Method for producing sulfide solid electrolyte

Abstract

The present invention relates to a method for producing a sulfide solid electrolyte, in which a sulfide solid electrolyte is obtained by heating and melting a mixture of sulfide solid electrolyte raw materials comprising Li2S and P2S5, and cooling and solidifying the obtained melt, if A is the volume-based average particle diameter of the Li2S as measured by a laser diffraction particle size distribution measurement method, and B is the volume-based average particle diameter of the P2S5 as measured by a laser diffraction particle size distribution measurement method, A < 250 [mu] m and B < 250 [mu] m are satisfied.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a sulfide solid electrolyte. Background Technology

[0002] Lithium-ion secondary batteries are widely used in portable electronic devices such as mobile phones and laptops. Previously, liquid electrolytes were used in lithium-ion secondary batteries. However, due to the anticipated improvements in safety, high-speed charging and discharging, and miniaturization of the casing, all-solid-state lithium-ion secondary batteries using solid electrolytes have gained significant attention in recent years. Examples of solid electrolytes used in all-solid-state lithium-ion secondary batteries include sulfide solid electrolytes.

[0003] In the case of manufacturing sulfide solid electrolytes by melt method, the raw materials volatilize when the mixed raw materials of sulfide solid electrolyte are heated. In particular, P2S5, one of the raw materials, is prone to volatilization due to its low melting and boiling points. Therefore, the sulfide solid electrolyte obtained after melting has the problem of deviating from the target composition (hereinafter also referred to as composition deviation).

[0004] To this end, for example, Patent Document 1 discloses a method in which a composite compound containing lithium, phosphorus and sulfur is melted and vitrified, and then the molten glass is rapidly cooled to prevent only the P2S5 component from evaporating during melting.

[0005] In addition, Patent Document 2 discloses a method that produces a melt by compressing and heating a solid raw material, thereby suppressing the volatilization of the raw material and suppressing compositional deviations.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2012-043654

[0007] Patent Document 2: Japanese Patent No. 5640665 Summary of the Invention

[0008] However, the method disclosed in Patent Document 1 requires the prior synthesis of the aforementioned composite compound, thus complicating the manufacturing process. Furthermore, it cannot suppress the volatilization of the raw materials themselves during melting.

[0009] Furthermore, in the method disclosed in Patent Document 2, the equipment structure is very complex due to the need to compress the raw materials, making it difficult to mass-produce solid electrolytes.

[0010] In view of the above, the object of the present invention is to provide a method for manufacturing a sulfide solid electrolyte with a target composition by suppressing the volatilization of raw materials during melting without the use of complex equipment when manufacturing sulfide solid electrolytes by melt method.

[0011] Through in-depth research, the inventors discovered that by setting the average particle size of Li2S and the average particle size of P2S5, which are used as raw materials for sulfide solid electrolytes, to be less than a specified value, the volatilization of the raw materials during melting can be suppressed, thus completing the present invention.

[0012] Specifically, this invention relates to a method for manufacturing a sulfide solid electrolyte, which involves heating and melting a mixture of sulfide solid electrolyte raw materials, and then cooling and solidifying the resulting melt to obtain the sulfide solid electrolyte.

[0013] The mixture of the above-mentioned sulfide solid electrolyte raw materials includes Li2S and P2S5. If the average particle size of the volume reference of the above-mentioned Li2S, determined by the laser diffraction particle size distribution method, is set as A, and the average particle size of the above-mentioned P2S5, determined by the laser diffraction particle size distribution method, is set as B, then A < 250 μm and B < 250 μm are satisfied.

[0014] According to the present invention, the volatilization of raw materials during melting can be suppressed without the use of complex equipment, and sulfide solid electrolytes with a target composition can be manufactured. Attached Figure Description

[0015] Figure 1 is a flowchart illustrating the method for manufacturing a sulfide solid electrolyte according to this embodiment. Detailed Implementation

[0016] The present invention will now be described in detail, but the present invention is not limited to the following embodiments and can be implemented in any way without departing from the spirit of the present invention.

[0017] The "~" symbol, which indicates a range of values, is used to encompass the values ​​listed before and after it as the lower and upper limits.

[0018] Manufacturing Method of Sulfide Solid Electrolytes

[0019] The manufacturing method involved in this embodiment is characterized by heating and melting a mixture of sulfide solid electrolyte raw materials, and then cooling and solidifying the resulting melt to obtain a sulfide solid electrolyte. The mixture of sulfide solid electrolyte raw materials includes Li2S and P2S5. If the average particle size of the volume reference of the Li2S measured by the laser diffraction particle size distribution method is set as A, and the average particle size of the volume reference of the P2S5 measured by the laser diffraction particle size distribution method is set as B, then A < 250 μm and B < 250 μm are satisfied.

[0020] like Figure 1 As shown, the manufacturing method involved in this embodiment includes the following steps.

[0021] (Step S1) The process of heating and melting a mixture of sulfide solid electrolyte raw materials containing Li2S and P2S5.

[0022] (Step S2) The process of cooling and solidifying the obtained molten liquid to obtain a sulfide solid electrolyte.

[0023] The following is a description of each step.

[0024] <Step S1: The process of heating and melting the mixture of sulfide solid electrolyte raw materials containing Li2S and P2S5>

[0025] • A mixture of sulfide solid electrolyte feedstocks containing Li2S and P2S5

[0026] A mixture of sulfide solid electrolyte raw materials containing Li2S and P2S5 (hereinafter also referred to as the raw material) (hereinafter also referred to as the mixture) can be obtained by mixing powdered Li2S, which is one of the raw materials contained in the raw material, with powdered P2S5, which is one of the raw materials contained in the raw material. The heating and melting of the mixture can be carried out by feeding the raw material into a heating furnace in the state of a mixed mixture. Alternatively, the raw material can be fed into a heating furnace, mixed to obtain the mixture, and then heated and melted. From the viewpoint of improving the homogeneity of the obtained sulfide solid electrolyte, it is preferable to feed the mixture into the heating furnace for heating and melting.

[0027] In the manufacturing method of this embodiment, if the average particle size of Li2S contained in the mixture, measured by laser diffraction particle size distribution method, is set as A, and the average particle size of P2S5 contained in the mixture, measured by laser diffraction particle size distribution method, is set as B, then A < 250 μm and B < 250 μm are satisfied. 。 Therefore, the volatilization of raw materials during melting is suppressed, enabling the production of sulfide solid electrolytes with the target composition. This is presumably due to the following mechanism.

[0028] That is, by reducing the average particle size of Li2S and P2S5 in the mixture of sulfide solid electrolyte raw materials to less than the aforementioned specified value, the specific surface area of ​​Li2S and P2S5 particles is increased, thereby expanding the contact interface between them. Since the synthesis reaction of the sulfide solid electrolyte first occurs at the contact interface between particles, and the reaction does not proceed in the non-contact areas and volatilizes, expanding the contact interface between P2S5 particles in this mixture can reduce the non-contact areas between particles. Therefore, it is believed that by promoting the synthesis reaction between the raw materials before volatilization and suppressing the volatilization of the raw materials during melting, a sulfide solid electrolyte with the target composition can be obtained.

[0029] It should be noted that the manufacturing method involved in this embodiment is not limited to the mechanism described above.

[0030] In addition, by reducing the average particle size of P2S5 and Li2S to less than the specified value, it is possible to suppress the dispersion of P2S5 and Li2S after they are fed into the heating furnace, thereby suppressing the volatilization of P2S5 and Li2S upon contact with the furnace wall.

[0031] In addition, by reducing the average particle size of P2S5 and Li2S to less than the specified values, the generation of unmelted material can be reduced, resulting in a more homogeneous sulfide solid electrolyte.

[0032] In the manufacturing method of this embodiment, A is less than 250 μm (A < 250 μm). Furthermore, A is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. Additionally, A is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 5 μm or more. Furthermore, A is preferably 1 μm or more and less than 250 μm (1 μm ≤ A < 250 μm).

[0033] In the manufacturing method of this embodiment, B is less than 250 μm (B < 250 μm). Furthermore, B is preferably 200 μm or less, more preferably 150 μm or less, and even more preferably 100 μm or less. Additionally, B is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 5 μm or more. Furthermore, B is preferably 1 μm or more and less than 250 μm (1 μm ≤ B < 250 μm).

[0034] In addition, there is no particular restriction on the ratio of A to B (A / B), which can be in the range of 1 / 250 to 250 / 1.

[0035] The average particle size of Li2S and P2S5 in this mixture, measured by laser diffraction particle size distribution determination method, refers to the average particle size of the Li2S powder and P2S5 powder, which are one of the raw materials, measured before mixing. For example, it can be measured using an MT3000II (manufactured by Microtrac). The aforementioned average particle size refers to the D50 of the particle size distribution on a volume basis as measured by laser diffraction particle size distribution determination method.

[0036] Furthermore, as described below, this mixture preferably contains lithium halide (LiHa). That is, this mixture is preferably obtained by mixing LiHa powder, which is one of the raw materials contained in this raw material, in addition to Li2S powder and P2S5 powder.

[0037] In this case, the average particle size of the LiHa powder, measured by laser diffraction particle size distribution method, is preferably 0.1 to 2000 μm on a volume basis. 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. Additionally, the average particle size is preferably 2000 μm or less, more preferably 1750 μm or less, and particularly preferably 1500 μm or less.

[0038] As for the raw materials, as long as they contain the aforementioned Li2S and P2S5, one or more other various raw materials can be used, and the sulfide solid electrolytes obtained using them can also be various sulfide solid electrolytes.

[0039] The raw materials contained herein may be synthesized separately or may be commercially available products. Each raw material may be in powder form, and the raw material itself containing each raw material may also be in powder form. Furthermore, the raw material may be a raw material that has undergone known pretreatment. That is, in the manufacturing method according to this embodiment, before step S1, step 0, as the step of preparing the raw material, may appropriately include at least one of the steps of manufacturing the raw material and the step of pretreating at least a portion of the raw material.

[0040] The raw material for the sulfide solid electrolyte containing Li2S and P2S5 can be appropriately determined based on the composition of the desired sulfide solid electrolyte.

[0041] One of the raw materials contained in this material includes substances such as alkali metal elements (R) and sulfur elements (S). Examples of alkali metal elements (R) include lithium (Li), sodium (Na), and potassium (K). When the sulfide solid electrolyte is used in lithium-ion secondary batteries, the alkali metal element (R) preferably includes substances such as lithium (Li).

[0042] As a source of alkali metal (R), it can be used in appropriate combinations of alkali metal elements, compounds containing alkali metals, and other substances containing alkali metals. When the alkali metal (R) is lithium (Li), it can be used as a source of lithium by appropriate combinations of elemental Li, compounds containing Li, and other substances containing Li. As mentioned above, this raw material contains at least Li₂S, which can be used as a source of lithium (Li).

[0043] In addition to lithium sulfide (Li₂S) mentioned above, other lithium compounds containing lithium (Li) include lithium iodide (LiI), lithium carbonate (Li₂CO₃), lithium sulfate (Li₂SO₄), lithium oxide (Li₂O), and lithium hydroxide (LiOH), as well as metallic lithium. One type of lithium-containing substance (Li) can be used, or two or more can be used in combination.

[0044] From the viewpoint of obtaining sulfide materials, lithium sulfide is preferred as the substance containing lithium (Li). Furthermore, when the obtained sulfide solid electrolyte contains halogen elements, lithium halide (LiHa, Ha being halogen elements) is also preferred as the substance containing lithium (Li). Lithium halide will be described later.

[0045] As a sulfur (S) source, substances containing S, such as elemental S and S-containing compounds, can be appropriately combined. One sulfur-containing substance can be used, or two or more can be used in combination. As mentioned above, this raw material contains at least Li₂S and P₂S₅, which can serve as sulfur (S) sources. Furthermore, Li₂S is a compound that contains both sulfur (S) and the aforementioned lithium (Li)-containing substance. Additionally, P₂S₅ is a compound that contains both sulfur (S) and, as described later, phosphorus (P)-containing substance.

[0046] As substances containing sulfur (S), besides phosphorus pentasulfide (P₂S₅), examples include phosphorus sulfides such as phosphorus trisulfide (P₂S₃), other phosphorus-containing sulfur compounds, elemental sulfur, and sulfur-containing compounds. Examples of sulfur-containing compounds include H₂S, CS₂, and iron sulfides (FeS, Fe₂S₃, FeS₂, Fe...). 1-x Bismuth sulfide (Bi2S3), copper sulfide (CuS, Cu2S, Cu, etc.), bismuth sulfide (Bi2S3), copper sulfide (CuS, Cu2S, Cu... 1-x S, etc.).

[0047] From the viewpoint of improving the ionic conductivity of the obtained sulfide solid electrolyte, it is preferable to further contain phosphorus (P) as the raw material. As a source of phosphorus (P), substances containing P, such as elemental P and compounds containing P, can be used in appropriate combinations. One substance containing phosphorus (P) can be used, or two or more can be used in combination. It should be noted that, as mentioned above, this raw material contains at least P₂S₅, which can be used as a source of phosphorus (P).

[0048] In addition to phosphorus pentasulfide (P2S5) mentioned above, other substances containing phosphorus (P) include phosphorus sulfides such as phosphorus trisulfide (P2S3), phosphorus compounds such as sodium phosphate (Na3PO4), and elemental phosphorus.

[0049] When the mixture obtained by mixing the raw materials is added to a heating furnace and then heated and melted, the mixing ratio of the raw materials can be appropriately determined, for example, according to the composition of the target sulfide solid electrolyte. Furthermore, when the mixture obtained by mixing the raw materials in a heating furnace is then heated and melted, the addition ratio of the raw materials can be appropriately determined, for example, according to the composition of the target sulfide solid electrolyte.

[0050] There is no particular limitation on the mixing ratio or input ratio of the raw materials. For example, from the viewpoint of improving the ionic conductivity of the obtained sulfide solid electrolyte, the molar ratio of sulfur (S) to alkali metal (R) in the mixture, S / R, is preferably 0.65 / 0.35 or less, and more preferably 0.5 / 0.5 or less.

[0051] When the mixture formed by mixing the raw materials is put into a heating furnace, it is preferable to mix them according to the prescribed stoichiometric ratio corresponding to the raw materials to obtain the mixture.

[0052] There are no particular limitations on the method of mixing the raw materials to obtain this mixture. Examples include mixing in a mortar and pestle, mixing using media such as a planetary ball mill, mixing without media such as a pin mill, powder mixer, and air-jet mixing.

[0053] When mixing or adding substances containing alkali metal elements and substances containing sulfur elements, in addition to the combination of Li2S and P2S5, combinations of Li2S, P2S5 and LiHa can be cited when the resulting sulfide solid electrolyte has halogen elements as constituent elements.

[0054] In the combination of Li₂S and P₂S₅, the molar ratio of Li to P, Li / P, is preferably 40 / 60 to 88 / 12, more preferably 50 / 50 to 88 / 12. By adjusting the mixing ratio or the input ratio to make P₂S₅ relatively less than Li₂S, it is easier to suppress the volatilization of sulfur and phosphorus components during heat treatment caused by the lower boiling point of P₂S₅ compared to the melting point of Li₂S.

[0055] On the other hand, since lithium sulfide is expensive, from the viewpoint of reducing the manufacturing cost of sulfide solid electrolytes, lithium compounds other than lithium sulfide, such as metallic lithium, can also be used.

[0056] Specifically, in this case, the raw materials containing Li can include metallic lithium, lithium halide (LiHa), lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), lithium oxide (Li2O), lithium hydroxide (LiOH), etc. One of these can be used, or two or more can be used in combination.

[0057] This raw material may contain substances other than those mentioned above (compounds, etc.), depending on the composition of the target sulfide solid electrolyte or as an additive. For example, in the case of manufacturing a sulfide solid electrolyte containing halogen elements such as F, Cl, Br, or I, the raw material preferably contains a halogen element (Ha). In this case, a compound containing a halogen element is preferred as the raw material.

[0058] Examples of compounds containing halogen elements include lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), lithium halides, phosphorus halides, phosphoryl halides, sulfur halides, sodium halides, and boron halides. From a reactivity point of view, lithium halides are preferred, LiCl, LiBr, and LiI are more preferred, and LiCl and LiBr are even more preferred. One of these compounds can be used, or two or more can be used in combination.

[0059] It should be noted that since lithium halides and other alkali metal halides are also compounds containing alkali metal elements such as Li, they can be used as the source of alkali metal elements (R) in this raw material.

[0060] When this mixture contains halogen (Ha) and phosphorus (P), the molar equivalent of halogen (Ha) relative to phosphorus (P) in this mixture is preferably 0.2 to 4 molar equivalents, more preferably 0.5 to 3 molar equivalents. Here, from the viewpoint of improving the ionic conductivity of the obtained sulfide solid electrolyte, the molar equivalent of the halogen 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 obtained sulfide solid electrolyte, the molar equivalent of the halogen is preferably 4 molar equivalents or less, more preferably 3 molar equivalents or less. It should be noted that when the above-mentioned powder raw material contains two or more halogen elements, their total content preferably meets the above-mentioned range of molar equivalents.

[0061] The sulfide solid electrolyte obtained by the manufacturing method according to this embodiment may also be amorphous, depending on its purpose. When the obtained sulfide solid electrolyte contains an amorphous phase, from the viewpoint that the amorphous phase is easily formed even when the rapid cooling rate is reduced and the equipment load can be reduced, it is preferable to include sulfides such as SiS2, B2S3, GeS2, and Al2S3 as raw materials. One of these can be used, or two or more can be used in combination.

[0062] From the viewpoint of imparting moisture resistance to the obtained sulfide solid electrolyte, the raw materials preferably include oxides such as SiO2, B2O3, GeO2, Al2O3, and P2O5. One or more of these can be used in combination.

[0063] In addition, when this mixture is put into a heating furnace, the aforementioned sulfides and oxides may be included in the mixture at the same time, or they may be added separately during heating.

[0064] The amount of the above-mentioned sulfides and oxides added relative to the total of the raw materials is preferably 0.1 to 50% by mass, more preferably 0.5 to 40% by mass. Here, the above-mentioned addition amount is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and preferably 50% by mass or less, more preferably 40% by mass or less.

[0065] This mixture may further contain compounds that serve as nuclei, as described later.

[0066] Furthermore, while the manufacturing method described in this embodiment aims to suppress compositional deviations caused by the low melting and boiling points and high volatility of P2S5, it also effectively suppresses compositional deviations caused by highly volatile compounds other than P2S5. Examples of highly volatile compounds other than P2S5 include LiI, B2S3, S, Se, and Sb2S3. Therefore, when using this raw material, which contains both P2S5 and the aforementioned highly volatile compounds, to manufacture a sulfide solid electrolyte, the manufacturing method comprising steps S1 and S2 described above is effective.

[0067] • Heating and melting

[0068] In step S1 of this embodiment, the raw material or the mixture is put into a heating furnace, and after the raw material is mixed as needed to obtain the mixture, the mixture is heated and melted.

[0069] As the furnace body for a heating furnace used in heating and melting, conventionally known furnace bodies with heating elements can be appropriately used, and the material and size of the furnace body can be arbitrarily selected.

[0070] The heating and melting temperature is not particularly limited as long as it is sufficient to melt the mixture, but is preferably 600°C or higher, more preferably 600–1000°C, even more preferably 630–950°C, and even more preferably 650°C or higher and lower than 900°C, and particularly preferably 650°C or higher and lower than 850°C. From the viewpoint of homogenizing the melt in a short time, the heating and 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 the deterioration and decomposition of components in the melt, the heating and melting temperature is preferably 1000°C or lower, more preferably 950°C or lower, even more preferably lower than 900°C, and particularly preferably lower than 850°C.

[0071] It should be noted that the heating and melting temperature refers to the temperature of the molten liquid generated inside the furnace, which can be adjusted by the heating element installed in the furnace.

[0072] There are no particular restrictions on the heating and melting time, as long as the mixture is melted. For example, it can be more than 0.5 hours, more than 1 hour, or more than 2 hours.

[0073] The pressure during heating and melting is not particularly limited as long as it is sufficient to melt the mixture; for example, atmospheric pressure or slight pressure is preferred, and atmospheric pressure is more preferred.

[0074] When heating and melting, from the viewpoint of preventing side reactions between the molten liquid and water vapor, oxygen, etc., the dew point inside the furnace is preferably below -20°C. There is no particular limitation on the lower limit of this dew point, and it is usually above -80°C. In addition, the oxygen concentration inside the furnace is preferably below 1000 ppm by volume.

[0075] The heating and melting are preferably carried out in a sulfur-containing gas atmosphere. By heating and melting the mixture in a sulfur-containing gas atmosphere, sulfur is introduced into the resulting melt, thus suppressing compositional changes associated with the volatilization of sulfur. Examples of sulfur-containing gases include sulfur gas, hydrogen sulfide gas, carbon disulfide gas, and other sulfur-containing compounds or gases containing elemental sulfur.

[0076] The aforementioned sulfur-containing gas atmosphere can be obtained by supplying a sulfur source to the molten liquid obtained by heating the mixture and then heating the sulfur source to generate a sulfur-containing gas. In this case, the sulfur source is not particularly limited to elemental sulfur or sulfur compounds that can produce a sulfur-containing gas by heating; examples include elemental sulfur, hydrogen sulfide, organic sulfur compounds such as carbon disulfide, and iron sulfides (FeS, Fe2S3, FeS2, Fe...). 1-x Bismuth sulfide (Bi2S3), copper sulfide (CuS, Cu2S, Cu, etc.), bismuth sulfide (Bi2S3), copper sulfide (CuS, Cu2S, Cu... 1-x Sulfur sources include sulfur powder, lithium polysulfides, sodium polysulfides, polysulfides, and rubber treated with sulfur.

[0077] Alternatively, a sulfur-containing gaseous atmosphere can be obtained by introducing pre-prepared sulfur vapor into the furnace. For example, sulfur is heated at 200–450°C to produce sulfur vapor, which is then transported into the furnace using inert gases such as N2, argon, or helium as carrier gases, thereby obtaining a sulfur-containing gaseous atmosphere.

[0078] Alternatively, a sulfur-containing gaseous atmosphere can be obtained by introducing a sulfur source into the mixture. Therefore, when the mixture is heated and melted, the sulfur source is also heated, thus enabling the melting of the raw material to be carried out in a sulfur-containing gaseous atmosphere.

[0079] In this manufacturing method, any one of the methods used to obtain the gaseous atmosphere containing sulfur can be used, or a combination of multiple methods can be used.

[0080] <Step S2: The process of cooling and solidifying the obtained molten liquid to obtain a sulfide solid electrolyte>

[0081] The manufacturing method described in this embodiment includes a step of cooling and solidifying the molten liquid obtained in step S1 to obtain a sulfide solid electrolyte. By cooling the molten liquid, a solid sulfide solid electrolyte can be obtained.

[0082] In step S2, the molten liquid obtained in step S1 is discharged from the outlet provided in the furnace body at any time and moved to the cooling and solidification process. The cooling of the molten liquid can be carried out by known methods and is not particularly limited. For example, from the viewpoint of increasing the cooling rate, the use of a twin-roll cooling system, which is considered to have the fastest cooling rate, is generally preferred.

[0083] From the viewpoint of maintaining the composition of the melt obtained in step S1, the cooling rate is preferably 0.01°C / second or higher, more preferably 0.05°C / second or higher, and even more preferably 0.1°C / second or higher. Furthermore, there is no particular upper limit to the cooling rate; for example, the cooling rate of the twin rollers is 1,000,000°C / second or lower.

[0084] When obtaining an amorphous sulfide solid electrolyte, it is preferable to increase the cooling rate to perform rapid cooling. The rapid cooling rate is preferably 10°C / second or higher, more preferably 100°C / second or higher, even more preferably 500°C / second or higher, and particularly preferably 700°C / second or higher. Furthermore, there is no particular upper limit to the rapid cooling rate; for example, the cooling rate of the two rollers is 1,000,000°C / second or lower.

[0085] On the other hand, a crystalline sulfide solid electrolyte can also be obtained by slow cooling during the cooling and solidification process. Alternatively, crystalline and amorphous sulfide solid electrolytes can also be formed.

[0086] The cooling rate during slow cooling is preferably 0.01 to 500°C / second, more preferably 0.05 to 450°C / second. Alternatively, it can be 0.01 to 10°C / second or 0.05 to 5°C / second.

[0087] Here, the cooling rate is preferably 0.01°C / second or higher, more preferably 0.05°C / second or higher, and preferably 500°C / second or lower, more preferably 450°C / second or lower. Alternatively, the cooling rate can be 10°C / second or lower, or 5°C / second or lower. The cooling rate can be appropriately adjusted according to the crystallization conditions.

[0088] The crystals of sulfide solid electrolytes are preferably ion-conducting crystals. Specifically, when the charge carrier is lithium ions, the ion-conducting crystals preferably have a lithium-ion conductivity exceeding 1.0 × 10⁻⁶.-4 For crystals with a conductivity of S / cm, the lithium-ion conductivity is more preferably greater than 1.0 × 10⁻⁶. -3 S / cm.

[0089] In order to obtain a sulfide solid electrolyte containing a crystalline phase, it is preferable to make the melt obtained in step S1 contain a compound that serves as a crystal nucleus in order to facilitate the precipitation of crystals.

[0090] There are no particular limitations on the method of making the melt contain the compound that becomes the crystal nucleus. For example, the method of adding the compound that becomes the crystal nucleus to the mixture in step S1, or the method of directly adding the compound that becomes the crystal nucleus to the heated melt, etc.

[0091] Compounds that can serve as crystal nuclei include oxides, oxynitrides, nitrides, carbides, other chalcogenides, and halides. Preferably, the compound serving as a crystal nucleus is one that has a certain degree of compatibility with the molten liquid. It should be noted that compounds that are completely incompatible with the molten liquid cannot serve as crystal nuclei.

[0092] The amount of the compound that forms the crystal nucleus relative to the molten liquid is preferably 0.01 to 20% by mass, more preferably 0.1 to 20% by mass, and even more preferably 1 to 10% by mass. From the viewpoint of appropriately forming a crystalline phase in the obtained sulfide solid electrolyte, the above-mentioned amount is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more. Furthermore, from the viewpoint of suppressing the decrease in lithium-ion conductivity, the above-mentioned amount is preferably 20% by mass or less, more preferably 10% by mass or less.

[0093] It should be noted that when it is desired to obtain a sulfide solid electrolyte with a high proportion of amorphous phases, the amount of compound that serves as a crystal nucleus should preferably be 1% by mass or less, more preferably 0.1% by mass or less, relative to the molten liquid, or if it is added. Alternatively, the amount added may also be 0.01% by mass or less.

[0094] Cooling and curing are preferably carried out under normal pressure. Normal pressure means that the pressure is not controlled during cooling. Specifically, it is approximately 0.8–1.2 atm.

[0095] In the manufacturing method of this embodiment, the sulfide solid electrolyte obtained in step S2 can be subjected to heat treatment by heating again. This heat treatment is particularly suitable when the sulfide solid electrolyte is amorphous or contains an amorphous phase.

[0096] In addition, the above heat treatment can rearrange the ions within the crystal structure, thereby improving the lithium-ion conductivity.

[0097] The aforementioned heat treatment refers to at least one of heat treatment for crystallizing the obtained solid and heat treatment for rearranging ions within the crystal structure. That is, crystallization treatment by heating an amorphous sulfide solid electrolyte or a sulfide solid electrolyte containing an amorphous phase is also included in the aforementioned heat treatment.

[0098] In the manufacturing method of this embodiment, steps S1 and S2 are preferably performed as a continuous process. That is, it is preferable to continuously feed the raw material or the mixture into the furnace, mix the raw material as needed to obtain the mixture, heat and melt it, and continuously discharge the obtained molten liquid to a cooling and solidification process, thereby continuously obtaining the sulfide solid electrolyte. It is preferable to manufacture the sulfide solid electrolyte in this continuous manner.

[0099] By continuously manufacturing sulfide solid electrolytes, the series of processes of heating and melting the mixture, discharging the molten liquid, and cooling and solidifying are completed continuously, enabling the production of large quantities of sulfide solid electrolytes more efficiently in a short time.

[0100] In a continuous process, as a more preferred method, in step S1 above, firstly, an amount of the mixture obtained by heating and melting the mixture is heated and melted in the furnace to at least form a molten liquid surface. Here, the molten liquid surface refers to the liquid surface formed by the molten liquid covering the entire bottom surface of the furnace. Once a molten liquid surface is formed in the furnace, any subsequent additions of the raw material or mixture will melt instantly due to the rapid increase in temperature. Therefore, as the raw material or mixture is added, molten liquid is continuously generated and continuously discharged. After a cooling and solidification process, a sulfide solid electrolyte can be continuously obtained in a short time.

[0101] By continuously manufacturing sulfide solid electrolytes in this way, large quantities of sulfide solid electrolytes can be produced in a short time. Furthermore, the reduced manufacturing time also helps to suppress the volatilization of raw materials during the manufacturing process.

[0102] Alternatively, in the manufacturing method described in this embodiment, steps S1 and S2 can also be performed intermittently. Intermittent refers to a method where, after adding sulfide solid electrolyte raw materials or mixtures thereof into the furnace, the materials are heated, melted, and then discharged in their entirety. In the context of the manufacturing method described in this embodiment, this means completely replacing the contents of the furnace.

[0103] <Sulfide Solid Electrolytes>

[0104] As a sulfide solid electrolyte obtained by the manufacturing method according to this embodiment, examples include sulfide solid electrolytes having elements of Li, P, and S, such as Li 10 GeP2S12 Sulfide solid electrolytes with LGPS-type crystal structures, Li6PS5Cl, Li 5.4 PS 4.4 Cl 1.6 and Li 5.4 PS 4.4 Cl 0.8 Br 0.8 Sulfide solid electrolytes with a sulfide-germanium sulfide crystal structure, Li-P-S-Ha-based microcrystalline glass (Ha represents at least one element selected from halogen elements), and Li7P3S 11 Examples include LPS microcrystalline glass.

[0105] Depending on their purpose, sulfide solid electrolytes can be amorphous, have a specific crystal structure, or contain both crystalline and amorphous phases. From the viewpoint of lithium-ion conductivity, a crystalline phase of argyroclase-germanium sulfide is more preferred.

[0106] From the viewpoint of lithium-ion conductivity, sulfide solid electrolytes containing elements Li, P, S, and Ha are preferred, and those containing a crystalline phase are even more preferred. Furthermore, the Ha element is preferably derived from one or more of lithium chloride, lithium bromide, and lithium iodide.

[0107] From the viewpoint of battery characteristics when used in lithium-ion secondary batteries, the lithium-ion conductivity of the sulfide solid electrolyte is preferably 1.0 × 10⁻⁶. -4 S / cm or higher, more preferably 5.0 × 10 -4 S / cm or higher, more preferably 1.0 × 10⁻⁶ - 3 S / cm or higher, especially preferably 5.0 × 10⁻⁶. -3 S / cm or higher.

[0108] It should be noted that the lithium-ion conductivity in this specification is a value measured using an AC impedance measuring device (e.g., a potentiostat / galvanostat VSP manufactured by Bio-Logic Sciences Instruments) under the following conditions: measurement frequency: 100Hz to 1MHz, measurement voltage: 100mV, and measurement temperature: 25°C.

[0109] The obtained sulfide solid electrolytes can be identified by various methods, including crystal structure analysis using X-ray diffraction (XRD), elemental composition analysis using ICP emission spectroscopy, atomic absorption spectrometry, and ion chromatography. For example, P and S can be determined by ICP emission spectroscopy, Li by atomic absorption spectrometry, and Ha by ion chromatography.

[0110] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the present invention. For example, the present invention is not limited to the embodiments described above, and appropriate modifications and improvements can be made. Furthermore, the material, shape, size, quantity, and arrangement of the constituent elements in the above embodiments can be arbitrary and not limited, as long as the present invention can be realized.

[0111] As stated above, this specification discloses the following matters.

[0112] 1. A method for manufacturing a sulfide solid electrolyte, comprising heating and melting a mixture of sulfide solid electrolyte raw materials, and then cooling and solidifying the resulting melt to obtain a sulfide solid electrolyte.

[0113] The mixture of the above-mentioned sulfide solid electrolyte raw materials includes Li2S and P2S5. If the average particle size of the volume reference of the above-mentioned Li2S, determined by the laser diffraction particle size distribution method, is set as A, and the average particle size of the above-mentioned P2S5, determined by the laser diffraction particle size distribution method, is set as B, then A < 250 μm and B < 250 μm are satisfied.

[0114] 2. The method for manufacturing a sulfide solid electrolyte according to 1 above, wherein 1μm≤A<250μm and 1μm≤B<250μm are satisfied.

[0115] 3. The method for manufacturing a sulfide solid electrolyte according to 1 or 2 above, wherein a sulfur source is supplied to the melt obtained by heating and melting the mixture of the above-mentioned sulfide solid electrolyte raw materials.

[0116] 4. The method for manufacturing a sulfide solid electrolyte according to any one of 1 to 3 above, wherein the mixture of the sulfide solid electrolyte raw materials is heated and melted after containing a sulfur source.

[0117] 5. The method for manufacturing a sulfide solid electrolyte according to any one of 1 to 4 above, wherein the mixture of the above-mentioned sulfide solid electrolyte raw materials is heated and melted at 600°C or above.

[0118] 6. A method for manufacturing a sulfide solid electrolyte according to any one of 1 to 5 above, wherein the above-mentioned sulfide solid electrolyte raw material or a mixture of the above-mentioned sulfide solid electrolyte raw materials is continuously fed into a furnace body and heated to melt, while the resulting molten liquid is continuously discharged, thereby continuously obtaining a sulfide solid electrolyte.

[0119] Example

[0120] The following examples illustrate the present invention in detail, but the invention is not limited thereto. Examples 1 and 2 are examples, and Examples 3 and 4 are comparative examples.

[0121] <Evaluation of Lithium-ion Conductivity>

[0122] The sulfide solid electrolytes obtained in each example were further pulverized in a mortar and passed through a 100 μm mesh sieve to obtain sulfide solid electrolyte powder with a D50 of 10 μm based on the volume reference particle size distribution determined by laser diffraction particle size distribution determination method. The powder was pressed into a powder body under a pressure of 380 MPa and used as a test sample. The lithium-ion conductivity was measured using an AC impedance gauging device (VSP potentiostat / galvanometer manufactured by Bio-Logic Sciences Instruments) and evaluated according to the following criteria.

[0123] The measurement conditions were set as follows: measurement frequency: 100Hz~1MHz, measurement voltage: 100mV, and measurement temperature: 25℃.

[0124] <ICP emission spectroscopy analysis and ion chromatography analysis>

[0125] For the sulfide solid electrolytes obtained in each example, the amount of phosphorus (P) was determined by ICP emission spectroscopy, the amount of chloride (Cl) was determined by ion chromatography, and the P / Ha(Cl) molar ratio was determined. Whether the P / Ha(Cl) ratio met the target composition was evaluated according to the following criteria.

[0126] ○: The difference between the P / Ha(Cl) molar ratio and the initial molar ratio is less than 5%.

[0127] ×: The difference between the molar ratio of P / Ha(Cl) and the molar ratio at the time of input is more than 5%.

[0128] 〈Example 1〉

[0129] (Li2S, P2S5, LiCl powder)

[0130] First, to reduce the particle size of Li₂S, P₂S₅, and LiCl, the Li₂S, P₂S₅, and LiCl raw materials were pulverized using a WARING MX1100XTM at 24,000 rpm for 300 seconds. Dibutyl ether was used as the measurement solvent, with the particle refractive index set to 1.81 and the solvent refractive index set to 1.353. The D50 of the volumetric particle size distribution of the pulverized Li₂S, P₂S₅, and LiCl was determined using a Microtrack MT3000II laser diffraction particle size distribution method, yielding values ​​of 12 μm, 16.5 μm, and 10 μm, respectively.

[0131] (Raw material mixing)

[0132] In a glove box with a nitrogen atmosphere adjusted to a dew point of -50°C, the pulverized Li₂S, P₂S₅, and LiCl raw material powders were sequentially mixed in a ratio of 1.9:0.5:1.6 (mol ratio) and thoroughly stirred to obtain a mixture. The ratio of the above raw material powders was designed with a P / Ha(Cl) molar ratio within the range of 0.59375 ± 0.00059.

[0133] 200g of the resulting mixture was placed into a carbon container that had been replaced with a nitrogen atmosphere with a dew point below -50°C.

[0134] (Heating and melting)

[0135] Add 10% by mass of sulfur powder relative to the total weight of the mixture obtained above, heat together with the mixture, and maintain at 700°C for 1 hour.

[0136] (Discharge and cooling / curing)

[0137] The molten liquid is discharged from the outlet of the container and recovered in a carbon container after being cooled by water, to obtain a sulfide solid electrolyte with an amorphous phase and a sulfide-germanium ore-type crystalline phase.

[0138] 〈Example 2〉

[0139] Under the same conditions as in Example 1, only Li2S and P2S5 were pulverized, dibutyl ether was used as the determination solvent, the particle refractive index was set to 1.81 and the solvent refractive index was set to 1.353, and Li2S raw material with a volume-based particle size distribution D50 of 12 μm and P2S5 raw material with a D50 of 16.5 μm were used, and LiCl raw material with a D50 of 380 μm was used without pulverization. Otherwise, the process was the same as in Example 1 to obtain the sulfide solid electrolyte of Example 2.

[0140] 〈Example 3〉

[0141] Without pulverizing the raw materials, dibutyl ether was used as the test solvent. The particle refractive index was set to 1.81 and the solvent refractive index was set to 1.353. Li2S raw material with a volume-based particle size distribution D50 of 720 μm, P2S5 raw material with a D50 of 900 μm, and LiCl raw material with a D50 of 380 μm were used, which were determined by laser diffraction particle size distribution measurement method using Microtrack MT3000II. Otherwise, the same procedure as in Example 1 was followed to obtain the sulfide solid electrolyte of Example 3.

[0142] 〈Example 4〉

[0143] Without pulverizing the raw materials, the Li2S raw material was simply passed through a sieve with a mesh size of 500 μm. Dibutyl ether was used as the determination solvent, and the particle refractive index was set to 1.81 and the solvent refractive index was set to 1.353. P2S5 raw material with a volume-based particle size distribution D50 of 300 μm and LiCl raw material with a D50 of 380 μm were used, which were determined by laser diffraction particle size distribution determination method using the MT3000II manufactured by Microtrack Corporation. Otherwise, the process was the same as in Example 1, and the sulfide solid electrolyte of Example 4 was obtained.

[0144] The composition (P / Ha(Cl) molar ratio) and lithium-ion conductivity of each example are summarized in Table 1.

[0145]

[0146] As shown in Table 1, since the D50 of Li2S and P2S5 in the mixture of raw material powders in Examples 1 and 2 is less than 250 μm, the P / Ha(Cl) molar ratio is within the target composition range. Furthermore, the lithium-ion conductivity results are also good.

[0147] On the other hand, since the D50 of both Li2S and P2S5 in the mixture of raw material powders in Examples 3 and 4 exceeded 250 μm, the P / Ha(Cl) molar ratio deviated from the target composition. Furthermore, the lithium-ion conductivity results were also poor.

[0148] The various embodiments have been described above, but the present invention is certainly not limited to these examples. Obviously, those skilled in the art will be able to conceive of various modifications or alterations within the scope of the claims, and these also fall within the technical scope of the present invention. Furthermore, the constituent elements of the above embodiments can be combined arbitrarily without departing from the spirit of the invention.

[0149] It should be noted that this application is based on Japanese Patent Application No. 2023-119363, filed on July 21, 2023, the contents of which are incorporated herein by reference.

Claims

1. A method for producing a sulfide solid electrolyte, which heats and melts a mixture of sulfide solid electrolyte raw materials, and cools and solidifies the resultant molten liquid, thereby obtaining a sulfide solid electrolyte, wherein the mixture of sulfide solid electrolyte raw materials contains Li2S and P2S5, and if the average particle diameter of the Li2S on a volume basis as measured by a laser diffraction type particle size distribution measurement method is set as A, and the average particle diameter of the P2S5 on a volume basis as measured by a laser diffraction type particle size distribution measurement method is set as B, A < 250 μm and B < 250 μm are satisfied. 1 μm ≤ A < 250 μm and 1 μm ≤ B < 250 μm are satisfied.

2. The method for producing a sulfide solid electrolyte according to claim 1, wherein A sulfur source is supplied to the molten liquid obtained by heating and melting the mixture of sulfide solid electrolyte raw materials.

3. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein The heating and melting is performed after the sulfur source is contained in the mixture of sulfide solid electrolyte raw materials.

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

5. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein The sulfide solid electrolyte raw materials or the mixture of sulfide solid electrolyte raw materials is continuously charged into a furnace body and heated and melted, while the resultant molten liquid is continuously discharged, thereby continuously obtaining a sulfide solid electrolyte.

6. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein ​

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