Method for producing burnt-green stone-type oxide

Abstract

This method for producing a pyrochlore-type oxide is provided with: a mixing step (S30) in which a composite oxide containing at least cations other than alkali metal cations is mixed with an alkali metal compound containing alkali metal cations; and a firing step (S40) for generating a pyrochlore-type oxide by heating the mixture containing the composite oxide and the alkali metal compound at a predetermined temperature. When the composite oxide contains alkali metal cations, the composition ratio of the alkali metal cations in the composite oxide is smaller than the composition ratio of the alkali metal cations in the alkali metal compound. The mixture contains an alkali metal compound in excess of the stoichiometric ratio with respect to the pyrochlore-type oxide. In the firing step, the alkali metal compound is liquefied by heating at a predetermined temperature.

Description

[0001] Cross-references to related applications

[0002] This application is based on Japanese Patent Application No. 2023-183094, filed on October 25, 2023, the contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to a method for manufacturing a pyrophyllite-type oxide. Background Technology

[0004] In Non-Patent Document 1, as a method for manufacturing pyrochlore-type oxides, it is described that a precursor composed of a Li-containing composite oxide is mixed with a raw material composed of LiF and LaF3, and when the precursor contains Ta, it is calcined at 1200°C.

[0005] Existing technical documents

[0006] Non-patent literature

[0007] Non-Patent Literature 1: Cyrille Galven et al, New Oxyfluoride Pyrochlores Li2-xLa(1+x) / 3□(2x-1) / 3B2O6F (B=Nb, Ta): Average and Local Structure Characterization by XRD, TEM and 19F Solid-State NMR Spectroscopy, European Journal of Inorganic Chemistry, Germany, October 11, 2010, 33, 5272-5283 (Cyrille Galven et al, “New Oxyfluoride Pyrochlores Li2-xLa(1+x) / 3□(2x-1) / 3B2O6F (B=Nb, Ta): Average and Local Structure Characterization by XRD, TEM and 19F Solid-State NMR Spectroscopy”, European Journal of Inorganic Chemistry, Germany, October 11, 2010, 33, 5272-5283) Summary of the Invention

[0008] However, in the manufacturing methods using the aforementioned conventional techniques, the high calcination temperature causes grain growth and coarsening of the resulting pyrochlore oxide particles. For example, if pyrochlore oxide is used as a solid electrolyte in a secondary battery, it is desirable to make the solid electrolyte as thin as possible to reduce resistance, which necessitates miniaturizing the pyrochlore oxide particles.

[0009] In view of the above, the present invention aims to provide a method for manufacturing pyrophyllite oxides that can refine pyrophyllite oxide particles.

[0010] To achieve the above objectives, one aspect of the present invention is a method for manufacturing a pyrochlore-type oxide containing multiple cations, wherein the multiple cations include alkali metal cations. The method includes a mixing step and a calcination step. In the mixing step, a composite oxide containing at least the alkali metal cations other than the alkali metal cations is mixed with an alkali metal compound containing the alkali metal cations. In the calcination step, the mixture containing the composite oxide and the alkali metal compound is heated at a predetermined temperature to generate the pyrochlore-type oxide. When the composite oxide contains alkali metal cations, the proportion of alkali metal cations in the composite oxide is less than the proportion of alkali metal cations in the alkali metal compound. The mixture contains an alkali metal compound in a proportion exceeding the stoichiometric ratio relative to the pyrochlore-type oxide. In the calcination step, the alkali metal compound is liquefied by heating at a predetermined temperature.

[0011] Therefore, pyroxene oxides can be generated through a solid-liquid reaction, in which a liquid alkali metal compound reacts with a solid composite oxide. In the solid-liquid reaction, pyroxene oxides can be generated at a lower temperature than in a solid-phase reaction, and the particle size of the pyroxene oxides can be refined by lowering the calcination temperature. Attached Figure Description

[0012] [ Figure 1 [Illustration 1] is a cross-sectional view showing the structure of the secondary battery according to the embodiment.

[0013] [ Figure 2 [Illustration 1] shows the crystal structure of pyroxene oxide.

[0014] [ Figure 3 [ ] is a diagram showing the manufacturing process of pyrophyllite-type oxides.

[0015] [ Figure 4 [Image 1] is a SEM image of pyrophyllite oxide.

[0016] [ Figure 5 [This is a graph showing the types and particle sizes of precursors and Li compounds used in the examples and comparative examples.] Detailed Implementation

[0017] Hereinafter, with reference to the accompanying drawings, embodiments of applying the pyroxene-type oxide of the present invention to a solid electrolyte for a secondary battery will be described. The secondary battery 10 of this embodiment is a lithium-ion battery that is charged and discharged by the movement of lithium ions between the negative electrode 12 and the positive electrode 14.

[0018] like Figure 1As shown, the secondary battery 10 includes a negative current collector 11, a negative electrode 12, a positive current collector 13, a positive electrode 14, and a solid electrolyte 15. The solid electrolyte 15 is equivalent to a solid electrolyte for a secondary battery.

[0019] A solid electrolyte 15 is sandwiched between the positive electrode 14 and the negative electrode 12. The negative electrode 12 is in contact with the solid electrolyte 15. The positive electrode 14 is in contact with the solid electrolyte 15. The negative electrode 12 and the positive electrode 14 are connected through the solid electrolyte 15. The secondary battery 10 in this embodiment is a lithium-ion battery, which is charged and discharged by the movement of lithium ions between the negative electrode 12 and the positive electrode 14 mediated by the solid electrolyte 15.

[0020] A laminate containing the negative electrode 12, positive electrode 14, and solid electrolyte 15 is disposed between the negative electrode current collector 11 and the positive electrode current collector 13. The negative electrode current collector 11 is in contact with the negative electrode 12. The positive electrode current collector 13 is in contact with the positive electrode 14. The negative electrode current collector 11 and the positive electrode current collector 13 are connected via the laminate.

[0021] The negative electrode current collector 11 and the positive electrode current collector 13 can be made of any material suitable for use as a current collector in a lithium-ion battery. In this embodiment, Cu is used as the negative electrode current collector 11, and Al is used as the positive electrode current collector 13.

[0022] The negative electrode material constituting the negative electrode 12 can be any material that can be used as a negative electrode active material for lithium-ion batteries, such as carbon-based negative electrode materials, oxide-based negative electrode materials, metal-based negative electrode materials, etc. In this embodiment, a lithium-based negative electrode material or a silicon-based negative electrode material is used.

[0023] The cathode material constituting the cathode 14 can be any material that can be used as a cathode active material for lithium-ion batteries. For example, cobalt-based cathode materials (LiCoO2), nickel-based cathode materials (LiNiO2), manganese-based cathode materials (LiMn2O4), iron phosphate-based cathode materials (LiFePO4), and ternary cathode materials (NMC) with nickel / manganese / cobalt as the main components can be used as cathode 14.

[0024] The solid electrolyte 15 has ionic conductivity, enabling lithium ions to move between the negative electrode 12 and the positive electrode 14. To reduce the resistance of the secondary battery 10, it is desirable to form the solid electrolyte 15 as thin as possible.

[0025] Solid electrolyte 15 is an oxide-based solid electrolyte with the chemical formula "Aa". 2-α Ab (1+α) / 3 B2O 7-β X γThe pyrochlore-type oxide with a pyrochlore structure is indicated by the symbol "". In order to reduce the thickness of the solid electrolyte 15 as much as possible, it is desirable that the particle size of the pyrochlore-type oxide constituting the solid electrolyte 15 be as small as possible. In this embodiment, the primary particle size of the pyrochlore-type oxide is in the range of 0.01 μm to 10 μm.

[0026] The particle size of pyrochlore-type oxides refers to the length of the largest diameter portion of the particle, also known as the maximum diameter or major diameter. In this embodiment, the mode (peak value) of the particle size distribution is used as the particle size. The particle size of pyrochlore-type oxides can be obtained in the following ways.

[0027] The geometry of the particles was observed using scanning electron microscopy (SEM, TEM) and atomic force microscopy (AFM), and the maximum diameter of the particles was measured. The number of samples N was set to, for example, 30 or more. It was assumed that the maximum diameter distribution of each measured particle followed a log-normal distribution, and the mode value estimated based on this was obtained as the particle diameter.

[0028] In the above chemical formula, O represents an oxygen atom, and Aa, Ab, B, and X represent any element or group. Aa, Ab, and B are different types of cations, and O and X are different types of anions. Aa is an alkali metal cation. Pyrochlore-type oxides contain multiple cations in their composition, including the alkali metal cation Aa and various cations Ab and B other than the alkali metal cation Aa. That is, the composition of pyrochlore-type oxides contains multiple cations containing the alkali metal cation Aa.

[0029] like Figure 2 As shown, the solid electrolyte 15 with a pyrochlore-type structure has a crystal structure formed by a three-dimensional octahedral network of BO6. BO6 is centered on cation B, with O positioned at the vertices and sharing vertices with adjacent BO6 cations. Within the three-dimensional network of BO6, hexagonal tunnel structures are formed, containing cation A and anion X.

[0030] In the above chemical formulas, 0.6 < α < 2.0, 0 < β ≤ 1, and 0 < γ ≤ 1. The composition ratio of Aa and Ab changes with the change of α; the composition ratio of O and X changes with the change of β.

[0031] The cation Aa is an alkali metal cation. The alkali metal represented by Aa can be any one of Li, Na, K, Rb, and Cs. Mg or H, other than alkali metals, can also be used as the cation Aa. That is, the cation Aa contains at least one selected from Li, Na, K, Rb, Cs, Mg, and H. In this embodiment, Li is used as Aa. The composition ratio (2-α) of Aa is in the range of 0 < (2-α) < 1.4.

[0032] The cation Ab contains at least one lanthanide element. At least one of La, Ce, Nd, and Sm can be used as the lanthanide element represented by Ab. In this embodiment, La is used as Ab. The composition ratio of Ab (1+α) / 3 is in the range of 0.53 < (1+α) / 3 < 1.

[0033] The basic structure of the cation Ab is composed of lanthanide elements, and some of the lanthanide elements constituting Ab can be replaced by alkaline earth metals (Ca, Mg, Sr, etc.). It can be considered that in the solid electrolyte 15 of this embodiment, by including lanthanide elements in the pyrochlore structure with 0.6 < α < 2.0 and 0 < β ≤ 1, defects are generated in the crystal structure, thus increasing the ionic conductivity. In this embodiment, La is used as Ab.

[0034] In the solid electrolyte 15 of this embodiment, the cation A in the chemical formula "A₂B₂O₇" of the typical pyrochlore structure is a composite cation using lithium metal and lanthanides. This is believed to contribute to improving the ionic conductivity of the solid electrolyte 15.

[0035] Cation B is a metal cation different from Aa and Ab, and can be selected from transition metals or metals from Groups 13 to 15. In the crystal, B is surrounded by six O atoms, forming an octahedron. As the transition metal represented by B, a Group 4 or Group 5 transition metal can be used; more specifically, at least one of Nb, Ta, Ti, Zr, Hf, and V can be used. As a Group 13 element represented by B, Al, Ga, and In can be used; as a Group 14 element, Ge and Sn can be used; and as a Group 15 element, Sb and Bi can be used. In this embodiment, Ta is used as B.

[0036] Anion X is an anion capable of replacing O atoms constituting the pyrochlore structure. X has a different electronegativity and polarizability than O atoms. At least one of O, F, Cl, Br, I, S, OH, and P can be used as the anion represented by X. The composition ratio γ of X is in the range of 0 < γ ≤ 1, and at least a portion of the O atoms constituting the pyrochlore structure are replaced by X. In this embodiment, F is used as X.

[0037] The solid electrolyte 15 of this embodiment has a defect structure containing lattice defects in the crystal because a portion of the O atoms constituting the pyrochlore structure are replaced by anions with electronegativity and polarizability different from those of the O atoms. It can be considered that the ionic conductivity of the solid electrolyte 15 of this embodiment is improved because of the presence of defect structures in the pyrochlore structure.

[0038] In the solid electrolyte 15 of this embodiment, the defect structure is a state in which a portion of Aa and Ab is missing. The chemical formula of the typical pyrochlore structure is "A₂B₂O₇", with a composition ratio of cation A of 2. In the solid electrolyte 15 of this embodiment, since the composition ratios of Aa and Ab are "2-α" and "(1+α) / 3" respectively, and 0.6 < α < 2.0, the sum of the composition ratios of Aa and Ab is less than 2. That is, in the crystal structure of the solid electrolyte 15 of this embodiment, at least a portion of either Aa or Ab is missing. Furthermore, the composition ratio corresponding to the missing portions of Aa and Ab is (2α-1) / 3.

[0039] In addition to deviations in composition ratios, in the above chemical formulas, defect structures can also be formed by making the sum of the valences of the cations composed of Aa, Ab, and B and the anions composed of O and X negative.

[0040] Furthermore, the solid electrolyte 15 of this embodiment is a composite anionic compound containing multiple anions such as O and X in a pyrochlore structure. Since the BO6 coordination octahedral structure contains anion represented by X, the alkali metal Aa can be located at the center of the space between it and the BO6 coordination octahedron without being biased towards the BO6 coordination octahedron. Therefore, the solid electrolyte 15 of this embodiment can be considered to have high ionic conductivity when used in an applied electric field, such as in a battery.

[0041] Furthermore, since α, β, and γ in the above chemical formulas affect lattice defects and ionic conductivity, it is desirable to use them within appropriate ranges. When the values ​​of α, β, and γ are large, the defect concentration within the lattice increases, but beyond a certain amount, the alkali metal concentration, expressed as Aa, decreases, and the ionic conductivity decreases. Therefore, it is desirable to control α within the range of 0.6 < α < 2.0, β within the range of 0 < β ≤ 1, and γ within the range of 0 < γ ≤ 1.

[0042] In this embodiment, Li is used as the solid electrolyte 15. 1.25 La 0.58 "Ta₂O₆F" indicates a pyrochlore-type oxide. That is, Li is used as the cation Aa, La as the cation Ab, Ta as the cation B, and F as the anion X, with α = 0.75, β = 1, and γ = 1. Hereinafter, "Li 1.25 La 0.58 Ta2O6F is also known as "LLTOF".

[0043] Next, use Figure 3The manufacturing method of the solid electrolyte 15 in this embodiment will be described. In the manufacturing method of the solid electrolyte 15, a first mixing step S10, a first calcination step S20, a second mixing step S30, and a second calcination step S40 are performed sequentially. The second mixing step S30 and the second calcination step S40 correspond to the mixing step and the calcination step, respectively.

[0044] (First mixing process)

[0045] In the first mixing step S10, multiple raw materials, each containing one of the multiple cations contained in the target compound LLTOF, are mixed to obtain a mixture. The multiple raw materials mixed in the first mixing step S10 include a lanthanum source and a tantalum source. The lanthanum source is a raw material for the cation Ab, and the tantalum source is a raw material for the cation B. Oxides, carbonates, fluorides, acetates, chlorides, and hydroxides can be used as the lanthanum source and tantalum source, respectively. In this embodiment, La2O3 is used as the lanthanum source, and Ta2O5 is used as the tantalum source. In the first mixing step, particles of La2O3 and Ta2O5 are mixed in a predetermined ratio.

[0046] (First roasting process)

[0047] Next, a first calcination step S20 is performed, in which the mixture of La₂O₃ and Ta₂O₅ is calcined. This first calcination step S20 can be considered a pre-calcination step. In this first calcination step S20, the mixture is heated in an atmospheric or inert atmosphere, calcining the precursor La. 0.29 TaO3.

[0048] The heating time for the first roasting step S20 is preferably 1 to 20 hours, more preferably 5 to 10 hours. The heating temperature for the first roasting step S20 is preferably in the range of 400°C to 1400°C, more preferably in the range of 500°C to 800°C.

[0049] In the first calcination step S20, a solid-phase reaction occurs where La₂O₃ and Ta₂O₅ react directly in the solid state. Through the first calcination step S20, La₂O₃, as a precursor to the target compound, is generated. 0.29 TaO3. In the first roasting process, besides the precursor La... 0.29 In addition to TaO3, sometimes the raw materials La2O3 and Ta2O5 may also remain in an unreacted state.

[0050] Precursor La 0.29 TaO3 is a perovskite oxide. Its precursor is La. 0.29TaO3 is a complex oxide containing multiple cations, and at least contains cations other than alkali metal cations. The precursor in this embodiment does not contain an alkali metal cation corresponding to cation Aa (Li in this embodiment), but instead contains La as cation Ab and Ta as cation B. That is, the precursor La... 0.29 TaO3 is a composite oxide containing at least a variety of cations Ab and B, other than the alkali metal cation Aa.

[0051] The precursor is essentially free of alkali metal cations, but may contain trace amounts. If the precursor contains alkali metal cations, the proportion of alkali metal cations in the precursor is less than that in LiF.

[0052] (Second mixing process)

[0053] Next, lithium and fluorine sources were prepared as raw materials for the target compound LLTof, and then reacted with the precursor La. 0.29 TaO3 is mixed to obtain a mixture, and a second mixing step S30 is performed. The lithium source is a raw material of cation Aa, and the fluorine source is a raw material of anion X. As the lithium source, oxides, carbonates, fluorides, acetates, chlorides, hydroxides, etc. can be used. In this embodiment, LiF is used as both the lithium source and the fluorine source. LiF is an alkali metal compound containing alkali metal cations.

[0054] In the second mixing step, LiF is mixed with the precursor La. 0.29 TaO3 is mixed in a predetermined ratio to obtain a mixture. This mixture contains an amount of LiF exceeding the stoichiometric ratio (molar ratio) relative to the target compound LLTOF. That is, the mixture contains an excess of LiF relative to the target compound. Therefore, in the second calcination step following the second mixing step, the LiF melts and liquefies, thereby allowing the liquid-phase LiF to react with the solid-phase La. 0.29 The TaO3 reaction is a solid-liquid reaction. The stoichiometric ratio refers to the ratio of the molar number of LiF as a reactant to the molar number of LLTOF as the target compound.

[0055] The amount of LiF is expected to be controlled within the range of 1.5 to 3 times the stoichiometry (molar ratio) relative to the target compound. If the amount of LiF is too small, it will decrease as the reaction proceeds in the second calcination step, resulting in insufficient LiF in the liquid phase, which may prevent the solid-liquid reaction from being sustained. Therefore, the amount of LiF is expected to be more than 1.5 times the stoichiometry. If the amount of LiF is too large, a large amount of LiF will remain after the formation of the target compound, leading to an increase in impurities. In addition, if the amount of LiF is too large, the composition of the product is likely to deviate from that of the target compound LLTOF. Therefore, the amount of LiF is expected to be less than 3 times the stoichiometry. In this embodiment, the amount of LiF is set to 2 times the stoichiometry relative to the target compound.

[0056] (Second roasting process)

[0057] Next, the second calcination process S40 is carried out, which involves calcining the precursor La. 0.29 A mixture of TaO3 and lithium source LiF is calcined. The second calcination step S40 can be considered as the main calcination step. In the second calcination step S40, La... 0.29 The mixture of TaO3 and LiF is heated at a predetermined temperature in an atmospheric or inert atmosphere to calcine the target compound LLTOF.

[0058] In the second calcination step S40, LiF is melted into a liquid phase by heating. That is, in the second calcination step S40, the liquid phase LiF reacts with the solid phase La. 0.29 The solid-liquid reaction of TaO3 produces the target compound LLTOF.

[0059] The mixture contains an excess of LiF relative to the target compound. Therefore, even as the LiF decreases with the progress of the reaction, a sufficient amount of liquid-phase LiF can be ensured for the solid-liquid reaction.

[0060] The heating time for the second roasting step S40 is preferably 1 to 20 hours, more preferably 1 to 10 hours. The heating temperature for the second roasting step S40 is preferably in the range of 500°C to 1000°C, more preferably in the range of 650°C to 850°C.

[0061] In the second calcination step S40, since calcination at high temperatures increases the particle size of the product, it is desirable to lower the heating temperature to reduce the particle size. Furthermore, during high-temperature calcination, Li and F readily volatilize, causing the composition of the product to deviate from the target compound LLTOF. Therefore, the heating temperature in the second calcination step S40 is preferably below 1000°C, more preferably below 850°C.

[0062] Furthermore, if the heating temperature of the second calcination step S40 is too low, the reactivity will decrease, the reaction rate will slow down, and the time required to generate pyroxene-type oxides will increase. Therefore, in order to suppress the slowing down of the reaction rate, the heating temperature of the second calcination step S40 is preferably 500°C or higher, and more preferably 650°C or higher.

[0063] In the second calcination process S40, La will occur. 0.29 The eutectic reaction of TaO3 and LiF. Due to the precursor La in this embodiment... 0.29 TaO3 does not contain Li, so it readily undergoes a eutectic reaction with LiF.

[0064] LiF melts at a temperature below its original melting point (848°C) through a eutectic reaction. Therefore, in this embodiment, the heating temperature of the second calcination step S40 is set below the melting point of LiF (848°C). Specifically, the heating temperature of the second calcination step S40 is set to 700°C.

[0065] In the second roasting process S40, La is roasted... 0.29 TaO3 and LiF are reacted to produce the target compound LLTOF. If impurities such as LiF remain in the product, they can be separated by washing with water or solvent. In the second calcination step S40, the liquid phase LiF reacts with the solid phase La... 0.29 The solid-liquid reaction of TaO3 can be carried out at a lower temperature than that of a solid-phase reaction. Therefore, the particle size of LLTOF, which is a pyroxene-type oxide, can be reduced.

[0066] Through the above steps, we can obtain the chemical formula "L i1.25 La 0.58 Ta2O6F” represents a calcined pyroxene oxide crystal.

[0067] Furthermore, by changing the mixing ratio of La2O3, Ta2O5, and LiF in the above manufacturing process, it is possible to obtain a product with the chemical formula "Li". 2-α La (1+α) / 3 Ta2O 7-β F γ The α, β, and γ values ​​in the chemical formula can be adjusted by changing the mixing ratios of La₂O₃, Ta₂O₅, and LiF. Additionally, some of the material sublimates during calcination. Therefore, α, β, and γ values ​​can also be adjusted by changing the calcination conditions of the first and second calcination processes, the ambient gas in the calcination furnace, and the size of the calcination furnace.

[0068] Figure 4 SEM images of the pyrophyllite-type oxides of this embodiment and the comparative example are shown.

[0069] In this embodiment, pyrophyllite-type oxide was generated via a solid-liquid reaction, while in the comparative example, it was generated via a solid-phase reaction. The pyrophyllite-type oxide in both this embodiment and the comparative example is LLTOF. The SEM image scale bar in this embodiment is 1 μm, while the SEM image scale bar in the comparative example is 10 μm.

[0070] In a comparative example, the precursor Li was obtained by calcining a mixture of La₂O₃, Li₂CO₃, and Ta₂O₅. 0.5 La 0.5 In Ta₂O₆, LiF and LaF₃ are mixed and calcined at 1200 °C to generate LLTOF via a solid-state reaction. LiF and LaF₃ are stoichiometric amounts relative to the target compound LLTOF.

[0071] like Figure 4 As shown, in the comparative example, the particle size of the pyroxene oxide was much larger than 10 μm, while in this embodiment, pyroxene oxide with a particle size of several μm or less was obtained. As described above, in this embodiment, the particle size of the pyroxene oxide can be miniaturized. By using the pyroxene oxide of this embodiment as the solid electrolyte 15 of the secondary battery 10, the solid electrolyte 15 can be thinned, thereby reducing the resistance of the secondary battery 10.

[0072] Here, the particle size of the calcined chlorite oxide in this embodiment will be discussed using... Figure 5 The examples and comparative examples shown are illustrated. Examples 1-6 involve calcining a mixture of a Li-free precursor and a Li compound in a stoichiometric ratio relative to the target compound via a solid-liquid reaction. Comparative Examples 1 and 2 involve calcining a mixture of a Li-containing precursor and a Li compound in a stoichiometric ratio relative to the target compound via a solid-liquid reaction.

[0073] The precursors of Examples 1-6 and Comparative Examples 1 and 2 are complex oxides containing multiple cations, and are perovskite-type oxides. The precursor of Examples 1-6 is La. 0.29 TaO3, the precursor of Comparative Examples 1 and 2 is Li 0.5 La 0.5 Ta2O6. The Li compound in Examples 1-4 and Comparative Examples 1 and 2 was LiF, the Li compound in Example 5 was LiF and LiCl, and the Li compound in Example 6 was LiF and Li2CO3.

[0074] The stoichiometric ratios (molar ratios) of the Li compounds relative to the target compound were as follows: 1.5 for Example 1, 2.0 for Examples 2, 4-6, 3.0 for Example 3, and 1.0 for Comparative Examples 1 and 2. In Example 5, the stoichiometric ratios of LiF and LiCl were each 1.0, with a total stoichiometric ratio of 2.0. Similarly, in Example 6, the stoichiometric ratios of LiF and Li₂CO₃ were each 1.0, with a total stoichiometric ratio of 2.0. The calcination temperature for Examples 1-3, 5, 6 and Comparative Example 2 was 700°C, the calcination temperature for Example 5 was 1000°C, and the calcination temperature for Comparative Example 1 was 1200°C.

[0075] The formation phases of the compounds obtained in Examples 1-6 and Comparative Examples 1 and 2 were evaluated by X-ray diffraction (XRD). The results showed that the formation of a pyrochlore phase was confirmed in Examples 1-6 and Comparative Example 1, but not in Comparative Example 2. That is, in Examples 1-6, which employed liquid-phase reactions, pyrochlore-type oxides were obtained at low temperatures below 1000°C. In contrast, in Comparative Examples 1 and 2, which employed solid-phase reactions, pyrochlore-type oxides were obtained at high temperatures such as 1200°C, but not at low temperatures such as 700°C.

[0076] Regarding the primary particle size of the obtained compounds, Example 1 was 0.4 μm, Example 2 was 1.0 μm, Example 3 was 3.0 μm, Example 4 was 7.5 μm, Example 5 was 2.5 μm, Example 6 was 2.3 μm, Comparative Example 1 was 20.6 μm, and Comparative Example 2 was 1.0 μm.

[0077] Compared to Comparative Example 1, which had a particle size of 20.6 μm at a calcination temperature of 1200 °C, Examples 1-6, which had calcination temperatures below 1000 °C, had particle sizes of 7.5 μm or less, representing a significant reduction in particle size. Furthermore, compared to Example 4, which had a calcination temperature of 1000 °C, Examples 1-3, 5, and 6, which had calcination temperatures of 700 °C, obtained even smaller particle sizes. Additionally, in Comparative Example 2, which had a calcination temperature of 700 °C, although a particle size of 1.0 μm was obtained, as mentioned above, the target compound was not formed because the solid-phase reaction was carried out at a low temperature.

[0078] In the above embodiment, calcined chlorite oxide is generated by heating and calcining a mixture of a composite oxide without alkali metal compounds, which serves as a precursor for calcined chlorite oxide, and an alkali metal compound in an amount exceeding the stoichiometric ratio of the calcined chlorite oxide. Thus, calcined chlorite oxide can be generated through a solid-liquid reaction, in which the alkali metal compound is liquefied and the liquid phase of the alkali metal compound reacts with the solid phase of the composite oxide. In the solid-liquid reaction, calcined chlorite oxide can be generated at a temperature lower than that of the solid phase reaction, and the particles of the calcined chlorite oxide can be miniaturized by setting the calcination temperature to a low temperature. By using the miniaturized calcined chlorite oxide as the solid electrolyte 15 of the secondary battery 10, the solid electrolyte 15 can be thinned, thereby reducing the resistance of the secondary battery 10.

[0079] Furthermore, the solid-phase composite oxide undergoes a eutectic reaction with the liquid-phase alkali metal compound, causing the alkali metal compound to melt at a temperature below its own melting point. Therefore, in this embodiment, the calcination temperature of the mixture of the composite oxide and the alkali metal compound is set below the melting point of the alkali metal compound. Since the eutectic reaction causes the alkali metal compound contained in the mixture to melt at a temperature below its melting point, the alkali metal compound can melt and undergo a solid-liquid reaction even when the calcination temperature is set below the melting point of the alkali metal compound. As a result, pyrophyllite-type oxides can be generated at a lower calcination temperature, and the particles of the pyrophyllite-type oxides can be made finer.

[0080] This invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. Furthermore, the methods described in the above embodiments can be appropriately combined within feasible limits.

[0081] For example, in the above embodiments, the pyrophyllite oxide of the present invention is applied to the solid electrolyte of a lithium-ion battery, but the pyrophyllite oxide of the present invention can also be applied to other secondary batteries. Specifically, when K is used as the alkali metal represented by Aa in the chemical formula of the pyrophyllite oxide, it can be used as a solid electrolyte for potassium-ion batteries; when Na is used as the alkali metal represented by Aa in the chemical formula, it can be used as a solid electrolyte for sodium-ion batteries.

[0082] The characteristics of the method for manufacturing pyrophyllite-type oxides disclosed in this specification are as follows.

[0083] (Project 1)

[0084] A method for manufacturing pyrochlore-type oxides, comprising a method for manufacturing pyrochlore-type oxides containing multiple cations, wherein the multiple cations include alkali metal cations.

[0085] The manufacturing method includes:

[0086] In the mixing step (S30), a composite oxide containing at least a cation other than the alkali metal cation is mixed with an alkali metal compound containing the alkali metal cation; and

[0087] The calcination process (S40) involves heating a mixture containing the composite oxide and an alkali metal compound at a predetermined temperature to generate the pyrochlore-type oxide, wherein...

[0088] When the composite oxide contains the alkali metal cation, the proportion of the alkali metal cation in the composite oxide is less than the proportion of the alkali metal cation in the alkali metal compound.

[0089] The mixture contains an alkali metal compound in a proportion exceeding the stoichiometric ratio relative to the pyrochlore-type oxide.

[0090] In the roasting process, the alkali metal compound is liquefied by heating at the predetermined temperature.

[0091] (Project 2)

[0092] According to the method for manufacturing pyrochlore-type oxides described in Project 1, the predetermined temperature is in the range of 500°C to 1000°C.

[0093] (Project 3)

[0094] According to the method for manufacturing pyrochlore-type oxides as described in Project 1 or 2, the predetermined temperature is a temperature lower than the melting point of the alkali metal compound.

[0095] (Project 4)

[0096] The method for manufacturing pyrochlore-type oxide according to any one of items 1 to 3, wherein the primary particle size of the pyrochlore-type oxide is in the range of 0.01 μm to 10 μm.

[0097] (Project 5)

[0098] The method for manufacturing pyrochlore-type oxides according to any one of items 1 to 4, wherein the composite oxide does not contain the alkali metal cations in its components.

[0099] (Project 6)

[0100] The method for manufacturing pyrochlore-type oxide according to any one of items 1 to 5, wherein the composite oxide is a perovskite-type oxide.

[0101] (Project 7)

[0102] The method for manufacturing pyrochlore-type oxide according to any one of items 1 to 6, wherein the pyrochlore-type oxide is manufactured using multiple raw materials each containing one of the multiple cations.

[0103] The various raw materials are selected from at least one of the group consisting of fluorides, acetates, chlorides, hydroxides, carbonates and oxides.

[0104] (Project 8)

[0105] The method for manufacturing pyrochlore-type oxide according to any one of items 1 to 7, wherein the pyrochlore-type oxide is a solid electrolyte (15) for secondary batteries.

[0106] While the present invention has been described with reference to embodiments, it should not be construed as being limited to those embodiments or structures. The invention also includes various modifications and equivalent variations. Furthermore, although various combinations and methods are shown in the invention, other combinations and methods containing only one element, or containing more than or less of those elements, also fall within the scope and spirit of the invention.

Claims

1. A method for manufacturing a pyrochlore-type oxide, comprising a method for manufacturing a pyrochlore-type oxide containing multiple cations in its components, wherein the multiple cations include alkali metal cations, characterized in that, The manufacturing method includes: In the mixing step (S30), a composite oxide containing at least a cation other than the alkali metal cation is mixed with an alkali metal compound containing the alkali metal cation; and The calcination process (S40) involves heating a mixture containing the composite oxide and an alkali metal compound at a predetermined temperature to generate the pyrochlore-type oxide, wherein... When the composite oxide contains the alkali metal cation, the proportion of the alkali metal cation in the composite oxide is less than the proportion of the alkali metal cation in the alkali metal compound. The mixture contains an alkali metal compound in a proportion exceeding the stoichiometric ratio relative to the pyrochlore-type oxide. In the roasting process, the alkali metal compound is liquefied by heating at the predetermined temperature.

2. The method for manufacturing pyrochlore-type oxides according to claim 1, characterized in that, The predetermined temperature is in the range of 500℃ to 1000℃.

3. The method for manufacturing pyrochlore-type oxides according to claim 1, characterized in that, The predetermined temperature is a temperature lower than the melting point of the alkali metal compound.

4. The method for manufacturing pyrochlore-type oxides according to claim 1, characterized in that, The primary particle size of the pyrochlore oxide is in the range of 0.01 μm to 10 μm.

5. The method for manufacturing pyrochlore-type oxides according to claim 1, characterized in that, The composite oxide does not contain the alkali metal cation in its components.

6. The method for manufacturing pyrochlore-type oxides according to claim 1, characterized in that, The composite oxide is a perovskite-type oxide.

7. The method for manufacturing pyrochlore-type oxides according to claim 1, characterized in that, The pyrochlore-type oxide is manufactured using multiple raw materials, each containing one of the aforementioned cations. The various raw materials are selected from at least one of the group consisting of fluorides, acetates, chlorides, hydroxides, carbonates and oxides.

8. The method for producing pyrochlore-type oxides according to any one of claims 1 to 7, characterized in that, The pyrochlore oxide is a solid electrolyte for secondary batteries (15).

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