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

Abstract

The present invention relates to a method for manufacturing a sulfide-based solid electrolyte, comprising heat-treating a raw material containing a lithium element, a sulfur element, and a phosphorus element to obtain an intermediate, and heating and melting the intermediate under a gas atmosphere containing a sulfur element.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing 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 notebook personal computers.

[0003] Conventionally, liquid electrolytes have been used in lithium-ion secondary batteries, but there were concerns about leakage or ignition, and it was necessary to enlarge the case for safety design. In addition, improvements were desired regarding the short battery life and narrow operating temperature range.

[0004] In contrast, all-solid-state lithium-ion secondary batteries that use a solid electrolyte as the electrolyte are attracting attention due to the potential for improved safety, high-speed charging and discharging, and miniaturization of the case.

[0005] Solid electrolytes are broadly classified into sulfide-based solid electrolytes and oxide-based solid electrolytes. Sulfide ions constituting sulfide-based solid electrolytes have a higher polarization rate and exhibit higher ionic conductivity compared to oxide ions constituting oxide-based solid electrolytes. Examples of sulfide-based solid electrolytes include sulfide-based solid electrolytes containing lithium, sulfur, and phosphorus elements, and methods for manufacturing them include the glass tube method, mechanical milling method, and melting method. However, the glass tube method and mechanical milling method are batch-type processes and require a long time for the reaction, so they are not suitable for mass production.

[0006] Meanwhile, although the melting method is a method capable of mass production, the boiling point of the raw material, phosphorus pentasulfide (P2S5), is 514°C, whereas the melting point of lithium sulfide (Li2S) is 938°C. Therefore, when Li2S is heated and melted, P2S5 volatilizes at a temperature significantly lower than that. For this reason, there was a problem in that it was difficult to control the composition of the resulting sulfide-based solid electrolyte.

[0007] Regarding such problems, for example, Patent Document 1 discloses that in the manufacture of a lithium ion conductive material, a composite compound comprising lithium, phosphorus, and sulfur is used as a raw material as a composition. It is disclosed that, as a result, only the P2S5 component volatilizes during melting, that is, the problem of the sulfur component or the phosphorus component volatilizing does not occur, and thus a homogeneous lithium ion conductive material having a desired composition can be stably manufactured. Prior art literature

[0008] Japanese Patent Publication No. 2012-43654 The problem to be solved

[0009] However, the composite compound described in Patent Document 1 itself is thought to be an intermediate obtained by heating a mixture of Li2S and P2S5, and in the process of obtaining the composite compound, sulfur or phosphorus components are still prone to volatilization. In the conventional technology, there was still room for improvement in terms of compositional controllability from the starting raw materials to the target sulfide-based solid electrolyte.

[0010] If compositional controllability is insufficient, a discrepancy between the target composition of the sulfide-based solid electrolyte and the composition actually obtained is likely to occur. In this case, the obtained sulfide-based solid electrolyte is likely to be heterogeneous. Furthermore, heterogeneous sulfide-based solid electrolytes may show a decline in lithium ion conductivity. In other words, in conventional technology, there was room for improvement regarding the homogeneity and lithium ion conductivity of the obtained sulfide-based solid electrolyte, along with compositional controllability.

[0011] Accordingly, the present invention aims to provide a method for manufacturing a sulfide-based solid electrolyte that suppresses the volatilization of sulfur or phosphorus components, has excellent compositional controllability with minimal deviation from the raw material composition, and is easy to mass-produce. Furthermore, the present invention aims to provide a sulfide-based solid electrolyte that has excellent homogeneity and excellent lithium ion conductivity. means of solving the problem

[0012] The inventors, through repeated careful examination, discovered that the above problem can be solved by heat-treating a raw material containing lithium, sulfur, and phosphorus elements to obtain an intermediate, and further by heating and melting the intermediate under a gas atmosphere containing sulfur elements, and thus completed the present invention.

[0013] That is, the present invention relates to the following [1] to

[13] .

[0014] [1] Obtaining an intermediate by heat-treating raw materials containing lithium, sulfur, and phosphorus elements, and

[0015] A process comprising heating and melting the intermediate under a gas atmosphere containing sulfur elements.

[0016] Method for manufacturing a sulfide-based solid electrolyte.

[0017] [2] A method for manufacturing a sulfide-based solid electrolyte described in (1), wherein the temperature at which the raw material is heated in the above heat treatment is in the range of 250 to 500°C.

[0018] [3] When obtaining the above intermediate, the process further includes recovering a component containing sulfur elements volatilized from the above raw material, and

[0019] A method for manufacturing a sulfide-based solid electrolyte as described in (1) or (2), using a gas derived from a component containing the sulfur element as at least part of the gas containing the sulfur element.

[0020] [4] A method for manufacturing a sulfide-based solid electrolyte as described in any one of (1) to (3), wherein the above raw material comprises one or more selected from the group consisting of metallic lithium, lithium sulfide, lithium carbonate, lithium sulfate, lithium oxide, and lithium hydroxide.

[0021] [5] A method for preparing a sulfide-based solid electrolyte as described in any one of (1) to (4), wherein the intermediate comprises at least one of Li4P2S6 and Li3PS4.

[0022] [6] A method for manufacturing a sulfide-based solid electrolyte as described in any one of (1) to (5), wherein the above raw material further comprises a halogen element.

[0023] [7] A method for manufacturing a sulfide-based solid electrolyte as described in any one of (1) to (6), wherein the above raw material comprises one or more selected from the group consisting of lithium chloride, lithium bromide and lithium iodide.

[0024] [8] A method for producing a sulfide-based solid electrolyte as described in any one of (1) to (7), wherein the obtained sulfide-based solid electrolyte has an agarodite-type crystal structure.

[0025] [9] A method for manufacturing a sulfide-based solid electrolyte, wherein the molten liquid obtained by heating and melting is further cooled to obtain a solid, the molten liquid contains at least 0.01 mass% of a compound that acts as a crystal nucleus, and the solid is a sulfide-based solid electrolyte containing a crystalline phase, as described in any one of (1) to (8).

[0026]

[10] A method for manufacturing a sulfide-based solid electrolyte described in any one of (1) to (8), further comprising rapidly cooling the molten liquid obtained by the above heating and melting to obtain a solid.

[0027]

[11] A method for manufacturing a sulfide-based solid electrolyte as described in (10), wherein the cooling rate in the above rapid cooling is 10°C / sec or more, and the ratio of the compound that becomes a crystal nucleus in the above molten liquid is 1 mass% or less.

[0028]

[12] A method for manufacturing a sulfide-based solid electrolyte described in any one of (9) to (11), further comprising reheating the solid.

[0029]

[13] When Raman spectrum measurements were taken with a spot diameter of 3 µm and 10 measurement points, 350 cm for each measurement point -1 up to 500cm -1 The standard deviation of the peak position of the peak derived from the PS bond in is 2 cm -1 In-e-in, sulfide-based solid electrolyte. Effects of the invention

[0030] According to the method for manufacturing a sulfide-based solid electrolyte of the present invention, volatilization of sulfur or phosphorus components in the raw material can be suppressed by passing through an intermediate from the raw material until the desired sulfide-based solid electrolyte is obtained. Furthermore, by passing through an intermediate, it becomes easier to control the composition compared to the case where the desired sulfide-based solid electrolyte is obtained directly from the raw material. Additionally, although a certain amount of sulfur components still volatilize when obtaining the intermediate, a sufficient amount of sulfur components to obtain a sulfide-based solid electrolyte of the desired composition can be introduced by heating and melting this intermediate under a gas atmosphere containing sulfur elements.

[0031] In particular, the intermediate in the manufacturing method of the present invention is in a thermodynamically stable state, and for this reason, after synthesizing the intermediate, the reaction temperature can be lowered to room temperature and extracted. The intermediate extracted in this manner may be temporarily stored, or it may be used in the subsequent melting process. Furthermore, since the intermediate in the manufacturing method of the present invention is synthesized by controlling the reaction, compositional information can be clarified by detailed compositional analysis. For the above reasons, the method for manufacturing a sulfide-based solid electrolyte of the present invention makes it easy to control the amount of sulfur introduced into the intermediate, which is carried out under a gas atmosphere containing sulfur element (S) in the molten state during the melting process, resulting in less sulfur deficiency and making it less likely for compositional deviation to occur.

[0032] By including these processes, a method for manufacturing a sulfide-based solid electrolyte can be provided in a melting method capable of mass production, wherein the discrepancy between the composition of the target sulfide-based solid electrolyte and the composition of the sulfide-based solid electrolyte obtained from the raw material is small and the composition is easy to control. According to the present manufacturing method, the controllability of the physical properties of the obtained sulfide-based solid electrolyte can be improved due to the excellent controllability of the composition, and as a result, it becomes easy to stably and with high reproducibility manufacture a sulfide-based solid electrolyte with high lithium ion conductivity suitable as an electrolyte for a lithium-ion secondary battery. Furthermore, because the present manufacturing method has excellent controllability of the composition, the obtained sulfide-based solid electrolyte has excellent homogeneity and excellent lithium ion conductivity. Brief explanation of the drawing

[0033] Figure 1 is a diagram showing the XRD measurement results of the sulfide-based solid electrolyte of Example 1. Figure 2 is a diagram showing the Raman spectrum measurement results of the sulfide-based solid electrolyte of Example 1. Figure 3 is a diagram showing the XRD measurement results of the sulfide-based solid electrolyte of Example 2. Figure 4 is a diagram showing the Raman spectrum measurement results of the sulfide-based solid electrolyte of Example 2. Specific details for implementing the invention

[0034] The present invention will be described in detail below, but the present invention is not limited to the following embodiments and may be implemented with arbitrary modifications within the scope that does not deviate from the gist of the present invention. Furthermore, the term "to" indicating a numerical range is used to mean including the values ​​described before and after it as lower and upper limits.

[0035] Method for manufacturing sulfide-based solid electrolytes

[0036] A method for manufacturing a sulfide-based solid electrolyte according to an embodiment of the present invention (hereinafter referred to as the present manufacturing method) comprises a process of obtaining an intermediate by heat-treating a raw material containing a lithium element, a sulfur element, and a phosphorus element (intermediate synthesis process), and a process of heating and melting the intermediate under a gas atmosphere containing a sulfur element (heating and melting process).

[0037] In addition, the present manufacturing method may further include other appropriate processes, such as a process for cooling the molten liquid obtained by heating and melting (cooling process), a process for reheating the solid obtained by the cooling process (reheating process), a grinding process, a drying process, etc. Each process is described below.

[0038] [Intermediate Synthesis Process]

[0039] The present manufacturing method includes an intermediate synthesis process for obtaining an intermediate by heat-treating raw materials containing lithium, sulfur, and phosphorus elements.

[0040] (raw material)

[0041] The raw materials of the present manufacturing method include lithium element (Li), sulfur element (S), and phosphorus element (P). As such raw materials, a suitable combination of materials (components) containing Li, such as Li element or a compound containing Li, materials (components) containing S, such as S element or a compound containing S, and materials (components) containing P, such as P element or a compound containing P, may be used. The compounds containing Li, the compounds containing S, and the compounds containing P may be compounds containing all of two or more selected from Li, S, and P. For example, compounds that are both compounds containing S and compounds containing P include diphosphorus pentasulfide (P2S5).

[0042] Examples of materials containing Li include lithium compounds such as lithium sulfide (Li2S), lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), lithium oxide (Li2O), and lithium hydroxide (LiOH), as well as metallic lithium. From the perspective of ease of intermediate synthesis and ease of handling, it is preferable to use lithium sulfide.

[0043] Meanwhile, since lithium sulfide is expensive, from the perspective of suppressing the manufacturing cost of sulfide-based solid electrolytes, it is desirable to use lithium compounds other than lithium sulfide or metallic lithium. Specifically, in this case, the raw material is a material containing Li, and it is desirable to include 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 materials may be used individually or in combination of two or more types.

[0044] Examples of substances containing S include phosphorus sulfides such as triphosphorus trisulfide (P2S3) and pentaphosphorus pentasulfide (P2S5), other sulfur compounds containing phosphorus, elemental sulfur, and compounds containing sulfur. Examples of compounds containing sulfur include H2S, CS2, and iron sulfide (FeS, Fe2S3, FeS2, Fe 1-x (S, etc.), bismuth sulfide (Bi2S3), copper sulfide (CuS, Cu2S, Cu 1-x Examples include S, etc. Among the S-containing substances, phosphorus sulfide is preferred from the perspective of facilitating the reaction in the intermediate synthesis process and preventing the inclusion of elements other than those constituting the target sulfide-based solid electrolyte, and phosphorus pentasulfide (P2S5) is more preferred. These substances may be used individually or in combination of two or more. In addition, phosphorus sulfide can be considered as a compound that combines both an S-containing substance and a P-containing substance.

[0045] Examples of materials containing P include phosphorus sulfides such as triphosphorus trisulfide (P2S3) and pentaphosphorus pentasulfide (P2S5), phosphorus compounds such as sodium phosphate (Na3PO4), and elemental phosphorus. Among the materials containing P, phosphorus sulfide is preferred from the perspective of facilitating the reaction in the intermediate synthesis process and preventing the inclusion of elements other than those constituting the target sulfide-based solid electrolyte, and pentaphosphorus pentasulfide (P2S5) is more preferred. These materials may be used individually or in combination of two or more types.

[0046] The raw material of the present manufacturing method is obtained by, for example, mixing the above-mentioned material appropriately according to 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 material Li / P is preferably 65 / 35 or higher, and more preferably 70 / 30 or higher, in order to synthesize the target intermediate with high precision.

[0047] As an example of a preferred combination of the above compounds, a combination of Li2S and P2S5 can be cited. When combining Li2S and P2S5, the molar ratio of Li to P, Li / P, is preferably 65 / 35 to 88 / 12, and more preferably 70 / 30 to 88 / 12. By adjusting the mixing ratio so that P2S5 is relatively smaller than Li2S, it becomes easier to suppress the volatilization of sulfur and phosphorus components during heat treatment, as the boiling point of P2S5 is smaller than the melting point of Li2S.

[0048] The raw materials of the present manufacturing method may include additional materials (compounds, etc.) in addition to the above materials, depending on the composition of the intended sulfide-based solid electrolyte or intermediate, or as additives.

[0049] For example, when manufacturing a sulfide-based solid electrolyte containing halogen elements such as F, Cl, Br, or I, it is preferable that the raw material contains a halogen element (Ha). In this case, it is preferable that the raw material 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 (Lil), phosphorus halides, phosphoryl halides, sulfur halides, sodium halides, and boron halides. Among the compounds containing a halogen element, lithium halides are preferred, and LiCl, LiBr, and Lil are more preferred, from the perspective of ease of reaction in the intermediate synthesis process and prevention of the inclusion of elements other than those constituting the target sulfide-based solid electrolyte. These compounds may be used individually or in combination of two or more types.

[0050] When a compound containing a halogen element is included in the raw material, there are cases where the compound containing the halogen element does not react and remains in the intermediate when heat treatment is performed to obtain an intermediate.

[0051] In addition, when manufacturing a sulfide-based solid electrolyte containing a halogen element, it is not mandatory for the raw material to 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 manufactured by adding a compound containing a halogen element during the heating and melting process after the intermediate synthesis process.

[0052] In addition, lithium halides are also compounds containing Li. When a raw material contains lithium halides, some or all of the Li in the raw material may be derived from lithium halides.

[0053] 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, and more preferably 0.5 molar equivalents or more, from the perspective of lowering the melting point when heating and melting the intermediate. In addition, from the perspective of the stability of the obtained sulfide-based solid electrolyte, the molar equivalent of Ha is preferably 4 molar equivalents or less, and more preferably 3 molar equivalents or less.

[0054] From the perspective of improving the glass formation state of the obtained sulfide-based solid electrolyte, it is desirable for the raw material to include sulfides such as SiS2, B2S3, GeS2, and Al2S3. By making glass formation easier, glass can be obtained even if the cooling rate is reduced when obtaining glass by rapid cooling, thereby reducing the load on the equipment. In addition, from the perspective of imparting moisture resistance to the sulfide solid electrolyte, it is desirable to include oxides such as SiO2, B2O3, GeO2, and Al2O3. These compounds may be used individually or in combination of two or more types.

[0055] In addition, their sulfides or oxides may be included in the raw materials, included as a composition in the intermediates obtained from the raw materials, or added separately when melting the intermediates.

[0056] The amount of these compounds added is preferably 0.1% by weight or more and more preferably 0.5% by weight or more with respect to the total amount of the raw material or intermediate. In addition, the amount added is preferably 50% by weight or less and more preferably 40% by weight or less.

[0057] In addition, the raw material may include a compound that serves as a crystal nucleus, as described below.

[0058] (Heat treatment in the intermediate synthesis process)

[0059] An intermediate is obtained by heat-treating a raw material containing the above-mentioned lithium, sulfur, and phosphorus elements. The specific method of heat treatment is not particularly limited, but for example, a method of placing the raw material in a heat-resistant container and heating it in a furnace may be used. As for the heat-resistant container, examples include a heat-resistant container made of carbon, a heat-resistant container containing oxides such as quartz, quartz glass, borosilicate glass, aluminosilicate glass, alumina, zirconia, and mullite, a heat-resistant container containing nitrides such as silicon nitride and boron nitride, and a heat-resistant container containing carbides such as silicon carbide. In addition, these heat-resistant containers may be formed as a bulk of the above-mentioned materials, or they may be containers in which layers such as carbon, oxides, nitrides, and carbides are formed.

[0060] In the heat treatment during the intermediate synthesis process, the temperature at which the raw material is heated is preferably 250°C or higher, more preferably 255°C or higher, and even more preferably 260°C or higher. It is desirable for the temperature to be above the lower limit value, as this facilitates the progress of the intermediate synthesis reaction. Additionally, the temperature is preferably 500°C or lower, more preferably 450°C or lower, and even more preferably 400°C or lower. It is desirable for the temperature to be below the upper limit value, as this suppresses the volatilization of low-boiling-point components such as P2S5 in the raw material and facilitates the progress of the reaction for synthesizing an intermediate containing a compound of the target composition.

[0061] In order to obtain an intermediate by heat treatment, it is desirable to maintain the temperature for a certain period of time within the aforementioned preferred temperature range. Furthermore, it is more desirable that the temperature range during maintenance be within a certain temperature range; for example, it is desirable to be within ±15℃ of a reference temperature, and more desirable to be within ±10℃.

[0062] Regarding the holding time, 1 minute or more is preferable, 5 minutes or more is more preferable, 10 minutes or more is even more preferable, 15 minutes or more is even more preferable, and 20 minutes or more is particularly preferable. Even if heated at the above-mentioned preferred temperature, if the holding time is insufficient, the reaction is likely to proceed insufficiently, and it is considered difficult to obtain an intermediate that yields the effects of the present manufacturing method. It is preferable to maintain the holding time at 1 minute or more to create conditions where the reaction proceeds and an intermediate is obtained. From the perspective of suppressing the volatilization of low-boiling point components such as P2S5 in the raw material, the holding time is 600 minutes or less, and 500 minutes or less is more preferable.

[0063] The holding time may also be shortened when a specific treatment is performed on the raw material. Such treatments include, for example, reducing the particle size of the raw material, removing or modifying the oxide layer on the surface of the particles contained in the raw material as much as possible by etching, making the particles porous, or increasing the reactivity between the particles contained in the raw material by adjusting the mixing conditions of the raw material and improving the homogeneity of the raw material. In this case, the holding time is preferably 1 second or more, more preferably 10 seconds or more, and even more preferably 20 seconds or more. From the perspective of suppressing the volatilization of low-boiling point components such as P2S5 in the raw material, the holding time is preferably 10 minutes or less, and more preferably 5 minutes or less.

[0064] From the perspective of shortening the retention time, that is, from the perspective of shortening the reaction time in the intermediate synthesis process, it is desirable to reduce the particle size of the raw material. In addition, if the particle size (D50) of the raw material is too large, it may affect the homogeneity of the sulfide-based solid electrolyte, and from this perspective as well, it is desirable for it to be somewhat small. However, since the present manufacturing method has excellent compositional controllability, even if raw materials with a particle size that may result in reduced homogeneity in, for example, conventional manufacturing methods are used, a more homogeneous sulfide-based solid electrolyte can be manufactured in the present manufacturing method. In this regard, specifically, the particle size (D50) of the raw material 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.

[0065] While it is preferable for the particle size to be smaller, a lower limit of approximately 0.1 μm is practical, 1 μm or more is preferable, and 5 μm or more is more preferable. Furthermore, as described above, according to the present manufacturing method, it is easy to obtain a homogeneous sulfide-based solid electrolyte even when using raw materials with relatively large particle sizes. Considering this, for example, from the perspective of reducing manufacturing costs, it is preferable to make the particle size of the raw material 10 μm or more, 100 μm or more is more preferable, and 250 μm or more is even more preferable.

[0066] In addition, the raw material may be a mixture of multiple substances (compounds, etc.) as described above. The raw material may be in the form of a mixture of multiple substances with different particle sizes. In that case, it is preferable that the particle size of each substance falls within the above range.

[0067] In this specification, the particle size (D50) of the raw material refers to the median diameter (D50) obtained from the volume-based particle size distribution chart obtained by measuring the particle size distribution using the Microtrac laser diffraction particle size distribution measuring instrument MT3300EXII.

[0068] The pressure during heat treatment in the intermediate synthesis process is not particularly limited, but, for example, atmospheric pressure to low pressure is preferred, and atmospheric pressure is more preferred.

[0069] In the intermediate synthesis process, heat treatment is preferably performed under an inert gas atmosphere to prevent side reactions between the raw materials and substances such as water vapor or oxygen. Specifically, examples include N2 gas, argon gas, and helium gas. Additionally, the dew point during heat treatment is preferably -20°C or lower; while the lower limit is not specifically restricted, it is typically around -80°C. The oxygen concentration is preferably 1000 ppm or lower.

[0070] In the intermediate synthesis process, intermediates of different compositions according to the purpose are obtained by adjusting the compounds contained in the raw materials or their mixing ratios, as well as controlling the conditions during heat treatment. The obtained intermediates may be used directly in the heating and melting process within the furnace used for intermediate synthesis without being removed from a heat-resistant container, or they may be removed after cooling to room temperature and stored temporarily. It is also possible to combine multiple types of intermediates of different compositions that have been removed and stored, and use them in the heating and melting process. In the heating and melting process, by controlling the amount of sulfur introduced into the intermediate under a gas atmosphere containing sulfur elements, it becomes easy to separately produce sulfide-based solid electrolytes with different compositions, physical properties, and performance.

[0071] Examples of the composition of the intermediate obtained in this process include compounds containing Li, P, and S, such as Li4P2S6 and Li3PS4. In the heating and melting process, from the perspective of controlling the amount of sulfur introduced into the intermediate under a gas atmosphere containing sulfur elements, it is preferable that the intermediate contains at least one of Li4P2S6 and Li3PS4. Furthermore, since Li4P2S6 and Li3PS4 are thermodynamically stable, they are also desirable from the perspective of stability during temporary storage of the intermediate.

[0072] Here, the reaction occurring in the intermediate synthesis process varies depending on the composition of the target sulfide-based solid electrolyte, but typically, it is a reaction characterized by the fact that Li2S and P2S5 contained in the raw material begin to react at about 250°C, and at least one of Li4P2S6 and Li3PS4 is formed. In addition, in the reaction, Li2S or P2S5 may start from a material containing Li (compound, etc.) or a material containing P (compound, etc.) in the preceding step of obtaining each.

[0073] In order to essentially accelerate this reaction, it is desirable to increase the reactivity between the 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 particles contained in the raw materials as much as possible through etching, making the particles porous, adjusting the mixing conditions of the raw materials, and improving the homogeneity of the raw materials. In particular, in this reaction, the particle size of Li2S, which is the initial counterpart to P2S5, is prone to affecting the intermediate formation reaction. Therefore, from the perspective of promoting the intermediate formation reaction, it is desirable to make the particle size of Li2S or the Li-containing material (compound, etc.) in the raw materials that is the step prior to obtaining Li2S fine. Furthermore, it is thought that lowering the crystallinity of the surface of Li2S or treatments that increase the surface area other than micronization are also effective from the above perspective. Additionally, reacting Li2S and P2S5 in a gas atmosphere containing sulfur is also thought to contribute to promoting the intermediate formation reaction.

[0074] When manufacturing a sulfide-based solid electrolyte containing a halogen element, it is preferable that the intermediate include a compound containing a halogen element. Additionally, when the raw material includes lithium halides such as LiCl and LiBr, since the composition of these compounds is difficult to change within the temperature range during heat treatment, the obtained intermediate may also include lithium halides.

[0075] According to the present manufacturing method, by undergoing an intermediate synthesis process, the volatilization of sulfur and phosphorus components in the raw materials can be suppressed compared to the case where the target sulfide-based solid electrolyte is obtained directly from the raw materials. Consequently, compounds with clear compositional information containing Li, P, and S, such as Li4P2S6 and Li3PS4, can be synthesized as intermediates. Since these intermediates are thermodynamically stable, they can be extracted by lowering the temperature to room temperature after heat treatment during intermediate synthesis. Compositional analysis can be performed on the intermediates extracted in this manner, thereby determining the amount of sulfur required for the heating and melting process. Furthermore, by passing the raw materials through an intermediate of a specific composition, it is easier to set the conditions during heating and melting more appropriately to match the intermediate composition. This allows for appropriate control of the amount of sulfur introduced under a gas atmosphere containing sulfur elements, making it difficult for compositional deviations to occur. Additionally, by passing through an intermediate with a composition closer to the target sulfide-based solid electrolyte than the raw materials before heating and melting, the composition of the obtained sulfide-based solid electrolyte can be made homogeneous. In addition, if multiple types of intermediates of different compositions are combined and heated and melted, it becomes easier to produce sulfide-based solid electrolytes with different compositions, physical properties, and performance.

[0076] [Heating and Melting Process]

[0077] In the heating and melting process, the aforementioned intermediate is heated and melted under a gas atmosphere containing sulfur elements. Furthermore, the intermediate heated and melted in this process may, if necessary, be an intermediate composition in which multiple types of intermediates are mixed, or an intermediate composition in which another substance (compound, etc.) is added to the intermediate.

[0078] The specific method of heating and melting is not particularly limited, but for example, a method of placing an intermediate in a heat-resistant container and heating it in a furnace may be used. As for the heat-resistant container, examples include a heat-resistant container made of carbon, a heat-resistant container containing oxides such as quartz, quartz glass, borosilicate glass, aluminosilicate glass, alumina, zirconia, and mullite, a heat-resistant container containing nitrides such as silicon nitride and boron nitride, and a heat-resistant container containing carbides such as silicon carbide. In addition, these heat-resistant containers may be formed as a bulk of the above materials, or they may be containers in which layers of carbon, oxides, nitrides, carbides, etc. are formed.

[0079] Heating and melting are carried out under a gas atmosphere containing the element sulfur. The gas containing the element sulfur is, for example, a compound containing the element sulfur or a gas containing sulfur, such as sulfur gas, hydrogen sulfide gas, carbon disulfide gas, etc.

[0080] The gas containing the element sulfur may consist solely of gaseous compounds containing the element sulfur, such as sulfur gas, hydrogen sulfide gas, and carbon disulfide gas; however, from the perspective of cost reduction and use as a carrier gas for transporting the sulfur component, it is also desirable to include inert gases such as N2 gas, argon gas, and helium gas. Furthermore, the gas containing the element sulfur may contain impurities derived from sulfur sources, etc., as long as they do not impair the effectiveness of the present manufacturing method.

[0081] When a gas containing a sulfur element contains sulfur gas, the sulfur gas (S) in the gas containing a sulfur element x The content of (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 perspective of ensuring a sufficient amount of sulfur element and carrying out the sulfur introduction reaction. In addition, the sulfur gas content is 100 vol% or less, and from the perspective of cost reduction or using an inert gas as a carrier gas, it is preferably 99 vol% or less, and more preferably 98 vol% or less. Sulfur gas (S x The content of (x=2 to 8)) can be measured by mass spectrometry gas chromatography.

[0082] Gases containing the elemental sulfur are 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 from which a gas containing the elemental sulfur is obtained by heating, but, for example, elemental sulfur, organic sulfur compounds such as hydrogen sulfide and carbon disulfide, and iron sulfide (FeS, Fe2S3, FeS2, Fe 1-x (S, etc.), bismuth sulfide (Bi2S3), copper sulfide (CuS, Cu2S, Cu 1-x Examples include polysulfides such as S, lithium polysulfide, and sodium polysulfide, and rubber that has undergone sulfur vulcanization treatment.

[0083] For example, these sulfur sources are heated in a separately provided sulfur source heating section to generate a gas containing sulfur elements, and an inert gas such as N2, argon, or helium is conveyed to the heating and melting furnace as a carrier gas to obtain a gas atmosphere containing sulfur elements. By separating the sulfur source heating section from the section where the heating and melting process is performed, even if the gas introduced into the heating and melting furnace contains oxygen or moisture, it can be removed by reacting it with the sulfur gas before introduction. This is desirable because it allows for the production of a high-quality sulfide-based solid electrolyte with low impurities and high purity.

[0084] The temperature at which the sulfur source is heated can be appropriately selected depending on the type of sulfur source used. For example, when using pure sulfur as the sulfur source, the heating temperature is preferably 250°C or higher and 750°C or lower.

[0085] Alternatively, among the above sulfur sources, a solid sulfur source such as elemental sulfur, H2S, Bi2S3, iron sulfide, copper sulfide, CS2, etc., in a fine powder state may be conveyed by a carrier gas to a heated melting furnace to obtain a gas atmosphere containing sulfur elements.

[0086] For example, the heating and melting process can be performed as follows. In a configuration in which a sulfur source heating section and a section for performing the heating and melting process are separated, a sulfur source is heated in the sulfur source heating section to generate a gas containing sulfur elements. The gas containing sulfur elements in an amount corresponding to the required sulfur partial pressure is supplied to the section for performing the heating and melting process, thereby obtaining a gas atmosphere containing sulfur elements. Under this atmosphere, an intermediate obtained from a raw material containing at least lithium elements, sulfur elements, and phosphorus elements is heated and melted. At this time, the sulfur partial pressure in the gas atmosphere containing sulfur elements is 10 -3 to 10 0 An ATM is desirable.

[0087] Here, in the intermediate synthesis process described above, volatilized sulfur components such as P2S5 can be recovered and used as a sulfur source in this process. Specifically, for example, the volatilized sulfur components can be cooled and solidified, and this can be used as the sulfur source mentioned above.

[0088] From the perspective of manufacturing costs or obtaining a high quantity of the desired sulfide-based solid electrolyte, the present manufacturing method further includes a process for recovering a component containing sulfur elements volatilized from the raw material in the intermediate synthesis process, and in the heating and melting process, it is preferable to use a gas derived from the recovered component containing sulfur elements as at least a portion of the gas containing sulfur elements.

[0089] By heating and melting the intermediate under a gas atmosphere containing sulfur elements, sulfur is introduced into the molten intermediate. In this way, a sufficient amount of sulfur can be introduced to obtain a sulfide-based solid electrolyte of the desired composition.

[0090] Furthermore, introducing sulfur in the liquid state of the molten intermediate is desirable because it shortens the reaction time for sulfur introduction compared to a reaction in the solid state. Additionally, since it is in a liquid state, it is easier to introduce sulfur homogeneously throughout the molten liquid, making it easier for the composition of the resulting sulfide-based solid electrolyte to be homogeneous. Moreover, the viscosity of the molten intermediate is lowered due to the fluidization of the solid, resulting in a highly homogeneous state. Consequently, the molten intermediate has high solubility and diffusivity for gases containing sulfur elements. Therefore, the effects of shortening the reaction time and homogenizing the composition by reacting in the liquid state are superior. Furthermore, it is more desirable to perform heating and melting while stirring the molten liquid and the gases containing sulfur elements, as this makes it easier to obtain the aforementioned effects.

[0091] In order to increase the fluidity of the molten liquid and promote the reaction of sulfur introduction, the heating and melting temperature is preferably 600°C or higher, more preferably 630°C or higher, and even more preferably 650°C or higher. In addition, from the perspective of suppressing deterioration or decomposition of components in the molten liquid due to heating, the heating and melting temperature is preferably 900°C or lower, more preferably 850°C or lower, and even more preferably 800°C or lower.

[0092] The heating and melting time is preferably 0.1 hours or more, more preferably 0.5 hours or more, more preferably 0.7 hours or more, and more preferably 1 hour or more in order to carry out the sulfur introduction reaction. In addition, the heating and melting time is preferably 10 hours or less, more preferably 9.5 hours or less, and more preferably 9 hours or less from the perspective of inhibiting deterioration or decomposition of components in the molten liquid due to heating.

[0093] Heating and melting may be performed as a continuous process. A continuous process is a process in which the molten liquid is continuously flowed from a heat-resistant vessel. The input may be continuous or intermittent. When heating and melting is performed as a continuous process, the liquid may be maintained in a molten state for a long time under appropriate conditions that take into account the progress of the sulfur introduction reaction and the deterioration of components within the liquid. A long time may be, for example, about 24 hours.

[0094] The pressure during heating and melting is not particularly limited, but, for example, atmospheric pressure to low pressure is preferred, and atmospheric pressure is more preferred. In addition, the sulfur partial pressure is 10 -3 to 10 0 It is preferable to set it to atm. By using this partial pressure of sulfur, sulfur can be introduced efficiently at low cost without complicating the equipment, making it easy to obtain the target sulfide-based solid electrolyte.

[0095] In order to prevent adverse reactions with steam or oxygen during heating and melting, the dew point is preferably -20°C or lower. The lower limit is not specifically restricted, but is typically around -80°C. In addition, the oxygen concentration is preferably 1000 ppm or lower.

[0096] (Cooling process)

[0097] The present manufacturing method preferably further includes a process of cooling a molten liquid obtained by heating and melting to obtain a solid. Cooling can be performed by a known method, and the method is not particularly limited.

[0098] With respect to maintaining the composition obtained by the heating and melting process, the cooling rate is preferably 0.01℃ / sec or higher, more preferably 0.05℃ / sec or higher, and even more preferably 0.1℃ / sec or higher. In addition, although no upper limit value for the cooling rate is specifically set, the cooling rate of the twin roller, which is generally said to have the fastest rapid cooling rate, is 1,000,000℃ / sec or lower.

[0099] Here, if the obtained solid is to be an amorphous sulfide-based solid electrolyte, it is preferable to obtain the solid by rapidly cooling the molten liquid obtained by heating and melting. Specifically, the cooling rate during rapid cooling is preferably 10°C / sec or higher, more preferably 100°C / sec or higher, even more preferably 500°C / sec or higher, and even more preferably 700°C / sec or higher. In addition, although the upper limit of the cooling rate is not particularly limited, the cooling rate of the twin roller, which is generally said to have the fastest rapid cooling rate, is 1,000,000°C / sec or lower.

[0100] Meanwhile, during the cooling process, slow cooling may be performed to crystallize at least a portion of the solid, thereby obtaining 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. When slow cooling, the cooling rate is preferably 0.01°C / sec or higher, and more preferably 0.05°C / sec or higher. Additionally, the cooling rate is preferably 500°C / sec or lower, and more preferably 450°C / sec or lower. The cooling rate may be less than 10°C / sec or 5°C / sec or lower. Furthermore, the cooling rate may be appropriately adjusted according to the crystallization conditions.

[0101] Here, the crystal contained in the sulfide-based solid electrolyte is preferably an ion-conducting crystal. Specifically, the ion-conducting crystal has a lithium ion conductivity of 10 -4 Greater than S / cm, and more preferably 10-3 It is a decision larger than S / cm.

[0102] In order to make the solid obtained after cooling a sulfide-based solid electrolyte containing a crystalline phase, it is desirable to include a compound that acts as a crystal nucleus in the molten liquid obtained from the heating and melting process. This makes it easier for crystals to precipitate during the cooling process. The method of including a compound that acts as a crystal nucleus in the molten liquid is not particularly limited, but examples include adding a compound that acts as a crystal nucleus to the raw material or intermediate, or adding a compound that acts as a crystal nucleus to the molten liquid during heating and melting.

[0103] Examples of compounds that serve as crystal nuclei include oxides, oxynitrides, nitrides, carbides, other chalcogen compounds, halides, etc. It is preferable that the crystal nucleus compound has some degree of compatibility with the melt. In addition, compounds that are not compatible with the melt at all cannot serve as crystal nuclei.

[0104] When the solid obtained after cooling is to be a sulfide-based solid electrolyte containing a crystalline phase, the content of the compound that acts as a crystal nucleus in the molten liquid is preferably 0.01 mass% or more, more preferably 0.1 mass% or more, and even more preferably 1 mass% or more. On the other hand, from the perspective of suppressing the decrease in lithium ion conductivity, the content of the compound that acts as a crystal nucleus in the molten liquid is preferably 20 mass% or less, and more preferably 10 mass% or less.

[0105] In cases where the solid obtained after cooling is to be an amorphous sulfide-based solid electrolyte, it is preferable that the molten solution does not contain a crystal nucleation compound, or that its content is less than or equal to a predetermined amount. Specifically, it is preferable that the content of the crystal nucleation compound in the molten solution be 1 mass% or less, and more preferable that it be 0.1 mass% or less. The content of the crystal nucleation compound in the molten solution may be less than 0.01 mass%.

[0106] (Reheating process)

[0107] Amorphous sulfide-based solid electrolytes or sulfide-based solid electrolytes containing an amorphous phase can promote high-temperature crystallization by heat treatment (post-annealing). The present manufacturing method may further include reheating the solid when the solid obtained in the cooling process is an amorphous sulfide-based solid electrolyte or a sulfide-based solid electrolyte containing an amorphous phase. Furthermore, by reheating a sulfide-based solid electrolyte containing sulfide-based solid electrolyte crystals, ions within the crystal structure can be rearranged to increase lithium ion conductivity. In addition, the reheating treatment in the present process refers to at least one of heat treatment for crystallization of the solid obtained by cooling in the cooling process and rearrangement of 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 is referred to as reheating treatment, including crystallization treatment.

[0108] 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 desirable for controlling lithium ion conductivity. To increase lithium ion conductivity, it is desirable to increase the ratio of the crystalline phase. Specifically, the ratio of the crystalline phase is preferably 10 mass% or more, and 20 mass% or more is more desirable. From the perspective of mechanical strength, the ratio of the crystalline phase is preferably 99.9 mass% or less, and 99 mass% or less is more desirable. The ratio of the crystalline phase can be measured by X-ray diffraction (XRD) measurement.

[0109] The specific conditions for the reheating treatment can be adjusted according to the composition of the sulfide-based solid electrolyte, etc., and are not particularly limited. It is preferable to perform the reheating treatment under an inert gas atmosphere such as N2 gas, argon gas, or helium gas. The reheating treatment may also be performed in a gas atmosphere containing sulfur elements.

[0110] For example, the temperature of the reheating treatment is preferably above the glass transition temperature of the sulfide-based solid electrolyte, specifically 200°C or higher, and more preferably 250°C or higher. In addition, the upper limit of the temperature is not particularly limited as long as it is within a range where the sulfide-based solid electrolyte does not undergo thermal degradation or thermal decomposition due to heating, but for example, 550°C or lower is preferred, and 500°C or lower is more preferred.

[0111] In addition, the reheating treatment time is preferably 0.1 hours or more and more preferably 0.2 hours or more in order to ensure crystal precipitation is carried out more reliably. From the perspective of suppressing thermal degradation by heating, the reheating treatment time is preferably 3 hours or less and more preferably 2 hours or less.

[0112] Depending on the intended use of the sulfide-based solid electrolyte obtained, the present manufacturing method may include a process of grinding the sulfide-based solid electrolyte obtained in the above process and a process of drying. The specific methods are not limited and may be carried out using known methods.

[0113] Sulfide-based solid electrolytes

[0114] The present manufacturing method allows for the control of the types and mixing ratios of raw materials or intermediates, and furthermore, since it involves obtaining intermediates and performing heating and melting under a gas atmosphere containing sulfur elements, it offers excellent compositional control. Therefore, various sulfide-based solid electrolytes can be manufactured using the present manufacturing method. Examples of sulfide-based solid electrolytes obtained by the present manufacturing method include Li 10 GeP2S 12 Sulfide-based solid electrolytes having an 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 0.8Sulfide-based solid electrolytes having an agirodite-type crystal structure, crystallized glasses of the Li-PS-Ha system (where Ha represents at least one element selected from halogen elements), and Li7P3S 11 Examples include LPS crystallized glass.

[0115] 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.

[0116] When a sulfide-based solid electrolyte contains a crystalline phase, the crystal contained in the sulfide-based solid electrolyte is preferably an ion-conducting crystal. Specifically, an ion-conducting crystal has a lithium ion conductivity of 10 -4 Greater than S / cm, and more preferably 10 -3 It is a crystal greater than S / cm. From the perspective of lithium ion conductivity, an agirodite-type crystal phase is more desirable.

[0117] As a sulfide-based solid electrolyte with excellent lithium ion conductivity, a sulfide-based solid electrolyte having an agirodite-type crystal structure is preferred. When a sulfide-based solid electrolyte having an agirodite-type crystal structure is used as the target compound, it is preferable that at least one of the raw material and intermediate of the present manufacturing method includes a halogen element. Furthermore, it is preferable that such halogen element is derived from one or more selected from the group consisting of lithium chloride, lithium bromide, and lithium iodide.

[0118] The obtained sulfide-based solid electrolyte can be identified by analyzing the elemental composition using various methods, such as the interpretation of the crystal structure by X-ray diffraction (XRD) measurement, or ICP emission analysis, atomic absorption measurement, and ion chromatography measurement. For example, P and S can be measured by ICP emission analysis, Li by atomic absorption measurement, and Cl by ion chromatography measurement.

[0119] In addition, the compositional homogeneity of the sulfide-based solid electrolyte can be evaluated by performing Raman spectrum measurements. Specifically, Raman spectrum measurements are performed at any two or more points on a sample obtained from the obtained sulfide-based solid electrolyte. Furthermore, from the perspective of increasing the precision of the evaluation, the number of measurement points is preferably 8 or more, and more preferably 10 or more.

[0120] As desirable conditions for Raman spectrum measurement when evaluating the compositional homogeneity of a sulfide-based solid electrolyte, for example, a spot diameter of 3 μm and a number of measurement points of 10 can be used. By setting the spot diameter to 3 μm, the analysis area in the Raman spectrum measurement becomes a size suitable for evaluating the compositional homogeneity of the sulfide-based solid electrolyte at the micro level.

[0121] PS4 in each measurement result 3- For example, the smaller the variation in peak wavenumber (peak position) originating from the structure of the sulfide-based solid electrolyte, the more homogeneous the composition of the sulfide-based solid electrolyte can be considered. Alternatively, the smaller the variation in full width at half maximum of the peak originating from the structure of the sulfide-based solid electrolyte, the more homogeneous the composition of the sulfide-based solid electrolyte can be considered.

[0122] Although it varies depending on the composition of the obtained sulfide-based solid electrolyte, as a peak originating from the structure of the sulfide-based solid electrolyte, PS4 3- It is desirable to identify the peak originating from.

[0123] PS4 3- The position of the peak originating from also varies depending on the compositional system, but typically, PS4 3- The peak originating from is 350cm -1 up to 500cm -1 It is a peak derived from the PS bond included between. For example, in a sulfide-based solid electrolyte having an agirodite-type crystal structure, this peak is at 420 to 430 cm⁻¹. -1 It is included between. Subsequently, in this specification, variation in peak position or variation in half-peak full width refers to PS4 3- It refers to what is confirmed regarding the peak originating from.

[0124] Variation in peak position can be evaluated as follows. That is, the standard deviation of the peak position for each measurement point obtained by Raman spectrum measurement is calculated, and if it is indicated as (average peak position) ± (standard deviation), the value of the standard deviation is 2 cm -1 It is preferable to be within 1 cm, and more preferably 1 cm -1 Within, and more preferably, 0.5cm -1 It is within. Also, here, the peak position refers to the position of the peak top.

[0125] For example, regarding the sulfide-based solid electrolyte obtained by the present manufacturing method, when Raman spectrum measurement is performed with a spot diameter of 3 μm and the number of measurement points as 10, 350 cm for each of the said measurement points -1 up to 500cm -1 The standard deviation of the peak position of the peak derived from the PS bond in is 2 cm -1 It is desirable that it be within, and more preferably 1cm -1 Within, and more preferably, 0.5cm -1 It is within.

[0126] The variation in the full width at half maximum of a peak can be evaluated as follows. That is, the standard deviation of the full width at half maximum of a peak for each measurement point obtained by Raman spectrum measurement is calculated by determining the full width at half maximum of each peak and calculating the standard deviation of that value. When this is expressed as (average full width at half maximum of peak) ± (standard deviation), the value of the standard deviation is 2 cm -1 Within is preferable, and more preferably 1.5 cm -1 It is within. Furthermore, the full width at half the peak refers here to the width at which the peak originating from the PS bond intersects with the value of half the peak intensity of the peak originating from the PS bond when plotting the Raman spectrum.

[0127] For example, regarding the sulfide-based solid electrolyte obtained by the present manufacturing method, when Raman spectrum measurement is performed with a spot diameter of 3 μm and the number of measurement points as 10, 350 cm for each of the said measurement points -1 up to 500cm -1 The standard deviation of the full width at half maximum of the peak derived from the PS bond in is 2 cm -1 It is preferable that it be within, and more preferably 1.5 cm -1 It is within.

[0128] The lithium ion conductivity of the obtained sulfide-based solid electrolyte is 1.0 × 10⁻⁶ in terms of improving battery characteristics when used in a lithium-ion secondary battery. -3 S / cm or higher is desirable, and 3.0×10 -3 S / cm or higher is more desirable, and 5.0×10 -3 S / cm or higher is more desirable.

[0129] Examples

[0130] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto. Examples 1 and 5 are examples of the manufacturing method of the present invention, and Examples 2 to 4 are comparative examples.

[0131] In addition, regarding the particle size of the material used as a raw material in each example, in Examples 1 to 3, Li2S, P2S5, and LiCl were used with particle sizes (D50) of 5㎛, 10㎛, and 50㎛, respectively. In Examples 4 and 5, only Li2S was used with a particle size (D50) of 100㎛.

[0132] [Example 1 Li 5.4 PS 4.4 Cl 1.6 Synthesis of

[0133] (Intermediate synthesis process)

[0134] The raw material powders of Li2S, P2S5, and LiCl were combined in a molar ratio of 1.9:0.5:1.6. This raw material powder was placed in a heat-resistant container, placed in a 30g test furnace, and heat-treated by maintaining it for 0.5 hours under a nitrogen atmosphere with a dew point of -50℃, pressure of 1 atm, and temperature of 300℃ (heating rate of 5℃ / min) to obtain an intermediate.

[0135] XRD measurements (equipment name: SmartLab, Rigaku Co., Ltd.) were performed on the obtained intermediate, and the crystal peak of P2S5 was not confirmed. In addition, compositional analysis revealed that the composition of the intermediate was, with the elemental ratio of P set to 1, Li 5.47 PS 4.08 Cl 1.62 In addition, compositional analysis was performed by measuring P and S by ICP emission analysis, Li by atomic absorption measurement, and Cl by ion chromatography measurement.

[0136] (Heating and melting process)

[0137] The obtained intermediate was placed in a heat-resistant container and heated and melted for 0.5 hours under conditions of pressure: 1 atm and temperature: 730°C. At this time, sulfur gas obtained by heating elemental sulfur at a temperature of 350°C was supplied with N2 as a carrier gas so that the partial pressure of the sulfur gas was 0.1 atm, thereby obtaining a gas atmosphere containing sulfur elements, and sulfur was introduced into the molten liquid by performing heating and melting under this gas atmosphere. The content of sulfur gas in the gas atmosphere containing sulfur elements was 0.1 vol%.

[0138] (Cooling process)

[0139] Afterwards, by cooling at a cooling rate of 10 to 1000℃ / sec, a solid was obtained as a sulfide-based solid electrolyte containing an amorphous phase and an agirodite-type crystalline phase.

[0140] (Reheating process)

[0141] Subsequently, this solid was reheated at 450°C for 1 hour under a nitrogen gas atmosphere and crystallized. By doing so, a sulfide-based solid electrolyte having an agirodite-type crystal structure with a crystalline phase ratio of 90 vol% or more was prepared, and Li 5.4 PS 4.4 Cl 1.6 A sulfide-based solid electrolyte was obtained. The obtained sulfide-based solid electrolyte was subjected to grinding treatment using a mortar and pestle to obtain a powder with a D50 of approximately 10 μm.

[0142] Compositional analysis was performed on the sulfide-based solid electrolyte powder after grinding as a sample, in the same manner as the intermediate synthesis process. As a result, with the elemental ratio of P set to 1, Li 5.43 PS 4.38 Cl 1.59 The crystalline phase was identified by XRD measurement (device name: SmartLab, Rigaku Co., Ltd.). As a result of the XRD measurement, the crystalline phase was a single phase of agirodite-type crystals. The XRD measurement results of the sulfide-based solid electrolyte of Example 1 are shown in Fig. 1.

[0143] (Homogeneity evaluation)

[0144] In addition, Raman spectrum measurements (device name: LabRAM HR Evolution, manufactured by Horiba Seisakusho Co., Ltd.) were performed, and the homogeneity of the obtained sulfide-based solid electrolyte was evaluated. For the measurements, the obtained sample powder was formed into pellets with a diameter of 1 cm, and measurements were performed at 10 random points. As an indicator of variation, (PS4) derived from an agirodite-type crystal structure 3- Raman band (420 to 430 cm) -1 Using a peak, 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 of 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).

[0145] In addition, Raman spectrum measurements were performed in an atmospheric non-exposure environment. The measurement conditions were as follows: excitation wavelength 532 nm, power during sample irradiation 5 mW, objective lens 10x, numeric aperture 0.25, confocal pinhole: 200 µm, grating: 1200 gr / mm, measurement time: 3 sec × 10 times, spot diameter: approximately 3 µm. Measurements were performed in an atmospheric non-exposure state.

[0146] The (average peak position ± standard deviation) of Example 1 is 428.1 ± 0.0 cm -1 The results of the Raman spectrum measurements of the sulfide-based solid electrolyte of Example 1 are shown in Table 1 and Figure 2. In addition, Figure 2 is a superimposed diagram of the Raman spectra at each of the 10 measurement points, and is normalized by the intensity on the vertical axis to make it easier to understand the variation in peak positions.

[0147] (Lithium ion conductivity evaluation)

[0148] Lithium ion conductivity was measured at 25°C by the AC impedance method (Solartron 1260A impedance analyzer, measurement frequency: 7 MHz to 20 Hz). The lithium ion conductivity at 25°C was 6.2 × 10⁻⁶. -3 It was S / cm. The measurement results are shown in Table 1.

[0149] [Example 2 Li 5.4 PS 4.4 Cl 1.6 Synthesis of

[0150] (Intermediate synthesis process)

[0151] The raw material powders of Li2S, P2S5, and LiCl were combined in a molar ratio of 1.9:0.5:1.6. This raw material powder was placed in a heat-resistant container, placed in a 30g test furnace, and heat-treated by maintaining it for 0.5 hours under a nitrogen atmosphere with a dew point of -50℃, pressure of 1 atm, and temperature of 300℃ (heating rate of 5℃ / min) to obtain an intermediate.

[0152] When XRD measurements (device name: SmartLab, Rigaku Co., Ltd.) were performed on the obtained intermediate, no crystal peak of P2S5 was detected. In addition, as a result of compositional analysis performed in the same manner as in Example 1, the composition of the intermediate was such that, with the elemental ratio of P set to 1, Li 5.47 PS 4.08 Cl 1.62 was.

[0153] (Heating and melting process)

[0154] The obtained intermediate was placed in a heat-resistant container and heated and melted for 0.5 hours under conditions of pressure: 1 atm and temperature: 730℃.

[0155] (Cooling process)

[0156] After that, the mixture was cooled at a cooling rate of 10 to 1000℃ / sec, and a solid was obtained as a sulfide-based solid electrolyte containing an amorphous phase, an agarodite-type crystalline phase, and an impurity phase.

[0157] (Reheating process)

[0158] Next, this solid was reheated at 450°C for 1 hour under a nitrogen gas atmosphere. The obtained sulfide-based solid electrolyte was subjected to grinding treatment using a mortar and pestle to obtain a powder with a D50 of approximately 10 μm.

[0159] Compositional analysis and XRD measurements were performed on the sulfide-based solid electrolyte powder after grinding, in the same manner as in Example 1. The composition was determined by setting the elemental ratio of P to 1, and Li 5.33 PS 3.88 Cl 1.65 It was. In addition, the XRD measurement results of the sulfide-based solid electrolyte of Example 2 are shown in Fig. 3.

[0160] (Homogeneity evaluation)

[0161] In addition, Raman spectrum measurements were performed as in Example 1, and the homogeneity of the obtained sulfide-based solid electrolyte was evaluated. The (average peak position ± standard deviation) of Example 2 was 425.2 ± 3.0 cm⁻¹. -1 The results of the Raman spectrum measurements of the sulfide-based solid electrolyte of Example 2 are shown in Table 1 and Figure 4. Figure 4 is a superimposed diagram of the Raman spectra at each of the 10 measurement points, and is normalized by the intensity on the vertical axis to make it easier to understand the variation in peak positions.

[0162] (Lithium ion conductivity evaluation)

[0163] As in Example 1, lithium ion conductivity was measured at 25°C by the AC impedance method. The lithium ion conductivity at 25°C was 0.4 × 10⁻⁶. -3 It was S / cm. The measurement results are shown in Table 1.

[0164] [Example 3 Li 5.4 PS 4.4 Cl 1.6 Synthesis of

[0165] (Heating and melting process)

[0166] The raw material powders of Li2S, P2S5, and LiCl were combined in a molar ratio of 1.9:0.5:1.6. This raw material powder was placed in a heat-resistant container and placed in a 30g test furnace. After adding 3g of sulfur powder to the container, it was heated and melted for 0.5 hours under a nitrogen atmosphere with a dew point of -50℃, pressure: 1 atm, and temperature: 950℃ (heating rate: 30℃ / min).

[0167] (Cooling process)

[0168] After that, the mixture was cooled at a cooling rate of 10 to 1000℃ / sec, and a solid was obtained as a sulfide-based solid electrolyte containing an amorphous phase, an agarodite-type crystalline phase, and an impurity phase.

[0169] (Reheating process)

[0170] Next, this solid was reheated at 450°C for 1 hour under a nitrogen gas atmosphere. The obtained sulfide-based solid electrolyte was subjected to grinding treatment using a mortar and pestle to obtain a powder with a D50 of approximately 10 μm.

[0171] As a result of compositional analysis performed on the sulfide-based solid electrolyte powder after grinding, with the elemental ratio of P set to 1, Li 5.93 PS 4.23 Cl 1.78 It was.

[0172] (Homogeneity evaluation, lithium ion conductivity evaluation)

[0173] In addition, Raman spectrum measurements were performed as in Example 1, and the homogeneity of the obtained sulfide-based solid electrolyte was evaluated. The (mean value ± standard deviation of peak position) of Example 3 was 425.0 ± 2.4 cm. -1 It was.

[0174] As in Example 1, lithium ion conductivity was measured at 25°C by the AC impedance method. The lithium ion conductivity at 25°C was 0.6 × 10⁻⁶. -3 It was S / cm.

[0175] [Example 4 Li 5.4 PS 4.4 Cl1.6 Synthesis of

[0176] (Heating and melting process)

[0177] The raw material powders of Li2S, P2S5, and LiCl were combined in a molar ratio of 1.9:0.5:1.6. This raw material powder was placed in a heat-resistant container and placed in a 30g test furnace. After adding 3g of sulfur powder to the container, it was heated and melted for 0.5 hours under a nitrogen atmosphere with a dew point of -50℃, pressure: 1 atm, and temperature: 750℃ (heating rate: 30℃ / min).

[0178] (Cooling process)

[0179] After that, the mixture was cooled at a cooling rate of 10 to 1000℃ / sec, and a solid was obtained as a sulfide-based solid electrolyte containing an amorphous phase, an agarodite-type crystalline phase, and an impurity phase.

[0180] (Reheating process)

[0181] Next, this solid was reheated at 450°C for 1 hour under a nitrogen gas atmosphere. The obtained sulfide-based solid electrolyte was subjected to grinding treatment using a mortar and pestle to obtain a powder with a D50 of approximately 10 μm.

[0182] As a result of compositional analysis performed on the sulfide-based solid electrolyte powder after grinding, with the elemental ratio of P set to 1, Li 5.73 PS 4.52 Cl 1.72 was.

[0183] (Homogeneity evaluation, lithium ion conductivity evaluation)

[0184] In addition, Raman spectrum measurements were performed as in Example 1, and the homogeneity of the obtained sulfide-based solid electrolyte was evaluated. The (mean value ± standard deviation of peak position) of Example 4 was 425.5 ± 3.4 cm. -1 It was.

[0185] As in Example 1, lithium ion conductivity was measured at 25°C by the AC impedance method. The lithium ion conductivity at 25°C was 0.8 × 10⁻⁶.-3 It was S / cm.

[0186] [Example 5 Li 5.4 PS 4.4 Cl 1.6 Synthesis of

[0187] (Intermediate synthesis process)

[0188] The raw material powders of Li2S, P2S5, and LiCl were combined in a molar ratio of 1.9:0.5:1.6. This raw material powder was placed in a heat-resistant container, placed in a 30g test furnace, and heat-treated by maintaining it for 0.5 hours under a nitrogen atmosphere with a dew point of -50℃, pressure of 1 atm, and temperature of 300℃ (heating rate of 5℃ / min) to obtain an intermediate.

[0189] (Heating and melting process)

[0190] The obtained intermediate was placed in a heat-resistant container and heated and melted for 0.5 hours under conditions of pressure: 1 atm and temperature: 750°C. At this time, sulfur gas obtained by heating elemental sulfur at a temperature of 350°C was supplied with N2 as a carrier gas so that the partial pressure of the sulfur gas was 0.1 atm, thereby obtaining a gas atmosphere containing sulfur elements, and sulfur was introduced into the molten liquid by performing heating and melting under this gas atmosphere. The content of sulfur gas in the gas atmosphere containing sulfur elements was 0.1 vol%.

[0191] (Cooling process)

[0192] After that, the solid was cooled at a cooling rate of 10 to 1000℃ / sec and obtained as a sulfide-based solid electrolyte containing an amorphous phase and an agirodite-type crystalline phase.

[0193] (Reheating process)

[0194] Next, this solid was reheated at 450°C for 1 hour under a nitrogen gas atmosphere. The obtained sulfide-based solid electrolyte was subjected to grinding treatment using a mortar and pestle to obtain a powder with a D50 of approximately 10 μm.

[0195] As a result of compositional analysis performed on the sulfide-based solid electrolyte powder after grinding, with the elemental ratio of P set to 1, Li 5.47 PS 4.32 Cl 1.62 was.

[0196] (Homogeneity evaluation, lithium ion conductivity evaluation)

[0197] In addition, Raman spectrum measurements were performed as in Example 1, and the homogeneity of the obtained sulfide-based solid electrolyte was evaluated. The (average peak position ± standard deviation) of Example 5 was 429.6 ± 0.5 cm. -1 It was.

[0198] As in Example 1, lithium ion conductivity was measured at 25°C by the AC impedance method. The lithium ion conductivity at 25°C was 5.8 × 10⁻⁶. -3 It was S / cm.

[0199] Table 1 shows the composition, lithium ion conductivity evaluation results, and homogeneity evaluation results of the sulfide-based solid electrolytes of Examples 1 to 5. In addition, as results of the homogeneity evaluation, (average peak position ± standard deviation) and (average peak half-width ± standard deviation) are each shown in Table 1.

[0200]

[0201] Examples 1 and 5, which are embodiments, showed small variations in the peak wavenumber (peak position) and peak full width at half maximum of the Raman spectrum in the homogeneity evaluation, and were able to obtain agarodite-type crystals as sulfide-based solid electrolytes with high homogeneity and high lithium ion conductivity. On the other hand, Comparative Examples 2 to 4 could only obtain sulfide-based solid electrolytes with low homogeneity, resulting in low lithium ion conductivity.

[0202] For example, it is known that the particle size (D50) of the solid electrolyte used in all-solid-state lithium-ion secondary batteries is generally 1 to 5 μm. The analysis region of the Raman spectrum in the homogeneity evaluation described above corresponds to a region that is equivalent in size to a single particle having such particle size, or slightly larger than a single particle. That is, in the homogeneity evaluation described above, the result of comparing the measured values ​​of each measurement point can be said to be a comparison of the measured values ​​of a region corresponding to approximately one particle of the target solid electrolyte powder.

[0203] Therefore, the small variation in the measured value at each measurement point means that even when ground into solid electrolyte powder, the solid electrolyte powder is homogeneous at the micrometer level, that is, the particles constituting the solid electrolyte powder are more homogeneous with each other. Accordingly, it is believed that the sulfide-based solid electrolyte of the present invention is excellent in terms of lithium ion conductivity and can improve battery characteristics when used in an all-solid-state lithium-ion secondary battery.

[0204] Meanwhile, when the solid electrolyte powder is an aggregate of heterogeneous particles, there are particles among the solid electrolyte powder that are inferior in terms of lithium ion conductivity. It is thought that these particles cannot conduct lithium ions well when in contact with active materials or other solid electrolyte particles.

[0205] Although the present invention has been described in detail with reference to specific embodiments, it is clear to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese patent application filed on July 31, 2020 (Japanese Patent Application No. 2020-130799), the contents of which are incorporated herein by reference.

Claims

Claim 1 A method for manufacturing a sulfide-based solid electrolyte, comprising obtaining an intermediate by heat treating a raw material containing a lithium element, a sulfur element, and a phosphorus element, and heating and melting the intermediate under a gas atmosphere containing a sulfur element, wherein in the heat treatment, the temperature at which the raw material is heated is in the range of 250 to 500°C. Claim 2 A method for manufacturing a sulfide-based solid electrolyte according to claim 1, further comprising recovering a component containing a sulfur element volatilized from the raw material when obtaining the intermediate, and using a gas derived from the component containing the sulfur element as at least a portion of the gas containing the sulfur element. Claim 3 A method for manufacturing a sulfide-based solid electrolyte according to claim 1 or 2, wherein the raw material comprises one or more selected from the group consisting of metallic lithium, lithium sulfide, lithium carbonate, lithium sulfate, lithium oxide, and lithium hydroxide. Claim 4 A method for manufacturing a sulfide-based solid electrolyte according to claim 1 or 2, wherein the intermediate comprises at least one of Li4P2S6 and Li3PS4. Claim 5 A method for manufacturing a sulfide-based solid electrolyte according to claim 1 or 2, wherein the raw material further comprises a halogen element. Claim 6 A method for manufacturing a sulfide-based solid electrolyte according to claim 1 or 2, wherein the raw material comprises one or more selected from the group consisting of lithium chloride, lithium bromide, and lithium iodide. Claim 7 A method for manufacturing a sulfide-based solid electrolyte according to claim 1 or 2, wherein the obtained sulfide-based solid electrolyte has an agirodite-type crystal structure. Claim 8 A method for manufacturing a sulfide-based solid electrolyte according to claim 1 or 2, further comprising cooling a molten liquid obtained by heating and melting to obtain a solid, wherein the molten liquid contains 0.01 mass% or more of a compound that forms a crystal nucleus, and the solid is a sulfide-based solid electrolyte containing a crystalline phase. Claim 9 A method for manufacturing a sulfide-based solid electrolyte, wherein, in claim 1 or 2, the molten liquid obtained by heating and melting is further quenched at a cooling rate of 10℃ / sec or more to obtain a solid. Claim 10 A method for manufacturing a sulfide-based solid electrolyte according to claim 9, wherein, in the rapid cooling above, the ratio of the compound that forms the crystal nucleation site in the molten liquid is 1 mass% or less. Claim 11 A method for manufacturing a sulfide-based solid electrolyte according to claim 8, further comprising reheating the solid. Claim 12 When performing Raman spectrum measurements with a spot diameter of 3㎛ and 10 measurement points, 350cm for each of the above measurement points -1 up to 500cm -1 The standard deviation of the peak position of the peak derived from the PS bond in is 2 cm -1 A sulfide-based solid electrolyte obtained by the method for manufacturing a sulfide-based solid electrolyte described in claim 1 or 2, which is within. Claim 13 delete

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