as long as it can mix the raw material inclusions, and can be performed using, for example, a pulverizer, a mixer, an agitator, or the like. Using a pulverizer results in pulverization of the solid electrolyte raw materials, but mixing also occurs at the same time. Mixing of raw materials can also occur using a mixer or an agitator. Therefore, it can be said that the solid electrolyte of this embodiment can be produced by stirring, mixing, pulverizing, or a combination of these processes for a raw material inclusion containing multiple solid electrolyte raw materials selected from solid electrolyte raw materials (substances) containing at least one atom selected from lithium atoms, sulfur atoms, phosphorus atoms, oxygen atoms, and halogen atoms.

[0112] Examples of the agitator, mixer, and pulverizer include the devices exemplified in the above-mentioned Production Method 1. The method of performing mixing accompanied by pulverization using a pulverizer is a method that has been conventionally adopted as a solid-phase method (mechanical milling method). The method using the solid-phase method (mechanical milling method) can be performed by pulverizing the solid electrolyte raw material using a pulverizer, and can be performed based on a known method.

[0113] The method of mixing using a stirrer or mixer is also called a liquid phase method, and examples thereof include methods using a complexing agent disclosed in International Publication No. 2020-105737 and International Publication No. 2023-132280. The method may also include pulverizing the solid electrolyte obtained in Production Method 2. The pulverization of the solid electrolyte in Production Method 2 can be carried out in the same manner as the pulverization of the fired product in Production Method 1.

[0114] The solid electrolyte obtained by Production Method 2 is an amorphous solid electrolyte or a crystalline solid electrolyte. Preferred examples of the crystalline solid electrolyte include solid electrolytes having the crystal structures described above as possible crystal structures of the solid electrolyte of this embodiment, i.e., solid electrolytes having a thiolisiconregion II crystal structure or an argyrodite crystal structure.

[0115] (Compression molding and pulverization) Compression molding and pulverization can also be included in Production Method 2. The details are the same as those described for compression molding and pulverization in Production Method 1 above.

[0116] (Applications) The solid electrolyte of this embodiment has high ionic conductivity and packing property. Therefore, it is suitable for use in electrode mixtures and batteries, especially lithium ion batteries, and particularly all-solid-state batteries. The solid electrolyte of this embodiment may be used in a positive electrode layer, a negative electrode layer, or an electrolyte layer. Each layer can be produced by a known method.

[0117] [Electrode Mixture] The electrode mixture of this embodiment is an electrode mixture containing the above-described solid electrolyte of this embodiment and an electrode active material.

[0118] As the electrode active material, a positive electrode active material or a negative electrode active material is adopted depending on whether the electrode mixture is used for a positive electrode or a negative electrode, and as the positive electrode active material and the negative electrode active material, materials conventionally used as these active materials can be used.

[0119] The compounding ratio (mass ratio) of the solid electrolyte to the electrode active material in the electrode mixture is preferably 99.5:0.5 to 40:60, more preferably 99:1 to 50:50, and even more preferably 98:2 to 60:40, in order to improve battery performance and in consideration of production efficiency.

[0120] The electrode mixture of this embodiment may contain, in addition to the solid electrolyte of this embodiment and the electrode active material, other components such as a conductive material such as a carbon-based material, a thermoplastic elastomer, a binder such as a resin, etc.

[0121] [Lithium-ion Battery] The lithium-ion battery of this embodiment includes at least one of the solid electrolyte of this embodiment and the electrode mixture of this embodiment.

[0122] The lithium ion battery of this embodiment is not particularly limited in its configuration as long as it contains either the solid electrolyte of this embodiment or an electrode composite containing the same, and for example, a solid electrolyte of another form or an electrode composite containing the same may be used. Furthermore, the configuration of the lithium ion battery may be any configuration of a commonly used lithium ion battery.

[0123] The lithium ion battery of this embodiment preferably includes, for example, a positive electrode layer, a negative electrode layer, an electrolyte layer, and a current collector. The positive electrode layer and the negative electrode layer preferably use the electrode mixture of this embodiment, and the electrolyte layer preferably uses the solid electrolyte of this embodiment. A lithium ion battery using a solid electrolyte as the electrolyte layer is also called an all-solid-state battery.

[0124] The battery preferably includes a current collector in addition to the positive electrode layer, the electrolyte layer, and the 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.

[0125] [Method for Producing Modified Solid Electrolyte] The method for producing a modified solid electrolyte of this embodiment includes uniaxial compression molding of a solid electrolyte at a molding pressure of 1000 MPa or more and a molding time of 5 minutes or more. As described above, the solid electrolyte of this embodiment has the above-mentioned crystallite diameter when compression molded into a test piece by the above-mentioned predetermined method, and has the property of easily maintaining this crystallite diameter even after subsequent pulverization. Furthermore, a solid electrolyte having such a crystallite diameter has excellent packing properties due to a high packing ratio, and also has high ionic conductivity, and is therefore a modified solid electrolyte. In other words, the solid electrolyte of this embodiment that constitutes the test piece obtained by compression molding by the above-mentioned predetermined method corresponds to a modified solid electrolyte.

[0126] The explanation of the compression molding process is the same as that of the compression molding process described above as the method for producing the solid electrolyte test piece. The molding pressure may be 1000 MPa or more, and the preferred range is the same as that of the compression molding process described above as the method for producing the solid electrolyte test piece, with the lower limit being 1000 MPa or more and the upper limit being preferably 1200 MPa or less. Alternatively, the pressure may be 1100 MPa or less or 1050 MPa or less.

[0127] The molding time may be 5 minutes or more, and the preferred range is the same as the molding time in the compression molding process described above as the method for producing the solid electrolyte test piece, and is preferably 8 minutes or less, but may also be 7 minutes or less, 6 minutes or less, or 5 minutes 30 seconds or less.

[0128] 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.

[0129] (Powder X-ray Diffraction (XRD) Measurement) Powder X-ray diffraction (XRD) measurement was carried out as follows. A solid electrolyte powder was filled into a groove having a diameter of 20 mm and a depth of 0.2 mm, and the groove was smoothed with glass to prepare a sample. This sample was sealed with a Kapton film for XRD and measured under the following conditions without exposing it to air. Measurement equipment: D8 DISCOVER Plus, manufactured by Bruker Corporation Tube voltage: 45 kV Tube current: 120 mA X-ray wavelength: Cu-Kα ray (1.5418 Å) Optical system: parallel method Slit configuration: solar slit 2.5°, divergence slit 1 mm, Twin Secondary 5.2 mm, light receiving solar 2.5° Detector: semiconductor detector Eiger 2R500K (1D mode) Measurement range: 2θ = 10-60° Step width, scan speed: 0.01°, 0.6 seconds / step With knife edge

[0130] When the sample to be measured is a molded body, the molded body of the sample is placed in the groove of the same holder as that used in the above-mentioned powder X-ray diffraction (XRD) measurement, fixed with Kapton film for XRD, sealed, and measured. Here, if the molded body protrudes from the holder surface, the optical axis is adjusted and then the measurement is performed under the above-mentioned conditions.

[0131] (Measurement of Crystallite Size) The crystallite size (L) was determined according to the method of P. Scherrer et al. Specifically, using the results of the above (powder X-ray diffraction (XRD) measurement), it was determined by calculation from the following formula. Crystallite size (L) = Kλ / (β × cos θ) K: constant, 0.9 was used. λ: 1.5418 Å (Cu-Kα radiation) β: calculated from β = w−B. w: half width of the 25.5° peak obtained by measurement B: instrument constant (a standard material (silicon) was measured in the same manner as above (powder X-ray diffraction (XRD) measurement), and B = 0.1469° was determined from the peak at 2θ = 28.5°.)

[0132] w (half width obtained by measurement) was determined from the FWHW obtained by reading data obtained by XRD measurement into analysis software PDXL manufactured by Rigaku Corporation, calculating peak information and background information by automatic profile processing, and analyzing the peak shape with a divided pseudo-Voigt function.

[0133] (Measurement of pellet density) The pellet volume was calculated from the product of the pellet thickness (L) and its cross-sectional area (S), and the pellet density was calculated by dividing the volume by the powder mass weighed during pellet production (or the mass measured on the pellet).

[0134] (Measurement of Ion Conductivity) In this example, the measurement of ion conductivity was carried out as follows. A 10 mm diameter (cross-sectional area S: 0.785 cm ) sample was taken from the measurement object obtained in the examples and comparative examples. ２ ) and a height (L) of 0.1 to 0.3 cm were molded into a circular pellet to prepare a sample. Electrode terminals were attached to the top and bottom of the sample, and measurements were made at 25°C using an AC impedance method (frequency range: 5 MHz to 0.5 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. The real part Z' (Ω) at the point where -Z'' (Ω) is minimum near the right end of the arc observed in the high-frequency region was taken as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (S / cm) was calculated according to the following formula. Here, if the curve does not form an arc, the intercept of the real part Z' (Ω) axis was taken as the bulk resistance R (Ω): R = ρ(L / S) σ = 1 / ρ

[0135] Example 1 Lithium sulfide (manufactured by Idemitsu Kosan Co., Ltd.) was pulverized under a nitrogen atmosphere using a pin mill equipped with a constant volume feeder (model "100UPZ" manufactured by Hosokawa Micron Corporation) to an average particle size of 7.7 μm. Similarly to lithium sulfide, diphosphorus pentasulfide (manufactured by Thermophos Corporation, average particle size: 125 μm), lithium chloride (manufactured by Honjo Chemical Co., Ltd., average particle size: 308 μm), and lithium bromide (manufactured by Honjo Chemical Co., Ltd., average particle size: 38 μm) were also pulverized using a pin mill to an average particle size of 8.7 μm, 10 μm, and 5.0 μm, respectively.

[0136] In a nitrogen atmosphere glove box, the solid electrolyte raw materials lithium sulfide, diphosphorus pentasulfide, lithium chloride, and lithium bromide were weighed out to a total of 110 g in a molar ratio of 47.5:12.5:25.0:15.0, and then placed in a glass container. The container was shaken to roughly mix. The roughly mixed raw material contents were dispersed in a mixed solvent of 1140 mL of dehydrated toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 7 mL of dehydrated isobutyronitrile (manufactured by Kishida Chemical Co., Ltd.) under a nitrogen atmosphere to obtain a slurry (containing approximately 10% by mass of the raw material contents). The slurry was then operated for 1 hour using a bead mill ("LMZ015 (model number)", manufactured by Ashizawa Finetech Co., Ltd.) to mix and grind the raw materials, resulting in a slurry containing the ground raw materials.

[0137] Next, the slurry containing the pulverized raw materials was placed in an autoclave (volume: 2000 mL, made of SUS316) equipped with a stirrer and a heating oil bath, and heat-treated at 200°C for 2 hours while stirring (rotation speed: 200 rpm). After heat treatment in the solvent, the slurry was transferred to a Schlenk flask purged with nitrogen, and the solvent was distilled off by drying under reduced pressure to obtain a heat-treated product. The obtained heat-treated product was fired in an electric furnace (model F-1404-A, manufactured by Tokyo Glass Instruments Co., Ltd.) in a glove box with a nitrogen atmosphere. Specifically, with the electric furnace maintained at 430°C, the door of the electric furnace was opened and a sagger (model 999-60S, Al) containing 50 g of the heat-treated product was quickly placed in the furnace. ２ O ３ (manufactured by Tokyo Glass Instrument Co., Ltd.) was placed in the furnace, the door was closed, and firing was carried out for 30 minutes. Thereafter, the sagger was removed from the electric furnace, slowly cooled, and then sieved with a sieve having openings of 300 μm to obtain a solid electrolyte.

[0138] 0.2 g of the obtained solid electrolyte was placed in a mold (φ10 mm) for pellet production, and using a uniaxial molding machine ("Single-acting cylinder MS-2 (model number)", manufactured by Riken Kiki Co., Ltd.), preliminary molding was performed three times at a molding pressure of 100 MPa, and then uniaxial compression molding was performed at a molding pressure of 1000 MPa for a molding time of 5 minutes. After this process, the mold was released to obtain a test piece (φ10 mm, thickness approximately 1.5 mm).

[0139] When the obtained test piece was subjected to powder XRD diffraction measurement by the above-mentioned method, diffraction peaks at 2θ = 25.5° and 29.9° due to the argyrodite-type crystal structure were confirmed. The X-ray diffraction spectrum resulting from the powder XRD diffraction measurement is shown in Figure 1. The crystallite size, pellet density, and ionic conductivity of the test piece measured by the above-mentioned method are shown in Table 1. The crystallite size and density of the solid electrolyte before being made into a test piece (before being subjected to compression molding), as well as the packing ratio and retention ratio calculated using the above measurement results, are shown in Table 1.

[0140] Example 2 The solid electrolyte obtained in Example 1 was dispersed in a mixed solvent of dehydrated toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and dehydrated isobutyronitrile (manufactured by Kishida Chemical Co., Ltd.) under a nitrogen atmosphere to prepare an approximately 8 wt % slurry. The slurry was pulverized using a bead mill (model LMZ015, manufactured by Ashizawa Finetech Co., Ltd.) while maintaining the nitrogen atmosphere, to obtain a slurry containing a pulverized heat-treated material. The pulverization energy required was 0.3 kWh / kg. The obtained slurry containing the pulverized heat-treated material was placed in a nitrogen-purged Schlenk flask and then dried under reduced pressure to obtain a solid electrolyte. The obtained solid electrolyte was prepared into a test specimen in the same manner as in Example 1. Powder XRD diffraction measurement of the obtained test specimen was performed using the above method, and diffraction peaks at 2θ = 25.5° and 29.9° due to the argyrodite-type crystal structure were confirmed. The X-ray diffraction spectrum obtained from the powder XRD diffraction measurement is shown in FIG. 1. The crystallite size, pellet density, and ionic conductivity of the test specimens were measured according to the above methods, and the results are shown in Table 1. The crystallite size and density of the solid electrolyte before being made into test specimens (before being subjected to compression molding), as well as the packing ratio and retention ratio calculated using the above measurement results, are also shown in Table 1.

[0141] Example 3 A solid electrolyte was obtained in the same manner as in Example 1, except that the grinding energy in Example 2 was changed to 0.74 kWh / kg. The obtained solid electrolyte was made into a test piece in the same manner as in Example 1. When the obtained test piece was subjected to powder XRD diffraction measurement using the method described above, diffraction peaks at 2θ = 25.5° and 29.9° attributable to an argyrodite-type crystal structure were confirmed. The X-ray diffraction spectrum obtained as a result of the powder XRD diffraction measurement is shown in Figure 1. The crystallite size, pellet density, and ionic conductivity of the test piece measured using the above method are shown in Table 1. The crystallite size and density of the solid electrolyte before being made into a test piece (before being subjected to compression molding), as well as the packing ratio and retention ratio calculated using the above measurement results, are shown in Table 1.

[0142] (Comparative Example 1) Lithium sulfide (manufactured by Idemitsu Kosan Co., Ltd.), diphosphorus pentasulfide (manufactured by Thermophos Corporation), lithium chloride (manufactured by Sigma-Aldrich Japan Co., Ltd.) and lithium bromide (manufactured by Sigma-Aldrich Japan Co., Ltd.) were weighed in a molar ratio of 1.9: 0.5: 1.0: 0.6 (lithium sulfide: 0.447 g, diphosphorus pentasulfide: 0.569 g, lithium chloride: 0.217 g, lithium bromide: 0.267 g) to form a raw material containing material. The raw material containing material and 30 g of zirconia balls (diameter: 10 mm) were placed in a zirconia pot (45 mL) of a planetary ball mill ("P-7 (model number)", manufactured by Fritsch) and completely sealed in a nitrogen atmosphere. Mechanical milling treatment (rotation speed: 450 rpm) was performed for 40 hours in a planetary ball mill to obtain an amorphous powder (intermediate). Next, 1.0 g of the amorphous powder was placed in a sagger in a glove box (argon atmosphere) and held in an electric furnace in the glove box at 430° C. for 2 hours. After holding for 2 hours, the sagger was removed from the electric furnace and slowly cooled. The resulting powder was crushed in a mortar and sieved with a sieve having 53 μm openings to obtain a solid electrolyte.

[0143] Next, the solid electrolyte was compression-molded to prepare a test specimen in the same manner as in Example 1. Powder XRD diffraction measurement of the obtained test specimen was performed using the method described above, and diffraction peaks at 2θ = 25.4° and 29.9° attributable to the argyrodite-type crystal structure were confirmed. The X-ray diffraction spectrum resulting from the powder XRD diffraction measurement is shown in Figure 1. The crystallite size, pellet density, and ionic conductivity of the test specimen, measured using the above method, are also shown in Table 1. The crystallite size and density of the solid electrolyte before preparation into a test specimen (before compression-molding), as well as the packing ratio and retention ratio calculated using the above measurement results, are also shown in Table 1.

[0144] Comparative Example 2 A solid electrolyte and a test piece were obtained in the same manner as in Comparative Example 1, except that the mechanical milling using a planetary ball mill in Comparative Example 1 was performed for 72 hours (rotation speed: 600 rpm) and the treatment at 430°C was not performed.

[0145] When the obtained test piece was subjected to powder XRD diffraction measurement by the above-mentioned method, diffraction peaks at 2θ = 25.6° and 30.2° due to the argyrodite-type crystal structure were confirmed. The X-ray diffraction spectrum resulting from the powder XRD diffraction measurement is shown in Figure 1. The crystallite size, pellet density, and ionic conductivity of the test piece measured by the above-mentioned method are also shown in Table 1. The crystallite size and density of the solid electrolyte before being made into a test piece (before being subjected to compression molding), as well as the packing ratio and retention ratio calculated using the above measurement results, are also shown in Table 1.

[0146] *1 The crystallite diameters in Examples 2 and 3 are the crystallite diameters of the solid electrolyte after further pulverization.

[0147] As shown in Table 1, the solid electrolyte of this embodiment was confirmed to have high packing properties, as the test piece compression-molded by the above-mentioned predetermined method had a crystallite diameter of more than 180 Å and less than 477 Å, and a packing ratio ((A) / (B)) of 2.7 to 3.0. Furthermore, the solid electrolyte of this embodiment was confirmed to have high ionic conductivity, as it had an ionic conductivity of 6.3 to 10.6 mS / cm.

[0148] On the other hand, the solid electrolyte obtained in Comparative Example 1 had a high ionic conductivity of 12.9 mS / cm, but a small packing ratio of 2.1 ((A) / (B)), and therefore was not found to have high packing properties. Furthermore, the solid electrolyte obtained in Comparative Example 2 had a high packing ratio of 3.2 ((A) / (B)), and therefore was found to have high packing properties, but an ionic conductivity of 5.5 mS / cm, and therefore was not found to have high ionic conductivity. From the above results, it was confirmed that the solid electrolyte of this embodiment has a crystallite diameter of more than 180 Å and less than 477 Å after compression molding by the above-mentioned predetermined method, and therefore has high ionic conductivity and packing properties.

[0149] The solid electrolyte of this embodiment has high ionic conductivity and packing property, and therefore the solid electrolyte and electrode composite of this embodiment are suitable for use in lithium ion batteries, particularly lithium ion batteries used in information-related devices and communication devices such as personal computers, video cameras, and mobile phones, and particularly all-solid-state batteries.

Claims

1. A solid electrolyte obtained by performing uniaxial compression molding treatment at a molding pressure of 1000 MPa and a molding time of 5 minutes, and having a crystallite diameter measured by X-ray diffraction measurement using CuKα rays of the test piece molded to a thickness of 1.0 to 2.0 mm being more than 180 Å and less than 477 Å.

2. The solid electrolyte according to claim 1, wherein the crystallite diameter of the powder obtained by pulverizing the test piece, measured by X-ray diffraction measurement using CuKα rays, is more than 180 Å and less than 477 Å.

3. The solid electrolyte according to claim 1 or 2, containing lithium atoms, phosphorus atoms, sulfur atoms and halogen atoms.

4. The solid electrolyte according to claim 3, wherein the halogen atom contains at least one atom selected from chlorine atoms, bromine atoms and iodine atoms.

5. The solid electrolyte according to any one of claims 1 to 4, which is a molded article.

6. The solid electrolyte according to any one of claims 1 to 4, which is a powder.

7. The solid electrolyte according to any one of claims 1 to 6, having an argyrodite-type crystal structure.

8. An electrode composite material containing the solid electrolyte according to any one of claims 1 to 7 and an electrode active material.

9. A lithium-ion battery containing at least one of the solid electrolyte according to any one of claims 1 to 7 and the electrode composite material according to claim 8.

10. A method for manufacturing a modified solid electrolyte, including performing uniaxial compression molding treatment on the solid electrolyte at a molding pressure of 1000 MPa or more and a molding time of 5 minutes or more.

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