Method for producing sulfide solid electrolyte

Abstract

The present invention pertains to a method for producing a sulfide solid electrolyte, the method comprising: introducing sulfide solid electrolyte raw materials into a heated furnace body and mixing the same to obtain a mixture of the sulfide solid electrolyte raw materials, or introducing a mixture of sulfide solid electrolyte raw materials into a heated furnace body; and heating and melting the mixture of the sulfide solid electrolyte raw materials, and cooling and solidifying the obtained melt to obtain a sulfide solid electrolyte, wherein the mixture of the sulfide solid electrolyte raw materials contains Li2S and P2S5, and when the volume-based average particle diameter of Li2S, as measured by the laser diffraction-type particle size distribution measurement method, is defined as A and the volume-based average particle diameter of P2S5, as measured by the laser diffraction-type particle size distribution measurement method, is defined as B, A≥50 μm and B≥50 μm are satisfied.

Description

Method for producing sulfide solid electrolyte

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

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

[0003] When a sulfide solid electrolyte is produced by a melting method, if the mixed raw materials are heated in a heating furnace, aggregation of raw material particles may occur. ２ S ５ Since the melting point of is low and the particles tend to stick together even at low temperatures, the raw material particles tend to aggregate at the supply section to the heating furnace (particularly near the inlet), causing the supply section to become clogged, resulting in the problem that the mixed raw material cannot be stably supplied to the heating furnace.

[0004] In contrast, for example, the method disclosed in Patent Document 1 involves synthesizing a composite compound containing lithium, phosphorus, and sulfur in advance, and using the composite compound as a raw material to perform heat melting increases the melting point, making it difficult for the composite compounds to adhere to each other, thereby suppressing clogging. Furthermore, the method disclosed in Patent Document 2 compresses solid raw materials to form a compact and then heat melts the compact, thereby suppressing volatilization of the raw materials, and thus enabling the synthesis of a sulfide solid electrolyte while suppressing clogging due to volatilization of the raw materials.

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

[0006] However, the method disclosed in Patent Document 1 requires the composite compound to be synthesized in advance, which complicates the manufacturing process. Furthermore, the method disclosed in Patent Document 2 does not solve the above problem because the entire compact solidifies during heating, making it difficult to charge the compact. Furthermore, the method disclosed in Patent Document 2 requires the raw materials to be compressed, which makes the equipment structure very complicated, making it difficult to mass-produce solid electrolytes.

[0007] In view of the above, an object of the present invention is to provide a method for stably producing a sulfide solid electrolyte by a melting method while suppressing aggregation and clogging due to raw materials.

[0008] As a result of extensive investigation, the inventors have found that Li, which is used as a raw material for the sulfide solid electrolyte, ２ The average particle size of S and P ２ S ５ The inventors have found that by setting the average particle size of the raw material to a predetermined value or more, clogging due to aggregation of the raw material can be suppressed, and a sulfide solid electrolyte can be stably produced, which led to the completion of the present invention.

[0009] That is, the present invention is a method for producing a sulfide solid electrolyte, comprising: charging sulfide solid electrolyte raw materials into a heated furnace body and mixing them to obtain a mixture of the sulfide solid electrolyte raw materials; or charging a mixture of sulfide solid electrolyte raw materials into a heated furnace body, heating and melting the mixture of sulfide solid electrolyte raw materials, and cooling and solidifying the resulting melt to obtain a sulfide solid electrolyte, wherein the mixture of sulfide solid electrolyte raw materials contains Li ２ S and P ２ S ５ and the Li ２ The volume-based average particle size of S measured by a laser diffraction particle size distribution measurement method is A, and the P ２ S ５ The present invention relates to a method for producing a sulfide solid electrolyte, wherein A≧50 μm and B≧50 μm are satisfied, where B is a volume-based average particle size measured by the laser diffraction particle size distribution measurement method described above.

[0010] According to the present invention, aggregation and clogging due to sulfide solid electrolyte raw materials can be suppressed, and a sulfide solid electrolyte can be stably produced.

[0011] FIG. 1 is a flow diagram showing a method for producing a sulfide solid electrolyte according to this embodiment.

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

[0013] <<Method for Producing Sulfide Solid Electrolyte>> A production method according to the present embodiment is a method for producing a sulfide solid electrolyte, comprising: charging sulfide solid electrolyte raw materials into a heated furnace body and mixing them to obtain a mixture of the sulfide solid electrolyte raw materials; or charging the mixture of sulfide solid electrolyte raw materials into a heated furnace body, heating and melting the mixture of the sulfide solid electrolyte raw materials, and cooling and solidifying the resulting melt to obtain a sulfide solid electrolyte, wherein the mixture of sulfide solid electrolyte raw materials contains Li ２ S and P ２ S ５ and the Li ２ The volume-based average particle size of S measured by a laser diffraction particle size distribution measurement method is A, and the P ２ S ５ The present invention is characterized in that, when the volume-based average particle size measured by the laser diffraction particle size distribution measurement method is defined as B, A≧50 μm and B≧50 μm are satisfied.

[0014] The manufacturing method according to this embodiment includes the following steps, as shown in Fig. 1: (Step S1) A step of charging sulfide solid electrolyte raw materials into a heated furnace body and mixing them to obtain a mixture of the sulfide solid electrolyte raw materials, or a step of charging the mixture of sulfide solid electrolyte raw materials into a heated furnace body, and (Step S2) A step of heating and melting the mixture of sulfide solid electrolyte raw materials, and cooling and solidifying the resulting melt to obtain a sulfide solid electrolyte. Each step will be described below.

[0015] <Step S1: Charging sulfide solid electrolyte raw materials into a heated furnace body and mixing to obtain a sulfide solid electrolyte raw material mixture, or charging the sulfide solid electrolyte raw material mixture into a heated furnace body> The production method according to this embodiment includes charging the sulfide solid electrolyte raw materials or the sulfide solid electrolyte raw material mixture into a heated furnace body. Here, charging the sulfide solid electrolyte raw materials or the sulfide solid electrolyte raw material mixture into the heated furnace body may mean starting the charging of the sulfide solid electrolyte raw materials or the sulfide solid electrolyte raw material mixture while the furnace body is heated, or may mean starting heating of the furnace body halfway through the charging of the sulfide solid electrolyte raw materials or the sulfide solid electrolyte raw material mixture.

[0016] The temperature of the heated furnace body is preferably, for example, 500 to 1000° C. 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 is preferably 1000° C. or lower, more preferably 950° C. or lower, particularly preferably 900° C. or lower.

[0017] The furnace body in the heating furnace used for heating and melting can be any conventionally known furnace having a supply section for supplying raw materials to the furnace body, a heating section, and a discharge section for discharging the molten liquid obtained by heating and melting the raw materials, and the material and size of the furnace body can also be selected as desired.

[0018] In step S1, the sulfide solid electrolyte raw materials may be charged into a heated furnace body and mixed to obtain a mixture of sulfide solid electrolyte raw materials, or the sulfide solid electrolyte raw material mixture may be charged into the heated furnace body. In particular, from the viewpoint of enhancing the homogeneity of the resulting sulfide solid electrolyte, it is preferable to charge the mixture into the heating furnace and heat-melt it, in a mixed state. When the raw materials are charged into the heating furnace and mixed to obtain a mixture, and then the heat-melting process described below is performed, the charging ratio of the raw materials may be determined appropriately depending on, for example, the composition of the target sulfide solid electrolyte. Furthermore, when the mixture obtained by mixing the raw materials is charged into the heating furnace and then the heat-melting process described below is performed, the mixing ratio of the raw materials may be determined appropriately depending on, for example, the composition of the target sulfide solid electrolyte. The sulfide solid electrolyte raw materials and the mixture of sulfide solid electrolyte raw materials are described in detail below.

[0019] A mixture of sulfide solid electrolyte raw materials (hereinafter also referred to as the present raw material) (hereinafter also referred to as the present mixture) contains at least Li ２ S and P ２ S ５ The mixture contains at least Li as one of the raw materials contained in the raw material. ２ S powder and P as one of the raw materials contained in this raw material ２ S ５ It may also be obtained by mixing with the powder of

[0020] In the production method according to this embodiment, the Li contained in the mixture ２ The volume-based average particle size of S measured by a laser diffraction particle size distribution measurement method is A, and P contained in this mixture is ２ S ５ Assuming that the volume-based average particle size measured by the laser diffraction particle size distribution measurement method is B, then A ≥ 50 μm and B ≥ 50 μm are satisfied. This makes it possible to suppress clogging by the raw materials, and to stably produce a sulfide solid electrolyte. This is presumably due to the following mechanism. The raw materials for the sulfide solid electrolyte tend to come into contact with each other and collide or are pressed together to form large lumps. In this specification, these large lumps are referred to as compacts. In particular, when the particle size of the sulfide solid electrolyte is small, they tend to form a compact by being closely packed together. If a compact is formed by the raw materials coming into contact with each other or colliding with the wall when being charged, P with a low melting point in the raw materials will melt. ２ S ５ On the other hand, the Li in the mixture of sulfide solid electrolyte raw materials ２ S and P ２ S ５ By increasing the average particle size of the raw material particles to be equal to or greater than the predetermined value, the contact area between the raw material particles is reduced, the formation of a compact can be suppressed, and clogging of the supply section by the raw material can be suppressed. Therefore, it is believed that the raw material can be stably charged into the heating furnace, and ultimately, a sulfide solid electrolyte can be stably produced. Note that the production method according to this embodiment should not be interpreted as being limited to the above mechanism.

[0021] Also, P ２ S５ and Li ２ By increasing the average particle size of S to the above-mentioned predetermined value or more, P ２ S ５ The temperature of the particles is less likely to rise, and clogging of the particles can be suppressed.

[0022] Also, P ２ S ５ and Li ２ By increasing the average particle size of S to the above-mentioned predetermined value or more, when the raw materials are charged into the heating furnace, the raw materials are easily charged into the melt without scattering to the surroundings, and therefore the composition ratio of the obtained sulfide solid electrolyte can be easily maintained within a desired range.

[0023] In the manufacturing method according to this embodiment, A is 50 μm or more (A≧50 μm). Furthermore, A is preferably 80 μm or more, and more preferably 100 μm or more. Furthermore, A is preferably 2000 μm or less (A≦2000 μm), and more preferably 1500 μm or less. Furthermore, A is preferably 50 μm or more and 2000 μm or less (50 μm≦A≦2000 μm).

[0024] In the manufacturing method according to this embodiment, B is 50 μm or more (B≧50 μm). B is preferably 80 μm or more, and more preferably 100 μm or more. B is preferably 2000 μm or less (B≦2000 μm), and more preferably 1500 μm or less. B is preferably 50 μm or more and 2000 μm or less (50 μm≦B≦2000 μm).

[0025] The ratio of A to B (A / B) is not particularly limited, but may be in the range of 50 / 2000 to 2000 / 50.

[0026] Li in this mixture ２ S, P ２ S ５ The volume-based average particle size measured by the laser diffraction particle size distribution measurement method is the average particle size of Li as one of the raw materials measured before mixing. ２ S powder and P ２ S ５The above-mentioned average particle size means the D50 of the volume-based particle size distribution measured by a laser diffraction particle size distribution measurement method.

[0027] The mixture preferably also contains lithium halide (LiHa) as described below. ２ S powder and P ２ S ５ It is preferable to obtain the raw material by mixing the LiHa powder, which is one of the raw materials contained in the raw material, with the LiHa powder. In this case, the volume-based average particle size of the LiHa powder measured by a laser diffraction particle size distribution measurement method is preferably 0.1 to 2000 μm. The average particle size is preferably 0.1 μm or more, more preferably 1 μm or more, and particularly preferably 2 μm or more. The average particle size is more preferably 2000 μm or less, even more preferably 1750 μm or less, and particularly preferably 1500 μm or less.

[0028] Furthermore, the mixture preferably has a volume-based average particle size of 50 μm or more, as measured by a laser diffraction particle size distribution measurement method. By increasing the average particle size of the mixture itself to the above-mentioned predetermined value or more, the contact area between raw material particles is reduced, suppressing the formation of a compact. This is thought to suppress clogging by the raw material at the supply section to the heating furnace, allowing the raw material to be stably charged, and ultimately enabling the stable production of a sulfide solid electrolyte. Furthermore, the average particle size is more preferably 80 μm or more, particularly preferably 100 μm or more, more preferably 2000 μm or less, even more preferably 1750 μm or less, and particularly preferably 1500 μm or less. Furthermore, the average particle size is preferably 50 μm or more and 2000 μm or less.

[0029] The raw material is the above-mentioned Li ２ S and P ２ S ５ One or more of various other raw materials may be used, and may be appropriately selected depending on the composition of the sulfide solid electrolyte to be obtained, as long as they contain the above. Similarly, the sulfide solid electrolyte obtained using these raw materials may be various sulfide solid electrolytes.

[0030] Each of the raw materials contained in the present raw material may be synthesized or commercially available. Each raw material may be in powder form, or the present raw material itself including each raw material may be in powder form. Furthermore, the present raw materials may be subjected to a known pretreatment. That is, the manufacturing method according to this embodiment may appropriately include, prior to step S1, at least one of a step of manufacturing the present raw material and a step of pretreating at least some of the raw materials of the present raw material as step 0, which is a step of preparing the present raw material.

[0031] One of the raw materials contained in the raw material includes, for example, a substance such as an alkali metal element (R) and an elemental sulfur (S). Examples of the alkali metal element (R) include substances such as an elemental lithium (Li), an elemental sodium (Na), and an elemental potassium (K). When the sulfide solid electrolyte is applied to a lithium ion secondary battery, the alkali metal element (R) preferably includes a substance such as an elemental lithium (Li).

[0032] As the alkali metal element (R) source, an appropriate combination of an alkali metal element, a substance containing an alkali metal element, such as a compound containing an alkali metal element, etc. can be used. When the alkali metal element (R) is lithium element (Li), an appropriate combination of Li-containing substances, such as Li element, a compound containing Li, etc. can be used as the lithium element source. As described above, the raw material contains at least Li. ２ It contains S, which can be a source of elemental lithium (Li).

[0033] As a substance containing lithium element (Li), the above-mentioned lithium sulfide (Li ２ In addition to lithium iodide (LiI), lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２ Examples of the substance containing lithium element (Li) include lithium compounds such as lithium hydroxide (LiOH), lithium ion (LiO), and metallic lithium. The substance containing lithium element (Li) may be used alone or in combination of two or more.

[0034] As the substance containing lithium element (Li), it is preferable to use lithium sulfide from the viewpoint of obtaining a sulfide material. Furthermore, when the obtained sulfide solid electrolyte contains a halogen element, it is also preferable to include lithium halide (LiHa, where Ha is a halogen element) as the substance containing lithium element (Li). Lithium halide will be described later.

[0035] As the sulfur element (S) source, a suitable combination of substances containing S, such as simple S or compounds containing S, can be used. The sulfur element (S) containing substance may be used alone or in combination of two or more. As described above, the raw material contains at least Li ２ S and P ２ S ５ These can be a source of elemental sulfur (S). ２ S is a compound that contains both a substance containing sulfur element (S) and the above-mentioned substance containing lithium element (Li). ２ S ５ is a compound that serves as both a substance containing sulfur element (S) and a substance containing phosphorus element (P) as described below.

[0036] Substances containing sulfur (S) include phosphorus pentasulfide (P ２ S ５ ), for example, diphosphorus trisulfide (P ２ S ３ ), other sulfur compounds containing phosphorus, elemental sulfur, and compounds containing sulfur. ２ S, CS ２ , iron sulfide (FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S, etc.), bismuth sulfide (Bi ２ S ３ ), copper sulfide (CuS, Cu ２ S, Cu １－ｘ S, etc.

[0037] From the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte, it is preferable that the raw material further contains phosphorus (P). As a source of phosphorus (P), a suitable combination of substances containing P, such as simple P or a compound containing P, can be used. One type of substance containing phosphorus (P) may be used, or two or more types may be used in combination. As described above, the raw material contains at least P. ２ S ５ which can be a source of elemental phosphorus (P).

[0038] The substance containing phosphorus (P) is the above-mentioned diphosphorus pentasulfide (P ２ S ５ ), for example, diphosphorus trisulfide (P ２ S ３ ) and other phosphorus sulfides, sodium phosphate (Na ３ P.O. ４ ) and elemental phosphorus.

[0039] When the present mixture obtained by mixing the present raw materials is charged into a heating furnace and then heat-melted, the mixing ratio of the present raw materials may be determined appropriately depending on, for example, the composition of the target sulfide solid electrolyte. Also, when the present mixture is obtained by charging the present raw materials into a heating furnace and mixing them, and then heat-melting is performed, the mixing ratio of the present raw materials may be determined appropriately depending on, for example, the composition of the target sulfide solid electrolyte.

[0040] The mixing ratio or input ratio of the raw materials is not particularly limited. For example, the molar ratio S / R of sulfur (S) to alkali metal (R) in the mixture is preferably 0.65 / 0.35 or less, and more preferably 0.5 / 0.5 or less, from the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte.

[0041] When the present mixture obtained by mixing the present raw materials is charged into a heating furnace, it is preferable to mix the present raw materials in a predetermined stoichiometric ratio according to the present raw materials to obtain a mixture.

[0042] The method for mixing the raw materials to obtain the mixture is not particularly limited, but examples thereof include mixing in a mortar, mixing using a media such as a planetary ball mill, and medialess mixing such as a pin mill, a powder mixer, or airflow mixing.

[0043] When mixing or charging the raw material, the combination of the substance containing an alkali metal element and the substance containing sulfur element is as follows: Li ２ S and P ２ S ５ In addition to the combination of Li and Li, when the obtained sulfide solid electrolyte has a halogen element as a constituent element, ２ S and P ２ S ５ and LiHa.

[0044] Li ２ S and P ２ S ５ In the combination of these, the molar ratio of Li to P, Li / P, is preferably 40 / 60 to 88 / 12, and more preferably 50 / 50 to 88 / 12. ２ S ５ Li ２ By adjusting the mixing ratio or the input ratio so that the amount of Li is relatively small compared to S, ２ Melting point of S is ２ S ５ Since the boiling point of the sulfur component is low, it is easy to suppress the volatilization of the sulfur component and the phosphorus component during the heat treatment.

[0045] On the other hand, since lithium sulfide is expensive, in order to reduce the production cost of the sulfide solid electrolyte, lithium compounds other than lithium sulfide, metallic lithium, etc. may be used in addition to lithium sulfide. Specifically, in this case, the raw material may be a substance containing Li, such as metallic lithium, lithium halide (LiHa), or lithium carbonate (Li ２ CO ３ ), lithium sulfate (Li ２ SO ４ ), lithium oxide (Li ２ These may be used alone or in combination of two or more.

[0046] The raw material may contain other substances (compounds, etc.) in addition to the above substances depending on the composition of the target sulfide solid electrolyte or as additives, etc. For example, when producing a sulfide solid electrolyte containing a halogen element such as F, Cl, Br, or I, the raw material preferably contains a halogen element (Ha). In this case, the raw material preferably contains a compound containing a halogen element.

[0047] Examples of compounds containing a halogen element include lithium halides such as lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), and lithium iodide (LiI), phosphorus halides, phosphoryl halides, sulfur halides, sodium halides, and boron halides. Among these, from the viewpoint of reactivity, lithium halides are preferred, LiCl, LiBr, and LiI are more preferred, and LiCl and LiBr are even more preferred. These compounds may be used alone or in combination of two or more.

[0048] In addition, since an alkali metal halide such as lithium halide is also a compound containing an alkali metal element such as Li, it can also serve as a source of the alkali metal element (R) in the raw material.

[0049] When the mixture contains a halogen element (Ha) and a phosphorus element (P), the molar equivalent of the halogen element (Ha) relative to the phosphorus element (P) in the mixture is preferably 0.2 to 4 molar equivalents, more preferably 0.5 to 3 molar equivalents. From the viewpoint of improving the ionic conductivity of the resulting sulfide solid electrolyte, the molar equivalent of the halogen element is preferably 0.2 molar equivalents or more, more preferably 0.5 molar equivalents or more. Furthermore, from the viewpoint of the stability of the resulting sulfide solid electrolyte, the molar equivalent of the halogen element is preferably 4 molar equivalents or less, more preferably 3 molar equivalents or less. When the powder raw material contains two or more halogen elements, it is preferable that the total content thereof satisfies the above-mentioned molar equivalent range.

[0050] The sulfide solid electrolyte obtained by the production method according to this embodiment may be amorphous depending on the purpose. When the obtained sulfide solid electrolyte contains an amorphous phase, the amorphous phase is easily formed even if the quenching rate is reduced during quenching, and from the viewpoint of reducing the equipment load, SiS is used as the raw material. ２ , B ２ S ３ , GeS ２ , Al ２ S ３ These may be used alone or in combination of two or more.

[0051] From the viewpoint of imparting moisture resistance to the resulting sulfide solid electrolyte, the raw material is SiO ２ , B ２ O ３ , GeO ２ , Al ２ O ３ , P ２ O ５ These may be used alone or in combination of two or more.

[0052] When the mixture is charged into a heating furnace, the sulfides and oxides may be contained in the mixture or may be added separately during heating.

[0053] The amount of the sulfide and oxide added is preferably 0.1 to 50 mass%, more preferably 0.5 to 40 mass%, based on the total amount of the raw material. Here, the amount is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and is preferably 50 mass% or less, more preferably 40 mass% or less.

[0054] The mixture may further contain a compound that will serve as a crystal nucleus, which will be described later.

[0055] In addition, the manufacturing method according to this embodiment is ２ S ５ The melting point of P is low, and the particles tend to stick together even at low temperatures, which causes clogging. ２ S ５ It also has an effect of suppressing clogging caused by compounds with low melting points other than P. ２ S５ Examples of compounds with low melting points other than those mentioned above include LiI, B ２ S ３ , S, Se, and Sb ２ S ３ Therefore, P ２ S ５ At the same time, the production method according to this embodiment is also effective when producing a sulfide solid electrolyte using the present raw material containing the above-mentioned compound having a low melting point.

[0056] <Step S2: Heating and Melting the Sulfide Solid Electrolyte Raw Material Mixture, and Cooling and Solidifying the Obtained Melt to Obtain a Sulfide Solid Electrolyte>

[0057] Heat Melting In step S2 of this embodiment, the present raw materials or the present mixture in step S1 are charged into a heating furnace, and the present raw materials are mixed as necessary to obtain the present mixture, and then the present mixture is heated and melted.

[0058] The heat-melting temperature is not particularly limited as long as the mixture is melted, but is preferably 600°C or higher, more preferably 600 to 1000°C, even more preferably 630 to 950°C, even more preferably 650°C or higher but less than 900°C, and particularly preferably 650°C or higher but less than 850°C. From the viewpoint of homogenizing the melt in a short time, the heat-melting temperature is preferably 600°C or higher, more preferably 630°C or higher, and even more preferably 650°C or higher. Furthermore, from the viewpoint of suppressing deterioration or decomposition of the components in the melt, the heat-melting temperature is preferably 1000°C or lower, more preferably 950°C or lower, even more preferably less than 900°C, and particularly preferably less than 850°C. The heat-melting temperature is the temperature of the melt produced in the furnace and can be adjusted by the heating unit provided in the furnace.

[0059] The heating and melting time is not particularly limited as long as the mixture is melted, but may be, for example, 0.5 hours or more, 1 hour or more, or 2 hours or more.

[0060] The pressure during heating and melting is not particularly limited as long as the mixture is melted, but for example, normal pressure or slight pressure is preferred, and normal pressure is more preferred.

[0061] From the viewpoint of preventing side reactions between the melt and water vapor, oxygen, etc. during heating and melting, the dew point inside the furnace is preferably −20° C. or lower, and although there is no particular lower limit for the dew point, it is usually −80° C. or higher. In addition, the oxygen concentration inside the furnace is preferably 1000 ppm by volume or lower.

[0062] The heat melting is preferably carried out in a gas atmosphere containing elemental sulfur. By heat melting the mixture in a gas atmosphere containing elemental sulfur, sulfur is introduced into the resulting melt, thereby suppressing changes in the sulfur composition due to volatilization. Examples of the gas containing elemental sulfur include sulfur gas, hydrogen sulfide gas, carbon disulfide gas, and other gases containing compounds containing elemental sulfur or elemental sulfur.

[0063] The gas atmosphere containing elemental sulfur may be obtained by supplying a sulfur source into a melt obtained by heating and melting the mixture, and then heating the sulfur source to generate a gas containing elemental sulfur. In this case, the sulfur source is not particularly limited as long as it is elemental sulfur or a sulfur compound that can generate a gas containing elemental sulfur by heating. For example, elemental sulfur, hydrogen sulfide, carbon disulfide and other organic sulfur compounds, iron sulfide (FeS, Fe ２ S ３ , FeS ２ , Fe １－ｘ S, etc.), bismuth sulfide (Bi ２ S ３ ), copper sulfide (CuS, Cu ２ S, Cu １－ｘ Examples of the sulfur source include sulfur powder, polysulfides such as lithium polysulfide and sodium polysulfide, polysulfides, rubbers vulcanized with sulfur, etc. As the sulfur source, sulfur powder is preferably used.

[0064] Alternatively, the gas atmosphere containing elemental sulfur may be obtained by introducing sulfur vapor obtained in advance into the furnace body. For example, sulfur is heated at 200 to 450°C to generate sulfur vapor, and N ２ A gas atmosphere containing elemental sulfur can be obtained by transporting an inert gas such as gas, argon gas, or helium gas into the furnace body as a carrier gas.

[0065] Alternatively, the gas atmosphere containing elemental sulfur may be obtained by incorporating a sulfur source into the mixture, which heats the sulfur source when the mixture is heated and melted, thereby enabling the raw material to be heated and melted in a generated gas atmosphere containing elemental sulfur.

[0066] In the present production method, the method for obtaining the gas atmosphere containing elemental sulfur may be any one of the above methods, or a combination of a plurality of methods may be used.

[0067] Cooling and Solidification Subsequently, the melt obtained by the above-mentioned heating and melting is cooled and solidified to obtain a sulfide solid electrolyte. By cooling the melt, a solid sulfide solid electrolyte is obtained.

[0068] The melt obtained by the above-mentioned heating and melting is discharged at any timing from a discharge port provided in the furnace body, and the process proceeds to a cooling and solidification step. The cooling of the melt can be performed by any known method, and is not particularly limited. For example, from the viewpoint of increasing the cooling rate, cooling using a twin roller, which is generally considered to have the fastest quenching rate, is preferred.

[0069] From the viewpoint of maintaining the composition of the melt obtained above, the cooling rate is preferably 0.01° C. / sec or more, more preferably 0.05° C. / sec or more, and even more preferably 0.1° C. / sec or more. There is no particular upper limit to the cooling rate, but the cooling rate of the twin rollers is, for example, 1,000,000° C. / sec or less.

[0070] When an amorphous sulfide solid electrolyte is desired, it is preferable to perform quenching at a higher cooling rate. The cooling rate during quenching is preferably 10°C / sec or higher, more preferably 100°C / sec or higher, even more preferably 500°C / sec or higher, and particularly preferably 700°C / sec or higher. The upper limit of the cooling rate during quenching is not particularly limited, but the cooling rate of the twin rollers is, for example, 1,000,000°C / sec or lower.

[0071] On the other hand, a sulfide solid electrolyte having a crystalline phase may be obtained by slow cooling during the cooling and solidification step. Alternatively, a sulfide solid electrolyte having both a crystalline phase and an amorphous phase may be obtained. The cooling rate during slow cooling is preferably 0.01 to 500°C / sec, more preferably 0.05 to 450°C / sec. It may also be 0.01 to 10°C / sec, or 0.05 to 5°C / sec. Here, the cooling rate is preferably 0.01°C / sec or more, more preferably 0.05°C / sec or more, and is preferably 500°C / sec or less, more preferably 450°C / sec or less. The cooling rate may also be 10°C / sec or less, or 5°C / sec or less. The cooling rate may be adjusted appropriately depending on the crystallization conditions.

[0072] The crystal of the sulfide solid electrolyte is preferably an ion-conductive crystal. Specifically, when the carrier is lithium ions, the ion-conductive crystal has a lithium ion conductivity of 1.0×10 －４ S / cm or more, and the lithium ion conductivity is 1.0×10 －３ More preferably, it is more than 5 S / cm.

[0073] When a sulfide solid electrolyte containing a crystalline phase is to be obtained, it is preferable to add a compound that will become a crystal nucleus to the melt in order to facilitate crystal precipitation. The method for adding the compound that will become a crystal nucleus to the melt is not particularly limited, but examples thereof include a method of adding the compound that will become a crystal nucleus to the mixture in step S1, and a method of directly adding the compound that will become a crystal nucleus to the melt that has been heated and melted.

[0074] Examples of compounds that can become crystal nuclei include oxides, oxynitrides, nitrides, carbides, other chalcogen compounds, and halides. Compounds that can become crystal nuclei are preferably compounds that have a certain degree of compatibility with the melt. Note that compounds that are completely incompatible with the melt cannot become crystal nuclei.

[0075] The amount of the compound that becomes the crystal nuclei added to the melt is preferably 0.01 to 20 mass%, more preferably 0.1 to 20 mass%, and even more preferably 1 to 10 mass%. From the viewpoint of favorably forming a crystalline phase in the resulting sulfide solid electrolyte, the amount added is preferably 0.01 mass% or more, more preferably 0.1 mass% or more, and even more preferably 1 mass% or more. Furthermore, from the viewpoint of suppressing a decrease in lithium ion conductivity, the amount added is preferably 20 mass% or less, and more preferably 10 mass% or less.

[0076] When a sulfide solid electrolyte having a large amorphous phase is desired, a compound serving as a crystal nucleus is not added to the melt, or if added, the amount of the compound added is preferably 1% by mass or less, more preferably 0.1% by mass or less. The amount may also be 0.01% by mass or less.

[0077] The cooling and solidification is preferably carried out under normal pressure. "Under normal pressure" means that the pressure is not controlled during cooling. Specifically, the pressure is about 0.8 to 1.2 atm.

[0078] In the manufacturing method according to the present embodiment, the sulfide solid electrolyte obtained in step S2 may be reheated for heat treatment. This heat treatment may be particularly effective when the sulfide solid electrolyte is amorphous or contains an amorphous phase. Furthermore, this heat treatment may rearrange ions within the crystal structure to increase lithium ion conductivity.

[0079] The heat treatment refers to at least one of a heat treatment for crystallizing the obtained solid and a heat treatment for rearranging ions in the crystal structure. That is, the heat treatment also includes a crystallization treatment by heating of an amorphous sulfide solid electrolyte or a sulfide solid electrolyte containing an amorphous phase.

[0080] In the production method according to this embodiment, it is preferable to carry out the above steps S1 and S2 as a continuous process. That is, it is preferable to continuously charge the raw materials or the mixture into a furnace body, mix the raw materials as needed to obtain the mixture, heat and melt it, and continuously discharge the resulting melt, followed by a step of cooling and solidifying it, thereby continuously obtaining a sulfide solid electrolyte. In this way, it is preferable to continuously produce a sulfide solid electrolyte.

[0081] By continuously producing the sulfide solid electrolyte, a series of steps, including heating and melting the mixture, discharging the melt, and cooling and solidifying it, are carried out continuously, allowing the sulfide solid electrolyte to be produced in large quantities more efficiently in a short period of time.

[0082] In a more preferred embodiment of the continuous process, the present mixture is first heated and melted in an amount sufficient to form at least a melt level in the furnace. Here, the melt level refers to the liquid level formed by the melt covering the entire bottom surface of the furnace. Once a melt level is formed in the furnace, any additional raw materials or mixture added to the melt subsequently undergoes a rapid temperature rise and instantaneous melting. Therefore, as the raw materials or mixture are added, melts are continuously generated one after another. These melts are continuously discharged and subjected to a cooling and solidification process, allowing sulfide solid electrolytes to be continuously produced in a short period of time. This continuous production of sulfide solid electrolytes allows for the production of large quantities of sulfide solid electrolytes in a short period of time. Furthermore, the shortening of the production process also reduces the volatilization of raw materials during the production process.

[0083] In the production method according to this embodiment, the processes of steps S1 and S2 may be performed batchwise. The batchwise method is a method in which the sulfide solid electrolyte raw material or a mixture thereof is charged into a furnace body, heated to melt it, and then the entire amount is discharged, and means a method in which the contents of the furnace body are all replaced every time the production method according to this embodiment is performed.

[0084] <Sulfide Solid Electrolyte> The sulfide solid electrolyte obtained by the production method according to this embodiment includes a sulfide solid electrolyte containing elements Li, P, and S. For example, Li １０GeP ２ S １２ sulfide solid electrolytes having an LGPS type crystal structure, such as Li ６ P.S. ５ Cl, Li ５．４ P.S. ４．４ Cl １．６ and Li ５．４ P.S. ４．４ Cl ０．８ Br ０．８ sulfide solid electrolytes having an argyrodite-type crystal structure, such as those described above, Li-P-S-Ha-based crystallized glasses (wherein Ha represents at least one element selected from halogen elements), and Li ７ P ３ S １１ Examples of such LPS crystallized glasses include:

[0085] The sulfide solid electrolyte may be an amorphous sulfide solid electrolyte, a sulfide solid electrolyte having a specific crystal structure, or a sulfide solid electrolyte containing a crystalline phase and an amorphous phase, depending on the purpose. From the viewpoint of lithium ion conductivity, the crystalline phase is preferably an argyrodite-type crystalline phase.

[0086] From the viewpoint of lithium ion conductivity, a sulfide solid electrolyte containing elements Li, P, S, and Ha is preferred, and more preferably has a crystalline phase. The Ha element is preferably derived from one or more selected from the group consisting of lithium chloride, lithium bromide, and lithium iodide.

[0087] The lithium ion conductivity of the sulfide solid electrolyte is 1.0 × 10 in terms of the battery characteristics when used in a lithium ion secondary battery. －４ S / cm or more is preferable, and 5.0 × 10 －４ S / cm or more is more preferable, and 1.0×10 －３ S / cm or more is more preferable, and 5.0 × 10 －３The lithium ion conductivity in this specification is a value measured using an AC impedance measuring device (for example, Potentiostat / Galvanostat VSP manufactured by Bio-Logic Sciences Instruments) under the conditions of a measurement frequency of 100 Hz to 1 MHz, a measurement voltage of 100 mV, and a measurement temperature of 25°C.

[0088] The obtained sulfide solid electrolyte can be identified by analyzing the crystal structure by X-ray diffraction (XRD) measurement, or by analyzing the elemental composition using various methods such as ICP emission spectrometry, atomic absorption spectrometry, and ion chromatography. For example, P and S can be measured by ICP emission spectrometry, Li can be measured by atomic absorption spectrometry, and Ha can be measured by ion chromatography.

[0089] The present invention is not limited to the above-described embodiments, and various modifications can be adopted within the scope of the present invention. For example, the present invention is not limited to the above-described embodiments, and modifications and improvements can be made as appropriate. In addition, the material, shape, size, number, and location of each component in the above-described embodiments are arbitrary and not limited as long as the present invention can be achieved.

[0090] As described above, the present specification discloses the following: 1. A method for producing a sulfide solid electrolyte, comprising: charging sulfide solid electrolyte raw materials into a heated furnace body and mixing them to obtain a mixture of the sulfide solid electrolyte raw materials; or charging a mixture of sulfide solid electrolyte raw materials into a heated furnace body; and heating and melting the mixture of sulfide solid electrolyte raw materials, and cooling and solidifying the resulting melt to obtain a sulfide solid electrolyte, wherein the mixture of sulfide solid electrolyte raw materials contains Li ２ S and P ２ S ５ and the Li ２ The volume-based average particle size of S measured by a laser diffraction particle size distribution measurement method is A, and the P ２ S ５1. A method for producing a sulfide solid electrolyte, wherein A≧50 μm and B≧50 μm are satisfied, where B is the volume-based average particle size measured by the laser diffraction particle size distribution measurement method in 1. 2. A method for producing a sulfide solid electrolyte according to above 1, wherein 50 μm≦A≦2000 μm and 50 μm≦B≦2000 μm are satisfied. 3. A method for producing a sulfide solid electrolyte according to above 1 or 2, wherein the volume-based average particle size of the mixture of sulfide solid electrolyte raw materials measured by the laser diffraction particle size distribution measurement method is 50 μm or more. 4. A method for producing a sulfide solid electrolyte according to above 3, wherein the volume-based average particle size of the mixture of sulfide solid electrolyte raw materials measured by the laser diffraction particle size distribution measurement method is 2000 μm or less. 5. A method for producing a sulfide solid electrolyte according to any of above 1 to 4, wherein a sulfur source is supplied to a melt obtained by heating and melting the mixture of sulfide solid electrolyte raw materials. 6. 6. A method for producing a sulfide solid electrolyte according to any one of items 1 to 5 above, wherein a sulfur source is added to the mixture of sulfide solid electrolyte raw materials and then the mixture is heated and melted. 7. A method for producing a sulfide solid electrolyte according to any one of items 1 to 6 above, wherein the mixture of sulfide solid electrolyte raw materials is heated and melted at 600°C or higher. 8. A method for producing a sulfide solid electrolyte according to any one of items 1 to 7 above, 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, and the resulting melt is continuously discharged, thereby continuously producing a sulfide solid electrolyte.

[0091] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Example 1 is an example, and Examples 2 and 3 are comparative examples.

[0092] Example 1 (Raw Material Mixing) First, Li ２ S raw material, P ２ S ５ The raw material, LiCl raw material, was prepared. ２ S, P ２ S ５The D50 values ​​of the volume-based particle size distribution were measured by a laser diffraction particle size distribution measurement method using a Microtrack MT3000II with dibutyl ether as a measurement solvent for each of the raw material powders of LiCl, LiCl, and LiCl, with a particle refractive index of 1.81 and a solvent refractive index of 1.353, and were found to be 719 μm, 892 μm, and 384 μm, respectively. ２ S, P ２ S ５ The raw material powders of LiCl were mixed in the order of 1.9:0.5:1.6 (molar ratio) and thoroughly stirred and mixed to obtain a mixed powder. The mixed powder was measured using a laser diffraction particle size distribution measurement method with a Microtrack MT3000II, with dibutyl ether as the measurement solvent, a particle refractive index of 1.81, and a solvent refractive index of 1.353. The D50 of the volumetric particle size distribution was measured and found to be 480 μm. (Heat Melting) 1000 g of the mixed powder obtained above was placed into the hopper of a constant-rate feeder, and the feeder was operated to heat-melt the mixed powder at 700°C. Further mixed powder was continuously added to the resulting melt at a rate of 15 g / min. The continuous addition of the mixed powder was carried out for a total of 120 minutes.

[0093] Example 2 (Raw Material Mixture) Li used in Example 1 ２ S, P ２ S ５ The raw material powders of LiCl were pulverized using a MX1100X™ machine manufactured by WARING Corporation at a rotation speed of 24,000 rpm for 300 seconds. ２ S, P ２ S ５ For each of the raw material powders of LiCl, dibutyl ether was used as a measurement solvent, and the particle refractive index was set to 1.81, the solvent refractive index was set to 1.353, and the D50 of the volume-based particle size distribution was measured by a laser diffraction particle size distribution measurement method using an MT3000II manufactured by Microtrack. The results were 12 μm, 10 μm, and 10 μm, respectively. ２ S, P ２ S ５The raw material powders of LiCl were mixed in the order of 1.9:0.5:1.6 (molar ratio) and thoroughly stirred and mixed to obtain a mixed powder. The mixed powder was measured using a laser diffraction particle size distribution measurement method with a Microtrack MT3000II under the same measurement solvent conditions of dibutyl ether, particle refractive index 1.81, and solvent refractive index 1.353, and the D50 of the volume-based particle size distribution was found to be 12 μm. (Heat Melting) The mixed powder was heat melted under the same conditions as in Example 1.

[0094] Example 3 (Raw Material Mixture) Li used in Example 1 ２ The S powder was pulverized using a WARING MX1100X™ pulverizer at a rotation speed of 24,000 rpm for 300 seconds. ２ S powder and the P powder used in Example 1 ２ S ５ For each of the raw material powders of LiCl, dibutyl ether was used as a measurement solvent, and the particle refractive index was 1.81, the solvent refractive index was 1.353, and the D50 of the volume-based particle size distribution was measured by a laser diffraction particle size distribution measurement method using an MT3000II manufactured by Microtrack. The results were 12 μm, 892 μm, and 384 μm, respectively. ２ S, P ２ S ５ The raw material powders of LiCl were mixed in the order of 1.9:0.5:1.6 (molar ratio) and thoroughly stirred and mixed to obtain a mixed powder. The mixed powder was measured using a laser diffraction particle size distribution measurement method with a Microtrack MT3000II under the same conditions as in Example 1, with dibutyl ether as the measurement solvent, a particle refractive index of 1.81, and a solvent refractive index of 1.353. The D50 of the volume-based particle size distribution was measured and found to be 310 μm. (Heat Melting) The mixed powder was heat melted under the same conditions as in Example 1.

[0095] In each example, it was confirmed whether the mixed raw material could be continuously charged and discharged in its entirety without clogging, and after cooling, the charging port was observed to check for the presence of foreign matter. The results are shown in Table 1.

[0096]

[0097] As can be seen from the results shown in Table 1, in Example 1, the Li in the mixture of raw material powders ２ S and P ２ S ５ Since the D50 of the raw material powder mixture was 50 μm or more, even when the raw material mixture was continuously charged, the entire amount could be discharged without clogging. Furthermore, no foreign matter was observed adhering to the charging port. That is, it was found that in Example 1, which is an example, a sulfide solid electrolyte can be stably produced while suppressing clogging due to aggregation of the raw material. On the other hand, in Examples 2 and 3, the Li in the raw material powder mixture was ２ S and / or P ２ S ５ Since the D50 of the mixed raw material was less than 50 μm, clogging occurred when the mixed raw material was continuously fed, and it was not possible to discharge the entire amount.

[0098] Although various embodiments have been described above, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any manner as long as they do not deviate from the spirit of the invention.

[0099] This application is based on a Japanese patent application (Patent Application No. 2023-119364) filed on July 21, 2023, the contents of which are incorporated herein by reference.

Claims

1. A method for producing a sulfide solid electrolyte, comprising: charging a sulfide solid electrolyte raw material into a heated furnace body and mixing to obtain a mixture of the sulfide solid electrolyte raw material; or charging a mixture of the sulfide solid electrolyte raw material into a heated furnace body; heating and melting the mixture of the sulfide solid electrolyte raw material, and cooling and solidifying the resulting melt to obtain a sulfide solid electrolyte, wherein the mixture of the sulfide solid electrolyte raw material contains Li ２ S and P ２ S ５ The Li ２ The volume-based average particle size of S measured by a laser diffraction particle size distribution measuring method is A, ２ S ５ a volume-based average particle size measured by a laser diffraction particle size distribution measurement method according to claim 1, wherein B satisfies A ≧ 50 μm and B ≧ 50 μm.

2. The method for producing a sulfide solid electrolyte according to claim 1, wherein 50 μm≦A≦2000 μm and 50 μm≦B≦2000 μm are satisfied.

3. The method for producing a sulfide solid electrolyte according to claim 1 or 2, wherein the mixture of raw materials for the sulfide solid electrolyte has a volume-based average particle size of 50 μm or more as measured by a laser diffraction particle size distribution measuring method.

4. The method for producing a sulfide solid electrolyte according to claim 3, wherein the mixture of raw materials for the sulfide solid electrolyte has a volume-based average particle size of 2000 μm or less as measured by a laser diffraction particle size distribution measuring method.

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

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

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

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

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