METHOD FOR PRODUCING HALIDE

Abstract

The production method of the present disclosure includes heat-treating a material mixture containing a compound containing Y, a compound containing Gd, NH.sub.4α, Liβ, and Caγ.sub.2 in an inert gas atmosphere. The compound containing Y is at least one selected from the group consisting of Y.sub.2O.sub.3 and Yδ.sub.3, and the compound containing Gd is at least one selected from the group consisting of Gd.sub.2O.sub.3 and Gdε.sub.3. The material mixture contains at least one selected from the group consisting of Y.sub.2O.sub.3 and Gd.sub.2O.sub.3, and α, β, γ, δ, and ε are each independently at least one selected from the group consisting of F, Cl, Br, and I.

Claims

1. A method for producing a halide, the method comprising: heat-treating a material mixture containing a compound containing Y, a compound containing Gd, NH.sub.4α, Liβ, and Caγ.sub.2 in an inert gas atmosphere, wherein the compound containing Y is at least one selected from the group consisting of Y.sub.2O.sub.3 and Yδ.sub.3, wherein the compound containing Gd is at least one selected from the group consisting of Gd.sub.2O.sub.3 and Gdε.sub.3, wherein the material mixture contains at least one selected from the group consisting of Y.sub.2O.sub.3 and Gd.sub.2O.sub.3, and wherein α, β, γ, δ, and ε are each independently at least one selected from the group consisting of F, Cl, Br, and I.

2. The method for producing according to claim 1, wherein the material mixture contains Y.sub.2O.sub.3, Gd.sub.2O.sub.3, NH.sub.4α, Lip, and Caγ.sub.2.

3. The method for producing according to claim 1, wherein, in the heat-treating, the material mixture is heat-treated at higher than or equal to 350° C.

4. The method for producing according to claim 1, wherein, in the heat-treating, the material mixture is heat-treated at lower than or equal to 700° C.

5. The method for producing according to claim 4, wherein, in the heat-treating, the material mixture is heat-treated at lower than or equal to 650° C.

6. The method for producing according to claim 1, wherein, in the heat-treating, the material mixture is heat-treated in more than or equal to 1 hour and less than or equal to 72 hours.

7. The method for producing according to claim 1, wherein the heat-treating includes first heat-treating and second heat-treating performed after the first heat-treating, wherein, in the first heat-treating, the material mixture is heat-treated at first heat treatment temperature T1, wherein, in the second heat-treating, the material mixture is heat-treated at second heat treatment temperature T2, and wherein the second heat treatment temperature T2 is higher than or equal to 350° C. and is higher than the first heat treatment temperature T1.

8. The method for producing according to claim 7, wherein the first heat treatment temperature T1 is higher than or equal to 160° C. and lower than 350° C.

9. The method for producing according to claim 7, wherein the second heat treatment temperature T2 is lower than or equal to 700° C.

10. The method for producing according to claim 7, wherein, in the first heat-treating, the material mixture is heat-treated in more than or equal to 1 hour and less than or equal to 72 hours.

11. The method for producing according to claim 7, wherein, in the second heat-treating, the material mixture is heat-treated in more than or equal to 1 hour and less than or equal to 72 hours.

12. The method for producing according to claim 7, wherein a time period for heat-treating the material mixture in the first heat-treating is more than a time period for heat-treating the material mixture in the second heat-treating.

13. The method for producing according to claim 1, wherein α, β, γ, δ, and ε are each independently at least one selected from the group consisting of Cl and Br.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a flowchart showing an example of a production method in a first embodiment;

[0008] FIG. 2 is a flowchart showing an example of the production method in the first embodiment;

[0009] FIG. 3 is a flowchart showing an example of the production method in the first embodiment;

[0010] FIG. 4 is a flowchart showing an example of a production method in a second embodiment;

[0011] FIG. 5 is a graph showing an example of a heat treatment temperature profile in the production method in the second embodiment;

[0012] FIG. 6 is a schematic illustration of a press forming die 200 used to evaluate the ionic conductivity of a solid electrolyte material; and

[0013] FIG. 7 is a graph showing a Cole-Cole plot obtained by the measurement of the impedance of a solid electrolyte material in sample 1.

DETAILED DESCRIPTIONS

[0014] Embodiments will next be described with reference to the drawings.

First Embodiment

[0015] FIG. 1 is a flowchart showing an example of a production method in a first embodiment.

[0016] The production method in the first embodiment includes a heat treatment step S1000. In the heat treatment step S1000, a material mixture is heat-treated in an inert gas atmosphere.

[0017] The material mixture heat-treated in the heat treatment step S1000 is a material prepared by mixing a compound containing Y, a compound containing Gd, NH.sub.4α, Liβ, and Caγ.sub.2. The compound containing Y is at least one selected from the group consisting of Y.sub.2O.sub.3 and Yδ.sub.3. The compound containing Gd is at least one selected from the group consisting of Gd.sub.2O.sub.3 and Gdε.sub.3. The material mixture contains at least one selected from the group consisting of Y.sub.2O.sub.3 and Gd.sub.2O.sub.3. α, β, γ, δ, and ε are each independently at least one selected from the group consisting of F, Cl, Br, and I. The “compound containing Y” and the “compound containing Gd” will be hereinafter referred to as an “Y-containing compound” and a “Gd-containing compound,” respectively.

[0018] The production method in the first embodiment is a halide production method with high industrial productivity. The method with high industrial productivity is, for example, a method capable of mass production at low cost. Specifically, this production method allows a halide containing Li (i.e., lithium), Y (i.e., yttrium), Gd (i.e., gadolinium), and Ca (i.e., calcium) to be produced in a simple manner (i.e., by sintering in an inert gas atmosphere).

[0019] In the production method in the first embodiment, a vacuum sealed tube and a planetary ball mill may not be used.

[0020] The material mixture may contain Y.sub.2O.sub.3, Gd.sub.2O.sub.3, NH.sub.4α, Liβ, and Caγ.sub.2. Y.sub.2O.sub.3, Gd.sub.2O.sub.3, and NH.sub.4α contained in the material mixture are inexpensive, so that the production cost can be reduced.

[0021] To further improve the ionic conductivity of the halide, α, β, γ, δ, and ε may each independently be at least one selected from the group consisting of Cl and Br.

[0022] For example, when Y.sub.2O.sub.3, Gd.sub.2O.sub.3, NH.sub.4α, Liα (i.e., β in Liβ is α) and Caα.sub.2 (i.e., γ in Caγ.sub.2 is α) are used to produce Li.sub.2.8Ca.sub.0.1Y.sub.0.5Gd.sub.0.5α.sub.6, the reaction represented by the following formula (1) may proceed in the system as a whole.

0.5Y.sub.2O.sub.3Gd.sub.2O.sub.3+12NH.sub.4α+6Liα+0.2Caα.sub.2.fwdarw.Li.sub.2.8Ca.sub.0.1Y.sub.0.5Gd.sub.0.5α.sub.6+12NH.sub.3+6Hα+3H.sub.2O  (1)

[0023] In the heat treatment step S1000, for example, the powder of the material mixture may be placed in a container (e.g., a crucible) and heat-treated in a heating furnace. In this case, the material mixture heated to a prescribed temperature in the inert gas atmosphere may be held at the prescribed temperature for a prescribed time period or more. The heat treatment time period may be the length of time that does not cause a change in the composition of the heat-treated product due to volatilization of the halide etc. The heat treatment time period that does not cause a change in the composition of the heat-treated product means a heat treatment time period that does not cause deterioration of the ionic conductivity of the heat-treated product. With the production method in the first embodiment, a halide having, for example, an ionic conductivity higher than or equal to 3.0×10.sup.−9 S/cm at around room temperature can be produced.

[0024] The inert gas atmosphere means, for example, an atmosphere in which the total concentration of gases other than the inert gas is lower than or equal to 1% by volume. Examples of the inert gas include helium, nitrogen and argon.

[0025] After the heat treatment step S1000, the heat-treated product may be pulverized.

[0026] In this case, a pulverizing apparatus (such as a mortar or a mixer) may be used.

[0027] Part of metal cations in at least one selected from the group consisting of the Y-containing compound, the Gd-containing compound, Liβ, and Caγ.sub.2 that are contained in the material mixture may be replaced with other metal cations. Specifically, part of Y, Gd, Li, and Ca may be replaced with other metal cations. In other words, the material mixture may further contain an Y-containing compound with part of Y replaced with other metal cations, a Gd-containing compound with part of Gd replaced with other metal cations, a compound containing Liβ with part of Li replaced with other metal cations, or a compound containing Caγ.sub.2 with part of Ca replaced with other metal cations. In this case, the characteristics (e.g., ionic conductivity) of the halide produced can be improved. The rate of replacement of Y, Gd, Li, and Ca with other metal cations may be less than 50 mol %. In this case, the halide obtained has a more stable structure.

[0028] Part of metal cations in at least one selected from the group consisting of the Y-containing compound, the Gd-containing compound, Liβ, and Caγ.sub.2 that are contained in the material mixture may be replaced with, for example, at least one type of cations selected from the group consisting of Na, K, Mg, Sr, Ba, Zn, In, Sn, Bi, La, Ce, Pr, Nd, Pm, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, and Lu.

[0029] The material mixture may be a material prepared by mixing the Y-containing compound, the Gd-containing compound, NH.sub.4α, Liβ, and Caγ.sub.2.

[0030] Alternatively, the material mixture may be a material prepared by mixing the Y-containing compound, the Gd-containing compound, NH.sub.4α, Liβ, and Caγ.sub.2 and further mixing a material other than Y.sub.2O.sub.3, Yδ.sub.3, Gd.sub.2O.sub.3, Gdε.sub.3, NH.sub.4α, Liβ, and Caγ.sub.2.

[0031] In the heat treatment step S1000, the material mixture may be heat-treated at higher than or equal to 350° C. In this case, the industrial productivity of the method is high, and the halide produced thereby can have high ionic conductivity. When the heat treatment temperature is higher than or equal to 350° C., the reaction of the material mixture can proceed sufficiently. Specifically, the Y-containing compound, the Gd-containing compound, NH.sub.4α, Liβ, and Caγ.sub.2 can be allowed to react sufficiently. When the material mixture is heat-treated at higher than or equal to 350° C., the halide produced can have, for example, an ionic conductivity higher than or equal to 1.0×10.sup.−4 S/cm at around room temperature. Here, the heat treatment temperature is an ambient temperature.

[0032] To produce a halide having higher ionic conductivity using the highly industrially productive method, the material mixture may be heat-treated at lower than or equal to 700° C. The material mixture may be heat-treated at, for example, higher than or equal to 350° C. and lower than or equal to 700° C. When the heat treatment temperature is lower than or equal to 700° C., the halide formed by the solid phase reaction can be prevented from undergoing thermal decomposition. In this case, the ionic conductivity of the halide, which is the heat-treated product, can be increased. Specifically, the halide solid electrolyte material obtained has high quality.

[0033] To produce a halide having higher ionic conductivity using the highly industrially productive method, the material mixture may be heat-treated at lower than or equal to 650° C. The material mixture may be heat-treated at, for example, higher than or equal to 350° C. and lower than or equal to 650° C. In this case, the halide formed by the solid phase reaction can be prevented from undergoing thermal decomposition. Therefore, the ionic conductivity of the halide, which is the heat-treated product, can be increased. Specifically, the halide solid electrolyte material obtained has high quality.

[0034] In formula (1) above, Y.sub.2O.sub.3, Gd.sub.2O.sub.3, and NH.sub.4α may be first reacted with each other, and then Y.sub.2O.sub.3 and Gd.sub.2O.sub.3 may be halogenated. Next, a heat treatment profile may be set such that the halogenated Y.sub.2O.sub.3 and Gd.sub.2O.sub.3 are reacted with Liβ and Caγ.sub.2. In this case, the heat treatment temperature may be a temperature that is lower than the sublimation point or melting point of NH.sub.4α and allows the halogenated Y.sub.2O.sub.3 and Gd.sub.2O.sub.3 to react with Liβ and Caγ.sub.2. Specifically, the heat treatment temperature may be a temperature that is lower than the sublimation point or melting point of NH.sub.4α and allows the halide solid electrolyte material to be formed.

[0035] For example, when Y.sub.2O.sub.3, Gd.sub.2O.sub.3, NH.sub.4Cl, LiCl, and CaCl.sub.2 are used to synthesize Li.sub.2.8Ca.sub.0.1Y.sub.0.5 Gd.sub.0.5 Cl.sub.6, the reaction represented by formula (2) below may proceed.

0.5Y.sub.2O.sub.3+0.5Gd.sub.2O.sub.312NH.sub.4Cl+5.6LiCl+0.2CaCl.sub.2.fwdarw.2Li.sub.2.8Ca.sub.0.1Y.sub.0.5Gd.sub.0.5Cl.sub.6+12NH.sub.3+6HCl+3H.sub.2O  (2)

[0036] The heat treatment temperature in this reaction may be set to about 300° C. Specifically, the heat treatment temperature may be set to a temperature that is lower than about 335° C., which is the sublimation point of NH.sub.4Cl, and allows the halide solid electrolyte material to be formed. To produce a halide having higher ionic conductivity, the heat treatment temperature may be higher than or equal to 350° C. In this case, as shown in a second embodiment described later, the heat treatment step may include two or more sub-steps. In this case, the heat treatment temperature in the first sub-step in the heat treatment step may be set to a temperature lower than the sublimation point of NH.sub.4α, and the heat treatment temperature in the second and later sub-steps in the heat treatment step may be set to a higher temperature.

[0037] The material mixture may be heat-treated in more than or equal to 1 hour and less than or equal to 72 hours. In this case, the industrial productivity of the method is high, and the halide produced thereby can have higher ionic conductivity. When the heat treatment time period is more than or equal to 1 hour, the reaction of the material mixture can proceed sufficiently. Specifically, the Y-containing compound, the Gd-containing compound, NH.sub.4α, Liβ, and Caγ.sub.2 can be allowed to react sufficiently. When the heat treatment time period is less than or equal to 72 hours, the halide, which is the heat-treated product, can be prevented from volatilizing. Specifically, the halide obtained has the target composition ratio. Therefore, a reduction in the ionic conductivity of the halide due to a change in the composition can be prevented. Specifically, the halide solid electrolyte material obtained can have better quality.

[0038] FIG. 2 is a flowchart showing an example of the production method in the first embodiment.

[0039] As shown in FIG. 2, the production method in the first embodiment may further include a mixing step S1100.

[0040] The mixing step S1100 is performed before the heat treatment step S1000.

[0041] In the mixing step S1100, the Y-containing compound, the Gd-containing compound, NH.sub.4α, Liβ, and Caγ.sub.2 are mixed. A material mixture is thereby obtained. Specifically, the material to be heat-treated in the heat treatment step S1000 is obtained.

[0042] To mix the raw materials, a well-known mixer (such as a mortar, a blender, or a ball mill) may be used.

[0043] For example, in the mixing step S1100, powders of the raw materials may be prepared and mixed. In this case, in the heat treatment step S1000, the material mixture in a powder form may be heat-treated. The powdery material mixture obtained in the mixing step S1100 may be pressed and formed into pellets. In the heat treatment step S1000, the material mixture in the form of pellets may be heat-treated.

[0044] In the mixing step S1100, in addition to the Y-containing compound, the Gd-containing compound, NH.sub.4α, up, and Caγ.sub.2, a material other than Y.sub.2O.sub.3, Yδ.sub.3, Gd.sub.2O.sub.3, Gdε.sub.3, NH.sub.4α, Liβ, and Caγ.sub.2 may be further mixed to obtain a material mixture.

[0045] In the mixing step S1100, a raw material containing the Y-containing compound as a main component, a raw material containing the Gd-containing compound as a main component, a raw material containing NH.sub.4α as a main component, a raw material containing Liβ as a main component, and a raw material containing Caγ.sub.2 as a main component may be mixed. The main component is a component whose molar ratio is highest.

[0046] In the mixing step S1100, the Y-containing compound, the Gd-containing compound, NH.sub.4α, Liβ, and Caγ.sub.2 may be prepared such that the target composition is satisfied and then mixed.

[0047] When Y.sub.2O.sub.3 and Gd.sub.2O.sub.3 are used as the Y-containing compound and the GD-containing compound, respectively, Y.sub.2O.sub.3, Gd.sub.2O.sub.3, NH.sub.4Cl, LiCl, and CaCl.sub.2 may be mixed such that, for example, Y.sub.2O.sub.3:Gd.sub.2O.sub.3:NH.sub.4Cl:LiCl:CaCl.sub.2=0.25:0.25:6:2.8:0.1. In this case, a halide having a composition represented by Li.sub.2.8Ca.sub.0.1Y.sub.0.5Gd.sub.0.5Cl.sub.6 can be produced.

[0048] The molar ratio of the Y-containing compound, the Gd-containing compound, NH.sub.4α, Liβ, and Caγ.sub.2 may be adjusted in advance so as to compensate for the change in the composition that may occur in the heat treatment step S1000.

[0049] To allow the synthesis reaction in the heat treatment step S1000 to proceed preferably, the amount of NH.sub.4α prepared may be in excess of the total amount of Y.sub.2O.sub.3 and Gd.sub.2O.sub.3. For example, the amount of NH.sub.4α prepared is larger by 5 to 15 mol % than the total amount of Y.sub.2O.sub.3 and Gd.sub.2O.sub.3.

[0050] In the mixing step S1100, part of metal cations in at least one selected from the group consisting of the Y-containing compound, the Gd-containing compound, Liβ, and Caγ.sub.2 may be replaced with other metal cations. Specifically, part of Y, Gd, Li, and Ca may be replaced with other metal cations. In other words, an Y-containing compound with part of Y replaced with other metal cations, a Gd-containing compound with part of Gd replaced with other metal cations, a compound containing Liβ with part of Li replaced with other metal cations, or a compound containing Caγ.sub.2 with part of Ca replaced with other metal cations may be further mixed to obtain a material mixture. The rate of replacement of Y, Gd, Li, and Ca with metal cations may be less than 50 mol %.

[0051] FIG. 3 is a flowchart showing an example of the production method in the first embodiment.

[0052] As shown in FIG. 3, the production method in the first embodiment may further include a preparation step S1200.

[0053] The preparation step S1200 is performed before the mixing step S1100.

[0054] In the preparation step S1200, raw materials such as the Y-containing compound, the Gd-containing compound, NH.sub.4α, Liβ, and Caγ.sub.2 are prepared. Specifically, the materials to be mixed in the mixing step S1100 are prepared.

[0055] In the preparation step S1200, the raw materials such as the Y-containing compound, the Gd-containing compound, NH.sub.4α, Liβ, and Caγ.sub.2 may be synthesized. Alternatively, in the preparation step S1200, for example, materials with a purity higher than or equal to 99% may be used.

[0056] The materials prepared may be dried.

[0057] Examples of the form of each of the materials prepared include a crystalline form, a lump form, a flake form, and a powder form. In the preparation step S1200, crystalline, lump-like, or flake-like raw materials may be pulverized to obtain powdery raw materials.

[0058] In the preparation step S1200, part of metal cations in at least one selected from the group consisting of the Y-containing compound, the Gd-containing compound, Liβ, and Caγ.sub.2 may be replaced with other metal cations. Specifically, part of Y, Gd, Li, and Ca may be replaced with other metal cations. In other words, an Y-containing compound with part of Y replaced with other metal cations, a Gd-containing compound with part of Gd replaced with other metal cations, a compound containing Liβ with part of Li replaced with other metal cations, or a compound containing Caγ.sub.2 with part of Ca replaced with other metal cations may be further prepared. The rate of replacement of Y, Gd, Li, and Ca with other metal cations may be less than 50 mol %.

[0059] The halide produced by the production method in the first embodiment can be used as a solid electrolyte material. This solid electrolyte material is, for example, a solid electrolyte material having lithium ion conductivity. This solid electrolyte material is used, for example, for an all-solid-state lithium ion secondary battery.

Second Embodiment

[0060] A second embodiment will next be described. Features already described in the first embodiment will be omitted appropriately.

[0061] FIG. 4 is a flowchart showing an example of a production method in the second embodiment.

[0062] In the production method in the second embodiment, a heat treatment step S1000 includes a first heat treatment step S1001 and a second heat treatment step S1002. The second heat treatment step S1002 is performed after the first heat treatment step S1001.

[0063] In the first heat treatment step S1001, the material mixture is heat-treated at first heat treatment temperature T1. In the second heat treatment step S1002, the material mixture is heat-treated at second heat treatment temperature T2. The second heat treatment temperature T2 is higher than or equal to 350° C. and is higher than the first heat treatment temperature T1.

[0064] The production method in the second embodiment is a highly industrially productive method for producing a halide having higher ionic conductivity.

[0065] The production method in the second embodiment will next be described using an example in which the material mixture contains Y.sub.2O.sub.3 and Gd.sub.2O.sub.3.

[0066] In the first heat treatment step S1001, Y.sub.2O.sub.3, Gd.sub.2O.sub.3, and NH.sub.4α are reacted with each other at the first heat treatment temperature T1. Specifically, Y.sub.2O.sub.3 and Gd.sub.2O.sub.3 are halogenated. In the second heat treatment step S1002, the halogenated Y.sub.2O.sub.3 and Gd.sub.2O.sub.3 are reacted with Liβ and Caγ.sub.2 at the second heat treatment temperature T2. In this case, the halide, which is the heat-treated product, has higher crystallinity. Therefore, the ionic conductivity of the halide that is the heat-treated product can be increased. Specifically, the halide solid electrolyte material obtained has high quality.

[0067] To produce a halide having higher ionic conductivity using the highly industrially productive method, the first heat treatment temperature T1 may be higher than or equal to 160° C. and lower than 350° C. When the first heat treatment temperature T1 is higher than or equal to 160° C., the reaction of the material mixture can proceed sufficiently. Specifically, Y.sub.2O.sub.3, Gd.sub.2O.sub.3, and NH.sub.4α can be allowed to react sufficiently. When the first heat treatment temperature T1 is lower than 350° C., the sublimation of NH.sub.4α can be prevented. In this manner, the ionic conductivity of the halide, which is the heat-treated product, can be increased. Specifically, the halide solid electrolyte material obtained has high quality.

[0068] To produce a halide having higher ionic conductivity using the highly industrially productive method, the second heat treatment temperature T2 may be higher than or equal to 350° C. and lower than or equal to 700° C. When the second heat treatment temperature T2 is higher than or equal to 350° C., the reaction of the material mixture can proceed sufficiently. Specifically, the Y-containing compound, the Gd-containing compound, NH.sub.4a, Liβ, and Caγ.sub.2 can be allowed to react sufficiently. In this case, the halide, which is the heat-treated product, has higher crystallinity. When the second heat treatment temperature T2 is lower than or equal to 700° C., the halide formed by the solid phase reaction can be prevented from undergoing thermal decomposition. In this case, the ionic conductivity of the halide that is the heat-treated product can be increased. Specifically, the halide solid electrolyte material obtained has high quality.

[0069] FIG. 5 is a graph showing an example of a heat treatment temperature profile in the production method in the second embodiment.

[0070] As shown in FIG. 5, in the first heat treatment step S1001, the material mixture may be heat-treated for a first heat treatment time period P1. In the second heat treatment step S1002, the material mixture may be heat-treated for a second heat treatment time period P2.

[0071] To produce a halide having higher ionic conductivity using the highly industrially productive method, the first heat treatment time period P1 may be more than or equal to 1 hour and less than or equal to 72 hours. When the first heat treatment time period P1 is more than or equal to 1 hour, the material mixture (i.e., Y.sub.2O.sub.3, Gd.sub.2O.sub.3, and NH.sub.4α) can be allowed to react sufficiently. When the first heat treatment time period P1 is less than or equal to 72 hours, the “reaction product of Y.sub.2O.sub.3 and NH.sub.4α” and the “reaction product of Gd.sub.2O.sub.3 and NH.sub.4α” can be prevented from volatilizing. Specifically, the halide obtained has the target composition ratio. Therefore, a reduction in the ionic conductivity of the halide due to a change in the composition can be prevented. Specifically, the halide solid electrolyte material obtained has higher quality.

[0072] To produce a halide having higher ionic conductivity using the highly industrially productive method, the second heat treatment time period P2 may be more than or equal to 1 hour and less than or equal to 72 hours. When the second heat treatment time period P2 is more than or equal to 1 hour, the reaction of the material mixture can proceed sufficiently. Specifically, the Y-containing compound, the Gd-containing compound, NH.sub.4a, Liβ, and Caγ.sub.2 can be allowed to react sufficiently. When the second heat treatment time period P2 is less than or equal to 72 hours, the halide, which is the heat-treated product, can be prevented from volatilizing. Specifically, the halide obtained has the target composition ratio. Therefore, a reduction in the ionic conductivity of the halide due to a change in the composition can be prevented. Specifically, the halide solid electrolyte material obtained has higher quality.

[0073] P1>P2 may be satisfied. Specifically, the first heat treatment time period P1 may be more than the second heat treatment time period P2. In this case, the halide produced using the highly industrially productive method can have higher ionic conductivity.

[0074] In the first heat treatment step S1001, the material mixture (i.e., Y.sub.2O.sub.3, Gd.sub.2O.sub.3, and NH.sub.4α) can be allowed to react sufficiently at the first heat treatment temperature T1 for the first heat treatment time period P1. Specifically, Y.sub.2O.sub.3 and Gd.sub.2O.sub.3 can be halogenated sufficiently. Next, in the second heat treatment step S1002, the sufficiently halogenated Y.sub.2O.sub.3 and Yδ.sub.3 and the sufficiently halogenated Gd.sub.2O.sub.3 and Gdε.sub.3 are reacted with Liβ and Caγ.sub.2 at the second heat treatment temperature T2 for the second heat treatment time period P2. In this case, the halide, which is the heat-treated product, has higher crystallinity. Therefore, the halide that is the heat-treated product can have higher ionic conductivity. Specifically, the halide solid electrolyte material obtained has high quality.

[0075] In the first heat treatment step S1001, (NH.sub.4).sub.aYβ.sub.3+a (0≤ a≤3) may be synthesized from Y.sub.2O.sub.3 and NH.sub.4α. (NH.sub.4).sub.bGdα.sub.3+b (0≤b≤3) may be synthesized from Gd.sub.2O.sub.3 and NH.sub.4α.

[0076] In the second heat treatment step S1002, the (NH.sub.4).sub.aYα.sub.3+a and (NH.sub.4).sub.bGdα.sub.3+b produced in the first heat treatment step S1001 may be reacted with Liβ and Caγ.sub.2 to thereby obtain a halide (i.e., a solid electrolyte material).

[0077] Suppose, for example, that Y.sub.2O.sub.3, Gd.sub.2O.sub.3, NH.sub.4Cl, LiCl, and CaCl.sub.2 are used to synthesize Li.sub.2.8Ca.sub.0.1Y.sub.0.5Gd.sub.0.5Cl.sub.6. The first heat treatment temperature T1 is about 200° C., and the second heat treatment temperature T2 is about 500° C. In this case, NH.sub.4Cl is reacted with Y.sub.2O.sub.3 and Gd.sub.2O.sub.3 without sublimation in the first heat treatment step S1001, and (NH.sub.4).sub.aYα.sub.3+a (0≤ a≤3) and (NH.sub.4).sub.bGdα.sub.3+b (0≤b≤3) are mainly produced. Next, in the second heat treatment step S1002, (NH.sub.4).sub.aYα.sub.3+a and (NH.sub.4).sub.bGdα.sub.3+b are reacted with LiCl and CaCl.sub.2, and a halide solid electrolyte material having high crystallinity is thereby obtained. The halide solid electrolyte material obtained in the manner described above has high ionic conductivity.

[0078] The heat treatment step S1000 may include, in addition to the first heat treatment step S1001 and the second heat treatment step S1002, an additional heat treatment step. Specifically, the heat treatment step S1000 may include three or more sub-steps depending on the types of raw materials or the number of raw materials.

EXAMPLES

[0079] The present disclosure will next be described in more detail.

[0080] In the following description, halides produced by the production method of the present disclosure were evaluated as solid electrolyte materials.

<Sample 1>

(Production of Solid Electrolyte Material)

[0081] In an argon atmosphere with a dew point lower than or equal to −60° C. and an oxygen concentration lower than or equal to 0.0001% by volume (this atmosphere is hereinafter referred to as a “dry argon atmosphere”), powders of Y.sub.2O.sub.3, Gd.sub.2O.sub.3, NH.sub.4Cl, LiCl, LiBr, and CaBr.sub.2O.sub.3 were prepared as raw material powders such that the molar ratio Y.sub.2O.sub.3:Gd.sub.2O.sub.3:NH.sub.4Cl:LiCl:LiBr:CaBr.sub.2=0.25:0.25:6.6:0.5:2.35:0.075. These materials were pulverized in an agate mortar and mixed. The mixture obtained was placed in an alumina crucible and heat-treated in a nitrogen atmosphere at 500° C. for 1 hour. Specifically, the heat treatment temperatures T1 and T2 were both 500° C. The heat-treated product obtained was pulverized in an agate mortar. A solid electrolyte material in sample 1 containing Li, Ca, Y, Gd, Br, and Cl was thereby obtained.

(Evaluation of ionic conductivity)

[0082] FIG. 6 is a schematic illustration of a press forming die 200 used to evaluate the ionic conductivity of the solid electrolyte material.

[0083] The press forming die 200 includes an upper punch 201, a frame die 202, and a lower punch 203. The frame die 202 is formed of insulating polycarbonate. The upper punch 201 and the lower punch 203 are formed of electron conductive stainless steel.

[0084] The press forming die 200 shown in FIG. 6 was used to measure the impedance of the solid electrolyte material in sample 1 using the following method.

[0085] The solid electrolyte material powder in sample 1 was filled into the press forming die 200 in the dry argon atmosphere. The upper punch 201 and the lower punch 203 were used to apply a pressure of 300 MPa to the solid electrolyte material in sample 1 disposed inside the press forming die 200.

[0086] With the pressure applied, the upper punch 201 and the lower punch 203 were connected to a potentiostat (VersaSTAT 4, Princeton Applied Research) equipped with a frequency response analyzer. The upper punch 201 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 solid electrolyte material was measured at room temperature using an electrochemical impedance measurement method.

[0087] FIG. 7 is a graph showing a Cole-Cole plot obtained by the measurement of the impedance of the solid electrolyte material in sample 1.

[0088] In FIG. 7, the real value of the complex impedance at a measurement point at which the absolute value of the phase of the complex impedance was minimum was regarded as the ionic conduction resistance of the solid electrolyte material. See an arrow RSE shown in FIG. 7 for this real value. This resistance value was used to compute the ionic conductivity from the following formula (3).

σ=(R.sub.SE×S/t).sup.−1  (3)

Here, σ represents the ionic conductivity. S represents the area of contact between the solid electrolyte material and the upper punch 201 (that is equal to the cross-sectional area of a hollow portion of the frame die 202 in FIG. 6). R.sub.SE represents the resistance value of the solid electrolyte material in the impedance measurement. t represents the thickness of the solid electrolyte material (the thickness of a layer formed of the solid electrolyte material powder 101 in FIG. 6).

[0089] The ionic conductivity of the solid electrolyte material in sample 1 was 2.5×10.sup.−3 S/cm as measured at 25° C.

<Samples 2 to 24>

(Production of Solid Electrolyte Materials)

[0090] For samples 2 to 7 and 24, the same procedure as in sample 1 was repeated except that the heat treatment temperature was changed, and solid electrolyte materials in samples 2 to 7 and 24 were thereby obtained. The heat treatment temperatures are shown in Table 1.

[0091] For samples 8 to 18 and 23, instead of the heat treatment at 500° C. for 1 hour in sample 1, two-stage heat treatment was performed. The mixture of the raw materials was heat-treated at temperature T1 for 15 hours and then heat-treated at temperature T2 for 1 hour. Solid electrolyte materials in samples 8 to 18 and 23 were obtained using the same procedure as in sample 1 except for the above operation. The values of the temperatures T1 and T2 are shown in Table 1.

[0092] For sample 19, powders of Y.sub.2O.sub.3, Gd.sub.2O.sub.3, NH.sub.4Br, LiCl, and CaCl.sub.2) were prepared as raw material powders in the dry argon atmosphere such that the molar ratio Y.sub.2O.sub.3:Gd.sub.2O.sub.3:NH.sub.4Br:LiCl:CaCl.sub.2=0.25:0.25:6.6:2.85:0.075. These materials were pulverized in an agate mortar and mixed. The mixture obtained was placed in an alumina crucible and heat-treated in a nitrogen atmosphere at 240° C. for 15 hours and then heat-treated at 500° C. for 1 hour. The heat-treated product obtained was pulverized in an agate mortar. A solid electrolyte material in sample 19 was thereby obtained.

[0093] For sample 20, powders of Y.sub.2O.sub.3, Gd.sub.2O.sub.3, NH.sub.4Br, LiBr, and CaBr.sub.2 were prepared as raw material powders such that the molar ratio Y.sub.2O.sub.3:Gd.sub.2O.sub.3:NH.sub.4Br:LiBr:CaBr.sub.2=0.25:0.25:6.6:2.85:0.075. A solid electrolyte material in sample 20 was obtained using the same procedure as in sample 19 except for the above operation.

[0094] For sample 21, powders of Y.sub.2O.sub.3, GdCl.sub.3, NH.sub.4Cl, LiCl, LiBr, and CaBr.sub.2 were prepared as raw material powders in the dry argon atmosphere such that the molar ratio Y.sub.2O.sub.3:GdCl.sub.3:NH.sub.4Cl:LiCl:LiBr:CaBr.sub.2=0.25:0.25:3.3:0.5:2.35:0.075. These materials were pulverized in an agate mortar and mixed. The mixture obtained was placed in an alumina crucible and heat-treated in a nitrogen atmosphere at 200° C. for 15 hours and then heat-treated at 500° C. for 1 hour. The heat-treated product obtained was pulverized in an agate mortar. A solid electrolyte material in sample 21 was thereby obtained.

[0095] For sample 22, powders of YCl.sub.3, Gd.sub.2O.sub.3, NH.sub.4Cl, LiCl, LiBr, and CaBr.sub.2 were prepared as raw material powders such that the molar ratio YCl.sub.3:Gd.sub.2O.sub.3:NH.sub.4Cl:LiCl:LiBr:CaBr.sub.2=0.25:0.25:3.3:0.5:2.35:0.075. A solid electrolyte material in sample 22 was obtained using the same procedure as in sample 21 except for the above operation.

(Evaluation of Ionic Conductivity)

[0096] The ionic conductivity of each of the solid electrolyte materials in samples 2 to 24 was measured in the same manner as in sample 1. The measurement results are shown in Table 1.

[0097] In Table 1, raw material 1 is an oxide or halide containing Y. Raw material 2 is an oxide or halide containing Gd. Raw material 3 is ammonium halide. Raw material 4 is LiCl. Raw material 5 is LiBr. Raw material 6 is a halide containing Ca.

TABLE-US-00001 TABLE 1 Heat Molar ratio of raw materials treatment Raw Raw Raw material 1:raw material temperature Ionic Raw Raw material 3 material 6 2:raw material 3:raw material T1 T2 conductivity material 1 material 2 NH.sub.4α Caγ.sub.2 4:raw material 5:raw material 6 (° C.) (° C.) (S/cm) Sample 1 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 500 2.5 × 10.sup.−3 Sample 2 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 350 3.2 × 10.sup.−4 Sample 3 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 400 5.2 × 10.sup.−4 Sample 4 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 450 2.8 × 10.sup.−3 Sample 5 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 550 3.4 × 10.sup.−3 Sample 6 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 600 2.8 × 10.sup.−3 Sample 7 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 650 2.8 × 10.sup.−3 Sample 8 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 160 500 3.0 × 10.sup.−3 Sample 9 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 180 500 3.3 × 10.sup.−3 Sample 10 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 200 350 1.7 × 10.sup.−4 Sample 11 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 200 400 1.0 × 10.sup.−4 Sample 12 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 200 450 2.9 × 10.sup.−3 Sample 13 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 200 500 3.1 × 10.sup.−3 Sample 14 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 200 550 2.8 × 10.sup.−3 Sample 15 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 200 600 1.6 × 10.sup.−3 Sample 16 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 200 650 1.8 × 10.sup.−3 Sample 17 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 250 500 3.2 × 10.sup.−3 Sample 18 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 300 500 3.3 × 10.sup.−3 Sample 19 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Br CaCl.sub.2 0.25:0.25:6.6:2.85:0:0.075 240 500 2.0 × 10.sup.−3 Sample 20 Y.sub.2O.sub.3 Gd.sub.2Cl.sub.3 NH.sub.4Br CaBr.sub.2 0.25:0.25:6.6:0:2.85:0.075 240 500 1.0 × 10.sup.−3 Sample 21 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:3.3:0.5:2.35:0.075 200 500 2.4 × 10.sup.−3 Sample 22 YCl.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:3.3:0.5:2.35:0.075 200 500 2.6 × 10.sup.−3 Sample 23 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 200 300 4.0 × 10.sup.−9 Sample 24 Y.sub.2O.sub.3 Gd.sub.2O.sub.3 NH.sub.4Cl CaBr.sub.2 0.25:0.25:6.6:0.5:2.35:0.075 300 3.0 × 10.sup.−9

Discussion

[0098] As can be seen from samples 1 to 24, the solid electrolyte materials obtained have an ionic conductivity higher than or equal to 3.0×10.sup.−9 S/cm.

[0099] As can be seen from samples 8 to 22, even when the heat treatment step includes two sub-steps, the solid electrolyte materials obtained have high ionic conductivity.

[0100] As can be seen by comparing samples 1 to 22 with samples 23 and 24, when the step in which the heat treatment temperature is higher than or equal to 350° C. is included, the solid electrolyte material obtained has higher ionic conductivity. As can be seen by comparing samples 1 and 4 to 7 with samples 2 and 3, when the heat treatment temperature is higher than or equal to 450° C. and lower than or equal to 650° C., the ionic conductivity of the solid electrolyte material is further increased. As can be seen by comparing samples 8, 9, and 12 to 22 with samples 10 and 11, even in the case where the heat treatment step includes two sub-steps, when the second heat treatment temperature T2 is higher than or equal to 450° C. and lower than or equal to 650° C., the ionic conductivity of the solid electrolyte material is further increased.

[0101] As described above, the solid electrolyte materials produced by the production method of the present disclosure have high lithium ion conductivity. Moreover, the production method of the present disclosure is a simple method and is a method with high industrial productivity. The method with high industrial productivity is, for example, a method capable of mass production at low cost.

[0102] The production method of the present disclosure is used, for example, as a method for producing a solid electrolyte material. The solid electrolyte material produced by the production method of the present disclosure is used, for example, for an all-solid-state lithium ion secondary battery.