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

Abstract

The present invention pertains to a method for producing a sulfide-based solid electrolyte in which a sulfide-based solid electrolyte raw material is supplied to a tank of a heating furnace, and the sulfide-based solid electrolyte raw material is heated and melted in a gas atmosphere containing elemental sulfur, comprising the steps of obtaining a melt by heating and melting, and setting the temperature of the bottom side of the melt to be higher than the temperature of the liquid surface side of the melt in the tank.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a sulfide-based solid electrolyte and a manufacturing apparatus for a sulfide-based solid electrolyte. Background Art

[0002] Lithium ion secondary batteries are widely used in portable electronic devices such as mobile phones and laptop computers. Conventionally, liquid electrolytes have been used in lithium ion secondary batteries. 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 in terms of expected improvements in safety, high-speed charge and discharge, and miniaturization of the casing.

[0003] As the solid electrolyte used in the all-solid-state lithium ion secondary battery, for example, a sulfide-based solid electrolyte can be cited.

[0004] As a synthesis method of the sulfide-based solid electrolyte, a method of heating and melting a raw material of the sulfide-based solid electrolyte to prepare a melt and then cooling and solidifying it can be cited. It is known that in this method, sulfur components volatilize during heating, and it is sometimes difficult to control the composition.

[0005] On the other hand, Patent Document 1 describes a method for manufacturing a sulfide-based lithium ion conductive solid electrolyte. After mixing the constituent compounds of the sulfide-based lithium ion conductive solid electrolyte in a predetermined stoichiometric ratio, the mixture is heated and melted in a state where sulfur is in excess. According to this method, they can react without reducing sulfur in the constituent compounds, and a sulfide lithium ion conductive solid electrolyte having a target chemical composition and excellent ionic conductivity can be obtained.

[0006] Patent Document 2 describes a manufacturing apparatus for a solid electrolyte glass having a compression section that compresses the raw material supplied from the raw material supply section. It is considered that the composition deviation can be suppressed and the productivity can be improved according to this manufacturing apparatus.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Laid-Open No. 6-115911

[0010] Patent Document 2: Japanese Patent Laid-Open No. 2012-096973 Summary of the Invention

[0011] However, in the method described in Patent Document 1, when the production amount is increased and the amount of the melt increases, it is difficult for the sulfur component supplemented on the surface of the melt to uniformly diffuse throughout the whole, and it is difficult to stably obtain a homogeneous sulfide-based solid electrolyte.

[0012] The structure of the manufacturing apparatus described in Patent Document 2 is complex, and it is difficult to stably obtain a homogeneous sulfide-based solid electrolyte. In addition, it is not suitable for mass production.

[0013] Therefore, an object of the present invention is to provide a method for manufacturing a sulfide-based solid electrolyte and a manufacturing apparatus for a sulfide-based solid electrolyte, which can stably synthesize a homogeneous sulfide-based solid electrolyte.

[0014] As a result of intensive studies by the present inventors, it has been found that in a method for manufacturing a sulfide-based solid electrolyte in which a sulfide-based solid electrolyte raw material is heated and melted in a gas atmosphere containing a sulfur element, by controlling the temperature at the lower part of the melt to be higher than the temperature at the upper part of the melt, the above problems can be solved, and thus the present invention has been completed.

[0015] That is, the present invention relates to the following 1 to 10.

[0016] 1. A method for manufacturing a sulfide-based solid electrolyte, which is a method for manufacturing a sulfide-based solid electrolyte in which a sulfide-based solid electrolyte raw material is supplied to a tank of a heating furnace and the sulfide-based solid electrolyte raw material is heated and melted in a gas atmosphere containing a sulfur element, including obtaining a melt by the above heating and melting, and a step of making the temperature on the bottom side of the melt higher than the temperature on the liquid surface side of the melt in the above tank.

[0017] 2. The method for manufacturing a sulfide-based solid electrolyte according to the above 1, wherein the step of supplying the sulfide-based solid electrolyte raw material to the above tank and the step of discharging the above melt to the outside of the above heating furnace are continuously performed.

[0018] 3. The method for manufacturing a sulfide-based solid electrolyte according to the above 1, wherein the depth of the above melt in the above tank is 50 mm or more.

[0019] 4. The method for manufacturing a sulfide-based solid electrolyte according to the above 1, wherein in the above tank, the temperature on the bottom side of the above melt is 700 °C or more.

[0020] 5. The method for manufacturing a sulfide-based solid electrolyte according to the above 1, wherein in the above tank, the temperature on the bottom side of the above melt is 10 °C or more higher than the temperature on the liquid surface side of the above melt.

[0021] 6. The method for manufacturing a sulfide-based solid electrolyte according to the above 1, wherein the above gas atmosphere containing a sulfur element is obtained by supplying a gas containing a sulfur element to the above heating furnace.

[0022] 7. The manufacturing method of the sulfide-based solid electrolyte according to Item 1 above, wherein the gas atmosphere containing sulfur element is obtained by supplying a solid containing sulfur element to the above heating furnace.

[0023] 8. The manufacturing method of the sulfide-based solid electrolyte according to any one of Items 1 to 7 above, wherein

[0024] the above heating furnace has: the above tank for supplying the raw material of the sulfide-based solid electrolyte, and an additional tank for supplying the melt of the raw material of the sulfide-based solid electrolyte heated and melted in the above tank,

[0025] The steps of continuously supplying the raw material of the sulfide-based solid electrolyte to the above tank and discharging the above melt from the above additional tank to the outside of the above heating furnace are carried out, and the temperature of the above melt in the above additional tank is controlled to be higher than the lowest temperature of the above melt in the above tank.

[0026] 9. A manufacturing apparatus for a sulfide-based solid electrolyte, comprising:

[0027] a heating furnace, having a tank and a heating unit for heating and melting the raw material of the sulfide-based solid electrolyte in a gas atmosphere containing sulfur element, and

[0028] a control unit that controls the calorific value of the above heating unit so that the temperature of the bottom side of the melt obtained by the above heating and melting is higher than the temperature of the liquid surface side of the above melt.

[0029] 10. The manufacturing apparatus for a sulfide-based solid electrolyte according to Item 9 above, wherein

[0030] the above heating furnace has: the above tank for supplying the raw material of the sulfide-based solid electrolyte, an additional tank for supplying the melt of the raw material of the sulfide-based solid electrolyte heated and melted in the above tank, the above heating unit for heating and melting the raw material of the sulfide-based solid electrolyte in the above tank, and an additional heating unit for heating the above melt in the above additional tank,

[0031] the above control unit controls the calorific value of the above heating unit and the calorific value of the above additional heating unit so that the temperature of the above melt in the above additional tank is higher than the lowest temperature of the above melt in the above tank.

[0032] According to the present invention, it is possible to provide a manufacturing method of a sulfide-based solid electrolyte and a manufacturing apparatus of a sulfide-based solid electrolyte that can stably synthesize a homogeneous sulfide-based solid electrolyte. Moreover, the productivity of this manufacturing method is also excellent. In addition, according to this manufacturing method, the quality of the obtained sulfide-based solid electrolyte can be stabilized. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a flowchart illustrating one mode of this manufacturing method.

[0034] Figure 2 It is a flowchart illustrating one mode of this manufacturing method.

[0035] Figure 3 It is a diagram schematically illustrating one mode of this manufacturing method and this manufacturing apparatus.

[0036] Figure 4 It is a diagram schematically illustrating one mode of this manufacturing method and this manufacturing apparatus.

[0037] Figure 5 It is a diagram schematically illustrating one mode of this manufacturing method and this manufacturing apparatus.

[0038] Figure 6 It is a diagram showing an analysis model used in the simulation. Detailed Embodiments

[0039] Hereinafter, the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented without departing from the gist of the present invention. In addition, "~" indicating a numerical range is used to mean including the numerical values described before and after it as the lower limit value and the upper limit value. In addition, in this specification, "mass" and "weight" are synonymous. In addition, in the following drawings, sometimes the same reference numerals are given to components and parts having the same function for description, and repeated descriptions are omitted or simplified. In addition, the embodiments shown in the drawings are schematically shown for clearly explaining the present invention, and do not necessarily accurately represent the dimensions and ratios of actual devices and the like.

[0040] (Manufacturing Method of Sulfide-Based Solid Electrolyte)

[0041] The manufacturing method of the sulfide-based solid electrolyte according to the embodiment of the present invention (hereinafter, also referred to as this manufacturing method) is a manufacturing method of a sulfide-based solid electrolyte in which a sulfide-based solid electrolyte raw material is supplied to a tank (first tank) of a heating furnace and the sulfide-based solid electrolyte raw material is heated and melted in a gas atmosphere containing sulfur element, and includes obtaining a melt by the above heating and melting, and a step of making the temperature on the bottom side of the melt higher than the temperature on the liquid surface side of the melt in the above tank (first tank).

[0042] Figure 1It is a flowchart illustrating one mode of this manufacturing method. This manufacturing method includes, for example: Step S11, in a tank of a heating furnace, heating and melting a sulfide-based solid electrolyte raw material in a gas atmosphere containing sulfur element; Step S12, in the above-mentioned tank, controlling the temperature of the bottom side of the melt obtained by heating and melting to be higher than the temperature of the liquid surface side of the melt. It should be noted that Step S11 and S12 can be executed in parallel, for example.

[0043] As will be described in detail later, in this manufacturing method, the heating furnace can have: the above-mentioned tank for supplying the sulfide-based solid electrolyte raw material, and an additional tank for supplying the melt of the sulfide-based solid electrolyte raw material heated and melted in this tank. Figure 2 It is a flowchart illustrating one mode of this manufacturing method in this case. This manufacturing method includes, for example: Step S21, in a tank of a heating furnace, heating and melting a sulfide-based solid electrolyte raw material in a gas atmosphere containing sulfur element; Step S22, continuously performing the step of supplying the sulfide-based solid electrolyte raw material to the above-mentioned tank and the step of discharging the melt from the additional tank to the outside of the heating furnace; Step S23, in the above-mentioned tank, controlling the temperature of the bottom side of the melt obtained by heating and melting to be higher than the temperature of the liquid surface side of the melt; Step S24, controlling the temperature of the melt in the additional tank of the heating furnace to be higher than the lowest temperature of the melt in the first tank. It should be noted that Steps S21 to S24 can be executed in parallel, for example.

[0044] Hereinafter, regarding this manufacturing method, an example of a manufacturing apparatus for a sulfide-based solid electrolyte used in the present invention (hereinafter, also referred to as this manufacturing apparatus) will be described. It should be noted that in this specification, the tank for supplying the sulfide-based solid electrolyte raw material to the heating furnace and heating and melting the sulfide-based solid electrolyte raw material is sometimes referred to as the first tank, and the heating part for heating and melting the sulfide-based solid electrolyte raw material in this tank (the first tank) is sometimes referred to as the first heating part. In addition, when the heating furnace has the above-mentioned additional tank, the additional tank is sometimes referred to as the second tank, and the additional heating part for heating the melt in this additional tank (the second tank) is sometimes referred to as the second heating part.

[0045] One mode of this manufacturing apparatus includes: a heating furnace having a tank (the first tank) for heating and melting a sulfide-based solid electrolyte raw material in a gas atmosphere containing sulfur element and a heating part (the first heating part); and a control part for controlling the calorific value of the heating part (the first heating part) so that the temperature of the bottom side of the melt obtained by heating and melting is higher than the temperature of the liquid surface side of the melt.

[0046] Figure 3 It is a diagram schematically illustrating one mode of this manufacturing method and this manufacturing apparatus. In Figure 3In the manufacturing apparatus 100 for a sulfide-based solid electrolyte, a heating furnace 1 includes a first tank 10 for heating and melting a sulfide-based solid electrolyte raw material in a gas atmosphere containing a sulfur element, and a first heating unit. Further, the manufacturing apparatus 100 includes a control unit CTL that controls the calorific value of the first heating unit so that the temperature on the bottom side of the melt 11 obtained by heating and melting in the first tank is higher than the temperature on the liquid surface side of the melt. Figure 3 The manufacturing apparatus 100 in it includes heating units 5a, 5b, and 5c as the first heating unit.

[0047] The first tank 10 of the heating furnace 1 is a heating chamber for heating and melting an object to be heated, that is, a sulfide-based solid electrolyte raw material in this manufacturing method. In this manufacturing method, the sulfide-based solid electrolyte raw material is supplied to the first tank 10 and heated and melted in a gas atmosphere containing a sulfur element. In order to heat and melt in a gas atmosphere containing a sulfur element, the first tank 10 may include a sulfur source supply unit 23.

[0048] The manufacturing apparatus 100 includes a control unit CTL that controls the calorific value of the first heating unit so that the temperature on the bottom side of the melt 11 obtained by heating and melting in the first tank 10 is higher than the temperature on the liquid surface side of the melt. In Figure 3 In the illustrated manner, the manufacturing apparatus 100 includes heating units 5a, 5b, and 5c that can heat the first tank 10 as the first heating unit. The heating units 5a, 5b, and 5c may be, for example, heating mechanisms that can independently control the calorific value respectively, or the calorific value of each may be controlled by the control unit. Specifically, for example, by the control unit controlling the calorific value of each heating unit so that the temperature of the melt mainly heated by the heating unit 5b disposed on the lower side of the side surface of the first tank and the heating unit 5c disposed on the bottom surface side of the first tank is higher than the temperature of the melt mainly heated by the heating unit 5a disposed on the upper side of the side surface of the first tank, the temperature on the bottom side of the melt 11 in the first tank 10 can be made higher than the temperature on the liquid surface side of the melt. Thus, as long as the temperature on the bottom side of the melt 11 in the first tank 10 can be made higher than the temperature on the liquid surface side of the melt, the specific manner of the control unit is not particularly limited, and a known configuration can be adopted. For example, the control unit has an input unit (not shown) and is connected to the first heating unit through a known mechanism capable of sending a signal for controlling the calorific value to the first heating unit. The control unit outputs a signal for controlling the calorific value of each heating unit according to the set temperature and set calorific value of each heating unit input from the input unit, and by controlling the calorific value of each heating unit, makes the temperature on the bottom side of the melt higher than the temperature on the liquid surface side of the melt. It should be noted that as long as the above control can be achieved as a whole for the manufacturing apparatus, the number of control units may be one or more.

[0049] The specific form of the first heating unit is not particularly limited. For example, the heating units 5a, 5b, and 5c may be well-known heating mechanisms such as heaters and high-frequency induction heating devices provided in the heating furnace 1. It should be noted that examples of the heater include heaters such as Kanthal heaters, carbon heaters, and SiC heaters that heat an object by passing an electric current through a heating material, and heaters such as halogen heaters that perform radiant heating.

[0050] The inventors of the present invention have found that in a method for manufacturing a sulfide-based solid electrolyte by heating and melting a sulfide-based solid electrolyte raw material in a gas atmosphere containing a sulfur element, by controlling the temperature of the lower part of the melt to be higher than the temperature of the upper part of the melt, a homogeneous sulfide-based solid electrolyte can be stably synthesized, and thus the present invention has been completed. When heating and melting a sulfide-based solid electrolyte raw material in a gas atmosphere containing a sulfur element, a sulfur component is introduced by bringing the liquid surface of the melt into contact with the gas atmosphere containing a sulfur element. On the other hand, although not regarded as a problem in the past, it is known that in the melt of a sulfide-based solid electrolyte (raw material), the sulfur component is difficult to diffuse in the depth direction. Even if the sulfur component is introduced into the liquid surface side of the melt in contact with the gas atmosphere containing a sulfur element, the sulfur component is difficult to be introduced into the part at the bottom side of the melt that is not in contact with the atmosphere. In contrast, in the present manufacturing method, in the first tank, by making the temperature of the bottom side of the melt higher than the temperature of the liquid surface side of the melt, the specific gravity of the melt at the bottom side of the first tank becomes further smaller, and it moves to the upper side of the melt. As a result, a circulation is generated in the melt, and the melt effectively contacts the gas atmosphere containing a sulfur element. Therefore, it is considered that the sulfur component is uniformly introduced throughout the melt, and the obtained sulfide-based solid electrolyte is also homogeneous. In addition, since the introduction of sulfur into the melt can be effectively performed, the productivity is excellent. Furthermore, in a sulfide-based solid electrolyte, a shortage of the sulfur component will reduce the lithium ion conductivity and deteriorate its quality. On the other hand, according to the present manufacturing method, an appropriate amount of sulfur can be introduced into the entire melt, and the quality of the obtained sulfide-based solid electrolyte is also stable.

[0051] It should be noted that although it is also considered to circulate the melt by introducing components such as stirring paddles into the furnace, when such components are introduced, generally, a component having a rotating shaft is introduced into the furnace. In this case, in a system where the furnace components volatilize or the introduced gas is present, device design and maintenance considering gas leakage from the shaft part are required, and stable production is difficult. On the other hand, according to the present manufacturing method and the present manufacturing apparatus, heating and melting can be performed in a state where the furnace body is sealed, and a homogeneous sulfide-based solid electrolyte can be manufactured more stably.

[0052] Figure 4 is a diagram schematically illustrating another aspect of the present manufacturing method and the present manufacturing apparatus. In Figure 4In the manufacturing apparatus 200 shown, the first tank 10 is provided with a raw material supply unit 21 and a discharge unit 25. Thus, in the present manufacturing method and the present manufacturing apparatus, the first tank may appropriately be provided with a raw material supply unit for supplying a sulfide-based solid electrolyte raw material into the tank, and a discharge unit for discharging the melt outside the heating furnace. The specific form of the discharge unit is not particularly limited. For example, there may be mentioned a form in which an opening (flow-through part) is provided in the wall part and the bottom part inside the first tank, and a form in which a pipe (nozzle) that can communicate with the outside of the heating furnace is arranged. In Figure 3 In the exemplified manufacturing apparatus 100, for example, it is considered to previously heat and melt the sulfide-based solid electrolyte raw material supplied to the first tank 10, and after the heating and melting is completed, the obtained sulfide-based solid electrolyte is recovered, and heating and melting is performed in a so-called batch system. On the other hand, as Figure 4 exemplified, while performing heating and melting in the first tank 10, the steps of supplying the sulfide-based solid electrolyte raw material from the raw material supply unit 21 and discharging the melt from the discharge unit 25 outside the heating furnace may be continuously performed, and heating and melting may be continuously performed. That is, in the present manufacturing method, when continuously performing heating and melting, it is preferable to continuously supply the sulfide-based solid electrolyte raw material to the tank (the first tank) of the heating furnace and discharge the melt outside the heating furnace.

[0053] It should be noted that in Figure 4 the exemplified manufacturing apparatus 100, a sulfur source (a gas or solid containing a sulfur element, etc.) can be supplied not only from the sulfur source supply unit 23 but also from the raw material supply unit 21. In addition, in order to take both the raw material supply unit 21 and the sulfur source supply unit 23 into account, a part that can supply the raw material and the sulfur source (a gas or solid containing a sulfur element, etc.) may be provided in the first tank 10, and the raw material and the sulfur source may be supplied from this part. In this case, the part in the first tank that can supply the raw material and the sulfur source may be only one part.

[0054] In the present manufacturing method, it is preferable that the heating furnace has: a tank for supplying a sulfide-based solid electrolyte raw material (the above-mentioned first tank), and an additional tank (the second tank) for supplying the melt of the sulfide-based solid electrolyte raw material heated and melted in this tank (the first tank); the steps of continuously supplying the sulfide-based solid electrolyte raw material to the tank (the first tank) and discharging the melt from the additional tank (the second tank) outside the heating furnace are continuously performed, and the temperature of the melt in the additional tank (the second tank) is controlled to be higher than the lowest temperature of the melt in the tank (the first tank).

[0055] In addition, in this case, in the present manufacturing apparatus, the heating furnace includes: a tank for supplying a sulfide-based solid electrolyte raw material (the above-described first tank), an additional tank (second tank) for supplying a melt of the sulfide-based solid electrolyte raw material heated and melted in this tank (first tank), a heating unit (first heating unit) for heating and melting the sulfide-based solid electrolyte raw material in the tank (first tank), and an additional heating unit (second heating unit) for heating the above melt in the additional tank (second tank).

[0056] The control unit preferably controls the calorific value of the heating unit (first heating unit) and the calorific value of the additional heating unit (second heating unit) such that the temperature of the melt in the additional tank (second tank) is higher than the lowest temperature of the melt in the tank.

[0057] Figure 5 It is a diagram schematically illustrating one mode of the present manufacturing method and the present manufacturing apparatus in the case where the heating furnace includes an additional tank (second tank). In Figure 5 In the illustrated manufacturing apparatus 300, the heating furnace 1 includes: a first tank 10 for supplying a sulfide-based solid electrolyte raw material, a second tank 20 for supplying a melt of the sulfide-based solid electrolyte raw material heated and melted in the first tank 10, a first heating unit for heating and melting the sulfide-based solid electrolyte raw material in the first tank 10, and a second heating unit for heating the melt in the second tank 20. For example, in order to supply the melt of the sulfide-based solid electrolyte raw material heated and melted in the first tank 10 to the second tank 20, the heating furnace 1 may include a passage portion 7 through which the melt can pass between the first tank 10 and the second tank 20. In addition, in order to continuously perform the step of supplying the sulfide-based solid electrolyte raw material to the first tank and the step of discharging the melt from the second tank to the outside of the heating furnace, the heating furnace 1 may have a discharging portion 25 provided in the second tank 20 for discharging the melt to the outside of the heating furnace. And the manufacturing apparatus 300 includes a second heating unit for heating the melt in the second tank. In Figure 5 In the configuration illustrated in, the second heating unit is composed of a heating unit 6a and a heating unit 6b. The second heating unit may be, for example, any heating mechanism that can independently control the calorific value from the first heating unit, and the calorific values of each are controlled by the control unit. In Figure 5In the exemplary configuration, the control unit is connected to each heating unit through a known mechanism that can send signals for controlling the calorific value of the first heating unit and the second heating unit to each heating unit. Then, the calorific value of the first heating unit is controlled so that the temperature of the bottom side of the molten liquid 11 in the first tank is higher than the temperature of the liquid surface side of the molten liquid, and the calorific value of the first heating unit and the calorific value of the second heating unit are controlled so that the temperature of the molten liquid in the second tank is higher than the lowest temperature of the molten liquid in the tank. It should be noted that, similar to the case where the temperature of the bottom side of the molten liquid in the first tank is higher than the temperature of the liquid surface side of the molten liquid, for example, according to the set temperature and set calorific value of each heating unit input from the input unit and other instructions, a signal for controlling the calorific value of each heating unit is output, and the calorific value of each heating unit is controlled, so that the control unit can make the temperature of the molten liquid in the second tank higher than the lowest temperature of the molten liquid in the first tank.

[0058] When using Figure 4 the exemplary manufacturing apparatus 200 to continuously perform heating and melting, as the molten liquid is discharged, the sulfide-based solid electrolyte raw material is continuously supplied into the first tank. In this case, although the effects of the present invention are obtained by the circulation of the molten liquid, there is a possibility that the molten liquid in a state where the reaction has not been fully carried out after being supplied to the first tank is discharged from the discharge portion. In contrast, as Figure 5 exemplified, the discharge portion is provided in the second tank communicated with the first tank through the passing portion. If the temperature of the molten liquid in the second tank is higher than the lowest temperature of the molten liquid in the first tank, it is difficult for the molten liquid to flow into the second tank before being heated to the same or higher temperature as the molten liquid in the second tank. Therefore, the molten liquid that has been sufficiently heated is preferentially discharged, and it is possible to suppress the discharge of the molten liquid in a state where the reaction has not been fully carried out from the discharge portion. It should be noted that the configurations of the first tank and the second tank are not limited to Figure 5 the exemplary manner in which the two tanks are communicated by the passing portion. For example, by providing a partition portion inside one tank, two tanks and a passing portion are substantially formed.

[0059] (sulfide-based solid electrolyte raw material)

[0060] In this manufacturing method, various raw materials can be used as the sulfide-based solid electrolyte raw material (hereinafter, sometimes referred to as this raw material).

[0061] As this raw material, commercially available sulfide-based solid electrolyte raw materials can be used, or sulfide-based solid electrolyte raw materials manufactured from materials can be used. In addition, these sulfide-based solid electrolyte raw materials can be further subjected to known pretreatment. That is, this manufacturing method can appropriately include a process of manufacturing this raw material and a process of performing pretreatment on this raw material.

[0062] Hereinafter, the sulfide-based solid electrolyte raw material will be specifically described. As the sulfide-based solid electrolyte raw material, it generally contains an alkali metal element (R) and a sulfur element (S).

[0063] As the alkali metal element (R), lithium (Li), sodium (Na), potassium (K), etc. can be cited, among which lithium (Li) is preferred. As the alkali metal element (R), substances (components) containing the alkali metal element such as the alkali metal element itself, compounds containing the alkali metal element, etc. can be appropriately combined and used. Among them, as the lithium element, substances (components) containing Li such as Li itself, compounds containing Li, etc. can be appropriately combined and used.

[0064] As the substance containing lithium element (Li), for example, lithium sulfide (Li 2 S), lithium iodide (LiI), lithium carbonate (Li 2 CO 3 ), lithium sulfate (Li 2 SO 4 ), lithium oxide (Li 2 O), lithium nitride (Li 3 N), lithium hydroxide (LiOH) and other lithium compounds, metallic lithium, etc. can be cited. As the substance containing lithium element (Li), from the viewpoint of obtaining the sulfide material, lithium sulfide is preferably used.

[0065] As the sulfur element (S), substances (components) containing S such as S itself, compounds containing S, etc. can be appropriately combined and used.

[0066] As the substance containing sulfur element (S), for example, diphosphorus trisulfide (P 2 S 3 ), diphosphorus pentasulfide (P 2 S 5 ) and other phosphorus sulfides, other sulfur compounds containing phosphorus, as well as elemental sulfur, compounds containing sulfur, etc. can be cited. As the sulfur-containing compound, H 2 S, CS 2 , Na 2 S, iron sulfide (FeS, Fe 2 S 3 , FeS 2 , Fe 1－x S, etc.), bismuth sulfide (Bi 2 S 3 ), antimony sulfide (Sb 2 S 3 ), copper sulfide (CuS, Cu 2 S, Cu 1－x S, etc.), tin sulfide (SnS 2 ), tungsten sulfide (WS 2 ), etc. can be cited. As the substance containing sulfur element (S), from the viewpoint of obtaining the sulfide material, phosphorus sulfide is preferred, and diphosphorus pentasulfide (P 2 S 5These substances may be used alone or in combination of two or more. It should be noted that phosphorus sulfide is considered to be a compound having both a substance containing S and a substance containing P described later.

[0067] From the viewpoint of improving the ionic conductivity of the obtained sulfide-based solid electrolyte, the raw material preferably further contains phosphorus (P). As phosphorus (P), P alone, P-containing compounds and other P-containing substances (components) can be used in appropriate combination.

[0068] Examples of substances containing phosphorus (P) include phosphorus trisulfide (P 2 S 3 ), phosphorus pentasulfide (P 2 S 5 ) and other phosphorus sulfide, sodium phosphate (Na 3 PO 4 ) and phosphorus compounds such as elemental phosphorus. As the substance containing phosphorus element (P), from the viewpoint of further exerting the effect of the present invention, phosphorus sulfide with high volatility is preferred, and phosphorus pentasulfide (P 2 S 5 ). These substances may be used alone or in combination of two or more.

[0069] This raw material can be obtained as a mixed raw material by, for example, appropriately mixing the above substances according to the composition of the target sulfide-based solid electrolyte. The mixing ratio is not particularly limited. For example, from the viewpoint of improving the ionic conductivity of the obtained sulfide-based solid electrolyte, the molar ratio S / R of the sulfur element (S) relative to the alkali metal element (R) in this raw material is preferably 0.65 / 0.35 or less, and more preferably 0.5 / 0.5 or less. In addition, the mixed raw material is preferably obtained by mixing in a prescribed stoichiometric ratio corresponding to the substance used for mixing. As the above-mentioned mixing method, for example, mixing in a mortar, mixing using a medium such as a planetary ball mill, a pin mill, a powder mixer, and mixing without a medium such as air flow can be cited.

[0070] An example of a preferred combination of the alkali metal element and sulfur element contained in the raw material is Li 2 S and P 2 S 5 When the combination Li 2 S and P 2 S 5 When the molar ratio of Li to P is Li / P, it is preferably 40 / 60 or more, and more preferably 50 / 50 or more. In addition, the molar ratio of Li to P is preferably 88 / 12 or less. In addition, the molar ratio of Li to P is preferably 40 / 60 to 88 / 12, and more preferably 50 / 50 to 88 / 12. By adjusting the mixing ratio, P2 S 5 relative to Li 2 There is less S, so it is easy to suppress due to P 2 S 5 The boiling point of S is lower than that of Li 2 The volatilization of sulfur and phosphorus components during heat treatment caused by the melting point of S.

[0071] On the other hand, since lithium sulfide is expensive, from the viewpoint of suppressing the manufacturing cost of sulfide solid electrolytes, lithium compounds other than lithium sulfide, metallic lithium, etc. can be used. Specifically, in this case, the raw material preferably contains one or more selected from metallic lithium, lithium iodide (LiI), lithium carbonate (Li 2 CO 3 ), lithium sulfate (Li 2 SO 4 ), lithium oxide (Li 2 O) and lithium hydroxide (LiOH) as substances containing Li. These substances can be used alone or in combination of two or more.

[0072] The raw material can further contain substances (compounds, etc.) other than the above substances according to the composition of the target sulfide solid electrolyte or as additives, etc.

[0073] For example, in the case of manufacturing a sulfide solid electrolyte containing halogen elements such as F, Cl, Br or I, the raw material preferably contains a halogen element (Ha). In this case, the raw material preferably contains a compound of a halogen element. Examples of compounds containing halogen elements include lithium halides (LiHa) such as lithium fluoride (LiF), lithium chloride (LiCl), lithium bromide (LiBr), lithium iodide (LiI), phosphorus halides, phosphoryl halides, sulfur halides, sodium halides such as sodium chloride (NaCl), barium halides such as barium fluoride (BaF 2 ), boron halides, yttrium halides such as yttrium chloride (YCl 3 ), indium halides such as indium chloride (InCl 3 ), zirconium halides such as zirconium chloride (ZrCl 4 ), lanthanum halides such as lanthanum fluoride (LaF 2 ), etc. From the viewpoint of the reactivity of the raw material, lithium halides are preferred, and LiCl, LiBr, and LiI are more preferred. These compounds can be used alone or in combination of two or more.

[0074] It should be noted that alkali metal halides such as lithium halides are also compounds containing alkali metal elements such as Li. When the raw material contains an alkali metal halide, part or all of the alkali metal elements such as Li in the raw material can be derived from the alkali metal halide such as lithium halide.

[0075] When this raw material contains a halogen element (Ha) and a phosphorus element (P), from the viewpoint of improving the ionic conductivity of the resulting sulfide-based solid electrolyte, etc., the molar equivalent of Ha relative to P in this raw material is preferably 0.2 molar equivalents or more, more preferably 0.5 molar equivalents or more. Further, from the viewpoint of the stability of the resulting sulfide-based solid electrolyte, the molar equivalent of Ha is preferably 4 molar equivalents or less, more preferably 3 molar equivalents or less.

[0076] The resulting sulfide-based solid electrolyte can be an amorphous sulfide-based solid electrolyte according to its purpose. From the viewpoint of improving the ease of forming an amorphous phase, it is also preferable that this raw material contains SiS 2 , B 2 S 3 , GeS 2 , Al 2 S 3 and other sulfides. Since an amorphous phase is easily formed, when obtaining an amorphous by rapid cooling, even if the cooling rate is decreased, an amorphous sulfide-based solid electrolyte can be obtained, and the equipment load can be reduced.

[0077] Further, from the viewpoint of imparting moisture resistance to the sulfide-based solid electrolyte, etc., it is also preferable to contain SiO 2 , B 2 O 3 , GeO 2 , Al 2 O 3 , P 2 O 5 , ZrO 2 , Ta 2 O 5 , TiO 2 , La 2 O 3 and other oxides. These compounds can be used alone or in combination of two or more.

[0078] It should be noted that the above-mentioned sulfides and oxides can be contained in this raw material or can be additionally added when heating and melting this raw material. Further, the addition amount of the above-mentioned sulfides and oxides is preferably 0.1 mass% or more, more preferably 0.5 mass% or more relative to the total amount of the raw material. Further, the addition amount is preferably 50 mass% or less, more preferably 40 mass% or less.

[0079] Further, this raw material can also contain a compound serving as a crystal nucleus described later.

[0080] This manufacturing method is applicable to the case where a compound with high volatility is contained in this raw material. As a compound with high volatility, for example, LiI, B 2 S 3, S, Se, Sb 2 S 3 and P 2 S 5 wait.

[0081] (Heating and melting)

[0082] In the present manufacturing method, the sulfide-based solid electrolyte raw material is supplied to the first tank of the heating furnace, and the sulfide-based solid electrolyte raw material is heated and melted in a gas atmosphere containing sulfur element. The supply of the raw material is carried out, for example, by supplying the above-mentioned sulfide-based solid electrolyte raw material mixed in a predetermined stoichiometric ratio from a raw material supply unit, for example, provided in the first tank. When heating and melting are performed continuously, the continuous supply of the sulfide-based solid electrolyte raw material is preferably quantitatively supplied. There is no particular limitation on the method of quantitative supply, and for example, methods using a screw feeder, a table feeder, air flow conveying, etc. can be cited.

[0083] The heating and melting of the sulfide-based solid electrolyte raw material is carried out in a gas atmosphere containing sulfur. By heating and melting the raw material in an atmosphere containing sulfur, sulfur is introduced into the melt. As a result, the volatilization of sulfur during heating can be suppressed, so the composition of the obtained sulfide-based solid electrolyte can be appropriately controlled. The gas containing sulfur is, for example, a sulfur gas, a hydrogen sulfide gas, a carbon disulfide gas, or a sulfur gas containing a compound or sulfur element.

[0084] As a method for forming a gas atmosphere containing sulfur element in the tank (first tank) of the heating furnace, for example, there can be cited a method of introducing a component containing sulfur element from a sulfur source supply portion provided in the first tank into the tank of the heating furnace. More specifically, there can be cited at least one of a method of introducing a gas containing sulfur element and a method of introducing a solid containing sulfur element. That is, in the present manufacturing method, a gas atmosphere containing sulfur element can be obtained by supplying a gas containing sulfur element to the heating furnace. In addition, in the present manufacturing method, a gas atmosphere containing sulfur element can be obtained by supplying a solid containing sulfur element to the heating furnace. For example, in Figures 3 - 5 When a component containing elemental sulfur is introduced from the sulfur source supply unit 23 , a gas atmosphere containing elemental sulfur is formed in the gas atmosphere unit 12 in contact with the melt 11 .

[0085] As a method of introducing the sulfur-containing gas, for example, there can be mentioned a method of introducing the sulfur-containing gas prepared in advance outside the heating furnace into the tank (first tank) of the heating furnace. The method of preparing the sulfur-containing gas outside the heating furnace is not particularly limited, and for example, it is preferable to heat a sulfur source outside the heating furnace to obtain the sulfur-containing gas.

[0086] The sulfur source may be elemental sulfur or a sulfur compound which is a gas containing sulfur element obtained by heating, without particular limitation. For example, elemental sulfur, hydrogen sulfide, organic sulfur compounds such as carbon disulfide, iron sulfide (FeS, Fe 2 S 3 , FeS 2 , Fe 1－x S, etc.), bismuth sulfide (Bi 2 S 3 ), copper sulfide (CuS, Cu 2 S, Cu 1－x S, etc.), polysulfides such as lithium polysulfide and sodium polysulfide, polysulfides, rubber vulcanized with sulfur, etc. can be cited.

[0087] For example, by heating these sulfur sources in a separately provided sulfur source heating section to generate a gas containing sulfur element, and using an inert gas such as N 2 gas, argon gas, or helium gas as a carrier gas to transport it to the heating section, a sulfur-excess atmosphere section can be formed.

[0088] The temperature for heating the sulfur source can be appropriately selected according to the type of sulfur source used. For example, the temperature for heating the sulfur source is preferably 200°C to 450°C, more preferably 300°C to 400°C.

[0089] Alternatively, a gas atmosphere containing sulfur element can also be formed by introducing a solid containing sulfur element. In this case, by heating the solid containing sulfur element in a heating furnace, a gas containing sulfur element can be obtained to form a gas atmosphere containing sulfur element.

[0090] As the solid containing sulfur element, for example, elemental sulfur, H 2 S, Bi 2 S 3 , iron sulfide, copper sulfide, CS 2 , etc. solid sulfur sources can be cited. For example, by pneumatically transporting the solid sulfur source in a fine state such as powder through a carrier gas to the tank (the first tank) of the heating furnace, the solid containing sulfur element can be introduced into the tank of the heating furnace. The introduction of the solid containing sulfur element can be carried out, for example, from the sulfur source supply section provided in the first tank, or by adding an excessive sulfur source to the sulfide-based solid electrolyte raw material.

[0091] In the sulfur-excess atmosphere section, the sulfur partial pressure is preferably set to 10 -3 to 100 atm. By achieving this sulfur partial pressure, sulfur can be introduced at low cost and efficiently without making the device complex.

[0092] This manufacturing method includes the step of making the temperature on the bottom side of the melt obtained by heating and melting in the first tank higher than the temperature on the liquid surface side of the melt. Thus, as described above, a sulfide-based solid electrolyte can be stably and efficiently manufactured. In the present embodiment, the temperature on the bottom side of the melt in the first tank can be measured by inserting a thermocouple or a thermocouple with a protective tube into the bottom surface portion of the first tank. Or it can be measured by installing a thermocouple on the bottom surface portion outside the first tank. In addition, the temperature on the liquid surface side of the melt in the first tank can be measured by inserting a thermocouple or a thermocouple with a protective tube into the liquid surface of the melt in the first tank. It can also be measured from above using a radiation thermometer. It can also be measured by installing a thermocouple at a position on the outer side surface of the first tank at the same height as the liquid surface portion. The measuring mechanism only needs to be able to measure the temperature of the target position, and it can also be other mechanisms such as a resistance temperature detector other than a thermocouple.

[0093] The temperature on the bottom side of the melt in the first tank is preferably 10 °C or more higher than the temperature on the liquid surface side, more preferably 25 °C or more higher, and still more preferably 50 °C or more higher. The greater the difference between the temperature on the bottom side and the temperature on the liquid surface side, the easier it is to cause the circulation of the melt and the easier it is to appropriately obtain the effects of the present invention. On the other hand, from the viewpoint of homogeneous dissolution of the input raw materials, the difference between the temperature on the bottom side and the temperature on the liquid surface side is preferably 750 °C or less, more preferably 700 °C or less, and still more preferably 650 °C or less. The difference between the temperature on the bottom side and the temperature on the liquid surface side can be 10 to 750 °C, can be 25 to 700 °C, and can be 50 to 650 °C.

[0094] The temperature on the bottom side of the melt in the first tank is preferably 600 °C or more, more preferably 650 °C or more, and still more preferably 700 °C or more. Thus, it is easy to appropriately carry out the melting of the sulfide-based solid electrolyte raw materials and the circulation of the melt. On the other hand, the temperature on the bottom side is preferably 1000 °C or less, more preferably 950 °C or less, still more preferably 900 °C or less, and further preferably 850 °C or less, 800 °C or less, 750 °C or less in sequence. Thus, the heating of the melt is not likely to be excessive, and the amount of components separated from the melt can be suppressed. The temperature on the bottom side of the melt in the first tank can be 600 to 1000 °C, can be 650 to 950 °C, can be 700 to 900 °C, can be 700 to 850 °C, 700 to 800 °C, or 700 to 750 °C.

[0095] The temperature on the liquid surface side of the melt in the first tank is preferably 150 °C or higher, more preferably 200 °C or higher, and still more preferably 250 °C or higher. Thereby, it is easy to appropriately melt the sulfide-based solid electrolyte raw material. On the other hand, the temperature on the liquid surface side is preferably 950 °C or lower, more preferably 900 °C or lower, and still more preferably 850 °C or lower. Thereby, it is easy to appropriately circulate the melt, and the heating of the melt is not likely to be excessive, and the amount of components separated from the melt can be suppressed. The temperature on the liquid surface side of the melt in the first tank can be 150 to 950 °C, can be 200 to 900 °C, or can be 250 to 850 °C.

[0096] The depth of the melt in the first tank is preferably 5 cm or more, more preferably 7.5 cm or more, and still more preferably 10 cm or more. The greater the depth of the melt, the less likely sulfur is to diffuse into the interior of the melt, and thus the effects of the present invention can be more appropriately obtained. In addition, the amount of the melt increases and the productivity improves. The upper limit of the depth of the melt is not particularly limited, and for example, it can also be 5 m or less.

[0097] As described above, in the present manufacturing method, it is preferable that the heating furnace has: a tank (the above-mentioned first tank) for supplying a sulfide-based solid electrolyte raw material, and an additional tank (second tank) for supplying the melt of the sulfide-based solid electrolyte raw material heated and melted in the tank (first tank); continuously performing the step of supplying the sulfide-based solid electrolyte raw material to the tank (first tank) and the step of discharging the melt from the additional tank (second tank) to the outside of the heating furnace, and controlling the temperature of the melt in the additional tank (second tank) to be higher than the lowest temperature of the melt in the tank (first tank). Thereby, it is possible to suppress the discharge of the melt in a state where the reaction has not been sufficiently carried out after being supplied to the first tank from the discharge portion. Here, in the present embodiment, the temperature on the liquid surface side of the melt in the above-mentioned first tank is defined as the lowest temperature of the first tank. In addition, the temperature of the melt in the second tank can be measured by inserting a thermocouple or a thermocouple with a protective tube inside the second tank. In addition, it can also be measured by installing a thermocouple on the outer wall surface of the second tank near the passing portion between the first tank and the second tank. The measuring mechanism only needs to be able to measure the temperature at the target position, and it can also be other mechanisms such as a resistance temperature detector other than a thermocouple.

[0098] The temperature of the molten liquid in the second tank is preferably 10 °C or more higher than the lowest temperature of the first tank, more preferably 25 °C or more higher, and further preferably 50 °C or more higher. The greater the difference between the temperature of the second tank and the lowest temperature of the first tank, the easier it is to appropriately obtain the effect of suppressing the discharge of the molten liquid in the unreacted portion. On the other hand, from the viewpoint of homogeneous dissolution of the input raw materials, the difference between the temperature of the second tank and the lowest temperature of the first tank is preferably 750 °C or less, more preferably 700 °C or less, and further preferably 650 °C or less. The difference between the temperature of the second tank and the lowest temperature of the first tank can be 10 to 750 °C, can also be 25 to 700 °C, or can be 50 to 650 °C.

[0099] The temperature of the molten liquid in the second tank is preferably 600 °C or more, more preferably 650 °C or more, and further preferably 700 °C or more. Therefore, it is easy to appropriately obtain the effect of suppressing the discharge of the molten liquid in the unreacted portion. On the other hand, the temperature of the molten liquid in the second tank is preferably 1000 °C or less, more preferably 950 °C or less, and further preferably 900 °C or less. Gradually, it is even more preferably 850 °C or less, 800 °C or less, 750 °C or less. Thus, the heating of the molten liquid is not likely to be excessive, and the amount of components separated from the molten liquid can be suppressed. The temperature of the molten liquid in the second tank can be 600 to 1000 °C, can also be 650 to 950 °C, can also be 700 to 900 °C, can also be 700 to 900 °C, can also be 700 to 850 °C, 700 to 800 °C, or 700 to 750 °C.

[0100] The time for heating and melting is not particularly limited. For example, it can be 0.5 hours or more, can also be 1 hour or more, or can also be 2 hours or more. In addition, when the components in the molten liquid are deteriorated and decomposed due to heating within an allowable range, the time for heating and melting can be longer. As an actual range, it is preferably 100 hours or less, more preferably 50 hours or less, and further preferably 25 hours or less. In addition, in the case of continuously performing heating and melting, heating and melting can also be continuously performed for a longer time. The time for heating and melting can be, for example, 0.5 to 100 hours, can also be 1 to 50 hours, or can also be 2 to 25 hours.

[0101] The pressure during heating and melting is not particularly limited. For example, normal pressure or slightly positive pressure is preferred, and normal pressure is more preferred.

[0102] During heating and melting, from the viewpoint of preventing side reactions with water vapor, oxygen, etc., the dew point in the furnace (in each tank) is preferably -20 °C or less, and the lower limit is not particularly limited and is usually -80 °C or more. The dew point in the furnace (in each tank) can also be -80 to -20 °C. In addition, the oxygen concentration is preferably 1000 volume ppm or less.

[0103] (Cooling process)

[0104] The present manufacturing method preferably further includes a step of cooling the molten metal obtained by heating and melting to obtain a solid. The cooling can be performed using a known method, and the method is not particularly limited. After the heating and melting step, the molten metal may be further cooled in the heating furnace, or it may be removed from the heating furnace for cooling. When the molten metal is removed from the heating furnace for cooling, the molten metal is discharged from the above-mentioned discharge portion, for example.

[0105] As a more specific method of cooling, for example, a method of making the molten metal flow out onto a water-cooled part, a method of flowing out onto a rotating roller with internal water cooling to obtain a thin sheet, and a method of clamping the molten metal with two pairs of rollers with internal water cooling to obtain a thin sheet, etc., can be cited. In the case of a plate-like body or a thin sheet obtained by cooling the molten metal using the above-mentioned method, from the viewpoint of improving the cooling efficiency, the thickness of the molten metal after flowing out and the obtained solid is preferably thinner. Specifically, the thickness is preferably less than 10 mm, more preferably less than 5 mm. The lower limit of the thickness is not particularly limited, and may be more than 0.01 mm, or more than 0.02 mm. In the case of pouring into a narrow gap and thinly forming, the cooling efficiency is excellent, and a thin sheet-like molded body, a fibrous solid, a powdery solid, etc. can be obtained. The obtained solid is crushed into a size that is easy to handle, etc., and any shape can be obtained. Among them, it is easier to recover with a block-like solid, so it is preferred. Blocks also include plate-like, thin sheet-like or fibrous situations.

[0106] From the viewpoint of maintaining the composition obtained by the heating and melting process, the cooling rate is preferably 0.01°C / sec or more, more preferably 0.05°C / sec or more, and even more preferably 0.1°C / sec or more. In addition, the upper limit of the cooling rate is not particularly limited, but it is generally believed that the cooling rate of the twin rolls with a fast quenching rate is 10 7 ℃ / second or less.

[0107] Here, in the case of a sulfide-based solid electrolyte that is intended to obtain an amorphous solid, it is preferred to quench the melt obtained by heating and melting to obtain a solid. Specifically, the cooling rate during quenching is preferably 10°C / sec or more, more preferably 100°C / sec or more, further preferably 500°C / sec or more, and further preferably 700°C / sec or more. In addition, there is no particular upper limit on the cooling rate, but it is generally believed that the cooling rate of the twin rolls with a fast quenching rate is 10 7 ℃ / second or less.

[0108] On the other hand, by performing slow cooling during the cooling process, at least a part of the solid can be crystallized to obtain a sulfide-based solid electrolyte having a specific crystal structure or a sulfide-based solid electrolyte composed of a crystalline phase and an amorphous phase. The cooling rate during slow cooling is preferably 0.01 °C / second or more, more preferably 0.05 °C / second or more. In addition, the cooling rate is preferably 500 °C / second or less, more preferably 450 °C / second or less. The cooling rate can be less than 10 °C / second or can be 5 °C / second or less. It should be noted that the cooling rate can be appropriately adjusted according to the crystallization conditions.

[0109] Here, the crystal contained in the sulfide-based solid electrolyte is preferably an ion-conductive crystal. Specifically, an ion-conductive crystal means a crystal having a lithium ion conductivity greater than 10 -4 S / cm, more preferably greater than 10 -3 S / cm.

[0110] When it is desired that the solid obtained after cooling is a sulfide-based solid electrolyte containing a crystalline phase, it is preferable to contain a compound serving as a crystal nucleus in the melt obtained in the heat melting process. Thereby, crystals are likely to precipitate in the cooling process. The method of containing a compound serving as a crystal nucleus in the melt is not particularly limited, and examples thereof include adding a compound serving as a crystal nucleus to a raw material, a heat-treated raw material, and adding a compound serving as a crystal nucleus to the melt during heat melting.

[0111] Examples of the compound serving as a crystal nucleus include oxides, oxynitrides, nitrides, carbides, other chalcogenides, halides, etc. The compound serving as a crystal nucleus is preferably a compound having a certain degree of compatibility with the melt. It should be noted that a compound that is completely incompatible with the melt cannot serve as a crystal nucleus.

[0112] When it is desired that the solid obtained after cooling is a sulfide-based solid electrolyte containing a crystalline phase, the content of the compound serving as a crystal nucleus in the melt is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and further preferably 1% by mass or more. On the other hand, from the viewpoint of suppressing a decrease in lithium ion conductivity, the content of the compound serving as a crystal nucleus in the melt is preferably 20% by mass or less, more preferably 10% by mass or less.

[0113] When it is desired that the solid obtained after cooling is an amorphous sulfide-based solid electrolyte, it is preferable that the melt does not contain a compound serving as a crystal nucleus or its content is below a specified amount. Specifically, the content of the compound serving as a crystal nucleus in the melt is preferably 1% by mass or less, more preferably 0.1% by mass or less. The content of the compound serving as a crystal nucleus in the melt can also be less than 0.01% by mass.

[0114] (Reheating treatment)

[0115] When the solid obtained by cooling the melt is an amorphous sulfide-based solid electrolyte or a sulfide-based solid electrolyte containing an amorphous phase, the manufacturing method further includes a step of reheating the solid electrolyte. In addition, by reheating a sulfide-based solid electrolyte containing crystals of the sulfide-based solid electrolyte, the ions in the crystal structure can be rearranged, improving the lithium ion conductivity. It should be noted that the reheating treatment refers to heating the powder obtained by cooling for at least one of crystallization and rearrangement of the ions in the crystal structure.

[0116] (Crushing)

[0117] The obtained sulfide-based solid electrolyte can be further crushed to make it finer. As a method of crushing, for example, a wet crushing method can be cited. In the case of the wet crushing method, the type of solvent used is not particularly limited. Since the sulfide-based solid electrolyte has the property of being easily deteriorated by reacting with moisture, it is preferable to use a non-aqueous organic solvent. The type of non-aqueous organic solvent is not particularly limited, and examples thereof include hydrocarbon solvents, organic solvents containing a hydroxyl group, organic solvents containing an ether group, organic solvents containing a carbonyl group, organic solvents containing an ester group, organic solvents containing an amino group, organic solvents containing a formyl group, organic solvents containing a carboxyl group, organic solvents containing an amide group, organic solvents containing a benzene ring, organic solvents containing a mercapto group, organic solvents containing a thioether group, organic solvents containing a thioester group, organic solvents containing a disulfide group, and halogenated alkanes. As hydrocarbon solvents, for example, cyclohexane, heptane, octane, and toluene can be cited. From the viewpoint of low saturated water concentration, cyclohexane, heptane, and octane are preferable. In addition, from the viewpoint of adjusting the water concentration, a mixed solvent of these hydrocarbon solvents and toluene or dibutyl ether is preferable. From the viewpoint of preventing the lithium ion conductivity from decreasing due to the reaction of the sulfide-based solid electrolyte with water during the crushing of the sulfide-based solid electrolyte, the lower the water concentration of the non-aqueous organic solvent, the more preferable. The water concentration of the non-aqueous organic solvent can be, for example, 170 mass ppm or less, 150 mass ppm or less, 120 mass ppm or less, or 100 mass ppm or less.

[0118] The wet crushing method can be carried out, for example, using a crusher such as a ball mill, a planetary ball mill, or a bead mill. In the wet crushing, in addition to the above solvent, an ether compound, an ester compound, or a nitrile compound can be added as an additive (dispersant).

[0119] In the sulfide-based solid electrolyte obtained by wet pulverization, when a solvent or an additive remains, a drying process can be performed. As drying conditions, for example, the temperature can be 100°C to 200°C. The drying time is not particularly limited and can be, for example, 10 minutes or more and 24 hours or less. In addition, the drying process can be carried out under reduced pressure. For example, the absolute pressure can be 50 kPa or less. The drying process can be carried out using a hot plate, a drying furnace, an electric furnace, or the like.

[0120] This manufacturing method can be used to manufacture various solid electrolytes, and specific examples thereof are shown in Table 1 and Table 2. That is, by melting and synthesizing the raw materials described in the raw material column of Table 1 or Table 2, the solid electrolytes described in the representative composition column can be manufactured. It should be noted that the values shown in Table 1 and Table 2 are only examples, and the scope of application of the present invention is not limited to these.

[0121]

[0122]

[0123] (Sulfide-based solid electrolyte)

[0124] As the sulfide-based solid electrolyte obtained in this manufacturing method, a sulfide-based solid electrolyte containing a lithium element can be cited. As the sulfide-based solid electrolyte obtained in this manufacturing method, for example, Li 10 GeP 2 S 12 and other sulfide-based solid electrolytes having an LGPS-type crystal structure; Li 6 PS 5 Cl, Li 5.4 PS 4.4 Cl 1.6 and Li 5.4 PS 4.4 Cl 0.8 Br 0.8 and other sulfide-based solid electrolytes having an argyrodite-type crystal structure; Li-P-S-Ha-based (Ha is at least one element selected from halogen elements) glass-ceramics; and Li 7 P 3 S 11 and other LPS glass-ceramics, etc.

[0125] In addition, as the sulfide-based solid electrolyte obtained in this manufacturing method, the substances described in Table 1 and Table 2 above can be cited.

[0126] The sulfide-based solid electrolyte can be an amorphous sulfide-based 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, depending on its purpose. From the viewpoint of lithium ion conductivity, the crystalline phase is more preferably the argyrodite-type crystalline phase.

[0127] As a sulfide-based solid electrolyte having excellent lithium ion conductivity, a sulfide-based solid electrolyte having elements of Li-P-S-Ha is preferred, and a crystalline phase is more preferred. In addition, for this halogen element, it is preferred that the halogen element is derived from one or more selected from lithium chloride, lithium bromide, and lithium iodide.

[0128] When the lithium ion conductivity of the sulfide-based solid electrolyte is used in a lithium ion secondary battery, from the viewpoint of making the battery characteristics good, it is preferably 1.0×10 -4 S / cm or more, more preferably 5.0×10 -4 S / cm or more, further preferably 1.0×10 -3 S / cm or more, and particularly preferably 5.0×10 -3 S / cm or more. The above lithium ion conductivity is measured using an AC impedance measurement device (for example, VSP, a potentiostat / galvanostat manufactured by Bio-LLogic Sciences Instruments), and the measurement conditions are set as follows: measurement frequency: 100 Hz to 1 MHz, measurement voltage: 100 mV, measurement temperature: 25°C.

[0129] The obtained sulfide-based solid electrolyte can be identified by analysis of the crystal structure by X-ray diffraction (XRD) measurement and analysis of the elemental composition by various methods such as ICP emission spectrometry, atomic absorption spectrometry, and ion chromatography. For example, P and S can be measured by ICP emission spectrometry, Li can be measured by atomic absorption spectrometry, and Ha can be measured by ion chromatography.

[0130] In addition, by performing Raman spectroscopy measurement, the homogeneity of the composition of the sulfide-based solid electrolyte can be evaluated. Specifically, Raman spectroscopy measurement is performed at two or more arbitrary points on a sample obtained from the obtained sulfide-based solid electrolyte. It should be noted that from the viewpoint of improving the accuracy of evaluation, the number of measurement points is preferably 8 or more, and more preferably 10 or more. As the preferred conditions for Raman spectroscopy measurement when evaluating the homogeneity of the composition of the sulfide-based solid electrolyte, for example, the spot diameter can be set to 3 μm and the number of measurement points can be set to 10. By setting the spot diameter to 3 μm, the analysis region in Raman spectroscopy measurement becomes a size suitable for evaluating the homogeneity of the composition of the sulfide-based solid electrolyte at the microscopic level.

[0131] It can be considered that in each measurement result, from PS4 3－ The smaller the deviation of the peak wavenumber (peak position) of the structure of the sulfide-based solid electrolyte, the more homogeneous the composition of the sulfide-based solid electrolyte. Alternatively, it can be considered that the smaller the deviation of the full width at half maximum of the peak from the structure of the sulfide-based solid electrolyte, the more homogeneous the composition of the sulfide-based solid electrolyte.

[0132] Although it also depends on the composition of the obtained sulfide-based solid electrolyte, it is preferable to identify the peak from the P-S bond as the peak from the structure of the sulfide-based solid electrolyte. The position of the peak from the P-S bond varies depending on the composition system, and typically it is included between 350 cm -1 ~500 cm -1 Hereinafter, in this specification, the deviation of the peak position and the deviation of the full width at half maximum of the peak refer to the values confirmed for the peak with the strongest intensity among the peaks from the P-S bond.

[0133] The deviation of the peak position can be evaluated as follows. That is, the standard deviation of the peak position at each measurement point obtained by Raman spectroscopy measurement is calculated. When it is recorded as (peak position average value) ± (standard deviation), the value of the standard deviation is preferably within 2 cm -1 or less, more preferably within 1 cm -1 or less, and further preferably within 0.5 cm -1 or less. It should be noted that here the peak position refers to the position of the peak top. For example, regarding the sulfide-based solid electrolyte obtained by this manufacturing method, when Raman spectroscopy measurement is performed with a spot diameter of 3 μm and the number of measurement points of 10, the standard deviation of the peak position of the peak from the P-S bond between 350 cm -1 ~500 cm -1 is preferably within 2 cm -1 or less, more preferably within 1 cm -1 or less, and further preferably within 0.5 cm -1 or less.

[0134] The deviation of the full width at half maximum of the peak can be evaluated as follows. That is, the standard deviation of the full width at half maximum of the peak at each measurement point obtained by Raman spectroscopy measurement is calculated by the method of obtaining the full width at half maximum of each peak and calculating the standard deviation of this value. When it is recorded as (average value of full width at half maximum of the peak) ± (standard deviation), the value of the standard deviation is preferably within 2 cm -1 or less, more preferably within 1.5 cm -1or less. It should be noted that the full width at half maximum of the peak refers to the width at which the value of half of the peak intensity of the peak from the above P-S bond intersects with the peak from the P-S bond when drawing the Raman spectrum. For example, regarding the sulfide-based solid electrolyte obtained by this manufacturing method, when performing spectral measurement with a spot diameter of 3 μm and the number of measurement points of 10, the standard deviation of the full width at half maximum of the peak from the P-S bond within 350 cm -1 to 500 cm -1 is preferably 2 cm -1 or less, and more preferably 1.5 cm -1 or less.

[0135] It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be adopted within the scope of the present invention. For example, the present invention is not limited to the above embodiments, and can be appropriately deformed and improved, etc. In addition, the materials, shapes, dimensions, numbers, and arrangement positions of the respective constituent elements in the above embodiments can be arbitrary as long as the present invention can be implemented, and there is no limitation.

[0136] Examples

[0137] Examples are given below to specifically describe the present invention, but the present invention is not limited thereto. Examples 1-3 to 1-5 are examples, Examples 1-1 and 1-2 are comparative examples, and Examples 2-1 to 2-5 are reference examples.

[0138] (Examples 1-1 to 1-5)

[0139] Assume a case where the raw material of the sulfide-based solid electrolyte is heated and melted in a gas atmosphere containing sulfur element. The temperature on the liquid surface side and the temperature on the bottom side of the melt in each example are set as shown in Table 3. Except for this, the simulations of Examples 1-1 to 1-5 are carried out according to the following conditions and methods. The amount of sulfur element introduced into the melt from the gas atmosphere containing sulfur element is estimated through this simulation. It should be noted that in the following simulations, the conditions are set using the representative physical property values of the sulfide-based solid electrolyte, and it is considered that the same results can be obtained in sulfide-based solid electrolytes with various compositions.

[0140] (Method)

[0141] (1) Assume that in the tank (the first tank) of the heating furnace, the melt occupies a cylindrical region with a diameter of 100 mm × a height of 100 mm, and a semi-cylindrical model (1 / 2 symmetry model) as shown in Figure 6 is used to model the melt according to the following conditions and analysis methods. The temperature of surface A in Figure 6 is set as the temperature on the liquid surface side of the melt (upper temperature), and the temperature of surface B is set as the temperature on the bottom side of the melt (lower temperature).

[0142] (2) Calculate the following reaction for the liquid level of the melt (surface A).

[0143] (Electrolyte before sulfur addition) + S → (Electrolyte after sulfur addition)

[0144] Reaction rate: 1 × Molar concentration before sulfur addition = Molar concentration of electrolyte after sulfur addition generated kmol / m 2 / s

[0145] (3) Conduct a reaction calculation for 120 seconds, and calculate the amount of sulfur added to the melt (wt%, average sulfur addition concentration) based on the following formula for the concentration of the melt after the reaction. The results are shown in Table 3.

[0146] 0.3 × 32 / 266 × Molar concentration of electrolyte after sulfur addition

[0147] Here, the molar concentration of the electrolyte after sulfur addition refers to the molar concentration of the electrolyte in the state after addition relative to the electrolyte before addition. That is, the molar concentration of the electrolyte after sulfur addition when sulfur fully enters the saturated state of the entire melt is 1. Assuming that if sulfur addition reaches the saturated state, the molar concentration of sulfur increases by 0.3, the formula for calculating the weight percentage concentration of the added sulfur is as above. In addition, calculations are performed with the molecular weight of sulfur being 32 and the molecular weight of the sulfide-based solid electrolyte being 266.

[0148] (Conditions)

[0149] · Viscosity of the melt: 0.01 Pa·s

[0150] · Specific gravity of the melt: Set to the value obtained by the following formula.

[0151] Density (kg / m 3 ) = -0.5812 × Temperature (°C) + 2236.874699

[0152] · Thermal conductivity of the melt: 0.620271 W / m·K

[0153] · Diffusion coefficient of the reaction melt to the unreacted part: 4E - 9 m 2 / s

[0154] · Analysis software: starCCM ver2022.1

[0155] · Turbulence model: K - ε turbulence

[0156] · Implicit solution unsteady analysis: Time step 0.005 s, calculation physical time 120 s

[0157] It should be noted that the "diffusion coefficient of the reaction melt to the unreacted part" refers to the velocity coefficient when the melt added with sulfur components diffuses into the melt without added sulfur components.

[0158] [Table 3]

[0159] Table 3

[0160]

[0161] (Examples 2-1 to 2-5)

[0162] Respectively, Li 2 S (manufactured by Sigma, purity 99.98%), P 2 S 5 (manufactured by Sigma, purity 99%) and LiCl (manufactured by Sigma, purity 99.99%) were blended in a molar ratio of 1.9:0.5:1.6. Sulfur (manufactured by Sigma, purity 99.998%) in the amount shown in Table 4 was added to the resulting mixed raw material, and the mixture was heated and melted at 750°C for 0.5 hours to produce sulfide-based solid electrolytes containing argyrodite-type crystals of Examples 2-1 to 2-5. The lithium ion conductivity of the obtained sulfide-based solid electrolytes was measured according to the following method. The results are shown in Table 4.

[0163] (Evaluation of lithium ion conductivity)

[0164] The sulfide-based solid electrolytes of each example were pulverized to obtain sulfide-based solid electrolyte powders with an average particle size of 10 μm. The sulfide-based solid electrolyte powders were formed into compacts at a pressure of 380 MPa and used as measurement samples. The measurement was carried out using an alternating current impedance measurement device (manufactured by Bio-Logic Sciences Instruments, potentiostat / galvanostat VSP). The measurement conditions were set as follows: measurement frequency: 100 Hz to 1 MHz, measurement voltage: 100 mV, measurement temperature: 25°C.

[0165] [Table 4]

[0166] Table 4

[0167]

[0168] According to the results in Table 3, in Examples 1-3 to 1-5 as the examples, compared with Examples 1-1 and 1-2 as the comparative examples, the concentration of sulfur element in the melt became larger. This can be considered that by making the temperature on the bottom side of the melt higher than the temperature on the liquid surface side of the melt, the reaction proceeds uniformly, and the sulfur component is introduced. As a result, as a whole, the addition concentration of sulfur becomes larger. In addition, according to Table 3, in Examples 1-3 to 1-5, a larger amount of sulfur can be introduced within the same reaction time, and excellent productivity is also obtained.

[0169] In addition, according to the results in Table 4, in the sulfide-based solid electrolyte, as the addition concentration of sulfur increases, the lithium ion conductivity tends to increase. Therefore, by uniformly introducing a sulfur component into the melt through the present manufacturing method, it is possible to suppress the shortage of the sulfur component that can reduce the lithium ion conductivity, and to stabilize the quality of the obtained sulfide-based solid electrolyte.

[0170] As described above, the present specification discloses the following matters.

[0171] 1. A method for manufacturing a sulfide-based solid electrolyte, which is a method for manufacturing a sulfide-based solid electrolyte by supplying a raw material for a sulfide-based solid electrolyte to a tank of a heating furnace and heating and melting the raw material for a sulfide-based solid electrolyte in a gas atmosphere containing a sulfur element, including obtaining a melt by the above heating and melting, and a step of making the temperature of the bottom side of the melt higher than the temperature of the liquid surface side of the melt in the tank.

[0172] 2. The method for manufacturing a sulfide-based solid electrolyte according to the above 1, wherein the steps of supplying the raw material for a sulfide-based solid electrolyte to the tank and discharging the melt out of the heating furnace are continuously performed.

[0173] 3. The method for manufacturing a sulfide-based solid electrolyte according to the above 1 or 2, wherein the depth of the melt in the tank is 50 mm or more.

[0174] 4. The method for manufacturing a sulfide-based solid electrolyte according to any one of the above 1 to 3, wherein in the tank, the temperature of the bottom side of the melt is 700 °C or more.

[0175] 5. The method for manufacturing a sulfide-based solid electrolyte according to any one of the above 1 to 4, wherein in the tank, the temperature of the bottom side of the melt is 10 °C or more higher than the temperature of the liquid surface side of the melt.

[0176] 6. The method for manufacturing a sulfide-based solid electrolyte according to any one of the above 1 to 5, wherein the gas atmosphere containing a sulfur element is obtained by supplying a gas containing a sulfur element to the heating furnace.

[0177] 7. The method for manufacturing a sulfide-based solid electrolyte according to any one of the above 1 to 6, wherein the gas atmosphere containing a sulfur element is obtained by supplying a solid containing a sulfur element to the heating furnace.

[0178] 8. The method for manufacturing a sulfide-based solid electrolyte according to any one of the above 1 to 7, wherein

[0179] The above heating furnace has: the above tank for supplying the above sulfide-based solid electrolyte raw material, and an additional tank for supplying the melt of the above sulfide-based solid electrolyte raw material heated and melted in the above tank.

[0180] The steps of continuously supplying the above sulfide-based solid electrolyte raw material to the above tank and discharging the above melt from the above additional tank to the outside of the above heating furnace are carried out, and the temperature of the above melt in the above additional tank is controlled to be higher than the lowest temperature of the above melt in the above tank.

[0181] 9. A manufacturing apparatus for a sulfide-based solid electrolyte, comprising:

[0182] A heating furnace, comprising a tank and a heating unit for heating and melting a sulfide-based solid electrolyte raw material in a gas atmosphere containing sulfur element, and

[0183] A control unit that controls the calorific value of the above heating unit so that the temperature of the bottom side of the melt obtained by the above heating and melting is higher than the temperature of the liquid surface side of the above melt.

[0184] 10. The manufacturing apparatus for a sulfide-based solid electrolyte according to the above 9, wherein

[0185] The above heating furnace has: the above tank for supplying the above sulfide-based solid electrolyte raw material, an additional tank for supplying the melt of the above sulfide-based solid electrolyte raw material heated and melted in the above tank, the above heating unit for heating and melting the above sulfide-based solid electrolyte raw material in the above tank, and an additional heating unit for heating the above melt in the above additional tank,

[0186] The above control unit controls the calorific value of the above heating unit and the calorific value of the above additional heating unit so that the temperature of the above melt in the above additional tank is higher than the lowest temperature of the above melt in the above tank.

[0187] Although the present invention has been described in detail with reference to specific embodiments, various changes and modifications can be made without departing from the spirit and scope of the present invention, which is obvious to those skilled in the art. This application is based on a Japanese patent application filed on November 2, 2022 (Japanese Patent Application No. 2022-176693), the content of which is incorporated herein by reference.

[0188] Symbolic Explanation

[0189] 100, 200, 300 Manufacturing Apparatus

[0190] 1 Heating Furnace

[0191] 10 First Tank (Tank)

[0192] 20 Second Tank (Additional Tank)

[0193] 11 melt

[0194] 12 gas atmosphere section

[0195] 5a, 5b, 5c First heating section (heating section)

[0196] 6a, 6b Second heating section (additional heating section)

[0197] 7 passage section

[0198] 21 raw material supply section

[0199] 23 sulfur source supply section

[0200] 25 discharge section

[0201] CTL control section

Claims

1. A method for manufacturing a sulfide-based solid electrolyte, which supplies a sulfide-based solid electrolyte raw material to a trough of a heating furnace and heats and melts the sulfide-based solid electrolyte raw material in a gas atmosphere containing sulfur element, includes a step of obtaining a melt through the heating and melting, and making the temperature of the bottom side of the melt higher than the temperature of the liquid surface side of the melt in the trough.

2. The method for manufacturing a sulfide-based solid electrolyte according to claim 1, wherein, the steps of supplying the sulfide-based solid electrolyte raw material to the trough and discharging the melt out of the heating furnace are continuously performed.

3. The method for manufacturing a sulfide-based solid electrolyte according to claim 1, wherein, the depth of the melt in the trough is 50 mm or more.

4. The method for manufacturing a sulfide-based solid electrolyte according to claim 1, wherein, in the trough, the temperature of the bottom side of the melt is 700 °C or more.

5. The method for manufacturing a sulfide-based solid electrolyte according to claim 1, wherein, in the trough, the temperature of the bottom side of the melt is 10 °C or more higher than the temperature of the liquid surface side of the melt.

6. The method for manufacturing a sulfide-based solid electrolyte according to claim 1, wherein, the gas atmosphere containing sulfur element is obtained by supplying a gas containing sulfur element to the heating furnace.

7. The method for manufacturing a sulfide-based solid electrolyte according to claim 1, wherein, the gas atmosphere containing sulfur element is obtained by supplying a solid containing sulfur element to the heating furnace.

8. The method for manufacturing a sulfide-based solid electrolyte according to any one of claims 1 to 7, wherein, the heating furnace has: the trough for supplying the sulfide-based solid electrolyte raw material, and an additional trough for supplying the melt of the sulfide-based solid electrolyte raw material heated and melted in the trough, the steps of supplying the sulfide-based solid electrolyte raw material to the trough and discharging the melt from the additional trough out of the heating furnace are continuously performed, and the temperature of the melt in the additional trough is controlled to be higher than the lowest temperature of the melt in the trough.

9. A manufacturing apparatus for a sulfide-based solid electrolyte, comprising: a heating furnace, which has a trough and a heating part for heating and melting a sulfide-based solid electrolyte raw material in a gas atmosphere containing sulfur element, and a control part, which controls the calorific value of the heating part so that the temperature of the bottom side of the melt obtained through the heating and melting is higher than the temperature of the liquid surface side of the melt.

10. The manufacturing apparatus for a sulfide-based solid electrolyte according to claim 9, wherein, the heating furnace has: the trough for supplying the sulfide-based solid electrolyte raw material, an additional trough for supplying the melt of the sulfide-based solid electrolyte raw material heated and melted in the trough, the heating part for heating and melting the sulfide-based solid electrolyte raw material in the trough, and an additional heating part for heating the melt in the additional trough. The control unit controls the calorific value of the heating unit and the calorific value of the additional heating unit so that the temperature of the molten liquid in the additional tank is higher than the lowest temperature of the molten liquid in the tank.

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