Method for manufacturing solid electrolyte and method for manufacturing secondary battery

Abstract

Provided is a method for manufacturing a pyrochlore-type solid electrolyte containing: a plurality of cations including metal cations; a halogen element; and a defect structure. The method includes: a mixing step (S16) for preparing a mixed starting material obtained by mixing a precursor of the solid electrolyte or a raw material of a precursor and a halogen-containing starting material containing a halogen element; and a firing step (S17) for firing the mixed starting material. In the firing step, the halogen element is volatilized from the solid electrolyte at a halogen volatilization rate Vout, and the halogen element is supplied into a firing atmosphere of the solid electrolyte at a halogen supply rate Vin. In the firing step, if Dp is the median particle diameter of the solid electrolyte, the mixed starting material is fired under an atmosphere having a relationship of Vin / (Vout x Dp) ≥ 0.015.

Description

Method for manufacturing a solid electrolyte and method for manufacturing a secondary battery Cross-reference of related applications

[0001] This application is based on Japanese Patent Application No. 2024-174937, filed on October 4, 2024, and its contents are incorporated herein by reference.

[0002] This disclosure relates to a method for producing a solid electrolyte having a pyrochlore structure and a method for producing a secondary battery.

[0003] Patent Document 1 describes a solid electrolyte for secondary batteries with compositional formula Aa ２－α Ab （１＋α）／３ B ２ O ７－β X γ Pyrochlore-type solid electrolytes (Aa: alkali metal, Ab: lanthanide, B: cationic metal, X: anion substitutable with O) have been proposed. The pyrochlore-type solid electrolyte described in Patent Document 1 has defects in its crystal structure, and some of the oxygen atoms constituting the pyrochlore structure are substituted with halogen elements, resulting in high ionic conductivity. Pyrochlore-type solid electrolytes are BO ６ It has a crystal structure in which a three-dimensional network of octahedra is formed, and tunnel structures are formed in which cations consisting of Aa / Ab and anions consisting of X are arranged.

[0004] Patent No. 7334813

[0005] However, when a halogen element is present in the pyrochlore structure, the halogen element exists as a weak bond with Aa / Ab within the tunnel structure and is in an unstable state due to the presence of defect structures, making it easily detached from the crystal structure. Therefore, when manufacturing pyrochlore-type solid electrolytes, halogen elements may detach from the pyrochlore-type solid electrolyte during the calcination process, potentially reducing the ionic conductivity of the pyrochlore-type solid electrolyte.

[0006] In view of the above, this disclosure aims to suppress the detachment of halogen elements from pyrochlore-type solid electrolytes when manufacturing pyrochlore-type solid electrolytes containing halogen elements.

[0007] To achieve the above objective, one aspect of the present disclosure provides a method for producing a solid electrolyte having a pyrochlore-type crystal structure including a plurality of cations including a metal cation, a halogen element, and a defect structure, comprising a mixing step of producing a mixed raw material by mixing a precursor or raw material for a solid electrolyte with a halogen-containing raw material including a halogen element, and a firing step of firing the mixed raw material. In the firing step, the halogen element volatilizes from the solid electrolyte at a halogen volatilization rate Vout, and the halogen element is supplied to the firing atmosphere of the solid electrolyte at a halogen supply rate Vin. In the firing step, the mixed raw material is fired in an atmosphere where Vin / (Vout × Dp) ≥ 0.015, where Dp is the particle size which is the particle median diameter of the solid electrolyte.

[0008] This suppresses halogen detachment from the solid electrolyte during the firing process, allowing a predetermined amount of halogen to be maintained within the crystal structure, thereby suppressing a decrease in ionic conductivity.

[0009] This is a cross-sectional view showing the configuration of a secondary battery according to an embodiment of this disclosure. This is a diagram showing the crystal structure of a pyrochlore-type solid electrolyte. This is a diagram showing a firing furnace for firing a pyrochlore-type solid electrolyte. This is a diagram showing a firing furnace for firing a pyrochlore-type solid electrolyte. This is a diagram showing the halogen supply rate Vin, halogen volatilization rate Vout, and particle size Dp of a pyrochlore-type solid electrolyte. This is a diagram showing the manufacturing process of a pyrochlore-type solid electrolyte. This is a chart showing the halogen retention rate and ionic conductivity of the examples and comparative examples of this disclosure. This is a chart showing the halogen retention rate and ionic conductivity of the examples and comparative examples of this disclosure.

[0010] Hereinafter, embodiments of applying the ion conductor of this disclosure to a solid electrolyte for a secondary battery will be described with reference to the drawings. The secondary battery 10 of this embodiment is a lithium-ion battery in which charging and discharging are performed by the movement of lithium ions between the negative electrode 12 and the positive electrode 14.

[0011] As shown in Figure 1, the secondary battery 10 comprises a negative electrode current collector 11, a negative electrode 12, a positive electrode current collector 13, a positive electrode 14, and a solid electrolyte 15. These components of the secondary battery 10 are stacked in layers.

[0012] A solid electrolyte 15 is sandwiched between a positive electrode 14 and a 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 via the solid electrolyte 15. The secondary battery 10 of this embodiment is a lithium-ion battery in which charge and discharge are performed by lithium ions moving between the negative electrode 12 and the positive electrode 14 through the solid electrolyte 15.

[0013] A laminate including these negative electrode 12, positive electrode 14, and solid electrolyte 15 is provided between a negative electrode current collector 11 and a 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.

[0014] The negative electrode current collector 11 and the positive electrode current collector 13 can be made of any material that can be used as a current collector for 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.

[0015] The negative electrode material constituting the negative electrode 12 can be any material that can be used as a negative electrode active material for a lithium-ion battery. For example, a carbon-based negative electrode material, an oxide-based negative electrode material, a metal-based negative electrode material, etc. can be used. In this embodiment, graphite is used as the negative electrode material. The negative electrode 12 may contain a conductive assistant, a binder, and a polymer. Furthermore, the negative electrode 12 may contain a solid electrolyte.

[0016] The positive electrode material constituting the positive electrode 14 can be any material that can be used as a positive electrode active material for a lithium-ion battery. As the positive electrode 14, for example, a layered rock salt type active material, an olivine type active material, a spinel type active material can be used. As the layered rock salt type active material, for example, LiNi ｘ Co ｙ Mn ｚ O ２ (NCM), LiNi ｘ Co ｙ Al ｚ O ２ (NCA) and other ternary system positive electrode materials can be used. As the olivine type active material, for example, LiFePO４ (LFP), LiMn １－ｘ Fe ｘ PO ４ (LMFP), LiMnPO ４ (LMP), LiCoPO ４ (LCP), LiNiPO ４ (LNP) can be used. As a spinel-type active material, for example, LiMn ２ O ４ (LMO), LiNi ０．５ Mn １．５ O ４ (LNMO) can be used.

[0017] The solid electrolyte 15 can move lithium ions between the negative electrode 12 and the positive electrode 14. In other words, the solid electrolyte 15 is an ion conductor with a structure that allows cations to conduct. In this embodiment, a pyrochlore-type oxide solid electrolyte having a pyrochlore-type crystal structure is used as the ion conductor constituting the solid electrolyte 15. Hereinafter, the pyrochlore-type oxide solid electrolyte will also be referred to as a pyrochlore-type solid electrolyte.

[0018] Pyrochlore-type solid electrolytes used as ion conductors have the composition formula "Aa ２－α Ab （１＋α）／３ B ２ O ７－β X γ It has a pyrochlore structure represented by the above compositional formula. In the above compositional formula, O is an oxygen atom, and Aa, Ab, B, and X represent any element or group. Aa, Ab, and B are each different types of cations, and O and X are each different types of anions. In this embodiment, a halogen is used as X. The pyrochlore-type solid electrolyte contains multiple cations, multiple anions, and vacancies in the crystal. The multiple cations include conductive ions that can conduct through the crystal and non-conductive ions that do not conduct through the crystal.

[0019] As shown in Figure 2, the pyrochlore-type solid electrolyte is BO ６ It has a crystal structure in which a three-dimensional network of octahedrons is formed. ６In this structure, cation B is at the center, with O at the vertices, and adjacent BO ６ It shares a vertex with BO. ６ In this three-dimensional network, hexagonal tunnel structures are formed in which cations Aa / Ab and halogen X are arranged.

[0020] In the above compositional formula, 0.6 < α < 2.0, 0 < β ≤ 1, and 0 < γ ≤ 1. A change in α alters the compositional ratio of Aa and Ab, and a change in β alters the compositional ratio of O and X.

[0021] As cation Aa, an alkali metal cation can be used. As the alkali metal represented by Aa, any of Li, Na, or K can be used. In this embodiment, Li is used as Aa. The composition ratio of Aa (2-α) is in the range of 0 < (2-α) < 1.4.

[0022] The cation Ab contains at least one lanthanide. At least one of La, Ce, Nd, and Sm can be used as the lanthanide 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.

[0023] The basic structure of cation Ab consists of lanthanides, and some of the lanthanides constituting Ab may be substituted with alkaline earth metals (Ca, Mg, Sr, etc.). In this embodiment, the pyrochlore-type solid electrolyte has a pyrochlore structure in which 0.6 < α < 2.0, 0 < β ≤ 1, and 0 < γ ≤ 1. It is thought that the inclusion of lanthanides in this pyrochlore structure creates defects in the crystal structure, thereby improving ionic conductivity. In this embodiment, La is used as Ab.

[0024] The pyrochlore-type solid electrolyte of this embodiment has a general composition formula "A ２ B ２ O ７ In this mixture, cation A is a composite cation using lithium metal and a lanthanide. This is thought to contribute to the improvement of the ionic conductivity of the pyrochlore-type solid electrolyte.

[0025] Cation B is a metal cation distinct from Aa and Ab, and is a transition metal or a metal selected from group 13 to 15 elements. In the crystal, B forms an octahedron surrounded by six oxygen atoms. As the transition metal represented by B, a group 4 transition metal or a group 5 transition metal can be used, and more specifically, at least one of Nb, Ta, Ti, Zr, Hf, or V can be used. As the group 13 element represented by B, Al, Ga, or In can be used; as the group 14 element, Ge or Sn can be used; and as the group 15 element, Sb or Bi can be used. In this embodiment, Nb or Ta is used as B.

[0026] Halogen X is substituted for the oxygen atoms that make up the pyrochlore structure. X has different electronegativity and polarizability from oxygen atoms. At least one of F, Cl, Br, or I can be used as halogen X. The composition ratio γ of X is in the range of 0 < γ ≤ 1, and at least a portion of the oxygen atoms that make up the pyrochlore structure are substituted with X. In this embodiment, F or Cl is used as X.

[0027] The pyrochlore-type solid electrolyte of this embodiment has a defect structure in which lattice defects are included in the crystal, as some of the oxygen atoms constituting the pyrochlore structure are replaced by anions with different electronegativity and polarizability from the oxygen atoms. It is believed that the ionic conductivity of the pyrochlore-type solid electrolyte of this embodiment is improved because the pyrochlore structure contains defect structures.

[0028] In the pyrochlore-type solid electrolyte of this embodiment, a portion of Aa and Ab is missing as a defect structure. The compositional formula of a typical pyrochlore structure is "A ２ B ２ O ７In this case, the composition ratio of cation A is 2. In contrast, in the pyrochlore-type solid electrolyte of this embodiment, the composition ratios of Aa and Ab are "2-α" and "(1+α) / 3", respectively, and since 0.6 < α < 2.0, the sum of the composition ratios of Aa and Ab is less than 2. In other words, in the crystal structure of the pyrochlore-type solid electrolyte of this embodiment, at least a portion of either Aa or Ab is missing, forming a vacancy. The composition ratio corresponding to the missing portion (vacancy) of Aa and Ab is (2α-1) / 3.

[0029] In this embodiment, the A site of the pyrochlore-type solid electrolyte contains at least one of cation Aa, cation Ab, or a vacancy. The A site of the pyrochlore-type solid electrolyte is a cation conduction site, cation Aa is a conduction ion that conducts through the crystal, and cation Ab is a nonconduction ion that does not conduct through the crystal.

[0030] In addition to deviations in composition ratios, defect structures can also be formed by making the sum of the valencies of the cations consisting of Aa, Ab, and B and the anions consisting of O and X in the above composition formula negative.

[0031] Furthermore, the pyrochlore-type solid electrolyte of this embodiment is a complex anion compound in which multiple anions such as O and X are included in the pyrochlore structure, and BO ６ Because there is an anion represented by X in the coordination octahedron structure, alkali metals Aa are BO ６ Without relying on the coordination octahedron, BO ６ It can be positioned in the center of the space with respect to the coordination octahedron. Therefore, it is believed that the pyrochlore-type solid electrolyte of this embodiment exhibits high ionic conductivity when used with an electric field, such as in a battery.

[0032] Furthermore, since α, β, and γ in the above compositional formula affect lattice defects and ionic conductivity, it is desirable to use them within an appropriate range. Larger values ​​of α, β, and γ increase the defect concentration in the crystal lattice, but beyond a certain amount, the concentration of alkali metal represented by Aa decreases, and the ionic conductivity declines. For this reason, 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.

[0033] Examples of pyrochlore-type solid electrolytes include Li １．２５ La ０．５８ Nb ２ O ６ F, Li １．２５ La ０．５８ Ta ２ O ６ F, Li １．２５ La ０．５８ Nb ２ O ６ Cl can be used as an example. Below, "Li １．２５ La ０．５８ Nb ２ O ６ F" to "LLNOF", Li １．２５ La ０．５８ Ta ２ O ６ "F" is "LLTOF", "Li １．２５ La ０．５８ Nb ２ O ６ "Cl" is also referred to as "LLNOCl".

[0034] In pyrochlore-type solid electrolytes, halogen X exists as a weak bond with cations Aa and Ab within the tunnel structure, and is also in an unstable state due to the presence of defect structures, making halogen X easily detached from the crystal structure. For this reason, in the manufacturing process of pyrochlore-type solid electrolytes, halogen elements are easily volatilized and detached during the calcination process, in which raw materials containing halogen elements are calcined at high temperatures to produce the pyrochlore-type solid electrolyte. The calcination process for calcining the pyrochlore-type solid electrolyte is the third calcination process S17 (Figure 6), which will be described later.

[0035] Therefore, in this embodiment, halogen elements are supplied to the firing atmosphere of the pyrochlore-type solid electrolyte during the firing process. By supplying halogen to the firing atmosphere, halogen desorption from the pyrochlore-type solid electrolyte can be suppressed, and a predetermined amount of halogen component can be maintained within the pyrochlore-type solid electrolyte.

[0036] Figures 3 and 4 show a firing furnace 200 for firing pyrochlore-type solid electrolytes. In the firing process, raw materials are placed in the firing furnace 200 and heated under an atmosphere of air, nitrogen, or argon to produce pyrochlore-type solid electrolytes. In this embodiment, nitrogen is used as the firing atmosphere.

[0037] As shown in Figure 3, halogen components can be supplied to the firing atmosphere by circulating a halogen-containing gas into the firing furnace 200 from the outside. The halogen-containing gas contains the same type of halogen as the halogen contained in the pyrochlore-type solid electrolyte. The halogen-containing gas may be circulated continuously or intermittently.

[0038] As for halogen-containing gases, if the halogen element contained in the pyrochlore-type solid electrolyte is fluorine, for example, F ２ HF, BF ３ NF ３ , PF ５ , SiF ４ SF ６ Fluorine-containing gases such as the above can be used. Furthermore, if the halogen element contained in the pyrochlore-type solid electrolyte is chlorine, for example, Cl ２ Chlorine-containing gases such as HCl can be used. Among these halogen-containing gases, F is selected from the viewpoint of not damaging the calcination furnace 200 and not having any of the elements other than the halogen components incorporated into the pyrochlore-type solid electrolyte. ２ or Cl ２ It is preferable to use the halogen-containing gas. The halogen-containing gas may be supplied to the firing furnace 200 alone, or it may be supplied to the firing furnace 200 in a mixture with an inert gas such as nitrogen or argon, or with air.

[0039] As shown in Figure 4, halogen components can be supplied to the firing atmosphere by adding a halogen-containing compound to the raw materials of the pyrochlore-type solid electrolyte. The halogen-containing compound contains the same type of halogen as the halogen contained in the pyrochlore-type solid electrolyte.

[0040] The raw materials for pyrochlore-type solid electrolytes to which halogen-containing compounds are added are mixed raw materials obtained by mixing a precursor of the pyrochlore-type solid electrolyte with halogen-containing raw materials containing halogen elements. The halogen components are supplied to the firing atmosphere by volatilization of halogen components from the halogen-containing compounds added to the raw materials of the pyrochlore-type solid electrolyte.

[0041] As the halogen-containing compound, at least one halide of a metal cation contained in a pyrochlore-type solid electrolyte can be used. As the metal cation halide, a fluoride of a metal cation (e.g., LiF, LaF) can be used. ３ ) and chlorides of metal cations (e.g., LiCl, LaCl) ３ ) is included.

[0042] If the halogen-containing compound is composed of a halide of at least one of the alkali metal cations contained in the pyrochlore-type solid electrolyte, then the halogen source material from the raw materials of the pyrochlore-type solid electrolyte should be added in excess of the theoretical amount. This allows halogen to be supplied to the firing atmosphere from the excess halogen source.

[0043] Here, the relationship between the halogen supply rate Vin, the halogen evaporation rate Vout, and the particle size Dp of a pyrochlore-type solid electrolyte will be explained using Figure 5. In the firing process, halogen elements are supplied to the firing atmosphere of the pyrochlore-type solid electrolyte at the halogen supply rate Vin, and halogen elements volatilize from the pyrochlore-type solid electrolyte at the halogen evaporation rate Vout.

[0044] The particle size Dp is the particle median diameter D50 of pyrochlore-type solid electrolyte particles, measured by laser diffraction and scattering. The particle median diameter D50 represents the volume-based particle size when the volume is integrated from the smallest particle size in the particle size distribution, reaching 50% of the total particle volume. In other words, the particle median diameter D50 represents the particle size corresponding to the median of the particle size distribution.

[0045] The halogen supply rate Vin is the amount of halogen supplied to the firing atmosphere per unit time, and its unit is ppm / min. More specifically, the halogen supply rate Vin is the ratio of the amount of halogen supplied per unit time to the theoretical amount of halogen in the pyrochlore-type solid electrolyte.

[0046] For example, if the theoretical halogen amount of a pyrochlore-type solid electrolyte is 100 g, the halogen supply amount is 10 g, and the halogen supply time is 5 hours (5 × 60 minutes), then the halogen supply rate Vin is Vin = (10 / 100) / (5 × 60) × 10⁶ = 333 ppm / min. Also, if 30 wt% of halogen is supplied in excess of the theoretical halogen amount, and the halogen supply time is 5 hours (5 × 60 minutes), then the halogen supply rate Vin is Vin = (30 / 100) / (5 × 60) × 10⁶ = 1000 ppm / min.

[0047] The halogen evaporation rate Vout is the amount of halogen evaporated from a pyrochlore-type solid electrolyte per unit time, and its unit is ppm / min. More specifically, the halogen evaporation rate Vout is the ratio of the amount of halogen evaporated per unit time to the theoretical amount of halogen in the pyrochlore-type solid electrolyte.

[0048] The theoretical amount of halogen in LLNOF is 4.87 wt%. For example, when LLNOF is fired under predetermined firing conditions for 7 hours and the amount of halogen vaporized is 0.5 wt%, the halogen vaporization rate Vout of LLNOF is Vout = (0.5 / 4.87) / (7 × 60) × 10⁶ = 244 ppm / min. The amount of halogen vaporized can be calculated, for example, from the weight loss when fired with a halogen supply amount Vin = 0 and the weight percentage of halogen in the fired product measured by an energy-dispersive X-ray fluorescence analyzer (EDX).

[0049] Specifically, the weight percentage of elements can be measured using an energy-dispersive X-ray fluorescence analyzer (EDX), and the amount of halogen volatilized can be calculated by dividing the product of the halogen weight percentage and the weight loss after calcination by the calcination time. However, if the solid electrolyte contains elements such as Li or O, these cannot be accurately detected by the EDX. Therefore, the element with the highest melting point among the quantitatively detected elements is assumed not to volatilize, and the halogen weight percentage in the solid electrolyte after calcination is calculated from the weight percentage of halogen relative to that element.

[0050] In pyrochlore-type solid electrolytes, the specific surface area decreases as the particle size Dp increases, resulting in a smaller amount of halogen evaporation. However, this also increases the required penetration distance of the halogen supplied to replenish the halogen evaporated from within the solid electrolyte. Therefore, in this embodiment, the halogen supply rate Vin is increased as the particle size Dp of the pyrochlore-type solid electrolyte increases, and the halogen supply rate Vin is increased as the halogen evaporation rate Vout increases.

[0051] Specifically, the relationship between the halogen supply rate Vin, the halogen evaporation rate Vout, and the particle size Dp of the pyrochlore-type solid electrolyte is set to satisfy Vin / (Vout × Dp) ≥ 0.015. If Vin / (Vout × Dp) < 0.015, the halogen supply will be insufficient to keep up with the halogen evaporation, and it will not be possible to maintain a predetermined amount of halogen in the pyrochlore-type solid electrolyte. In order to ensure a sufficient halogen supply to keep up with the halogen evaporation of the pyrochlore-type solid electrolyte, it is desirable to set Vin / (Vout × Dp) ≥ 0.05, more desirable to set Vin / (Vout × Dp) ≥ 0.07, and even more desirable to set Vin / (Vout × Dp) ≥ 0.10.

[0052] If the halogen supply rate Vin becomes too high, the halogen in the firing atmosphere will be in excess, reacting with residual moisture in the raw materials and firing atmosphere gas, leading to the excessive generation of hydrogen halides such as hydrogen fluoride and hydrogen chloride, which may damage the firing furnace 200 and other components. For this reason, it is desirable to set Vin / (Vout × Dp) ≤ 100, and even more desirable to set Vin / (Vout × Dp) ≤ 50.

[0053] Furthermore, in order to suppress halogen detachment from pyrochlore-type solid electrolytes, it is desirable to seal the pyrochlore-type solid electrolyte with a chemically stable substance. By sealing the pyrochlore-type solid electrolyte, the halogen components volatilized from the pyrochlore-type solid electrolyte remain in the sealed atmosphere and reach a saturated state. As a result, the apparent volatilization of halogen components is suppressed, and the halogen volatilization rate Vout can be reduced.

[0054] For example, a pyrochlore-type solid electrolyte can be sealed by firing the raw materials for the pyrochlore-type solid electrolyte in a container made of a material that is chemically stable to the pyrochlore-type solid electrolyte. Platinum, copper, Al ２ O ３ It is a chemically stable material for pyrochlore-type solid electrolytes, and the calcination of the raw materials for pyrochlore-type solid electrolytes is performed using platinum, copper, and Al. ２ O ３This can be done using a container made of at least one of the following materials. Such a container may be made of platinum, copper, Al ２ O ３ A crucible made of at least one of the following, or at least one of a metal foil container made of at least one of platinum foil or copper foil, can be used. Platinum, copper, Al ２ O ３ A crucible made of at least one of the above, and a container made of metal foil made of at least one of platinum foil or copper foil, may be used individually or in combination. Here, a sealed state does not necessarily have to be completely sealed, and may be arbitrarily adjusted within a range in which halogen volatilization is suppressed.

[0055] When using a crucible, making it as dense as possible will suppress the leakage of halogens through the pores and improve the degree of airtightness. Furthermore, by minimizing the irregularities on the contact surface between the crucible lid and the body, the leakage of halogens between the lid and the body will be suppressed and the degree of airtightness will improve.

[0056] Using metal foil and a crucible together can enhance the sealing effect of pyrochlore-type solid electrolytes.

[0057] Furthermore, if the mixed raw materials for the pyrochlore-type solid electrolyte contain a large amount of water, hydrogen atoms in the water react with halogen atoms, promoting halogen volatilization from the pyrochlore-type solid electrolyte. For this reason, it is desirable to lower the water content of the mixed raw materials for the pyrochlore-type solid electrolyte in order to suppress halogen detachment from the pyrochlore-type solid electrolyte. For example, raw materials with a low water content can be obtained by pre-drying the mixed raw materials for the pyrochlore-type solid electrolyte. It is desirable that the water content of the raw materials for the pyrochlore-type solid electrolyte, as measured by the Karl Fischer method, be 2500 ppm or less. In this disclosure, the water content of the mixed raw materials for the pyrochlore-type solid electrolyte is the measurement taken immediately before supplying halogen to the firing atmosphere in the third firing step S17.

[0058] Also, it is desirable to lower the firing temperature in the firing step of firing the pyrochlore-type solid electrolyte to a low temperature within a range that does not hinder the synthesis of the pyrochlore-type solid electrolyte. By lowering the firing temperature in the firing step, the volatilization of the halogen component from the pyrochlore-type solid electrolyte can be suppressed.

[0059] Also, it is desirable to make the particle diameter of the mixed raw materials of the pyrochlore-type solid electrolyte within a predetermined range. Specifically, it is desirable to make the particle diameter of the mixed raw materials of the pyrochlore-type solid electrolyte within the range of 0.05 to 5 μm. The particle diameter of the mixed raw materials of the pyrochlore-type solid electrolyte is the particle median diameter D50, and it is the measured value immediately before supplying halogen to the firing atmosphere in the third firing step S17.

[0060] When the particle diameter of the mixed raw materials is too small, halogen is likely to volatilize from the particle surface. Therefore, in order to suppress the volatilization of halogen from the raw material particles, it is desirable to make the particle diameter of the mixed raw materials 0.05 μm or more. On the other hand, when the particle diameter of the mixed raw materials is too large, although the amount of halogen volatilization decreases, the specific surface area decreases, and the synthesis reaction of the pyrochlore-type solid electrolyte becomes difficult to proceed. Therefore, when the particle diameter of the mixed raw materials is too large, it is necessary to raise the firing temperature, which instead promotes halogen volatilization. Therefore, in order to facilitate the progress of the synthesis reaction of the pyrochlore-type solid electrolyte, it is desirable to make the particle diameter of the mixed raw materials 5 μm or less.

[0061] Next, the manufacturing method of the pyrochlore-type solid electrolyte of the present embodiment will be described using FIG. 6. FIG. 6 shows the flow of the manufacturing method of LLNOF (Li １．２５ La ０．５８ Nb ２ O ６ F).

[0062] In the present embodiment, in the third firing step S17, a halogen component is supplied to the firing atmosphere of the pyrochlore-type solid electrolyte. Note that FIG. 6 shows an example of the manufacturing method in which a halogen source is added in the second raw material preparation step S15, but the halogen source can also be added in the first raw material preparation step S10, and at least a part of the steps from the first mixing step S11 to the second raw material preparation step S15 can be omitted.

[0063] First, a first raw material preparation step S10 of preparing a lanthanum source, a lithium source, and a niobium source as raw materials of LLNOF is performed. As the lanthanum source, the lithium source, and the niobium source, metal oxides, metal carbonates, etc. can be used. In the present embodiment, La ２ O ３ is used as the lanthanum source, Li ２ CO ３ is used as the lithium source, and Nb ２ O ５ is used as the niobium source. In addition, when manufacturing LLTOF (Li １．２５ La ０．５８ Ta ２ O ６ F), a tantalum source (for example, Ta ２ O ５ ) may be used instead of the niobium source.

[0064] Next, a first mixing step S11 of weighing La ２ O ３ and Li ２ CO ３ and Nb ２ O ５ and mixing them at a predetermined ratio and pulverizing them to prepare a mixture is performed.

[0065] Next, a first firing step S12 of firing the mixture of raw materials is performed. In the first firing step, a calcination of heating the mixture at 500°C for 6 hours in the air is performed. By the calcination, moisture and the like are removed from the mixture, and the reactivity can be enhanced. Further, by removing moisture from the mixture, generation of hydrogen fluoride can be suppressed in the third firing step S17 described later.

[0066] Next, after performing a second mixing step S13 of mixing and pulverizing the fired mixture, a second firing step S14 of firing the mixture is performed. In the second firing step, a full firing of heating the mixture at 1200°C for 4 hours in the air is performed. By the second firing step S14, Li ０．５ La ０．５ Nb ２ O ６ , which is a precursor of the pyrochlore-type solid electrolyte as the target product, is obtained.

[0067] Next, a second raw material preparation step S15 is performed to prepare a halogen source as a raw material for the pyrochlore-type solid electrolyte. The halogen source is a halogen-containing raw material containing a halogen element. For example, a metal fluoride can be used as the halogen source. In this embodiment, LiF and LaF are used as the halogen source. ３ It uses LiF, which is both a halogen source and a lithium source, and LaF ３ It is both a halogen source and a lanthanum source. When manufacturing LLNOCl, for example, LiCl and LaCl are used as halogen sources. ３ You can use it.

[0068] Next, the precursors of pyrochlore-type solid electrolytes, LiF, and LaF ３ A third mixing step S16 is performed in which the materials are weighed, mixed in a predetermined ratio, and ground to produce a mixture of the precursor and the halogen source. If the halogen source is added in the first raw material preparation step S10 and at least part of the first mixing step S11 to the second raw material preparation step S15 is omitted, then in the third mixing step S16, a mixture of the raw materials for the precursor of the pyrochlore-type solid electrolyte and the halogen source may be produced. The third mixing step S16 corresponds to the mixing step in this disclosure, and the mixture of the precursor or raw materials for the precursor and the halogen source corresponds to the mixed raw materials in this disclosure.

[0069] Next, a third calcination step S17 is performed, in which the mixture of the precursor and the halogen source is heated and calcined at a predetermined temperature. In the third calcination step S17, the mixture of the precursor and the halogen source is placed in a calcination furnace 200 and calcined by heating at 1000°C for 6 hours under a nitrogen atmosphere. To create a nitrogen atmosphere inside the calcination furnace 200, nitrogen gas is supplied to the calcination furnace 200 at a rate of, for example, 5 L / min. The third calcination step S17 yields the target product, a pyrochlore-type solid electrolyte LLNOF. The third calcination step S17 corresponds to the calcination step of this disclosure.

[0070] In the third firing step S17, halogen components volatilize from the pyrochlore-type solid electrolyte due to heating. Therefore, in this embodiment, in the third firing step S17, halogen components are supplied to the firing atmosphere of the pyrochlore-type solid electrolyte inside the firing furnace 200, thereby increasing the halogen gas concentration in the firing atmosphere and suppressing halogen volatilization from the pyrochlore-type solid electrolyte.

[0071] The halogen supply in the third calcination step S17 can be carried out, for example, by adding more LiF to the raw materials in the third mixing step S16 than the theoretical amount required for the synthesis of the target compound LLNOF. In other words, in the third mixing step S16, an amount of LiF exceeding the stoichiometric ratio (molar ratio) for the target compound LLNOF should be added to the mixture of the precursor and the halogen source. The stoichiometric ratio is the ratio of the number of moles of the reactant LiF to the number of moles of the target compound LLNOF. The stoichiometric ratio for the target compound LLNOF can also be called the theoretical amount or stoichiometric amount.

[0072] By adding an excess of LiF to a raw material mixture containing a precursor and a halogen source, some of the halogen components volatilize, enabling the supply of halogen to the firing atmosphere.

[0073] In the third firing process S17, halogen is supplied to the firing furnace 200. ２ This can also be done by supplying halogen-containing gases such as the above.

[0074] In the third firing step S17, the halogen supply is performed such that the relationship between the halogen supply rate Vin, the halogen desorption rate Vout, and the particle size Dp of the pyrochlore-type solid electrolyte satisfies Vin / (Vout × Dp) ≥ 0.015.

[0075] Next, if necessary, a micronization step S18 is performed to micronize the generated pyrochlore-type solid electrolyte, thereby obtaining the composition formula "Li １．２５ La ０．５８ Nb ２ O ６A pyrochlore-type solid electrolyte represented by "F" can be manufactured. The generated pyrochlore-type solid electrolyte is particulate and can be used as a constituent material for the solid electrolyte 15. A secondary battery 10 can be manufactured by stacking the solid electrolyte 15 using the pyrochlore-type solid electrolyte, a positive electrode 14, and a negative electrode 12. In this disclosure, the particle size Dp of the pyrochlore-type solid electrolyte is the particle size before processing in the micronization step S18.

[0076] Furthermore, in the above manufacturing process, La ２ O ３ , Nb ２ O ５ By changing the mixing ratio of LiF, the composition formula "Li ２－α La （１＋α）／３ Nb ２ O ７－β F γ A pyrochlore crystal represented by " can be obtained. ２ O ３ , Nb ２ O ５ By changing the mixing ratio of the chemicals and the mixing ratio of LiF, the elements α, β, and γ in the composition formula can be adjusted. Furthermore, some of the material sublimes during firing. Therefore, α, β, and γ can also be adjusted by changing the firing conditions, firing furnace atmosphere, and firing furnace size in the first firing step S12, the second firing step S14, and the third firing step S17.

[0077] Next, examples and comparative examples of this disclosure will be described with reference to Figures 7 and 8. The raw materials in the examples and comparative examples are mixed raw materials obtained by mixing a precursor of a pyrochlore-type solid electrolyte and a halogen source in the third mixing step S16. The physical properties of the examples and comparative examples were measured by the following method.

[0078] [Moisture content of mixed raw materials] The moisture content of the mixed raw materials before firing was measured using the Karl Fischer coulometric titration method, with a Kyoto Electronics Manufacturing ADP-611 as the moisture vaporizer and an MKC-610 as the moisture meter.

[0079] [Particle Size of Mixed Raw Materials] The particle size of the mixed raw materials before calcination was obtained by dispersing the mixed raw materials before calcination in ethanol and using a Partica LA-960 laser diffraction / scattering particle size distribution analyzer manufactured by Horiba, Ltd. to obtain the volume-averaged particle size distribution. The particle size of the mixed raw materials is the particle median diameter D50, and is the volume-based particle size when the volume is integrated from the smallest particle size in the particle size distribution until it reaches 50% of the total particle volume. [Particle Size Dp of Solid Electrolyte] The particle size Dp of the solid electrolyte was obtained by dispersing the solid electrolyte before fine grinding in ethanol and using a Partica LA-960 laser diffraction / scattering particle size distribution analyzer manufactured by Horiba, Ltd. to obtain the volume-averaged particle size distribution. The particle size Dp of the solid electrolyte is the particle median diameter D50, and is the volume-based particle size when the volume is integrated from the smallest particle size in the particle size distribution until it reaches 50% of the total particle volume.

[0080] [Halogen Retention Rate] The halogen retention rate of a solid electrolyte is the ratio of the amount of halogen in the solid electrolyte after firing to the theoretical amount of halogen in the solid electrolyte. The amount of halogen in the solid electrolyte after firing was measured using an energy-dispersive X-ray fluorescence analyzer (EDX), specifically the Shimadzu EDX-8100, to determine the weight percentage of elements. In cases where the solid electrolyte contains elements such as Li or O, which cannot be detected accurately, the element with the highest melting point among the quantitatively detected elements was assumed not to volatilize. The amount of halogen in the solid electrolyte after firing was determined from the weight percentage of the amount of halogen to that element, and the ratio to the theoretical amount of halogen was defined as the halogen retention rate.

[0081] [Ionic Conductivity] The ionic conductivity of the solid electrolyte was measured by the AC impedance method. In the impedance measurement, an AC signal was applied to the solid electrolyte at multiple frequencies, and the AC impedance was measured for each frequency. By plotting the measured impedance on the complex plane, a complex impedance plot including a circular arc trajectory was obtained. The resistance value of the measurement sample was obtained from the point of contact between the extension line of the multiple measurement points where the impedance decreases in an arc shape and the horizontal axis, and the reciprocal of the resistance value was multiplied by the thickness of the measurement sample (cm) / electrode area (cm²). ２The ionic conductivity was calculated by multiplying by ).

[0082] In all of Examples 1 to 18, the relationship between the halogen supply rate Vin, the halogen evaporation rate Vout, and the particle size Dp of the pyrochlore-type electrolyte satisfies Vin / (Vout × Dp) ≥ 0.015, and furthermore, Vin / (Vout × Dp) ≤ 50. In contrast, Comparative Examples 1 and 2 show Vin / (Vout × Dp) < 0.015.

[0083] In Examples 1, 5-13, 15-18, and Comparative Examples 1 and 2, Li was used as a raw material. ２ CO ３ La ２ O ３ , Nb ２ O ５ LiF, LaF ３ Using LLNOF(Li １．２５ La ０．５８ Nb ２ O ６ F) was manufactured. In Examples 2, 3, and 14, Li was used as a raw material. ２ CO ３ La ２ O ３ Ta ２ O ５ LiF, LaF ３ Using LLTOF(Li １．２５ La ０．５８ Ta ２ O ６ F) was manufactured. In Example 4, Li was used as a raw material. ２ CO ３ La ２ O ３ , Nb ２ O ５ , LiCl, LaCl ３ Using LLNOCl(Li １．２５ La ０．５８ Nb ２ O ６ Cl) was manufactured.

[0084] In Examples 1-12, 15, 16, 18, and Comparative Example 2, halogen was supplied to the firing atmosphere by adding an excess amount of LiF to the raw materials relative to the theoretical amount. In Examples 1, 2, 5, 6, 9-12, 15, 16, 18, and Comparative Example 2, LiF was added in an excess of 68% relative to the theoretical amount. In Examples 3 and 8, LiF was added in an excess of 200% relative to the theoretical amount. In Example 7, LiF was added in an excess of 20% relative to the theoretical amount. In Example 4, LiCl was added in an excess of 68% relative to the theoretical amount.

[0085] In Examples 13, 14, and 17, a halogen-containing gas F was introduced into the firing furnace 200. ２ By circulating the halogen solution, halogen was supplied to the firing atmosphere. In Comparative Example 1, halogen was not supplied to the firing atmosphere.

[0086] In Examples 1-14, 16-18, and Comparative Example 2, the above-described steps S10-S17 were carried out, and halogen was supplied to the firing atmosphere in the third firing step S17. In Example 15, steps S12-S15 of the above-described steps S10-S17 were omitted, LiF was added in an excess of 68% relative to the theoretical amount in the first raw material preparation step S10, and halogen was supplied to the firing atmosphere in the third firing step S17.

[0087] In Examples 1-8, 11, 12, 15, 16, and Comparative Examples 1 and 2, the mixed raw materials were contained in a platinum crucible to suppress halogen volatilization. In Example 9, the mixed raw materials were sealed in a platinum foil container. ２ O ３ The mixture was contained in a crucible made of Al to suppress halogen volatilization. In Example 10, the mixed raw materials were sealed in a copper foil container. ２ O ３ In Examples 13 and 14, halogen volatilization was suppressed by placing the mixed raw materials in a platinum foil container without placing them in a crucible. In Example 18, the mixed raw materials were placed in an aluminum crucible. ２ O ３ The material was placed in a crucible made of [material name] to suppress halogen volatilization.

[0088] The halogen evaporation rate Vout for Examples 1-12, 15, 16, 18, and Comparative Examples 1 and 2 is 240 ppm / min. The halogen evaporation rate Vout for Examples 13, 14, and 17 is 1500 ppm / min.

[0089] The halogen supply rate Vin for Examples 1, 2, 4-6, 9-12, 15, and 18 is 1620 ppm / min. The halogen supply rate Vin for Examples 3 and 8 is 4760 ppm / min. The halogen supply rate Vin for Example 7 is 480 ppm / min. The halogen supply rate Vin for Examples 13 and 14 is 145,000 ppm / min. The halogen supply rate Vin for Example 16 is 380 ppm / min. The halogen supply rate Vin for Example 17 is 1,400,000 ppm / min. The halogen supply rate Vin for Comparative Example 2 is 200 ppm / min.

[0090] In Examples 1, 4-13, 15-18, and Comparative Examples 1 and 2, the firing temperature in the third firing step S17 is 1000°C. In Examples 2, 3, and 14, the firing temperature in the third firing step S17 is 1200°C.

[0091] In Examples 1-10, 13-18, and Comparative Examples 1 and 2, the moisture content of the mixed raw materials was 300 ppm. In Example 12, the moisture content of the raw materials was 120 ppm. In Example 13, the moisture content of the raw materials was 2900 ppm.

[0092] In Examples 1-4, 7, 9-15, 17, 18, and Comparative Example 1, the particle size of the raw material particles is 0.15 μm. In Examples 5 and 8, the particle size of the raw material particles is 0.03 μm. In Examples 6 and 16, and Comparative Example 2, the particle size of the raw material particles is 5.5 μm.

[0093] The ionic conductivity of the pyrochlore-type solid electrolytes obtained in Examples 1, 4-13, and 15-18 was 2.7 × 10⁻⁶. －３ S / cm~5.8×10 －３ The conductivity was S / cm. The ionic conductivity of the pyrochlore-type solid electrolytes obtained in Comparative Examples 1 and 2 was 1.6 × 10⁻⁶. －３ S / cm~1.9×10 －３ The conductivity was S / cm. In other words, Examples 1, 4-13, and 15-18 all obtained higher ionic conductivity than Comparative Examples 1 and 2.

[0094] The ionic conductivity of the pyrochlore-type solid electrolytes obtained in Examples 2, 3, and 14 was 0.5 × 10⁻⁶. －３ S / cm~0.7×10 －３ The conductivity was S / cm. In Examples 2, 3, and 14, Ta was used as the constituent element of the solid electrolyte, resulting in a slightly lower ionic conductivity compared to when Nb was used.

[0095] In Example 12, the moisture content of the raw materials was higher than 2500 ppm. Therefore, it is thought that the hydrogen atoms in the moisture combined with fluorine to produce HF, promoting halogen volatilization. As a result, the halogen retention rate of the pyrochlore-type solid electrolyte was slightly lower at 99%, and the ionic conductivity was also lower at 3.9 × 10⁻⁶. －３ The S / cm is slightly lower.

[0096] In Example 5, since the particle size of the raw materials is smaller than 0.05 μm, it is thought that halogens volatilized more easily from the particle surface. As a result, the halogen retention rate of the pyrochlore-type solid electrolyte was slightly lower at 99%, and the ionic conductivity was also lower at 3.8 × 10⁻⁶. －３ The S / cm is slightly lower.

[0097] In Examples 6 and 16, the particle size of the raw materials is larger than 5 μm, resulting in a smaller reaction area. Therefore, the synthesis reaction of the pyrochlore-type solid electrolyte becomes less efficient, and it is thought that the product contains trace amounts of impurities due to insufficient reaction. The ionic conductivity of Example 6 was 3.5 × 10⁻⁶. －３ S / cm, Example 16 is 2.8 × 10 －３ The S / cm is slightly lower.

[0098] According to the embodiment described above, the relationship between the halogen supply rate Vin and the halogen volatilization rates Vout and Dp in the firing process S17 is set to Vin / (Vout × Dp) ≥ 0.015, and further, Vin / (Vout × Dp) ≤ 50. In the firing process S17, a pyrochlore-type solid electrolyte is synthesized by firing a mixed material of a precursor of the pyrochlore-type solid electrolyte and a halogen source. As a result, halogen desorption from the pyrochlore-type solid electrolyte can be suppressed in the third firing process S17, and the decrease in ionic conductivity can be suppressed.

[0099] Furthermore, by increasing the halogen supply rate Vin to Vin / (Vout × Dp) ≥ 0.05, halogen desorption from the pyrochlore-type solid electrolyte in the third firing step S17 can be effectively suppressed, and the decrease in ionic conductivity can be effectively suppressed. Moreover, by further increasing the halogen supply rate Vin to Vin / (Vout × Dp) ≥ 0.10, halogen desorption from the pyrochlore-type solid electrolyte in the third firing step S17 can be suppressed even more effectively, and the decrease in ionic conductivity can be suppressed even more effectively.

[0100] Furthermore, according to this embodiment, halogen can be supplied to the firing atmosphere of the pyrochlore-type solid electrolyte by adding a halogen-containing compound to the raw materials of the pyrochlore-type solid electrolyte. If the halogen-containing compound is a halide of an alkali metal cation that constitutes the pyrochlore-type solid electrolyte, halogen can be supplied to the firing atmosphere from the excess halogen source by adding an excess amount of halogen source to the pyrochlore-type solid electrolyte.

[0101] Furthermore, according to this embodiment, halogen can be supplied to the firing atmosphere of the pyrochlore-type solid electrolyte by circulating halogen-containing gas through the firing furnace 200.

[0102] Furthermore, according to this embodiment, in the third firing step S17, by firing the raw materials of the pyrochlore-type solid electrolyte while wrapped in metal foil, the raw materials can be sealed and halogen volatilization from the raw materials can be suppressed. Similarly, in the third firing step S17, by firing the raw materials of the pyrochlore-type solid electrolyte while placed in a crucible, halogen volatilization from the raw materials can be suppressed.

[0103] Furthermore, according to this embodiment, the particle size of the raw materials for the pyrochlore-type solid electrolyte is set within the range of 0.05 to 5 μm. This suppresses halogen volatilization caused by the particle size of the raw materials being too small, and suppresses insufficient reaction of the pyrochlore-type solid electrolyte caused by the particle size of the raw materials being too large.

[0104] Furthermore, according to this embodiment, halogen volatilization can be further suppressed by reducing the moisture content of the raw materials for the pyrochlore-type solid electrolyte to 2500 ppm or less. This suppresses the reaction of halogen atoms contained in the pyrochlore-type solid electrolyte with hydrogen atoms in the water, thereby suppressing halogen volatilization from the pyrochlore-type solid electrolyte.

[0105] This disclosure is not limited to the embodiments described above, and can be modified in various ways without departing from the spirit of this disclosure. Furthermore, the means disclosed in the embodiments may be combined as appropriate to the extent that they are feasible.

[0106] For example, in the above embodiment, an example was described in which the active material composite particles of this disclosure were applied to a lithium-ion battery in which the conductive ions are lithium ions, but they may also be applied to secondary batteries with different conductive ions. Specifically, the active material composite particles of this disclosure can be applied to potassium-ion batteries in which potassium ions conduct, sodium-ion batteries in which sodium ions conduct, and the like.

[0107] The characteristics of the method for producing a solid electrolyte disclosed herein are as follows: (Item 1) A method for producing a solid electrolyte having a pyrochlore-type crystal structure comprising a plurality of cations including a metal cation, a halogen element, and a defect structure, comprising: a mixing step (S16) of producing a mixed raw material by mixing a precursor of the solid electrolyte or a raw material for the precursor with a halogen-containing raw material containing the halogen element; and a firing step (S17) of firing the mixed raw material, wherein in the firing step, the halogen element volatilizes from the solid electrolyte at a halogen volatilization rate Vout, and the halogen element is supplied to the firing atmosphere of the solid electrolyte at a halogen supply rate Vin, and in the firing step, the mixed raw material is fired in an atmosphere where Vin / (Vout × Dp) ≥ 0.015, where Dp is the particle size which is the particle median diameter of the solid electrolyte. (Item 2) The method for producing a solid electrolyte according to Item 1, wherein in the firing step, at least one of supplying a halogen-containing gas containing the halogen element to the mixed raw materials and adding a halogen-containing compound containing the halogen element to the mixed raw materials is performed, thereby supplying the halogen element to the firing atmosphere of the solid electrolyte. (Item 3) The method for producing a solid electrolyte according to Item 2, wherein the halogen element is F and the halogen-containing compound contains a fluoride of at least one of the metal cations. (Item 4) The halogen element is F and the halogen-containing gas is F ２ HF, BF ３ NF ３ , PF ５ , SiF ４ SF ６A method for producing a solid electrolyte according to item 2, wherein at least one of the following is specified: (Item 5) A method for producing a solid electrolyte according to any one of items 1 to 4, wherein the firing step is performed in a container made of a material that is chemically stable to the pyrochlore-type solid electrolyte. (Item 6) A method for producing a solid electrolyte according to any one of items 1 to 6, wherein the moisture content of the mixed raw materials measured by the Karl Fischer method is 2500 ppm or less. (Item 7) A method for producing a solid electrolyte according to any one of items 1 to 6, wherein the particle size of the mixed raw materials is in the range of 0.05 to 5 μm. (Item 8) The solid electrolyte has a compositional formula Aa ２－α Ab （１＋α）／３ B ２ O ７－β X γ A method for producing a solid electrolyte according to any one of items 1 to 7, wherein Aa is an alkali metal, Ab contains at least a lanthanide, B is a cation different from Aa and Ab, X is an anion that can be replaced with an O atom constituting the solid electrolyte, and in the composition formula, α is in the range of 0.6 < α < 2.0, β is in the range of 0 < β ≤ 1, and γ is in the range of 0 < γ ≤ 1, and the composition formula includes a defect structure. (Item 9) A method for producing a solid electrolyte according to any one of items 1 to 8, wherein in the calcination step, the mixed raw materials are calcined in an atmosphere having the relationship Vin / (Vout × Dp) ≥ 0.05. (Item 10) A method for producing a solid electrolyte according to any one of items 1 to 9, wherein in the calcination step, the mixed raw materials are calcined in an atmosphere having the relationship Vin / (Vout × Dp) ≥ 0.10. (Item 11) A method for producing a solid electrolyte according to any one of Items 1 to 10, wherein in the firing step, the mixed raw materials are fired in an atmosphere having the relationship Vin / (Vout × Dp) ≤ 50. (Item 12) The container is made of platinum, copper, Al ２ O ３ A method for producing a solid electrolyte according to item 5, wherein the container is made of at least one of the following materials. (Item 13) The container is made of platinum, copper, Al ２ O ３A method for manufacturing a solid electrolyte according to item 12, wherein the crucible is made of at least one of the following, or at least one of a metal foil container made of at least one of platinum foil or copper foil. (Item 14) A method for manufacturing a secondary battery comprising stacking a solid electrolyte (15) manufactured by the manufacturing method according to any one of items 1 to 13, a positive electrode (14), and a negative electrode (12).

[0108] This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence. In addition, while various combinations and forms are shown in this disclosure, other combinations and forms that include one, more, or fewer of those elements also fall within the scope and concept of this disclosure.

Claims

1. A method for producing a solid electrolyte having a pyrochlore-type crystalline structure comprising a plurality of cations including a metal cation, a halogen element, and a defect structure, comprising: a mixing step (S16) of producing a mixed raw material by mixing a precursor of the solid electrolyte or a raw material for the precursor with a halogen-containing raw material containing the halogen element; and a firing step (S17) of firing the mixed raw material, wherein in the firing step, the halogen element volatilizes from the solid electrolyte at a halogen volatilization rate Vout, and the halogen element is supplied to the firing atmosphere of the solid electrolyte at a halogen supply rate Vin, and in the firing step, the mixed raw material is fired in an atmosphere where Vin / (Vout × Dp) ≥ 0.015, where Dp is the particle size which is the particle median diameter of the solid electrolyte.

2. The method for producing a solid electrolyte according to claim 1, wherein in the firing step, at least one of supplying a halogen-containing gas containing the halogen element to the mixed raw materials and adding a halogen-containing compound containing the halogen element to the mixed raw materials is performed, thereby supplying the halogen element to the firing atmosphere of the solid electrolyte.

3. The method for producing a solid electrolyte according to claim 2, wherein the halogen element is F, and the halogen-containing compound contains a fluoride of at least one of the metal cations.

4. The halogen element is F, and the halogen-containing gas is F ２ HF, BF ３ NF ３ , PF ５ , SiF ４ SF ６ A method for producing a solid electrolyte according to claim 2, wherein at least one of the above.

5. The method for producing a solid electrolyte according to claim 1, wherein the firing step is performed in a container made of a material that is chemically stable to the pyrochlore-type solid electrolyte.

6. The method for producing a solid electrolyte according to claim 1, wherein the moisture content of the mixed raw materials, as measured by the Karl Fischer method, is 2500 ppm or less.

7. The method for producing a solid electrolyte according to claim 1, wherein the particle size of the mixed raw materials is in the range of 0.05 to 5 μm.

8. The solid electrolyte 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 capable of substituting for the O atom constituting the solid electrolyte, in the composition formula, α is within the range of 0.6 < α < 2.0, β is within the range of 0 < β ≤ 1, γ is within the range of 0 < γ ≤ 1, and the method for producing the solid electrolyte according to claim 1, which contains a defect structure.

9. The method for producing a solid electrolyte according to claim 1, wherein in the firing step, the mixed raw materials are fired in an atmosphere having the relationship Vin / (Vout × Dp) ≥ 0.

05.

10. The method for producing a solid electrolyte according to claim 1, wherein in the firing step, the mixed raw materials are fired in an atmosphere having the relationship Vin / (Vout × Dp) ≥ 0.

10.

11. The method for producing a solid electrolyte according to claim 1, wherein in the firing step, the mixed raw materials are fired in an atmosphere having the relationship Vin / (Vout × Dp) ≤ 50.

12. The container is made of platinum, copper, and aluminum. ２ O ３ A method for producing a solid electrolyte according to claim 5, wherein the container is made of at least one of the materials.

13. The container is made of platinum, copper, and aluminum. ２ O ３ A method for producing a solid electrolyte according to claim 12, wherein the crucible is made of at least one of the following, or at least one of a metal foil container made of at least one of platinum foil or copper foil.

14. A method for manufacturing a secondary battery comprising stacking a solid electrolyte (15) manufactured by the manufacturing method described in any one of claims 1 to 13, a positive electrode (14), and a negative electrode (12).

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