Modified sulfide solid electrolyte

Abstract

Provided is a modified sulfide solid electrolyte having excellent water resistance and an improved ionic conductivity retention rate, said modified sulfide solid electrolyte comprising a sulfide solid electrolyte that has an argyrodite crystal structure, and a compound that has an oxygen atom and an aromatic group.

Description

Modified sulfide solid electrolyte

[0001] This invention relates to modified sulfide solid electrolytes.

[0002] In recent years, with the rapid proliferation of information-related devices and communication equipment such as personal computers, video cameras, and mobile phones, the development of batteries used as power sources has become increasingly important. Traditionally, batteries used in such applications have employed electrolytes containing flammable organic solvents. However, because the electrolyte is both liquid and flammable, there are safety concerns regarding leakage, ignition, and other issues when used in batteries. In particular, in automotive applications, there is a demand for higher capacity and higher output, and concerns about the safety of conventional batteries using electrolytes are growing. Therefore, by making batteries entirely solid, it is possible to eliminate the use of flammable organic solvents within the battery, simplify safety devices, and improve manufacturing costs and productivity. As a result, development of all-solid-state batteries, in which the electrolyte is replaced with a solid electrolyte layer, is underway.

[0003] Sulfide solid electrolytes have long been known as solid electrolytes used in solid electrolyte layers. Various crystal structures of sulfide solid electrolytes are known, one of which is the argyrodite type crystal structure. Sulfide solid electrolytes having an argyrodite type crystal structure are known to have high stability and high ionic conductivity.

[0004] In recent years, there has been a growing demand for improved battery performance when sulfide solid electrolytes are used in lithium-ion batteries. Methods for improving this performance include, for example, coating the surface of the solid electrolyte and using it as a composition containing the solid electrolyte and an organic compound.

[0005] For example, Patent Document 1 describes a modified sulfide solid electrolyte that, even if it has a large specific surface area, exhibits excellent coating suitability when applied as a paste and can efficiently achieve excellent battery performance, with a specific surface area of ​​10 m². ２A modified sulfide solid electrolyte has been proposed that contains a sulfide solid electrolyte with a concentration of 1 / g or more and an epoxy compound, and has a predetermined peak in the infrared absorption spectrum obtained by FT-IR analysis (ATR method). Furthermore, Patent Document 2 proposes a positive electrode layer containing a sulfide solid electrolyte that can reduce the resistance increase rate of a solid-state battery, and which contains lithium atoms, sulfur atoms, and halogen atoms, and has a coating layer on its surface containing at least one selected from a compound having an ether structure, a polymer of said compound, a compound having a silyl ether group, a polymer of said compound, and a polymer of a compound having an ether structure and a compound having a silyl ether group.

[0006] International Publication No. 2022 / 158458 Pamphlet, Japanese Patent Publication No. 2024-93769

[0007] This invention has been made in view of the above circumstances, and aims to provide a modified sulfide solid electrolyte that has excellent water resistance and improved ionic conductivity retention.

[0008] The modified sulfide solid electrolyte according to the present invention is a modified sulfide solid electrolyte comprising a sulfide solid electrolyte having an argyrodite-type crystal structure and a compound having an oxygen atom and an aromatic group.

[0009] According to the present invention, it is possible to provide a modified sulfide solid electrolyte that has excellent water resistance and improved ionic conductivity retention.

[0010] This is a schematic diagram of the exposure test apparatus used in water resistance evaluation.

[0011] The embodiments of the present invention (hereinafter sometimes referred to as "these embodiments") will be described below. In this specification, the upper and lower limit values ​​related to the numerical ranges of "greater than or equal to," "less than or equal to," and "~" can be any combination of values, and the values ​​of the examples can also be used as the upper and lower limit values.

[0012] (Knowledge gained by the inventors to arrive at the present invention) The inventors diligently studied to solve the above-mentioned problems and, as a result, discovered the following, and completed the present invention.

[0013] A sulfide solid electrolyte has high ionic conductivity, but when it comes into contact with moisture, its ionic conductivity decreases, and the performance of a lithium ion battery using the same also decreases. Therefore, the production of a sulfide solid electrolyte and a lithium ion battery using the same is performed in a low-humidity environment. However, since achieving a low-humidity environment requires high cost, improvement of water resistance of the sulfide solid electrolyte itself is demanded.

[0014] Accordingly, the present inventors focused on the use of a compound capable of modifying a sulfide solid electrolyte having an argyrodite-type crystal structure by adding it to the sulfide solid electrolyte, and studied the structure of the compound.

[0015] In the above-mentioned Patent Documents 1 and 2, the water resistance of the sulfide solid electrolyte is not studied, and whether the ionic conductivity is sufficiently maintained when the sulfide solid electrolyte comes into contact with moisture is unclear, so there is room for improvement.

[0016] Based on the above studies, the present inventors have found that a modified sulfide solid electrolyte excellent in water resistance and having an improved ionic conductivity retention rate can be obtained by including a sulfide solid electrolyte having an argyrodite-type crystal structure and a compound having an oxygen atom and an aromatic group.

[0017] (Regarding various aspects of the present embodiment) The modified sulfide solid electrolyte according to a first aspect of the present embodiment includes a sulfide solid electrolyte having an argyrodite-type crystal structure and a compound having an oxygen atom and an aromatic group.

[0018] As used herein, the "sulfide solid electrolyte" means an electrolyte that contains a sulfur atom and remains solid at 25°C under a nitrogen atmosphere. In the present embodiment, the sulfide solid electrolyte is a sulfide solid electrolyte having an argyrodite-type crystal structure, and is preferably a sulfide solid electrolyte that contains a lithium atom, a sulfur atom, a phosphorus atom and a halogen atom, and has ionic conductivity derived from the lithium atom.

[0019] The "sulfide solid electrolyte" includes crystalline sulfide solid electrolytes.

[0020] As described above, the present inventors have found that a modified sulfide solid electrolyte having excellent water resistance and an improved ionic conductivity retention rate can be obtained by including a sulfide solid electrolyte having an argyrodite-type crystal structure and a compound having an oxygen atom and an aromatic group. That is, the modified sulfide solid electrolyte according to the present embodiment has the property of water resistance "modified", and should be referred to as a "modified sulfide solid electrolyte".

[0021] Although the reason why the modified sulfide solid electrolyte of the present embodiment is excellent in water resistance and improves the ionic conductivity retention rate is not clear, the compound has an oxygen atom, resulting in a structure that easily interacts with the sulfide solid electrolyte. Therefore, it is considered that the surface of the sulfide solid electrolyte and the compound are physically adsorbed, or the sulfide solid electrolyte and the compound react to form a C-S bond. It is presumed that this allows the compound to cover at least a part of the surface of the sulfide solid electrolyte, making it difficult for moisture to come into contact therewith. It is also presumed that the bulky structure of the aromatic group of the compound causes great steric hindrance to the sulfide solid electrolyte, thereby making it more difficult for moisture to come into contact. Further, when a sulfide solid electrolyte comes into contact with moisture, sulfur atoms among the atoms constituting the sulfide solid electrolyte may react to generate hydrogen sulfide. However, as described above, the physical adsorption of the compound or the formation of C-S bonds on the surface of the sulfide solid electrolyte suppresses the reaction with sulfur atoms even if the electrolyte comes into contact with moisture, which is considered to improve water resistance.

[0022] The modified sulfide solid electrolyte according to the second embodiment of this embodiment is characterized in that, in the first embodiment, the compound has two or more oxygen atoms, one oxygen atom forms an ether bond, and the other oxygen atoms form a heterocycle or a carbonyl group.

[0023] The aforementioned compound has a bulkier structure and is more readily interacts with the sulfide solid electrolyte. Therefore, the modified sulfide solid electrolyte of this embodiment, by containing a compound having the aforementioned structure, exhibits superior water resistance and improved ionic conductivity retention.

[0024] The modified sulfide solid electrolyte according to the third embodiment of this model is characterized in that, in the first or second embodiment, the compound has eight or more carbon atoms.

[0025] In this embodiment, the modified sulfide solid electrolyte has a bulkier structure when the compound has eight or more carbon atoms, resulting in superior water resistance and improved ionic conductivity retention.

[0026] The modified sulfide solid electrolyte according to the fourth embodiment of this embodiment is characterized in that, in the second or third embodiment, the compound has a group formed by the direct bonding of the aromatic group and the oxygen atom of 1.

[0027] In this embodiment, if the modified sulfide solid electrolyte has a group formed by the direct bonding of the aromatic group and the oxygen atom of 1, it becomes bulkier and has a structure that interacts more readily with the sulfide solid electrolyte, resulting in superior water resistance and improved ionic conductivity retention.

[0028] The fifth embodiment of this embodiment is a modified sulfide solid electrolyte in which, in any one of the first to fourth embodiments, the compound has a tert-alkyl group and a glycidyl ether group.

[0029] In this embodiment, the modified sulfide solid electrolyte, when the compound has a tert-alkyl group and a glycidyl ether group, has a bulkier structure that interacts more readily with the sulfide solid electrolyte, resulting in superior water resistance and improved ionic conductivity retention.

[0030] The sixth embodiment of this embodiment of the modified sulfide solid electrolyte is characterized in that, in any one of the first to fifth embodiments, the compound has a carbonyl group.

[0031] In this embodiment, the modified sulfide solid electrolyte has a structure that interacts more readily with the sulfide solid electrolyte when the compound has a carbonyl group, resulting in superior water resistance and improved ionic conductivity retention.

[0032] The seventh embodiment of this modified sulfide solid electrolyte is characterized in that, in any one of the first to sixth embodiments, the ratio of the mass of the compound to the mass of the sulfide solid electrolyte is 0.5% or more and 15.0% or less.

[0033] In this embodiment, if the ratio of the mass of the compound to the mass of the sulfide solid electrolyte is within the specified range, it is possible to achieve both higher ionic conductivity and a higher ionic conductivity retention rate.

[0034] The modified sulfide solid electrolyte of this embodiment will be described in more detail below, following the above-described aspects.

[0035] [Modified Sulfide Solid Electrolyte] The modified sulfide solid electrolyte of this embodiment contains a sulfide solid electrolyte having an argyrodite-type crystal structure and a compound having an oxygen atom and an aromatic group. As a result, the modified sulfide solid electrolyte of this embodiment has excellent water resistance and improved ionic conductivity retention.

[0036] The modified sulfide solid electrolyte of this embodiment is not particularly limited in its form, as long as it contains the aforementioned compounds having oxygen atoms and aromatic groups. For example, it may simply be in a state where the compounds are "contained," or it may be in a state where the compounds are "adsorbed" or "bound" by some physical or chemical force.

[0037] In the modified sulfide solid electrolyte of the present embodiment, the compound may be physically adsorbed or bonded so as to cover the entire surface of the sulfide solid electrolyte, or may be physically adsorbed or bonded so as to cover a part of the surface of the sulfide solid electrolyte, and either case is acceptable. The more the surface of the sulfide solid electrolyte is covered with the compound, the more excellent the water resistance of the resulting modified sulfide solid electrolyte is, and the more the ionic conductivity retention rate is improved. It should be noted that the physical adsorption or bonding of the compound on the surface of the sulfide solid electrolyte can be confirmed, for example, by analyzing the surface composition of the sulfide solid electrolyte.

[0038] Further, when the compound reacts with the sulfide solid electrolyte, and the compound is physically adsorbed on the surface of the sulfide solid electrolyte or a C-S bond is formed, oxygen atoms having unpaired electrons or new unshared electron pairs are generated in the compound, and it is inferred that a Li-O bond is formed as a result. The Li-O bond can be grasped, for example, by the Li-O bond ratio obtained through measurement using X-ray photoelectron spectroscopy (XPS). The Li-O bond ratio A is obtained by the following formula: Li-O bond ratio A = (I ＯＬｉ / I ＯＡｌｌ ) / (N ＯＲ / N ＯＡｌｌ )×100 (%) In the formula, I ＯＬｉ is the proportion of oxygen atoms forming Li-O bonds contained in the modified sulfide solid electrolyte, I ＯＡｌｌ is the proportion of all oxygen atoms contained in the modified sulfide solid electrolyte, N ＯＲ is the number of oxygen atoms that can form Li-O bonds through reaction with the sulfide solid electrolyte, which are contained in one molecule of the compound, and N ＯＡｌｌ is the number of all oxygen atoms contained in one molecule of the compound.

[0039] The Li-O bond ratio A is preferably 40% or more, more preferably 60% or more, still more preferably 70% or more, and even more preferably 80% or more. The upper limit of the Li-O bond ratio A is not particularly limited, but is usually 98% or less.

[0040] In the modified sulfide solid electrolyte of this embodiment, the ratio of the mass of the compound to the mass of the sulfide solid electrolyte is preferably 0.5% to 20.0%, more preferably 0.5% to 15.0%, even more preferably 0.6% to 12.0%, and even more preferably 0.8% to 8.0%. When the ratio of the mass of the compound is within the above range, it is possible to achieve both higher ionic conductivity and ionic conductivity retention rate.

[0041] (Sulfide Solid Electrolyte) The sulfide solid electrolyte used in this embodiment has an argyrodite crystal structure. The argyrodite crystal structure is Li ７ PS ６ It basically has a structural framework and is a crystal structure in which some of the P is replaced with Si. For example, Li is a compositional formula for an argyrodite type crystal structure. ７－ｘ P １－ｙ Si ｙ S ６ Li ７＋ｘ P １－ｙ Si ｙ S ６ Examples include (x = -0.6 to 0.6, y = 0.1 to 0.6). The argyrodite-type crystal structure represented by these compositional formulas is cubic or orthorhombic, preferably cubic, and has peaks that appear mainly at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0° in X-ray diffraction measurements using CuKα rays.

[0042] The chemical formula for the argyrodite type crystal structure is Li ７－ｘ－２ｙ PS ６－ｘ－ｙ Cl ｘ Examples include (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5). The argyrodite crystal structure represented by this compositional formula is preferably cubic, and in X-ray diffraction measurements using CuKα rays, peaks appear mainly at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°. Furthermore, the compositional formula for the argyrodite crystal structure is Li ７－ｘ PS ６－ｘ Ha ｘ(Ha is Cl or Br, and x is preferably 0.2 to 1.8) is also an example. The argyrodite crystal structure represented by this compositional formula is preferably cubic, and in X-ray diffraction measurements using CuKα rays, it has peaks that mainly appear at positions 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0° and 52.0°.

[0043] Here, the sulfide solid electrolyte obtained by the method described later preferably contains lithium atoms, sulfur atoms, phosphorus atoms and halogen atoms, therefore the above "Li ７－ｘ P １－ｙ Si ｙ S ６ Li ７＋ｘ P １－ｙ Si ｙ S ６ In the empirical formula (where x is -0.6 to 0.6 and y is 0.1 to 0.6), if an atom other than a chlorine atom is used as the halogen atom, then "Li ７－ｘ－２ｙ PS ６－ｘ－ｙ Cl ｘ The composition formula (0.8 ≤ x ≤ 1.7, 0 < y ≤ -0.25x + 0.5) may not always be applicable. However, if the diffraction peak is the same as the diffraction peak described as having an "argyrodite-type crystal structure," then the sulfide solid electrolyte obtained by the method described later can be said to preferably have an argyrodite-type crystal structure formed of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms.

[0044] In the sulfide solid electrolyte obtained by the method described later, 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.

[0045] When bromine and iodine, or bromine and chlorine are used as halogen atoms, the composition ratio (molar ratio) of lithium atoms, phosphorus atoms, sulfur atoms, bromine, and chlorine (or iodine) 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 even 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.

[0046] The types of atoms and compositional ratios (molar ratios) constituting the sulfide solid electrolyte obtained by the method described later can be confirmed, for example, by an ICP emission spectrometer. While the composition of the crystalline modified sulfide solid electrolyte in this embodiment can be confirmed by an ICP emission spectrometer as previously described, there may be discrepancies between the actual composition and the measured value due to the presence of oxygen atoms. In such cases, since it has been confirmed that there is almost no discrepancy between the raw materials and their mixing ratios and the composition calculated from those materials and their mixing ratios, the composition can also be considered as the composition calculated from the raw materials and their mixing ratios.

[0047] The shape of the sulfide solid electrolyte obtained by the method described later is not particularly limited, but for example, particulate form can be given. The average particle size (D) of the particulate (crystalline) sulfide solid electrolyte ５０ The average particle size of the sulfide solid electrolyte is preferably 0.1 μm or more and 2.0 μm or less, more preferably 0.2 μm or more and 1.5 μm or less, and even more preferably 0.3 μm or more and 1.1 μm or less. It is preferable that the average particle size of the sulfide solid electrolyte is within the above range because it improves the battery characteristics when used as a lithium-ion battery.

[0048] The sulfide solid electrolyte obtained by the method described later has a particle size (D90) of 90% of the cumulative volume as measured by laser diffraction scattering particle size distribution analysis, preferably between 0.5 μm and 5.0 μm, more preferably between 0.7 μm and 4.0 μm, and even more preferably between 0.8 μm and 3.0 μm. A D90 of the sulfide solid electrolyte within the above range is preferable because it improves the battery characteristics when used in a lithium-ion battery.

[0049] (Manufacturing of Sulfide Solid Electrolytes) The sulfide solid electrolyte used in this embodiment is not particularly limited as long as it contains sulfur atoms and has an argyrodite-type crystal structure. Commercial products can be used as is, or they can be manufactured and used. The manufacturing method for the sulfide solid electrolyte used in this embodiment will be described below. The sulfide solid electrolyte used in this embodiment can be obtained by a manufacturing method that includes, for example, heat-treating the raw materials in a solvent using a pressure vessel or under reflux.

[0050] (Raw Materials) The raw materials can be selected according to the sulfide solid electrolyte to be obtained, and examples include two or more raw materials selected from compounds containing at least one atom of lithium, sulfur, phosphorus, and halogen. Compounds that can be used as raw materials include, for example, lithium sulfide; lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; and diphosphorus trisulfide (P ２ S ３ ), diphosphorus pentasulfide (P ２ S ５ Examples include phosphorus sulfides such as ) and elemental sulfur.

[0051] The aforementioned raw materials may be used in a blending ratio that matches the composition of a sulfide solid electrolyte having a desired crystalline structure. Examples of the blending ratio of lithium sulfide to other raw materials include those described in International Publication No. 2020 / 105737 (see paragraphs

[0024] to

[0028] ), etc. Furthermore, the raw materials can be appropriately selected from the substances exemplified in International Publication No. 2020 / 105737 (see paragraphs

[0020] to

[0022] ), etc.

[0052] (Mixing and Grinding) When heat treatment is performed using a pressure vessel, it is preferable to grind the raw materials in advance to adjust the particle size. When grinding in advance, it is preferable to make the average particle size 20 μm or less, more preferably 15 μm or less, and even more preferably 12 μm or less. A grinder can be used to grind the raw materials, and container-driven grinders such as ball mills and bead mills are preferred, as are pin mills, which have a short processing time and allow for continuous grinding operations.

[0053] It is preferable to pre-mix the raw materials. There are no particular restrictions on the type of mixer that can be used for pre-mixing, but examples of preferred mixers include mechanical agitators, conical screw type mixers such as Nauta mixers, and high-speed agitators such as FM mixers.

[0054] Furthermore, it is preferable to mix and grind the raw materials in a solvent. As the solvent used during mixing and grinding, nonpolar solvents such as hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents, and polar solvents such as solvents containing heteroatoms are preferably used, and it is preferable to use a combination of a nonpolar solvent and a polar solvent. When a combination of a nonpolar solvent and a polar solvent is used, aromatic hydrocarbon solvents, particularly toluene and ethylbenzene, are preferred as the nonpolar solvent, and nitrile solvents that have the property of azeotropic formation with aromatic hydrocarbon solvents such as toluene and are easily removed together with aromatic hydrocarbon solvents such as toluene are preferred as the polar solvent.

[0055] There are no particular restrictions on the equipment used for mixing and grinding the raw materials; generally available equipment can be used. For example, grinders such as planetary ball mills, vibratory mills, rolling mills, and bead mills are preferred.

[0056] (Heat Treatment) When the heating temperature exceeds the boiling point of the organic solvent used, it is preferable to use an autoclave as the pressure vessel used for heat treatment. The heating temperature in the heat treatment can be appropriately selected depending on the type of raw material used, 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 an upper limit of 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.

[0057] When heat treatment is carried out while refluxing an organic solvent, there are no particular limitations on the method; for example, a condenser (e.g., a Liebig condenser) that cools the vapor back into the solvent can be used.

[0058] (Drying) It is preferable that the process includes removing the solvent after heat treatment in the pressure vessel described above. 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. The solvent can be removed by methods such as solid-liquid separation, drying by heating, reduced-pressure drying (vacuum drying), or a combination thereof. The drying by heating can be carried out using a dryer such as a flow-through heater. Preferred flow-through heaters include airflow dryers, spray dryers, and fluidized bed dryers using a medium.

[0059] (Castration) When heat treatment is performed in a pressure vessel, it is preferable to remove the solvent and calcine the heat-treated product. The heating temperature in calcining the heat-treated product can be appropriately selected according to the composition of the sulfide solid electrolyte to be obtained, for example, preferably 300°C or higher, more preferably over 300°C, even more preferably 320°C or higher, even more preferably 350°C or higher, particularly preferably 380°C or higher, with an upper limit of preferably 470°C or lower, more preferably 460°C or lower, even more preferably 450°C or lower, even more preferably 440°C or lower, and particularly preferably 430°C or lower.

[0060] (Compounds having an oxygen atom and an aromatic group) The compounds used in this embodiment have an oxygen atom and an aromatic group. Examples of aromatic groups that the compounds have include: a group obtained by removing one hydrogen atom from a monocyclic aromatic compound such as benzene, toluene, and styrene; a group obtained by removing one hydrogen atom from a polycyclic aromatic compound in which multiple aromatic rings are bonded, such as biphenyl, diphenylmethane (benzylbenzene), diphenylethane (bibenzyl), methylidinetrisphenol, and triphenylcyclohexane; a group obtained by removing one hydrogen atom from a condensed polycyclic aromatic compound in which multiple aromatic rings are condensed, such as naphthalene, phenanthrene, anthracene, pyrene, triphenylene, tetracene, and pentacene, or a group obtained by removing one hydrogen atom from a polycyclic aromatic compound in which an aromatic ring and an alicyclic ring are condensed; and so on. In particular, from the viewpoint of better demonstrating the effects of the present invention, a group obtained by removing one hydrogen atom from a monocyclic aromatic compound is preferred, and a group obtained by removing one hydrogen atom from benzene or toluene is more preferred.

[0061] In the monocyclic aromatic compounds, bonded polycyclic aromatic compounds, and condensed polycyclic aromatic compounds exemplified above, the aromatic group may be one in which at least some of the hydrogen atoms are substituted with an alkyl group, an alkenyl group, a halogen atom, a hydroxyl group, or an amino group. Among these substituents, alkyl groups, alkenyl groups, and halogen atoms are preferred.

[0062] From the viewpoint of better exhibiting the effects of the present invention, the carbon atoms in the compound are preferably 8 or more, more preferably 9 or more, even more preferably 10 or more, with an upper limit of preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less.

[0063] The compound may have one oxygen atom, but it is preferable that the compound has two or more oxygen atoms, as this increases the interaction between the compound and lithium in the sulfide solid electrolyte, making it easier to physically adsorb or form C-S bonds with the sulfide solid electrolyte. When the compound has two or more oxygen atoms, it is preferable that one oxygen atom forms an ether bond and the other oxygen atoms form a heterocycle or a carbonyl group. The formation of an ether bond by one oxygen atom makes the compound bulkier. Furthermore, the formation of a heterocycle or a carbonyl group by the other oxygen atoms increases the electrophilicity of the carbon adjacent to the other oxygen atom, making it easier to physically adsorb or form C-S bonds with the sulfide solid electrolyte. It is believed that these factors enhance the effects of the present invention. Examples of heterocycles include oxirane rings, oxetane rings, tetrahydrofuran rings, 1,3-dioxane rings, 1,4-dioxane rings, furan rings, benzofuran rings, isobenzofuran rings, pyran rings, and benzopyran rings.

[0064] From the viewpoint of having a bulkier structure that interacts more readily with sulfide solid electrolytes, the compound preferably has a group formed by a direct bond between the aromatic group and the oxygen atom of 1, and more preferably has a phenyl ether group.

[0065] From the viewpoint of having a bulkier structure that interacts more readily with sulfide solid electrolytes, the aforementioned compound preferably has a tert-alkyl group and a glycidyl ether group. For example, p-tert-butylphenylglycidyl ether is a preferred example of such a compound.

[0066] Furthermore, from the viewpoint of having a structure that interacts more readily with sulfide solid electrolytes, it is preferable that the compound has a carbonyl group. For example, phenoxyacetone is a preferred example of such a compound.

[0067] The aforementioned compound may be used individually, or two or more compounds may be used in combination.

[0068] (Production of Modified Sulfide Solid Electrolyte) The modified sulfide solid electrolyte of this embodiment is obtained by a production method that includes, for example, mixing a sulfide solid electrolyte having an argyrodite-type crystal structure, a compound having an oxygen atom and an aromatic group, and an organic solvent, and then removing the organic solvent. The sulfide solid electrolyte is the same as the sulfide solid electrolyte described above as being used in the modified sulfide solid electrolyte of this embodiment. Therefore, a commercially available product may be used as the sulfide solid electrolyte, or one produced by the method for producing the sulfide solid electrolyte may be used. Furthermore, the compound may be one of those described in the section above (compound having an oxygen atom and an aromatic group).

[0069] Examples of the organic solvent include, for example, the solvents described as usable in the method for producing the sulfide solid electrolyte. From the viewpoint of promoting the mixing of the sulfide solid electrolyte with the compound having an oxygen atom and an aromatic group, efficiently obtaining a modified sulfide solid electrolyte containing the sulfide solid electrolyte and the compound having an oxygen atom and an aromatic group, and further from the viewpoint of promoting the physical adsorption or binding of the compound having an oxygen atom and an aromatic group to the sulfide solid electrolyte, among the solvents mentioned above, aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, aromatic hydrocarbon solvents, as well as ether solvents, ester solvents, and nitrile solvents are preferred, and aromatic hydrocarbon solvents are more preferred. The organic solvent can be used individually or in combination from among these.

[0070] There are no particular restrictions on the method for mixing a sulfide solid electrolyte, a compound having an oxygen atom and an aromatic group, and an organic solvent; for example, it can be done using a pulverizer, mixer, agitator, etc. There are no particular restrictions on the equipment used for mixing, such as pulverizers, mixers, agitators, etc., and commonly available equipment can be used.

[0071] The removal of the organic solvent can be carried out by the same method as "drying" in the method for producing the sulfide solid electrolyte.

[0072] (Properties of Modified Sulfide Solid Electrolyte) The ionic conductivity of the modified sulfide solid electrolyte of this embodiment is typically 0.1 mS / cm or higher. Furthermore, in the modified sulfide solid electrolyte of this embodiment, by appropriately adjusting the ratio of the mass of the compound having oxygen atoms and aromatic groups to the mass of the sulfide solid electrolyte, the ionic conductivity of the modified sulfide solid electrolyte can be further increased to 0.5 mS / cm or higher, or even 1.0 mS / cm or higher, resulting in a lithium battery with high ionic conductivity and excellent battery performance.

[0073] The ionic conductivity retention rate of the modified sulfide solid electrolyte in this embodiment is preferably 60% or more, more preferably 65% ​​or more, and even more preferably 70% or more. Since high ionic conductivity can be maintained, a lithium battery with excellent battery performance can be obtained.

[0074] (Applications) The modified sulfide solid electrolyte of this embodiment has excellent water resistance and improved ionic conductivity retention, and therefore has excellent battery performance, making it suitable for use in batteries. A battery using the sulfide solid electrolyte of this embodiment is also called a lithium-ion battery, and as will be described later, a battery in which it is used in the electrolyte layer is called an all-solid-state battery. The sulfide solid electrolyte of this embodiment may be used in the positive electrode layer, the negative electrode layer, or the electrolyte layer. Each layer can be manufactured by known methods.

[0075] Furthermore, the above-mentioned battery preferably uses a current collector in addition to the positive electrode layer, electrolyte layer, and negative electrode layer, and known current collectors can be used. For example, a layer coated with Au or the like, which reacts with the above-mentioned solid electrolyte, can be used.

[0076] The present invention will now be specifically described with reference to examples, but the present invention is not limited in any way by these examples.

[0077] (Manufacturing Example 1: Manufacturing of Sulfide Solid Electrolytes) As raw materials, lithium sulfide, phosphorus pentasulfide, lithium bromide, and lithium chloride are prepared under a nitrogen atmosphere in a molar ratio of Li ２ S:P ２ S ５The raw materials were weighed to a ratio of LiBr:LiCl = 47.5:12.5:15.0:25.0 and placed in a stainless steel container. The container was then stirred with a stirring blade to perform a rough mixing. Dehydrated toluene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added as the solvent to a reaction vessel equipped with a stirring blade. The roughly mixed raw materials were then added under a nitrogen atmosphere to disperse the raw materials in the solvent to obtain a slurry (containing approximately 10% by mass of the raw materials). The slurry was mixed and pulverized using a bead mill (LMZ015, manufactured by Ashizawa Finetech Co., Ltd.) while maintaining a nitrogen atmosphere. The slurry obtained above was placed in an autoclave (capacity 500 mL, made of SUS316) equipped with a stirrer and a temperature control jacket, and heated at 180°C for 4 hours while stirring at a rotation speed of 70 rpm to obtain a heat-treated product.

[0078] The slurry containing the heat-treated product was transferred to a Schlenk bottle purged with nitrogen, and the solvent was removed by vacuum drying to obtain a dried product. The dried product was calcined in an electric furnace (model "F-1404-A", manufactured by Tokyo Glass Machinery Co., Ltd.) in a glove box under a nitrogen atmosphere. Specifically, Al ２ O ３ After placing the dried material into a sagger (999-60S, manufactured by Tokyo Glass Machinery Co., Ltd.), the sagger was placed in an electric furnace preheated to 410°C and heated for 2 hours. After that, the sagger was removed from the electric furnace and allowed to cool slowly to obtain powder (calcined material).

[0079] Powder XRD diffraction measurements of the obtained powder revealed peaks mainly at 2θ = 15.5°, 18.0°, 25.0°, 30.0°, 31.4°, 45.3°, 47.0°, and 52.0°, confirming that it is a crystalline sulfide solid electrolyte with an argyrodite-type crystal structure.

[0080] (Example 1: Production of Modified Sulfide Solid Electrolyte) In a 500 mL separable flask equipped with a mechanical stirrer with four baffle plates and stirring blades, 15 g of the sulfide solid electrolyte obtained in Production Example 1 was weighed and added under a nitrogen atmosphere, and 110 g of toluene was added. The mixture was stirred at a rotation speed of 144 rpm to prepare a slurry with a solid content of 12% by mass. To the slurry, 0.75 g of p-tert-butylphenyl glycidyl ether (5% by mass relative to 100% by mass of crystalline sulfide solid electrolyte), which is a compound having oxygen atoms and aromatic groups, was added dropwise over 5 minutes and stirred at a rotation speed of 144 rpm for 24 hours. The stirred slurry was then transferred to a 500 mL Schlenk flask and dried under vacuum at room temperature (23°C). Toluene was removed by drying under vacuum (room temperature: 23°C, drying time: 3 hours) to obtain a powder. The obtained powder was heated under reduced pressure at 60°C for 1 hour using a vacuum pump and an oil bath to obtain a modified sulfide solid electrolyte.

[0081] (Examples 2-5 and Comparative Examples 1 and 2) Modified sulfide solid electrolytes were obtained in the same manner as in Example 1, except that the ratio of the mass of the compound to the mass of the compound and sulfide solid electrolyte was changed as shown in Table 1.

[0082] The modified sulfide solid electrolytes obtained in each example and comparative example were sieved to a size of 300 μm, and these were used as samples to evaluate water resistance (exposure test, measurement of ionic conductivity, and calculation of ionic conductivity retention rate) based on the following method. The results are shown in Table 1.

[0083] (1) Powder XRD Diffraction Measurement Powder X-ray diffraction (XRD) measurement was performed as follows. The sulfide solid electrolyte powder obtained in Production Example 1 was packed into a groove with a diameter of 20 mm and a depth of 0.2 mm, and leveled with glass to prepare the sample. This sample was sealed with XRD Kapton film and measured under the following conditions without exposure to air. Measurement device: D2 PHASER, manufactured by Bruker Co., Ltd. Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα ray (1.5418 Å) Optical system: Focusing method Slit configuration: Solar slit 4°, diverging slit 1 mm, Kβ filter (Ni plate) used Detector: Semiconductor detector Measurement range: 2θ = 10⁻⁶⁰ deg Step width, scan speed: 0.05 deg, 0.05 deg / sec

[0084] (2) Water Resistance Evaluation (2-1) Exposure Test Figure 1 is a schematic diagram of the exposure test apparatus used in the water resistance evaluation. The exposure test apparatus 1 shown in Figure 1 mainly consists of a flask 10 for humidifying nitrogen, a static mixer 20 for mixing humidified nitrogen and unhumidified nitrogen, a dew point meter 30 (VAISALA, M170 / DMT152) for measuring the moisture content of the mixed nitrogen, a double reaction tube 40 for placing the sample to be measured, a dew point meter 50 for measuring the moisture content of the nitrogen discharged from the double reaction tube 40, and a hydrogen sulfide meter 60 (AMI, Model 3000RS) for measuring the hydrogen sulfide concentration contained in the discharged nitrogen, which are connected by tubes (not shown). Note that 6 mm diameter Teflon® tubing was used for the tubes connecting each component. In Figure 1, the tubes are not shown, and instead the flow of nitrogen is indicated by arrows.

[0085] The evaluation procedure was as follows: Approximately 1.0 g of the powder sample 41 was weighed in a nitrogen glow box with a dew point of -70°C, and placed inside the reaction tube 40, sandwiched between quartz wool 42, and then sealed.

[0086] Nitrogen was supplied to the apparatus 1 from a nitrogen source (not shown) at 0.02 MPa. The supplied nitrogen passed through a bifurcated pipe BP, and a portion was supplied to flask 10 for humidification. The remainder was supplied directly to the static mixer 20 as unhumidified nitrogen. The amount of nitrogen supplied to flask 10 was adjusted by a needle valve V. The dew point was controlled by adjusting the flow rates of unhumidified and humidified nitrogen with a mass flow controller (KOFLOC, MODEL 8500) FM. Specifically, the flow rate of unhumidified nitrogen was supplied to the static mixer 20 at 750 to 900 mL / min, and the flow rate of humidified nitrogen was supplied at 1 to 90 mL / min. The mixture was mixed, and the dew point of the mixed gas (a mixture of unhumidified and humidified nitrogen) was confirmed with a dew point meter 30.

[0087] After adjusting the dew point to -45°C, the three-way stopcock 43 was rotated to allow the mixed gas to flow through the reaction tube 40 for two hours. The amount of hydrogen sulfide contained in the mixed gas that passed through the sample 41 was measured using a hydrogen sulfide meter 60. After measurement, the gas was passed through an alkaline trap 70 to remove the hydrogen sulfide. After the sample was exposed for a predetermined time, the supply of humidified nitrogen was stopped, and the reaction tube 40 was sealed with unhumidified nitrogen.

[0088] (2-2) Ionic conductivity The ionic conductivity of the sulfide solid electrolyte before and after the exposure test described in (2-1) above was measured as follows: From the sulfide solid electrolyte, a diameter of 10 mm (cross-sectional area S: 0.785 cm²) was measured. ２ Circular pellets with a height (L) of 0.1 to 0.3 cm were formed as samples. Electrode terminals were taken from the top and bottom of the samples, and measurements were taken at 25°C using the AC impedance method (frequency range: 1 MHz to 100 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. Near the right end of the arc observed in the high-frequency region, the real part Z' (Ω) at the point where -Z'' (Ω) is minimized was taken as the bulk resistance R (Ω) of the electrolyte, and the ionic conductivity σ (mS / cm) was calculated according to the following formula: R = ρ (L / S) σ = 1 / ρ

[0089] (2-3) Ionic Conductivity Retention Rate For each sulfide solid electrolyte, the ionic conductivity retention rate was calculated from the ionic conductivity values ​​measured in (2-2) above, both before and after the exposure test, using the following formula: Ionic Conductivity Retention Rate (%) = (Ionic Conductivity Before Exposure Test / Ionic Conductivity After Exposure Test) × 100

[0090] (3) X-ray photoelectron spectroscopy (XPS) The modified sulfide solid electrolyte obtained in Example 2 was measured by XPS. In a glove box controlled to an Ar atmosphere with a dew point of -60°C or lower, double-sided tape (made of carbon) was attached to a metal substrate, and the powder sample (modified sulfide solid electrolyte) was pressed onto the tape with a spatula (approximately 5 mm in diameter). The spatula used had its surface cleaned with an organic solvent such as acetone. To prevent the sample from being exposed to the atmosphere, it was introduced into the XPS apparatus using a transfer vessel, and the measurement was performed. The apparatus and detailed measurement conditions used for the XPS measurement are shown below.

[0091] XPS system: VersaProbe II (product name), manufactured by ULVAC-PHI, Inc. X-ray source: Monochromatic AlKα rays (1486.6 eV), 50 W, 15 kV X-ray diameter: 200 μm Element measured: O1s Pass energy: 23.5 eV Step energy: 0.1 eV Photoelectron detection angle: 45°

[0092] The analysis software used was "MultiPak" (product name) (manufactured by ULVAC-PHI, Inc.). From each spectrum, the background was subtracted using the Shirley method, and the relative sensitivity coefficient was used from the obtained area intensity to determine the proportion of all oxygen atoms contained in the modified sulfide solid electrolyte of Example 2. ＯＡｌｌ And the proportion of oxygen atoms that form a Li-O bond and have a peak at 531 eV I ＯＬｉ The following was calculated.

[0093] Specific ratio I of the modified sulfide solid electrolyte in Example 2 ＯＬｉ / I ＯＡｌｌThe calculated value was 0.41. The p-tert-butylphenylglycidyl ether, a compound having an oxygen atom and an aromatic group used in Example 2, has oxygen atoms contained in the glycidyl group and oxygen atoms contained in the ether group, and of these, the oxygen atom contained in the glycidyl group can form an O-Li bond through ring opening of the glycidyl group. Therefore, the N of the compound ＯＲ = 1, N Ａｌｌ = 2. Substituting this into the following formula, the Li-O bond ratio A of Example 2 was calculated to be 82%. Li-O bond ratio A = (I ＯＬｉ / I ＯＡｌｌ ) / (N ＯＲ / N ＯＡｌｌ ) × 100 (%) This means that 82% of the p-tert-butylphenyl glycidyl ether used was physically adsorbed or bound to the sulfide solid electrolyte, i.e., a modified sulfide solid electrolyte was formed.

[0094]

[0095] From the results of the examples and comparative examples, it was confirmed that the modified sulfide solid electrolyte of this embodiment exhibits excellent water resistance and improved ionic conductivity retention.

[0096] The modified sulfide solid electrolyte of this embodiment has excellent water resistance and improved ionic conductivity retention, and therefore possesses excellent battery performance. For this reason, it is particularly suitable for use in lithium-ion batteries, especially those used in automotive applications, as well as in information-related equipment and communication devices such as personal computers, video cameras, and mobile phones, and especially in all-solid-state batteries.

[0097] 1. Exposure test apparatus 10. Flask 11. Cooling tank 20. Static mixer 30. Dew point meter 40. Double reaction tube 41. Powdered sample 42. Quartz wool 43. Three-way stopcock 50. Dew point meter 60. Hydrogen sulfide meter 70. Alkali trap BP. Two-way branch pipe V. Needle valve FM. Mass flow controller

Claims

1. A modified sulfide solid electrolyte comprising a sulfide solid electrolyte having an argyrodite-type crystal structure and a compound having an oxygen atom and an aromatic group.

2. The modified sulfide solid electrolyte according to claim 1, wherein the compound has two or more oxygen atoms, one oxygen atom forming an ether bond and the other oxygen atoms forming a heterocycle or a carbonyl group.

3. The modified sulfide solid electrolyte according to claim 1 or 2, wherein the compound has 8 or more carbon atoms.

4. The modified sulfide solid electrolyte according to claim 2 or 3, wherein the compound has a group formed by the direct bonding of the aromatic group and the oxygen atom of claim 1.

5. The modified sulfide solid electrolyte according to any one of claims 1 to 4, wherein the compound has a tert-alkyl group and a glycidyl ether group.

6. The modified sulfide solid electrolyte according to any one of claims 1 to 5, wherein the compound has a carbonyl group.

7. The modified sulfide solid electrolyte according to any one of claims 1 to 6, wherein the ratio of the mass of the compound to the mass of the sulfide solid electrolyte is 0.5% or more and 15.0% or less.

Images