Method for manufacturing sulfide solid electrolyte

Abstract

The present invention relates to a method for producing a sulfide solid electrolyte, the method comprising heating / melting a mixture of sulfide solid electrolyte raw material and cooling / solidifying the acquired melt to obtain a sulfide solid electrolyte. The mixture of sulfide solid electrolyte raw material contains Li2S and P2S5. When the volume average particle diameter of Li2S measured by the laser diffraction particle size distribution measurement method is noted as A, and the volume average particle diameter of P2S5 measured by the laser diffraction particle size distribution measurement method is noted as B, A<B is satisfied.

Description

Method for producing sulfide solid electrolyte

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

[0002] Lithium ion secondary batteries are widely used in portable electronic devices such as mobile phones and laptop computers. Conventionally, liquid electrolytes have been used in lithium ion secondary batteries. Meanwhile, all-solid-state lithium ion secondary batteries, which use solid electrolytes as the electrolyte for lithium ion secondary batteries, have been attracting attention in recent years due to their potential for improved safety, high-speed charging and discharging, and compact casings. Examples of solid electrolytes used in all-solid-state lithium ion secondary batteries include sulfide solid electrolytes.

[0003] When a sulfide solid electrolyte is produced by a melting method, the raw materials for the sulfide solid electrolyte volatilize when the raw materials are heated. ２ S ５ Since sulfide has a low melting point and boiling point and is easily volatilized, there is a problem that the sulfide solid electrolyte obtained after heating and melting may deviate from the target composition (hereinafter also referred to as composition deviation).

[0004] In contrast to this, for example, in Patent Document 1, a composite compound containing lithium, phosphorus, and sulfur is melted and vitrified, and then the molten glass is rapidly cooled, thereby reducing P during melting. ２ S ５ Patent Literature 2 discloses a method for preventing the volatilization of only the components. Patent Literature 2 also discloses a method for suppressing the volatilization of raw materials and suppressing composition deviation by heating and compressing solid raw materials to form a melt.

[0005] Japanese Patent Publication No. 2012-043654 Japanese Patent No. 5640665

[0006] However, the method disclosed in Patent Document 1 requires the composite compound to be synthesized in advance, which complicates the manufacturing process. Furthermore, it is not possible to suppress the volatilization of the raw materials during melting. Furthermore, the method disclosed in Patent Document 2 requires the raw materials to be compressed, which makes the equipment structure very complicated, making it difficult to mass-produce solid electrolytes.

[0007] In view of the above, an object of the present invention is to provide a method for producing a sulfide solid electrolyte by a melting method, which can suppress volatilization of raw materials during melting without using complicated equipment, and can produce a sulfide solid electrolyte having a target composition.

[0008] As a result of extensive investigation, the inventors have found that Li, which is used as a raw material for the sulfide solid electrolyte, ２ The average particle size of S is P ２ S ５ The present inventors have found that by making the average particle size smaller than that of the raw material, volatilization of the raw material during melting can be suppressed, and have completed the present invention.

[0009] That is, the present invention is a method for producing a sulfide solid electrolyte, which comprises heating and melting a mixture of sulfide solid electrolyte raw materials, and cooling and solidifying the resulting melt to obtain a sulfide solid electrolyte, wherein the mixture of sulfide solid electrolyte raw materials contains Li ２ S and P ２ S ５ and wherein the Li ２ The volume-based average particle size of S measured by a laser diffraction particle size distribution measurement method is A, and the P ２ S ５ The present invention relates to a method for producing a sulfide solid electrolyte, in which A<B is satisfied, where B is the volume-based average particle size measured by the laser diffraction particle size distribution measurement method described above.

[0010] According to the present invention, it is possible to suppress volatilization of raw materials during melting and to produce a sulfide solid electrolyte having a target composition without using complicated equipment.

[0011] Fig. 1 is a flow diagram showing a method for producing a sulfide solid electrolyte according to the present embodiment. Fig. 2A is a micrograph of a mixture in Example 1. Fig. 2B is a micrograph of a mixture in Example 4.

[0012] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be implemented with any modifications within the scope of the present invention. The term "to" indicating a numerical range is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0013] <<Method for Producing Sulfide Solid Electrolyte>> A production method according to this embodiment is a method for producing a sulfide solid electrolyte, which comprises heating and melting a mixture of sulfide solid electrolyte raw materials, and cooling and solidifying the resulting melt to obtain a sulfide solid electrolyte, and the mixture of sulfide solid electrolyte raw materials contains Li ２ S and P ２ S ５ and wherein the Li ２ The volume-based average particle size of S measured by a laser diffraction particle size distribution measurement method is A, and the P ２ S ５ The particle size distribution measuring method of the present invention is characterized in that, when the volume-based average particle size measured by the laser diffraction particle size distribution measuring method is B, the relationship A<B is satisfied.

[0014] As shown in FIG. 1, the manufacturing method according to this embodiment includes the following steps: (Step S1) Li ２ S and P ２ S ５ (Step S2) A step of heating and melting the mixture of sulfide solid electrolyte raw materials containing the above-mentioned components; and (Step S3) A step of cooling and solidifying the obtained melt to obtain a sulfide solid electrolyte. Each step will be described below.

[0015] <Step S1: Li ２ S and P ２ S ５ a step of heating and melting a mixture of sulfide solid electrolyte raw materials containing Li ２ S and P ２ S ５ A mixture of sulfide solid electrolyte raw materials containing Li ２ S and P ２ S ５ The mixture (hereinafter also referred to as the present mixture) of a sulfide solid electrolyte raw material (hereinafter also referred to as the present raw material) containing at least Li as one of the raw materials contained in the present raw material. ２ S powder and P as one of the raw materials contained in this raw material ２ S ５The mixture may be obtained by mixing the raw materials with a powder of the above. The mixture may be heated and melted by being charged into a heating furnace as a mixed mixture. Alternatively, the raw materials may be charged into a heating furnace and mixed to obtain the mixture, and then the mixture may be heated and melted. In particular, from the viewpoint of increasing the homogeneity of the resulting sulfide solid electrolyte, it is preferable to charge the mixture into a heating furnace and heat and melt it.

[0016] In the production method according to this embodiment, the Li contained in the mixture ２ The volume-based average particle size of S measured by a laser diffraction particle size distribution measurement method is A, and P contained in this mixture is ２ S ５ When the volume-based average particle size measured by the laser diffraction particle size distribution measurement method is B, the relationship A<B is satisfied. ２ S ５ Many Li atoms on the particle surface ２ It is believed that the synthesis of a sulfide solid electrolyte first proceeds at the interface where the particles come into contact with each other, and the synthesis reaction between the raw materials can be promoted before the raw materials volatilize, thereby suppressing the volatilization of the raw materials during melting and obtaining a sulfide solid electrolyte having the desired composition. This is because the synthesis of a sulfide solid electrolyte first proceeds at the interface where the particles come into contact with each other, and if there is a non-contact area, the reaction will not proceed and the particles will volatilize. ２ The particle diameter of S is P ２ S ５ By making the particle size smaller than that of Li ２ S particle is P ２ S ５ It becomes easier to penetrate into the gaps around the particles, ２ S ５ Many Li atoms on the particle surface ２ It is presumed that the reaction is promoted by contacting the S particles.

[0017] Also, P ２ S ５ The average particle size of Li ２ By making the average particle size larger than that of S, the P ２ S ５ Since scattering of P can be suppressed ２ S ５ It is possible to prevent P from coming into contact with the furnace wall and volatilizing.２ S ５ By increasing the average particle size, the temperature rise can be suppressed and the progress of volatilization can be inhibited.

[0018] The above A is preferably 0.1 to 50 μm. Also, the above A is preferably 0.1 μm or more, more preferably 1 μm or more, and particularly preferably 2 μm or more. Also, the above A is preferably 50 μm or less, more preferably 40 μm or less, and particularly preferably 30 μm or less.

[0019] The above B is preferably 50 μm or more (B≧50 μm), more preferably 75 μm or more, even more preferably 100 μm or more, and particularly preferably 150 μm or more. Furthermore, the above B is more preferably 2000 μm or less, even more preferably 1750 μm or less, and particularly preferably 1500 μm or less. Furthermore, the above B may be 50 to 2000 μm.

[0020] The ratio of A to B (A / B) is preferably 0.5 or less (A / B≦0.5). A / B is more preferably 0.4 or less, and particularly preferably 0.3 or less. A / B is more preferably 0.0025 or more, even more preferably 0.005 or more, and particularly preferably 0.0075 or more. A / B may be 0.0025 to 0.5.

[0021] Li in this mixture ２ S, P ２ S ５ The volume-based average particle size measured by the laser diffraction particle size distribution measurement method is the average particle size of Li as one of the raw materials measured before mixing. ２ S powder and P ２ S ５ The average particle size of the powder is D50 of the volume-based particle size distribution measured by a laser diffraction particle size distribution measurement method, and can be measured, for example, using an MT3000II (manufactured by Microtrac).

[0022] The mixture preferably also contains lithium halide (LiHa) as described below. ２ S powder and P ２ S ５In addition to the powder of LiHa, it is preferable to mix it with a powder of LiHa, which is one of the raw materials contained in the raw material. In this case, the volume-based average particle size of the LiHa powder measured by a laser diffraction particle size distribution measurement method is preferably 0.1 to 2000 μm. Furthermore, the average particle size is preferably 0.1 μm or more, more preferably 1 μm or more, and particularly preferably 2 μm or more. Furthermore, the average particle size is preferably 2000 μm or less, more preferably 1750 μm or less, and particularly preferably 1500 μm or less.

[0023] The raw material is the above-mentioned Li ２ S and P ２ S ５ As long as it contains the above, one or more other various raw materials can be used, and the sulfide solid electrolyte obtained using these may also be various sulfide solid electrolytes.

[0024] Each of the raw materials contained in the present raw material may be synthesized or commercially available. Each raw material may be in powder form, or the present raw material itself including each raw material may be in powder form. Furthermore, the present raw materials may be subjected to a known pretreatment. That is, the manufacturing method according to this embodiment may appropriately include, prior to step S1, at least one of a step of manufacturing the present raw material and a step of pretreating at least some of the raw materials of the present raw material as step 0, which is a step of preparing the present raw material.

[0025] Li ２ S and P ２ S ５ The sulfide solid electrolyte raw material containing the above may be appropriately determined depending on the composition of the sulfide solid electrolyte to be obtained.

[0026] One of the raw materials contained in the raw material includes, for example, a substance such as an alkali metal element (R) and an elemental sulfur (S). Examples of the alkali metal element (R) include substances such as an elemental lithium (Li), an elemental sodium (Na), and an elemental potassium (K). When the sulfide solid electrolyte is applied to a lithium ion secondary battery, the alkali metal element (R) preferably includes a substance such as an elemental lithium (Li).

[0027] As the alkali metal element (R) source, an appropriate combination of an alkali metal element, a substance containing an alkali metal element, such as a compound containing an alkali metal element, etc. can be used. When the alkali metal element (R) is lithium element (Li), an appropriate combination of Li-containing substances, such as Li element, a compound containing Li, etc. can be used as the lithium element source. As described above, the raw material contains at least Li. ２ It contains S, which can be a source of elemental lithium (Li).

[0028] As a substance containing lithium element (Li), the above-mentioned lithium sulfide (Li ２ In addition to lithium iodide (LiI), lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２ Examples of the substance containing lithium element (Li) include lithium compounds such as lithium hydroxide (LiOH), lithium ion (LiO), and metallic lithium. The substance containing lithium element (Li) may be used alone or in combination of two or more.

[0029] As the substance containing lithium element (Li), it is preferable to use lithium sulfide from the viewpoint of obtaining a sulfide material. Furthermore, when the obtained sulfide solid electrolyte contains a halogen element, it is also preferable to include lithium halide (LiHa, where Ha is a halogen element) as the substance containing lithium element (Li). Lithium halide will be described later.

[0030] As the sulfur element (S) source, a suitable combination of substances containing S, such as simple S or compounds containing S, can be used. The sulfur element (S) containing substance may be used alone or in combination of two or more. As described above, the raw material contains at least Li ２ S and P ２ S ５ These can be a source of elemental sulfur (S). ２ S is a compound that contains both a substance containing sulfur element (S) and the above-mentioned substance containing lithium element (Li). ２ S ５is a compound that serves as both a substance containing sulfur element (S) and a substance containing phosphorus element (P) as described below.

[0031] Substances containing sulfur (S) include phosphorus pentasulfide (P ２ S ５ ), for example, diphosphorus trisulfide (P ２ S ３ ), other sulfur compounds containing phosphorus, elemental sulfur, and compounds containing sulfur. ２ S, CS ２ , iron sulfide (FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S, etc.), bismuth sulfide (Bi ２ S ３ ), copper sulfide (CuS, Cu ２ S, Cu １－ｘ S, etc.

[0032] From the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte, it is preferable that the raw material further contains phosphorus (P). As a source of phosphorus (P), a suitable combination of substances containing P, such as simple P or a compound containing P, can be used. One type of substance containing phosphorus (P) may be used, or two or more types may be used in combination. As described above, the raw material contains at least P. ２ S ５ which can be a source of elemental phosphorus (P).

[0033] The substance containing phosphorus (P) is the above-mentioned diphosphorus pentasulfide (P ２ S ５ ), for example, diphosphorus trisulfide (P ２ S ３ ) and other phosphorus sulfides, sodium phosphate (Na ３ P.O. ４ ) and elemental phosphorus.

[0034] When the present mixture obtained by mixing the present raw materials is charged into a heating furnace and then heat-melted, the mixing ratio of the present raw materials may be determined appropriately depending on, for example, the composition of the target sulfide solid electrolyte. Furthermore, when the present mixture is obtained by charging the present raw materials into a heating furnace and then mixing them, and then heat-melting is performed, the mixing ratio of the present raw materials may be determined appropriately depending on, for example, the composition of the target sulfide solid electrolyte.

[0035] The mixing ratio or input ratio of the raw materials is not particularly limited. For example, the molar ratio S / R of sulfur (S) to alkali metal (R) in the mixture is preferably 0.65 / 0.35 or less, and more preferably 0.5 / 0.5 or less, from the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte.

[0036] When the present mixture obtained by mixing the present raw materials is charged into a heating furnace, it is preferable to mix the present raw materials in a predetermined stoichiometric ratio according to the present raw materials to obtain a mixture.

[0037] The method for mixing the raw materials to obtain the mixture is not particularly limited, but examples thereof include mixing in a mortar, mixing using a media such as a planetary ball mill, and medialess mixing such as a pin mill, a powder mixer, or airflow mixing.

[0038] When mixing or charging the raw material, the combination of the substance containing an alkali metal element and the substance containing sulfur element is as follows: Li ２ S and P ２ S ５ In addition to the combination of Li and Li, when the obtained sulfide solid electrolyte has a halogen element as a constituent element, ２ S and P ２ S ５ and LiHa.

[0039] Li ２ S and P ２ S ５ In the combination of these, the molar ratio of Li to P, Li / P, is preferably 40 / 60 to 88 / 12, and more preferably 50 / 50 to 88 / 12. ２ S ５ Li ２ By adjusting the mixing ratio or the input ratio so that the amount of Li is relatively small compared to S, ２ Melting point of S is２ S ５ Since the boiling point of the sulfur component is low, it is easy to suppress the volatilization of the sulfur component and the phosphorus component during the heat treatment.

[0040] On the other hand, since lithium sulfide is expensive, in order to reduce the production cost of the sulfide solid electrolyte, lithium compounds other than lithium sulfide, metallic lithium, etc. may be used in addition to lithium sulfide. Specifically, in this case, the raw material may be a substance containing Li, such as metallic lithium, lithium halide (LiHa), or lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２ These may be used alone or in combination of two or more.

[0041] The raw material may contain other substances (compounds, etc.) in addition to the above substances depending on the composition of the target sulfide solid electrolyte or as additives, etc. For example, when producing a sulfide solid electrolyte containing a halogen element such as F, Cl, Br, or I, the raw material preferably contains a halogen element (Ha). In this case, the raw material preferably contains a compound containing a halogen element.

[0042] Examples of compounds containing a halogen element include lithium halides such as lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), phosphorus halides, phosphoryl halides, sulfur halides, sodium halides, and boron halides. Among these, from the viewpoint of reactivity, lithium halides are preferred, LiCl, LiBr, and LiI are more preferred, and LiCl and LiBr are even more preferred. These compounds may be used alone or in combination of two or more.

[0043] In addition, since an alkali metal halide such as lithium halide is also a compound containing an alkali metal element such as Li, it can also serve as a source of the alkali metal element (R) in the raw material.

[0044] When the mixture contains a halogen element (Ha) and a phosphorus element (P), the molar equivalent of the halogen element (Ha) relative to the phosphorus element (P) in the mixture is preferably 0.2 to 4 molar equivalents, more preferably 0.5 to 3 molar equivalents. From the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte, the molar equivalent of the halogen element is preferably 0.2 molar equivalents or more, more preferably 0.5 molar equivalents or more. Furthermore, from the viewpoint of the stability of the resulting sulfide solid electrolyte, the molar equivalent of the halogen element is preferably 4 molar equivalents or less, more preferably 3 molar equivalents or less. When the powder raw material contains two or more halogen elements, it is preferable that the total content thereof satisfies the above-mentioned molar equivalent range.

[0045] The sulfide solid electrolyte obtained by the production method according to this embodiment may be amorphous depending on the purpose. When the obtained sulfide solid electrolyte contains an amorphous phase, the amorphous phase is easily formed even if the quenching rate is reduced during quenching, and from the viewpoint of reducing the equipment load, SiS is used as the raw material. ２ , B ２ S ３ , GeS ２ , Al ２ S ３ These may be used alone or in combination of two or more.

[0046] From the viewpoint of imparting moisture resistance to the resulting sulfide solid electrolyte, the raw material is SiO ２ , B ２ O ３ , GeO ２ , Al ２ O ３ , P ２ O ５ These may be used alone or in combination of two or more.

[0047] When the mixture is charged into a heating furnace, the sulfides and oxides may be contained in the mixture or may be added separately during heating.

[0048] The amount of the sulfide and oxide added is preferably 0.1 to 50 mass%, more preferably 0.5 to 40 mass%, based on the total amount of the raw material. Here, the amount is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and is preferably 50 mass% or less, more preferably 40 mass% or less.

[0049] The mixture may further contain a compound that will serve as a crystal nucleus, which will be described later.

[0050] In addition, the manufacturing method according to this embodiment is ２ S ５ The objective of this invention is to suppress the composition deviation caused by the fact that P has a low melting point and boiling point and is easily volatilized. ２ S ５ It also has the effect of suppressing composition deviation caused by highly volatile compounds other than P. ２ S ５ Examples of highly volatile compounds other than those mentioned above include LiI, B ２ S ３ , S, Se, and Sb ２ S ３ Therefore, P ２ S ５ At the same time, the production method including the above steps S1 and S2 is also effective when producing a sulfide solid electrolyte using the present raw material containing the highly volatile compound.

[0051] Heat Melting In step S1 of this embodiment, the present raw material or the present mixture is placed in a heating furnace, and the present raw material is mixed as necessary to obtain the present mixture, which is then heated and melted.

[0052] As the furnace body in the heating furnace used for heating and melting, a conventionally known furnace having a heating section can be used as appropriate, and the material and size of the furnace body can also be selected arbitrarily.

[0053] The heat-melting temperature is not particularly limited as long as the mixture is melted, but is preferably 600°C or higher, more preferably 600 to 1000°C, even more preferably 630 to 950°C, even more preferably 650°C or higher but less than 900°C, and particularly preferably 650°C or higher but less than 850°C. From the viewpoint of homogenizing the melt in a short time, the heat-melting temperature is preferably 600°C or higher, more preferably 630°C or higher, and even more preferably 650°C or higher. Furthermore, from the viewpoint of suppressing deterioration or decomposition of the components in the melt, the heat-melting temperature is preferably 1000°C or lower, more preferably 950°C or lower, even more preferably less than 900°C, and particularly preferably less than 850°C. The heat-melting temperature is the temperature of the melt produced in the furnace and can be adjusted by the heating unit provided in the furnace.

[0054] The heating and melting time is not particularly limited as long as the mixture is melted, but may be, for example, 0.5 hours or more, 1 hour or more, or 2 hours or more.

[0055] The pressure during heating and melting is not particularly limited as long as the mixture is melted, but for example, normal pressure or slight pressure is preferred, and normal pressure is more preferred.

[0056] From the viewpoint of preventing side reactions between the melt and water vapor, oxygen, etc. during heating and melting, the dew point inside the furnace is preferably −20° C. or lower, and although there is no particular lower limit for the dew point, it is usually −80° C. or higher. In addition, the oxygen concentration inside the furnace is preferably 1000 ppm by volume or lower.

[0057] The heat melting is preferably carried out in a gas atmosphere containing elemental sulfur. By heat melting the mixture in a gas atmosphere containing elemental sulfur, sulfur is introduced into the resulting melt, thereby suppressing changes in the sulfur composition due to volatilization. Examples of the gas containing elemental sulfur include sulfur gas, hydrogen sulfide gas, carbon disulfide gas, and other gases containing compounds containing elemental sulfur or elemental sulfur.

[0058] The gas atmosphere containing elemental sulfur may be obtained by supplying a sulfur source into a melt obtained by heating and melting the mixture, and then heating the sulfur source to generate a gas containing elemental sulfur. In this case, the sulfur source is not particularly limited as long as it is elemental sulfur or a sulfur compound that can generate a gas containing elemental sulfur by heating. For example, elemental sulfur, hydrogen sulfide, carbon disulfide and other organic sulfur compounds, iron sulfide (FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S, etc.), bismuth sulfide (Bi ２ S ３ ), copper sulfide (CuS, Cu ２ S, Cu １－ｘ Examples of the sulfur source include sulfur powder, polysulfides such as lithium polysulfide and sodium polysulfide, polysulfides, rubbers that have been subjected to sulfur vulcanization treatment, etc. As the sulfur source, sulfur powder is preferably used.

[0059] Alternatively, the gas atmosphere containing elemental sulfur may be obtained by introducing sulfur vapor obtained in advance into the furnace body. For example, sulfur is heated at 200 to 450°C to generate sulfur vapor, and N ２ A gas atmosphere containing elemental sulfur can be obtained by transporting an inert gas such as gas, argon gas, or helium gas into the furnace body as a carrier gas.

[0060] Alternatively, the gas atmosphere containing elemental sulfur may be obtained by incorporating a sulfur source into the mixture, which heats the sulfur source when the mixture is heated and melted, thereby allowing the raw material to be heated and melted in a generated gas atmosphere containing elemental sulfur.

[0061] In the present production method, the method for obtaining the gas atmosphere containing elemental sulfur may be any one of the above methods, or a combination of a plurality of methods may be used.

[0062] <Step S2: Step of cooling and solidifying the obtained melt to obtain a sulfide solid electrolyte> The production method according to this embodiment includes a step of cooling and solidifying the melt obtained in step S1 to obtain a sulfide solid electrolyte. By cooling the melt, a solid sulfide solid electrolyte is obtained.

[0063] In step S2, the melt obtained in step S1 is discharged at any time from a discharge port provided in the furnace body, and the process proceeds to a step of cooling and solidifying. The melt can be cooled by any known method, and is not particularly limited. For example, from the viewpoint of increasing the cooling rate, cooling using a twin roller, which is generally considered to have the fastest quenching rate, is preferred.

[0064] From the viewpoint of maintaining the composition of the melt obtained in step S1, the cooling rate is preferably 0.01° C. / sec or more, more preferably 0.05° C. / sec or more, and even more preferably 0.1° C. / sec or more. There is no particular upper limit to the cooling rate, but the cooling rate of the twin rollers is, for example, 1,000,000° C. / sec or less.

[0065] When an amorphous sulfide solid electrolyte is desired, it is preferable to perform quenching at a higher cooling rate. The cooling rate during quenching is preferably 10°C / sec or higher, more preferably 100°C / sec or higher, even more preferably 500°C / sec or higher, and particularly preferably 700°C / sec or higher. The upper limit of the cooling rate during quenching is not particularly limited, but the cooling rate of the twin rollers is, for example, 1,000,000°C / sec or lower.

[0066] On the other hand, a sulfide solid electrolyte having a crystalline phase may be obtained by slow cooling during the cooling and solidification step. Alternatively, a sulfide solid electrolyte having both a crystalline phase and an amorphous phase may be obtained. The cooling rate during slow cooling is preferably 0.01 to 500°C / sec, more preferably 0.05 to 450°C / sec. It may also be 0.01 to 10°C / sec, or 0.05 to 5°C / sec. Here, the cooling rate is preferably 0.01°C / sec or more, more preferably 0.05°C / sec or more, and is preferably 500°C / sec or less, more preferably 450°C / sec or less. The cooling rate may also be 10°C / sec or less, or 5°C / sec or less. The cooling rate may be adjusted appropriately depending on the crystallization conditions.

[0067] The crystal of the sulfide solid electrolyte is preferably an ion-conductive crystal. Specifically, when the carrier is lithium ions, the ion-conductive crystal has a lithium ion conductivity of 1.0×10 －４ S / cm or more, and the lithium ion conductivity is 1.0×10－３ More preferably, it is more than 5 S / cm.

[0068] When a sulfide solid electrolyte containing a crystalline phase is to be obtained, in order to facilitate crystal precipitation, it is preferable to include a compound that will become a crystal nucleus in the melt obtained in step S1. The method for including the compound that will become a crystal nucleus in the melt is not particularly limited, but examples thereof include a method of adding the compound that will become a crystal nucleus to the mixture in step S1, and a method of directly adding the compound that will become a crystal nucleus to the melt that has been heated and melted.

[0069] Examples of compounds that can become crystal nuclei include oxides, oxynitrides, nitrides, carbides, other chalcogen compounds, and halides. Compounds that can become crystal nuclei are preferably compounds that have a certain degree of compatibility with the melt. Note that compounds that are completely incompatible with the melt cannot become crystal nuclei.

[0070] The amount of the compound that becomes the crystal nuclei added to the melt is preferably 0.01 to 20 mass%, more preferably 0.1 to 20 mass%, and even more preferably 1 to 10 mass%. From the viewpoint of favorably forming a crystalline phase in the resulting sulfide solid electrolyte, the amount added is preferably 0.01 mass% or more, more preferably 0.1 mass% or more, and even more preferably 1 mass% or more. Furthermore, from the viewpoint of suppressing a decrease in lithium ion conductivity, the amount added is preferably 20 mass% or less, and more preferably 10 mass% or less.

[0071] When a sulfide solid electrolyte having a large amorphous phase is desired, a compound serving as a crystal nucleus is not added to the melt, or if added, the amount of the compound added is preferably 1% by mass or less, more preferably 0.1% by mass or less. The amount may also be 0.01% by mass or less.

[0072] The cooling and solidification is preferably carried out under normal pressure. "Under normal pressure" means that the pressure is not controlled during cooling. Specifically, the pressure is about 0.8 to 1.2 atm.

[0073] In the manufacturing method according to the present embodiment, the sulfide solid electrolyte obtained in step S2 may be reheated for heat treatment. This heat treatment may be particularly effective when the sulfide solid electrolyte is amorphous or contains an amorphous phase. Furthermore, this heat treatment may rearrange ions within the crystal structure to increase lithium ion conductivity.

[0074] The heat treatment refers to at least one of a heat treatment for crystallizing the obtained solid and a heat treatment for rearranging ions in the crystal structure. That is, the heat treatment also includes a crystallization treatment by heating of an amorphous sulfide solid electrolyte or a sulfide solid electrolyte containing an amorphous phase.

[0075] In the production method according to this embodiment, it is preferable to carry out the above steps S1 and S2 as a continuous process. That is, it is preferable to continuously charge the raw materials or the mixture into a furnace body, mix the raw materials as needed to obtain the mixture, heat and melt it, and continuously discharge the resulting melt, followed by a step of cooling and solidifying it, thereby continuously obtaining a sulfide solid electrolyte. In this way, it is preferable to continuously produce a sulfide solid electrolyte.

[0076] By continuously producing the sulfide solid electrolyte, a series of steps, including heating and melting the mixture, discharging the melt, and cooling and solidifying it, are carried out continuously, allowing the sulfide solid electrolyte to be produced in large quantities more efficiently in a short period of time.

[0077] In a more preferred embodiment of the continuous process, in step S1, the mixture is first heated and melted in an amount sufficient to form at least a melt level in the furnace. Here, the melt level refers to the liquid level formed by the melt covering the entire bottom surface of the furnace. Once a melt level is formed in the furnace, any additional raw materials or mixture added to the melt subsequently undergoes a rapid temperature increase and instantaneous melting. Therefore, as the raw materials or mixture are added, melts are continuously generated one after another. These melts are continuously discharged and subjected to a cooling and solidification process, allowing sulfide solid electrolytes to be continuously produced in a short period of time. This continuous production of sulfide solid electrolytes allows for the production of large quantities of sulfide solid electrolytes in a short period of time. Furthermore, the shortening of the production process also reduces the volatilization of raw materials during the production process.

[0078] In the production method according to this embodiment, the processes of steps S1 and S2 may be performed batchwise. The batchwise method is a method in which the sulfide solid electrolyte raw material or a mixture thereof is charged into a furnace body, heated to melt it, and then the entire amount is discharged, and means a method in which the contents of the furnace body are all replaced every time the production method according to this embodiment is performed.

[0079] <Sulfide Solid Electrolyte> The sulfide solid electrolyte obtained by the production method according to this embodiment includes a sulfide solid electrolyte containing elements Li, P, and S. For example, Li １０ GeP ２ S １２ sulfide solid electrolytes having an LGPS type crystal structure, such as Li ６ P.S. ５ Cl, Li ５．４ P.S. ４．４ Cl １．６ and Li ５．４ P.S. ４．４ Cl ０．８ Br ０．８ sulfide solid electrolytes having an argyrodite-type crystal structure, such as those described above, Li-P-S-Ha-based crystallized glasses (wherein Ha represents at least one element selected from halogen elements), and Li ７ P ３ S １１Examples of suitable LPS crystallized glasses include those mentioned above.

[0080] The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte, a sulfide solid electrolyte having a specific crystal structure, or a sulfide solid electrolyte containing a crystalline phase and an amorphous phase, depending on the purpose. From the viewpoint of lithium ion conductivity, the crystalline phase is preferably an argyrodite-type crystalline phase.

[0081] From the viewpoint of lithium ion conductivity, a sulfide solid electrolyte containing elements Li, P, S, and Ha is preferred, and more preferably has a crystalline phase. The Ha element is preferably derived from one or more selected from the group consisting of lithium chloride, lithium bromide, and lithium iodide.

[0082] The lithium ion conductivity of the sulfide solid electrolyte is 1.0 × 10 in terms of the battery characteristics when used in a lithium ion secondary battery. －４ S / cm or more is preferable, and 5.0 × 10 －４ S / cm or more is more preferable, and 1.0 × 10 －３ S / cm or more is more preferable, and 5.0×10 －３ The lithium ion conductivity in this specification is a value measured using an AC impedance measuring device (for example, Potentiostat / Galvanostat VSP manufactured by Bio-Logic Sciences Instruments) under the conditions of a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C.

[0083] The obtained sulfide solid electrolyte can be identified by analyzing the crystal structure by X-ray diffraction (XRD) measurement, or by analyzing the elemental composition using various methods such as ICP optical emission spectrometry, atomic absorption spectrometry, and ion chromatography. For example, P and S can be measured by ICP optical emission spectrometry, Li can be measured by atomic absorption spectrometry, and Ha can be measured by ICP optical emission spectrometry or ion chromatography.

[0084] The present invention is not limited to the above-described embodiments, and various modifications can be adopted within the scope of the present invention. For example, the present invention is not limited to the above-described embodiments, and modifications and improvements can be made as appropriate. In addition, the material, shape, size, number, and location of each component in the above-described embodiments are arbitrary and not limited as long as the present invention can be achieved.

[0085] As described above, the present specification discloses the following: 1. A method for producing a sulfide solid electrolyte, comprising heating and melting a mixture of sulfide solid electrolyte raw materials, and cooling and solidifying the resulting melt to obtain a sulfide solid electrolyte, wherein the mixture of sulfide solid electrolyte raw materials contains Li, ２ S and P ２ S ５ and wherein the Li ２ The volume-based average particle size of S measured by a laser diffraction particle size distribution measurement method is A, and the P ２ S ５ 1. A method for producing a sulfide solid electrolyte, wherein A<B is satisfied, where B is the volume-based average particle size measured by the laser diffraction particle size distribution measurement method of 1. 2. A method for producing a sulfide solid electrolyte according to item 1 above, wherein A / B≦0.5 is satisfied. 3. A method for producing a sulfide solid electrolyte according to item 1 or 2 above, wherein B≧50 μm is satisfied. 4. A method for producing a sulfide solid electrolyte according to any one of items 1 to 3 above, wherein a sulfur source is supplied to a melt obtained by heating and melting the mixture of sulfide solid electrolyte raw materials. 5. A method for producing a sulfide solid electrolyte according to any one of items 1 to 4 above, wherein a sulfur source is contained in the mixture of sulfide solid electrolyte raw materials and then the mixture is heated and melted. 6. A method for producing a sulfide solid electrolyte according to any one of items 1 to 5 above, wherein the mixture of sulfide solid electrolyte raw materials is heated and melted at 600° C. or higher. 7. 7. The method for producing a sulfide solid electrolyte according to any one of 1 to 6 above, wherein the sulfide solid electrolyte raw material or a mixture of the sulfide solid electrolyte raw materials is continuously charged into a furnace body and heated to melt, and the resulting melt is continuously discharged, thereby continuously producing a sulfide solid electrolyte.

[0086] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Examples 1 and 2 are working examples, and Examples 3 and 4 are comparative examples.

[0087] <Evaluation of Lithium Ion Conductivity> The sulfide solid electrolyte obtained in each example was further crushed in a mortar and passed through a 100 μm mesh sieve to obtain a sulfide solid electrolyte powder having a D50 of 10 μm in the volume-based particle size distribution measured by a laser diffraction particle size distribution measurement method. This powder was compressed at a pressure of 380 MPa to prepare a measurement sample, and the lithium ion conductivity was measured using an AC impedance measurement device (potentiostat / galvanostat VSP, manufactured by Bio-Logic Sciences Instruments) and evaluated according to the following criteria. The measurement conditions were: measurement frequency: 100 Hz to 1 MHz, measurement voltage: 100 mV, and measurement temperature: 25°C.

[0088] <ICP optical emission spectroscopy> ICP optical emission spectroscopy was performed on the sulfide solid electrolyte obtained in each example to measure the P / Ha(Cl) molar ratio. Whether or not the P / Ha composition was as targeted was evaluated according to the following criteria: ○: The P / Ha(Cl) molar ratio was less than 5% different from the molar ratio at the time of addition; ×: The P / Ha(Cl) molar ratio was 5% or more different from the molar ratio at the time of addition.

[0089] Example 1 (Li ２ S crushing) First, Li ２ In order to reduce the diameter of S, Li ２ The S raw material was pulverized using a WARING MX1100X™ at a rotation speed of 24,000 rpm for 300 seconds. ２ The particle size distribution D50 of the volume-based particle size distribution was measured by a laser diffraction particle size distribution measurement method using a Microtrack MT3000II with dibutyl ether as the measurement solvent, a particle refractive index of 1.81, and a solvent refractive index of 1.353, and was found to be 12 μm. (Raw Material Mixing) In a glove box adjusted to a nitrogen atmosphere with a dew point of −50° C., the pulverized Li ２ S, P ２ S ５The raw material powders of LiCl were mixed in the molar ratio of 1.9:0.5:1.6, and the mixture was thoroughly stirred and mixed to obtain a mixture. The ratio of the raw material powders was designed so that the P / Ha(Cl) molar ratio was within the range of 0.59375±0.00059. ２ S ５ The volume-based particle size distribution D50 was measured using a laser diffraction particle size distribution measurement method with a Microtrack MT3000II, using dibutyl ether as the measurement solvent, a particle refractive index of 1.81, and a solvent refractive index of 1.353, and was found to be 230 μm. 400 g of the resulting mixture was placed in a carbon container purged with a nitrogen atmosphere with a dew point of -50°C or lower. A micrograph of the resulting mixture is shown in Figure 2A. (Heat Melting) 10 mass% of sulfur powder was added to the total weight of the mixture obtained above, and the mixture was heated and maintained at 700°C for 1 hour. (Discharge / Cooling Solidification) The melt was discharged from the discharge port of the container and collected in a water-cooled carbon container, yielding a solid sulfide solid electrolyte containing an amorphous phase and an argyrodite-type crystalline phase.

[0090] Example 2: Li ２ The S raw material was passed through a 100 μm mesh sieve, and dibutyl ether was used as the measurement solvent, with a particle refractive index of 1.81 and a solvent refractive index of 1.353. The volume-based particle size distribution D50 measured by a laser diffraction particle size distribution measurement method using a Microtrack MT3000II was 70 μm. ２ A sulfide solid electrolyte of Example 2 was obtained in the same manner as in Example 1, except that an S raw material was used.

[0091] Example 3: Using dibutyl ether as the measurement solvent, with a particle refractive index of 1.81 and a solvent refractive index of 1.353, a volume-based particle size distribution D50 of 532 μm was measured by a laser diffraction particle size distribution measurement method using a Microtrack MT3000II. ２ A sulfide solid electrolyte of Example 3 was obtained in the same manner as in Example 1, except that an S raw material was used.

[0092] Example 4: Li ２The S raw material was passed through a 500 μm mesh sieve, and dibutyl ether was used as the measurement solvent, with a particle refractive index of 1.81 and a solvent refractive index of 1.353. The volume-based particle size distribution D50 measured by a laser diffraction particle size distribution measurement method using a Microtrack MT3000II was 365 μm. ２ A sulfide solid electrolyte of Example 4 was obtained in the same manner as in Example 1, except that raw material S was used. A micrograph of the mixture before heating and melting is shown in FIG. 2B.

[0093] Table 1 shows the composition (P / Ha(Cl) molar ratio) and lithium ion conductivity of each example.

[0094]

[0095] As can be seen from the results shown in Table 1, in Examples 1 and 2, the Li in the mixture of raw material powders ２ S's D50 is P ２ S ５ Since the D50 of the mixture is smaller than that of the mixture of P / Ha(Cl), the P / Ha(Cl) molar ratio is within the target composition range. The lithium ion conductivity was also good. This is because the P in this mixture is ２ S ５ Many Li atoms on the particle surface ２ It is believed that this is because the S particles can be brought into contact with each other, and the synthesis reaction between the raw materials can be promoted before the raw materials volatilize, thereby suppressing the volatilization of the raw materials during melting, and a sulfide solid electrolyte having the target composition can be obtained. ２ S's D50 is P ２ S ５ Since the D50 of the P / Ha(Cl) molar ratio was larger than that of the target composition, the lithium ion conductivity was also poor. ２ The large particle size of the S particles allows the P ２ S ５ Li on the particle surface ２ This is thought to be because the S particles could not be brought into sufficient contact with the raw material, and therefore the volatilization of the raw material could not be sufficiently suppressed.

[0096] Although various embodiments have been described above, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any manner as long as they do not deviate from the spirit of the invention.

[0097] This application is based on a Japanese patent application (Patent Application No. 2023-119361) filed on July 21, 2023, the contents of which are incorporated herein by reference.

Claims

1. A method for producing a sulfide solid electrolyte, comprising heating and melting a mixture of sulfide solid electrolyte raw materials, and cooling and solidifying the resulting melt to obtain a sulfide solid electrolyte, wherein the mixture of sulfide solid electrolyte raw materials contains Li ２ S and P ２ S ５ The Li ２ The volume-based average particle size of S measured by a laser diffraction particle size distribution measuring method is A, ２ S ５ wherein A<B is satisfied, where B is a volume-based average particle size measured by a laser diffraction particle size distribution measurement method.

2. The method for producing a sulfide solid electrolyte according to claim 1, wherein A / B≦0.5 is satisfied.

3. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein B≧50 μm is satisfied.

4. The method for producing a sulfide solid electrolyte according to claim 1 or 2, further comprising heating and melting the mixture of raw materials for the sulfide solid electrolyte to obtain a melt, and then supplying a sulfur source into the melt.

5. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein a sulfur source is added to the mixture of raw materials for the sulfide solid electrolyte and then the mixture is heated and melted.

6. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the mixture of raw materials for the sulfide solid electrolyte is heated and melted at 600° C. or higher.

7. A method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the sulfide solid electrolyte raw material or a mixture of the sulfide solid electrolyte raw materials is continuously charged into a furnace body and heated to melt, and the resulting molten liquid is continuously discharged, thereby continuously producing a sulfide solid electrolyte.

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