Method for producing sulfide-based solid electrolyte and sulfide-based solid electrolyte

Abstract

To provide a method for producing a sulfide solid electrolyte, which is excellent in composition controllability and facilitates mass production.SOLUTION: The method for producing a sulfide solid electrolyte comprises: obtaining an intermediate by heating treatment of ingredients including elemental lithium, elemental sulfur and elemental phosphorus; and heating and melting the intermediate in a gas atmosphere that contains elemental sulfur.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a sulfide-based solid electrolyte and a sulfide-based solid electrolyte. [Background technology]

[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, but concerns about leakage and fire have led to the need for larger cases for safety reasons. Improvements were also desired regarding the short battery life and narrow operating temperature range.

[0003] In response to this, all-solid-state lithium ion secondary batteries that use solid electrolytes as the electrolyte of lithium ion secondary batteries are attracting attention because they are expected to offer improved safety, high-speed charging and discharging, and a smaller case.

[0004] Solid electrolytes are broadly classified into sulfide-based solid electrolytes and oxide-based solid electrolytes. Sulfide ions that constitute sulfide-based solid electrolytes have higher polarizability and exhibit higher ionic conductivity than oxide ions that constitute oxide-based solid electrolytes. Examples of sulfide-based solid electrolytes include sulfide-based solid electrolytes containing lithium, sulfur, and phosphorus. Known methods for producing these solid electrolytes include a sealed glass tube method, a mechanical milling method, and a melting method. However, the sealed glass tube method and the mechanical milling method are batch processes and require long reaction times, making them unsuitable for mass production.

[0005] On the other hand, although the melting method is a manufacturing method that allows for mass production, the boiling point of the raw material, diphosphorus pentasulfide (P2S5), is 514°C, while the melting point of lithium sulfide (Li2S) is 938°C. Therefore, when Li2S is heated to melt, P2S5 volatilizes at a temperature significantly lower than that temperature. This poses the challenge of making it difficult to control the composition of the resulting sulfide-based solid electrolyte.

[0006] To address this issue, for example, Patent Document 1 discloses the use of a composite compound containing lithium, phosphorus, and sulfur as a raw material in the production of a lithium ion conductive material. This method volatilizes only the P2S5 component during melting, i.e., does not pose the problem of volatilization of sulfur and phosphorus components, and therefore discloses that a homogeneous lithium ion conductive material having a desired composition can be stably produced. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2012-43654 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the composite compound described in Patent Document 1 is itself considered to be an intermediate obtained by heating a mixture of Li2S and P2S5, and sulfur and phosphorus components are still likely to volatilize during the process of obtaining the composite compound. Conventional technologies still have room for improvement in terms of composition control from the starting materials to the target sulfide-based solid electrolyte.

[0009] Insufficient composition controllability tends to result in a discrepancy between the target composition of the sulfide-based solid electrolyte and the composition actually obtained. In this case, the resulting sulfide-based solid electrolyte tends to be heterogeneous. Furthermore, heterogeneous sulfide-based solid electrolytes may have poor lithium ion conductivity. That is, conventional techniques have left room for improvement not only in composition controllability but also in the homogeneity and lithium ion conductivity of the resulting sulfide-based solid electrolyte.

[0010] Therefore, an object of the present invention is to provide a method for producing a sulfide-based solid electrolyte that suppresses volatilization of sulfur and phosphorus components, has excellent composition control with little deviation from the raw materials, and is easy to mass-produce. Another object of the present invention is to provide a sulfide-based solid electrolyte that is excellent in homogeneity and lithium ion conductivity. [Means for solving the problem]

[0011] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by heat-treating raw materials containing lithium, sulfur, and phosphorus to obtain an intermediate, and further by heating and melting the intermediate in a gas atmosphere containing sulfur, thereby completing the present invention.

[0012] That is, the present invention relates to the following [1] to

[13] . [1] heat-treating a raw material containing lithium, sulfur, and phosphorus to obtain an intermediate; and heating and melting the intermediate in a gas atmosphere containing elemental sulfur. A method for producing a sulfide-based solid electrolyte. [2] The method for producing a sulfide-based solid electrolyte according to item 1, wherein the temperature at which the raw material is heated in the heat treatment is in the range of 250 to 500°C. [3] The method further comprises recovering a component containing sulfur element volatilized from the raw material when obtaining the intermediate, 3. The method for producing a sulfide-based solid electrolyte according to 1 or 2 above, wherein a gas derived from a component containing elemental sulfur is used as at least a part of the gas containing elemental sulfur. [4] The method for producing a sulfide-based solid electrolyte according to any one of [1] to [3] above, wherein the raw material contains at least one selected from the group consisting of metallic lithium, lithium sulfide, lithium carbonate, lithium sulfate, lithium oxide, and lithium hydroxide. [5] The method for producing a sulfide-based solid electrolyte according to any one of [1] to [4] above, wherein the intermediate contains at least one of Li4P2S6 and Li3PS4. [6] The method for producing a sulfide-based solid electrolyte according to any one of [1] to [5] above, wherein the raw material further contains a halogen element. [7] The method for producing a sulfide-based solid electrolyte according to any one of [1] to [6] above, wherein the raw material includes at least one selected from the group consisting of lithium chloride, lithium bromide, and lithium iodide. [8] The method for producing a sulfide-based solid electrolyte according to any one of 1 to 7 above, wherein the obtained sulfide-based solid electrolyte has an argyrodite-type crystal structure. [9] A method for producing a sulfide-based solid electrolyte according to any one of items 1 to 8, further comprising cooling the melt obtained by the heating and melting to obtain a solid, wherein the melt contains 0.01 mass % or more of a compound that becomes a crystal nucleus, and the solid is a sulfide-based solid electrolyte containing a crystalline phase.

[10] The method for producing a sulfide-based solid electrolyte according to any one of 1 to 8 above, further comprising quenching the melt obtained by the heating and melting to obtain a solid.

[11] The method for producing a sulfide-based solid electrolyte according to

[10] above, wherein the rapid cooling is performed at a cooling rate of 10°C / sec or more, and the proportion of the compound that becomes the crystal nucleus in the melt is 1 mass% or less.

[12] The method for producing a sulfide-based solid electrolyte according to any one of [9] to

[11] above, further comprising reheating the solid.

[13] When Raman spectroscopy was performed with a spot diameter of 3 μm and 10 measurement points, the 350 cm -1 ~500cm -1 The standard deviation of the peak positions of the peaks derived from PS bonds is 2 cm -1 Sulfide-based solid electrolyte. [Effects of the Invention]

[0013] According to the method for producing a sulfide-based solid electrolyte of the present invention, the volatilization of sulfur and phosphorus components in the raw materials can be suppressed by passing through an intermediate before obtaining the target sulfide-based solid electrolyte from the raw materials. Furthermore, passing through an intermediate makes it easier to control the composition compared to obtaining the target sulfide-based solid electrolyte directly from the raw materials. Although a certain amount of sulfur component still volatilizes when obtaining the intermediate, heating and melting the intermediate in a gas atmosphere containing elemental sulfur allows for the introduction of a sufficient amount of sulfur component to obtain a sulfide-based solid electrolyte with the target composition.

[0014] In particular, the intermediate in the manufacturing method of the present invention is in a thermodynamically stable state. Therefore, after the intermediate is synthesized, the reaction temperature can be lowered to room temperature and the intermediate can be removed. The intermediate removed in this manner can be temporarily stored, or the removed intermediate can be used in the next step, the melting step. Furthermore, since the intermediate in the manufacturing method of the present invention is synthesized by controlling the reaction, detailed composition analysis can clarify the composition information. For the above reasons, in the manufacturing method of the sulfide-based solid electrolyte of the present invention, the amount of sulfur introduced into the intermediate in a molten state in the melting step under a gas atmosphere containing elemental sulfur (S) can be easily controlled, and sulfur deficiency is reduced, making it less likely that composition deviation will occur.

[0015] By including these steps, a melting method capable of mass production can be provided for producing a sulfide-based solid electrolyte in which the deviation between the composition of the target sulfide-based solid electrolyte and the composition of the sulfide-based solid electrolyte obtained from the raw materials is small, and composition control is easy. This production method provides excellent composition controllability, which also improves control of the physical properties of the resulting sulfide-based solid electrolyte. As a result, it becomes easier to stably and reproducibly produce a sulfide-based solid electrolyte with high lithium ion conductivity suitable as an electrolyte for lithium ion secondary batteries. Furthermore, the excellent composition controllability of this production method means that the resulting sulfide-based solid electrolyte has excellent homogeneity and lithium ion conductivity. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 shows the results of XRD measurement of the sulfide-based solid electrolyte of Example 1. [Figure 2] FIG. 2 is a diagram showing the results of Raman spectrum measurement of the sulfide-based solid electrolyte of Example 1. [Figure 3] FIG. 3 is a diagram showing the results of XRD measurement of the sulfide-based solid electrolyte of Example 2. [Figure 4] FIG. 4 is a diagram showing the results of Raman spectrum measurement of the sulfide-based solid electrolyte of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and can be modified as desired without departing from the spirit of the present invention. Furthermore, the symbol "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.

[0018] <Method for producing sulfide-based solid electrolyte> The method for producing a sulfide-based solid electrolyte according to an embodiment of the present invention (hereinafter, sometimes referred to as the present production method) includes a step of heat-treating raw materials containing lithium, sulfur, and phosphorus to obtain an intermediate (intermediate synthesis step), and a step of heat-melting the intermediate in a gas atmosphere containing sulfur (heat-melting step). The present production method may further include other steps as appropriate, such as a step of cooling the melt obtained by heat melting (cooling step), a step of reheating the solid obtained by the cooling step (reheating step), a pulverizing step, a drying step, etc. Each step will be described below.

[0019] [Intermediate synthesis process] The present production method includes an intermediate synthesis step of heat-treating raw materials containing lithium, sulfur, and phosphorus to obtain an intermediate.

[0020] (raw materials) The raw materials used in this manufacturing method include lithium (Li), sulfur (S), and phosphorus (P). Such raw materials can be appropriately combined and include Li-containing substances (components), such as elemental Li or compounds containing Li, S-containing substances (components), such as elemental S or compounds containing S, and P-containing substances (components), such as elemental P or compounds containing P. The Li-containing compound, S-containing compound, and P-containing compound may be a compound containing two or more elements selected from Li, S, and P. For example, diphosphorus pentasulfide (PS) is an example of a compound that serves as both an S-containing compound and a P-containing compound.

[0021] Examples of substances containing Li include lithium compounds such as lithium sulfide (LiS), lithium carbonate (LiCO), lithium sulfate (LiSO), lithium oxide (LiO), and lithium hydroxide (LiOH), as well as metallic lithium, etc. From the viewpoints of ease of intermediate synthesis and ease of handling, it is preferable to use lithium sulfide. On the other hand, because lithium sulfide is expensive, it is preferable to use lithium compounds other than lithium sulfide, metallic lithium, etc., from the viewpoint of reducing the production costs of sulfide-based solid electrolytes. Specifically, in this case, the raw material preferably contains, as a Li-containing substance, one or more selected from the group consisting of metallic lithium, lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), lithium oxide (Li2O), and lithium hydroxide (LiOH). These substances may be used alone or in combination of two or more.

[0022] Examples of substances containing sulfur include phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5), other sulfur compounds containing phosphorus, elemental sulfur, and compounds containing sulfur. Examples of compounds containing sulfur include H2S, CS2, iron sulfide (FeS, Fe2S3, FeS2, Fe 1-x S, etc.), bismuth sulfide (Bi2S3), copper sulfide (CuS, Cu2S, Cu 1-x Examples of the S-containing substance include phosphorus sulfide, and more preferably diphosphorus pentasulfide (P2S5), from the viewpoints of ease of reaction in the intermediate synthesis step and prevention of inclusion of elements other than those constituting the target sulfide-based solid electrolyte. These substances may be used alone or in combination of two or more. Phosphorus sulfide can be considered as a compound that serves as both an S-containing substance and a P-containing substance.

[0023] Examples of P-containing substances include phosphorus sulfides such as diphosphorus trisulfide (P2S3) and diphosphorus pentasulfide (P2S5), phosphorus compounds such as sodium phosphate (Na3PO4), and elemental phosphorus. As the P-containing substance, phosphorus sulfide is preferred, and diphosphorus pentasulfide (P2S5) is more preferred, from the viewpoints of ease of reaction in the intermediate synthesis step and preventing the inclusion of elements other than those constituting the target sulfide-based solid electrolyte. These substances may be used alone or in combination of two or more.

[0024] The raw materials for this production method can be obtained by, for example, appropriately mixing the above-mentioned substances depending on the composition of the target sulfide-based solid electrolyte or intermediate. The mixing ratio is not particularly limited, but for example, the molar ratio of Li to P in the raw materials, Li / P, is preferably 65 / 35 or more, and more preferably 70 / 30 or more, in order to accurately synthesize the target intermediate.

[0025] A preferred example of the combination of the above compounds is the combination of Li2S and P2S5. When Li2S and P2S5 are combined, the molar ratio of Li to P (Li / P) is preferably 65 / 35 to 88 / 12, more preferably 70 / 30 to 88 / 12. By adjusting the mixing ratio so that the amount of P2S5 is relatively small relative to Li2S, it becomes easier to suppress the volatilization of sulfur and phosphorus components during heat treatment, which is caused by the boiling point of P2S5 being lower than the melting point of Li2S.

[0026] The raw materials for the present production method may contain further substances (compounds, etc.) in addition to the above substances, depending on the composition of the desired sulfide-based solid electrolyte or intermediate, or as additives, etc.

[0027] For example, when producing a sulfide-based 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. 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. As the compound containing a halogen element, lithium halides are preferred, and LiCl, LiBr, and LiI are more preferred, from the viewpoints of ease of reaction in the intermediate synthesis step and preventing the inclusion of elements other than those constituting the target sulfide-based solid electrolyte. These compounds may be used alone or in combination of two or more. When a compound containing a halogen element is contained in a raw material, the compound containing a halogen element may remain in the intermediate without reacting when the intermediate is obtained by heat treatment.

[0028] Furthermore, when producing a sulfide-based solid electrolyte containing a halogen element, it is not essential that the raw material contain a halogen element (Ha). Even if the raw material does not contain a compound containing a halogen element, a sulfide-based solid electrolyte containing a halogen element may be produced by adding a compound containing a halogen element during the heating and melting step after the intermediate synthesis step.

[0029] Lithium halide is also a compound containing Li. When the raw material contains lithium halide, part or all of the Li in the raw material may be derived from the lithium halide.

[0030] When the raw material contains a halogen element, the molar equivalent of Ha relative to P in the raw material is preferably 0.2 molar equivalents or more, more preferably 0.5 molar equivalents or more, from the viewpoint of lowering the melting point when the intermediate is heated and melted. Furthermore, from the viewpoint of the stability of the obtained sulfide-based solid electrolyte, the molar equivalent of Ha is preferably 4 molar equivalents or less, more preferably 3 molar equivalents or less.

[0031] From the viewpoint of improving the glass-forming state of the resulting sulfide-based solid electrolyte, it is also preferable that the raw materials contain sulfides such as SiS2, B2S3, GeS2, and Al2S3. By facilitating glass formation, glass can be obtained even if the cooling rate is reduced when obtaining glass by rapid cooling, thereby reducing the load on the equipment. Furthermore, from the viewpoint of imparting moisture resistance to the sulfide solid electrolyte, it is also preferable that the raw materials contain oxides such as SiO2, B2O3, GeO2, and Al2O3. These compounds may be used alone or in combination of two or more.

[0032] These sulfides and oxides may be contained in the raw materials, may be contained as a composition in an intermediate obtained from the raw materials, or may be added separately when the intermediate is melted. The amount of these compounds added is preferably 0.1% by weight or more, more preferably 0.5% by weight or more, based on the total amount of the raw material or intermediate, and is preferably 50% by weight or less, more preferably 40% by weight or less. The raw material may also contain a compound that will serve as a crystal nucleus, as described below.

[0033] (Heat treatment in intermediate synthesis process) The raw materials containing lithium, sulfur, and phosphorus are heat-treated to obtain an intermediate. The specific heat-treatment method is not particularly limited, but examples include placing the raw materials in a heat-resistant container and heating them in a heating furnace. Examples of heat-resistant containers include, but are not limited to, heat-resistant containers made of carbon, quartz, quartz glass, borosilicate glass, aluminosilicate glass, heat-resistant containers containing oxides such as alumina, zirconia, and mullite, heat-resistant containers containing nitrides such as silicon nitride and boron nitride, and heat-resistant containers containing carbides such as silicon carbide. These heat-resistant containers may be bulk-formed from the above-mentioned materials, or may be containers with layers of carbon, oxides, nitrides, carbides, or the like formed thereon.

[0034] In the heat treatment in the intermediate synthesis step, the temperature at which the raw materials are heated is preferably 250°C or higher, more preferably 255°C or higher, and even more preferably 260°C or higher. A temperature at or above the lower limit mentioned above is preferred because it facilitates the reaction of synthesizing the intermediate. Furthermore, the temperature is preferably 500°C or lower, more preferably 450°C or lower, and even more preferably 400°C or lower. A temperature at or below the upper limit mentioned above is preferred because it suppresses the volatilization of low-boiling-point components such as P2S5 in the raw materials and facilitates the reaction of synthesizing an intermediate containing a compound of the target composition.

[0035] To obtain an intermediate by heat treatment, it is preferable to maintain the temperature within the above-mentioned preferred range for a certain period of time. The temperature range during maintenance is more preferably within a certain temperature range, for example, preferably within ±15°C of the reference temperature, more preferably within ±10°C. The holding time is preferably 1 minute or more, more preferably 5 minutes or more, even more preferably 10 minutes or more, even more preferably 15 minutes or more, and particularly preferably 20 minutes or more. Even when heated at the above-mentioned preferred temperature, if the holding time is insufficient, the reaction is likely to proceed insufficiently, making it difficult to obtain an intermediate that can achieve the effects of the present production method. A holding time of 1 minute or more is preferable, as it creates conditions for the reaction to proceed and obtain an intermediate. From the viewpoint of suppressing the volatilization of low-boiling point components such as P2S5 in the raw material, the holding time is preferably 600 minutes or less, more preferably 500 minutes or less.

[0036] The retention time can be further shortened in some cases when the raw material is subjected to a predetermined treatment. Examples of such treatments include reducing the particle size of the raw material, removing or modifying the oxide layer on the surface of particles contained in the raw material as much as possible by etching or the like, making the particles porous, and adjusting the raw material mixing conditions to improve the homogeneity of the raw material, thereby increasing the reactivity between particles contained in the raw material. In this case, the retention time is preferably 1 second or more, more preferably 10 seconds or more, and even more preferably 20 seconds or more. From the viewpoint of suppressing the volatilization of low-boiling point components such as P2S5 in the raw material, the retention time is preferably 10 minutes or less, more preferably 5 minutes or less.

[0037] From the viewpoint of shortening the retention time, i.e., shortening the reaction time in the intermediate synthesis step, it is preferable to reduce the particle size of the raw materials. Furthermore, if the particle size (D50) of the raw materials is too large, it may affect the homogeneity of the sulfide-based solid electrolyte, so from this viewpoint as well, it is preferable that the particle size (D50) of the raw materials is relatively small. However, since the present production method has excellent composition controllability, even if raw materials with particle sizes that would reduce homogeneity in conventional production methods are used, the present production method can produce a more homogeneous sulfide-based solid electrolyte. From these viewpoints, specifically, the particle size (D50) of the raw materials is preferably 1 mm or less, more preferably 500 μm or less, even more preferably 250 μm or less, even more preferably 100 μm or less, and particularly preferably 50 μm or less.

[0038] Although the smaller the particle size, the more preferable, a practical lower limit of about 0.1 μm is preferred, with 1 μm or more being preferred, and 5 μm or more being more preferred. Furthermore, as described above, according to the present production method, a homogeneous sulfide-based solid electrolyte can be easily obtained even when raw materials with relatively large particle sizes are used. Taking this into consideration, for example, from the viewpoint of reducing production costs, it is also preferable for the raw material particle size to be 10 μm or more, more preferably 100 μm or more, and even more preferably 250 μm or more.

[0039] As described above, the raw material may be a mixture of multiple substances (compounds, etc.). The raw material may be a mixture of multiple substances with different particle sizes. In this case, it is preferable that the particle sizes of each substance are within the above ranges. In this specification, the particle size (D50) of the raw material refers to the median diameter (D50) determined from the volume-based particle size distribution chart obtained by measuring the particle size distribution using a laser diffraction particle size distribution analyzer MT3300EXII manufactured by Microtrac.

[0040] The pressure during the heat treatment in the intermediate synthesis step is not particularly limited, but for example, normal pressure to slight pressure is preferred, and normal pressure is more preferred.

[0041] The heat treatment in the intermediate synthesis step is preferably carried out under an inert gas atmosphere to prevent side reactions between the raw materials and water vapor, oxygen, etc. Specific examples include N2 gas, argon gas, and helium gas. The dew point during the heat treatment is preferably -20°C or lower, and although there is no particular lower limit, it is usually around -80°C. The oxygen concentration is preferably 1000 ppm or lower.

[0042] In the intermediate synthesis process, intermediates with different compositions depending on the purpose can be obtained by adjusting the compounds contained in the raw materials and their mixing ratios, and by controlling the conditions during the heat treatment. The obtained intermediates may be used in the heat-melting process directly in the heating furnace used for intermediate synthesis without being removed from the heat-resistant container, or may be removed and temporarily stored after cooling to room temperature. It is also possible to combine multiple intermediates with different compositions that have been removed and stored and use them in the heat-melting process. In the heat-melting process, by controlling the amount of sulfur introduced into the intermediate in a gas atmosphere containing elemental sulfur, it becomes easy to produce sulfide-based solid electrolytes with different compositions, physical properties, and performance.

[0043] Examples of the composition of the intermediate obtained in this step include compounds containing Li, P, and S, such as Li4P2S6 and Li3PS4. From the viewpoint of controlling the amount of sulfur introduced into the intermediate in a gas atmosphere containing elemental sulfur in the heat-melting step, it is preferable that the intermediate contains at least one of Li4P2S6 and Li3PS4. Furthermore, because Li4P2S6 and Li3PS4 are thermodynamically stable, they are also preferred from the viewpoint of the stability of the intermediate during temporary storage.

[0044] Here, the reaction occurring in the intermediate synthesis step varies depending on the composition of the target sulfide-based solid electrolyte, but is typically a reaction characterized by the reaction of Li2S and P2S5 contained in the raw materials starting at about 250°C to form at least one of Li4P2S6 and Li3PS4. In this reaction, Li2S and P2S5 may also be produced starting from a Li-containing substance (compound, etc.) or a P-containing substance (compound, etc.) at a stage prior to obtaining the respective compounds. To substantially accelerate this reaction, it is preferable to increase the reactivity between particles contained in the raw materials by reducing the particle size of the raw materials, removing or modifying the oxide layer on the surface of the raw material particles as much as possible by etching, making the particles porous, or adjusting the raw material mixing conditions to improve the homogeneity of the raw materials. In particular, the particle size of Li2S, which is the initial reactant of P2S5, is likely to affect the intermediate formation reaction. Therefore, from the perspective of accelerating the intermediate formation reaction, it is preferable to reduce the particle size of Li2S or the Li-containing substance (compound, etc.) that is the precursor to Li2S production. In addition, reducing the surface crystallinity of Li2S and other processes that increase the surface area other than atomization are also considered effective from the above perspective. Furthermore, reacting Li2S with P2S5 in a gas atmosphere containing elemental sulfur is also considered to contribute to accelerating the intermediate formation reaction.

[0045] When producing a sulfide-based solid electrolyte containing a halogen element, the intermediate preferably contains a compound containing a halogen element. Note that when the raw material contains a lithium halide such as LiCl or LiBr, the composition of these compounds is unlikely to change within the temperature range during heat treatment, so the resulting intermediate may also contain a lithium halide.

[0046] This manufacturing method suppresses the volatilization of sulfur and phosphorus components in the raw materials compared to directly obtaining the target sulfide-based solid electrolyte from the raw materials by using an intermediate synthesis process. This allows the synthesis of compounds with well-defined compositional information containing Li, P, and S, such as Li4P2S6 and Li3PS4, as intermediates. These intermediates are thermodynamically stable, so they can be extracted by lowering the temperature to room temperature after the heat treatment during intermediate synthesis. Composition analysis of the extracted intermediates allows the amount of sulfur required for the heat-melting process to be determined. Furthermore, by producing intermediates with specific compositions from the raw materials, it is easier to set the heat-melting conditions appropriately to match the intermediate composition. This allows for appropriate control of the amount of sulfur introduced under a sulfur-containing gas atmosphere, reducing compositional deviations. Furthermore, by using an intermediate with a composition closer to the target sulfide-based solid electrolyte than the raw materials before heat-melting, the resulting sulfide-based solid electrolyte can be made more homogeneous in composition. In addition, by combining multiple intermediates with different compositions and melting them under heat, it becomes easy to create sulfide-based solid electrolytes with different compositions, properties, and performance.

[0047] [Heat melting process] In the heat-melting step, the intermediate is heat-melted in a gas atmosphere containing elemental sulfur. The heat-melted intermediate in this step may be an intermediate composition in which multiple types of intermediates are mixed, or an intermediate composition in which other substances (compounds, etc.) are further added to the intermediate, as needed.

[0048] The specific method of heat melting is not particularly limited, but an example is a method in which raw materials are placed in a heat-resistant container and heated in a heating furnace. Examples of heat-resistant containers include, but are not limited to, heat-resistant containers made of carbon, quartz, quartz glass, borosilicate glass, aluminosilicate glass, heat-resistant containers containing oxides such as alumina, zirconia, and mullite, heat-resistant containers containing nitrides such as silicon nitride and boron nitride, and heat-resistant containers containing carbides such as silicon carbide. These heat-resistant containers may be bulk-formed from the above-mentioned materials, or may be containers on which a layer of carbon, oxide, nitride, carbide, or the like is formed.

[0049] The heat melting is carried out in an atmosphere of a gas containing elemental sulfur, such as sulfur gas, hydrogen sulfide gas, or carbon disulfide gas, or a gas containing a compound containing elemental sulfur or elemental sulfur. The sulfur-containing gas may consist solely of a gaseous compound containing sulfur, such as sulfur gas, hydrogen sulfide gas, or carbon disulfide gas, or it may also preferably contain an inert gas, such as N gas, argon gas, or helium gas, from the viewpoint of cost reduction and use as a carrier gas for transporting the sulfur component. The sulfur-containing gas may also contain impurities derived from the sulfur source, etc., as long as the impurities do not impair the effects of the present production method.

[0050] When the gas containing sulfur element contains sulfur gas, the sulfur gas (S x The content of sulfur gas (S (x=2 to 8)) is preferably 0.01 vol% or more, more preferably 0.1 vol% or more, and even more preferably 0.2 vol% or more, from the viewpoint of providing a sufficient amount of sulfur element and promoting the reaction of sulfur introduction. The content of sulfur gas is 100 vol% or less, and from the viewpoint of cost reduction and using an inert gas as a carrier gas, it is preferably 99 vol% or less, and more preferably 98 vol% or less. x The content of (x=2 to 8)) can be measured by gas chromatography mass spectrometry.

[0051] The gas containing elemental sulfur can be obtained by heating a sulfur source. Therefore, the sulfur source is not particularly limited as long as it is elemental sulfur or a sulfur compound that can be heated to obtain a gas containing elemental sulfur. For example, elemental sulfur, hydrogen sulfide, carbon disulfide and other organic sulfur compounds, iron sulfide (FeS, FeS, FeS, Fe), 1-x S, etc.), bismuth sulfide (Bi2S3), copper sulfide (CuS, Cu2S, Cu 1-x S, etc.), polysulfides such as lithium polysulfide and sodium polysulfide, polysulfides, rubber that has been subjected to sulfur vulcanization, etc.

[0052] For example, these sulfur sources can be heated in a separately provided sulfur source heating section to generate a gas containing elemental sulfur, which can then be transported to a heat-melting furnace using an inert gas such as N gas, argon gas, or helium gas as a carrier gas, thereby obtaining a gas atmosphere containing elemental sulfur. By separating the sulfur source heating section from the section where the heat-melting step is performed, even if the gas introduced into the heat-melting furnace contains oxygen or moisture, these can be removed by reacting them with sulfur gas before introduction. This is preferable because it allows for the production of a high-quality, high-purity sulfide-based solid electrolyte with few impurities.

[0053] The temperature at which the sulfur source is heated may be appropriately selected depending on the type of sulfur source used. For example, when elemental sulfur is used as the sulfur source, the heating temperature is preferably 250°C or higher and 750°C or lower.

[0054] Alternatively, a gas atmosphere containing elemental sulfur may be obtained by transporting a solid sulfur source, such as elemental sulfur, H2S, Bi2S3, iron sulfide, copper sulfide, or CS2, in a fine powder state or the like, by a carrier gas into a heating and melting furnace.

[0055] For example, the heat-melting step can be performed as follows. In a configuration in which a sulfur source heating section and a section performing the heat-melting step are separated, a sulfur source is heated in the sulfur source heating section to generate a gas containing elemental sulfur. The gas containing elemental sulfur in an amount corresponding to the required sulfur partial pressure is sent to the section performing the heat-melting step to obtain a gas atmosphere containing elemental sulfur. In this atmosphere, an intermediate obtained from raw materials containing at least elemental lithium, elemental sulfur, and elemental phosphorus is heat-melted. At this time, the sulfur partial pressure in the gas atmosphere containing elemental sulfur is 10 -3 ~10 0 atm is preferred.

[0056] Here, the sulfur components such as P2S5 evaporated in the intermediate synthesis step can be recovered and used as the sulfur source in this step. Specifically, for example, the evaporated sulfur components can be cooled and solidified, and this can be used as the sulfur source. From the viewpoint of production costs and obtaining the target sulfide-based solid electrolyte in high yield, it is preferred that the production method further includes a step of recovering a component containing sulfur element that volatilizes from the raw material in the intermediate synthesis step, and that a gas derived from the recovered component containing sulfur element is used as at least a part of the gas containing sulfur element in the heat-melting step.

[0057] By heating and melting the intermediate in a gas atmosphere containing elemental sulfur, sulfur is introduced into the molten intermediate, allowing the introduction of a sufficient amount of sulfur to obtain a sulfide-based solid electrolyte with the desired composition.

[0058] Furthermore, introducing sulfur into the intermediate in a molten liquid state is preferable because it shortens the reaction time for sulfur introduction compared to a reaction in a solid state. Furthermore, the liquid state makes it easier to introduce sulfur uniformly throughout the melt, and the resulting sulfide-based solid electrolyte tends to have a homogeneous composition. The viscosity of the intermediate melt is reduced by fluidizing the solid, resulting in a highly homogeneous state. This results in high solubility and diffusibility of the sulfur-containing gas in the intermediate melt. Therefore, the reaction in a liquid state results in a more effective reduction in reaction time and homogenization of the composition. Furthermore, it is more preferable to heat and melt the melt while stirring the melt and the sulfur-containing gas, as this makes it easier to achieve the above-mentioned effects.

[0059] The heat-melting temperature is preferably 600°C or higher, more preferably 630°C or higher, and even more preferably 650°C or higher, in order to increase the fluidity of the melt and promote the reaction of introducing sulfur. The heat-melting temperature is preferably 900°C or lower, more preferably 850°C or lower, and even more preferably 800°C or lower, in order to prevent deterioration or decomposition of components in the melt due to heating.

[0060] The heat-melting time is preferably 0.1 hours or more, more preferably 0.5 hours or more, even more preferably 0.7 hours or more, and even more preferably 1 hour or more in order to allow the sulfur introduction reaction to proceed, and is preferably 10 hours or less, more preferably 9.5 hours or less, and even more preferably 9 hours or less, in order to prevent deterioration or decomposition of components in the melt due to heating.

[0061] The heat melting may be carried out as a continuous process. A continuous process is a process in which the melt is continuously allowed to flow down from a heat-resistant container. The material to be added may be an intermediate or a raw material. The addition may be continuous or intermittent. When the heat melting is carried out as a continuous process, the melt may be kept in a molten state for a long period of time under appropriate conditions that take into consideration the progress of the sulfur introduction reaction, deterioration of the components in the melt, and the like. A long period of time may be, for example, about 24 hours.

[0062] The pressure during heating and melting is not particularly limited, but is preferably normal pressure to slightly increased pressure, more preferably normal pressure. -3 ~10 0 By setting the sulfur partial pressure at this level, the apparatus does not become complicated, sulfur can be introduced efficiently at low cost, and the target sulfide-based solid electrolyte can be easily obtained.

[0063] From the viewpoint of preventing side reactions with water vapor, oxygen, etc. during heat melting, the dew point is preferably −20° C. or lower. There is no particular lower limit, but it is usually about −80° C. The oxygen concentration is preferably 1000 ppm or lower.

[0064] (cooling process) The present production method preferably further comprises a step of cooling the melt obtained by heating and melting to obtain a solid. The cooling may be performed by a known method, and the method is not particularly limited.

[0065] From the viewpoint of maintaining the composition obtained in the heat-melting step, 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 a twin roller, which is generally said to have the fastest rapid cooling rate, is 1,000,000°C / sec or less.

[0066] Here, when it is desired to obtain an amorphous sulfide-based solid electrolyte, it is preferable to obtain the solid by rapidly cooling the melt obtained by heating and melting. Specifically, the cooling rate in the case of rapid cooling is preferably 10°C / sec or more, more preferably 100°C / sec or more, even more preferably 500°C / sec or more, and even more preferably 700°C / sec or more. In addition, the upper limit of the cooling rate is not particularly limited, but the cooling rate of a twin roller, which is generally said to have the fastest rapid cooling rate, is 1,000,000°C / sec or less.

[0067] On the other hand, slow cooling during the cooling step can be used to crystallize at least a portion of the solid, resulting in a sulfide-based solid electrolyte having a specific crystal structure or a sulfide-based solid electrolyte composed of a crystalline phase and an amorphous phase. The cooling rate during slow cooling is preferably 0.01°C / sec or higher, more preferably 0.05°C / sec or higher. The cooling rate is preferably 500°C / sec or lower, more preferably 450°C / sec or lower. The cooling rate may be less than 10°C / sec or 5°C / sec or lower. The cooling rate may be adjusted appropriately depending on the crystallization conditions. Here, the crystal contained in the sulfide-based solid electrolyte is preferably an ion-conductive crystal. Specifically, the ion-conductive crystal has a lithium ion conductivity of 10 -4 S / cm, more preferably 10 -3 The crystals are larger than S / cm.

[0068] When the solid obtained after cooling is to be a sulfide-based solid electrolyte containing a crystalline phase, it is preferable to include a compound that will become a crystal nucleus in the melt obtained in the heat-melting step. This makes it easier for crystals to precipitate in the cooling step. The method for including the compound that will become a crystal nucleus in the melt is not particularly limited, but examples include adding the compound that will become a crystal nucleus to a raw material or an intermediate, or adding the compound that will become a crystal nucleus to the melt during heat-melting.

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

[0070] If the solid obtained after cooling is intended to be a sulfide-based solid electrolyte containing a crystalline phase, the content of the compound that will become the crystal nuclei in the melt 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. On the other hand, from the viewpoint of suppressing a decrease in lithium ion conductivity, the content of the compound that will become the crystal nuclei in the melt is preferably 20% by mass or less, more preferably 10% by mass or less.

[0071] If the solid obtained after cooling is to be an amorphous sulfide-based solid electrolyte, the melt preferably does not contain a compound that will become a crystal nucleus, or the content of the compound is preferably a predetermined amount or less. Specifically, the content of the compound that will become a crystal nucleus in the melt is preferably 1% by mass or less, more preferably 0.1% by mass or less. The content of the compound that will become a crystal nucleus in the melt may be less than 0.01% by mass.

[0072] (Reheating process) High-temperature crystallization of amorphous sulfide-based solid electrolytes or sulfide-based solid electrolytes containing an amorphous phase can be promoted by heat treatment (post-annealing). This manufacturing method may further include reheating the solid when the solid obtained in the cooling step is an amorphous sulfide-based solid electrolyte or a sulfide-based solid electrolyte containing an amorphous phase. Furthermore, reheating a sulfide-based solid electrolyte containing sulfide-based solid electrolyte crystals can rearrange ions within the crystal structure and increase lithium ion conductivity. The reheating in this step refers to at least one of heating the solid obtained by cooling in the cooling step to crystallize it and rearranging ions within the crystal structure. Hereinafter, the heat treatment of these amorphous sulfide-based solid electrolytes or sulfide-based solid electrolytes containing an amorphous phase, including crystallization treatment, will be referred to as reheating.

[0073] By controlling the temperature and time of the reheating treatment, the ratio of the amorphous phase to the crystalline phase can be controlled, which is preferable because it allows for control of the lithium ion conductivity. In order to increase the lithium ion conductivity, it is preferable to increase the proportion of the crystalline phase. Specifically, the proportion of the crystalline phase is preferably 10 mass% or more, more preferably 20 mass% or more. From the viewpoint of mechanical strength, the proportion of the crystalline phase is preferably 99.9 mass% or less, more preferably 99 mass% or less. The proportion of the crystalline phase can be measured by X-ray diffraction (XRD) measurement.

[0074] The specific conditions for the reheating treatment are not particularly limited and may be adjusted according to the composition of the sulfide-based solid electrolyte, etc. The reheating treatment is preferably carried out in an inert gas atmosphere such as N gas, argon gas, or helium gas. The reheating treatment may also be carried out in a gas atmosphere containing elemental sulfur.

[0075] For example, the temperature of the reheating treatment is preferably equal to or higher than the glass transition temperature of the sulfide-based solid electrolyte, specifically, preferably equal to or higher than 200° C., more preferably equal to or higher than 250° C. The upper limit of the temperature is not particularly limited as long as it is within a range in which the sulfide-based solid electrolyte is not thermally deteriorated or thermally decomposed by heating, but is preferably equal to or lower than 550° C., for example, and more preferably equal to or lower than 500° C.

[0076] The reheating time is preferably 0.1 hours or more, more preferably 0.2 hours or more, to ensure crystal precipitation, and is preferably 3 hours or less, more preferably 2 hours or less, to prevent thermal deterioration due to heating.

[0077] The present production method may include a step of pulverizing the sulfide-based solid electrolyte obtained in the above step, a step of drying the sulfide-based solid electrolyte, etc., depending on the application of the obtained sulfide-based solid electrolyte, etc. The specific method for either step is not limited, and any known method may be used.

[0078] <Sulfide solid electrolyte> This manufacturing method allows for the adjustment of the types and mixing ratios of raw materials and intermediates, and furthermore, since it involves obtaining an intermediate and performing heat melting under a gas atmosphere containing elemental sulfur, it has excellent composition controllability. Therefore, this manufacturing method can produce various sulfide-based solid electrolytes. Examples of sulfide-based solid electrolytes obtained by this manufacturing method include Li 10 GeP2S 12 Sulfide-based solid electrolytes with LGPS-type crystal structure, such as Li6PS5Cl, Li 5.4 PS 4.4 Cl 1.6 and Li 5.4 PS 4.4 Cl 0.8 Br 0.8 sulfide-based solid electrolytes having an argyrodite-type crystal structure, such as Li-PS-Ha-based (Ha represents at least one element selected from halogen elements) glass-ceramics, and Li7P3S 11 Examples of such LPS crystallized glass include:

[0079] Depending on the purpose, the sulfide-based solid electrolyte may be an amorphous solid electrolyte, a sulfide-based solid electrolyte having a specific crystal structure, or a sulfide-based solid electrolyte containing a crystalline phase and an amorphous phase. When the sulfide-based solid electrolyte contains a crystalline phase, the crystal contained in the sulfide-based solid electrolyte is preferably an ion-conductive crystal. Specifically, the ion-conductive crystal has a lithium ion conductivity of 10-4 S / cm, more preferably 10 -3 From the viewpoint of lithium ion conductivity, the crystalline phase is preferably an argyrodite-type crystalline phase.

[0080] As a sulfide-based solid electrolyte having excellent lithium ion conductivity, a sulfide-based solid electrolyte having an argyrodite-type crystal structure is preferable. When a sulfide-based solid electrolyte having an argyrodite-type crystal structure is used as the target compound, at least one of the raw materials and intermediates in the present production method preferably contains a halogen element. Furthermore, the halogen element is preferably derived from one or more halogen elements selected from the group consisting of lithium chloride, lithium bromide, and lithium iodide.

[0081] The obtained sulfide-based solid electrolyte can be identified by analyzing its crystal structure using X-ray diffraction (XRD) measurement, and by analyzing its 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 by atomic absorption spectrometry, and Cl by ion chromatography.

[0082] Furthermore, Raman spectroscopy can be performed to evaluate the compositional homogeneity of the sulfide-based solid electrolyte. Specifically, Raman spectroscopy is performed at any two or more points on a sample obtained from the obtained sulfide-based solid electrolyte. From the viewpoint of improving the accuracy of the evaluation, the number of measurement points is preferably eight or more, and more preferably ten or more. Preferable conditions for Raman spectroscopy when evaluating the compositional homogeneity of a sulfide-based solid electrolyte include, for example, a spot diameter of 3 μm and the number of measurement points of 10. By setting the spot diameter to 3 μm, the analysis area in Raman spectroscopy becomes a size suitable for evaluating the compositional homogeneity of a sulfide-based solid electrolyte at a microscopic level.

[0083] In each measurement result, PS4 3-The smaller the variation in peak wavenumber (peak position) resulting from the structure of the sulfide-based solid electrolyte, the more homogeneous the composition of the sulfide-based solid electrolyte. Alternatively, the smaller the variation in full width at half maximum of the peak resulting from the structure of the sulfide-based solid electrolyte, the more homogeneous the composition of the sulfide-based solid electrolyte.

[0084] Although it depends on the composition of the obtained sulfide-based solid electrolyte, the peaks derived from the structure of the sulfide-based solid electrolyte include PS4 3- It is preferable to confirm the peaks derived from PS4 3- The position of the peak due to PS4 also varies depending on the composition system. 3- The peak at 350 cm -1 ~500cm -1 For example, in a sulfide-based solid electrolyte having an argyrodite-type crystal structure, such a peak occurs at 420 to 430 cm -1 Hereinafter, in this specification, the variation in peak position and the variation in full width at half maximum of the peak refer to the variation in PS4 3- This refers to the peaks identified as originating from

[0085] The variation in peak position can be evaluated as follows. That is, when the standard deviation of the peak position for each measurement point obtained by Raman spectrum measurement is calculated and expressed as (average peak position) ± (standard deviation), the value of the standard deviation is 2 cm. -1 Preferably within 1 cm, more preferably within 1 cm -1 Within 0.5 cm, more preferably -1 The peak position here refers to the position of the peak top. For example, when Raman spectroscopy was performed on the sulfide-based solid electrolyte obtained by the present production method with a spot diameter of 3 μm and 10 measurement points, the 350 cm -1 ~500cm -1 The standard deviation of the peak positions of the PS bond-derived peaks is 2 cm -1 It is preferable that the distance is within 1 cm, and more preferably within 1 cm.-1 Within 0.5 cm, more preferably -1 Within.

[0086] The variation in the full width at half maximum of the peak can be evaluated as follows. That is, the standard deviation of the full width at half maximum of the peak at each measurement point obtained by Raman spectrum measurement is calculated by determining the full width at half maximum of each peak and then calculating the standard deviation of that value. When this is expressed as (average full width at half maximum of the peak) ± (standard deviation), the value of the standard deviation is 2 cm -1 Preferably within 1.5 cm, more preferably -1 The full width at half maximum of the peak herein refers to the width at which the half peak intensity of the peak derived from the PS bond intersects with the peak derived from the PS bond when a Raman spectrum is plotted. For example, when Raman spectroscopy was performed on the sulfide-based solid electrolyte obtained by the present production method with a spot diameter of 3 μm and 10 measurement points, the 350 cm -1 ~500cm -1 The standard deviation of the full width at half maximum of the peak derived from the PS bond in -1 It is preferable that the distance is within 1.5 cm. -1 Within.

[0087] The lithium ion conductivity of the obtained sulfide-based solid electrolyte is 1.0 × 10 in order to improve the battery characteristics when used in a lithium ion secondary battery. -3 S / cm or more is preferable, and 3.0×10 -3 S / cm or more is more preferable, and 5.0×10 -3 S / cm or more is more preferable. [Example]

[0088] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. Examples 1 and 5 are examples of the present production method, and Examples 2 to 4 are comparative examples. Regarding the particle sizes of the materials used as raw materials in each example, the particle sizes (D50) of Li2S, P2S5, and LiCl used were 5 μm, 10 μm, and 50 μm, respectively, in Examples 1 to 3. In Examples 4 and 5, only Li2S with a particle size (D50) of 100 μm was used.

[0089] Example 1 Li 5.4 PS 4.4 Cl 1.6 Synthesis of (Intermediate synthesis process) The raw material powders of Li2S, P2S5, and LiCl were mixed in a molar ratio of 1.9:0.5:1.6. This raw material powder was placed in a heat-resistant container, and 30 g of it was placed in a test furnace. It was then heat-treated by holding it for 0.5 hours under the conditions of a nitrogen atmosphere with a dew point of -50°C, a pressure of 1 atmosphere, and a temperature of 300°C (heating rate of 5°C / min), to obtain an intermediate. The obtained intermediate was subjected to XRD measurement (device name: SmartLab manufactured by Rigaku Corporation), and no P2S5 crystal peak was confirmed. In addition, as a result of composition analysis, the composition of the intermediate was determined to be 1, with the element ratio of P being 1, and Li 5.47 PS 4.08 Cl 1.62 The composition analysis was carried out by measuring P and S by ICP emission spectrometry, Li by atomic absorption spectrometry, and Cl by ion chromatography. (heat melting process) The resulting intermediate was placed in a heat-resistant container and heated to melting conditions of 1 atmosphere and 730°C for 0.5 hours. Sulfur gas, obtained by heating elemental sulfur at 350°C, was supplied to the melt with N2 as a carrier gas at a partial pressure of 0.1 atm, resulting in a sulfur-containing gas atmosphere. The sulfur content in the sulfur-containing gas atmosphere was 0.1 vol%. (cooling process) Thereafter, the mixture was cooled at a cooling rate of 10 to 1000°C / sec to obtain a solid as a sulfide-based solid electrolyte containing an amorphous phase and an argyrodite-type crystalline phase. (Reheating process) Next, this solid was reheated at 450°C for 1 hour in a nitrogen gas atmosphere to crystallize it. As a result, a sulfide-based solid electrolyte having an argyrodite-type crystal structure with a crystalline phase ratio of 90 vol% or more was obtained. 5.4 PS 4.4 Cl 1.6 The obtained sulfide-based solid electrolyte was pulverized using a mortar to obtain a powder having a D50 of approximately 10 μm. The sulfide-based solid electrolyte powder after pulverization was used as a sample and the composition was analyzed in the same manner as in the intermediate synthesis process. As a result, the composition was as follows: 5.43 PS 4.38 Cl 1.59 The crystalline phase was identified by XRD measurement (device name: SmartLab manufactured by Rigaku Corporation). As a result of the XRD measurement, the crystalline phase was found to be a single phase of argyrodite-type crystals. The XRD measurement results for the sulfide-based solid electrolyte of Example 1 are shown in Figure 1. (Homogeneity evaluation) Furthermore, Raman spectroscopy (instrument name: LabRAM HR Evolution manufactured by Horiba Ltd.) was performed to evaluate the homogeneity of the obtained sulfide-based solid electrolyte. The obtained sample powder was cut into pellets with a diameter of 1 cm, and the measurement was performed at 10 random points. As an index of variation, (PS4) derived from the argyrodite-type crystal structure was measured. 3- Raman band (420-430cm -1 ) peaks, the variation in peak wavenumbers at 10 measurement points was evaluated in the form of (average peak position ± standard deviation). The average peak position is the average value of the peak wavenumbers for each spectrum. The smaller the absolute value of the standard deviation in (average peak position ± standard deviation), the smaller the variation in peak wavenumbers (peak positions). The Raman spectrum measurements were performed in a non-exposed environment. The measurement conditions were as follows: excitation wavelength 532 nm, power at sample irradiation 5 mW, objective lens 10x, numerical aperture 0.25, confocal pinhole: 200 μm, grating: 1200 gr / mm, measurement time: 3 sec x 10 times, spot diameter: approximately 3 μm. The measurements were performed in a non-exposed environment. The average peak position ± standard deviation for Example 1 is 428.1 ± 0.0 cm-1 The results of Raman spectrum measurement of the sulfide-based solid electrolyte of Example 1 are shown in Table 1 and Figure 2. Note that Figure 2 is a diagram in which Raman spectra at each of 10 measurement points are superimposed, and the spectra are normalized by intensity on the vertical axis to make it easier to understand the variations in peak positions. (Lithium ion conductivity evaluation) The lithium ion conductivity was measured at 25°C by an AC impedance method (Solartron 1260A impedance analyzer, measurement frequency: 7 MHz to 20 Hz). The lithium ion conductivity was 6.2 × 10 at 25°C. -3 The measurement results are shown in Table 1.

[0090] Example 2 Li 5.4 PS 4.4 Cl 1.6 Synthesis of (Intermediate synthesis process) The raw material powders of Li2S, P2S5, and LiCl were mixed in a molar ratio of 1.9:0.5:1.6. This raw material powder was placed in a heat-resistant container, and 30 g of it was placed in a test furnace. It was then heat-treated by holding it for 0.5 hours under the conditions of a nitrogen atmosphere with a dew point of -50°C, a pressure of 1 atmosphere, and a temperature of 300°C (heating rate of 5°C / min), to obtain an intermediate. When the obtained intermediate was subjected to XRD measurement (device name: SmartLab manufactured by Rigaku Corporation), no P2S5 crystal peak was confirmed. Furthermore, as a result of performing composition analysis in the same manner as in Example 1, the composition of the intermediate was found to be 1, with the element ratio of P being 1, and 5.47 PS 4.08 Cl 1.62 It was. (heat melting process) The obtained intermediate was placed in a heat-resistant container and heated and melted under conditions of a pressure of 1 atmosphere and a temperature of 730°C for 0.5 hours. (cooling process) Thereafter, the mixture was cooled at a cooling rate of 10 to 1000°C / sec to obtain a solid as a sulfide-based solid electrolyte containing an amorphous phase, an argyrodite-type crystalline phase, and an impurity phase. (Reheating process) Next, this solid was reheated for 1 hour at 450° C. in a nitrogen gas atmosphere. The obtained sulfide-based solid electrolyte was pulverized using a mortar to obtain a powder having a D50 of about 10 μm. The sulfide-based solid electrolyte powder after pulverization was subjected to composition analysis and XRD measurement in the same manner as in Example 1. The composition was determined as follows: the element ratio of P was 1, 5.33 PS 3.88 Cl 1.65 The results of XRD measurement of the sulfide-based solid electrolyte of Example 2 are shown in FIG. (Homogeneity evaluation) The homogeneity of the resulting sulfide-based solid electrolyte was evaluated by Raman spectroscopy in the same manner as in Example 1. The (average peak position ± standard deviation) of Example 2 was 425.2 ± 3.0 cm -1 The results of Raman spectrum measurement of the sulfide-based solid electrolyte of Example 2 are shown in Table 1 and Figure 4. Figure 4 is a diagram in which Raman spectra at each of the 10 measurement points are superimposed, and the spectra are normalized by intensity on the vertical axis to make it easier to understand the variations in peak positions. (Lithium ion conductivity evaluation) The lithium ion conductivity was measured at 25°C by the AC impedance method in the same manner as in Example 1. The lithium ion conductivity was 0.4 × 10 at 25°C. -3 The measurement results are shown in Table 1.

[0091] Example 3 Li 5.4 PS 4.4 Cl 1.6 Synthesis of (heat melting process) The raw material powders of Li2S, P2S5, and LiCl were mixed in a molar ratio of 1.9:0.5:1.6. The raw material powders were placed in a heat-resistant container, which was then placed in a 30g test furnace. 3g of sulfur powder was added to the container, and the mixture was heated and melted for 0.5 hours under conditions of a nitrogen atmosphere with a dew point of -50°C, a pressure of 1 atmosphere, and a temperature of 950°C (heating rate of 30°C / min). (cooling process) Thereafter, the mixture was cooled at a cooling rate of 10 to 1000°C / sec to obtain a solid as a sulfide-based solid electrolyte containing an amorphous phase, an argyrodite-type crystalline phase, and an impurity phase. (Reheating process) Next, this solid was reheated for 1 hour at 450° C. in a nitrogen gas atmosphere. The obtained sulfide-based solid electrolyte was pulverized using a mortar to obtain a powder having a D50 of about 10 μm. The composition of the sulfide-based solid electrolyte powder after pulverization was analyzed, and the element ratio of P was set to 1, and the ratio of Li 5.93 PS 4.23 Cl 1.78 It was. (Homogeneity evaluation, lithium ion conductivity evaluation) The homogeneity of the resulting sulfide-based solid electrolyte was evaluated by Raman spectroscopy in the same manner as in Example 1. The (average peak position ± standard deviation) of Example 3 was 425.0 ± 2.4 cm -1 It was. The lithium ion conductivity was measured at 25°C by the AC impedance method in the same manner as in Example 1. The lithium ion conductivity was 0.6 × 10 at 25°C. -3 It was S / cm.

[0092] Example 4 Li 5.4 PS 4.4 Cl 1.6 Synthesis of (heat melting process) The raw material powders of Li2S, P2S5, and LiCl were mixed in a molar ratio of 1.9:0.5:1.6. The raw material powders were placed in a heat-resistant container and placed in a 30g test furnace. 3g of sulfur powder was added to the container, and the mixture was heated and melted for 0.5 hours under conditions of a nitrogen atmosphere with a dew point of -50°C, a pressure of 1 atmosphere, and a temperature of 750°C (heating rate of 30°C / min). (cooling process) Thereafter, the mixture was cooled at a cooling rate of 10 to 1000°C / sec to obtain a solid as a sulfide-based solid electrolyte containing an amorphous phase, an argyrodite-type crystalline phase, and an impurity phase. (Reheating process) Next, this solid was reheated for 1 hour at 450° C. in a nitrogen gas atmosphere. The obtained sulfide-based solid electrolyte was pulverized using a mortar to obtain a powder having a D50 of about 10 μm. The composition of the sulfide-based solid electrolyte powder after pulverization was analyzed, and the element ratio of P was set to 1, and the ratio of Li 5.73 PS4.52 Cl 1.72 It was. (Homogeneity evaluation, lithium ion conductivity evaluation) The homogeneity of the resulting sulfide-based solid electrolyte was evaluated by Raman spectroscopy in the same manner as in Example 1. The (average peak position ± standard deviation) of Example 4 was 425.5 ± 3.4 cm -1 It was. The lithium ion conductivity was measured at 25°C by the AC impedance method in the same manner as in Example 1. The lithium ion conductivity was 0.8 × 10 at 25°C. -3 It was S / cm.

[0093] Example 5 Li 5.4 PS 4.4 Cl 1.6 Synthesis of (Intermediate synthesis process) The raw material powders of Li2S, P2S5, and LiCl were mixed in a molar ratio of 1.9:0.5:1.6. This raw material powder was placed in a heat-resistant container, and 30 g of it was placed in a test furnace. It was then heat-treated by holding it for 0.5 hours under the conditions of a nitrogen atmosphere with a dew point of -50°C, a pressure of 1 atmosphere, and a temperature of 300°C (heating rate of 5°C / min), to obtain an intermediate. (heat melting process) The resulting intermediate was placed in a heat-resistant container and heated to melting conditions of 1 atmosphere and 750°C for 0.5 hours. Sulfur gas, obtained by heating elemental sulfur at 350°C, was supplied to the melt with N2 as a carrier gas at a partial pressure of 0.1 atm, resulting in a sulfur-containing gas atmosphere. The sulfur content in the sulfur-containing gas atmosphere was 0.1 vol%. (cooling process) Thereafter, the mixture was cooled at a cooling rate of 10 to 1000°C / sec to obtain a solid as a sulfide-based solid electrolyte containing an amorphous phase and an argyrodite-type crystalline phase. (Reheating process) Next, this solid was reheated for 1 hour at 450° C. in a nitrogen gas atmosphere. The obtained sulfide-based solid electrolyte was pulverized using a mortar to obtain a powder having a D50 of about 10 μm. The composition of the sulfide-based solid electrolyte powder after pulverization was analyzed, and the element ratio of P was set to 1, and the ratio of Li 5.47 PS 4.32 Cl 1.62 It was. (Homogeneity evaluation, lithium ion conductivity evaluation) The homogeneity of the obtained sulfide-based solid electrolyte was evaluated by Raman spectroscopy in the same manner as in Example 1. The (average peak position ± standard deviation) of Example 5 was 429.6 ± 0.5 cm -1 It was. The lithium ion conductivity was measured at 25°C by the AC impedance method in the same manner as in Example 1. The lithium ion conductivity was 5.8 × 10 at 25°C. -3 It was S / cm.

[0094] Table 1 shows the compositions of the sulfide-based solid electrolytes, the lithium ion conductivity evaluation results, and the homogeneity evaluation results of Examples 1 to 5. As the homogeneity evaluation results, Table 1 also shows (average peak position ± standard deviation) and (average full width at half maximum of peak ± standard deviation).

[0095] [Table 1]

[0096] In Examples 1 and 5, which are working examples, the variation in peak wavenumber (peak position) and full width at half maximum of the peak in the Raman spectrum was small in the homogeneity evaluation, and argyrodite-type crystals were obtained as sulfide-based solid electrolytes with high homogeneity, and the lithium ion conductivity was also high. On the other hand, in Examples 2 to 4, which are comparative examples, only sulfide-based solid electrolytes with low homogeneity were obtained, and the lithium ion conductivity was also low.

[0097] For example, the particle size (D50) of solid electrolytes used in all-solid-state lithium-ion secondary batteries is known to be generally 1 to 5 μm. The analysis region of the Raman spectrum in the above-mentioned homogeneity evaluation corresponds to a region equivalent in size to a single particle having such particle size or slightly larger than a single particle. In other words, in the above-mentioned homogeneity evaluation, the results of comparing the measured values ​​at each measurement point can be said to be a comparison of values ​​measured in a region roughly corresponding to one particle of the target solid electrolyte powder. Therefore, the small variation in the measured values ​​at each measurement point means that the solid electrolyte powder is homogeneous at the micron level even when pulverized to form a solid electrolyte powder, i.e., the particles constituting the solid electrolyte powder are more homogeneous with each other. As a result, the sulfide-based solid electrolyte of the present invention is superior in lithium ion conductivity, and is thought to be able to improve the battery characteristics when used in an all-solid-state lithium ion secondary battery. On the other hand, if the solid electrolyte powder is an aggregate of heterogeneous particles, the solid electrolyte powder will contain particles with poor lithium ion conductivity to some extent, and it is believed that such particles cannot conduct lithium ions well when they come into contact with the active material or other solid electrolyte particles.

[0098] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application (Patent Application No. 2020-130799) filed on July 31, 2020, the contents of which are incorporated herein by reference.

Claims

1. heat-treating a raw material containing lithium, sulfur, and phosphorus to obtain an intermediate; and heating and melting the intermediate in a gas atmosphere containing elemental sulfur; The heating and melting temperature is 900°C or less, The method further comprises recovering a component containing sulfur element volatilized from the raw material when obtaining the intermediate, a gas derived from a component containing sulfur element used as at least a part of the gas containing sulfur element;

2. heat-treating a raw material containing lithium, sulfur, and phosphorus to obtain an intermediate; and heating and melting the intermediate in a gas atmosphere containing elemental sulfur; The heating and melting temperature is 900°C or less, The method for producing a sulfide-based solid electrolyte, wherein the intermediate contains at least one of Li 4 P 2 S 6 and Li 3 PS 4 .

3. heat-treating a raw material containing lithium, sulfur, and phosphorus to obtain an intermediate; heating and melting the intermediate in a gas atmosphere containing elemental sulfur; and rapidly cooling the melt obtained by the heating and melting (excluding rapid cooling using liquid nitrogen) to obtain a solid, The method further comprises recovering a component containing sulfur element volatilized from the raw material when obtaining the intermediate, a gas derived from a component containing sulfur element used as at least a part of the gas containing sulfur element;

4. heat-treating a raw material containing lithium, sulfur, and phosphorus to obtain an intermediate; heating and melting the intermediate in a gas atmosphere containing elemental sulfur; and rapidly cooling the melt obtained by the heating and melting (excluding rapid cooling using liquid nitrogen) to obtain a solid, The method for producing a sulfide-based solid electrolyte, wherein the intermediate contains at least one of Li 4 P 2 S 6 and Li 3 PS 4 .

5. The method for producing a sulfide-based solid electrolyte according to any one of claims 1 to 4, wherein the raw material contains one or more selected from the group consisting of lithium chloride, lithium bromide, and lithium iodide.

6. The method for producing a sulfide-based solid electrolyte according to any one of claims 1 to 5, wherein the obtained sulfide-based solid electrolyte has an argyrodite-type crystal structure.

7. 7. The method for producing a sulfide-based solid electrolyte according to claim 1, further comprising cooling the melt obtained by the heating and melting to obtain a solid, wherein the melt contains 0.01 mass % or more of a compound that becomes a crystal nucleus, and the solid is a sulfide-based solid electrolyte containing a crystalline phase.

8. heat-treating a raw material containing lithium, sulfur, and phosphorus to obtain an intermediate; and heating and melting the intermediate in a gas atmosphere containing elemental sulfur; The method further comprises recovering a component containing sulfur element volatilized from the raw material when obtaining the intermediate, a gas derived from a component containing sulfur element is used as at least a part of the gas containing sulfur element; The method for producing a sulfide-based solid electrolyte, wherein the obtained sulfide-based solid electrolyte has an argyrodite-type crystal structure.

9. heat-treating a raw material containing lithium, sulfur, and phosphorus to obtain an intermediate; and heating and melting the intermediate in a gas atmosphere containing elemental sulfur; the intermediate comprises at least one of Li 4 P 2 S 6 and Li 3 PS 4 ; The method for producing a sulfide-based solid electrolyte, wherein the obtained sulfide-based solid electrolyte has an argyrodite-type crystal structure.

10. The method for producing a sulfide-based solid electrolyte according to claim 8 or 9, wherein the raw material contains at least one of lithium chloride and lithium bromide.

11. The method further comprises cooling the melt obtained by the heat melting to obtain a solid, The method for producing a sulfide-based solid electrolyte according to any one of claims 8 to 10, wherein the melt contains 0.01 mass% or more of a compound that serves as a crystal nucleus, and the solid is a sulfide-based solid electrolyte that includes a crystalline phase having the argyrodite-type crystal structure.

12. The method for producing a sulfide-based solid electrolyte according to any one of claims 8 to 11, further comprising rapidly cooling the melt obtained by the heating and melting to obtain a solid.

13. The method for producing a sulfide-based solid electrolyte according to claim 11 or 12, further comprising reheating the solid.

14. The method for producing a sulfide-based solid electrolyte according to any one of claims 1 to 13, wherein the temperature at which the raw material is heated in the heat treatment is in the range of 250 to 500°C.

15. The method for producing a sulfide-based solid electrolyte according to any one of claims 1 to 14, wherein the raw material contains one or more selected from the group consisting of metallic lithium, lithium sulfide, lithium carbonate, lithium sulfate, lithium oxide, and lithium hydroxide.

16. The method for producing a sulfide-based solid electrolyte according to any one of claims 1 to 4, 8 and 9, wherein the raw material further contains a halogen element.

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