Method for producing fluoride

Abstract

A method for producing a fluoride according to the present disclosure comprises firing a mixture containing a titanium oxide, an aluminum oxide, a raw material fluoride having a composition different from that of the produced fluoride, and a lithium-containing compound in an inert gas atmosphere. The titanium oxide contains TiO2. The aluminum oxide contains Al2O3. The raw material fluoride contains NH4F. The lithium-containing compound includes at least one selected from the group consisting of lithium fluoride, lithium carbonate, and lithium nitrate.

Description

Fluoride manufacturing method

[0001] The present disclosure relates to a method for producing fluorides.

[0002] Patent Document 1 discloses a solid electrolyte material containing Li, Ti, M, and F, where M is at least one selected from the group consisting of Al and Y. Patent Document 1 describes that the solid electrolyte material is synthesized, for example, by mechanochemically reacting raw material powders, in which LiF, TiF4, and AlF3 are mixed, in a mixing device such as a planetary ball mill, or by firing the raw material powders in a vacuum sealed tube.

[0003] International Publication No. 2021 / 186809

[0004] In the prior art, it is desirable to produce fluorides in an industrially productive manner.

[0005] The method for producing a fluoride according to the present disclosure includes firing a mixture containing titanium oxide, aluminum oxide, a raw material fluoride having a composition different from that of the fluoride, and a lithium-containing compound under an inert gas atmosphere.

[0006] According to the present disclosure, fluorides can be produced by a method with high industrial productivity.

[0007] FIG. 1A is a flowchart showing an example of a method for producing a fluoride according to the first embodiment. FIG. 1B is a flowchart showing another example of the method for producing a fluoride according to the first embodiment. FIG. 1C is a flowchart showing yet another example of the method for producing a fluoride according to the first embodiment. FIG. 1D is a flowchart showing yet another example of the method for producing a fluoride according to the first embodiment. FIG. 1E is a flowchart showing yet another example of the method for producing a fluoride according to the first embodiment. FIG. 2 is a diagram showing X-ray diffraction patterns of powders of the fired products of Samples 1 to 10. FIG. 3 is a schematic diagram showing a pressure forming die used to evaluate the ionic conductivity of the fluorides.

[0008] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The following embodiments are merely examples, and the present disclosure is not limited to the following embodiments.

[0009] First Embodiment FIG. 1A is a flowchart showing an example of a method for producing a fluoride according to a first embodiment.

[0010] The method for producing a fluoride in the first embodiment includes a firing step S10.

[0011] In the calcination step S10, a mixture Mx containing titanium oxide, aluminum oxide, a raw material fluoride, and a lithium-containing compound is calcined in an inert gas atmosphere. The raw material fluoride is a fluoride having a composition different from that of the fluoride to be produced.

[0012] According to the above configuration, fluorides can be produced by a method with high industrial productivity. For example, materials such as TiF4 and AlF3 used in Patent Document 1 are expensive and difficult to obtain. In contrast, according to the fluoride production method of the present embodiment, fluorides can be produced by a simple method using relatively inexpensive and readily available materials such as titanium oxide and aluminum oxide, i.e., by simply firing the mixture Mx in an inert gas atmosphere. Therefore, fluorides can be produced in large quantities at low cost.

[0013] The fluoride produced by the fluoride production method of the present embodiment may contain Li, Ti, Al, and F. The fluoride may consist essentially of Li, Ti, Al, and F. Here, "the fluoride consists essentially of Li, Ti, Al, and F" means that the molar ratio (i.e., molar fraction) of the total amount of substance of Li, Ti, Al, and F to the total amount of substance of all elements constituting the fluoride is 90% or more. As an example, the molar ratio (i.e., molar fraction) may be 95% or more. The fluoride may consist only of Li, Ti, Al, and F.

[0014] The fluoride produced by the fluoride production method of the present embodiment may further contain Zr. The fluoride may consist essentially of Li, Ti, Zr, Al, and F. Here, "the fluoride consists essentially of Li, Ti, Zr, Al, and F" means that the ratio of the total amount of substance of Li, Ti, Zr, Al, and F to the total amount of substance of all elements constituting the fluoride (i.e., molar fraction) is 90% or more. As an example, the ratio (i.e., molar fraction) may be 95% or more. The fluoride may consist only of Li, Ti, Zr, Al, and F.

[0015] The fluoride produced by the fluoride production method of the present embodiment may contain a solid electrolyte represented by the following composition formula (1): In composition formula (1), α, β, γ, and δ are each independently a value greater than 0.

[0016] Li α Ti β M γ F δ ...(1)

[0017] The fluoride produced by the fluoride production method of the present embodiment may include a solid electrolyte represented by the following composition formula (2): In composition formula (2), M2 is at least one selected from the group consisting of Zr, Ni, Fe, and Cr, m is the valence of M2, and 0.1<x<0.9, 0≦y<0.1, 0≦z<0.1, and 0.8<b≦1.2 are satisfied.

[0018] Li6-(4-x-4y+my)b (Ti 1-x-y Al x M2 y ) b F 6-2z O z ... (2)

[0019] In the composition formula (2), when M2 contains a plurality of elements, m is the sum of the products of the composition ratios of the respective elements and the valences of the elements. For example, when M2 contains an element Me1 and an element Me2, and the element Me1 has a composition ratio of a1 and a valence of m1, and the element Me2 has a composition ratio of a2 and a valence of m2, m is expressed as m1 × a1 + m2 × a2.

[0020] To further enhance ion conductivity, in the solid electrolyte, the ratio of the amount of substance of Li to the total amount of substance of Ti and Al may be 1.12 or more and 5.07 or less.

[0021] The fluoride produced by the fluoride production method of the present embodiment may include a solid electrolyte represented by the following composition formula (3): In composition formula (3), 0<x<1 and 0<b≦1.5 are satisfied.

[0022] Li 6-(4-x)b (Ti 1-x Al x ) b F6...(3)

[0023] In order to enhance ionic conductivity, the formula (3) may satisfy the relationship 0.1≦x≦0.9.

[0024] In order to further increase the ionic conductivity, the formula (3) may satisfy the relationship 0.1≦x≦0.7.

[0025] The upper and lower limits of the range of x in composition formula (3) can be defined by any combination selected from the following numerical values: 0.1, 0.3, 0.4, 0.5, 0.6, 0.67, 0.7, 0.8, and 0.9.

[0026] In order to enhance ionic conductivity, the range of 0.8≦b≦1.2 may be satisfied in the composition formula (3).

[0027] The upper and lower limits of the range of b in composition formula (3) can be defined by any combination selected from the following numerical values: 0.8, 0.9, 0.94, 1.0, 1.06, 1.1, and 1.2.

[0028] The solid electrolyte may be crystalline or amorphous.

[0029] The fluoride produced by the fluoride production method of the present embodiment may contain elements that are inevitably mixed in. Examples of such elements are hydrogen, oxygen, or nitrogen. Such elements may be present in the raw material powder of the fluoride or in the atmosphere for producing or storing the fluoride.

[0030] Examples of titanium oxides include TiO2, Ti2O3, and TiO. The titanium oxide may contain TiO2. According to the above configuration, the ionic conductivity of the fluoride can be improved. The titanium oxide may be TiO2.

[0031] Examples of aluminum oxide include Al2O3. The aluminum oxide may contain Al2O3. According to the above configuration, the ionic conductivity of the fluoride can be improved. The aluminum oxide may be Al2O3.

[0032] The raw material fluoride may include at least one selected from the group consisting of inorganic fluorides and organic fluorides. According to the above configuration, the ionic conductivity of the fluoride can be improved.

[0033] Examples of inorganic fluorides include NH4F, CuF2, etc. Examples of organic fluorides include fluororesins, etc.

[0034] The starting fluoride may include an inorganic fluoride containing a non-metallic cation.

[0035] The raw material fluoride may contain NH4F. According to the above configuration, the ionic conductivity of the fluoride can be improved. The raw material fluoride may be NH4F.

[0036] In the present disclosure, the lithium-containing compound refers to a compound of lithium and another element or atomic group. The lithium-containing compound may be an inorganic compound. The lithium-containing compound may include at least one selected from the group consisting of lithium fluoride, lithium carbonate, and lithium nitrate. According to the above configuration, the ionic conductivity of the fluoride can be improved.

[0037] The mixture Mx may be a mixture of a material in which Ti in TiO2 and / or Al in Al2O3 are partially substituted with other cations, NH4F, and at least one selected from the group consisting of lithium fluoride, lithium carbonate, and lithium nitrate. This configuration can improve the ionic conductivity of the fluoride. The cation substitution rate of each of Ti and Al with other cations may be less than 50 mol%. This configuration can provide a fluoride with excellent structural stability.

[0038] The firing step S10 is performed in an inert gas atmosphere, such as an atmosphere containing helium gas, argon gas, nitrogen gas, or a mixture thereof.

[0039] In this embodiment, the firing temperature (ambient temperature) in the firing step S10 is higher than 100°C and not higher than 650°C. According to the above configuration, the materials contained in the mixture Mx can be sufficiently reacted, thereby improving the ionic conductivity of the fluoride. Furthermore, thermal decomposition of the fluoride produced by the solid-state reaction is suppressed. Therefore, a high-quality fluoride can be obtained.

[0040] The firing temperature in the firing step S10 may be 110° C. or higher and 650° C. or lower, 120° C. or higher and 650° C. or lower, 130° C. or higher and 650° C. or lower, 140° C. or higher and 650° C. or lower, or even 150° C. or higher and 650° C. According to the above configuration, the ionic conductivity of the fluoride can be further improved.

[0041] In the firing step S10, the mixture Mx may be heated to a predetermined temperature in an inert gas atmosphere and maintained for a predetermined time or longer. The firing time in the firing step S10 is preferably long enough to prevent compositional deviations in the fired product due to factors such as volatilization of fluorides. Such compositional deviations in the fired product reduce the ionic conductivity of the fluorides. The firing time in the firing step S10 is, for example, 1 hour to 48 hours.

[0042] In the firing step S10, the powder of the mixture Mx may be placed in a container such as a crucible and fired in a heating furnace.

[0043] The firing temperature in the firing step S10 may be higher than 150° C. and equal to or lower than 400° C. According to the above configuration, the ionic conductivity of the fluoride can be further improved.

[0044] The firing temperature in the firing step S10 may be 250° C. or higher and 400° C. or lower. According to the above configuration, the ionic conductivity of the fluoride can be further improved.

[0045] The firing temperature in the firing step S10 may be 300° C. or higher and 400° C. or lower. According to the above configuration, the ionic conductivity of the fluoride can be further improved.

[0046] The fired product obtained through the firing step S10 may contain a Li2TiF6 phase. According to the above-described configuration, the ionic conductivity of the fluoride can be improved.

[0047] A fired product containing a Li2TiF6 phase is more likely to be obtained when the firing temperature is higher than 150°C and not higher than 400°C, more likely to be obtained when the firing temperature is 250°C or higher and 400°C or lower, and even more likely to be obtained when the firing temperature is 300°C or higher and 400°C or lower.

[0048] The presence of the Li2TiF6 phase in the fired product obtained through firing step S10 can be confirmed, for example, by subjecting the fired product to X-ray diffraction measurement. Specifically, the presence of the Li2TiF6 phase in the fired product can be confirmed by observing reflections attributable to tetragonal Li2TiF6 belonging to the space group P42 / mnm in the X-ray diffraction pattern.

[0049] Although not shown in the drawings, the fired product removed from the container after the firing step S10 may be pulverized using a pulverizing tool such as a mortar or a mixer.

[0050] FIG. 1B is a flowchart showing another example of the method for producing a fluoride according to the first embodiment.

[0051] As shown in FIG. 1B, the method for producing a fluoride according to the first embodiment may further include a mixing step S11.

[0052] The mixing step S11 is performed before the firing step S10. In the mixing step S11, raw materials, titanium oxide, aluminum oxide, raw fluoride, and a lithium-containing compound, are mixed. According to the above configuration, a uniformly mixed mixture Mx can be obtained. The mixture Mx is fired in an inert gas atmosphere in the firing step S10.

[0053] The mixing method is not limited, and known mixing tools or mixing devices can be used, such as a ball mill, a pot mill, a V-type mixer, a double-cone type mixer, and an automatic mortar.

[0054] For example, powders of titanium oxide, aluminum oxide, raw fluoride, and lithium-containing compound may be mixed in the mixing step S11. In this case, the powder mixture Mx may be fired in the firing step S10.

[0055] For example, the powder mixture Mx obtained through the mixing step S11 may be formed into pellets by uniaxial pressing. In this case, the pellet-shaped mixture Mx may be fired in the firing step S10.

[0056] In the mixing step S11, the titanium oxide, the aluminum oxide, the raw fluoride, and the lithium-containing compound may be mixed to a desired molar ratio.

[0057] FIG. 1C is a flowchart showing yet another example of the method for producing a fluoride according to the first embodiment.

[0058] As shown in FIG. 1C, the method for producing a fluoride according to the first embodiment may further include a preparation step S12.

[0059] The preparation step S12 is performed before the mixing step S11. In the preparation step S12, materials such as titanium oxide, aluminum oxide, raw fluoride, and lithium-containing compound are prepared.

[0060] In the preparation step S12, materials such as titanium oxide, aluminum oxide, raw fluoride, and lithium-containing compound may be prepared by synthesis. Commercially available materials such as titanium oxide, aluminum oxide, raw fluoride, and lithium-containing compound may be used. Commercially available products preferably have a purity of 99% or higher. Dried materials may be used as the materials. The shape of the materials is not particularly limited. The material may be, for example, powder or lumps. A powdered material may be obtained by pulverizing a lumpy material. The shape of the particles in the powdered material is not particularly limited and may be, for example, spherical, oval, fibrous, or scaly. Each material may be crystalline or amorphous.

[0061] FIG. 1D is a flowchart showing yet another example of the method for producing a fluoride according to the first embodiment.

[0062] As shown in FIG. 1D, the method for producing a fluoride according to the first embodiment may further include a pulverization step S20.

[0063] The pulverization step S20 is performed after the firing step S10. In the pulverization step S20, the fired product B obtained through the firing step S10 is pulverized. According to the above configuration, the particle size of the fluoride can be adjusted.

[0064] The grinding process in the grinding step S20 may be a wet grinding process or a dry grinding process. In the wet grinding process, the material is mixed with a solvent and then ground using mainly shear and friction forces. In the wet grinding process, the surface of the material particles is scraped to generate small particles. In the dry grinding process, the dried material is ground mainly by impact force in air or an inert gas atmosphere. In the dry grinding process, the entire material particles are divided into multiple clumps.

[0065] The pulverization treatment in the pulverization step S20 may be a wet pulverization treatment. In this case, in the pulverization step S20, the fired product B is pulverized in a solvent.

[0066] The solvent used in the wet grinding treatment may be an organic solvent or an inorganic solvent such as water.

[0067] The dielectric constant of the organic solvent may be 2 or more and 70 or less. By using an organic solvent having a dielectric constant in the above range, phase separation of the obtained fluoride is easily suppressed. Therefore, according to the above configuration, a high-quality fluoride can be obtained.

[0068] The organic solvent may contain at least one selected from the group consisting of γ-butyrolactone, propylene carbonate, butyl acetate, and tetralin. The fired product B obtained through the firing step S10 exhibits excellent dispersibility in the organic solvent. Therefore, the above configuration can improve the ionic conductivity of the fluoride.

[0069] In the grinding step S20, grinding media may be used. The shape of the grinding media is not particularly limited, and may be spherical, bale-shaped, or the like. The particle size of the material after grinding depends greatly on the particle size of the grinding media. In this embodiment, for example, when the grinding media is spherical, it is desirable that the grinding media have a diameter of 1.0 mm or less.

[0070] When grinding media are used, the fired product B, the solvent, and the grinding media may be placed in a container and the container may be rotated to grind the fired product B. The grinding method is not particularly limited, and mechanical grinding may be used. The grinding method may employ a grinding device such as a roll mill, a pot mill, or a planetary ball mill. A bead mill may be used to grind the material using grinding media. After grinding, the grinding media can be separated using a sieve or the like. The grinding conditions may be set appropriately depending on the device used.

[0071] Fig. 1E is a flowchart showing yet another example of the method for producing a fluoride according to Embodiment 1. The example shown in Fig. 1E is an example in which the pulverization treatment in the pulverization step S20 is a wet pulverization treatment.

[0072] As shown in FIG. 1E, the method for producing a fluoride according to the first embodiment may further include a removal step S30.

[0073] The removal step S30 is performed after the pulverization step S20. In the removal step S30, the solvent contained in the pulverized product Pv obtained through the pulverization step S20 is removed. According to the above configuration, the solvent can be removed from the fluoride whose particle size has been adjusted by the pulverization step S20.

[0074] In the removal step S30, the solvent may be removed from the pulverized product Pv by reduced pressure drying. Reduced pressure drying is a method of removing the solvent from the pulverized product under a pressure atmosphere lower than atmospheric pressure. The pressure atmosphere lower than atmospheric pressure is, for example, -0.01 MPa or less in gauge pressure. In the removal step S30, the solvent may be removed from the pulverized product Pv by vacuum drying. Vacuum drying is, for example, a method of removing the solvent from the pulverized product at or below the vapor pressure at a temperature 20°C lower than the boiling point of the solvent. The heating temperature of the pulverized product Pv in reduced pressure drying or vacuum drying is, for example, 50°C or higher and 300°C or lower.

[0075] In the removal step S30, the solvent may be removed from the pulverized material Pv by heating the pulverized material Pv under an inert gas atmosphere. The heating temperature is, for example, 50°C or higher and 300°C or lower.

[0076] The fluoride produced by the fluoride producing method according to the present embodiment can be used as a solid electrolyte material. The solid electrolyte material may be, for example, a solid electrolyte having lithium ion conductivity. The solid electrolyte material can be used in, for example, a battery (for example, an all-solid-state secondary battery).

[0077] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0078] (Technology 1) A method for producing a fluoride, comprising: firing a mixture containing titanium oxide, aluminum oxide, a raw material fluoride having a composition different from the fluoride, and a lithium-containing compound under an inert gas atmosphere.

[0079] According to the method for producing a fluoride according to Technology 1, a fluoride can be produced by a method with high industrial productivity.

[0080] (Technology 2) The method for producing a fluoride according to Technology 1, wherein the firing temperature is higher than 100°C and not higher than 650°C. This configuration allows the materials contained in the mixture to react sufficiently, thereby improving the ionic conductivity of the fluoride. Furthermore, thermal decomposition of the fluoride produced by the solid-state reaction is suppressed. Therefore, a high-quality fluoride can be obtained.

[0081] (Technology 3) The method for producing a fluoride according to Technology 1 or 2, wherein the firing temperature is 150° C. or higher and 650° C. or lower. According to this configuration, the ionic conductivity of the fluoride can be further improved.

[0082] (Technology 4) The method for producing a fluoride according to any one of Technologies 1 to 3, further comprising pulverizing the fired product obtained through the firing. With this configuration, the particle size of the fluoride can be adjusted.

[0083] (Technology 5) The method for producing a fluoride according to Technology 4, wherein the pulverization includes pulverizing the fired product in a solvent, and the production method further includes removing the solvent contained in the pulverized product obtained through the pulverization. With this configuration, it is possible to remove the solvent from the fluoride whose particle size has been adjusted by pulverization.

[0084] (Technology 6) The method for producing a fluoride according to any one of Technologies 1 to 5, wherein the titanium oxide contains TiO2. According to this configuration, the ionic conductivity of the fluoride can be improved.

[0085] (Technology 7) The method for producing a fluoride according to any one of Technologies 1 to 6, wherein the aluminum oxide contains Al2O3. According to this configuration, the ionic conductivity of the fluoride can be improved.

[0086] (Technology 8) The method for producing a fluoride according to any one of Technologies 1 to 7, wherein the raw material fluoride includes at least one selected from the group consisting of inorganic fluorides and organic fluorides. With this configuration, the ionic conductivity of the fluoride can be improved.

[0087] (Technology 9) The method for producing a fluoride according to Technology 8, wherein the raw material fluoride contains NH4F. According to this configuration, the ionic conductivity of the fluoride can be improved.

[0088] (Technology 10) The method for producing a fluoride according to any one of Technologies 1 to 9, wherein the lithium-containing compound includes at least one selected from the group consisting of lithium fluoride, lithium carbonate, and lithium nitrate. With this configuration, the ionic conductivity of the fluoride can be improved.

[0089] (Technology 11) The method for producing a fluoride according to any one of Technologies 1 to 10, wherein the firing temperature is higher than 150° C. and not higher than 400° C. According to this configuration, the ionic conductivity of the fluoride can be further improved.

[0090] (Technology 12) The method for producing a fluoride according to any one of Technologies 1 to 11, wherein the firing temperature is 300° C. or more and 400° C. or less. According to this configuration, the ionic conductivity of the fluoride can be further improved.

[0091] (Technology 13) The method for producing a fluoride according to Technology 5, wherein the relative dielectric constant of the solvent is from 2 to 70. According to this configuration, a high-quality fluoride can be obtained.

[0092] (Technology 14) The method for producing a fluoride according to Technology 5, wherein the solvent contains at least one selected from the group consisting of γ-butyrolactone, propylene carbonate, butyl acetate, and tetralin. With this configuration, the ionic conductivity of the fluoride can be improved.

[0093] (Technology 15) The method for producing a fluoride according to any one of Technologies 1 to 14, wherein the fired product obtained through the firing contains a Li2TiF6 phase. According to this configuration, the ionic conductivity of the fluoride can be improved.

[0094] The present disclosure will be described in more detail below using examples. The following are illustrative and not limiting of the present disclosure. In the following examples, the fluoride produced by the production method of the present disclosure is produced and evaluated as a solid electrolyte material.

[0095] (Preparation of fired product) <Sample 1> TiO2, Al2O3, NH4F, and LiF were prepared in an argon atmosphere with a dew point of -60°C or less, in a molar ratio of TiO2:Al2O3:NH4F:LiF = 0.3:0.35:6:2. These materials were mixed while being pulverized in an agate mortar. The resulting mixture was placed in an alumina crucible, heated to 150°C in a nitrogen atmosphere, and fired at a firing temperature of 150°C (ambient temperature) for 2 hours. In this way, the fired product of Sample 1 was obtained.

[0096] <Sample 2> The obtained mixture was placed in an alumina crucible, heated to 250°C in a nitrogen atmosphere, and fired at the firing temperature of 250°C for 2 hours to obtain a fired product of Sample 2 in the same manner as Sample 1.

[0097] <Sample 3> The obtained mixture was placed in an alumina crucible, heated to 300°C in a nitrogen atmosphere, and fired at 300°C for 2 hours, to obtain a fired product of Sample 3 in the same manner as Sample 1.

[0098] <Sample 4> The obtained mixture was placed in an alumina crucible, heated to 350°C in a nitrogen atmosphere, and fired at the firing temperature of 350°C for 2 hours, to obtain a fired product of Sample 4 in the same manner as Sample 1.

[0099] <Sample 5> The obtained mixture was placed in an alumina crucible, heated to 400°C in a nitrogen atmosphere, and fired at 400°C for 2 hours, to obtain a fired product of Sample 5 in the same manner as Sample 1.

[0100] <Sample 6> The obtained mixture was placed in an alumina crucible, heated to 500°C in a nitrogen atmosphere, and fired at the firing temperature of 500°C for 2 hours, to obtain a fired product of Sample 6 in the same manner as Sample 1.

[0101] <Sample 7> The obtained mixture was placed in an alumina crucible, heated to 600°C in a nitrogen atmosphere, and fired at the firing temperature of 600°C for 2 hours, to obtain a fired product of Sample 7 in the same manner as Sample 1.

[0102] <Sample 8> The obtained mixture was placed in an alumina crucible, heated to 650°C in a nitrogen atmosphere, and fired at the firing temperature of 650°C for 2 hours, to obtain a fired product of Sample 8 in the same manner as Sample 1.

[0103] <Sample 9> TiO2, Al2O3, NH4F, and Li2CO3 were prepared in a molar ratio of TiO2:Al2O3:NH4F:Li2CO3 = 0.3:0.35:6:1 in an argon atmosphere with a dew point of -60°C or lower. These materials were mixed while being ground in an agate mortar. The resulting mixture was placed in an alumina crucible, heated to 400°C in a nitrogen atmosphere, and fired at 400°C for 2 hours. In this way, the fired product of Sample 9 was obtained.

[0104] <Sample 10> TiO2, Al2O3, NH4F, and LiNO3 were prepared in a molar ratio of TiO2:Al2O3:NH4F:LiNO3 = 0.3:0.35:6:2 in an argon atmosphere with a dew point of -60°C or lower. These materials were mixed while being ground in an agate mortar. The resulting mixture was placed in an alumina crucible, heated to 400°C in a nitrogen atmosphere, and fired at 400°C for 2 hours. In this way, the fired product of Sample 10 was obtained.

[0105] <Sample 11> The obtained mixture was placed in an alumina crucible, heated to 100°C in a nitrogen atmosphere, and fired at the firing temperature of 100°C for 2 hours to obtain a fired product of Sample 11 in the same manner as Sample 1.

[0106] (X-ray diffraction measurement of fired products) The fired products of Samples 1 to 11 were placed in an agate mortar and pulverized. The X-ray diffraction patterns of each fired product were measured using the following method. An X-ray diffractometer (MiniFlex600, manufactured by Rigaku) ​​was used to evaluate the crystalline structure of the fired products. Using this device, the X-ray diffraction patterns of the powders of the fired products of Samples 1 to 11 were measured in a dry environment with a dew point of -50°C or lower. Cu-Kα radiation was used as the X-ray source. That is, the X-ray diffraction patterns were measured using the θ-2θ method using Cu-Kα radiation (wavelengths 1.5405 Å and 1.5444 Å) as the X-rays. Figure 2 shows the X-ray diffraction patterns of the powders of the fired products of Samples 1 to 10.

[0107] In Figure 2, the four dashed lines indicate the positions of the diffraction peaks attributable to LiTiF. As shown in Figure 2, all four diffraction peaks attributable to LiTiF were observed in the powders of the fired products of Samples 2 to 5 and Samples 9 to 10. On the other hand, all four diffraction peaks attributable to LiTiF were not observed in the powders of the fired products of Samples 1 and 6 to 8. In other words, fired products containing a LiTiF phase were more likely to be obtained when the firing temperature was greater than 150°C and less than 400°C, and fired products containing a LiTiF phase were even more likely to be obtained when the firing temperature was greater than 250°C and less than 400°C. Furthermore, in the X-ray diffraction patterns of the powders of the fired products of Samples 3 to 5, the four diffraction peaks attributable to LiTiF were particularly prominent. In other words, fired products containing a LiTiF phase were even more likely to be obtained when the firing temperature was greater than 300°C and less than 400°C.

[0108] Although not shown, all four diffraction peaks due to Li2TiF6 were observed in the powder of the fired product of Sample 11.

[0109] (Preparation of Fluorides) 0.5 g of the calcined material of Samples 1 to 11 was prepared. 14 g of γ-butyrolactone was prepared as a solvent. These materials were placed in the grinding pot of a planetary ball mill (Fritsch, PULVERISETTE 7) and gently stirred with a spatula. 5 g of grinding media was then placed in the grinding pot of the planetary ball mill. Zirconia balls with a diameter of 0.5 mm were used as the grinding media. The calcined material was ground at 500 rpm for 24 hours. The grinding media was then separated from the ground material using a sieve with 212 μm openings. The separated ground material was placed in a sealed glass beaker. While flowing nitrogen gas into the sealed beaker at 10 L / min, the temperature was increased to 250°C and the ground material was heated at 250°C for 2 hours. In this way, the solvent was removed from the ground material, and the fluorides of Samples 1 to 11 were obtained.

[0110] (Evaluation of ionic conductivity) Fig. 3 is a schematic diagram showing a pressure-molding die 200 used to evaluate the ionic conductivity of fluoride. The pressure-molding die 200 included a frame 201, an upper punch 202, and a lower punch 203. The frame 201 was made of electronically insulating polycarbonate. Both the upper punch 202 and the lower punch 203 were made of electronically conductive stainless steel.

[0111] Using the pressure molding die 200 shown in FIG. 3, the ionic conductivity of fluoride in Samples 1 to 11 was measured by the following method.

[0112] Fluoride powder 101 was filled into a pressing die 200 in a dry atmosphere having a dew point of −60° C. or lower. A pressure of 300 MPa was uniaxially applied to the fluoride powder 101 using an upper punch 202 and a lower punch 203. While the pressure was applied, the upper punch 202 and the lower punch 203 were connected to a potentiostat (VersaSTAT4, manufactured by Princeton Applied Research) equipped with a frequency response analyzer. The upper punch 202 was connected to a working electrode and a potential measurement terminal. The lower punch 203 was connected to a counter electrode and a reference electrode. The impedance of the fluoride powder 101 was measured by electrochemical impedance measurement at room temperature (25° C.).

[0113] Table 1 shows the ionic conductivities of the fluoride powders of Samples 1 to 11 together with the firing temperatures and the like.

[0114]

[0115] <Discussion> As shown in Table 1, the fluorides of Samples 1 to 10 were 2.0 × 10 at room temperature. -3 The ion conductivity of Sample 11 was high at 2.0 × 10 s / cm or more. This is thought to be because the firing temperature in the firing step was higher than 100°C and not higher than 650°C, which allowed the mixture containing titanium oxide, aluminum oxide, raw fluoride, and lithium-containing compound to react sufficiently. In contrast, the fluoride of Sample 11 exhibited a high ionic conductivity of 2.0 × 10 s / cm or more at room temperature. -4The ionic conductivity was low at μS / cm, which is thought to be due to the fact that the firing temperature in the firing step was 100° C., which resulted in insufficient reaction of the mixture.

[0116] The fluoride content of Samples 2 to 5 and Samples 9 to 10 was 2.9×10 at room temperature. -2 The ionic conductivity was particularly high at more than μS / cm. This is thought to be because the firing temperature in the firing step was higher than 150° C. and not higher than 400° C., which made it easier for Li2TiF6 to be produced.

[0117] From the above results, it can be seen that the manufacturing method of the present disclosure enables the production of fluorides in an industrially highly productive manner. Specifically, fluorides can be produced in a simple manner using relatively inexpensive and readily available materials such as titanium oxide and aluminum oxide. Therefore, the manufacturing method of the present disclosure enables the production of large quantities of fluorides at low cost. Furthermore, the fluorides produced by the manufacturing method of the present disclosure can have high lithium ion conductivity.

[0118] The manufacturing method of the present disclosure can be used, for example, as a manufacturing method of a solid electrolyte material. Furthermore, the solid electrolyte material manufactured by the manufacturing method of the present disclosure can be used, for example, in a battery (e.g., an all-solid-state secondary battery).

Claims

1. A method for producing a fluoride, comprising: firing a mixture containing titanium oxide, aluminum oxide, a raw material fluoride having a composition different from that of the fluoride, and a lithium-containing compound under an inert gas atmosphere.

2. The method for producing a fluoride according to claim 1, wherein the firing temperature is higher than 100°C and not higher than 650°C.

3. The method for producing a fluoride according to claim 1, wherein the firing temperature is 150°C or higher and 650°C or lower.

4. The method for producing a fluoride according to claim 1, further comprising pulverizing the fired product obtained through the firing.

5. The method for producing a fluoride according to claim 4, wherein the pulverization comprises pulverizing the fired product in a solvent, and the production method further comprises removing the solvent contained in the pulverized product obtained through the pulverization.

6. The method for producing a fluoride according to claim 1, wherein the titanium oxide includes TiO2.

7. The method for producing a fluoride according to claim 1, wherein the aluminum oxide includes Al2O3.

8. The method for producing a fluoride according to claim 1, wherein the raw material fluoride includes at least one selected from the group consisting of inorganic fluorides and organic fluorides.

9. The method for producing a fluoride according to claim 8, wherein the raw fluoride contains NH4F.

10. The method for producing a fluoride according to claim 1, wherein the lithium-containing compound includes at least one selected from the group consisting of lithium fluoride, lithium carbonate, and lithium nitrate.

11. The method for producing a fluoride according to claim 1, wherein the firing temperature is higher than 150°C and not higher than 400°C.

12. The method for producing a fluoride according to claim 1, wherein the firing temperature is 300°C or higher and 400°C or lower.

13. The method for producing a fluoride according to claim 5, wherein the solvent has a relative dielectric constant of 2 or more and 70 or less.

14. The method for producing a fluoride according to claim 5, wherein the solvent includes at least one selected from the group consisting of γ-butyrolactone, propylene carbonate, butyl acetate, and tetralin.

15. The method for producing a fluoride according to claim 1, wherein the fired product obtained through the firing step contains a Li2TiF6 phase.

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