Composite powder used in raw material for sulfide solid electrolyte, method for producing same, and method for producing sulfide solid electrolyte

Abstract

The present invention relates to a method for producing a composite powder to be used in a raw material for a sulfide solid electrolyte, the composite powder containing a lithium halide and elemental sulfur, the method comprising a step for removing a solvent by heating an aqueous lithium halide solution at a temperature equal to or higher than a boiling point in the presence of elemental sulfur.

Description

Technical Field

[0001] The present invention relates to a composite powder used in raw materials of a sulfide solid electrolyte and a method for manufacturing the same. Further, the present invention also relates to a method for manufacturing a sulfide solid electrolyte obtained by using the composite powder obtained above. Background Art

[0002] Lithium ion secondary batteries are widely used in portable electronic devices such as mobile phones and laptop computers.

[0003] Conventionally, liquid electrolytes have been used in lithium ion secondary batteries. On the other hand, in recent years, all-solid-state lithium ion secondary batteries using a solid electrolyte as the electrolyte of the lithium ion secondary battery have attracted attention from the viewpoints of expecting improvement in safety, high-speed charge and discharge, and miniaturization of the casing.

[0004] As an example of the solid electrolyte used in the all-solid-state lithium ion secondary battery, a sulfide solid electrolyte can be cited. As raw materials of the sulfide solid electrolyte, lithium halide and elemental sulfur can be cited.

[0005] It is known that lithium halide in the above raw materials can generally be synthesized by the reaction of lithium carbonate and hydrohalic acid. Since lithium halide has strong deliquescence, it easily contains moisture. On the other hand, from the viewpoint of suppressing the reduction of the lithium ion conductivity of the sulfide solid electrolyte, it is preferably moisture-free.

[0006] In order to dry lithium halide with strong deliquescence and obtain a powder free of moisture, excessive temperature and time are required for drying.

[0007] Therefore, in Patent Document 1, for lithium iodide as lithium halide, it is disclosed that anhydrous lithium iodide from which moisture has been removed can be manufactured by mixing solid lithium iodide hydrate with an organic solvent, performing azeotropy, and drying it.

[0008] Further, in Patent Documents 2 and 3, for lithium iodide as lithium halide, it is disclosed that moisture can be removed by heating an aqueous solution of lithium iodide under reduced pressure while stirring.

[0009] Elemental sulfur in the above raw materials is also a common raw material as a raw material of the sulfide solid electrolyte. For example, a method of using elemental sulfur as a powder raw material is disclosed in Patent Document 4.

[0010] Prior Art Documents

[0011] Patent Documents

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-256416

[0013] Patent Document 2: Japanese Patent Laid-Open No. 2014-065637

[0014] Patent Document 3: Japanese Patent Laid-Open No. 2014-065638

[0015] Patent Document 4: Japanese Patent Laid-Open No. 2020-027715 Summary of the Invention

[0016] However, if heating is performed at a temperature above the boiling point of the lithium halide aqueous solution for drying to remove moisture from the lithium halide aqueous solution, bumping is likely to occur. The liquid ejected due to bumping is in a superheated state, but if it comes into contact with the piping, the device wall surface, etc. in the manufacturing device and cools, it will suddenly change to a supercooled state, causing the lithium halide to rapidly crystallize. As a result, it will lead to pipe blockage, a decrease in the accuracy of the measuring instrument due to crystal adhesion inside the device, obstruction of the opening and closing of the raw material input / discharge port, etc. Therefore, continuous operation of the device is difficult, and regular cleaning inside the device is required.

[0017] On the other hand, in order to prevent bumping, methods such as reducing the heating rate or removing moisture at a lower temperature during drying of the lithium halide aqueous solution are considered, but the time required to remove moisture becomes very long, resulting in a decrease in productivity.

[0018] Therefore, an object of the present invention is to provide a method for manufacturing a complex powder containing lithium halide used in a raw material of a sulfide solid electrolyte, which prevents bumping and has excellent productivity. Another object is to provide a novel complex powder used in a raw material of a sulfide solid electrolyte, and a new method for manufacturing a sulfide solid electrolyte using the complex powder.

[0019] The present inventors found that by heating the lithium halide aqueous solution in the presence of elemental sulfur, bumping does not occur even when heated at a high temperature, and thus completed the present invention.

[0020] That is, the present invention relates to the following [1] to

[11] .[[]END]]

[0021] [1] A method for manufacturing a complex powder, the complex powder being used in a raw material of a sulfide solid electrolyte, comprising lithium halide and elemental sulfur,

[0022] The manufacturing method includes the following steps: heating the lithium halide aqueous solution at a temperature above the boiling point in the presence of elemental sulfur to remove the solvent.

[0023] [2] The method for manufacturing a complex powder according to the above [1], wherein the presence state of the elemental sulfur is formed by adding elemental sulfur powder to the above lithium halide aqueous solution.

[0024] [3] According to the method for manufacturing the composite powder described in [1] above, wherein the lithium halide aqueous solution contains SO3 2－ and is a lithium halide aqueous solution,

[0025] and the state of existence of the elemental sulfur is formed by adding an alkali metal sulfide to the lithium halide aqueous solution.

[0026] [4] According to the method for manufacturing the composite powder described in [1] above, wherein the lithium halide aqueous solution contains SO3 2－ and is a lithium halide aqueous solution,

[0027] and the state of existence of the elemental sulfur is formed by introducing hydrogen sulfide into the lithium halide aqueous solution.

[0028] [5] According to the method for manufacturing the composite powder described in [3] or [4] above, which includes the following steps: obtaining the lithium halide aqueous solution containing SO3 2－ from at least one of lithium carbonate and lithium hydroxide,

[0029] and at least one of the lithium carbonate and lithium hydroxide contains SO3 2－ .

[0030] [6] According to the method for manufacturing the composite powder described in any one of [1] to [4] above, wherein the lithium halide aqueous solution includes an aqueous solution of lithium bromide.

[0031] [7] A method for manufacturing a sulfide solid electrolyte, which includes the following steps:

[0032] mixing a raw material containing Li element, a raw material containing P element, and a raw material containing S element to obtain a raw material mixture,

[0033] heating the raw material mixture to obtain a melt, and

[0034] cooling the melt to precipitate crystals,

[0035] and using, at least as the raw material containing Li element, the composite powder obtained by the manufacturing method described in any one of [1] to [6] above.

[0036] [8] A method for manufacturing a sulfide solid electrolyte, which includes the following steps:

[0037] mixing a raw material containing Li element, a raw material containing P element, and a raw material containing S element to obtain a raw material mixture, and

[0038] heating the raw material mixture to obtain a sintered body,

[0039] At least as the raw material containing Li element, use the composite powder obtained by the manufacturing method described in any one of the above [1] to [6].

[0040] [9] A composite powder used in the raw material of a sulfide solid electrolyte, comprising lithium halide and elemental sulfur.

[0041]

[10] The composite powder according to the above [9], wherein the dispersion degree of the elemental sulfur with respect to the composite powder is 15% or less.

[0042]

[11] The composite powder according to the above [9] or

[10] , wherein the lithium halide contains lithium bromide.

[0043] According to the manufacturing method of the present invention, even when heated at a high temperature above the boiling point, bumping of the lithium halide aqueous solution can be prevented. Therefore, although the lithium halide is dried at a high temperature, contamination inside the manufacturing apparatus is prevented and the productivity is excellent. In addition, since the composite powder of the present invention contains lithium halide and elemental sulfur, it is also very useful as a raw material for a sulfide solid electrolyte.

[0044] In addition, besides the above, elemental sulfur as a raw material is a problematic raw material when processed in powder form.

[0045] Specifically, elemental sulfur is a combustible powder, and when charged, there is a risk of dust explosion. Therefore, when charging elemental sulfur, the following countermeasures are taken: by restricting the charging amount, or using coarser particles of sulfur, etc. to avoid generating a dust cloud. In particular, the environment where the sulfide solid electrolyte raw material is used is usually a dry environment such as a dry room, and since the possibility of ignition due to static electricity is high, extra care is required.

[0046] However, in the case of restricting the charging amount, the charging takes time and the productivity decreases. In addition, in the case of using coarse particles, the subsequent homogeneity deteriorates.

[0047] On the contrary, it is known that by using the composite powder containing lithium halide and elemental sulfur obtained by the manufacturing method of the present invention as a raw material, dust explosion can be prevented. Therefore, there is no need to take countermeasures such as restricting the charging amount and using coarse particles, and it is also very useful from the viewpoints of productivity and homogeneity. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a flowchart showing a manufacturing method of the composite powder of the present embodiment.

[0049] Figure 2 is a flowchart showing one mode of the manufacturing method of the composite powder of the present embodiment.

[0050] Figure 3 is a flowchart showing one mode of the method for manufacturing the composite powder of the present embodiment.

[0051] Figure 4 is a flowchart showing one mode of the method for manufacturing the composite powder of the present embodiment.

[0052] Figure 5 is a flowchart showing one mode of the method for manufacturing the raw material of the composite powder of the present embodiment.

[0053] Figure 6 is a flowchart showing one mode of the method for manufacturing the sulfide solid electrolyte of the present embodiment.

[0054] Figure 7 is a flowchart showing one mode of the method for manufacturing the sulfide solid electrolyte of the present embodiment. Detailed Embodiments

[0055] Hereinafter, although the present invention will be described in detail, the present invention is not limited to the following embodiments and can be arbitrarily modified and implemented within the scope not departing from the gist of the present invention. In addition, "~" indicating a numerical range is used in the meaning of including the numerical values described before and after it as the lower limit value and the upper limit value.

[0056] [Composite Powder and Method for Manufacturing the Same]

[0057] As Figure 1 shown, the method for manufacturing the composite powder of the present embodiment includes, as step S1, a step of heating an aqueous solution of lithium halide at a temperature above the boiling point in the presence of elemental sulfur to remove the solvent.

[0058] Thereby, a composite powder containing lithium halide and elemental sulfur can be obtained.

[0059] The composite powder containing lithium halide and elemental sulfur is different from a simple mixture of a single powder of lithium halide and a single powder of elemental sulfur, and is a powder showing a state in which these powders are uniformly dispersed. More specifically, it is a powder in which elemental sulfur is contained in the form of domains in lithium halide.

[0060] Regarding whether it is a composite powder, 0.1 g of each of the five-point composite powders is taken, the S element is measured by high-frequency furnace combustion-infrared absorption method, and the quantification of sulfur with respect to the composite powder is performed. Then, if the dispersion degree of the above quantification values at the five points is 15% or less, it can be said to be a composite powder, and thus it can be clearly distinguished from a simple mixture.

[0061] If heating is carried out at a temperature above the boiling point of an aqueous lithium halide solution in order to remove moisture by drying the aqueous lithium halide solution, bumping usually easily occurs. However, in the manufacturing method of the present embodiment, by carrying out the above heating in the presence of elemental sulfur, the aqueous lithium halide solution is boiled in the presence of elemental sulfur powder to remove moisture. The presence of the elemental sulfur powder serves as nuclei for bubble formation, thereby preventing bumping of the aqueous lithium halide solution.

[0062] In addition to the above, if the composite powder obtained by the manufacturing method of the present embodiment is used as a raw material for a sulfide solid electrolyte, dust explosion of elemental sulfur can be prevented, and thus a sulfide solid electrolyte can be manufactured without reducing productivity and homogeneity.

[0063] As a method for realizing the presence state of elemental sulfur in step S1, for example, as Figure 2 shown, a method of adding elemental sulfur powder to an aqueous lithium halide solution can be cited as step S1a. In addition, as Figure 3 shown, a method of adding an alkali metal sulfide to an aqueous lithium halide solution containing sulfite ions (SO3 2－ ) can be cited as step S1b. Further, as Figure 4 shown, a method of introducing hydrogen sulfide into an aqueous lithium halide solution containing sulfite ions can be cited as step S1c.

[0064] In step S1a, after adding elemental sulfur powder to the aqueous lithium halide solution, preferably dispersing the elemental sulfur in the above aqueous solution, heating is carried out at a temperature above the boiling point of the aqueous lithium halide solution to remove the solvent. In this case, due to the addition of the elemental sulfur powder itself, bumping of the aqueous lithium halide solution can be inhibited by the added elemental sulfur powder.

[0065] The elemental sulfur powder can be added before heating for removing the solvent of the aqueous lithium halide solution, or can be added during heating. When further performing a dispersion treatment after adding elemental sulfur, from the viewpoint of workability, it is preferably added before heating the aqueous lithium halide solution.

[0066] As elemental sulfur with good dispersibility, colloidal sulfur, precipitated sulfur, etc. can be used.

[0067] In addition, sulfur can be dispersed in the aqueous lithium halide solution by dispersing with an ultrasonic homogenizer after adding elemental sulfur, adding a dispersant, or pulverizing with a wet air classifier, etc.

[0068] The addition amount of the sulfur powder is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, and still more preferably 0.1 to 1 part by mass with respect to 100 parts by mass of lithium halide contained in the aqueous lithium halide solution. Here, from the viewpoint of exerting the effects brought about by the addition of sulfur, the addition amount of the sulfur powder is preferably 0.01 part by mass or more, more preferably 0.05 part by mass or more, and still more preferably 0.1 part by mass or more. On the other hand, from the viewpoint of preventing aggregation due to reduced dispersibility, the addition amount of the sulfur powder is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, and still more preferably 1 part by mass or less.

[0069] The average particle diameter of the sulfur powder is not particularly limited. For example, it is preferably 0.1 to 10 μm, more preferably 0.5 to 6 μm, and still more preferably 1 to 3 μm. Here, since it is easily obtained, the average particle diameter of sulfur is preferably 0.1 μm or more, more preferably 0.5 μm or more, and still more preferably 1 μm or more. On the other hand, from the viewpoint of maintaining dispersibility, the average particle diameter of sulfur is preferably 10 μm or less, more preferably 6 μm or less, and still more preferably 3 μm or less.

[0070] It should be noted that the average particle diameter in this specification refers to the median diameter (D50) of the particle size representing that 50% by volume of the particles is below this value, which is obtained by measuring the particle size distribution using a particle size distribution meter using the laser diffraction method and based on the obtained volume-based particle size distribution diagram.

[0071] The added sulfur powder preferably exists in a dispersed state in the aqueous lithium halide solution. It is considered that during the process of heating the aqueous lithium halide solution containing the sulfur powder to remove its solvent, sulfur is used to form the nucleus of lithium halide, forming a form in which sulfur is contained in the lithium halide in the form of domains, and a uniformly dispersed composite powder is obtained.

[0072] In step S1b, in the presence of sulfur formed by adding an alkali metal sulfide to an aqueous lithium halide solution containing SO3 2－ When an alkali metal sulfide is added to an aqueous lithium halide solution containing SO3, the aqueous lithium halide solution becomes turbid. Taking the case where H2SO3 is contained in the aqueous lithium halide solution as an example, the above reaction is expressed as H2SO3 + 2R2S + H2O → 3S (elemental sulfur) + 4ROH, and the turbidity indicates the precipitation of elemental sulfur. Here, R refers to an alkali metal element, and R2S represents an alkali metal sulfide. Thus, the existence state of sulfur is formed.

[0073] If an alkali metal sulfide is added to an aqueous lithium halide solution containing SO3 2－ If an alkali metal sulfide is added to an aqueous lithium halide solution containing SO3, the aqueous lithium halide solution becomes turbid. As for SO3 2－ When an alkali metal sulfide is added to an aqueous lithium halide solution containing SO3, the aqueous lithium halide solution becomes turbid. Taking the case where H2SO3 is contained in the aqueous lithium halide solution as an example, the above reaction is expressed as H2SO3 + 2R2S + H2O → 3S (elemental sulfur) + 4ROH, and the turbidity indicates the precipitation of elemental sulfur. Here, R refers to an alkali metal element, and R2S represents an alkali metal sulfide. Thus, the existence state of sulfur is formed.

[0074] The alkali metal sulfide can be used to remove SO32－ Prior to heating the solvent of the aqueous lithium halide solution, it can also be added during the heating process. SO3 2－ Volatilized in the form of SO2 gas, from the viewpoint of preventing its content from decreasing, the addition of the alkali metal sulfide is preferably before heating the aqueous lithium halide solution containing SO3 2－ .

[0075] If heating is continued to remove the solvent of the aqueous lithium halide solution in a state where elemental sulfur has precipitated, a composite powder in which powder of elemental sulfur is contained in domains in lithium halide powder is obtained.

[0076] The alkali metal sulfide is not particularly limited as long as it is a sulfide of an alkali metal element. For example, lithium sulfide, sodium sulfide, potassium sulfide, rubidium sulfide, cesium sulfide, etc. can be cited. One kind can be used, or two or more kinds can be used in combination. Among them, from the viewpoints of being easily available and the introduced element having less influence on the electrolyte, lithium sulfide and sodium sulfide are preferred, and lithium sulfide is more preferred.

[0077] The addition amount of the alkali metal sulfide is preferably 0.5 to 10 moles, more preferably 1 to 5 moles, and further preferably 2 to 3 moles relative to 1 mole of sulfite ion (SO3 2－ ) contained in the aqueous lithium halide solution. Here, from the viewpoint of effectively reacting most of the contained sulfite ions, the addition amount of the alkali metal sulfide is preferably 0.5 mole or more, more preferably 1 mole or more, and further preferably 2 moles or more. On the other hand, from the viewpoint of not adding an excessive amount that is not used for the reaction, the addition amount of the alkali metal sulfide is preferably 10 moles or less, more preferably 5 moles or less, and further preferably 3 moles or less.

[0078] In addition, the concentration of SO3 2－ contained in the aqueous lithium halide solution is preferably 0.0001 to 0.05 moles, more preferably 0.0002 to 0.02 moles, and further preferably 0.0005 to 0.01 moles relative to 1 mole of lithium halide contained in the aqueous lithium halide solution. Here, from the viewpoint of generating an amount of elemental sulfur suitable for exhibiting the effects of the present embodiment, the above SO3 2－ concentration is preferably 0.0001 mole or more, more preferably 0.0002 mole or more, and further preferably 0.0005 mole or more. On the other hand, from the viewpoint of preventing excessive SO3 2－ from forming SO2 gas during drying, the above SO3 2－ concentration is preferably 0.05 mole or less, more preferably 0.02 mole or less, and further preferably 0.01 mole or less.

[0079] In step S1c, by adding to the solution containing SO3 2－In the state where sulfur is present, hydrogen sulfide is introduced into an aqueous solution of lithium halide.

[0080] If hydrogen sulfide is introduced into an aqueous solution of lithium halide containing SO3 2－ the aqueous solution of lithium halide becomes turbid. Taking the case where H2SO3 is contained as an example, the above reaction is expressed as H2SO3 + 2H2S → 3S (elemental sulfur) + 3H2O, and the turbidity indicates the precipitation of elemental sulfur. Thus, the state where elemental sulfur is present is formed. 2－ As a method for introducing hydrogen sulfide, bubbling of a gas containing hydrogen sulfide, addition of an aqueous solution containing hydrogen sulfide, etc. can be cited. Among them, from the viewpoint of not easily increasing the amount of solvent removed by drying for the obtained aqueous solution containing the composite powder, bubbling of a gas containing hydrogen sulfide is preferred.

[0081] The gas containing hydrogen sulfide can be a gas composed only of hydrogen sulfide or a mixed gas containing hydrogen sulfide and other gases. For other gases, for example, nitrogen, argon, etc. can be cited. Among them, from the viewpoint of higher reaction efficiency based on bubbling, a gas composed only of hydrogen sulfide is preferred.

[0082] When introducing a gas containing hydrogen sulfide into an aqueous solution of lithium halide containing SO3

[0083] by bubbling, it is preferred to adjust the gas flow rate to avoid too strong bubbling. The gas flow rate is preferably, for example, 0.01 to 0.5 SLM (Standard Litter Min, standard liter / minute). 2－ When introducing a gas containing hydrogen sulfide into an aqueous solution of lithium halide containing SO3

[0084] When adding an aqueous solution containing hydrogen sulfide as the introduction of hydrogen sulfide, the hydrogen sulfide concentration in the aqueous solution is preferably 0.04 to 0.10 mol / L. Here, from the viewpoint of efficiently generating elemental sulfur, and also from the viewpoint of not easily increasing the amount of solvent removed by drying for the obtained aqueous solution containing the composite powder, the higher the hydrogen sulfide concentration in the aqueous solution, the better. The hydrogen sulfide concentration is preferably 0.04 mol / L or more, more preferably 0.06 mol / L or more, and further preferably 0.08 mol / L or more. On the other hand, if introduced under atmospheric pressure, there is no equipment load, so the hydrogen sulfide concentration in the aqueous solution is preferably 0.1 mol / L or less, which is the saturation concentration of hydrogen sulfide in water.

[0085] The introduction of hydrogen sulfide can be added before heating the solvent of the aqueous solution of lithium halide for removing SO3 2－ or can be added during heating. SO3 2－ volatilizes in the form of SO2 gas. From the viewpoint of preventing its content from decreasing, the introduction of hydrogen sulfide is preferably during heating the aqueous solution containing SO3 2－before the aqueous lithium halide solution.

[0086] As the lithium halide in step S1, for example, lithium fluoride, lithium chloride, lithium bromide, lithium iodide, etc. can be cited. One of them can be used, or two or more of them can be used in combination. Among them, from the viewpoint of improving the lithium ion conductivity of the sulfide solid electrolyte obtained when the resulting composite powder is used as a raw material, lithium chloride and lithium bromide are preferred, and lithium bromide is more preferred.

[0087] The concentration of lithium halide in the aqueous lithium halide solution is not particularly limited. For example, it is preferably 10 to 40% by mass, more preferably 15 to 35% by mass, and further preferably 20 to 30% by mass. Here, for the obtained aqueous solution containing the composite powder, from the viewpoint of not easily increasing the amount of solvent removed by drying, the concentration of lithium halide is preferably 10% by mass or more, more preferably 15% by mass or more, and further preferably 20% by mass or more. On the other hand, from the viewpoint of preventing dissolution residues, the concentration of lithium halide is preferably 40% by mass or less, more preferably 35% by mass or less, and further preferably 30% by mass or less. It should be noted that when two or more kinds of lithium halides are used, the total concentration of them is preferably within the above range.

[0088] When the aqueous lithium halide solution contains SO3 as in step S1b and step S1c 2－ the case is as Figure 5 shown, the manufacturing method of the present embodiment preferably further includes a step of obtaining an aqueous lithium halide solution containing SO3 2－ from at least one of lithium carbonate and lithium hydroxide as step S0.

[0089] At least one of the above lithium carbonate and lithium hydroxide contains SO3 2－ . By reacting at least one of the lithium carbonate and lithium hydroxide containing SO3 2－ with, for example, a hydrohalic acid, an aqueous lithium halide solution containing SO3 2－ is obtained.

[0090] The hydrohalic acid is, for example, an aqueous solution of a hydrogen halide such as hydrofluoric acid, hydrochloric acid, hydrogen bromide, or hydrogen iodide. By reacting this hydrohalic acid with, for example, lithium carbonate containing SO3 2－ , a chemical reaction of Li2CO3 + 2HX → 2LiX + H2CO3 occurs to obtain an aqueous lithium halide solution. In addition, the SO3 2－ contained in lithium carbonate is directly contained in the obtained aqueous lithium halide solution. However, if the pH is on the acidic side, SO3 2－ tends to fly off in the form of SO2 gas, so it is preferable to perform the treatment at a pH of 7 or more.

[0091] Using a containing SO3 2－to replace lithium hydroxide containing SO3 2－ The same applies to the case of lithium carbonate.

[0092] In addition, after forming an aqueous solution of lithium halide, SO3 is generated through the redox reaction of the sulfur component contained in the aqueous solution 2－ , whereby an aqueous solution of lithium halide containing SO3 can be obtained 2－ . Examples of the sulfur component include S, SO4 2－ , HSO3 － , S2O3 － , SO2, HS － , S 2－ , and their metal compounds, salts, etc.

[0093] Lithium carbonate and lithium hydroxide containing SO3 are obtained, for example, by adding an aqueous solution of H2SO3 (sulfurous acid) to lithium carbonate and lithium hydroxide, or by reacting them with SO2 gas (sulfurous acid gas). In addition, when synthesizing lithium carbonate and lithium hydroxide from an aqueous solution, SO3 is generated through the redox reaction of the sulfur component contained in the aqueous solution 2－ etc., whereby lithium carbonate and lithium hydroxide containing SO3 can be obtained 2－ . Examples of the sulfur component include S, SO4 2－ , HSO3 2－ , S2O3 － , SO2, HS － , S － , and their metal compounds, salts, etc. 2－

[0094] The concentration of SO3 contained in lithium carbonate and lithium hydroxide, relative to 1 mole of lithium contained in lithium carbonate and lithium hydroxide, is preferably 0.0001 to 0.05 mole, more preferably 0.0002 to 0.02 mole, and still more preferably 0.0005 to 0.01 mole. Here, from the viewpoint of generating the amount of elemental sulfur suitable for exhibiting the effects of the present embodiment, the concentration of the above SO3 2－ is preferably 0.0001 mole or more, more preferably 0.0002 mole or more, and still more preferably 0.0005 mole or more. On the other hand, from the viewpoint of preventing the formation of SO2 gas by excessive SO3 2－ during drying, the concentration of the above SO3 2－ is preferably 0.05 mole or less, more preferably 0.02 mole or less, and still more preferably 0.01 mole or less. 2－

[0095] An aqueous solution of lithium halide containing SO3, in addition to being obtained as described above from an aqueous solution containing SO3 2－ 2－In addition to obtaining lithium carbonate and lithium hydroxide, it can also be obtained by directly adding an aqueous solution of H2SO3 (sulfurous acid), Li2SO3, Na2SO3, etc. to an aqueous solution of lithium halide.

[0096] The heating in step S1 is carried out at a temperature above the boiling point of the aqueous solution of lithium halide or the aqueous solution of lithium halide containing SO3 2－ until the solvent is removed. It should be noted that the temperature here is not the temperature of the aqueous solution of lithium halide or the aqueous solution of lithium halide containing SO3 2－ but the heating temperature in the heating device used for heat drying, that is, the set temperature.

[0097] Since the solvent is water, the boiling point of the aqueous solution of lithium halide is about 100 °C under normal pressure. The above heating temperature is preferably 100 - 240 °C, more preferably 150 - 240 °C, further preferably 170 - 220 °C, and particularly preferably 190 - 200 °C. Here, since lithium halide has strong deliquescence, in order to obtain a powder without moisture, it is preferable to use excessive temperature and time during drying. From the above viewpoints, the heating temperature under normal pressure is more preferably 150 °C or higher, further preferably 170 °C or higher, and particularly preferably 190 °C or higher.

[0098] According to the manufacturing method of the present embodiment, the bumping of the aqueous solution of lithium halide can be suppressed. Therefore, even if drying is carried out at an excessive temperature as described above, blockage of the device piping, reduction in the accuracy of the measuring instrument due to crystal attachment inside the device, obstruction of the opening and closing of the raw material input / discharge port, etc. can be prevented. Therefore, continuous operation of the device can be achieved, and in addition, the cleaning frequency inside the device can be reduced.

[0099] In addition, from the viewpoint that the device cost increases when the heat resistance required for the device is improved, the heating temperature under normal pressure is preferably 240 °C or lower, more preferably 220 °C or lower, and further preferably 200 °C or lower.

[0100] Since it can lower the boiling point of the solvent and can remove the solvent more effectively, the heating of the aqueous solution of lithium halide is preferably carried out under reduced pressure. The pressure during heating is preferably 50 kPa or lower, more preferably 40 kPa or lower, and further preferably 30 kPa or lower. The lower limit of the pressure is not particularly limited and is usually 1 kPa or higher.

[0101] When heating an aqueous lithium halide solution under reduced pressure, the preferred heating temperature also varies depending on the degree of reduced pressure. For example, when heating at 20 kPa, the heating temperature is preferably 120 to 240 °C, more preferably 140 to 220 °C, and further preferably 160 to 200 °C. Here, the above heating temperature is preferably 120 °C or higher, more preferably 140 °C or higher, and further preferably 160 °C or higher. In addition, from the perspective that the cost of the device increases when the heat resistance required for the device is improved, the heating temperature is preferably 240 °C or lower, more preferably 220 °C or lower, and further preferably 200 °C or lower.

[0102] When heating an aqueous lithium halide solution under reduced pressure, the preferred heating temperature also varies depending on the degree of reduced pressure. For example, when heating at 2 kPa, the heating temperature is preferably 120 to 240 °C, more preferably 140 to 220 °C, and further preferably 160 to 200 °C. Here, the above heating temperature is preferably 120 °C or higher, more preferably 140 °C or higher, and further preferably 160 °C or higher. In addition, from the perspective that the cost of the device increases when the heat resistance required for the device is improved, the heating temperature is preferably 240 °C or lower, more preferably 220 °C or lower, and further preferably 200 °C or lower.

[0103] The heating time of the aqueous lithium halide solution varies depending on the concentration of lithium halide and the amount of solvent. In addition, as long as the solvent can be removed, there is no particular limitation. For example, the above heating time is preferably 100 to 1000 hours, more preferably 100 to 500 hours, and further preferably 100 to 200 hours. Here, from the perspective of productivity, the above heating time is preferably 1000 hours or less, more preferably 500 hours or less, and further preferably 200 hours or less. In addition, from the perspective of fully completing drying, the heating time is preferably 100 hours or more.

[0104] The complex powder obtained by removing the solvent can be confirmed to contain lithium halide and elemental sulfur by Raman spectroscopy analysis.

[0105] In addition, if necessary, the water content contained in the complex powder can be measured by the Karl Fischer method.

[0106] As described above, the complex powder of the present embodiment contains lithium halide and elemental sulfur, and shows a state in which the powder of lithium halide and the powder of elemental sulfur are uniformly dispersed.

[0107] The content of elemental sulfur in the composite powder is preferably 0.01 to 5.0% by mass, more preferably 0.02 to 3.0% by mass, and still more preferably 0.05 to 1.0% by mass. Here, from the viewpoints of suppressing bumping when drying the lithium halide aqueous solution to remove the solvent and appropriately achieving excellent productivity, the content of elemental sulfur is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and still more preferably 0.05% by mass or more. In addition, when the obtained composite powder is used as a raw material for a sulfide solid electrolyte, from the viewpoint of preventing an excessive amount of sulfur required for blending, the content of elemental sulfur is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and still more preferably 1.0% by mass or less.

[0108] The content of the above-mentioned elemental sulfur can be adjusted according to the amount of elemental sulfur powder added to achieve the existence state of elemental sulfur, the concentration of sulfite ions, the concentration of alkali metal sulfide, the concentration of hydrogen sulfide, etc. In addition, the content of elemental sulfur in the composite powder is obtained by measuring the S element using a high-frequency furnace combustion-infrared absorption method.

[0109] The homogeneity of the above-mentioned composite powder can be evaluated by the dispersion degree of elemental sulfur relative to the composite powder. The above-mentioned dispersion degree is preferably 15% or less, more preferably 12% or less, and still more preferably 10% or less. The lower limit of the dispersion degree is not particularly limited and is usually 5% or more.

[0110] The dispersion degree of elemental sulfur relative to the composite powder means taking 0.1 g of each of 5 points of the composite powder, measuring the S element using a high-frequency furnace combustion-infrared absorption method, and quantifying the elemental sulfur relative to the composite powder.

[0111] Let the contents (mass%) of elemental sulfur relative to the composite powder at 5 points obtained under the above conditions be A1 to A5. Then, the arithmetic average Aave. of A1 to A5 represented by the following formula is obtained.

[0112] Aave. = (A1 + A2 + A3 + A4 + A5) / 5

[0113] The dispersion degree (%) is obtained by the following formula using A1 to A5 and Aave. obtained from the above formula.

[0114]

[0115] The above-mentioned dispersion degree can be reduced by optimizing the dispersion state of elemental sulfur in the lithium halide aqueous solution. For example, in the case of adding elemental sulfur powder, the dispersion state can be optimized by using a method of using a powder with a smaller particle size, a method of pulverizing the powder using a jet mill to make the particle size smaller, etc.

[0116] The composite powder of the present embodiment is used as a raw material for a sulfide solid electrolyte.

[0117] In addition to the raw materials containing Li element, P element, and S element in the raw materials for the sulfide solid electrolyte, raw materials containing other elements can also be arbitrarily used, and the composite powder of the present embodiment is used as the raw material containing at least Li element among the above.

[0118] In the raw materials for the sulfide solid electrolyte, when elemental sulfur is used as the raw material containing S element, the composite powder of the present embodiment can be used as the raw material that also serves as the raw material containing Li element and the raw material containing S element.

[0119] In addition, when a raw material containing a halogen element is used as the raw material for the sulfide solid electrolyte, the composite powder of the present embodiment can be used as the raw material that also serves as the raw material containing the halogen element in addition to the raw material containing Li element.

[0120] It should be noted that when the composite powder of the present embodiment is used as the raw material containing Li element and not used as the raw material containing S element, the composite powder is heated at a temperature above the boiling point of elemental sulfur to volatilize and remove the elemental sulfur. Thus, it can be used as a powder of lithium halide alone. The elemental sulfur can be volatilized, for example, by heating at 450 - 900 °C for 1 - 10 hours in a nitrogen atmosphere.

[0121] In addition to the above, by heating at a temperature above the boiling point of elemental sulfur during or after the synthesis of the sulfide solid electrolyte, the elemental sulfur can also be volatilized and removed.

[0122] [Manufacturing method of sulfide solid electrolyte]

[0123] One mode of the manufacturing method of the sulfide solid electrolyte of the present embodiment is as Figure 6 shown, and successively includes the following steps s1 - s3.

[0124] Step s1: A step of mixing the raw material containing Li element, the raw material containing P element, and the raw material containing S element to obtain a raw material mixture

[0125] Step s2: A step of heating the above raw material mixture to obtain a melt

[0126] Step s3: A step of cooling the above melt to precipitate crystals

[0127] Another mode of the manufacturing method of the sulfide electrolyte of the present embodiment is as Figure 7 shown, and successively includes the following steps s’1 and s’2.

[0128] Step s’1: A step of mixing raw materials containing Li element, raw materials containing P element, and raw materials containing S element to obtain a raw material mixture

[0129] Step s’2: A step of heating the above raw material mixture to obtain a sintered body

[0130] The manufacturing method including the above steps s1 - s3 is the melting method, and the manufacturing method including the above steps s’1 and s’2 is the solid-phase synthesis method.

[0131] The crystal structure of the sulfide solid electrolyte obtained by the above manufacturing method is not particularly limited. For example, sulfide solid electrolytes having a crystal structure containing Li element, P element, and S element, such as Li7P3S 11 etc., called LPS series, sulfide solid electrolytes having a crystal structure containing Li element, Ge element, P element, and S element, such as Li 10 GeP2S 12 etc., called LGPS series, sulfide solid electrolytes having a thiogermanate crystal structure containing Li element, P element, S element, and Ha element, sulfide solid electrolytes composed of Li - P - S - Ha series crystallized glass, sulfide solid electrolytes having a crystal structure containing Sn element, etc. powders.

[0132] The sulfide solid electrolyte may contain a crystalline phase and an amorphous phase.

[0133] The above-mentioned thiogermanate crystal structure refers to the crystal structure possessed by the compound group of minerals represented by the composition formula Ag8GeS6. In addition, the sulfide solid electrolyte of the present embodiment is not limited to the above crystal structure, and some elements can be replaced by other elements.

[0134] When the sulfide solid electrolyte of the present embodiment has a thiogermanate crystal structure, as the Ha element, it is more preferably to contain at least 1 element selected from Cl, Br, and I, and further preferably to contain 2 or more elements.

[0135] In addition, for the sulfide solid electrolyte of the present embodiment, as the Ha element, it is further preferably to contain at least 1 of Cl and Br, and also further preferably to contain Cl and Br.

[0136] The thiogermanate crystal structure preferably adopts the above structure, and preferably has a composition formula of Li α PS β Ha γIt represents and satisfies the relationships of 5 ≤ α ≤ 7, 4 ≤ β ≤ 6 and 1.3 ≤ γ ≤ 2. The above element ratio more preferably satisfies the relationships of 5.1 < α < 6.3, 4 < β < 5.3 and 1.4 ≤ γ ≤ 1.9, and further preferably satisfies the relationships of 5.2 < α < 6.2, 4.1 < β < 5.2 and 1.5 ≤ γ ≤ 1.8.

[0137] That is, for α, it is preferably 5 or more, more preferably greater than 5.1, and further preferably greater than 5.2. In addition, it is preferably 7 or less, more preferably less than 6.3, and further preferably less than 6.2. For β, it is preferably 4 or more, more preferably greater than 4, and further preferably greater than 4.1. In addition, it is preferably 6 or less, more preferably less than 5.3, and further preferably less than 5.2. For γ, it is preferably 1.3 or more, more preferably 1.4 or more, and further preferably 1.5 or more. In addition, it is preferably 2 or less, more preferably 1.9 or less, and further preferably 1.8 or less.

[0138] In the argyrodite crystal structure, a part of the S element and a part of the P element can be replaced by other elements. A part of the S element can be replaced by, for example, the Ha element, the O element, and the Se element, the Te element, BH4, CN, etc. In addition, a part of the P element can be replaced by, for example, the Si element, the Al element, the Sn element, the In element, the Cu element, the Sb element, the Ge element, etc.

[0139] In the method for manufacturing a sulfide solid electrolyte of the present embodiment, in step s1 of the melting method and step s'1 of the solid-phase synthesis method, the composite powder described in the above [Composite Powder and Its Manufacturing Method] is used as a raw material containing at least the Li element.

[0140] The manufacturing method of the sulfide solid electrolyte using the melting method will be described.

[0141] Step s1 is a step of mixing a raw material containing the Li element, a raw material containing the P element, and a raw material containing the S element to obtain a raw material mixture. According to the target sulfide solid electrolyte, the above raw material mixture further contains a raw material containing the Ha element. It should be noted that in this specification, the Ha element refers to at least one element selected from F, Cl, Br, and I.

[0142] According to the composition of the desired sulfide solid electrolyte, the raw material may contain other elements. For example, when a part of the Li element, the P element, the S element, etc. are replaced by other elements according to the composition of the sulfide solid electrolyte, a raw material containing the replaced other elements may also be included.

[0143] As other elements, for example, the Si element, the Al element, the Sn element, the In element, the Cu element, the Sb element, the Ge element, the O element, etc. can be cited.

[0144] As the raw material containing the Li element, the composite powder containing lithium halide and elemental sulfur described in the above-mentioned [Composite powder and its production method] was used.

[0145] In addition, other raw materials containing the Li element may be used together with the composite powder. In this case, other raw materials containing the Li element may be conventionally known materials.

[0146] The composite powder described above contains elemental sulfur in addition to the lithium halide. However, if the composite powder is not used as a raw material containing the S element, the composite powder can be heated to volatilize and remove the elemental sulfur before being used as a raw material containing the Li element. Alternatively, by using the composite powder containing elemental sulfur as a raw material containing the Li element, the elemental sulfur can be volatilized and removed by heating during or after the synthesis of the sulfide solid electrolyte.

[0147] Other raw materials containing the lithium element include metallic lithium and compounds containing lithium. Examples of compounds containing lithium include lithium compounds such as lithium sulfide (Li2S), lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), lithium oxide (Li2O), and lithium hydroxide (LiOH). Furthermore, lithium halide may be used separately from the composite powder.

[0148] When other raw materials containing the Li element are used, lithium sulfide is preferred from the perspective of easy operation and reactivity. On the other hand, since lithium sulfide is expensive, lithium compounds other than lithium sulfide, metallic lithium, etc. are preferred from the perspective of suppressing manufacturing costs. Specifically, it is preferred to use one or more selected from metallic lithium, lithium carbonate (Li2CO3), lithium sulfate (Li2SO4), lithium oxide (Li2O) and lithium hydroxide (LiOH). These can be used alone or in combination with two or more.

[0149] As the raw material containing the P element, a conventionally known material can be used.

[0150] Specifically, P alone or a compound containing P can be used. In addition, as a compound serving as both a raw material containing the P element and a raw material containing the S element, phosphorus pentasulfide (P2S5) or the like can be used.

[0151] Examples of P-containing compounds in the raw materials containing P elements include phosphorus sulfides such as phosphorus trisulfide (P2S3) and phosphorus pentasulfide (P2S5), sodium phosphate (Na3PO4), lithium thiophosphate (Li3PS 4－x O x ) and other phosphorus compounds.

[0152] From the viewpoint of preventing the inclusion of elements other than those constituting the target sulfide solid electrolyte, phosphorus sulfide is preferably used as the raw material containing P element, and phosphorus pentasulfide (P2S5) is more preferably used. These can be used alone or in combination of two or more.

[0153] In addition, when the sulfide solid electrolyte contains oxygen element, as the raw material containing P element, for example, P-containing compounds such as P2O5, Li3PO4, and Li4P2O7 can be cited. Among them, P2O5 is preferably used from the viewpoint of easy manufacture. These compounds can be used alone or in combination of two or more.

[0154] As the raw material containing S element, conventionally known materials can be used. Specifically, elemental sulfur and S-containing compounds can be used. On the other hand, since the composite powder of the present embodiment also contains elemental sulfur in addition to lithium halide, the above composite powder can be used as a raw material that also serves as a raw material containing Li element and a raw material containing S element, or the composite powder and other raw materials containing S element can be used in combination.

[0155] As the S-containing compound in other raw materials containing S element, for example, phosphorus sulfides such as phosphorus trisulfide (P2S3) and phosphorus pentasulfide (P2S5), other sulfur compounds containing phosphorus, and sulfur-containing compounds can be cited. As the sulfur-containing compound, H2S, CS2, FeS, Fe2S3, FeS2, Fe 1－x S and other iron sulfides, bismuth sulfide (Bi2S3), CuS, Cu2S, Cu 1－x S and other copper sulfides can be cited.

[0156] From the viewpoints of reactivity and preventing the inclusion of elements other than those constituting the target sulfide solid electrolyte, phosphorus sulfide is preferably used as other raw materials containing S element, and phosphorus pentasulfide (P2S5) is more preferably used. They can be used alone or in combination of two or more. It should be noted that phosphorus sulfide is a compound that also serves as a substance containing S and a substance containing P.

[0157] When a raw material containing Ha element is included as an optional component, since the composite powder of the present embodiment contains lithium halide, the above composite powder can be used as a raw material that also serves as a raw material containing Li element and a raw material containing Ha element, or the composite powder and other raw materials containing Ha element can be used in combination.

[0158] Here, when the sulfide solid electrolyte of the present embodiment has a thiogermanate-type crystal structure, the composite powder described in the above [Composite Powder and Its Manufacturing Method] is very useful as a raw material that also serves as a raw material containing Li element and a raw material containing Ha element, or as a raw material that also serves as a raw material containing Li element, a raw material containing Ha element, and a raw material containing S element.

[0159] As other raw materials containing Ha element, known materials can be used. Specifically, for example, 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, boron halides, etc. can be cited.

[0160] From the viewpoint of preventing elements other than the elements constituting the target sulfide solid electrolyte, other raw materials containing Ha element are preferably lithium halides, and more preferably LiCl, LiBr, and LiI. These compounds can be used alone or in combination of two or more.

[0161] When elements other than Li, S, P, and Ha are also included as elements constituting the sulfide solid electrolyte, raw materials containing other elements are also mixed to obtain a raw material mixture.

[0162] For raw materials containing Si element as an optional component, for example, SiO2 and SiS2 can be cited. Among them, from the viewpoints of lithium ion conductivity and water resistance, SiO2 is more preferred. These compounds can be used alone or in combination of two or more.

[0163] For raw materials containing Al element as an optional component, for example, Al2S3, Al2O3, and AlCl3 can be cited. Among them, from the viewpoint of lithium ion conductivity, Al2S3 and AlCl3 are preferred, and Al2S3 is more preferred. These compounds can be used alone or in combination of two or more.

[0164] For raw materials containing Sn element as an optional component, for example, SnS, SnS2, SnO, SnO2, and SnCl2 can be cited. Among them, from the viewpoint of lithium ion conductivity, SnS2 and SnCl2 are preferred, and SnS2 is more preferred. These compounds can be used alone or in combination of two or more.

[0165] For raw materials containing In element as an optional component, for example, In2O3, In2S3, and InCl3 can be cited. Among them, from the viewpoint of lithium ion conductivity, In2S3 and InCl3 are preferred, and In2S3 is more preferred. These compounds can be used alone or in combination of two or more.

[0166] Regarding raw materials containing Cu element as an arbitrary component, for example, Cu2O, CuO, Cu2S, CuS, and CuCl2 can be cited. Among them, from the viewpoint of lithium ion conductivity, CuS and CuCl2 are preferred, and CuS is more preferred. These compounds can be used alone or in combination of two or more.

[0167] Regarding raw materials containing Sb element as an arbitrary component, for example, Sb2O3, Sb2S3, and SbCl3 can be cited. Among them, from the viewpoint of lithium ion conductivity, Sb2S3 and SbCl3 are preferred, and Sb2S3 is more preferred. These compounds can be used alone or in combination of two or more.

[0168] Regarding raw materials containing Ge element as an arbitrary component, for example, GeO2, GeS, GeS2, and GeCl2 can be cited. Among them, from the viewpoint of lithium ion conductivity, GeS2 and GeCl2 are preferred, and GeS2 is more preferred. These compounds can be used alone or in combination of two or more.

[0169] Regarding raw materials containing B element as an arbitrary component, for example, B2S3, B2O3, and BCl3 can be cited. Among them, from the viewpoint of lithium ion conductivity, B2S3 and BCl3 are preferred, and B2S3 is more preferred. These compounds can be used alone or in combination of two or more.

[0170] The mixing of the raw materials is carried out, for example, by mixing using a mortar, mixing using a medium such as a planetary ball mill, a needle mill, a powder blender, or medium-free mixing such as pneumatic mixing.

[0171] Step s2 is a process of heating the raw material mixture obtained in step s1 to obtain a melt.

[0172] The specific method of heating and melting the raw material mixture in step s2 is not particularly limited. The raw materials are placed in a heat-resistant container and heated using a heating furnace. The raw material mixture can be sealed in the heat-resistant container. In addition, melting can also be carried out in an atmosphere containing sulfur element. As the atmosphere containing sulfur element, a mixed gas atmosphere of a gas containing sulfur element such as sulfur gas, hydrogen sulfide gas, sulfur dioxide gas, etc. and an inert gas can be cited.

[0173] For heat-resistant containers, heat-resistant containers made of carbon, quartz, quartz glass, borosilicate glass, aluminosilicate glass, alumina, zirconia, mullite and other heat-resistant containers containing oxides, silicon nitride, boron nitride and other heat-resistant containers containing nitrides, silicon carbide and other heat-resistant containers containing carbides can be used. In addition, these heat-resistant containers can be formed into a mass from the above materials, or can be containers formed with layers of carbon, oxides, nitrides, carbides, etc., such as a quartz tube coated with carbon.

[0174] The heating temperature when heating and melting the raw material mixture varies depending on the raw materials used and the composition of the raw material mixture. For example, it is preferably 550 to 1000 °C, more preferably 600 to 950 °C, further preferably 630 to 900 °C, and particularly preferably 650 to 800 °C. Here, from the viewpoints of improving the meltability of the raw materials and homogenizing the melt in a short time, the heating temperature is preferably 550 °C or higher, more preferably 600 °C or higher, further preferably 630 °C or higher, and particularly preferably 650 °C or higher. In addition, from the viewpoints of suppressing deterioration caused by heating of the components, suppressing compositional deviation caused by volatilization of the components, and suppressing decomposition, the heating temperature is preferably 1000 °C or lower, more preferably 950 °C or lower, further preferably 900 °C or lower, and particularly preferably 800 °C or lower.

[0175] The heating and melting time also does not vary depending on the scale, and is preferably 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, further preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. Here, from the viewpoint of enabling the reaction to proceed well, the heating and melting time is preferably 10 minutes or longer, more preferably 30 minutes or longer, further preferably 45 minutes or longer, and particularly preferably 1 hour or longer. In addition, from the viewpoint of productivity, the heating and melting time is preferably 10 hours or shorter, more preferably 9.5 hours or shorter, further preferably 9 hours or shorter.

[0176] The pressure during heating and melting is not particularly limited. For example, normal pressure or slightly increased pressure is preferred, and normal pressure is more preferred.

[0177] The dew point during heating and melting is preferably -20 °C or lower, and the lower limit is not particularly limited and is usually around -80 °C. The oxygen concentration is preferably 1000 volume ppm or lower.

[0178] In step s2, it can be confirmed that the melt is completely melted by the absence of peaks from crystals in high-temperature X-ray diffraction measurement.

[0179] Subsequently, step s3 is a process of cooling the melt obtained in the above step s2 to precipitate crystals. The crystals obtained by precipitation become the sulfide solid electrolyte.

[0180] Cooling can be carried out by using a known method, and the method is not particularly limited. As a more specific method of cooling, for example, a method of pouring the melt onto a plate-like body such as made of carbon for cooling; a method of flowing into a narrow gap and thinly forming, represented by the twin-roll method; a gas atomization method, etc.

[0181] The cooling rate is preferably 0.1 to 10,000 °C / second, more preferably 0.5 to 5,000 °C / second, and further preferably 1 to 1,000 °C / second. Here, from the viewpoints of improving compositional homogeneity and suppressing quality deviation, the cooling rate is preferably 0.1 °C / second or more, more preferably 0.5 °C / second or more, and further preferably 1 °C / second or more. In addition, the upper limit value of the cooling rate is not particularly limited. If further considering the cooling rate of the twin-roll, which is generally considered to have the fastest quenching rate, the upper limit value is 1,000,000 °C / second or less. From the viewpoint of actual production, the cooling rate is more preferably 10,000 °C / second or less, further preferably 5,000 °C / second or less, and even more preferably 1,000 °C / second or less.

[0182] The atmosphere during cooling is preferably a low moisture content and non-reactive atmosphere, similar to that during the heating and melting in step s2.

[0183] In the method for manufacturing a sulfide solid electrolyte including the above steps s1 to s3, a step of performing pulverization and a step of performing heat treatment may be further included as needed.

[0184] Either wet pulverization or dry pulverization can be used for the step of performing pulverization. In addition, when an atomization method that can simultaneously perform cooling and powdering is used as the cooling method in step s3, step s3 also serves as the step of performing pulverization.

[0185] It is preferable that the average particle diameter of the sulfide solid electrolyte is 1 to 100 μm by performing the step of pulverization. Here, the average particle diameter refers to the median diameter (D50) of the particle size, which is obtained by measuring the particle size distribution using a particle size distribution meter using the laser diffraction method and based on the volume-based particle size distribution diagram obtained, and represents the particle diameter below which 50% by volume of the particles are this value.

[0186] The purpose of the step of performing heat treatment is to improve homogeneity and stabilize the quality as the sulfide solid electrolyte.

[0187] When the obtained sulfide solid electrolyte is heat-treated, the heating temperature varies depending on the composition of the sulfide solid electrolyte. For example, it is preferably 200 to 600 °C, more preferably 350 to 500 °C, further preferably 380 to 460 °C, and particularly preferably 400 to 450 °C. Here, from the viewpoints of homogenization of the sulfide solid electrolyte and stabilization of quality, the heating temperature is preferably 200 °C or higher, more preferably 350 °C or higher, further preferably 380 °C or higher, and particularly preferably 400 °C or higher. In addition, from the viewpoint of preventing sintering between particles, it is preferably 600 °C or lower, more preferably 500 °C or lower, further preferably 460 °C or lower, and particularly preferably 450 °C or lower.

[0188] In addition, when an excessive amount of elemental sulfur from the composite powder remains in the obtained sulfide solid electrolyte, the above excessive elemental sulfur can also be removed by performing the above heat treatment at a temperature higher than the boiling point of elemental sulfur. It should be noted that the substance removed by this heat treatment is elemental sulfur, and the S element constituting the crystal structure of the sulfide solid electrolyte will not be removed.

[0189] When the sulfide solid electrolyte is heat-treated, the heating time varies depending on the composition of the sulfide solid electrolyte. For example, it is preferably 10 minutes to 10 hours, more preferably 30 minutes to 9.5 hours, further preferably 45 minutes to 9 hours, and particularly preferably 1 to 9 hours. Here, from the viewpoints of homogenization of the sulfide solid electrolyte and stabilization of quality, the heating time of the heat treatment is preferably 10 minutes or longer, more preferably 30 minutes or longer, further preferably 45 minutes or longer, and particularly preferably 1 hour or longer. In addition, from the viewpoint of manufacturing cost, the heating time of the heat treatment is preferably 10 hours or shorter, more preferably 9.5 hours or shorter, and further preferably 9 hours or shorter.

[0190] When the sulfide solid electrolyte is heat-treated, the atmosphere other than the SO2 concentration during the heat treatment is preferably an inert atmosphere. Examples of the inert atmosphere include a nitrogen atmosphere, an argon atmosphere, and a helium atmosphere.

[0191] The dew point during the above heat treatment is preferably -20 °C or lower, and the lower limit is not particularly limited and is usually around -80 °C. The oxygen concentration is preferably 1000 volume ppm or lower.

[0192] A manufacturing method of a sulfide solid electrolyte using a solid-phase synthesis method will be described.

[0193] Step s'1 is a step of mixing a raw material containing a Li element, a raw material containing a P element, and a raw material containing an S element to obtain a raw material mixture.

[0194] Each raw material in step s'1 is the same as each raw material in step s1 of the above-mentioned melting method, including the preferred methods.

[0195] The mixing in step s'1 can be carried out by a conventionally well-known method, preferably mixing based on mechanical grinding. When using a mechanical grinding method using a ball mill, examples include a rotary ball mill that causes the container to rotate, a vibration ball mill that generates a vibration motion, a planetary ball mill that generates a revolution and rotation motion, a bead mill, an Atritor (registered trademark), etc. Among them, a planetary ball mill and a bead mill with higher mixing force and crushing force are preferred.

[0196] The ball mill can be dry mixing or wet mixing using a dispersion medium. From the viewpoint of efficient energy transfer, dry mixing is preferred.

[0197] The raw materials are mixed by the above mixing to form a raw material mixture. This raw material mixture becomes a precursor of the sulfide solid electrolyte. The above precursor can be a homogeneous amorphous intermediate compound that is non-crystallized by adopting mixing conditions much more severe than before. The amorphous intermediate compound means that no XRD peak from the raw materials can be observed.

[0198] Step s'2 is a process of heating the above raw material mixture to obtain a sintered body. The sintered body obtained by crystallization based on heating becomes a sulfide solid electrolyte.

[0199] Although the heating temperature of the raw material mixture varies depending on the composition of the target sulfide solid electrolyte, it is preferably 350 to 600 °C, more preferably 400 to 575 °C, and further preferably 450 to 550 °C. Here, from the viewpoint of promoting crystallization, the heating temperature is preferably 350 °C or higher, more preferably 400 °C, and further preferably 450 °C. In addition, from the viewpoint of suppressing thermal decomposition, the heating temperature is preferably 600 °C or lower, more preferably 575 °C or lower, and further preferably 550 °C or lower.

[0200] It should be noted that the solid-phase synthesis method is usually not carried out in an open system and is mostly carried out in a closed system. If it is a closed system, the above temperature range can also be adopted when using the elemental sulfur contained in the composite powder of the present embodiment as the raw material containing the S element that constitutes the sulfide solid electrolyte. This is because even if the elemental sulfur is vaporized by the above heating, the vaporized elemental sulfur will stay in the system, so it can become the S element of the crystal structure that constitutes the sulfide solid electrolyte.

[0201] In addition, when the elemental sulfur contained in the composite powder is not used as the raw material containing the S element constituting the sulfide solid electrolyte, the elemental sulfur can be removed by heating the sulfide solid electrolyte at a temperature equal to or higher than the boiling point of the elemental sulfur after obtaining the sulfide solid electrolyte.

[0202] When obtaining the sulfide solid electrolyte by subjecting the raw material mixture to heat treatment for crystallization, the heat treatment time varies depending on the composition of the target sulfide solid electrolyte. For example, it is preferably 1 to 100 hours, more preferably 2 to 50 hours, and still more preferably 4 to 24 hours. Here, from the viewpoint of promoting crystallization, the heat treatment time is preferably 1 hour or more, more preferably 2 hours or more, and still more preferably 4 hours or more. In addition, from the viewpoint of manufacturing cost, the heat treatment time is preferably 100 hours or less, more preferably 50 hours or less, and still more preferably 24 hours or less.

[0203] The atmosphere during the heat treatment when obtaining the sulfide solid electrolyte by heating the raw material mixture for crystallization is preferably an inert atmosphere. Examples of the inert atmosphere include a nitrogen atmosphere, an argon atmosphere, and a helium atmosphere.

[0204] The dew point during the above heat treatment is preferably -20°C or lower, and there is no particular limitation on the lower limit, which is usually around -80°C. The oxygen concentration is preferably 1000 volume ppm or lower.

[0205] In the method for manufacturing a sulfide solid electrolyte including the above steps s’1 and s’2, a pulverizing step and a heat treatment step can be further included as needed.

[0206] In this case, the pulverizing step and the heat treatment step are the same as the pulverizing step and the heat treatment step that can be included in the method for manufacturing a sulfide solid electrolyte including the above steps s1 to s3, and the preferred modes are also the same.

[0207] Examples

[0208] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

[0209] Examples 1-1 to 1-4 and Examples 2-1 to 2-4 are examples, and Example 1-5 is a comparative example.

[0210] [Example 1-1]

[0211] 75.0 g of lithium carbonate was added to 300.0 g of water and reacted with 342.2 g of 48 mass% hydrobromic acid to prepare a 26.2 mass% aqueous lithium bromide solution.

[0212] 1.0 g of elemental sulfur (colloidal sulfur) was added to 672.5 g of the obtained 26.2 mass% lithium bromide aqueous solution to form a state of existence of elemental sulfur. After the addition of elemental sulfur, ultrasonic homogenization was carried out for 1 minute to improve the dispersion of elemental sulfur.

[0213] Under the above state, 672.5 g of the 26.2 mass% lithium bromide aqueous solution was placed in a vibration drying device, and the solvent was removed at a pressure of 2 kPa and a jacket temperature of 160 °C covering the periphery of the container. For the above jacket temperature, the temperature was raised from room temperature to 160 °C in 100 hours, held at 160 °C for 24 hours, and then the temperature was lowered to room temperature. Thus, the solvent was removed to obtain a dry powder.

[0214] For the obtained powder, it was confirmed by Raman spectroscopic analysis that it contained elemental sulfur in addition to lithium bromide. In addition, five samples of 0.1 g each were taken from the obtained powder, and the content of elemental sulfur relative to the composite powder, A1 - A5, was determined by high-frequency furnace combustion - infrared absorption method. Then, the arithmetic mean Aave. of A1 - A5 represented by the following formula was calculated.

[0215] Aave. = (A1 + A2 + A3 + A4 + A5) / 5

[0216] Using A1 - A5 and Aave. obtained from the above formula, the dispersion (%) was calculated according to the following formula. The obtained value of Aave. was used as the "elemental sulfur content", and the dispersion was used as the "homogeneity, dispersion" and shown in Table 1 respectively, and it was confirmed that the obtained powder was a composite powder with high homogeneity.

[0217]

[0218] [Example 1 - 2]

[0219] 75.0 g of lithium carbonate was added to 300.0 g of water and reacted with 342.2 g of 48 mass% hydrobromic acid to prepare a 26.2 mass% lithium bromide aqueous solution.

[0220] 15 g of 5 mass% sulfurous acid aqueous solution was added to 672.5 g of the obtained 26.2 mass% lithium bromide aqueous solution to obtain a 26.2 mass% lithium bromide aqueous solution containing sulfite ions.

[0221] After adding 1.1 g of lithium sulfide to 672.5 g of the obtained 26.2 mass% lithium bromide aqueous solution containing sulfite ions, the solution became turbid, forming a state of existence of elemental sulfur. It is considered that this is because SO3 2－ was reduced by Li2S to generate S. Next, ultrasonic homogenization was carried out for 1 minute to improve the dispersion of elemental sulfur.

[0222] Under the above conditions, 672.5 g of a 26.2 mass% aqueous lithium bromide solution was placed in a vibration drying apparatus and operated in the same manner as in Example 1-1 to obtain a dry powder from which the solvent was removed.

[0223] For the obtained powder, it was confirmed by Raman spectroscopic analysis that it contained elemental sulfur in addition to lithium bromide. In addition, in the same manner as in Example 1-1, the high-frequency furnace combustion-infrared absorption method was used to quantify elemental sulfur relative to the composite powder, and the dispersion was confirmed. The results are shown in Table 1, and it was confirmed that the obtained powder was a composite powder with high homogeneity.

[0224] [Example 1-3]

[0225] 75.0 g of lithium carbonate was added to 300.0 g of water and reacted with 342.2 g of a 48 mass% hydrobromic acid to prepare a 26.2 mass% aqueous lithium bromide solution.

[0226] 15 g of a 5 mass% aqueous sulfurous acid solution was added to 672.5 g of the obtained 26.2 mass% aqueous lithium bromide solution to obtain a 26.2 mass% aqueous lithium bromide solution containing sulfite ions.

[0227] After bubbling hydrogen sulfide gas at a flow rate of 0.1 SLM for 10 minutes in 672.5 g of the obtained 26.2 mass% aqueous lithium bromide solution containing sulfite ions, the solution became turbid and a state of existence of elemental sulfur was formed. It is considered that this is because SO3 2－ was reduced by H2S to form S. Next, ultrasonic homogenization was performed for 1 minute to improve the dispersion of elemental sulfur.

[0228] Under the above conditions, 672.5 g of a 26.2 mass% aqueous lithium bromide solution was placed in a vibration drying apparatus and operated in the same manner as in Example 1-1 to obtain a dry powder from which the solvent was removed.

[0229] For the obtained powder, it was confirmed by Raman spectroscopic analysis that it contained elemental sulfur in addition to lithium bromide. In addition, in the same manner as in Example 1-1, the high-frequency furnace combustion-infrared absorption method was used to quantify elemental sulfur relative to the composite powder, and the dispersion was confirmed. The results are shown in Table 1, and it was confirmed that the obtained powder was a composite powder with high homogeneity.

[0230] [Example 1-4]

[0231] 75.0 g of lithium carbonate containing a sulfurous acid component was added to 300.0 g of water and reacted with 342.2 g of a 48 mass% hydrobromic acid to prepare a 26.2 mass% aqueous lithium bromide solution containing sulfite ions. The above lithium carbonate containing a sulfurous acid component was obtained by adding 15 g of a 5 mass% aqueous sulfurous acid solution to 75.0 g of lithium carbonate.

[0232] After bubbling hydrogen sulfide gas at a flow rate of 0.1 SLM for 10 minutes in 672.5 g of the obtained 26.2 mass% lithium bromide aqueous solution containing sulfite ions, the solution became turbid, and the state of existence of elemental sulfur was formed. It is considered that this is because SO3 2－ was reduced by H2S to form S. Next, ultrasonic homogenization was performed for 1 minute to improve the dispersibility of elemental sulfur.

[0233] In the above state, 672.5 g of the 26.2 mass% lithium bromide aqueous solution was placed in a vibration drying device and operated in the same manner as in Example 1-1 to obtain a dry powder from which the solvent was removed.

[0234] For the obtained powder, it was confirmed by Raman spectroscopy that in addition to lithium bromide, it also contained elemental sulfur. In addition, in the same manner as in Example 1-1, the combustion-infrared absorption method using a high-frequency furnace was used to quantify elemental sulfur relative to the composite powder, and the dispersion was confirmed. The results are shown in Table 1, and it was confirmed that the obtained powder was a composite powder with high homogeneity.

[0235] [Example 1-5]

[0236] 75.0 g of lithium carbonate was added to 300.0 g of water and reacted with 342.2 g of 48 mass% hydrobromic acid to prepare a 26.2 mass% lithium bromide aqueous solution.

[0237] 672.5 g of the obtained 26.2 mass% lithium bromide aqueous solution was placed in a vibration drying device and operated in the same manner as in Example 1-1 to obtain a dry powder from which the solvent was removed.

[0238] For the obtained powder, it was confirmed by Raman spectroscopy that it was a powder of lithium bromide that did not contain elemental sulfur. Since the obtained powder did not contain elemental sulfur, the evaluation of the dispersion related to homogeneity was not performed.

[0239] [Evaluation: Boiling Over Inhibition]

[0240] For Examples 1-1 to 1-5, the powders recovered from the vibration drying device were respectively examined to confirm the contamination status inside the device. Specifically, the contamination status caused by the solid containing lithium halide scattered due to the boiling over of the lithium halide aqueous solution inside the device was confirmed at the following three positions. (1) The exhaust port filter for decompression, (2) The thermocouple for temperature measurement, (3) The movable part of the discharge port for discharging the obtained powder.

[0241] The results are respectively shown in "Filter", "Thermocouple", and "Discharge Port" in Table 1, and their evaluation criteria are as follows.

[0242] (1) Filter

[0243] ○: Not attached to the exhaust port filter, or slightly attached, allowing decompression inside the device

[0244] ×: The exhaust port filter is clogged due to attachment, making it difficult to decompress inside the device

[0245] (2) Thermocouple

[0246] ○: Not attached to the thermocouple, or slightly attached, allowing accurate temperature measurement

[0247] ×: Considerable attachment to the thermocouple, preventing accurate temperature measurement

[0248] (3) Discharge port

[0249] ○: Not attached to the movable part of the discharge port, or slightly attached, allowing the discharge port to open and close

[0250] ×: Considerable attachment to the movable part of the discharge port, obstructing the opening and closing of the discharge port

[0251] In addition, as a comprehensive evaluation, when all of the above (1) to (3) are ○, it is evaluated as good: ○; when one of the above (1) to (3) is ×, it is in a state where the inside of the device needs to be cleaned, and as a state where it is impossible to continuously produce composite powder, it is evaluated as bad: ×.

[0252] [Evaluation: Ignition property evaluation]

[0253] The composite powders containing LiBr and S obtained in Examples 1-1 to 1-4 were brought close to fire to evaluate the ignition property. As a result, it was confirmed that none of them caught fire.

[0254] [Table 1]

[0255]

[0256] [Examples 2-1 to 2-4]

[0257] The composite powders of Examples 1-1 to 1-4 obtained above were pulverized using an agate mortar to form powders with an average particle size of 200 μm or less. Then, in a manner to achieve a composition ratio of Li 5.3 PS 4.2 Cl 0.8 Br 0.8 the above composite powders, lithium sulfide powder (manufactured by Sigma), phosphorus pentasulfide powder (manufactured by Sigma), lithium chloride powder (manufactured by Sigma), and lithium bromide powder (manufactured by Sigma) were mixed in a mortar in a specified amount to obtain a raw material mixture.

[0258] After heating the raw material mixture at 700 °C for 1 hour to obtain a melt, it was cooled at 1000 °C / minute, whereby the sulfide solid electrolytes of Examples 2-1 to 2-4 were obtained.

[0259] Powder X-ray diffraction measurement was performed on the obtained sulfide solid electrolyte, and the results of Rietveld analysis confirmed that all had a thiogermanate-type crystal structure with a composition having Li 5.3 PS 4.2 Cl 0.8 Br 0.8 .

[0260] Based on the above results, it was found that bumping can be suppressed by heating an aqueous lithium halide solution in the presence of elemental sulfur. Therefore, it was shown that an excessively high temperature above the boiling point can be used in the removal of the solvent from the aqueous lithium halide solution, and as a result, lithium halide powder can be obtained in a short time with high productivity.

[0261] In addition, by suppressing bumping and preventing contamination inside the apparatus, it can also be said that the productivity is high in terms of being able to continuously produce lithium halide using the same apparatus.

[0262] In addition, it was found that the composite powder obtained by the manufacturing method of the present embodiment does not catch fire even when close to fire, and different from when it is appropriately elemental sulfur, dust explosion can be prevented.

[0263] Furthermore, the composite powder obtained by the manufacturing method of the present embodiment was used as a raw material to obtain a sulfide solid electrolyte as shown in Examples 2-1 to 2-4. In Examples 2-1 to 2-4, since a melt was obtained at 700 °C which is higher than the boiling point of elemental sulfur, the composite powder can be used as a raw material that also serves as a raw material containing a Li element and a raw material containing a halogen element.

[0264] On the other hand, by obtaining a melt below the boiling point of elemental sulfur, the composite powder can be used as a material that further also serves as a raw material containing an S element. In addition, by using the composite powder obtained by the manufacturing method of the present embodiment as a raw material and obtaining a sulfide solid electrolyte by a solid-phase synthesis method in a closed system, the above composite powder can be used as a material that also serves as a raw material containing an S element.

[0265] Although the present invention has been described in detail with reference to specific embodiments, those skilled in the art can obviously make various changes and modifications without departing from the spirit and scope of the present invention. This application is based on a Japanese patent application filed on December 28, 2022 (Japanese Patent Application No. 2022-212574), and its content is incorporated herein by reference.

Claims

1. A method for manufacturing a composite powder, which is used in a raw material of a sulfide solid electrolyte and contains lithium halide and elemental sulfur, The manufacturing method includes the following steps: heating an aqueous solution of lithium halide at a temperature above the boiling point in the presence of elemental sulfur to remove the solvent.

2. The manufacturing method of the composite powder according to claim 1, wherein, The presence state of elemental sulfur is formed by adding a powder of elemental sulfur to the aqueous solution of lithium halide.

3. The manufacturing method of the composite powder according to claim 1, wherein, The aqueous lithium halide solution contains SO3 2－ in the aqueous lithium halide solution, The presence state of elemental sulfur is formed by adding an alkali metal sulfide to the aqueous solution of lithium halide.

4. The method for manufacturing the composite powder according to claim 1, wherein, The aqueous lithium halide solution contains SO3 2－ and is an aqueous lithium halide solution. The presence state of elemental sulfur is formed by introducing hydrogen sulfide into the aqueous solution of lithium halide.

5. The method for manufacturing the composite powder according to claim 3 or 4, wherein comprising the following steps: obtaining the aqueous lithium halide solution containing SO3 2－ from at least one of lithium carbonate and lithium hydroxide At least one of the lithium carbonate and lithium hydroxide contains SO3 2－ .

6. The method for manufacturing the composite powder according to any one of claims 2 to 4, wherein, The aqueous solution of lithium halide includes an aqueous solution of lithium bromide.

7. A method for manufacturing a sulfide solid electrolyte, including the following steps: Mixing a raw material containing Li element, a raw material containing P element, and a raw material containing S element to obtain a raw material mixture, Heating the raw material mixture to obtain a melt, and Cooling the melt to precipitate crystals, At least as the raw material containing Li element, using the composite powder obtained by the manufacturing method according to any one of claims 1 to 4.

8. A method for manufacturing a sulfide solid electrolyte, including the following steps: Mixing a raw material containing Li element, a raw material containing P element, and a raw material containing S element to obtain a raw material mixture, and Heating the raw material mixture to obtain a sintered body, At least as the raw material containing Li element, using the composite powder obtained by the manufacturing method according to any one of claims 1 to 4.

9. A composite powder, which is used in a raw material of a sulfide solid electrolyte and contains lithium halide and elemental sulfur.

10. The composite powder according to claim 9, wherein, The dispersion degree of the elemental sulfur with respect to the composite powder is 15% or less.

11. The composite powder according to claim 9 or 10, wherein, The lithium halide includes lithium bromide.

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