Method for producing sulfide solid electrolyte, and sulfide solid electrolyte

Abstract

The present invention provides a method for producing a sulfide solid electrolyte, with which it is possible to easily produce a sulfide solid electrolyte having excellent oxidation resistance and high ion conductivity, and such a sulfide solid electrolyte by mean of a method for producing a modified sulfide solid electrolyte, the method including mechanically processing a crystalline sulfide solid electrolyte and a dispersant while heating the same, and heating a processed product that is obtained by the mechanical processing, and a sulfide solid electrolyte which has a prescribed specific surface area as measured by a BET method, and a prescribed 10% cumulative volume particle diameter (D10), a prescribed 50% cumulative volume particle diameter (D50), and a prescribed 90% cumulative volume particle diameter (D90) as determined by a laser diffraction / scattering particle size distribution measurement method.

Description

Method for producing sulfide solid electrolyte and sulfide solid electrolyte

[0001] This invention relates to a method for producing a sulfide solid electrolyte and to a sulfide solid electrolyte.

[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 their power sources has become increasingly important. Among batteries, lithium-ion batteries are attracting attention due to their high energy density. Currently, commercially available lithium-ion batteries use electrolytes containing flammable organic solvents, requiring improvements in safety devices to suppress temperature rise during short circuits, as well as improvements in structure and materials to prevent short circuits. In particular, for automotive applications, there is a demand for higher capacity and higher output, making safety considerations for conventional batteries using electrolytes increasingly important. In contrast, lithium-ion batteries that replace the electrolyte with a solid electrolyte, making the battery entirely solid, do not use flammable organic solvents inside the battery, thus simplifying safety devices and offering advantages in manufacturing cost and productivity. Development of batteries in which the electrolyte is replaced with a solid electrolyte layer, so-called all-solid-state batteries, is underway.

[0003] Sulfide solid electrolytes have been conventionally known as solid electrolytes used in solid electrolyte layers. High oxidation-reduction resistance (also simply referred to as "oxidation resistance") is desired for sulfide solid electrolytes, and there is also a growing demand for improved battery performance when used in lithium-ion batteries. As methods to improve these properties, techniques such as coating the surface of the solid electrolyte and using it as a composition containing the solid electrolyte and an organic compound are being investigated.

[0004] For example, Patent Document 1 describes a BET specific surface area of ​​10 m². ２A modified sulfide solid electrolyte has been proposed, comprising a sulfide solid electrolyte containing lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, and at least two compounds selected from compounds such as compounds having two or more heterocycles having carbon atoms and oxygen atoms. Furthermore, Patent Document 2 discloses a sulfide solid electrolyte and a method for processing the same, which allows for easy adjustment of the morphology of the sulfide solid electrolyte to achieve desired properties by adjusting the specific surface area and particle size, by performing at least one mechanical treatment selected from crushing and granulation.

[0005] International Publication No. 2024 / 024825 Brochure International Publication No. 2020 / 105737 Brochure

[0006] The present invention aims to provide a method for producing a sulfide solid electrolyte and a sulfide solid electrolyte that can be easily produced, which has excellent oxidation resistance and high ionic conductivity.

[0007] The present invention relates to a method for producing a sulfide solid electrolyte, which comprises mechanically treating a crystalline sulfide solid electrolyte and a dispersant while heating, and heating the treated product obtained by the mechanical treatment.

[0008] Furthermore, the sulfide solid electrolyte according to the present invention has a specific surface area of ​​20 m² as measured by the BET method. ２ The sulfide solid electrolyte has a particle size distribution of less than 1 / g, and the particle size at 10% of the cumulative volume (D10) is 0.01 μm or more and less than 0.5 μm, the particle size at 50% of the cumulative volume (D50) is 0.5 μm or more and less than 1.6 μm, and the particle size at 90% of the cumulative volume (D90) is 1.6 μm or more and 10 μm or less.

[0009] According to the present invention, it is possible to provide a method for producing a sulfide solid electrolyte and a sulfide solid electrolyte that can be easily produced, which has excellent oxidation resistance and high ionic conductivity.

[0010] This is the X-ray diffraction spectrum of the modified sulfide solid electrolyte obtained in Example 1. These are the CV curves obtained by CV measurement of the sulfide solid electrolytes obtained in Examples 1 and 2 and Comparative Example 1. This is the X-ray diffraction spectrum of the modified sulfide solid electrolyte obtained in Example 2. This is the X-ray diffraction spectrum of the sulfide solid electrolyte obtained in Comparative Example 1. This is an SEM image of the modified sulfide solid electrolyte obtained in Example 1. This is an SEM image of the modified sulfide solid electrolyte obtained in Example 2. This is an SEM image of the sulfide solid electrolyte obtained in Comparative Example 1.

[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 numerical values ​​related to the numerical ranges indicated by "greater than or equal to," "less than or equal to," and "~" can be combined in any way, and the numerical values ​​of the examples can also be used as the upper and lower numerical values. Furthermore, any provisions that are considered preferable can be adopted at will. That is, one provision that is considered preferable can be adopted in combination with one or more other provisions that are considered preferable. Combinations of preferred provisions are considered even more preferable.

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

[0013] Sulfide solid electrolytes, when used as electrode composites to form the positive and negative electrodes of lithium-ion batteries, and also when used to form the electrolyte layer, can undergo oxidation reactions upon contact with the atmosphere, potentially leading to a decrease in battery performance. Therefore, sulfide solid electrolytes require oxidation resistance that can suppress the progression of oxidation reactions.

[0014] As described in Patent Document 1, there have been conventional techniques for modifying sulfide solid electrolytes by coating or incorporating a compound onto the surface of the sulfide solid electrolyte. Patent Document 1 discloses a modified sulfide solid electrolyte that, even if it has a large specific surface area, exhibits excellent coating suitability when applied as a paste during the manufacturing stage of lithium-ion batteries, and can efficiently exhibit excellent battery performance. It also discloses that the electrolyte exhibits performance depending on the compound used for coating, for example, by using a compound having two or more heterocycles with carbon and oxygen atoms, excellent oxidation resistance can be exhibited. Thus, coating or incorporating a compound is a known technique for improving oxidation resistance.

[0015] On the other hand, as the practical application of lithium-ion batteries using sulfide solid electrolytes progresses, the need for sulfide solid electrolytes with excellent oxidation resistance is increasing, and further research and development is underway on methods to achieve oxidation resistance. In the practical application of lithium-ion batteries using sulfide solid electrolytes, the inventors investigated whether excellent oxidation resistance could be obtained without using compounds, rather than using methods that utilize compounds as described in Patent Document 1 above, given the need for cost reduction.

[0016] When sulfide solid electrolytes are used as positive and negative electrodes, or as electrolyte layers, as described above, particle size adjustment by crushing may be performed depending on the application. The inventors of the present invention have found that crushing while heating affects the improvement of oxidation resistance. Further investigation revealed that adding a dispersant during crushing further improves oxidation resistance, resulting in a sulfide solid electrolyte with excellent oxidation resistance. Thus, the phenomenon that crushing a sulfide solid electrolyte to adjust its particle size improves oxidation resistance is not recognized in the prior art, such as in the aforementioned Patent Documents 1 and 2, and is a surprising phenomenon. Furthermore, it was found that heating to remove the dispersant after crushing and adjusting the particle size improves ionic conductivity while maintaining oxidation resistance.

[0017] Based on the above findings, we have developed a manufacturing method for easily producing a sulfide solid electrolyte with excellent oxidation resistance and high ionic conductivity by crushing a crystalline sulfide solid electrolyte while heating it together with a dispersant, and then further heating to remove the dispersant. We have also obtained a sulfide solid electrolyte with excellent oxidation resistance and high ionic conductivity.

[0018] (Regarding various embodiments of this embodiment) The method for producing a modified sulfide solid electrolyte according to the first embodiment of this embodiment is a method for producing a modified sulfide solid electrolyte that includes mechanically treating a crystalline sulfide solid electrolyte and a dispersant while heating, and heating the treated product obtained by the mechanical treatment.

[0019] By mechanically treating a crystalline sulfide solid electrolyte and a dispersant while heating, that is, by mechanically treating a crystalline sulfide solid electrolyte that can be used as a product together with a dispersant while heating, the oxidation resistance can be improved. Subsequently, by heating the treated material obtained from the mechanical treatment, the dispersant can be removed, thereby reducing impurities contained in the sulfide solid electrolyte. On the other hand, it has been confirmed that the ionic conductivity of the treated material obtained by the above mechanical treatment decreases. This is thought to be because a part of the crystalline sulfide solid electrolyte becomes amorphous. However, by heating the treated material, the amorphous part is expected to recrystallize, and the ionic conductivity is expected to improve. In other words, it is thought that heating the treated material improves the ionic conductivity of the obtained crystalline sulfide solid electrolyte by removing the dispersant and promoting the recrystallization of the amorphous part. Furthermore, it is thought that once the oxidation resistance is improved, it will be maintained without decreasing even if recrystallization occurs due to heating.

[0020] As described above, according to the manufacturing method of this embodiment, the oxidation resistance and ionic conductivity of a crystalline sulfide solid electrolyte that can be used as a product are improved by mechanical treatment, etc., and can be said to have been modified by mechanical treatment, etc. The reason why such a modification effect is obtained is not clear, but the modified sulfide solid electrolyte obtained by the manufacturing method of this embodiment has a specific BET specific surface area and a specific particle size distribution, as will be described later. Therefore, it is thought that the shape having a specific BET specific surface area and particle size distribution makes it less likely for contact with moisture in the air to occur, and even if such contact occurs, the progress of the oxidation reaction is easily suppressed, and the deterioration of battery performance is suppressed. Thus, according to the manufacturing method of the modified sulfide solid electrolyte of this embodiment, it is thought that a modified sulfide solid electrolyte with excellent oxidation resistance and high ionic conductivity can be easily produced by improving the oxidation resistance and ionic conductivity of a crystalline sulfide solid electrolyte that can be used as a product.

[0021] The method for producing a modified sulfide solid electrolyte according to the second embodiment of this embodiment is characterized in that, in the first embodiment, the dispersant is an organic solvent containing a heteroatom, and the method for producing a modified sulfide solid electrolyte according to the third embodiment of this embodiment is characterized in that, in the second embodiment, the heteroatom is an oxygen atom.

[0022] If the dispersant is an organic solvent containing a heteroatom, and the heteroatom is an oxygen atom, it becomes easier to improve oxidation resistance and ionic conductivity.

[0023] The fourth embodiment of this present invention is a method for producing a modified sulfide solid electrolyte, wherein, in any one of the first to third embodiments described above, the amount of the dispersant used per 100 parts by mass of the crystalline sulfide solid electrolyte is 0.1 parts by mass or more and 5.0 parts by mass or less.

[0024] By keeping the amount of dispersant used within the above range, oxidation resistance and ionic conductivity can be improved more efficiently.

[0025] The fifth embodiment of this embodiment is a method for producing a modified sulfide solid electrolyte, wherein, in the embodiment described in any one of the first to fourth above, the heating temperature in the mechanical treatment is 25°C or higher and 65°C or lower.

[0026] By keeping the heating temperature during mechanical processing within the above range, it is possible to perform mechanical processing more efficiently, thereby improving oxidation resistance.

[0027] The sixth embodiment of this embodiment is a method for producing a modified sulfide solid electrolyte, wherein, in the embodiment described in any one of the first to fifth above, the heating temperature for heating the treated material is 110°C or higher.

[0028] By heating the processed material to 110°C or higher, the dispersant can be removed more efficiently, and the recrystallization of the amorphous portions due to mechanical treatment can be efficiently promoted, thereby more efficiently improving the ionic conductivity of the resulting crystalline sulfide solid electrolyte.

[0029] The method for producing a modified sulfide solid electrolyte according to the seventh embodiment of this embodiment is characterized in that, in the embodiment described in any one of the first to sixth above, a hydrocarbon solvent is further used in the mechanical treatment, and the method for producing a modified sulfide solid electrolyte according to the eighth embodiment of this embodiment is characterized in that, in the embodiment described in the seventh above, the hydrocarbon solvent is an aliphatic hydrocarbon solvent.

[0030] In mechanical processing, using hydrocarbon solvents, particularly aliphatic hydrocarbon solvents, allows for more uniform mechanical treatment of crystalline sulfide solid electrolytes, and also facilitates the dispersion of dispersants, thus improving oxidation resistance.

[0031] The method for producing a modified sulfide solid electrolyte according to the ninth embodiment of this embodiment is characterized in that, in the embodiment described in any one of the first to eighth of the above, the crystalline sulfide solid electrolyte is obtained by mixing a solid electrolyte raw material with a complexing agent, performing complex decomposition to remove the complexing agent from the electrolyte precursor obtained by the mixing, and heating the complex decomposition product obtained by the complex decomposition.

[0032] By using a crystalline sulfide solid electrolyte obtained by the above-mentioned manufacturing method using a complexing agent as the target of mechanical treatment, the crystalline sulfide solid electrolyte can be manufactured more efficiently, and a sulfide solid electrolyte with high ionic conductivity can be more easily obtained. As a result, the manufacturing method of this embodiment allows for the more efficient acquisition of a sulfide solid electrolyte with higher ionic conductivity.

[0033] The sulfide solid electrolyte according to the tenth embodiment of this present invention has a specific surface area of ​​20 m² as measured by the BET method. ２ This means that the particle size is less than 1 / g, the particle size at 10% of the cumulative volume (D10) according to the laser diffraction scattering particle size distribution method is 0.01 μm or more and less than 0.5 μm, the particle size at 50% of the cumulative volume (D50) is 0.5 μm or more and less than 1.6 μm, and the particle size at 90% of the cumulative volume (D90) is 1.6 μm or more and 10 μm or less.

[0034] The sulfide solid electrolyte of this embodiment can be easily manufactured by the method for manufacturing the modified sulfide solid electrolyte of this embodiment described above. In other words, the sulfide solid electrolyte of this embodiment corresponds to the sulfide solid electrolyte modified by the manufacturing method of this embodiment described above. According to the manufacturing method of this embodiment, as described above, a crystalline sulfide solid electrolyte that can be used as a product can be modified by mechanical treatment or the like to obtain one having the above-mentioned specific BET specific surface area and particle size distribution. As a result, the obtained modified sulfide solid electrolyte, i.e., the sulfide solid electrolyte of this embodiment, has excellent oxidation resistance and high ionic conductivity.

[0035] (Solid Electrolyte) In this specification, "solid electrolyte" means an electrolyte that maintains a solid state at 25°C under a nitrogen atmosphere. The sulfide solid electrolyte in this embodiment is a solid electrolyte that contains at least a sulfur atom, and includes lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, and has ionic conductivity due to the lithium atom.

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

[0037] [Method for producing modified sulfide solid electrolyte] The method for producing a modified sulfide solid electrolyte according to this embodiment is a method for producing a modified sulfide solid electrolyte that includes mechanically treating a crystalline sulfide solid electrolyte and a dispersant while heating, and heating the treated product obtained by the mechanical treatment.

[0038] [Mechanical Treatment] The method for producing a modified sulfide solid electrolyte according to the present embodiment includes mechanically treating a crystalline sulfide solid electrolyte and a dispersant while heating. As the crystalline sulfide solid electrolyte, a commercially available product may be used, or a crystalline sulfide solid electrolyte obtained by the method for producing a sulfide solid electrolyte described later may be used. From the viewpoint of improving ionic conductivity, it is preferable to use a crystalline sulfide solid electrolyte obtained by the method for producing a sulfide solid electrolyte described later. First, the method for producing the crystalline sulfide solid electrolyte used in the method for producing a modified sulfide solid electrolyte according to the present embodiment will be described.

[0039] (Method for Producing Sulfide Solid Electrolyte) The crystalline sulfide solid electrolyte used in the method for producing a modified sulfide solid electrolyte according to the present embodiment is obtained by a production method including: mixing a solid electrolyte raw material and a complexing agent; performing complex decomposition to remove the complexing agent from an electrolyte precursor obtained by the mixing; and heating a complex decomposition product obtained by the complex decomposition. It is preferable that the crystalline sulfide solid electrolyte is obtained by said production method.

[0040] (Solid Electrolyte Raw Material) The solid electrolyte raw material used in the present embodiment is a compound or substance containing one or more selected from a lithium atom, a sulfur atom, a phosphorus atom and a halogen atom. In the present embodiment, it is preferable to use a raw material-containing material containing two or more of these compounds or substances, that is, solid electrolyte raw materials.

[0041] The solid electrolyte raw material includes those containing at least one atom selected from a lithium atom, a sulfur atom, a phosphorus atom and a halogen atom, more specifically, lithium sulfide; phosphorus trisulfide (P ２ S ３ ), phosphorus pentasulfide (P ２ S ５ ) and other phosphorus sulfides; typical preferable examples include raw materials containing at least two types of atoms selected from the above atoms such as the aforementioned, and raw materials consisting of one type of atom selected from the above atoms such as phosphorus molecules and sulfur molecules. Among these, lithium sulfide, phosphorus trisulfide (P ２ S ３ ), phosphorus pentasulfide (P ２ S ５Phosphorus sulfides such as ) are preferred, and among phosphorus sulfides, diphosphorus pentasulfide (P ２ S ５ ) is preferable.

[0042] Furthermore, raw materials include substances containing halogen atoms. For example, lithium halides such as lithium fluoride, lithium chloride, lithium bromide, and lithium iodide; and fluorine (F ２ ), chlorine (Cl ２ ), bromine (Br ２ ), iodine (I ２ Typical examples of halogen molecules include chlorine (Cl) and other halogen molecules. In the manufacturing method of this embodiment, chlorine, bromine and iodine atoms are preferred as halogen atoms in the crystalline sulfide solid electrolyte, and bromine and iodine atoms are more preferred. Considering this, lithium chloride, lithium bromide and lithium iodide are preferred as lithium halides, lithium bromide and lithium iodide are more preferred, and chlorine (Cl) is a typical example of a halogen molecule. ２ ), bromine (Br ２ ), iodine (I ２ ) is preferred, and bromine (Br ２ ), iodine (I ２ ) is preferable.

[0043] In the method for producing a sulfide solid electrolyte, the above-mentioned raw materials should be blended in a ratio that matches the composition of the sulfide solid electrolyte to be obtained. 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 also be appropriately selected from the substances exemplified in International Publication No. 2020 / 105737 (see paragraphs

[0020] to

[0022] ), Japanese Patent Application Publication No. 2024-116072 (see paragraphs

[0101] to

[0109] ), etc.

[0044] (Complexing agent) The complexing agent is a compound that readily forms complexes with solid electrolyte raw materials contained in the raw material mixture. For example, lithium sulfide and phosphorus pentasulfide, which are preferably used as solid electrolyte raw materials, and the Li obtained when these are used. ３ PS ４Furthermore, it is a compound capable of forming complexes with solid electrolyte raw materials containing halogen atoms (hereinafter, these will be collectively referred to as "solid electrolyte raw materials, etc.").

[0045] As a complexing agent, any agent having the above-described properties can be used without particular limitations. Compounds containing heteroatoms with high affinity for lithium atoms, such as nitrogen atoms, oxygen atoms, and chlorine atoms, are particularly preferred, and compounds having groups containing these heteroatoms are even more preferred. This is because these heteroatoms and the groups containing them can coordinate (bond) with lithium.

[0046] The heteroatoms present in the complexing agent molecule have a high affinity for lithium atoms and possess properties that make them readily combine with solid electrolyte raw materials to form complexes (hereinafter also simply referred to as "complexes"). Therefore, by mixing the solid electrolyte raw materials with the complexing agent, a complex is formed, and the dispersion state of the solid electrolyte raw materials, particularly the dispersion state of halogen atoms, is more easily maintained. As a result, it is thought that a sulfide solid electrolyte with high ionic conductivity can be obtained.

[0047] The complex obtained by mixing a solid electrolyte raw material with a complexing agent can be subjected to complex decomposition, which removes the complexing agent from the complex as described later, to obtain a sulfide solid electrolyte. Therefore, the above complex can also be called an electrolyte precursor, and it can be said that an electrolyte precursor can be obtained by mixing a solid electrolyte raw material with a complexing agent.

[0048] As a complexing agent, for example, complexing agents exemplified in International Publication No. 2020 / 105737 can be used. As a complexing agent, among solvents containing the above heteroatoms, a solvent containing a nitrogen atom is preferred, an amine solvent having an amino group is more preferred, and a diamine solvent having two amino groups is even more preferred. Among these, a diamine having two tertiary amino groups is preferred, and a diamine having two tertiary amino groups at both ends is even more preferred. Furthermore, as the above amine solvent, an aliphatic amine is preferred. As such amine solvents, for example, tetramethylethylenediamine, tetraethylethylenediamine, tetramethyldiaminopropane, and tetraethyldiaminopropane are preferred, and considering the ease of availability, tetramethylethylenediamine and tetramethyldiaminopropane are preferred.

[0049] From the viewpoint of efficiently forming the complex, the amount of complexing agent added should preferably have a molar ratio of the amount of complexing agent added to the total molar amount of lithium atoms contained in the raw material, which is 0.1 to 2.0, more preferably 0.5 to 1.5, even more preferably 0.8 to 1.2, and most preferably 1.0.

[0050] (Mixing) The solid electrolyte raw material and the complexing agent can be mixed using equipment such as a mixer or agitator. A pulverizer can also be used if necessary. For example, a mixer or agitator may be used individually, or a mixer or agitator may be used in combination with a pulverizer. For easier mixing, it is preferable to use a mixer or agitator.

[0051] Regarding the equipment used for mixing the raw materials, such as pulverizers, mixers, and agitators, there are no particular restrictions, and generally available equipment can be used. Examples of mixers and agitators include mechanical agitators such as high-speed agitators and dual-arm mixers. High-speed agitators are preferred from the viewpoint of more uniformly mixing the solid electrolyte raw materials and complexing agents and preparing a more homogeneous electrolyte precursor. Examples of high-speed agitators include vertical-axis rotary mixers and horizontal-axis rotary mixers, and either type of mixer may be used.

[0052] As for the grinder, for example, a media-type grinder using a grinding medium can be used. Media-type grinders are broadly classified into container-driven grinders and media-agitated grinders. Examples of container-driven grinders include agitation tanks, grinding tanks, and combinations thereof such as ball mills and bead mills. Examples of media-agitated grinders include impact grinders such as cutter mills, hammer mills, and pin mills; tower-type grinders such as tower mills; agitation tank-type grinders such as attritors, aquamizers, and sand grinders; flow-tank type grinders such as visco mills and pearl mills; flow-tube type grinders; annular-type grinders such as coball mills; continuous dynamic grinders; and various grinders such as single-shaft or multi-shaft kneaders. Among these, considering the ease of adjusting the particle size of the obtained sulfide, ball mills and bead mills, as exemplified as container-driven grinders, are preferred, and planetary types are particularly preferred.

[0053] Furthermore, among the above-mentioned pulverizers, ball mills and bead mills that combine a stirring tank and a pulverizing tank are also preferred. Preferred examples of such pulverizers include those comprising a pulverizer (pulverizer / mixer) such as a ball mill or bead mill, and a temperature-holding tank (reaction vessel), in which the fluid to be pulverized is circulated between the pulverizer (pulverizer / mixer) and the temperature-holding tank (reaction vessel) while performing mechanical processing.

[0054] The mixing of the solid electrolyte raw material and the complexing agent can also be carried out by adding a solvent other than the complexing agent mentioned above. Suitable solvents for mixing include, for example, those exemplified in International Publication No. 2020 / 105737, and more specifically, those exemplified as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, aromatic hydrocarbon solvents, and ether-based solvents.

[0055] (Performing complex decomposition) The method for producing a sulfide solid electrolyte includes, following the above mixing, performing complex decomposition to remove the complexing agent from the electrolyte precursor obtained by mixing. The complex decomposition product obtained by complex decomposition is a sulfide solid electrolyte from which the complexing agent has been removed from the electrolyte precursor, that is, from which the complexing agent has been removed from the complex formed by the solid electrolyte raw material and the complexing agent.

[0056] Complex decomposition can be carried out by methods such as drying by heating, drying under reduced pressure (vacuum drying), or a combination of these. Drying by heating can be carried out by using a dryer, for example. Preferred dryers include flow-through heaters (dryers) such as airflow dryers, spray dryers, and fluidized bed dryers using a medium.

[0057] The heating temperature for complex decomposition should be determined according to the structure of the crystalline sulfide solid electrolyte obtained by further heating the amorphous sulfide solid electrolyte obtained by complex decomposition of the electrolyte precursor. Specifically, the amorphous sulfide solid electrolyte should be subjected to differential thermal analysis (DTA) using a differential thermal analyzer (DTA) under a heating rate of 10°C / min, and the temperature should be set to a range of preferably 5°C or lower, more preferably 10°C or lower, and even more preferably 20°C or lower, starting from the temperature of the peak top of the exothermic peak observed at the lowest temperature. There is no particular limit to the lower limit, but it should be approximately -40°C or higher from the temperature of the peak top of the exothermic peak observed at the lowest temperature. By using such a temperature range, amorphous sulfide solid electrolyte can be obtained by complex decomposition, which removes the complexing agent from the electrolyte precursor more efficiently and reliably.

[0058] The heating temperature for the above-mentioned complex decomposition cannot be specified in general, as it varies depending on the structure of the crystalline sulfide solid electrolyte obtained, as described above. However, it is preferably 135°C or lower, more preferably 130°C or lower, and even more preferably 125°C or lower. There is no particular lower limit, but it is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 105°C or higher.

[0059] (Content of complexing agent in complex decomposition product) The electrolyte precursor obtained by the above complex decomposition becomes an amorphous sulfide solid electrolyte. However, if not all of the complexing agent is removed from the electrolyte precursor, the electrolyte precursor may remain, or the complexing agent may remain in the amorphous sulfide solid electrolyte. In this case, it is preferable that the complexing agent content in the sulfide solid electrolyte be 0% by mass, i.e., no complexing agent is present at all. However, from the viewpoint of efficiently obtaining a sulfide solid electrolyte with high ionic conductivity, it is usually 50% by mass or less, and more preferably 45% by mass or less, 35% by mass or less, 25% by mass or less, 15% by mass or less, 10% by mass or less, and 5% by mass or less, with a lower limit of approximately 0.1% by mass or more.

[0060] Furthermore, similar to the complexing agent, if a solvent is used, some solvent may remain. The solvent content in this case is within the same numerical range as the complexing agent content. In this specification, the content of the complexing agent and the solvent used as needed in the sulfide solid electrolyte was measured by dissolving the powder obtained in the examples, etc., in a mixture of water and pentanol, and measuring it using a gas chromatography (GC) apparatus. The complexing agent and high-boiling point solvent were then quantified using an absolute calibration curve (GC calibration curve method).

[0061] (Drying) The method for producing a sulfide solid electrolyte may include drying after the mixing described above and before the complex decomposition. The mixing may yield a fluid (usually a slurry) containing the electrolyte precursor, excess complexing agent that did not contribute to the formation of the electrolyte precursor, and a solvent used as needed. In such cases, drying can remove the remaining complexing agent that did not contribute to the formation of the electrolyte precursor, as well as the solvent used as needed. By removing the remaining complexing agent and the solvent used as needed in advance, the electrolyte precursor can be heated more directly during the complex decomposition described above, allowing for more efficient separation and removal of the complexing agent, and enabling the preparation of an amorphous sulfide solid electrolyte.

[0062] Drying methods include solid-liquid separation, drying by heating, reduced-pressure drying (vacuum drying), and methods combining these. Solid-liquid separation methods include filtration using a glass filter, solid-liquid separation by decantation, and methods using a centrifuge. Specifically, solid-liquid separation can be easily performed by decantation, in which the suspension is transferred to a container, and after the solid settles, the complexing agent and any solvent used as needed are removed from the supernatant. Alternatively, filtration using a glass filter with a pore size of approximately 10 to 200 μm, preferably 20 to 150 μm, is also easily performed.

[0063] Drying can also be performed by heating using a dryer or the like. Drying by heating can be done in the same way as the drying by heating used in the complex decomposition described above. The temperature conditions for drying should be above the boiling point of the remaining complexing agent or the solvent used as needed. The specific temperature conditions cannot be stated in general, as they may vary depending on the type of complexing agent and solvent used, but are preferably 5°C or higher, more preferably 10°C or higher, even more preferably 15°C or higher, with an upper limit of preferably 110°C or lower, more preferably 85°C or lower, and even more preferably 70°C or lower.

[0064] (Heating) The manufacturing method of this embodiment includes heating the complex decomposition product obtained by the complex decomposition described above. The complex decomposition product is an amorphous sulfide solid electrolyte as described above, and a crystalline sulfide solid electrolyte can be obtained by heating it. Furthermore, heating can promote the complex decomposition of electrolyte precursors that remained undecomposed by the complex decomposition described above, and a crystalline sulfide solid electrolyte with improved crystallinity of the crystalline sulfide solid electrolyte crystallized by the complex decomposition can be obtained. As a result, the crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment has high ionic conductivity, and the modified sulfide solid electrolyte obtained by modifying it also has high ionic conductivity.

[0065] Heating can be done using heating equipment, and depending on the scale of the process, examples include hot plates, vacuum heating devices, argon gas atmosphere furnaces, calcination furnaces, vacuum calcination furnaces, and kilns such as rotary kilns.

[0066] The heating temperature should be determined according to the structure of the crystalline sulfide solid electrolyte, and is preferably higher than the heating temperature used for the complex decomposition described above. Specifically, the amorphous sulfide solid electrolyte obtained by complex decomposition of the electrolyte precursor is subjected to differential thermal analysis (DTA) using a differential thermal analyzer (DTA) under a heating rate of 10°C / min, and the temperature should be set to a range of preferably 5°C or higher, more preferably 10°C or higher, and even more preferably 20°C or higher, starting from the temperature of the peak top of the exothermic peak observed at the lowest temperature. There is no particular upper limit, but it should be around 40°C or lower. By using such a temperature range, the crystalline sulfide solid electrolyte can be obtained more efficiently and reliably.

[0067] The heating temperature during heating cannot be specified in general, as it varies depending on the composition and structure of the resulting crystalline sulfide solid electrolyte. However, it is preferably above 135°C, more preferably above 140°C, and even more preferably above 150°C. There is no particular upper limit, but it is preferably 300°C or less, more preferably 280°C or less, and even more preferably 250°C or less.

[0068] Furthermore, heating is preferably carried out in an inert gas atmosphere (e.g., nitrogen atmosphere, argon atmosphere) because it prevents deterioration (e.g., oxidation) of the crystalline solid electrolyte.

[0069] (Crystalline sulfide solid electrolyte) The crystalline sulfide solid electrolyte obtained by the method for producing a sulfide solid electrolyte (i.e., the crystalline sulfide solid electrolyte preferably used in the modified sulfide solid electrolyte of this embodiment) is a so-called glass ceramic obtained by heating an amorphous sulfide solid electrolyte above its crystallization temperature, and its crystal structure is Li ３ PS ４ Crystal structure, Li ４ P ２ S ６ Crystal structure, Li ７ PS ６ Crystal structure, Li ７ P ３ S １１Examples include crystal structures, and crystal structures having peaks near 2θ = 20.2° and 23.6° (for example, Japanese Patent Publication No. 2013-16423).

[0070] Li ４－ｘ Ge １－ｘ P ｘ S ４ The thio-LISICON Region II type crystal structure (see Kanno et al., Journal of The Electrochemical Society, 148(7) A742-746 (2001)), Li ４－ｘ Ge １－ｘ P ｘ S ４ Other examples include crystal structures similar to the thio-LISICON Region II type (see Solid State Ionics, 177 (2006), 2721-2725). Among the above, the thio-LISICON Region II type crystal structure is preferred for the crystalline sulfide solid electrolyte obtained by the manufacturing method of this embodiment because it provides higher ionic conductivity. Here, "thio-LISICON Region II type crystal structure" refers to Li ４－ｘ Ge １－ｘ P ｘ S ４ Thio-Lisicon Region II type crystal structure, Li ４－ｘ Ge １－ｘ P ｘ S ４ This indicates that the crystal structure is either a thio-LISICON Region II type or a similar crystal structure. As will be discussed later, the thio-LISICON Region II type crystal structure and the similar crystal structures are very similar in structure, as evidenced by their similar diffraction peaks. Therefore, it is technically reasonable to treat the "thio-LISICON Region II type crystal structure" as encompassing both the thio-LISICON Region II type crystal structure and the similar crystal structures.

[0071] Here, the above "Li ４－ｘ Ge １－ｘ P ｘ S ４The notation "thio-LISICON Region II type" for the crystal structure means that it was found in the above-mentioned literature as a crystal structure composed of Li, Ge, P, and S atoms. The sulfide solid electrolyte obtained by the above-mentioned method for producing sulfide solid electrolytes contains lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms, therefore "Li ４－ｘ Ge １－ｘ P ｘ S ４ In the "thio-LISICON Region II" system, "Li ４－ｘ Ge １－ｘ P ｘ S ４ In some cases, the compositional formula cannot be shown as described above. However, if it has the same diffraction peak as the "thiolysicon region type II crystal structure" (including the "similar crystal structure" described above), then the sulfide solid electrolyte obtained by the above method for producing sulfide solid electrolytes can be said to have a thiolysicon region type II crystal structure formed by lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms.

[0072] The crystalline sulfide solid electrolyte obtained by the above method for producing a sulfide solid electrolyte (i.e., the crystalline sulfide solid electrolyte preferably used in the modified sulfide solid electrolyte of this embodiment) may contain the above thiolysicon region II type crystal structure, or it may contain it as the main crystal, but from the viewpoint of obtaining higher ionic conductivity, it is preferable that it contains it as the main crystal. In this specification, "contained as the main crystal" means that the proportion of the target crystal structure in the crystal structure is 80% or more, preferably 90% or more, and more preferably 95% or more. Furthermore, the crystalline sulfide solid electrolyte obtained by the above method for producing a sulfide solid electrolyte may contain crystalline Li ３ PS ４ (β-Li ３ PS ４ It is preferable that it does not contain ).

[0073] In X-ray diffraction measurements using CuKα rays, Li ３PS ４ Diffraction peaks of the crystal structure appear, for example, around 2θ = 17.5°, 18.3°, 26.1°, 27.3°, and 30.0°, Li ４ P ２ S ６ Diffraction peaks of the crystal structure appear, for example, around 2θ = 16.9°, 27.1°, and 32.5°, Li ７ PS ６ The diffraction peaks of the crystal structure appear, for example, around 2θ = 15.3°, 25.2°, 29.6°, and 31.0°, and Li ７ P ３ S １１ Diffraction peaks of the crystal structure appear, for example, around 2θ = 17.8°, 18.5°, 19.7°, 21.8°, 23.7°, 25.9°, 29.6°, and 30.0°, Li ４－ｘ Ge １－ｘ P ｘ S ４ The diffraction peaks of the thio-LISICON Region II type crystal structure appear, for example, around 2θ = 20.1°, 23.9°, and 29.5°, Li ４－ｘ Ge １－ｘ P ｘ S ４ Diffraction peaks for crystal structures similar to the thio-LISICON Region II type appear, for example, around 2θ = 20.2° and 23.6°. Note that these peak positions may vary within a range of ±0.5°.

[0074] The composition ratio of atoms contained in the crystalline sulfide solid electrolyte obtained by the above-described method for producing a sulfide solid electrolyte (i.e., the crystalline sulfide solid electrolyte preferably used in the modified sulfide solid electrolyte of this embodiment) is the composition ratio according to the composition formula corresponding to the various crystal structures described above. More specifically, the mixing ratio (molar ratio) of each atom, i.e., the mixing ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms, is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.6, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.05 to 0.5, and even more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.08 to 0.4. Furthermore, when bromine and iodine are used in combination as halogen atoms, the mixing ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, bromine, and iodine is preferably 1.0 to 1.8: 1.0 to 2.0: 0.1 to 0.8: 0.01 to 0.3: 0.01 to 0.3, more preferably 1.1 to 1.7: 1.2 to 1.8: 0.2 to 0.6: 0.02 to 0.25: 0.02 to 0.25, more preferably 1.2 to 1.6: 1.3 to 1.7: 0.25 to 0.5: 0.03 to 0.2: 0.03 to 0.2, and even more preferably 1.35 to 1.45: 1.4 to 1.7: 0.3 to 0.45: 0.04 to 0.18: 0.04 to 0.18. By setting the mixing ratio (molar ratio) of lithium atoms, sulfur atoms, phosphorus atoms, and halogen atoms within the above range, it becomes easier to obtain a solid electrolyte with higher ionic conductivity having a thiolysiconregion II type crystal structure. Since the modified sulfide solid electrolyte of this embodiment preferably has a thiolysiconregion II type crystal structure, it is also preferable that the crystalline sulfide solid electrolyte obtained by the above method for producing the sulfide solid electrolyte also has a thiolysiconregion II type crystal structure.

[0075] (Content of complexing agent in crystalline sulfide solid electrolyte) The content of complexing agent in the crystalline sulfide solid electrolyte obtained by the method for producing sulfide solid electrolyte (i.e., the crystalline sulfide solid electrolyte preferably used in the modified sulfide solid electrolyte of this embodiment) is preferably 0% by mass, i.e., no complexing agent is contained at all. However, from the viewpoint of efficiently obtaining a sulfide solid electrolyte with high ionic conductivity, it is usually 10% by mass or less, and more preferably 8% by mass or less, 5% by mass or less, 3% by mass or less, or 1% by mass or less, with a lower limit of approximately 0.01% by mass or more.

[0076] Furthermore, similar to the complexing agent, if a solvent is used, some of the solvent may remain. In this case, the solvent content is within the same numerical range as the complexing agent content.

[0077] (Properties of crystalline sulfide solid electrolyte) There are no particular restrictions on the shape of the crystalline sulfide solid electrolyte obtained by the method for producing the sulfide solid electrolyte (i.e., the crystalline sulfide solid electrolyte preferably used in the modified sulfide solid electrolyte of this embodiment), but for example, particulate can be given. The particle size at 10% of the cumulative volume (D10) of the particulate crystalline sulfide solid electrolyte, as measured by laser diffraction scattering particle size distribution analysis, is 0.1 μm or more and less than 1.0 μm as the upper limit, the particle size at 50% of the cumulative volume (D50), i.e., the average particle size, is 1.0 μm or more and less than 5.0 μm as the upper limit, and the particle size at 90% of the cumulative volume (D90) is 5.0 μm or more and less than 15 μm as the upper limit.

[0078] The specific surface area of ​​the crystalline sulfide solid electrolyte obtained by the method for producing sulfide solid electrolytes (i.e., the crystalline sulfide solid electrolyte preferably used in the modified sulfide solid electrolyte of this embodiment) is typically 10 m². ２ / g or more, and even 15m ２ / g or more, 20m ２ / g or more, 25m ２ It will be 1g or more. There is no particular upper limit; for example, 50m ２It is approximately less than or equal to / g. In this specification, the specific surface area is a value measured by the BET method (gas adsorption method), and more specifically, it is a value measured by the BET flow method (three-point method) using nitrogen gas or helium as the adsorbate, in accordance with JIS R 1626:1996. For example, it can be measured using commercially available equipment such as a gas adsorption amount measuring device (e.g., AUTOSORB6 (manufactured by Sysmex Corporation), etc.).

[0079] (Dispersant) The dispersant used in mixing the modified sulfide solid electrolyte in this embodiment is preferably an organic solvent containing heteroatoms such as nitrogen atoms, oxygen atoms, and chlorine atoms, and among these, an organic solvent containing oxygen atoms is preferred.

[0080] Preferred organic solvents containing oxygen atoms used as dispersants include ether solvents and ester solvents, with ether solvents being particularly preferred.

[0081] Preferred ether solvents include, for example, aliphatic ethers such as aliphatic monoethers having one ether linkage, such as dimethyl ether, diethyl ether, dipropyl ether, diisopropyl ether, and tert-butyl methyl ether; aliphatic ethers such as dimethoxymethane, dimethoxyethane, diethylene glycol dimethyl ether (diglym), triethylene oxide glycol dimethyl ether (trilym), and aliphatic polyethers having two or more ether links, such as diethylene glycol and triethylene glycol; alicyclic ethers such as alicyclic monoethers having one ether linkage, such as ethylene oxide, propylene oxide, tetrahydrofuran, tetrahydropyran, and cyclopentyl methyl ether, and alicyclic ethers such as alicyclic polyethers having two or more ether links, such as dimethoxytetrahydrofuran and dioxane; aromatic ethers having one ether linkage, such as phenyl ether, methylphenyl ether, and ethylphenyl ether; and aromatic ethers such as aromatic polyethers having two or more ether links, such as dimethoxybenzene, diethoxybenzene, trimethoxybenzene, and triethoxybenzene.

[0082] As the ether solvent, an aliphatic ether is preferred, and an aliphatic monoether is more preferred. The aliphatic ether has two or more carbon atoms, more preferably three or more, even more preferably five or more, with an upper limit of preferably 12 or less, more preferably 10 or less, and even more preferably 8 or less. The aliphatic ether preferably has linear and branched alkyl groups, and more preferably has branched alkyl groups.

[0083] Furthermore, preferred ester solvents include, for example, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate; and aliphatic esters such as methyl propionate, ethyl propionate, dimethyl oxalate, diethyl oxalate, dimethyl malonate, diethyl malonate, dimethyl succinate, and diethyl succinate.

[0084] The amount of dispersant used is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1.0 part by mass or more, per 100 parts by mass of crystalline sulfide solid electrolyte, with an upper limit of preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less. When the amount of dispersant used is within the above range, the effect of using the dispersant, i.e., the effect of improving oxidation resistance, can be efficiently obtained.

[0085] (Solvent) In the method for producing the modified sulfide solid electrolyte of this embodiment, a solvent can be used in addition to the crystalline sulfide solid electrolyte and the complexing agent when performing the mechanical treatment. A hydrocarbon solvent is preferably used as the solvent.

[0086] Preferred hydrocarbon solvents include aliphatic hydrocarbon solvents such as pentane, hexane, heptane, octane, 2-ethylhexane, decane, undecane, dodecane, and tridecane; alicyclic hydrocarbon solvents such as cyclohexane and methylcyclohexane; and aromatic hydrocarbon solvents such as benzene, toluene, xylene, mesitylene, ethylbenzene, and tert-butylbenzene, with aliphatic hydrocarbon solvents being preferred.

[0087] As the aliphatic hydrocarbon solvent, either a linear or branched solvent can be used, with linear aliphatic hydrocarbon solvents being preferred. Furthermore, the number of carbon atoms in the aliphatic hydrocarbon solvent is preferably 5 or more, more preferably 6 or more, with an upper limit of preferably 14 or less, more preferably 12 or less, and even more preferably 8 or less.

[0088] When using a solvent, the amount used should be such that the content of the crystalline sulfide solid electrolyte on a basis of the total amount of the fluid containing the crystalline sulfide solid electrolyte, dispersant, and solvent is preferably 5.0% by mass or more, more preferably 10.0% by mass or more, even more preferably 15.0% by mass or more, with an upper limit of preferably 30.0% by mass or less, more preferably 20.0% by mass or less, and even more preferably 15.0% by mass or less.

[0089] (Mechanical Processing) There are no particular restrictions on mechanical processing as long as it includes at least one process selected from crushing and granulation. For example, methods using mechanical processing equipment such as agitators and pulverizers can be used. Crushing and granulation can be adjusted by adjusting the peripheral speed of the rotating body of the mechanical processing equipment. For example, crushing can be performed by rotating the rotating body at a low peripheral speed, and granulation can be performed by rotating the rotating body at a high peripheral speed. The appropriate peripheral speed can vary depending on the amount of material to be processed mechanically, so it is not possible to generalize, but the threshold for whether to crush or granulate for a given amount of material can be easily determined by actually performing the processing.

[0090] As for the agitator, it is acceptable to select one from among the agitators exemplified as devices that can be used in mixing the solid electrolyte raw material and the complexing agent in the above-mentioned method for producing a sulfide solid electrolyte. In addition to the agitators exemplified above, other agitators such as high-speed swirling thin-film agitators and high-speed shear agitators can also be mentioned. Among these, a high-speed swirling thin-film agitator (also referred to as a "thin-film swirling high-speed mixer," etc.) is preferred considering the ease of adjusting the crushing and granulation processes.

[0091] As the grinder, it is appropriate to select from among the agitators exemplified as devices that can be used in the mixing of the solid electrolyte raw material and the complexing agent in the above-mentioned method for producing a sulfide solid electrolyte.

[0092] When a solvent is used, the material to be mechanically treated with a crystalline sulfide solid electrolyte and a dispersant becomes a slurry containing the crystalline sulfide solid electrolyte, dispersant, and solvent. Ball mills and bead mills, which combine the above-mentioned stirring tank and grinding tank, are preferably used for mechanical treatment when the fluid to be ground is a slurry.

[0093] As ball mills and bead mills combining a stirring tank and a grinding tank, preferred examples include a grinding machine (grinding mixer) such as a ball mill or bead mill, which can be used in the mixing of solid electrolyte raw materials and complexing agents in the above-described method for producing a sulfide solid electrolyte, and a temperature-holding tank (reaction vessel), wherein the grinding machine performs mechanical processing while circulating the fluid to be ground between the grinding machine (grinding mixer) and the temperature-holding tank (reaction vessel). Furthermore, grinding machines that perform mechanical processing while circulating the fluid are also preferable because they facilitate mechanical processing while maintaining a predetermined heating temperature in the temperature-holding tank.

[0094] The mechanical treatment is carried out while heating. The heating temperature during the mechanical treatment should be below the boiling point of the dispersant, preferably 65°C or lower, more preferably 60°C or lower. The lower limit should be higher than the ambient temperature during the mechanical treatment, preferably 25°C or higher, more preferably 30°C or higher. By setting the heating temperature within the above range, the mechanical treatment can be carried out more efficiently, i.e., oxidation resistance can be improved.

[0095] [Heating the processed material] The method for producing a modified sulfide solid electrolyte according to this embodiment includes heating the processed material obtained by mechanical treatment. The heating of the processed material can be carried out using the heating equipment described in the above-mentioned method for producing a sulfide solid electrolyte, and the heating temperature may be the same as the heating temperature described in the above-mentioned method.

[0096] (Properties of Modified Sulfide Solid Electrolyte) The modified sulfide solid electrolyte obtained by the method for producing the modified sulfide solid electrolyte of this embodiment is a crystalline sulfide solid electrolyte. The crystalline structure of the modified sulfide solid electrolyte is the same as the crystalline structure of the crystalline sulfide solid electrolyte used in the method for producing the modified sulfide solid electrolyte of this embodiment. Therefore, the crystalline structure of the modified sulfide solid electrolyte obtained by the method for producing the modified sulfide solid electrolyte of this embodiment is preferably a thiolysicon region II type crystalline structure.

[0097] The modified sulfide solid electrolyte obtained by the method for producing the modified sulfide solid electrolyte of this embodiment has the same atoms as a crystalline sulfide solid electrolyte, preferably lithium atoms, phosphorus atoms, sulfur atoms, and halogen atoms. The halogen atoms preferably include at least one of chlorine atoms, bromine atoms, and iodine atoms, more preferably include at least one of bromine atoms and iodine atoms, and even more preferably include bromine atoms and iodine atoms.

[0098] Furthermore, the atomic composition ratio contained in the modified sulfide solid electrolyte is the same as the atomic composition ratio described for the crystalline sulfide solid electrolyte obtained by the above-described method for producing the sulfide solid electrolyte (i.e., the crystalline sulfide solid electrolyte preferably used in the modified sulfide solid electrolyte of this embodiment). In the method for producing the modified sulfide solid electrolyte of this embodiment, even after mechanical treatment and heating of the crystalline sulfide solid electrolyte, atoms are not lost and are maintained as they are, so the atomic composition ratio contained in the modified sulfide solid electrolyte and the atomic composition ratio contained in the crystalline sulfide solid electrolyte are substantially the same.

[0099] There is no particular limitation on the shape of the modified sulfide solid electrolyte, and for example, a particulate shape may be mentioned. Regarding the particle size of the particulate modified sulfide solid electrolyte, the particle size at a cumulative volume of 10% (D10) measured by laser diffraction scattering particle size distribution analysis is preferably 0.01 µm or more, more preferably 0.05 µm or more, still more preferably 0.1 µm or more, and the upper limit thereof is preferably less than 0.5 µm, more preferably 0.4 µm or less. The particle size at a cumulative volume of 50% (D50), that is, the average particle diameter, is preferably 0.5 µm or more, more preferably 0.6 µm or more, still more preferably 0.75 µm or more, and the upper limit thereof is preferably less than 1.6 µm, more preferably 1.5 µm or less, still more preferably 1.35 µm or less. Further, the particle size at a cumulative volume of 90% (D90) is preferably 1.6 µm or more, more preferably 2.0 µm or more, still more preferably 3.0 µm or more, and the upper limit thereof is preferably 10 µm or less, more preferably 9.5 µm or less.

[0100] The specific surface area of the modified sulfide solid electrolyte measured by the BET method is preferably 20 m ２ / g or less, more preferably 19.5 m ２ / g or less, still more preferably 18.5 m ２ / g or less, and the lower limit thereof is preferably 5.0 m ２ / g or more, more preferably 7.5 m ２ / g or more, still more preferably 10.0 m ２ / g or more.

[0101] [Sulfide Solid Electrolyte] The sulfide solid electrolyte of the present embodiment has a specific surface area measured by the BET method of 20 m ２ / g or less, a particle size at a cumulative volume of 10% (D10) measured by laser diffraction scattering particle size distribution analysis of 0.01 µm or more and less than 0.5 µm, a particle size at a cumulative volume of 50% (D50) of 0.5 µm or more and less than 1.6 µm, and a particle size at a cumulative volume of 90% (D90) of 1.6 µm or more and 10 µm or less.

[0102] As described above, the sulfide solid electrolyte of this embodiment can be easily manufactured by the method for manufacturing the modified sulfide solid electrolyte of this embodiment. In other words, the sulfide solid electrolyte of this embodiment has the same properties as the modified sulfide solid electrolyte obtained by the method for manufacturing the modified sulfide solid electrolyte of this embodiment. Therefore, the properties, the composition ratio of atoms, and the crystal structure of the sulfide solid electrolyte of this embodiment are the same as those described for the modified sulfide solid electrolyte.

[0103] (Applications) The modified sulfide solid electrolyte obtained by the manufacturing method of this embodiment (which is also the sulfide solid electrolyte of this embodiment) has excellent oxidation resistance, high ionic conductivity, and excellent battery performance, making it suitable for use in batteries. Batteries using the modified sulfide solid electrolyte obtained by the manufacturing method of this embodiment (which is also the sulfide solid electrolyte of this embodiment) are also called lithium-ion batteries, and batteries in which it is used in the electrolyte layer, as described later, are called all-solid-state batteries. The modified sulfide solid electrolyte obtained by the manufacturing method of this embodiment (which is also 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.

[0104] 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.

[0105] 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.

[0106] (Measurement of Powder XRD Diffraction) Powder X-ray diffraction (XRD) measurement was carried out as follows. The powder of the sulfide solid electrolyte obtained in Examples and Comparative Examples was filled into a groove with a diameter of 20 mm and a depth of 0.2 mm, leveled with glass to prepare a sample. This sample was sealed with a Kapton film for XRD, and measured under the following conditions without exposure to air. Measuring apparatus: D2 PHASER, manufactured by Bruker Co., Ltd. Tube voltage: 30 kV Tube current: 10 mA X-ray wavelength: Cu-Kα radiation (1.5418 Å) Optical system: Concentrated method Slit configuration: Solar slit 4°, divergence slit 1 mm, Kβ filter (Ni plate) used Detector: Semiconductor detector Measurement range: 2θ = 10-60 deg Step width, scanning speed: 0.05 deg, 0.05 deg / sec

[0107] (Measurement of Ionic Conductivity) In the present example, ionic conductivity was measured as follows. From the crystalline solid electrolyte obtained in Examples and Comparative Examples, a specimen with a diameter of 10 mm (cross-sectional area S: 0.785 cm ２ ) and a height (L) of 0.1 to 0.3 cm was molded into a circular pellet to serve as a sample. Electrode terminals were attached from the top and bottom of the sample, and measurement was performed by the AC impedance method at 25°C (frequency range: 5 MHz to 0.5 Hz, amplitude: 10 mV) to obtain a Cole-Cole plot. In the vicinity of the right end of the arc observed in the high-frequency side 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 (S / cm) was calculated according to the following formula. R = ρ(L / S) σ = 1 / ρ

[0108] (CV Measurement (Measurement of Oxidation Current)) For CV measurement (measurement of oxidation current), the following CV measurement cell was used. A total of 100 mg of the powder obtained in Examples and Comparative Examples and granular Denka Black (particle diameter: 35 nm, manufactured by Denka Company Limited) (powder : Denka Black (mass ratio) = 85:15) was mixed in a mortar for 10 minutes to obtain powder (1) for measurement. 100 mg of the electrolyte for the separator layer was added to a battery cell with a diameter of 10 mm, and pressed at 400 MPa / cm ２ using a SUS mold.

[0109] The electrolyte for the above separator was synthesized under the following conditions: Li was added to a 1 L reaction vessel with a stirring blade under a nitrogen atmosphere. ２ S: 20.5g, P ２ S ５ 33.1 g of , 10.0 g of LiI, and 6.5 g of LiBr were added. After rotating the stirring blade, 630 g of toluene was introduced and the slurry was stirred for 10 minutes. The reaction vessel was connected to a bead mill capable of circulating operation ("Star Mill LMZ015 (product name)", manufactured by Ashizawa Finetech Co., Ltd., bead material: zirconia, bead diameter: 0.5 mmφ, amount of beads used: 456 g), and a grinding treatment was performed for 45 hours (pump flow rate: 650 mL / min, bead mill peripheral speed: 12 m / s, mill jacket temperature: 45°C). The obtained slurry was dried at room temperature under vacuum (25°C), and then heated (80°C) to obtain an amorphous solid electrolyte white powder. Furthermore, the obtained white powder was heated at 195°C under vacuum for 2 hours to obtain a crystalline solid electrolyte white powder. XRD spectroscopy of the crystalline solid electrolyte revealed crystallization peaks at 2θ = 20.2° and 23.6°, confirming the presence of a thiolysicon region II type crystal structure. The average particle size (D50) of the obtained crystalline solid electrolyte was 4.5 μm, and the ionic conductivity was 5.0 mS / cm.

[0110] On the opposite side of the measuring powder (1) for the electrolyte for the separator layer, a Li / Cu foil (forming a layered structure, where " / " indicates the space between each layer; Li: 9 mmφ × 0.03 mm / Cu: 10 mmφ × 0.01 mm) is placed so that Li faces the separator layer, and the pressure is 40 MPa / cm². ２ A single press was performed for 5 minutes. The cell was secured by four screws with an insulator in between to prevent a short circuit between the measurement powder (1) and the Li / Cu foil, and the screws were tightened with a torque of 8 N·m to obtain the measurement cell.

[0111] The obtained measurement cell was connected to a measuring instrument ("VSP-3 (model number)", manufactured by Biologic Corporation), and a CV curve was obtained under the following conditions. The maximum current in the CV curve was defined as the oxidation current. Measurement temperature: 25°C Sweep speed: 0.5 mV / s Potential measurement range: Open circuit voltage (+2.7V) → +5.0V → +2.7V Number of cycles: 5

[0112] (Measurement of particle size distribution) The particle size at 10% cumulative volume (D10), 50% cumulative volume (D50), and 90% cumulative volume (D90) were measured using a laser diffraction scattering particle size distribution analyzer (HORIBA, LA-950V2 model LA-950S2) as follows, and determined from the resulting integrated particle size distribution curve. Dehydrated toluene (Wako Pure Chemical Industries, special grade) was used as the dispersion medium. 50 mL of the dispersion medium was injected into the flow cell of the apparatus and circulated. The sample to be measured was pre-portioned to 20 mg in a screw vial, 1.3 mL of dibutyl ether was added, and it was sonicated for 5 minutes in a sealed state. Then, approximately 0.1 mL of the prepared sample was added to the flow cell of the apparatus, and the particle size distribution was measured.

[0113] (Measurement of BET specific surface area) For the sulfide solid electrolytes obtained in the examples and comparative examples, the adsorbate was measured using nitrogen and helium with a gas adsorption amount measuring device ("AUTOSORB6", manufactured by Sysmex Corporation) in accordance with JIS R 1626:1996.

[0114] (Preparation Example: Preparation of Crystalline Sulfide Solid Electrolytes) The crystalline sulfide solid electrolytes used in the examples and comparative examples were prepared by the following method.

[0115] In a reaction vessel with a stirring blade (capacity: 1 L), 41.38 g of lithium sulfide, 66.72 g of phosphorus pentasulfide, 13.04 g of lithium bromide, and 20.08 g of lithium iodide were introduced under a nitrogen atmosphere. To this, 246 mL of tetramethylethylenediamine (TMEDA) as a complexing agent and 700 mL of cyclohexane as a solvent were added, and the mixture was stirred by operating the stirring blade. In a bead mill capable of circulating operation ("Labostar Mini LMZ015 (product name)", manufactured by Ashizawa Finetech Co., Ltd.), 456 g of zirconia balls (diameter: 0.5 mmφ) were loaded (bead filling rate in the grinding chamber: 80%), and grinding was performed for 60 minutes while circulating between the above reaction vessel and the grinding chamber under the conditions of pump flow rate: 550 mL / min, peripheral speed: 8 m / s, and mill jacket temperature: 20°C to obtain an electrolyte precursor (complex) slurry. The obtained electrolyte precursor (complex) slurry was immediately dried under vacuum at room temperature (23°C) to obtain a powdered electrolyte precursor (complex). The obtained electrolyte precursor (complex) was dried at 110°C under reduced pressure for 6 hours to obtain an amorphous sulfide solid electrolyte. Then, it was heated under reduced pressure at 180°C for 2 hours to obtain a crystalline sulfide solid electrolyte.

[0116] (Example 1) In a reaction vessel with a stirring blade (capacity: 1 L), 120 g of the crystalline sulfide solid electrolyte obtained in the above preparation example, 2.4 g of diisopropyl ether as a dispersant, and 545 g of heptane as a solvent were added. After rotating the stirring blade, a bead mill capable of circulating operation ("Labostar Mini LMZ015 (product name)", manufactured by Ashizawa Finetech Co., Ltd.), which was connected to the reaction vessel, was used for mechanical treatment for 5 minutes under predetermined conditions (bead material: zirconia, bead diameter: 0.3 mmφ, amount of beads used: 456 g, pump flow rate: 650 mL / min, peripheral speed: 12 m / s, mill jacket temperature: 40 °C). The treated material was dried under vacuum (room temperature: 23 °C) to obtain a powder, and then heated under reduced pressure at 180 °C for 2 hours to obtain a modified sulfide solid electrolyte.

[0117] The ionic conductivity of the obtained modified sulfide solid electrolyte was measured to be 4.28 (mS / cm). Furthermore, the obtained modified sulfide solid electrolyte was subjected to powder XRD diffraction using the method described above. The X-ray diffraction spectrum is shown in Figure 1. As shown in Figure 1, crystallization peaks were mainly detected at 2θ = 20.2° and 23.6° in the X-ray diffraction spectrum, confirming that it is a crystalline sulfide solid electrolyte with a thiolysicon region II type crystal structure.

[0118] When the particle size distribution of the obtained modified sulfide solid electrolyte was measured using the method described above, the particle sizes (D10), (D50), and (D90) were 0.11 μm, 0.92 μm, and 2.9 μm, respectively, and the BET specific surface area was 18 m². ２ The result was / g. Furthermore, the obtained modified sulfide solid electrolyte was subjected to CV measurement using the method described above. The results are shown in Figure 2. The oxidation current was 0.27 mA.

[0119] (Example 2) A modified sulfide solid electrolyte was obtained in the same manner as in Example 1, except that the mechanical treatment time was 10 minutes. The particle size distribution, BET specific surface area, and oxidation current of the obtained modified sulfide solid electrolyte are shown in Table 1. The X-ray diffraction spectrum is shown in Figure 3, and the results of the CV measurement are shown in Figure 2. From the X-ray diffraction spectrum, it was confirmed that the crystalline sulfide solid electrolyte has a thiolysicon region type II crystal structure.

[0120] (Comparative Example 1) Comparative Example 1 is the crystalline sulfide solid electrolyte obtained in the preparation example in Example 1, in which no mechanical treatment or heating of the treated material was performed. The particle size distribution, BET specific surface area, and oxidation current of the crystalline sulfide solid electrolyte are shown in Table 1. The X-ray diffraction spectrum is shown in Figure 4, and the results of the CV measurement are shown in Figure 2. From the X-ray diffraction spectrum, it was confirmed that the crystalline sulfide solid electrolyte has a thiolysicon region type II crystal structure.

[0121] *1, DiPE: Diisopropyl ether

[0122] From the results of the examples and comparative examples, it was confirmed that the method for producing modified sulfide solid electrolytes of this embodiment can produce sulfide solid electrolytes having higher ionic conductivity (i.e., the sulfide solid electrolyte of this embodiment). Furthermore, the oxidation currents were 0.27 mA and 0.29 mA, which are smaller than the oxidation current of 0.42 mA in the comparative example, confirming excellent oxidation resistance. Thus, it was confirmed that by performing mechanical treatment using a dispersant and then heating, the ionic conductivity is improved and the oxidation current is reduced, i.e., oxidation resistance is improved.

[0123] Furthermore, it has been confirmed that the modified sulfide solid electrolyte obtained by the method for producing the modified sulfide solid electrolyte of this embodiment (i.e., the sulfide solid electrolyte of this embodiment) exhibits a particularly small particle size distribution for D50 and D90, resulting in a smaller average particle size, fewer coarse particles, and a more uniform particle size. This can also be confirmed by scanning electron microscope (SEM) images. The sulfide solid electrolytes obtained in Examples 1 and 2 and Comparative Example 1 were observed using a scanning electron microscope (SEM). SEM images of Examples 1 and 2 and Comparative Example 1 are shown in Figures 5 to 7, respectively. Figures 5 and 6, which are SEM images of Examples 1 and 2, show that the particle size is generally smaller than that of Comparative Example 1 (Figure 7), and that no aggregation or other issues have occurred. As a result, it is considered that D50 and D90 particles, in particular, have become smaller.

[0124] According to the manufacturing method of this embodiment, a sulfide solid electrolyte with excellent oxidation resistance and high ionic conductivity can be easily produced. Therefore, the modified sulfide solid electrolyte obtained by the manufacturing method of this embodiment, i.e., the sulfide solid electrolyte of this embodiment, is suitably used in batteries, particularly lithium-ion batteries used in information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones, as well as vehicles such as automobiles, and especially in all-solid-state batteries.

Claims

1. A method for producing a modified sulfide solid electrolyte, comprising mechanically treating a crystalline sulfide solid electrolyte and a dispersant while heating them, and heating the treated product obtained by the mechanical treatment.

2. The method for producing a modified sulfide solid electrolyte according to claim 1, wherein the dispersant is an organic solvent containing a heteroatom.

3. The method for producing a modified sulfide solid electrolyte according to claim 2, wherein the heteroatom is an oxygen atom.

4. A method for producing a modified sulfide solid electrolyte according to any one of claims 1 to 3, wherein the amount of the dispersant used per 100 parts by mass of the crystalline sulfide solid electrolyte is 0.1 parts by mass or more and 5.0 parts by mass or less.

5. A method for producing a modified sulfide solid electrolyte according to any one of claims 1 to 4, wherein the heating temperature in the mechanical treatment is 25°C or higher and 65°C or lower.

6. A method for producing a modified sulfide solid electrolyte according to any one of claims 1 to 5, wherein the heating temperature for heating the treated material is 110°C or higher.

7. A method for producing a modified sulfide solid electrolyte according to any one of claims 1 to 6, wherein a hydrocarbon solvent is further used in the mechanical treatment.

8. The method for producing a modified sulfide solid electrolyte according to claim 7, wherein the hydrocarbon solvent is an aliphatic hydrocarbon solvent.

9. A method for producing a modified sulfide solid electrolyte according to any one of claims 1 to 8, wherein the crystalline sulfide solid electrolyte is obtained by mixing a solid electrolyte raw material with a complexing agent, performing complex decomposition to remove the complexing agent from the electrolyte precursor obtained by the mixing, and heating the complex decomposition product obtained by the complex decomposition.

10. The specific surface area measured by the BET method is 20 m². ２ A sulfide solid electrolyte having a particle size distribution of less than 1 / g, with a particle size of 0.01 μm or more and less than 0.5 μm at 10% of the cumulative volume (D10) measured by laser diffraction scattering particle size distribution analysis, a particle size of 0.5 μm or more and less than 1.6 μm at 50% of the cumulative volume (D50) being 0.5 μm or more and less than 1.6 μm, and a particle size of 1.6 μm or more and 10 μm or less at 90% of the cumulative volume (D90) being 1.6 μm or more and 10 μm or less.

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