US-20260125274-A1 - METHOD FOR PRODUCING PYROCHLORE-TYPE OXIDE

Abstract

A method for producing a pyrochlore-type oxide containing a plurality of cations, including an alkali metal cation, in a composition, includes a mixing process in which a plurality of raw materials, each containing one of the plurality of cations, are mixed, and a heating process in which a mixture containing the plurality of raw materials is heated by a liquid-phase method at a predetermined temperature to generate a composite oxide having a corundum structure and containing at least the alkali metal cation in a composition.

Inventors

• Hitoshi Onodera
• Shuhei Yoshida
• Yuta SHIMONISHI

Assignees

• DENSO CORPORATION

Dates

Publication Date

20260507

Application Date

20251229

Priority Date

20231025

Claims (12)

1. 1 . A method for producing a pyrochlore-type oxide containing a plurality of cations, including an alkali metal cation, in a composition, the method comprising: a mixing process in which a plurality of raw materials, each containing one of the plurality of cations, are mixed; and a heating process in which a mixture containing the plurality of raw materials is heated by a liquid-phase method at a predetermined temperature to produce a composite oxide having a corundum structure and containing at least the alkali metal cation in a composition, wherein the composite oxide is a precursor of the pyrochlore-type oxide as a target compound.
2. 2 . The method for producing the pyrochlore-type oxide according to claim 1 , wherein the pyrochlore-type oxide has a composition formula of Aa 2−α Ab (1+α)/3 B 2 O 7−β X γ , where Aa is an alkali metal, Ab contains at least a lanthanoid, B is a cation different from Aa and Ab, X is an anion substitutable for an O atom constituting the pyrochlore-type oxide, α is in a range of 0.6<α<2.0, β is in a range of 0<β≤1, and γ is in a range of 0<γ≤1, and the pyrochlore-type oxide has a defect structure.
3. 3 . The method for producing the pyrochlore-type oxide according to claim 1 , wherein, in the liquid-phase method, at least one of the plurality of raw materials is at least partially dissolved or melted.
4. 4 . The method for producing the pyrochlore-type oxide according to claim 1 , wherein the liquid-phase method is a hydrothermal synthesis method.
5. 5 . The method for producing the pyrochlore-type oxide according to claim 1 , wherein the predetermined temperature is within a range of 150° C. to 1000° C.
6. 6 . The method for producing the pyrochlore-type oxide according to claim 1 , wherein a liquid used in the liquid-phase method is a solution or melt of an alkali metal compound containing the alkali metal cation.
7. 7 . The method for producing the pyrochlore-type oxide according to claim 1 , wherein a liquid used in the liquid-phase method is alkaline.
8. 8 . The method for producing the pyrochlore-type oxide according to claim 1 , wherein the pyrochlore-type oxide produced from the composite oxide has a particle size on an order of nanometers to micrometers.
9. 9 . The method for producing the pyrochlore-type oxide according to claim 1 , wherein the heating process is defined as a first heating process, and the method further comprising a second heating process in which the composite oxide produced in the first heating process is heated to produce the pyrochlore-type oxide.
10. 10 . The method for producing the pyrochlore-type oxide according to claim 9 , wherein a heating temperature in the second heating process is higher than a heating temperature in the first heating process.
11. 11 . The method for producing the pyrochlore-type oxide according to claim 1 , wherein each of the plurality of raw materials includes at least one selected from a group consisting of fluorides, acetates, chlorides, hydroxides, carbonates, and oxides.
12. 12 . The method for producing the pyrochlore-type oxide according to claim 1 , wherein the pyrochlore-type oxide is an electrolyte for a secondary battery.

Description

CROSS REFERENCE TO RELATED APPLICATIONS The present application is a continuation application of International Patent Application No. PCT/JP2024/037864 filed on Oct. 24, 2024, which designated the U.S. and claims the benefit of priority from Japanese Patent Application No. 2023-183092 filed on Oct. 25, 2023. The entire disclosures of all of the above applications are incorporated herein by reference. TECHNICAL FIELD The present disclosure relates to a method for producing a pyrochlore-type oxide. BACKGROUND Conventionally, there has been known a method for producing a pyrochlore-type oxide, in which a precursor composed of a lithium-containing complex oxide is mixed with raw materials including LiF and LaF3. SUMMARY The present disclosure provides a method for producing a pyrochlore-type oxide including a mixing process and a heating process. The pyrochlore-type oxide contains a plurality of cations, including an alkali metal cation, in a composition. In the mixing process, a plurality of raw materials, each containing one of the plurality of cations, is mixed. In the heating process, a mixture containing the plurality of raw materials may be heated by a liquid-phase method at a predetermined temperature to generate a composite oxide having a corundum structure and containing at least the alkali metal cation in a composition. The composite oxide may be a precursor of the pyrochlore-type oxide as a target compound. BRIEF DESCRIPTION OF DRAWINGS Objects, features and advantages of the present disclosure will become apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: FIG. 1 is a cross-sectional view showing a configuration of a secondary battery according to a first embodiment; FIG. 2 is a diagram showing a crystal structure of a pyrochlore-type oxide; FIG. 3 is a diagram showing a method for producing a pyrochlore-type oxide according to the first embodiment; FIG. 4 is an SEM image of the pyrochlore-type oxide according to the first embodiment; FIG. 5 is a diagram showing particle sizes of pyrochlore-type oxides according to the first embodiment, using examples and a comparative example; FIG. 6 is a diagram showing a method for producing a pyrochlore-type oxide according to a second embodiment; FIG. 7 is an SEM image of the pyrochlore-type oxide according to the second embodiment; and FIG. 8 is a diagram showing particle sizes of pyrochlore-type oxides according to the second embodiment, using examples and a comparative example. DETAILED DESCRIPTION In a method for producing a pyrochlore-type oxide, a precursor composed of a lithium-containing complex oxide is mixed with raw materials including LiF and LaF3 and the precursor contains Ta, the mixture may be calcined at 1200° C. However, when the calcination temperature is high, the particles of the resulting pyrochlore-type oxide undergoes grain growth and becomes coarser. For example, when a pyrochlore-type oxide is used as a solid electrolyte for secondary batteries, it is desirable to make a solid electrolyte layer as thin as possible in order to reduce resistance, and therefore it is preferable to refine the particles of the pyrochlore-type oxide. According to one aspect of the present disclosure, a method for producing a pyrochlore-type oxide containing a plurality of cations, including an alkali metal cation, in a composition, includes a mixing process and a heating process. The mixing process includes mixing a plurality of raw materials each containing one of the plurality of cations. The heating process includes heating a mixture containing the plurality of raw materials at a predetermined temperature by a liquid-phase method to produce a composite oxide having a corundum structure and containing at least the alkali metal cation in a composition. The composite oxide is a precursor of the pyrochlore-type oxide as a target compound. As a result, in the heating process, the composite oxide with the corundum structure produced by the liquid-phase method can further react to generate a pyrochlore-type oxide. With the liquid-phase method, a pyrochlore-type oxide can be produced at a lower temperature compared to solid-phase reactions, and by lowering the heating temperature, the particles of the pyrochlore-type oxide can be made finer. The following will describe embodiments for carrying out the present disclosure with reference to the drawings. In each embodiment, portions corresponding to the elements described in the preceding embodiments are denoted by the same reference numerals, and redundant explanations may be omitted. When only a part of a configuration is described in an embodiment, another preceding embodiment may be applied to the other parts of the configuration. In addition to the combinations of parts specifically shown in the respective embodiments, the embodiments can be partly combined even if not explicitly suggested, unless such combinations are contradictory. First Embodimen