METHOD FOR PRODUCING SOLID ELECTROLYTE MATERIAL HAVING α-Li3PS4 PHASE, AND SOLID ELECTROLYTE MATERIAL

Abstract

The present invention addresses the problem of providing a method for producing a solid electrolyte material having an α-Li3PS4 phase. The problem is solved by a method for producing a solid electrolyte material having an α-Li3PS4 phase, the method comprising a step for heating a Li-ion conductive sulfide material, which contains Li, P, and S but does not contain F and Cl and does not have an α-Li3PS4 phase, to a temperature in the range of 230°C to 350°C, wherein the temperature increase rate at 200°C is at least 100 °C / min.

Description

Method for producing a solid electrolyte material having an α-Li3PS4 phase, solid electrolyte material

[0001] The present invention relates to a method for producing a solid electrolyte material having an α-Li3PS4 phase, and the solid electrolyte material.

[0002] In recent years, there has been an increasing demand for lithium-ion secondary batteries to store power in automobiles such as electric vehicles and hybrid vehicles, and in power generation devices such as solar cells and wind power generators. Furthermore, from the perspective of ensuring safety, active research has been conducted into all-solid-state batteries that use solid electrolytes instead of liquid electrolytes in the electrolyte layer. Further improvements in the performance of these lithium-ion secondary batteries and all-solid-state batteries are being sought.

[0003] As a solid electrolyte for all-solid-state lithium batteries, LPS-based sulfide-based solid electrolytes have attracted attention due to their high electrical conductivity, and various studies are being conducted. For example, Patent Document 1 discloses an LPS-based sulfide-based solid electrolyte obtained by mechanical milling Li2S, P2S5, and LiBr. Furthermore, Patent Documents 2 and 3 describe the crystal structure of LPS-based sulfide-based solid electrolytes.

[0004] JP 2017-095351 A JP 2017-033770 A JP 2018-174130 A

[0005] Among the crystalline structures of LPS-based sulfide-based solid electrolytes, the α-Li3PS4 phase, known as the high-temperature phase, is known to have excellent electrical conductivity. However, it is difficult to maintain the α-Li3PS4 phase at room temperature. Therefore, a new method for producing LPS-based sulfide-based solid electrolytes that have the α-Li3PS4 phase even at room temperature has been desired.

[0006] The present inventors discovered that a solid electrolyte material having the α-Li3PS4 phase at room temperature can be provided by examining the processing conditions according to the composition of a Li-ion conductive sulfide material, and thus arrived at the present invention. Thus, in a first aspect, the present invention provides a method for producing a solid electrolyte material having the α-Li3PS4 phase, the method comprising the steps of heating a Li-ion conductive sulfide material containing Li, P, and S but not containing F or Cl and not having the α-Li3PS4 phase, to a temperature in the range of 230°C to 350°C, wherein the heating rate at 200°C is 100°C / min or more.

[0007] Furthermore, the present inventors have found that by examining the composition of a Li-ion conductive sulfide material, it is possible to provide a solid electrolyte material having the α-Li3PS4 phase at room temperature without controlling the heating rate, and have arrived at the present invention. Thus, in a second aspect, the present invention provides a method for producing a solid electrolyte material having the α-Li3PS4 phase, the method comprising the step of heating a Li-ion conductive sulfide material containing Li, P, and S, and F and / or Cl, and not having the α-Li3PS4 phase, to a temperature within the range of 200°C to 300°C.

[0008] According to the present invention, there is provided a solid electrolyte material containing Li, P, S, and F, having a composition represented by Li3PS4·aLiF (wherein a satisfies the formula 0<a≦2.0), and having an α-Li3PS4 phase at room temperature.

[0009] According to the present invention, there is provided a solid electrolyte material having an α-Li3PS4 phase, which is obtained by the above production method.

[0010] According to the present invention, there is provided a method for producing a solid electrolyte material having an α-Li3PS4 phase.

[0011] FIG. 1 is a reference diagram of a peak containing the α-Li3PS4 phase in an XRD pattern. FIG. 2 is a diagram showing the specific volume and Li3PS4 phase transition during crystallization of Li3PS4 by rapid heating and rapid cooling. FIG. 3 is a diagram showing XRD patterns of solid electrolyte materials of Examples 1 to 4 and Comparative Example 2. FIG. 4 is a diagram showing XRD patterns of solid electrolyte materials of Examples 5 to 11 and Comparative Examples 3 and 4. FIG. 5 is a diagram showing XRD patterns of solid electrolyte materials of Examples 12 to 18 and Comparative Example 5. FIG. 6 is a diagram showing XRD patterns of solid electrolyte materials of Comparative Examples 1 and 6 to 9. FIG. 7 is a diagram showing XRD patterns of solid electrolyte materials of Examples 19 and 20 and Comparative Examples 10 and 11. FIG. 8 is a diagram showing XRD patterns of solid electrolyte materials of Examples 19, 21 to 24 and Comparative Example 6. FIG. 9 is a diagram showing XRD patterns of solid electrolyte materials of Examples 25 to 28 and Comparative Examples 12 and 13. FIG. 10 is a diagram showing XRD patterns of solid electrolyte materials of Examples 29 to 32 and Comparative Examples 14 and 15. FIG. 11 is a diagram showing XRD patterns of solid electrolyte materials of Examples 33 to 37 and Comparative Examples 16 and 17. 1 shows XRD patterns of the solid electrolyte materials of Examples 38 to 42 and Comparative Examples 6 and 17. 1 shows XPS spectra of F1S after mechanochemical treatment at each LPS-F system composition. 1 shows XPS spectra of F1S after heat treatment at each LPS-F system composition. 1 shows XPS spectra of FKL1 after mechanochemical treatment at each LPS-F system composition. 1 shows XPS spectra of FKL1 after heat treatment at each LPS-F system composition. 1 shows Arrhenius plots of the solid electrolyte materials of Examples 19 and 23 and Comparative Examples 1, 6 to 8. 1 shows the results of TG-DTA measurements on the solid electrolyte materials of Comparative Examples 1, 6, 12, 14 and 16. 1 shows Raman spectra (100-600 cm) of the solid electrolyte materials of Examples 28, 32, 36 and 41. -1 ) is a diagram showing the Raman spectra (100-600 cm) of the solid electrolyte materials of Comparative Examples 6, 12, 14, and 16. -11 is a diagram showing the composition and heat treatment temperature dependence of precipitated phases in a Li3PS4 system and a Li3PS4-LiF system; FIG. 2 is a reference diagram showing XRD patterns of Li3PS4 crystal polymorphs; and FIG. 3 is a diagram showing XRD patterns of the solid electrolyte material of Example 40 immediately after production and the solid electrolyte material of Example 40 stored at 25°C for 500 hours after production.

[0012] In this specification, "x to y" (x and y are specific values) means at least x and at most y (that is, both ends are included) unless otherwise specified.

[0013] (Method for Producing a Solid Electrolyte Material Having an α-Li3PS4 Phase) The present invention provides a method for producing a solid electrolyte material having an α-Li3PS4 phase, comprising the step of heating a Li-ion conductive sulfide material containing Li, P, and S but not containing F or Cl, and not containing the α-Li3PS4 phase, to a temperature within a range of 230°C to 350°C, wherein the heating rate at 200°C is 100°C / min or more. In one specific embodiment, the present invention provides a method for producing a solid electrolyte material having an α-Li3PS4 phase, comprising the step of heating a Li-ion conductive sulfide material containing Li, P, and S, and F and / or Cl, and not containing the α-Li3PS4 phase, to a temperature within a range of 200°C to 300°C.

[0014] In one specific embodiment, the present invention provides a method for producing a solid electrolyte material having the α-Li3PS4 phase, comprising the step of heating a Li-ion conductive sulfide material containing Li, P, and S but not containing F or Cl, and not having the α-Li3PS4 phase, to a temperature within the range of 230°C to 350°C, wherein the heating rate at 200°C is 150°C / min or more. In one specific embodiment, the present invention provides a method for producing a solid electrolyte material having the α-Li3PS4 phase, comprising the step of heating a Li-ion conductive sulfide material containing Li, P, and S but not containing F or Cl, and in an amorphous state, to a temperature within the range of 230°C to 350°C, wherein the heating rate at 200°C is 100°C / min or more. In one specific embodiment, the present invention provides a method for producing a solid electrolyte material having an α-Li3PS4 phase, comprising the step of heating a Li-ion conductive sulfide material containing Li, P, and S but not containing F or Cl, and which does not have an α-Li3PS4 phase or is in an amorphous state, to a temperature within a range of 230°C to 350°C, wherein the heating rate at 200°C is 100°C / min or more. In one specific embodiment, the present invention provides a method for producing a solid electrolyte material having an α-Li3PS4 phase, comprising the step of heating a Li-ion conductive sulfide material containing Li, P, and S but not containing F or Cl, and which does not have an α-Li3PS4 phase or is in an amorphous state, to a temperature within a range of 230°C to 350°C, wherein the heating rate at 200°C is 150°C / min or more. In one specific embodiment, the present invention provides a method for producing a solid electrolyte material having an α-Li3PS4 phase, comprising the step of heating a Li-ion conductive sulfide material that contains Li, P, and S, and F and / or Cl, and that is in an amorphous state, to a temperature within a range of 200° C. to 300° C. In one specific embodiment, the present invention provides a method for producing a solid electrolyte material having an α-Li3PS4 phase, comprising the step of heating a Li-ion conductive sulfide material that contains Li, P, and S, and F and / or Cl, and that does not have an α-Li3PS4 phase or is in an amorphous state, to a temperature within a range of 200° C. to 300° C.

[0015] In one specific embodiment, the present invention provides a method for producing a solid electrolyte material having the α-Li3PS4 phase at room temperature, comprising the step of heating a Li-ion conductive sulfide material containing Li, P, and S but not containing F or Cl and not having the α-Li3PS4 phase, to a temperature within the range of 230°C to 350°C, wherein the heating rate at 200°C is 100°C / min or more. In one specific embodiment, the present invention provides a method for producing a solid electrolyte material having the α-Li3PS4 phase at room temperature, comprising the step of heating a Li-ion conductive sulfide material containing Li, P, and S, and F and / or Cl, and not having the α-Li3PS4 phase, to a temperature within the range of 200°C to 300°C. Hereinafter, these production methods may be simply referred to as the present production methods.

[0016] (Li-ion Conductive Sulfide Material) The Li-ion conductive sulfide material (hereinafter also simply referred to as sulfide material) in this production method is not particularly limited as long as it is a material that has Li-ion conductivity, contains Li, P, and S but does not contain F or Cl, and does not have an α-Li3PS4 phase, or a material that has Li-ion conductivity, contains Li, P, and S, and F and / or Cl, and does not have an α-Li3PS4 phase. Examples of materials that have Li-ion conductivity, contain Li, P, and S but do not contain F or Cl, and do not have an α-Li3PS4 phase include Li3PS4, Li4P2S6, Li7PS6, and Li7P3S (which do not have an α-Li3PS4 phase). 11 , Li 13 P3S 12Examples of materials that have Li ion conductivity, contain Li, P, and S, and F and / or Cl, and do not have the α-Li3PS4 phase include Li3PS4·LiF, Li3PS4·0.8LiF, Li3PS4·0.5LiF, Li3PS4·0.2LiF, Li3PS4·0.1LiF, Li3PS4·LiCl, Li3PS4·0.8LiCl, Li3PS4·0.5LiCl, Li3PS4·0.2LiCl, and Li3PS4·0.1LiCl. The sulfide material not having the α-Li3PS4 phase includes the sulfide material being substantially free of the α-Li3PS4 phase. The substantial absence of the α-Li3PS4 phase can be confirmed, for example, by the absence of a peak between 2θ=17.5° and 18.5° in the X-ray diffraction pattern when X-ray diffraction (XRD) (using CuKα radiation) is performed on the sulfide material at room temperature (herein, room temperature refers to a temperature of 20 to 30°C).

[0017] A material having Li-ion conductivity, containing Li, P, and S, and F and / or Cl, and not having an α-Li3PS4 phase, can be expressed, for example, by the following formula (I): Li3PS4·aLiX (I) (where X is F and / or Cl, and a satisfies 0≦a≦2.0). Here, a represents the molar ratio of LiX to Li3PS4. When a is within this range, battery performance can be improved; specifically, a sulfide material with excellent ionic conductivity can be provided. The range of a is not particularly limited as long as it is within the above range, but preferably satisfies 0<a≦2.0, more preferably satisfies 0.1≦a≦2.0, more preferably satisfies 0.1≦a≦1.5, and more preferably satisfies 0.1≦a≦1.0. X may be F, Cl, or both; however, it preferably contains F, and more preferably consists of F only. When X is F, a sulfide material that can further improve battery performance can be provided.

[0018] The ratio of Li to P contained in the sulfide material is not particularly limited, but for example, it is preferable that the molar ratio of Li to P is in the range (molar ratio) of Li / P = 1.0 to 10.0. By having the molar ratio of Li to P in this range, it is possible to provide a sulfide material that can further improve battery performance. It is more preferable that the range (molar ratio) of Li / P is 2.0 to 5.0, and even more preferable that the range (molar ratio) of Li / P is 2.9 to 3.1.

[0019] The sulfide material may or may not be amorphous, but is preferably amorphous. The amorphous state of a sulfide material may refer to, for example, when X-ray diffraction (XRD) is performed on the sulfide material (using CuKα radiation), all peaks in the XRD 2θ pattern have a half-width (full width at half maximum: unit: angle) of 2.0 or more, a half-width (full width at half maximum: unit: angle) of 1.5 or more, a half-width (full width at half maximum: unit: angle) of 1.0 or more, a half-width (full width at half maximum) of 0.5 or more, or no peaks. It may also refer to a state in which no clear crystallites are observed using a transmission electron microscope. The sulfide material may be obtained by mechanochemical treatment of the material.

[0020] Preferably, the sulfide material does not have either the βLi3PS4 phase or the γLi3PS4 phase. Whether the sulfide material has the βLi3PS4 phase or the γLi3PS4 phase can be confirmed by X-ray diffraction (XRD) of the sulfide material at room temperature (using CuKα radiation) showing two or more independent (i.e., non-overlapping) peaks between 2θ = 17.5° and 18.5° in the X-ray diffraction pattern.

[0021] The present production method may further include a step of producing a sulfide material. The method for producing a sulfide material is not particularly limited as long as it can physically integrate the raw materials of the sulfide material. Examples of integration methods include using a V-type mixer, mechanochemical treatment, a sand mill, a mixer (such as a homomixer or a planetary mixer), etc. Among these, mechanochemical treatment is preferred. Therefore, in one specific embodiment, the present production method may further include a step of producing a sulfide material by mechanochemical treatment of the raw materials.

[0022] The treatment device for mechanochemical treatment is not particularly limited as long as it can mix while applying mechanical energy, and examples that can be used include a ball mill, bead mill, jet mill, vibration mill, disk mill, turbo mill, and mechanofusion. A ball mill is preferred because it can generate large mechanical energy. Among ball mills, a planetary ball mill is preferred because it can efficiently generate high impact energy by rotating the pot on its axis and revolving the base in the opposite direction to the rotation. Treatment conditions for mechanochemical treatment can be set appropriately depending on the treatment device used.

[0023] When a planetary ball mill is used for mechanochemical treatment, the diameter of the balls is not particularly limited and may be selected from the range of 3 to 10 mm, for example. The rotation speed may be selected from the range of 10 to 600 rpm, for example. The output is also not particularly limited and may be selected from the range of 1 to 100 kWh / kg of raw material, for example. The duration of the integration treatment, e.g., mechanochemical treatment, is not particularly limited and may be set in the range of 1 to 120 hours, for example.

[0024] Examples of raw materials for materials that have Li-ion conductivity, contain Li, P, and S but do not contain F or Cl, and do not have the α-Li3PS4 phase include simple substances such as Li, P, and S, or any combination of compounds that contain at least one of Li, P, and S but do not contain F or Cl. Specific examples of such materials include Li2S, P2S3, P2S5, Li, P, and S. Of these, materials that contain at least Li2S or P2S5 are preferred, and materials that contain at least Li2S and P2S5 are more preferred, with Li2S and P2S5 being more preferably present in a molar ratio of Li2S:P2S5=3:1.

[0025] Raw materials for materials that have Li-ion conductivity, contain Li, P, and S, and F and / or Cl, and do not have an α-Li3PS4 phase, include any combination of simple substances such as Li, P, and S, or compounds containing one or more of Li, P, S, F, and Cl. Specific examples of such materials include Li2S, P2S3, P2S5, LiF, LiCl, PF3, PF5, PCl3, PCl5, Li, P, and S. Of these, it is preferable to contain at least Li2S or P2S5, and it is more preferable to contain at least Li2S and P2S5, and it is more preferable that Li2S and P2S5 are contained in a molar ratio of Li2S:P2S5=3:1.

[0026] The sulfide material during heating may be in the form of a powder, particles, film, layer, or pellet. The pellet may be obtained by pressing a powder or particulate sulfide material. The layer may be a layer covering another electrode material, such as an electrode active material, or its raw material. The pressing pressure may be selected from a range of 50 to 2000 MPa. The coating method is not particularly limited, but examples include gas-phase methods such as PVD and CVD, liquid-phase or solid-phase methods such as electroplating and coating, coating by applying shear force using milling methods such as ball milling, and coating by spraying. Examples of PVD methods include vacuum deposition and sputtering. The electrode active material is not particularly limited, and examples include the positive electrode active material and negative electrode active material described below.

[0027] The heating method is not particularly limited. For example, a heating medium at a temperature in the range of 200°C to 350°C or higher can be used. By contacting the sulfide material with the heating medium maintained at such a temperature, the sulfide material can be heated to the desired temperature. As the heating medium, for example, an electric furnace, a hot plate, a heater, a hot press, a muffle furnace, a high-frequency induction heater, a vacuum heater, a rotary kiln, a sand bath, a salt bath, or other heating device may be used. Alternatively, a gas that does not react with the sulfide material, such as argon gas, may be used. It is preferable that the heating medium has the ability to adjust the temperature and time.

[0028] The heating temperature of a material that has Li-ion conductivity, contains Li, P, and S but does not contain F or Cl, and does not have the α-Li3PS4 phase, is preferably in the range of 230°C to 2000°C. This range of heating temperature can provide a sulfide material that can further improve battery performance. The heating temperature is preferably in the range of 230°C to 1000°C, and more preferably in the range of 230°C to 700°C. The heating temperature here refers to the temperature of the portion of the heating medium that comes into contact with the sulfide material. For example, if the heating medium is a heating device, it refers to the surface temperature of the heating portion that comes into contact with the sulfide material. If the heating medium is a gas such as argon gas, it refers to the temperature of the gas that comes into contact with the sulfide material. Heating may be performed once or multiple times, but a single heating is preferred. If heating is performed multiple times, it is preferable that each heating temperature be within these temperature ranges.

[0029] The heating temperature of the material having Li-ion conductivity, containing Li, P, and S, and F and / or Cl, and not having the α-Li3PS4 phase, is preferably in the range of 200°C to 2000°C. By using a heating temperature in this range, it is possible to provide a sulfide material that can further improve battery performance. The heating temperature is preferably in the range of 200°C to 1000°C, and more preferably in the range of 200°C to 500°C. Heating may be performed once or multiple times, but is preferably performed once. If heating is performed multiple times, it is preferable that each heating temperature is within this temperature range.

[0030] When heating is performed multiple times, for example, when heating is performed twice, a cooling step (the cooling step will be described later) may or may not be performed between the first and second heatings. The second heating may be performed at a higher or lower temperature than the first heating. For example, when heating is performed three times, a cooling step, if present, may be performed between the first and second heatings, between the second and third heatings, or only one of them. When treating a large amount of sulfide material at once, a step of stirring and mixing the sulfide material before, during, between, and / or after heating may be included. The mixing method is not particularly limited as long as it is usable in the relevant field, and examples thereof include a V-type mixer, a sand mill, a mixer (such as a homomixer or a planetary mixer), and the like.

[0031] The heating time can be set appropriately depending on the sulfide material. The heating time is preferably in the range of 1 second to 1200 seconds. By setting the heating time within this range, it is possible to provide a sulfide material that can further improve battery performance. The heating time is preferably in the range of 1 second to 600 seconds, and more preferably in the range of 30 seconds to 360 seconds. When the heating step is performed multiple times, the heating time can be set appropriately for each step. Note that the temperature of the sulfide material in this specification refers to the temperature (actual measured value) of the surface of the sulfide material. The surface temperature of the sulfide material can be measured, for example, using a thermocouple or a radiation thermometer.

[0032] Regarding the temperature rise rate of the sulfide material when it reaches, for example, 200°C, for example, the temperature of the sulfide material is measured over time to obtain measurements. The temperature rise rate of the sulfide material when it reaches 200°C can be determined by taking the temperature of the sulfide material over time and taking the point at which it reaches 200°C as the reference point (reference point) and taking the difference between the measurements taken x seconds before and after (where x is a point above 0 and within 10 seconds of heating) (the measurement value x seconds after the reference point minus the measurement value x seconds before the reference point) and multiplying it by 30 / x. Alternatively, if the sulfide material is heated to 200°C or higher using a heating device capable of adding a constant amount of heat, the set temperature (e.g., 100°C if the sulfide material is heated at a constant rate of 100°C / min) can be considered to be the temperature rise rate of the sulfide material when it reaches 200°C. Furthermore, if a heating medium of 230°C or higher is used and there is no reason for the temperature rise rate to decrease, the temperature rise rate at 200°C can be considered to be substantially 100°C / min or higher.

[0033] The heating rate during heating can be appropriately set depending on the sulfide material. For example, if the sulfide material has Li-ion conductivity, contains Li, P, and S, and F and / or Cl, and does not have the α-Li3PS4 phase, the heating rate at 200°C is 100°C / min or more, and the sulfide material is heated to a temperature within the range of 200°C to 350°C, thereby providing a sulfide material that has the α-Li3PS4 phase and can improve battery performance. The heating rate for a material that has Li-ion conductivity, contains Li, P, and S, and F and / or Cl, and does not have the α-Li3PS4 phase is preferably 100°C / min to 3000°C / min, more preferably 100°C / min to 1500°C / min, more preferably 100°C / min to 1000°C / min, and even more preferably 150°C / min to 1000°C / min. The temperature may be increased at a constant rate of 100° C. / min or more from the start of heating, not just at the time when the temperature reaches 200° C. In this case, the temperature may be increased at a rate of 100° C. / min or more within the above-mentioned temperature range.

[0034] The heating time can be adjusted appropriately in combination with the heating temperature to prevent the temperature of the sulfide material from becoming too high. For example, if the heating temperature is higher than 500°C, shortening the heating time (e.g., within 60 seconds) can prevent the temperature of the sulfide material from becoming too high and forming crystalline phases other than the α-Li3PS4 phase, such as the β-Li3PS4 phase. The formation of crystalline phases other than the α-Li3PS4 phase can be confirmed by the appearance of two or more independent peaks between 2θ = 17.5° and 18.5° in the X-ray diffraction pattern using CuKα radiation. The preferred combination of heating temperature and heating time is a heating temperature between 300°C and 500°C for a heating time between 10 and 360 seconds. This combination of heating temperature and heating time can provide a sulfide material that can further improve battery performance.

[0035] When the sulfide material is in an amorphous state, it is preferable that the temperature of the sulfide material be heated at least once to a temperature exceeding the glass transition temperature of the sulfide material. Heating the sulfide material to a temperature exceeding the glass transition temperature can provide a sulfide material that can further improve battery performance. Since the glass transition temperature varies depending on the composition of the sulfide material, the heating temperature is adjusted appropriately depending on the composition of the sulfide material. The temperature of the sulfide material may be, for example, heated to a temperature 5°C or more higher than the glass transition temperature of the sulfide material, heated to a temperature 10°C or more higher, heated to a temperature 20°C or more higher, heated to a temperature 30°C or more higher, or heated to a temperature 50°C or more higher.

[0036] The sulfide material is preferably heated to a temperature exceeding the crystallization temperature of the sulfide material at least once. Heating the sulfide material to a temperature exceeding the crystallization temperature can provide a sulfide material that can further improve battery performance. The crystallization temperature varies depending on the composition of the sulfide material, so the heating temperature is adjusted appropriately depending on the composition of the sulfide material. The sulfide material may be heated to a temperature that is 5°C or more higher than the crystallization temperature of the sulfide material, 30°C or more higher, or 50°C or more higher. The glass transition temperature and crystallization temperature of the sulfide material can be measured, for example, by thermogravimetric differential thermal analysis (TG-DTA).

[0037] After the heat treatment, the sulfide material may be maintained at a temperature within the above-mentioned range for a certain period of time. The maintenance time is not particularly limited, but may be, for example, 1 to 1000 seconds, 1 to 800 seconds, or 1 to 600 seconds. By appropriately adjusting the heating temperature, heating time, temperature rise time, and temperature maintenance time, a solid electrolyte material having the α-Li3PS4 phase can be produced.

[0038] The present production method may include a step of cooling the material after heating. The cooling method is not particularly limited, and cooling may be performed by natural cooling or using any cooling device, but cooling using a cooling device is preferred. Examples of cooling devices that can be used include a liquid quenching and solidification device, a quenching flake manufacturing device, a submerged spinning device, a gas atomization device, a water atomization device, and a rotating disk device. Also, a cooling medium that does not react with the sulfide material, such as liquid nitrogen, may be used.

[0039] The cooling rate during cooling is not particularly limited and can be set appropriately. The cooling rate may be, for example, 10°C / min to 60,000°C / min, 50°C / min to 12,000°C / min, or 100°C / min to 6,000°C / min. Cooling may be performed at a rate of 50°C / min or less, or at a rate of 50°C / min or more, and is preferably performed at a rate of 100°C / min or more.

[0040] In one specific embodiment, the present invention provides a method for producing a solid electrolyte material having an α-Li3PS4 phase, the method comprising the steps of heating a Li-ion conducting sulfide material containing Li, P, and S, but not containing F or Cl, and not having an α-Li3PS4 phase, to a temperature in the range of 230°C to 350°C, wherein the heating rate at 200°C is 100°C / min or greater, and cooling the heated Li-ion conducting sulfide material.

[0041] In one specific embodiment, the present invention provides a method comprising heating a Li-ion conducting sulfide material comprising Li, P, and S, and F and / or Cl, and not having the α-Li3PS4 phase, to a temperature in the range of 200°C to 300°C, and cooling the heated Li-ion conducting sulfide material.

[0042] Each treatment step is preferably carried out in an inert atmosphere (e.g., an argon atmosphere) using a glove box or the like, in an environment with a moisture concentration of 10,000 ppm or less and an oxygen concentration of 10,000 ppm or less, and more preferably in an environment with a moisture concentration of 1,000 ppm or less and an oxygen concentration of 1,000 ppm or less. Each treatment step may be carried out under pressure lower or higher than atmospheric pressure. Normal pressure refers to, for example, a range of 200 hPa around 1,013 hPa. Pressure conditions may also be varied, such as gradually increasing pressure, gradually decreasing pressure, or using atmospheric pressure during heating but increasing pressure during cooling.

[0043] Whether the produced solid electrolyte material has the α-Li3PS4 phase can be confirmed, for example, by observing a combination of characteristic peaks in an X-ray diffraction pattern using CuKα radiation that a person skilled in the art would determine to have the α-Li3PS4 phase (X-ray diffraction patterns of the α-Li3PS4 phase are described, for example, in JP 2017-033770 A (Patent Document 2)). Alternatively, it can be confirmed by the appearance of only one unimodal peak between 2θ = 17.5° and 18.5° in an X-ray diffraction pattern using CuKα radiation. Alternatively, the solid electrolyte material can be determined to contain the α-Li3PS4 phase when a smoothed and background-processed X-ray diffraction pattern using CuKα radiation has two overlapping peaks between 2θ = 17.5° and 18.5°, and the lowest peak intensity (based on the baseline) between the two peaks (bottom peak intensity) is 10% or more of the peak intensity (based on the baseline) of either of the two peaks (see Figure 1). The bottom peak intensity is preferably 40% or more, and more preferably 90% or more, of the peak intensity of either of the two peaks. Smoothing of the X-ray diffraction pattern, background processing, and baseline calculation can be performed using commercially available analysis software (e.g., SmartLab Studio II, manufactured by Rigaku Corporation). The produced solid electrolyte material may have lattice constants of a-axis=8.707 Å, b-axis=8.766 Å, and c-axis=8.310 Å (α=β=γ=90°) calculated by fitting an X-ray diffraction pattern of the solid electrolyte material measured at room temperature using CuKα radiation with an orthorhombic crystal structure and a space group of Pbcn using crystal structure analysis software.

[0044] The method for producing a solid electrolyte material of the present invention can provide a solid electrolyte material having an α-Li3PS4 phase (at room temperature). The inventors' thoughts on why a solid electrolyte material having an α-Li3PS4 phase (at room temperature) can be obtained are described here.

[0045] Li3PS4 has three crystalline phases: α-Li3PS4 (high-temperature phase), β-Li3PS4 (intermediate-temperature phase), and γ-Li3PS4 (low-temperature phase). The α-Li3PS4 phase typically appears when amorphous Li3PS4 is heated to a high temperature of nearly 500°C. When the heating is stopped and the temperature is lowered to room temperature, the α-Li3PS4 phase undergoes a phase transition to γ-Li3PS4. Furthermore, when Li3PS4 is slowly heated to approximately 230°C and maintained at that temperature, the β-Li3PS4 phase precipitates. When the heated Li3PS4 is then lowered to room temperature, the β-Li3PS4 phase remains as a crystalline phase. Thus, the α-Li3PS4 phase does not typically exist as a crystalline phase at room temperature. The inventors have discovered that by heating (amorphous) Li3PS4 at a controlled heating rate of at least 100°C / min at 200°C, the α-Li3PS4 phase appears even at temperatures around 250°C, and that even when the temperature is returned to room temperature from this state, the α-Li3PS4 phase is maintained and no transition to the γ-Li3PS4 phase occurs. This was previously unknown.

[0046] Figure 2 shows the relationship between the heating rate and the temperature reached, as envisioned by the inventors, and the phases ultimately formed. The horizontal axis of Figure 2 represents temperature, and the vertical axis represents the change in specific volume with temperature. Figure 2 (1) shows a Li-ion conductive sulfide material heated to the glass transition temperature or higher. Figure 2 (2) to (4) show the crystalline phases formed from the heated Li-ion conductive sulfide material. The arrows in Figure 2 indicate the phase transitions. When the heating rate at 200°C is slower than 100°C / min, the intermediate-temperature β-Li3PS4 phase precipitates during heat treatment (Figure 2 (A)). The inventors believe that this is because, at a slow heating rate, the nucleation and growth of the β-Li3PS4 phase is faster than the formation of the α-Li3PS4 phase in the supercooled liquid due to the difference in the temperature dependence of the crystal nucleation rate between the α-Li3PS4 and β-Li3PS4 phases, and the embryos of the α-Li3PS4 phase formed in the supercooled liquid dissolve and eventually disappear. When the heating rate at 200°C is faster than 100°C / min, the crystalline phase formed varies depending on the temperature reached by the heated Li-ion conductive sulfide material. For example, if the temperature reached is too low (below 230°C), no crystalline phase is formed (Figure 2B), or the β-Li3PS4 phase precipitates (Figure 2C). The inventors believe that this is because the temperature reached is too low, so no nuclei are formed, or only the formation and growth of the β-Li3PS4 phase crystal nuclei occurs. The β-Li3PS4 phase also precipitates when the temperature is high (over 350°C) (Fig. 2(C)). The inventors believe that this is because the Li-ion conductive sulfide material passes through a temperature range where the phase transition from α-Li3PS4 to β-Li3PS4 phase can occur when it returns to room temperature after heating. When the temperature is in the range of 230°C to 350°C, the α-Li3PS4 phase is formed (Fig. 2(D)).The inventors believe that this is because the α-Li3PS4 phase precipitates because the formation and growth of the α-Li3PS4 phase is faster than the nucleation of the β-Li3PS4 phase in the supercooled liquid, and because the Li-ion conductive sulfide material does not pass through the temperature range where the phase transition from the α-Li3PS4 phase to the β-Li3PS4 phase can occur when it returns to room temperature after heating.

[0047] We have also found that, for solid electrolyte materials containing Li3PS4 and additionally containing F or Cl, the α-Li3PS4 phase appears when heated to a temperature in the range of 200°C to 300°C without controlling the heating rate, and that the α-Li3PS4 phase is maintained even at room temperature. This was previously unknown. Thus, the method for producing a solid electrolyte material of the present invention can produce a solid electrolyte material having the α-Li3PS4 phase at room temperature. Furthermore, the solid electrolyte material having the α-Li3PS4 phase at room temperature obtained by the method for producing a solid electrolyte material of the present invention stably maintains the α-Li3PS4 phase without losing it even after time has passed since production. Therefore, the method for producing a solid electrolyte material of the present invention can produce a solid electrolyte material that can maintain the excellent conductivity due to the α-Li3PS4 phase for a long period of time.

[0048] (Solid Electrolyte Material) The present invention provides a solid electrolyte material containing Li, P, S, and F, having a composition represented by Li3PS4·aLiF (wherein a satisfies 0<a≦2.0), and having an α-Li3PS4 phase at room temperature. The present invention also provides a solid electrolyte material containing Li, P, S, and F, having a composition represented by Li3PS4·aLiF (wherein a satisfies 0<a≦2.0), and having an α-Li3PS4 phase at room temperature. In one specific embodiment, the present invention provides a solid electrolyte material containing Li, P, S, and F, having a composition represented by Li3PS4·aLiF (wherein a satisfies 0<a≦2.0), and having an α-Li3PS4 phase at room temperature (provided that the following formula (II) Li 4-4β-α-γ P 1+β S 4-γ F γ (II) [wherein 0.2≦α<1.0, 0≦β≦0.075, 0<γ≦0.2] is also provided.

[0049] While the range of a for the solid electrolyte material is not particularly limited, ensuring that a is in the range of 0 < a ≦ 2.0 can improve battery performance; specifically, a sulfide material with excellent ionic conductivity can be provided. The range of a may be 0 < a ≦ 1.5, 0 < a ≦ 1.0, or 0.1 ≦ a ≦ 1.0. Examples of Li3PS4·aLiF include Li3PS4·0.01LiF, Li3PS4·0.05LiF, Li3PS4·0.1LiF, Li3PS4·0.2LiF, Li3PS4·0.3LiF, Li3PS4·0.4LiF, Li3PS4·0.5LiF, Li3PS4·0.6LiF, Li3PS4·0.7LiF, Li3PS4·0.8LiF, Li3PS4·0.9LiF, Li3PS4·LiF, Li3PS4·1.5LiF, and Li3PS4·2.0LiF. The reason for the α-Li3PS4 phase at room temperature is as described above.

[0050] In the Raman spectrum, the solid electrolyte material exhibits a peak intensity of 370 to 400 cm -1 P2S6 4- It is preferable that no peaks derived from the Raman spectrum are observed. The Raman spectrum can be measured, for example, using a laser Raman spectrometer LabRAM HR-800 with a green laser (532 nm) as the oscillation line.

[0051] The solid electrolyte material can be produced by physically combining raw materials such as LiS, P2S5, and LiF, and the combining method is preferably mechanochemical treatment, as described above.

[0052] In a Li-ion conductive solid electrolyte material (e.g., the above-mentioned Li3PS4·aLiF (where a satisfies the formula: 0<a≦2.0)) obtained by a method including a step of heating a Li-ion conductive sulfide material containing Li, P, and S, and F and / or Cl, and not having the α-Li3PS4 phase, to a temperature in the range of 200°C to 300°C, the inventors believe that F and Cl are present in the solid electrolyte material in the form of LiF and LiCl, respectively, but the state in which this LiF and LiCl exist in the solid electrolyte material is unknown. In other words, while it is possible to produce a Li-ion conductive solid electrolyte material having the α-Li3PS4 phase (at room temperature) without being limited by the heating rate by heating a Li-ion conductive sulfide material containing F and / or Cl, the state in which this F and Cl exist is unknown, and the inventors believe that it is difficult to specifically identify their states.

[0053] (Solid Electrolyte Composite) The present invention provides a solid electrolyte composite containing the solid electrolyte material of the present invention. In addition to the solid electrolyte material of the present invention, the solid electrolyte composite may be mixed with a solid electrolyte other than the solid electrolyte material of the present invention, a binder, a conductive material, etc. The proportion of the solid electrolyte material of the present invention in the solid electrolyte composite can be, for example, 50 mass % or more, 70 mass % or more, or 95 mass % or more.

[0054] The binder is not particularly limited, and any binder that can be commonly used in battery materials can be used. The binder may be one type of binder or a combination of multiple binders. The binder content in the solid electrolyte composite can be appropriately selected from the range of 0 to 40% by mass. Of this range, it is preferably 30% by mass or less, more preferably 10% by mass or less, and more preferably no binder is contained.

[0055] The conductive material is not particularly limited, and any material that can be commonly used in battery materials can be used. The conductive material may be one type of conductive material or a combination of multiple conductive materials. The content of the conductive material in the solid electrolyte composite can be appropriately selected from the range of 0 to 40% by mass. Within this range, it is preferably 30% by mass or less, and more preferably 20% by mass or less.

[0056] The solid electrolyte other than the solid electrolyte material of the present invention contained in the solid electrolyte composite is not particularly limited, and any solid electrolyte commonly used in battery materials can be used. The solid electrolyte other than the solid electrolyte material of the present invention may be glass or glass ceramic. Glass ceramic refers to a material having a glass phase and a crystalline phase dispersed (precipitated) in the glass phase. Glass ceramic can be formed, for example, by heating the glass phase at a temperature equal to or higher than its glass transition point to crystallize (at least a portion of) the material. The glass transition point can be measured, for example, by differential thermal analysis (DTA). The fact that the solid electrolyte material is a glass ceramic can be confirmed, for example, by observing the presence of multiple crystalline phases in the glass phase using a transmission electron microscope (TEM). The content of the solid electrolyte other than the solid electrolyte material of the present invention contained in the solid electrolyte composite can be appropriately selected from the range of 0 to 50% by mass. Within this range, 40% by mass or less is more preferable, and 30% by mass or less is even more preferable.

[0057] The sum of the contents of the binder, the conductive material, and the solid electrolyte in the solid electrolyte composite is not particularly limited, but is preferably 60 mass % or less, more preferably 50 mass % or less, more preferably 40 mass % or less, and even more preferably 30 mass % or less.

[0058] The solid electrolyte composite can be formed by mixing the solid electrolyte material of the present invention with a solid electrolyte other than the solid electrolyte material of the present invention, a binder, a conductive material, etc. The mixing method is not particularly limited as long as it can be used in the relevant field.

[0059] The solid electrolyte composite or the solid electrolyte material of the present invention can be formed into a solid electrolyte layer by, for example, pressing it to a predetermined thickness. The pressing pressure may be selected from the range of 50 to 2000 MPa.

[0060] (Electrode) One embodiment of the present invention provides an electrode containing the solid electrolyte material of the present invention. The electrode may be a positive electrode or a negative electrode. The amount of the solid electrolyte material of the present invention contained in the electrode is not particularly limited, but may be, for example, in the range of 1 to 50 mass %. The electrode may contain a positive electrode active material and a negative electrode active material commonly used in the relevant field, the above-mentioned binder, conductive material, and a solid electrolyte other than the solid electrolyte material of the present invention.

[0061] The electrode can be obtained in the form of a pellet or sheet by, for example, mixing an electrode active material and, optionally, a binder, a conductive material, an electrolyte, or the like, and pressing the resulting mixture.

[0062] (Electrode Composite) The present invention also provides an electrode composite in which the electrode of the present invention is combined with a current collector. The material, shape, etc. of the current collector are not particularly limited as long as it can be combined with the electrode of the present invention and functions as a current collector. The shape of the current collector may be a uniform alloy plate or a perforated shape. It may also be in the form of a foil, sheet, or film. Examples of materials for the current collector include Al, Ni, Ti, Mo, Ru, Pd, stainless steel, and steel. The electrode composite of the present invention may be formed by combining an electrode and a current collector formed separately, or the electrode may be formed directly on the current collector. When directly formed, an electrode active material may be applied to the surface of the current collector using a known method.

[0063] (All-Solid-State Secondary Battery) The present invention provides an all-solid-state secondary battery comprising the solid electrolyte composite of the present invention and / or the electrode of the present invention. The all-solid-state secondary battery may combine a solid electrolyte layer comprising the solid electrolyte composite of the present invention with a positive electrode and a negative electrode commonly used in the relevant field, or may combine a solid electrolyte layer comprising the solid electrolyte composite of the present invention with the electrode of the present invention, or may combine a solid electrolyte layer commonly used in the relevant field with the electrode of the present invention. The all-solid-state secondary battery can be obtained, for example, by laminating and pressing a positive electrode, a solid electrolyte layer, a negative electrode, and a current collector to obtain a cell, and then fixing the cell in a container.

[0064] [Embodiment 1] A method for producing a solid electrolyte material having the α-Li3PS4 phase, comprising the steps of: heating a Li-ion conductive sulfide material containing Li, P, and S, but not containing F or Cl, and not having the α-Li3PS4 phase, to a temperature in the range of 230°C to 350°C, wherein the heating rate at 200°C is 100°C / min or greater.

[0065] [Embodiment 2] The method according to embodiment 1, wherein the heating step at 200°C has a temperature increase rate of 150°C / min or more.

[0066] [Embodiment 3] The method of embodiment 1 or 2, further comprising obtaining the Li-ion conducting sulfide material by mechanochemical treatment of its raw material.

[0067] Embodiment 4: A method for producing a solid electrolyte material having the α-Li3PS4 phase, comprising the step of heating a Li-ion conducting sulfide material containing Li, P, and S, and F and / or Cl, and not having the α-Li3PS4 phase, to a temperature in the range of 200°C to 300°C.

[0068] [Embodiment 5] The method according to embodiment 4, wherein the solid electrolyte material has a composition represented by the following formula (I): Li3PS4·aLiX (I) (wherein X is F and / or Cl, and a satisfies 0≦a≦2.0).

[0069] [Embodiment 6] The method of embodiment 4 or 5, further comprising obtaining the Li-ion conducting sulfide material by mechanochemical treatment of its raw material.

[0070] [Embodiment 7] A solid electrolyte material containing Li, P, S, and F, having a composition represented by Li3PS4·aLiF (wherein a satisfies the formula 0<a≦2.0), and having an α-Li3PS4 phase at room temperature.

[0071] [Embodiment 8] A solid electrolyte material having an α-Li3PS4 phase, obtained by the method according to any one of embodiments 4 to 6.

[0072] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited thereto. In the following examples and comparative examples, Li2S (purity >99.9%) manufactured by Mitsuwa Chemical Co., Ltd., LiI, LiBr, LiCl, and P2S5 (Sigma-Aldrich), and LiF (Stellar Chemifa) were used. Furthermore, in the following examples and comparative examples, a Fritsch Pulverisette P-7 planetary ball mill was used. A Rigaku SmartLab fully automated multipurpose X-ray diffractometer was used as the X-ray diffractometer. An SI-1260 impedance analyzer manufactured by Solartron was used to measure ionic and electronic conductivity. A LabRAM HR-800 laser Raman spectrometer manufactured by Horiba, Ltd. was used to measure Raman spectra. The heating device used was a Corning hot plate (PC-420D), and the thermal analyzers used were a Rigaku TG-DTA (Thermo plus EVO2 TG-DTA8121) and a Rigaku DSC (Thermo plus EVO2 DSCvesta). X-ray photoelectron spectroscopy (XPS) was performed using a Thermo Fisher Scientific K-Alpha X-ray photoelectron spectroscopy system, using monochromated Al-Kα (1486.6 eV) X-rays. The measurement area was approximately 400 μm. 2 And, Ar is used for charge neutralization. +A neutralization gun was used to etch the sample, and Ar ions were used. Liquid nitrogen or an iron press using a stainless steel plate was used as a cooling means.

[0073] The measurement conditions of the devices used to evaluate each sample in the Examples and Comparative Examples are shown below.

[0074] <X-ray diffraction measurement> The SmartLab mentioned above was used as the X-ray diffraction device, and CuKα radiation (=1.54056×10 -10 m), tube voltage 45 kV, tube current 200 mA, scan angle 2θ = 10° to 60°, sampling interval 0.02°, and scan speed 10° min -1 (All XRD analysis below was performed under these conditions.)

[0075] <Calculation of ionic conductivity and activation energy> AC impedance was measured using the above-mentioned impedance analyzer (SI-1260) by preparing a polycarbonate cell (polycarbonate cell) as follows. Die steel (SKD) was used for the current collector, and polycarbonate with an inner diameter of 10 mm was used for the insulator. 150 mg of each solid electrolyte material was weighed and added to a rod, and pellets were produced by uniaxial pressing using a hydraulic press at 360 MPa for 5 minutes. The shaft and rod were fixed by tightening the screws, placed in a glass container, and sealed with a rubber stopper. The measurement frequency was 0.1 Hz to 1 x 10 6 The impedance plot was measured at a frequency of 10 Hz, with an AC amplitude of 10 mV. The intersection of the semicircle and the real axis of the obtained impedance plot was taken as the resistance R of the sample, and the ionic conductivity σ was calculated using the following formula: σ = (1 / R) × (L / S) (1), where L is the thickness of the pellet (cm) and S is the electrode surface area (0.785 cm). 2 )

[0076] Activation energy (E a ) was calculated from the slope of the graph of the temperature dependence of ionic conductivity, which is a plot of the ionic conductivity measured at each temperature against the reciprocal of the absolute temperature, using the following formula, assuming that it follows the Arrhenius law: σ = A exp(-E a / RT) (2) [σ = ionic conductivity (S cm -1), A : pre-exponential factor (S cm -1 ), T: Measured temperature (K), E a : Activation energy (kJ mol -1 ), R: gas constant (kJ mol -1 K -1 )]

[0077] <Thermal Analysis: TG-DTA> Thermogravimetric Differential Calorimetry (TG-DTA) was performed using the Rigaku TG-DTA (Thermo plus EVO2 TG-DTA8121). Approximately 10 mg of powder sample was placed in an aluminum hermetically sealed pan and heated from room temperature to 550°C at a heating rate of 10°C / min under a nitrogen stream (flow rate 100 ml / min). The same apparatus was also used for the heat treatment of the sample after mechanochemical treatment, which will be described later. The heating rate during the heat treatment was 100°C / min.

[0078] <Thermal analysis: DSC> Differential scanning calorimetry (DSC) was performed using the Rigaku Thermo Plus EVO2 DSCvesta under a nitrogen atmosphere. The same device was also used for the heat treatment of the samples after the mechanochemical treatment described below. The heating rate during the heat treatment was 150°C / min.

[0079] <Raman Spectroscopy> The Raman spectra were measured using the above-mentioned laser Raman spectrometer LabRAM HR-800. The powder sample was packed and fixed in an Al pan in argon gas, and measurements were performed using an airtight sample stage (LIBCell-P11D5, nano photon). Measurements were performed using a green laser (532 nm) as the oscillation line.

[0080] Solid electrolyte materials (hereinafter also referred to as LPS-based solid electrolyte materials) were produced by treating a Li-ion conductive sulfide material containing Li, P, and S but not F or Cl and not having the α-Li3PS4 phase under various conditions, and solid electrolyte materials (hereinafter also referred to as LPX-X-based solid electrolyte materials) were produced by treating a Li-ion conductive sulfide material containing Li, P, and S, and F and / or Cl, not having the α-Li3PS4 phase under various conditions, and their properties were investigated.

[0081] First, we will explain the synthesis of the samples of each composition. We will explain the synthesis of the halogen-free system (Li2S-P2S5 system), and then we will explain the synthesis of the halogen-containing Li2S-P2S5-LiX system (X is a halogen).

[0082] [LPS-Based Solid Electrolyte Material] In a glove box under an argon atmosphere, 5 g of raw materials, Li2S and P2S5, were weighed out at a molar ratio of Li2S:P2S5 = 75:25. The raw materials were mixed and subjected to mechanochemical treatment in a planetary ball mill to obtain a 75 Li2S·25 P2S5 amorphous material. Hereinafter, the halogen-free Li2S-P2S5 system will also be referred to as the LPS system. Hereinafter, the sample obtained by mechanochemical treatment will be referred to as "milled" (the same applies to LPS-X-based solid electrolyte materials). This 75 Li2S·25 P2S5 amorphous material will be referred to as Li3PS4 (milled). The raw materials used and their composition (molar ratio) at the time of charging are listed in Table 1. The mechanochemical treatment conditions were a rotation speed of 210 rpm for 70 hours. A 225 ml pot made of ZrO2 and 450 g of 4 mm diameter ZrO2 balls were also used. The 75 Li2S:25 P2S5 amorphous solid electrolyte obtained by mechanochemical treatment, i.e., Li3PS4 (milled), is hereinafter referred to as the solid electrolyte sample of Comparative Example 1. The environment inside the glove box under an argon atmosphere was such that the moisture content was less than -70°C and the oxygen concentration was 10 ppm or less (these conditions were used for all work performed inside the glove box hereinafter).

[0083]

[0084] [LPS-X-Based Solid Electrolyte Material: LPS-F-Based] In a glove box under an argon atmosphere, 3 g of raw materials, Li2S, P2S5, and LiF, were weighed out in a molar ratio of Li2S:P2S5:LiF = 75:25:50. The weighed raw materials were mixed and subjected to mechanochemical treatment in a planetary ball mill to obtain Li3PS4·LiF (milled). The mechanochemical treatment was performed at a rotation speed of 210 rpm for 20 hours. A 225 ml pot made of ZrO2 and 450 g of 4 mm diameter ZrO2 balls were used. The Li3PS4·LiF (milled) obtained by mechanochemical treatment is referred to as the solid electrolyte sample of Comparative Example 6 below.

[0085] [LPS-X-based solid electrolyte material: LPS-F-based solid electrolyte with modified composition] In the above-mentioned Li2S-P2S5-LiF system (hereinafter sometimes referred to as LPS-F system), each raw material was weighed out to obtain the molar ratios shown in Table 2, and mechanochemical treatment was performed to obtain Li3PS4·0.1LiF (milled) (Comparative Example 12), Li3PS4·0.2LiF (milled) (Comparative Example 14), and Li3PS4·0.5LiF (milled) (Comparative Example 16), respectively. The mechanochemical treatment conditions were the same as those in Comparative Example 6.

[0086]

[0087] [LPS-X-Based Solid Electrolyte Materials: LPS-Cl, LPS-Br, and LPS-I Systems] In addition to the LPS-F system described above, we also performed mechanochemical treatment on Li2S-P2S5-LiCl systems (hereinafter sometimes referred to as LPS-Cl systems), Li2S-P2S5-LiBr systems (hereinafter sometimes referred to as LPS-Br systems), and Li2S-P2S5-LiI systems (hereinafter sometimes referred to as LPS-I systems) with different halogen elements to obtain milled solid electrolyte samples. In a glove box under an argon atmosphere, 1 g of the raw materials Li2S, P2S5, and LiX were weighed out in a molar ratio of Li2S:P2S5:LiX = 75:25:50. The weighed raw materials were mixed and subjected to mechanochemical treatment in a planetary ball mill to obtain milled Li3PS4-LiX. The mechanochemical treatment was performed for 20 hours at a rotation speed of 510 rpm. A 45 ml pot made of ZrO2 and 90 g of 4 mm diameter ZrO2 balls were used. The solid electrolyte samples obtained by the mechanochemical treatment were designated Li3PS4·LiCl (milled) (hereinafter, Comparative Example 7), Li3PS4·LiBr (milled) (hereinafter, Comparative Example 8), and Li3PS4·LiI (milled) (hereinafter, Comparative Example 9) (see Table 3 below).

[0088]

[0089] [LPS-based solid electrolyte material] The above Li3PS4 (milled) was heat-treated at various temperatures to obtain an LPS-based solid electrolyte material. To perform the heat treatment, the Li3PS4 (milled) powder was first placed in a 4 mm diameter tablet press and pressed at 360 MPa using a hydraulic uniaxial press to produce pellets with a thickness of less than 1 mm. Two stainless steel metal plates were placed on a hot plate and heated to the specified temperature. The pellets were heated by placing the prepared pellet on one metal plate and sandwiching it between the other metal plate. The heating time was 1 minute. After heating for 1 minute, the pellet was pressed between stainless steel plates and quenched (quenched using a so-called iron press). Here, the heat-treated sample is referred to as "heated" (the same applies hereafter to LPS-X-based solid electrolyte materials). The heat treatment temperature is sometimes expressed as ht (short for heat treatment) and a three-digit number. The heating rate was calculated to be approximately 750°C / min at 200°C, since it took 1.83 seconds to raise the temperature from 188°C to 211°C. The following calculations of the heating rate were also carried out in the same manner, except when the heating rate was fixed.

[0090] Example 1 A Li3PS4 (milled) (Comparative Example 1) pellet was heat-treated by adjusting the heating temperature so that the measured temperature reached 338°C (the heating rate at 200°C was 750°C / min or more), to obtain a sample of Example 1.

[0091] Examples 2 to 4, Comparative Example 2 Li3PS4 (milled) (Comparative Example 1) pellets were heat-treated while changing the measured temperature as shown in Table 4 (column for temperature rise rate of 750°C / min or more). Except for changing the heat treatment temperature, the procedure was the same as in Example 1.

[0092] Example 5 Li3PS4 (milled) (Comparative Example 1) pellets were heat-treated by adjusting the heating temperature so that the measured temperature reached 336°C, to obtain a sample of Example 5. Specifically, Li3PS4 (milled) (Comparative Example 1) was heat-treated using a DSC apparatus. The heating rate of the DSC apparatus was set to 150°C / min, and heating was stopped when the measured temperature of the Li3PS4 (milled) reached 336°C, and the pellets were quenched in liquid nitrogen.

[0093] Examples 6 to 11, Comparative Examples 3 and 4 Li3PS4 (milled) (Comparative Example 1) was heat-treated while changing the measured temperature as shown in Table 4 (column for temperature rise rate 150°C / min). Except for changing the heat treatment temperature, the same procedure as in Example 5 was followed.

[0094] Example 12 Li3PS4 (milled) (Comparative Example 1) was heat-treated by adjusting the heating temperature so that the measured temperature reached 330°C, thereby obtaining a sample of Example 12. Specifically, Li3PS4 (milled) (Comparative Example 1) was heat-treated using a TG-DTA apparatus. The heating rate of the TG-DTA apparatus was set to 100°C / min, and heating was stopped when the measured temperature of the Li3PS4 (milled) reached 330°C. After heating, the sample was cooled at a rate of 50°C / min using the same TG-DTA apparatus.

[0095] Examples 13 to 18, Comparative Example 5 Li3PS4 (milled) (Comparative Example 1) was heat-treated while changing the measured temperature as shown in Table 4 (column for temperature rise rate 100°C / min). Except for changing the heat treatment temperature, the same procedure as in Example 12 was followed.

[0096]

[0097] X-ray diffraction (XRD) measurements were performed on the solid electrolyte materials of Examples 1 to 18 and Comparative Examples 2 to 5. The results are shown in Figures 3 to 5. The diffraction patterns shown in Figures 3 to 5 reveal a peak characteristic of the α-Li3PS4 phase near 18°. Some of the diffraction peaks are split. This indicates that the α-phase is present, sufficient to be seen in the diffraction patterns, rather than a single β-phase. Because this can be interpreted as the precipitation of mixed α- and β-phase crystals, we refer to this as the α-like phase for convenience. These results demonstrate that heat treatment using rapid heating up to 350°C at heating rates of 750°C / min, 150°C / min, and 100°C / min yields Li3PS4 with the α-phase, which is not stable at room temperature. Furthermore, rapid cooling (quenching) using liquid nitrogen or similar in combination with rapid heating yields Li3PS4 with the α-phase (α-Li3PS4-like phase).

[0098] [LPS-based and LPS-X-based (X is a halogen) solid electrolyte materials] Figure 6 shows the results of X-ray diffraction measurements on samples (milled) that were subjected to only mechanochemical treatment for the LPS-based and LPS-X-based (X is a halogen) materials shown in Table 3. As shown in Figure 6, although some raw materials remain, a halo pattern indicating an amorphous structure was observed.

[0099] These samples of Comparative Examples 6 to 9 were heat-treated at 330°C. The heat treatment conditions were the same as those of Example 1, except for the measured temperature. Specifically, pellets of Li3PS4·LiF (milled) (Comparative Example 6), Li3PS4·LiCl (milled) (Comparative Example 7), Li3PS4·LiBr (milled) (Comparative Example 8), and Li3PS4·LiI (milled) (Comparative Example 9) were prepared. Each of these pellets was heat-treated by adjusting the heating temperature so that the measured temperature reached 330°C (heating rate at 200°C was 750°C / min or more). As a result, samples of Li3PS4·LiF(ht330) (Example 19), Li3PS4·LiCl(ht330) (Example 20), Li3PS4·LiBr(ht330) (Comparative Example 10), and Li3PS4·LiI(ht330) (Comparative Example 11) were obtained.

[0100] The results of X-ray diffraction measurements for heat-treated Examples 19 and 20, and Comparative Examples 10 and 11 are shown in Figure 7. As shown in Figure 7, diffraction lines derived from the α-phase were observed in Example 19, an LPS-F system containing fluorine (F) as a halogen, and Example 20, an LPS-Cl system containing chlorine (Cl). On the other hand, diffraction lines derived from the α-Li3PS4 were not observed in Comparative Example 10, an LPS-Br system containing bromine (Br), or Comparative Example 11, an LPS-I system containing iodine (I). In particular, diffraction lines derived from the β-phase were observed in Comparative Example 10 (LPS-Br system). This indicates that, among halogens, the α-phase or α-like phase of Li3PS4 crystals precipitates in the LPS-F and LPS-Cl systems. On the other hand, the α-phase (or α-like phase) does not precipitate in systems containing Br or I, even with the same halogen element. In the LPS-F and LPS-Cl systems, it can be said that F and Cl contribute in some way to the formation of the α phase, in other words, the retention of the α phase, which is originally a high-temperature phase, even at room temperature.

[0101] [LPS-F-based solid electrolyte material] Li3PS4·LiF (milled) (Comparative Example 6) obtained by mechanochemical processing with the composition shown in Table 5 below was heat-treated at various temperatures to obtain the samples of Example 19 and Examples 21 to 24. The heat treatment conditions (including cooling conditions) were the same as in Example 1 except for the actual measured temperature. The heat treatment temperatures for Example 19 and Examples 21 to 24 are as shown in Table 6 below.

[0102]

[0103]

[0104] The results of X-ray diffraction measurements for heat-treated Examples 19, 21 to 24, and Comparative Example 6 are shown in Figure 8. As shown in Figure 8, diffraction lines characteristic of the α phase were observed around 18° in all of Example 19 and Examples 21 to 24 (indicated by stars in the figure). Based on the peak intensity of the diffraction lines, it can be said that the LPS-F system contributes more to the precipitation (generation and stabilization at room temperature) of the α phase than the above-mentioned LPS-Cl system (see Figure 7).

[0105] [LPS-X-based solid electrolyte material: LPS-F-based compositions] Mechanochemical treatment was performed using the molar ratios shown in Table 2 above, and the resulting Li3PS4·0.1LiF (milled) (Comparative Example 12), Li3PS4·0.2LiF (milled) (Comparative Example 14), Li3PS4·0.5LiF (milled) (Comparative Example 16), and Li3PS4·LiF (milled) (Comparative Example 6) were then heat-treated at various temperatures. The measured temperatures for the heat treatment are shown in Table 7. The heat treatment conditions (including cooling conditions) were the same as in Example 1, except that the measured temperatures were different.

[0106]

[0107] The results of X-ray diffraction measurements on the Li3PS4·0.1LiF samples of Examples 25 to 28 and Comparative Example 13 are shown in Figure 9, the results of X-ray diffraction measurements on the Li3PS4·0.2LiF samples of Examples 29 to 32 and Comparative Examples 14 and 15 are shown in Figure 10, the results of X-ray diffraction measurements on the Li3PS4·0.5LiF samples of Examples 33 to 37 and Comparative Examples 16 and 17 are shown in Figure 11, and the results of X-ray diffraction measurements on the samples of Examples 38 to 42 and Comparative Examples 6 and 17 are shown in Figure 12. Figures 9 to 12 also show the results of X-ray diffraction measurements on Li3PS4·0.1LiF (milled) (Comparative Example 12), Li3PS4·0.2LiF (milled) (Comparative Example 14), Li3PS4·0.5LiF (milled) (Comparative Example 16), and Li3PS4·LiF (milled) (Comparative Example 6).

[0108] 9 to 12, it can be seen that in each sample of Examples 25 to 42, diffraction lines characteristic of the α phase are observed around 18°. This indicates that the α phase precipitates even in Li3PS4·LiF, which has a high LiF content (molar ratio), and Li3PS4·0.1LiF, which has a low LiF content, and that this crystalline phase is maintained even at room temperature. In contrast, it was also found that at temperatures below 200°C, as in Comparative Examples 13, 15, and 17, crystals clearly recognizable as the α phase do not precipitate.

[0109] Figures 13A-13D show XPS spectra for each LPS-F system composition. Specifically, Figures 13A and 13C show XPS spectra for F1S (Figure 13A) and FKL1 (Figure 13C) at each composition after mechanochemical treatment, while Figures 13B and 13D show XPS spectra for F1S (Figure 13B) and FKL1 (Figure 13D) at each composition after heat treatment. Note that the spectra shown at the top of each figure are for LiF only and are presented as a reference for spectral attribution. Figures 13A-D show that the spectra of the heat-treated samples for both F1S (Figure 13A or Figure 13B) and FKL1 (Figure 13C or Figure 13D) differ from the spectra of the mechanochemically treated samples (i.e., samples not subjected to heat treatment). Focusing on the F1S spectrum, the peak at around 685 eV attributable to LiF increases after heat treatment. This is thought to be due to the precipitation of LiF crystals from an amorphous (glass) state. Referring to FIG. 13A, it can be seen that the peak intensity derived from LiF increases as the amount of LiF added increases, from 0.1 LiF to LiF. Because the state of existence of LiF is unclear, it is conveniently referred to as LiF, but it can also be said that there is an upper limit to the dissolution of LiF into glass. On the other hand, a peak near 684 eV that is not derived from LiF is also observed, which suggests the presence of LiF in a non-crystalline state. However, as mentioned above, the state of existence of LiF cannot be clearly defined.

[0110] <Calculation of Ionic Conductivity and Activation Energy> The ionic conductivity (σ) of the solid electrolyte samples of Examples 19 and 23, and Comparative Examples 1 and 6 to 8 was measured, and the activation energy (E a ) was calculated.

[0111] An Arrhenius plot based on the measured ionic conductivity is shown in Figure 14. Table 8 below shows the measured ionic conductivity and activation energy at room temperature.

[0112]

[0113] 14 and Table 8, it can be seen that the solid electrolyte materials of Examples 19 and 23, which have the α-Li3PS4 phase (or a phase similar to the α-Li3PS4 phase), have higher ionic conductivity than the solid electrolyte materials of Comparative Examples, which do not have the α-Li3PS4 phase. In other words, the high ionic conductivity indicates that the α phase exists as the main phase.

[0114] <TG-DTA Measurement> Thermogravimetric measurements (TG-DTA) were performed on each of the materials of Comparative Examples 1, 6, 12, 14, and 16, and DTA curves were obtained. The measurement results are shown in Figure 15. Figure 15 shows that the exothermic peak shifts to the lower temperature side as the LiF content increases. Referring to Figures 9 to 12, it can be seen that this also corresponds to each heat treatment temperature (crystal precipitation temperature, crystallization temperature).

[0115] <Calculation of Ionic Conductivity and Activation Energy> The ionic conductivity (σ) of the solid electrolyte materials of Examples 32, 36, and 41 and the solid electrolyte materials of Comparative Examples 6, 14, and 16 was measured, and the activation energy (E a ) was calculated. The measurement method etc. were as described above. The results are shown in Table 9 below.

[0116]

[0117] From Table 9, the solid electrolyte materials of Examples 32, 36 and 41 having the α-Li3PS4 phase (or a phase similar to the α-Li3PS4 phase) all had a solubility of 1.0 × 10 -3 S cm -1 It was shown that the material has a high ionic conductivity of at least 1000 kJ / cm2. This indicates that, regardless of the LiF content (composition), heat treatment results in high ionic conductivity that is thought to be due to the α-Li3PS4 phase (or a phase similar to the α-Li3PS4 phase). These results demonstrate that by producing a solid electrolyte material having the α-Li3PS4 phase (or a phase similar to the α-Li3PS4 phase) using the above-mentioned production method, the α-phase, which normally only exists at high temperatures, can be maintained even at room temperature, resulting in a solid electrolyte with excellent ionic conductivity.

[0118] (Measurement of Raman Spectrum) The solid electrolyte materials of Examples 28, 32, 36, and 41 and the solid electrolyte materials of Comparative Examples 6, 12, 14, and 16 were subjected to Raman spectrum measurement.

[0119] The measurement results are shown in Figures 16 and 17. From Figures 16 and 17, it can be seen that the sample before heating had P2S6 4- The peak of P2S6 is observed in the heated sample. 4- It can be seen that there is no peak at 420cm -1 The peak nearby is PS4 3- This indicates that Li3PS4 crystals are present in the solid electrolyte material after heat treatment, that is, in each of the samples of the examples.

[0120] <Composition and Heat Treatment Temperature Dependence of Precipitated Phases in Li3PS4 and Li3PS4-LiF Systems> Based on the results of X-ray diffraction measurements of each material in the Li3PS4 and Li3PS4-LiF systems, the composition and heat treatment temperature dependence of the presence or absence of the α-Li3PS4 phase (or a phase similar to the α-Li3PS4 phase) was evaluated. The plot is shown in Figure 18. In the figure, ● indicates a glass-ceramic having the α-Li3PS4 phase or a phase similar to the α-Li3PS4 phase (sometimes referred to here as the α phase for convenience), ▲ indicates a glass-ceramic having the β-Li3PS4 phase or a phase close to the β-Li3PS4 phase, and ■ indicates an amorphous (glass) state. The X-ray diffraction results for each material shown in Figure 18 and Figures 3 to 12 show that an LPS-based solid electrolyte material produced by heating a Li-ion conductive sulfide material that contains Li, P, and S but does not contain F or Cl and does not have the α-Li3PS4 phase to a temperature in the range of 230°C to 350°C at a heating rate of 100°C / min or more at 200°C has the α-Li3PS4 phase, and that an LPS-X-based solid electrolyte material produced by heating a Li-ion conductive sulfide material that contains Li, P, and S, and F and / or Cl and does not have the α-Li3PS4 phase to a temperature in the range of 200°C to 300°C has the α-Li3PS4 phase. This indicates that by setting appropriate heat treatment conditions for a Li-ion conductive sulfide material containing Li, P, and S (optionally with F and / or Cl), it is possible to obtain a solid electrolyte material that can maintain the α-Li3PS4 phase, which is originally a high-temperature phase with high ionic conductivity, even at room temperature.

[0121] Furthermore, as mentioned above, it was shown that in the system containing F (LPS-F system), the α-phase can be reliably precipitated even by heat treatment at a low temperature of less than 300°C, and the α-phase can be maintained even at room temperature, compared to the system not containing F (i.e., the LPS system). Furthermore, in the system containing F (LPS-F system), although its structure is unknown and cannot be identified, it was shown that the presence of LiF in the system allows the α-phase to be precipitated regardless of heat treatment conditions such as rapid heating, as in the LPS system.

[0122] (Storage Test of Solid Electrolyte Material) The storage stability of the α-Li3PS4 phase was examined for the solid electrolyte material of Example 40. The experiment was conducted by storing the solid electrolyte material of Example 40 in a nitrogen-filled container at 25°C for 500 hours and then performing XRD measurement. The results are shown in Figure 20. Figure 20 also shows the results of XRD measurement of the solid electrolyte material of Example 40 immediately after production for comparison. As shown in Figure 20, no difference was observed in the X-ray diffraction pattern between the sample immediately after production and the sample after 500 hours of storage. This indicates that the solid electrolyte material obtained by the production method of the present invention can maintain the α-Li3PS4 phase for a long period of time.

[0123] (Reference: XRD Pattern of Li3PS4 Crystal Polymorphs) For reference, Figure 19 shows the XRD pattern (using CuKα radiation) of the Li3PS4 crystal polymorphs. As shown in Figure 19, in the X-ray diffraction pattern using CuKα radiation, α-Li3PS4 exhibits only one unimodal peak near 2θ=18°. In contrast, β-Li3PS4 and γ-Li3PS4 exhibit two peaks near 2θ=18°. Based on this property, it is possible to determine whether a solid electrolyte material containing Li3PS4 has the α-Li3PS4 phase by observing the peak near 2θ=18° in the X-ray diffraction pattern using CuKα radiation.

Claims

1. α-Li ３ P.S. ４ 1. A method for producing a solid electrolyte material having a phase, comprising: Contains Li, P, and S but does not contain F or Cl, and is α-Li ３ P.S. ４ 1. A method comprising heating a phase-free Li-ion conducting sulfide material to a temperature in the range of 230°C to 350°C, wherein the heating rate at 200°C is 100°C / min or greater.

2. 2. The method according to claim 1, wherein the heating rate at 200°C in the heating step is 150°C / min or more.

3. 3. The method of claim 1 or 2, further comprising the step of obtaining the Li-ion conducting sulfide material by mechanochemical treatment of its raw material.

4. α-Li ３ P.S. ４ 1. A method for producing a solid electrolyte material having a phase, comprising: Contains Li, P, S, and F, and α-Li ３ P.S. ４ 1. A method comprising heating a phase-free Li-ion conducting sulfide material to a temperature in the range of 200°C to 300°C.

5. The solid electrolyte material has the following formula (I): Li ３ PS ４ ・aLiX (I) (Wherein, X is F, and a satisfies 0≦a≦2.0) The method of claim 4 having a composition represented by the formula:

6. 6. The method of claim 4 or 5, further comprising the step of obtaining the Li-ion conducting sulfide material by mechanochemical treatment of its raw material.

7. Contains Li, P, S, and F, and has a composition of Li ３ P.S. ４ aLiF (wherein a satisfies 0<a≦2.0), and is α-LiF at room temperature ３ P.S. ４ A solid electrolyte material having a phase.

8. α-Li obtained by the method according to claim 4 or 5 ３ P.S. ４ A solid electrolyte material having a phase.