Mixture of sulfide solid electrolyte raw materials and method for producing sulfide solid electrolyte

Abstract

The present invention relates to a mixture of raw materials for a sulfide solid electrolyte, which contains Li2S and P2S5, and satisfies A < B, where A is the average particle diameter of the Li2S and B is the average particle diameter of the P2S5. Furthermore, the present invention relates to a method for producing a sulfide solid electrolyte, the method comprising: a step in which a sulfide solid electrolyte raw material is introduced into a heated furnace and mixed to obtain a mixture of the sulfide solid electrolyte raw material; or a step of feeding a mixture of sulfide solid electrolyte raw materials into the heated furnace body, and a step of heating and melting the mixture of sulfide solid electrolyte raw materials, and cooling and solidifying the obtained molten liquid to obtain a sulfide solid electrolyte; the mixture of the sulfide solid electrolyte raw materials contains Li2S and P2S5, and when the average particle diameter of the Li2S is A and the average particle diameter of the P2S5 is B, A < B is satisfied.

Description

Technical Field

[0001] This invention relates to a mixture of sulfide solid electrolyte raw materials and a method for manufacturing sulfide solid electrolytes. 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 processing, if the mixed raw materials are heated in a furnace, the raw material particles may agglomerate. In particular, since P2S5, one of the raw materials, has a low melting point, the particles tend to stick together even at low temperatures. Therefore, the raw material particles agglomerate in the feed section to the furnace, causing blockage and making it difficult to stably supply the mixed raw materials to the furnace.

[0004] In response, for example, in Patent Document 1, by pre-synthesizing a composite compound containing lithium, phosphorus and sulfur, and using the composite compound as a raw material to perform heating and melting, it is possible to suppress the coagulation blockage caused by the raw material.

[0005] In addition, in Patent Document 2, a sulfide solid electrolyte is synthesized by compressing and heating a solid raw material to form a melt, thereby suppressing the volatilization of the raw material and suppressing the coagulation blockage caused by the raw material.

[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 above-mentioned composite compound to be synthesized in advance, thus complicating the manufacturing process.

[0009] Furthermore, Patent Document 2 does not describe the low-temperature condensation of the raw materials, thus failing to solve the aforementioned problem. Additionally, the method disclosed in Patent Document 2 requires compressing the raw materials, resulting in a highly complex equipment structure, making it difficult to mass-produce solid electrolytes.

[0010] In view of the above, the object of the present invention is to provide a mixture of sulfide solid electrolyte raw materials that can suppress coagulation blockage caused by raw materials and stably produce sulfide solid electrolytes when manufacturing sulfide solid electrolytes by a melt method, and a method for manufacturing sulfide solid electrolytes using the mixture.

[0011] Through in-depth research, the inventors discovered that by making the average particle size of Li2S in the mixture of sulfide solid electrolyte raw materials smaller than the average particle size of P2S5, it is possible to suppress agglomeration and blockage during raw material supply and achieve stable production, thus completing the present invention.

[0012] That is, one aspect of the present invention relates to a mixture of sulfide solid electrolyte raw materials, comprising Li2S and P2S5, wherein if the average particle size of the Li2S measured by laser diffraction particle size distribution method is set as A, and the average particle size of the P2S5 measured by laser diffraction particle size distribution method is set as B, then A < B is satisfied.

[0013] Another aspect of the present invention relates to a method for manufacturing a sulfide solid electrolyte, comprising: a step of feeding a sulfide solid electrolyte raw material into a heated furnace body for mixing to obtain a mixture of the sulfide solid electrolyte raw material; or a step of feeding the mixture of sulfide solid electrolyte raw material into a heated furnace body; and a step of heating and melting the mixture of the sulfide solid electrolyte raw material, and cooling and solidifying the resulting melt to obtain the sulfide solid electrolyte; wherein the mixture of the sulfide solid electrolyte raw material comprises Li₂S and P₂S₅.

[0014] If we define the average particle size of the volume reference of Li2S as A, determined by the laser diffraction particle size distribution method, and define the average particle size of the volume reference of P2S5 as B, then A < B.

[0015] According to the present invention, it is possible to suppress coagulation and blockage during the supply of sulfide solid electrolyte raw materials, and to stably manufacture sulfide solid electrolytes. Attached Figure Description

[0016] Figure 1 is a flowchart illustrating the method for manufacturing a sulfide solid electrolyte according to this embodiment.

[0017] Figure 2A This is a microscope photograph of the mixture in Example 1.

[0018] Figure 2B This is a microscope photograph of the mixture in Example 4.

[0019] Figure 3This is a schematic diagram of a device used to measure the temperature during blockage, as shown in the embodiment. Detailed Implementation

[0020] 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.

[0021] 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.

[0022] Mixtures of sulfide solid electrolyte feedstocks

[0023] The mixture of sulfide solid electrolyte raw materials involved in this embodiment is characterized in that it contains Li2S and P2S5. If the average particle size of the Li2S measured by the laser diffraction particle size distribution method is set as A, and the average particle size of the P2S5 measured by the laser diffraction particle size distribution method is set as B, then A < B.

[0024] • A mixture of sulfide solid electrolyte feedstocks containing Li2S and P2S5

[0025] In a mixture of sulfide solid electrolyte raw materials containing Li₂S and P₂S₅ (hereinafter also referred to as the raw material), if the average particle size of the Li₂S contained in the mixture, measured by laser diffraction particle size distribution method, is set as A, and the average particle size of the P₂S₅ contained in the mixture, measured by laser diffraction particle size distribution method, is set as B, then A < B. Therefore, if... Figure 2A As shown, it is possible to bring many Li2S particles in this mixture into contact with the surface of P2S5 particles or to coat the surface of P2S5 particles with Li2S particles. This suppresses the contact between P2S5 particles and brings the higher melting point Li2S particles into contact with each other, thereby suppressing the aggregation of raw material particles and thus suppressing blockages in the supply section, etc.

[0026] In addition, it can be speculated that this is because by making the particle size of Li2S smaller than that of P2S5, Li2S particles can easily enter the gaps around P2S5 particles, enabling many Li2S particles to come into contact with the surface of P2S5 particles, or enabling the surface of P2S5 particles to be covered with Li2S particles.

[0027] In addition, by making the average particle size of P2S5 larger than that of Li2S, the dispersion of P2S5 after it is fed into the heating furnace can be suppressed, thereby suppressing the volatilization of P2S5 upon contact with the furnace wall.

[0028] The aforementioned A is preferably 0.1 to 50 μm. Furthermore, the aforementioned A is preferably 0.1 μm or more, more preferably 1 μm or more, and particularly preferably 2 μm or more. Additionally, the aforementioned A is preferably 50 μm or less, more preferably 40 μm or less, and particularly preferably 30 μm or less.

[0029] The aforementioned 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 aforementioned B is more preferably 2000 μm or less, even more preferably 1750 μm or less, and particularly preferably 1500 μm or less. Alternatively, the aforementioned B may also be 50 to 2000 μm.

[0030] Furthermore, the ratio of A to B (A / B) is preferably 0.5 or less (A / B ≤ 0.5). More preferably, A / B is 0.4 or less, and particularly preferably 0.3 or less. More preferably, A / B is 0.0025 or more, further preferably 0.005 or more, and particularly preferably 0.0075 or more. Alternatively, A / B can be from 0.0025 to 0.5.

[0031] The average particle size of Li2S and P2S5 in a volumetric reference, determined by laser diffraction particle size distribution measurement, can be measured, for example, using an MT3000II (manufactured by Microtrac). The aforementioned average particle size refers to the D50 of the particle size distribution in the volumetric reference, as determined by laser diffraction particle size distribution measurement.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] The composition of the sulfide solid electrolyte containing Li2S and P2S5 can be appropriately determined based on the desired composition of the sulfide solid electrolyte.

[0037] 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).

[0038] 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).

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.).

[0043] 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).

[0044] 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.

[0045] The mixing ratio of these raw materials is not particularly limited. 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 this mixture, S / R, is preferably 0.65 / 0.35 or less, and more preferably 0.5 / 0.5 or less.

[0046] For this mixture, it is preferable to mix it according to the prescribed stoichiometric ratio corresponding to the raw material to obtain the mixture.

[0047] 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.

[0048] When mixing raw materials, combinations of substances containing alkali metal elements and substances containing sulfur elements can be used, in addition to the combination of Li2S and P2S5, combinations of Li2S, P2S5 and LiHa can be used when the resulting sulfide solid electrolyte has halogen elements as constituent elements.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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, the raw material preferably contains a compound containing a halogen element.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] When the sulfide solid electrolyte obtained using this mixture contains an amorphous phase, from the viewpoint that the amorphous phase can be 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 the raw material. One of these can be used, or two or more can be used in combination.

[0057] From the viewpoint of imparting moisture resistance to the sulfide solid electrolyte obtained by using this mixture, it is preferable that the raw materials contain oxides such as SiO2, B2O3, GeO2, Al2O3, and P2O5. One of these can be used, or two or more can be used in combination.

[0058] The content of the aforementioned sulfides and oxides relative to the total content of the raw material is preferably 0.1 to 50% by mass, more preferably 0.5 to 40% by mass. Here, the aforementioned content 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.

[0059] This mixture may further contain compounds that serve as nuclei, as described later.

[0060] Furthermore, this embodiment aims to suppress agglomeration and blockage caused by the low melting point of P2S5, which makes particles easily adhere to each other even at low temperatures. However, it also suppresses agglomeration and blockage caused by low-melting-point compounds other than P2S5. Examples of low-melting-point compounds other than P2S5 include LiI, B2S3, S, Se, and Sb2S3. Therefore, this mixture is effective even when using this raw material containing P2S5 and the aforementioned low-melting-point compounds to manufacture sulfide solid electrolytes.

[0061] Manufacturing Method of Sulfide Solid Electrolytes

[0062] The manufacturing method involved in this embodiment is characterized by including: a step of feeding a sulfide solid electrolyte raw material into a heated furnace body for mixing to obtain a mixture of the aforementioned sulfide solid electrolyte raw materials, or a step of feeding the mixture of sulfide solid electrolyte raw materials into a heated furnace body, and a step of heating and melting the mixture of the aforementioned sulfide solid electrolyte raw materials, and cooling and solidifying the obtained melt to obtain a sulfide solid electrolyte; the mixture of the aforementioned sulfide solid electrolyte raw materials includes Li2S and P2S5, and if the average particle size of the aforementioned Li2S measured by the laser diffraction particle size distribution method is set as A, and the average particle size of the aforementioned P2S5 measured by the laser diffraction particle size distribution method is set as B, then A < B.

[0063] like Figure 1 As shown, the manufacturing method involved in this embodiment includes the following steps.

[0064] (Step S1) The process of feeding the sulfide solid electrolyte raw material into the heated furnace body for mixing to obtain the above-mentioned mixture of sulfide solid electrolyte raw materials, or the process of feeding the mixture of sulfide solid electrolyte raw materials into the heated furnace body.

[0065] (Step S2) The process of heating and melting the mixture of sulfide solid electrolyte raw materials, and then cooling and solidifying the resulting melt to obtain the sulfide solid electrolyte.

[0066] The following is a description of each step.

[0067] <Step S1: The process of adding the sulfide solid electrolyte raw material into the heated furnace body for mixing to obtain the above-mentioned mixture of sulfide solid electrolyte raw materials, or the process of adding the mixture of sulfide solid electrolyte raw materials into the heated furnace body>

[0068] In the manufacturing method described in this embodiment, a sulfide solid electrolyte raw material or a mixture of sulfide solid electrolyte raw materials is fed into a heated furnace body. Here, feeding the sulfide solid electrolyte raw material or a mixture of sulfide solid electrolyte raw materials into the heated furnace body can mean starting to feed the sulfide solid electrolyte raw material or the mixture of sulfide solid electrolyte raw materials while the furnace body is already heated, or it can mean starting to heat the furnace body midway through feeding the sulfide solid electrolyte raw material or the mixture of sulfide solid electrolyte raw materials.

[0069] The temperature of the heated furnace body is preferably 500 to 1000°C. Furthermore, the temperature of the heated furnace body is preferably 500°C or higher, more preferably 550°C or higher, particularly preferably 600°C or higher, and preferably 1000°C or lower, more preferably 950°C or lower, and particularly preferably 900°C or lower.

[0070] 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.

[0071] In step S1, the sulfide solid electrolyte raw material can be added to the heated furnace body for mixing to obtain a mixture of sulfide solid electrolyte raw materials, or the mixture of sulfide solid electrolyte raw materials can be added to the heated furnace body. Here, the sulfide solid electrolyte raw material and the mixture of sulfide solid electrolyte raw materials refer to the mixture of the aforementioned sulfide solid electrolyte raw materials and sulfide solid electrolyte raw materials in the "Mixture of Sulfide Solid Electrolyte Raw Materials".

[0072] From the viewpoint of improving the homogeneity of the obtained sulfide solid electrolyte, it is preferable to put the mixture into a heating furnace and perform the heating and melting process described later.

[0073] When the raw material is added to a heating furnace and mixed to obtain a mixture, and then heated and melted as described later, the addition ratio of the raw material can be appropriately determined based on the composition of the target sulfide solid electrolyte. Furthermore, when the mixture obtained by mixing the raw material is added to a heating furnace and then heated and melted as described later, the mixing ratio of the raw material can be appropriately determined based on the composition of the target sulfide solid electrolyte.

[0074] <Step S2: The process of heating and melting the mixture of sulfide solid electrolyte raw materials, and then cooling and solidifying the resulting melt to obtain the sulfide solid electrolyte>

[0075] • Heating and melting

[0076] In step S2 of this embodiment, after the raw material or the mixture is put into a heating furnace, and the raw material is mixed as needed to obtain the mixture, the mixture is heated and melted.

[0077] 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.

[0078] 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.

[0079] There are no particular restrictions on the heating time as long as the mixture can be melted; for example, it can be more than 0.5 hours, more than 1 hour, or more than 2 hours.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] In this manufacturing method, any one method or a combination of multiple methods can be used to obtain the gaseous atmosphere containing sulfur.

[0087] Cooling and curing

[0088] Next, the molten liquid obtained by heating and melting is cooled and solidified to obtain a sulfide solid electrolyte. A solid sulfide solid electrolyte can be obtained by cooling the molten liquid.

[0089] The molten liquid obtained by the above heating and melting process 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.

[0090] From the viewpoint of maintaining the composition of the obtained melt, the cooling rate is preferably 0.01°C / second or more, more preferably 0.05°C / second or more, and even more preferably 0.1°C / second or more. 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 less.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] In the case of obtaining a sulfide solid electrolyte containing a crystalline phase, it is preferable to contain a compound that serves as a crystal nucleus in the melt to facilitate crystal precipitation.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] 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.

[0103] In addition, the above heat treatment can rearrange the ions within the crystal structure, thereby improving the lithium-ion conductivity.

[0104] 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.

[0105] In the manufacturing method of this embodiment, steps S1 and S2 are preferably performed as consecutive processes. 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.

[0106] By continuously manufacturing sulfide solid electrolytes, the series of processes of heating and melting the mixture, draining the molten liquid, and cooling and solidifying are completed in a continuous manner, enabling the production of large quantities of sulfide solid electrolytes more efficiently in a short time.

[0107] In a continuous process, a more preferred method is to first heat and melt an amount of the mixture to form a molten liquid within the furnace, sufficient to create 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 within the furnace, any subsequent additions of the raw material or mixture will melt instantly due to a rapid increase in temperature. Therefore, as the raw material or mixture is added, molten liquid is continuously generated and discharged, and after a cooling and solidification process, a sulfide solid electrolyte can be continuously obtained in a short time.

[0108] 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.

[0109] Alternatively, in the manufacturing method of this embodiment, steps S1 and S2 can also be performed intermittently. Intermittent means that after adding sulfide solid electrolyte raw materials or their mixtures into the furnace, heating and melting them and then discharging the entire amount, the contents of the furnace are completely replaced each time the manufacturing method of this embodiment is implemented.

[0110] <Sulfide Solid Electrolytes>

[0111] 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 GeP2S 12 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] As stated above, this specification discloses the following matters.

[0119] 1. A mixture of sulfide solid electrolyte raw materials, comprising Li2S and P2S5, wherein if the average particle size of the Li2S measured by laser diffraction particle size distribution method is set as A, and the average particle size of the P2S5 measured by laser diffraction particle size distribution method is set as B, then A < B.

[0120] 2. A mixture of sulfide solid electrolyte raw materials according to 1 above, wherein A / B ≤ 0.5.

[0121] 3. A mixture of sulfide solid electrolyte raw materials according to 1 or 2 above, wherein B ≥ 50 μm.

[0122] 4. A method for manufacturing a sulfide solid electrolyte, comprising: a step of feeding sulfide solid electrolyte raw materials into a heated furnace body for mixing to obtain a mixture of the aforementioned sulfide solid electrolyte raw materials, or a step of feeding the mixture of sulfide solid electrolyte raw materials into a heated furnace body, and

[0123] The step of heating and melting the mixture of the above-mentioned sulfide solid electrolyte raw materials, and then cooling and solidifying the resulting melt to obtain the sulfide solid electrolyte;

[0124] 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 < B.

[0125] 5. The method for manufacturing sulfide solid electrolyte according to 4 above, wherein A / B ≤ 0.5.

[0126] 6. The method for manufacturing a sulfide solid electrolyte according to 4 or 5 above, wherein B ≥ 50 μm.

[0127] 7. The method for manufacturing sulfide solid electrolyte according to any one of 4 to 6 above, wherein the above-mentioned sulfide solid electrolyte raw material or a mixture of sulfide solid electrolyte raw materials is continuously fed into a heated furnace body and heated to melt, while the obtained molten liquid is continuously discharged, thereby continuously obtaining sulfide solid electrolyte.

[0128] 8. The method for manufacturing a sulfide solid electrolyte according to any one of 4 to 7 above, wherein a sulfur source is supplied to the molten liquid obtained by heating and melting the mixture of the above-mentioned sulfide solid electrolyte raw materials.

[0129] 9. The method for manufacturing a sulfide solid electrolyte according to any one of 4 to 8 above, wherein the mixture of the sulfide solid electrolyte raw materials is heated and melted after containing a sulfur source.

[0130] 10. The method for manufacturing a sulfide solid electrolyte according to any one of 4 to 9 above, wherein the mixture of the above-mentioned sulfide solid electrolyte raw materials is heated and melted at 600°C or above.

[0131] Example

[0132] 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.

[0133] <Temperature during blockage>

[0134] To simulate the process of feeding the mixed raw materials from the furnace supply section into the heated furnace body, such as... Figure 3As shown, firstly, the metal pipe 1 is vertically erected on the heating plate 2, with its end in contact with the heating surface of the heating plate. Next, the mixed raw material 3 of each example is introduced into the upper part of the metal pipe 1 to heat the heating plate 2. A thermocouple 4 is installed at the lower front end of the metal pipe 1 to measure the temperature of the lower front end. After heating, nitrogen gas, pressurized to 0.1 MPa, is supplied from the upper part, and the temperature of the lower front end of the metal pipe 1 is measured when the nitrogen gas cannot flow.

[0135] 〈Example 1〉

[0136] (Li2S pulverized)

[0137] First, to achieve a small particle size for Li₂S, the Li₂S raw material was pulverized using a WARIN MX1100XTM at a rotation speed of 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 was measured using a Microtrack MT3000II laser diffraction particle size distribution method, and the result was 12 μm.

[0138] (Raw material mixing)

[0139] In a glove box with a nitrogen atmosphere adjusted to a dew point of -50°C, the above-mentioned pulverized Li2S, P2S5, and LiCl raw material powders were mixed in sequence at a ratio of 1.9:0.5:1.6 (mol ratio) and thoroughly stirred to obtain the mixture of sulfide solid electrolyte raw materials of Example 1.

[0140] It should be noted that 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. The D50 of the volume standard particle size distribution of the P2S5 used above was measured by laser diffraction particle size distribution measurement method using the MT3000II of Microtrack, and the result was 230 μm.

[0141] 〈Example 2〉

[0142] The Li2S raw material was passed through a 100 μm mesh sieve. 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. The volume-based particle size distribution was determined using a Microtrack MT3000II laser diffraction particle size distribution determination method. The Li2S raw material with a D50 of 70 μm was used. Otherwise, the procedure was the same as in Example 1, to obtain the mixture of sulfide solid electrolyte raw materials of Example 2.

[0143] 〈Example 3〉

[0144] Dibutyl ether was used as the solvent for determination. The particle refractive index was set to 1.81 and the solvent refractive index was set to 1.353. The particle size distribution based on volume was determined by laser diffraction particle size distribution determination method using an MT3000II manufactured by Microtrack. Li2S raw material with D50 of 720 μm was used. Otherwise, the procedure was the same as in Example 1, and a mixture of sulfide solid electrolyte raw materials of Example 3 was obtained.

[0145] 〈Example 4〉

[0146] Li2S and P2S5 raw materials were passed through a sieve with a mesh size of 500 μm. 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. The Li2S raw materials with volume-based particle size distributions D50 of 365 μm and 150 μm, respectively, were used 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 to obtain the sulfide solid electrolyte of Example 4.

[0147] The temperature and other parameters during blockage in each case are summarized in Table 1.

[0148]

[0149] As shown in Table 1, the D50 of Li₂S in the mixture of raw material powders in Examples 1 and 2 is smaller than that of P₂S₅, resulting in a higher temperature at which blockage occurs. This indicates that sulfide solid electrolytes can be synthesized while suppressing agglomeration blockage caused by the raw materials. That is, as... Figure 2A As shown, it can be considered that many Li2S particles in this mixture can come into contact with the surface of P2S5 particles, or that the surface of P2S5 particles can be coated with Li2S particles, thereby inhibiting the contact between P2S5 particles and allowing Li2S particles with higher melting points to come into contact with each other. Therefore, it is believed that the aggregation of raw material particles can be inhibited, thereby inhibiting the blockage of the supply section, etc.

[0150] On the other hand, since the D50 of Li2S in the mixture of raw material powders in Examples 3 and 4 is greater than the D50 of P2S5, the temperature at which blockage occurs is low. This indicates that the agglomeration blockage caused by the raw materials cannot be sufficiently suppressed. That is, as... Figure 2B As shown, due to the large particle size of Li2S particles, it is impossible for the Li2S particles in this mixture to fully contact the surface of P2S5 particles, or for the surface of P2S5 particles to be covered with Li2S particles. Therefore, it is believed that it is impossible to fully suppress the aggregation of raw material particles.

[0151] 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.

[0152] It should be noted that this application is based on Japanese Patent Application No. 2023-119362, filed on July 21, 2023, the contents of which are incorporated herein by reference.

Claims

1. A mixture of sulfide solid electrolyte raw materials, comprising Li2S and P2S5, wherein if a volume-based average particle diameter of the Li2S measured by a laser diffraction particle size distribution measurement method is set as A and a volume-based average particle diameter of the P2S5 measured by the laser diffraction particle size distribution measurement method is set as B, A < B is satisfied.

2. The mixture of sulfide solid electrolyte raw materials according to claim 1, wherein, A / B ≤ 0.5 is satisfied.

3. The mixture of sulfide solid electrolyte raw materials according to claim 1 or 2, wherein, B ≥ 50 μm is satisfied.

4. A method for producing a sulfide solid electrolyte, comprising: a step of mixing sulfide solid electrolyte raw materials in a heated furnace or a step of mixing a mixture of sulfide solid electrolyte raw materials in a heated furnace, and a step of heating and melting the mixture of sulfide solid electrolyte raw materials and solidifying a resultant molten liquid to obtain a sulfide solid electrolyte; the mixture of sulfide solid electrolyte raw materials comprises Li2S and P2S5, wherein if a volume-based average particle diameter of the Li2S measured by a laser diffraction particle size distribution measurement method is set as A and a volume-based average particle diameter of the P2S5 measured by the laser diffraction particle size distribution measurement method is set as B, A < B is satisfied.

5. The method for producing a sulfide solid electrolyte according to claim 4, wherein A / B ≤ 0.5 is satisfied.

6. The method for producing a sulfide solid electrolyte according to claim 4 or 5, wherein B ≥ 50 μm is satisfied.

7. The method for producing a sulfide solid electrolyte according to claim 4 or 5, wherein The mixture of sulfide solid electrolyte raw materials is continuously fed to a heated furnace and heated and melted, and a resultant molten liquid is continuously discharged, thereby continuously obtaining a sulfide solid electrolyte.

8. The method for producing a sulfide solid electrolyte according to claim 4 or 5, wherein A sulfur source is supplied to a molten liquid obtained by heating and melting the mixture of sulfide solid electrolyte raw materials.

9. The method for producing a sulfide solid electrolyte according to claim 4 or 5, wherein The mixture of sulfide solid electrolyte raw materials is heated and melted after a sulfur source is contained therein.

10. The method for producing a sulfide solid electrolyte according to claim 4 or 5, wherein The mixture of sulfide solid electrolyte raw materials is heated and melted at 600°C or higher. The mixture of sulfide solid electrolyte raw materials is heated and melted at 600°C or higher.

Images