Method for manufacturing a solid electrolyte and method for manufacturing a secondary battery

Abstract

A method for producing a pyrochlore-type solid electrolyte comprising a plurality of cations including a metal cation, a halogen element, and a defect structure, comprising a mixing step (S16) for producing a mixed raw material by mixing a precursor or raw material for a precursor of a solid electrolyte with a halogen-containing raw material containing a halogen element, and a firing step (S17) for 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 median diameter of the solid electrolyte.

Description

Cross - reference to related applications

[0001] This application is based on Japanese Patent Application No. 2024 - 174937 filed on October 4, 2024, the content of which is incorporated herein by reference.

Technical Field

[0002] The present disclosure relates to a method for manufacturing a solid electrolyte having a pyrochlore structure and a method for manufacturing a secondary battery.

Background Art

[0003] In Patent Document 1, a pyrochlore - type solid electrolyte with a composition formula Aa Ab (1+α) / 3 B2O 7-β X γ (Aa: alkali metal, Ab: lanthanoid, B: cation metal, X: anion capable of being substituted with O) has been proposed. The pyrochlore - type solid electrolyte described in Patent Document 1 has defects in its crystal structure, and a part of the oxygen atoms constituting the pyrochlore structure is substituted with a halogen element, and high ionic conductivity is obtained. The pyrochlore - type solid electrolyte has a crystal structure in which a three - dimensional network of octahedrons composed of BO6 is formed, and a tunnel structure in which cations composed of Aa / Ab and anions composed of X are arranged is formed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] However, when a halogen element is included in the pyrochlore structure, the halogen element exists as a weak complex with Aa / Ab in the tunnel structure and is in an unstable state including a defect structure, so it is likely to desorb from the crystal structure. Therefore, when manufacturing a pyrochlore-type solid electrolyte, the halogen element may desorb from the pyrochlore-type solid electrolyte in the firing process, which may reduce the ionic conductivity of the pyrochlore-type solid electrolyte.

[0006] In view of the above points, an object of the present disclosure is to suppress the desorption of halogen elements from a pyrochlore-type solid electrolyte when manufacturing a pyrochlore-type solid electrolyte containing a halogen element.

[0007] To achieve the above object, in one aspect of the present disclosure, there is provided a method for manufacturing a solid electrolyte having a pyrochlore-type crystal structure including a plurality of cations containing a metal cation, a halogen element, and a defect structure, the method comprising: a mixing step of producing a mixed raw material in which a precursor of the solid electrolyte or a raw material of the precursor and a halogen-containing raw material containing a halogen element are mixed; 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, when the particle diameter, which is the particle median diameter of the solid electrolyte, is Dp, the mixed raw material is fired in an atmosphere having a relationship of Vin / (Vout×Dp)≧0.015.

[0008] Thereby, the desorption of halogen from the solid electrolyte in the firing step can be suppressed, a predetermined amount of halogen can be maintained in the crystal structure, and the decrease in ionic conductivity can be suppressed.

Brief Description of Drawings

[0009] [[ID=十九]] [Figure 1] It is a cross-sectional view showing the configuration of a secondary battery according to an embodiment of the present disclosure. [Figure 2] It is a diagram showing the crystal structure of a pyrochlore-type solid electrolyte. [Figure 3] It is a diagram showing a firing furnace for firing a pyrochlore-type solid electrolyte. [Figure 4] This is a diagram showing a firing furnace for firing pyrochlore-type solid electrolytes. [Figure 5] This figure shows the halogen supply rate Vin, halogen evaporation rate Vout, and particle size Dp of a pyrochlore-type solid electrolyte. [Figure 6] This diagram shows the manufacturing process for pyrochlore-type solid electrolytes. [Figure 7] This chart shows the halogen retention rate and ionic conductivity of the examples and comparative examples of this disclosure. [Figure 8] This chart shows the halogen retention rate and ionic conductivity of the examples and comparative examples of this disclosure. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments in which the ion conductor of this disclosure is applied 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 the positive electrode 14 and the negative electrode 12. The negative electrode 12 and the solid electrolyte 15 are in contact. The positive electrode 14 and the solid electrolyte 15 are in contact. 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 charging and discharging are performed by lithium ions moving between the negative electrode 12 and the positive electrode 14 via 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 and the negative electrode 12 are in contact. The positive electrode current collector 13 and the positive electrode 14 are in contact. 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 aid, 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 O2 (NCM), LiNi x Co y Al z O2 (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 PO4 (LMFP), LiMnPO4 (LMP), LiCoPO4 (LCP), LiNiPO4 (LNP) can be used. As the spinel type active material, for example, LiMn2O4 (LMO), LiNi 0.5 Mn 1.5 O4 (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 B2O 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, pyrochlore-type solid electrolytes have a crystalline structure in which a three-dimensional octahedral network of BO6 atoms is formed. In BO6, cation B is at the center, with oxygen atoms at its vertices, and these vertices are shared with adjacent BO6 atoms. Within the three-dimensional network of BO6 atoms, hexagonal tunnel structures are formed in which cations Aa / Ab and halogen X atoms 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 (2-α) of Aa 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, or 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 the cation Ab consists of lanthanides, and some of the lanthanides constituting Ab may be substituted with alkaline earth metals (such as Ca, Mg, and Sr). In this embodiment, the pyrochlore-type solid electrolyte has a pyrochlore structure where 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] In this embodiment, the pyrochlore-type solid electrolyte has a composite cation consisting of lithium metal and a lanthanide, where cation A is typically represented by the chemical formula "A2B2O7". This is thought to contribute to the improved ionic conductivity of the pyrochlore-type solid electrolyte.

[0025] Cation B is a metallic 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, group 4 or group 5 transition metals 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 some 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 composition formula of a typical pyrochlore structure is "A2B2O7", and 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, a portion of at least one of Aa and Ab is missing, resulting in a vacancy. The composition ratio corresponding to the missing portion (vacancy) of Aa and Ab is (2α-1) / 3.

[0029] The A site of the pyrochlore-type solid electrolyte in this embodiment 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 compositional 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 compositional formula negative.

[0031] Furthermore, the pyrochlore-type solid electrolyte of this embodiment is a complex anionic compound in which multiple anions such as O and X are contained in the pyrochlore structure. Because the anion represented by X is present in the BO6 coordination octahedron structure, the alkali metal Aa can be located in the center of the space between the BO6 coordination octahedron and the BO6 coordination octahedron without being pushed towards it. Therefore, it is believed that the pyrochlore-type solid electrolyte of this embodiment exhibits high ionic conductivity when used with an electric field applied, 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 Nb2O6F, Li 1.25 La 0.58 Ta2O6F, Li 1.25 La 0.58 Nb2O6Cl can be used as an example. Below, "Li 1.25 La 0.58 Nb2O6F" is "LLNOF", "Li 1.25 La 0.58 Ta2O6F is "LLTOF", Li 1.25 La 0.58 Nb2O6Cl 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] If the halogen element in the pyrochlore-type solid electrolyte is fluorine, then fluorine-containing gases such as F2, HF, BF3, NF3, PF5, SiF4, and SF6 can be used as the halogen-containing gas. If the halogen element in the pyrochlore-type solid electrolyte is chlorine, then chlorine-containing gases such as Cl2 and HCl can be used. Among these halogen-containing gases, it is desirable to use F2 or Cl2 from the viewpoint of not damaging the firing furnace 200 and not having any elements other than the halogen component incorporated into the pyrochlore-type solid electrolyte. 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. Examples of metal cation halides include metal cation fluorides (e.g., LiF, LaF3) and metal cation chlorides (e.g., LiCl, LaCl3).

[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 volatilization 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 volatilization rate Vout.

[0044] The particle size Dp is the particle median diameter D50, measured by laser diffraction and scattering for particles of a pyrochlore-type solid electrolyte. 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 content of a pyrochlore-type solid electrolyte is 100g, the halogen supply amount is 10g, 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 content, 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 volatilized 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 volatilized 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 volatilized is 0.5 wt%, the halogen volatilization rate Vout of LLNOF is Vout = (0.5 / 4.87) / (7 × 60) × 10⁶ = 244 ppm / min. The amount of halogen volatilized 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 with 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 for Vin / (Vout × Dp) ≥ 0.05, more desirable for Vin / (Vout × Dp) ≥ 0.07, and even more desirable for 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 gases to cause an excess 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 keep Vin / (Vout×Dp)≦100, and even more desirable to keep 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 with respect to the pyrochlore-type solid electrolyte. Platinum, copper, and Al2O3 are chemically stable materials with respect to the pyrochlore-type solid electrolyte, and the firing of the raw materials for the pyrochlore-type solid electrolyte can be carried out using a container made of at least one of these materials. As such a container, at least one of a crucible made of at least one of platinum, copper, or Al2O3, or at least one of a metal foil container made of at least one of platinum foil or copper foil can be used. The crucible made of at least one of platinum, copper, or Al2O3 and the metal foil container 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 increase 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 increase.

[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] Furthermore, it is desirable to keep the firing temperature in the firing process for pyrochlore-type solid electrolytes as low as possible without hindering the synthesis of pyrochlore-type solid electrolytes. Lowering the firing temperature in the firing process can suppress the volatilization of halogen components from the pyrochlore-type solid electrolyte.

[0059] Furthermore, it is desirable to keep the particle size of the mixed raw materials for the pyrochlore-type solid electrolyte within a predetermined range. Specifically, it is desirable to keep the particle size of the mixed raw materials for the pyrochlore-type solid electrolyte within the range of 0.05 to 5 μm. The particle size of the mixed raw materials for the pyrochlore-type solid electrolyte is the particle median diameter D50, and is the measurement taken immediately before supplying halogen to the firing atmosphere in the third firing process S17.

[0060] If the particle size of the mixed raw materials is too small, halogens will easily volatilize from the particle surface. Therefore, to suppress halogen volatilization from the raw material particles, it is desirable to make the particle size of the mixed raw materials 0.05 μm or larger. On the other hand, if the particle size of the mixed raw materials is too large, although the amount of halogen volatilization will decrease, the specific surface area will decrease, making it difficult for the synthesis reaction of pyrochlore-type solid electrolytes to proceed. Therefore, if the particle size of the mixed raw materials is too large, it will be necessary to increase the firing temperature, which will actually promote halogen volatilization. For this reason, it is desirable to keep the particle size of the mixed raw materials to 5 μm or less in order to facilitate the synthesis reaction of pyrochlore-type solid electrolytes.

[0061] Next, the method for producing the pyrochlore-type solid electrolyte of this embodiment will be explained with reference to Figure 6. Figure 6 shows LLNOF(Li 1.25 La 0.58 This shows the manufacturing process for Nb2O6F.

[0062] In this embodiment, the halogen component is supplied to the firing atmosphere of the pyrochlore-type solid electrolyte in the third firing step S17. Although Figure 6 shows an example of a manufacturing method in which the halogen source is added in the second raw material preparation step S15, the halogen source can also be added in the first raw material preparation step S10, and at least a portion of 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 is performed to prepare a lanthanum source, a lithium source, and a niobium source as raw materials for LLTOF. Metal oxides and metal carbon oxides can be used as the lanthanum source, lithium source, and niobium source. In this embodiment, La2O3 is used as the lanthanum source, Li2CO3 as the lithium source, and Nb2O5 as the niobium source. 1.25 La 0.58 When producing Ta2O6F, a tantalum source (e.g., Ta2O5) can be used instead of a niobium source.

[0064] Next, a first mixing step S11 is performed in which La2O3, Li2CO3, and Nb2O5 are weighed, mixed in a predetermined ratio, and then ground to produce a mixture.

[0065] Next, a first calcination step S12 is performed to calcine the mixture of raw materials. In the first calcination step, the mixture is calcined in air at 500°C for 6 hours. Calcination removes moisture and other substances from the mixture, thereby increasing its reactivity. Furthermore, by removing moisture from the mixture, the generation of hydrogen fluoride in the third calcination step S17, which will be described later, can be suppressed.

[0066] Next, a second mixing step S13 is performed in which the calcined mixture is mixed and pulverized, followed by a second calcination step S14 in which the mixture is calcined. In the second calcination step, the mixture is heated in air at 1200°C for 4 hours to perform the final calcination. Through the second calcination step S14, Li, a precursor of the target pyrochlore-type solid electrolyte, is produced. 0.5 La 0.5 Nb2O6 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 LaF3 are used as the halogen source. LiF is both a halogen source and a lithium source, and LaF3 is both a halogen source and a lanthanum source. When producing LLNOCl, for example, LiCl and LaCl3 can be used as the halogen source.

[0068] Next, a third mixing step S16 is performed in which the precursor of the pyrochlore-type solid electrolyte, LiF, and LaF3 are weighed, mixed in a predetermined ratio, and pulverized 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 pyrochlore-type solid electrolyte precursor and the halogen source may be produced. Note that 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 firing process S17 corresponds to the firing process 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 achieved, 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 can be volatilized, thereby supplying halogen to the firing atmosphere.

[0073] The halogen supply in the third firing process S17 can also be carried out by supplying a halogen-containing gas such as F2 to the firing furnace 200.

[0074] In the third firing step S17, 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 A pyrochlore-type solid electrolyte represented by "Nb2O6F" 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, by changing the mixing ratio of La2O3, Nb2O5, and LiF in the above manufacturing process, the composition formula "Li2-α La (1+α) / 3 Nb2O 7-β F γ Crystals with a pyrochlore structure represented by can be obtained. By changing the mixing ratio of La2O3, Nb2O5, and LiF, the α, β, and γ in the composition formula can be adjusted. In addition, some of the material sublimes when fired. 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 ingredients] The moisture content of the mixed raw materials before calcination was measured using the Karl Fischer coulometric titration method, with a Kyoto Electronics Manufacturing ADP-611 moisture vaporizer and an MKC-610 moisture meter.

[0079] [Particle size of mixed raw materials] The particle size of the mixed raw materials before calcination was determined by dispersing the mixed raw materials in ethanol and obtaining the volume-averaged particle size distribution using a Horiba Partica LA-960 laser diffraction / scattering particle size distribution analyzer. The particle size of the mixed raw materials is the particle median diameter D50, which 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 electrolytes] The particle size Dp of the solid electrolyte was determined by dispersing the solid electrolyte in ethanol before fine grinding and obtaining the volume-averaged particle size distribution using a Horiba Partica LA-960 laser diffraction / scattering particle size distribution analyzer. The particle size Dp of the solid electrolyte is the particle median diameter D50, which 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 maintenance 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 and 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 halogen amount 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 using the AC impedance method. In the impedance measurement, AC signals were applied to the solid electrolyte at multiple frequencies, and the AC impedance was measured for each frequency. By plotting the measured impedances 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. The reciprocal of the resistance value was then multiplied by the thickness (cm) of the measurement sample and the electrode area (cm²). 2 The ionic conductivity was calculated by multiplying by ).

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

[0083] In Examples 1, 5-13, 15-18, and Comparative Examples 1 and 2, Li2CO3, La2O3, Nb2O5, LiF, and LaF3 were used as raw materials for LLNOF(Li 1.25 La 0.58 Nb2O6F) was produced. In Examples 2, 3, and 14, Li2CO3, La2O3, Ta2O5, LiF, and LaF3 were used as raw materials to produce LLTOF (Li 1.25 La 0.58 Ta2O6F) was produced. In Example 4, Li2CO3, La2O3, Nb2O5, LiCl, and LaCl3 were used as raw materials to produce LLNOCl(Li 1.25 La 0.58 We manufactured Nb2O6Cl.

[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, halogen was supplied to the firing atmosphere by circulating halogen-containing gas F2 through the firing furnace 200. 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, and 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, halogen volatilization was suppressed by placing the mixed raw materials in a platinum crucible. In Example 9, halogen volatilization was suppressed by placing the mixed raw materials in an Al2O3 crucible while sealed in a platinum foil container. In Example 10, halogen volatilization was suppressed by placing the mixed raw materials in an Al2O3 crucible while sealed in a copper foil container. 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, halogen volatilization was suppressed by placing the mixed raw materials in an Al2O3 crucible.

[0088] The halogen volatilization rate Vout for Examples 1-12, 15, 16, 18, and Comparative Examples 1 and 2 was 240 ppm / min. The halogen volatilization rate Vout for Examples 13, 14, and 17 was 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, so the ionic conductivity was slightly lower than 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 form 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. -3The S / cm ratio 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 ratio 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 is less likely to proceed, 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 ratio 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. 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, the raw materials for the pyrochlore-type solid electrolyte are fired while wrapped in metal foil, thereby sealing the raw materials and suppressing halogen volatilization from the raw materials. Similarly, in the third firing step S17, the raw materials for the pyrochlore-type solid electrolyte are fired while placed in a crucible, thereby suppressing halogen volatilization from the raw materials.

[0103] Furthermore, according to this embodiment, the particle size of the raw materials for the pyrochlore-type solid electrolyte is 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 solid electrolytes 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, A mixing step (S16) to produce a mixed raw material by mixing the precursor of the solid electrolyte or the raw material of the precursor with a halogen-containing raw material containing the halogen element, The system includes a firing step (S17) for firing the mixed raw materials, In the firing process, 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. A method for producing a solid electrolyte, comprising the firing step, in which the mixed raw materials are fired in an atmosphere where Vin / (Vout × Dp) ≥ 0.015, where Dp is the particle size which is the 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) A method for producing a solid electrolyte according to item 2, wherein the halogen element is F, and the halogen-containing gas is at least one of F2, HF, BF3, NF3, PF5, SiF4, and SF6. (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, as 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 the composition formula Aa 2-α Ab (1+α) / 3 B2O 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 by 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, γ is in the range of 0 < γ ≤ 1, and the composition formula includes a defect structure. (Item 9) The method for producing a solid electrolyte according to any one of items 1 to 8, wherein the calcination step involves calcining the mixed raw materials in an atmosphere having the relationship Vin / (Vout×Dp)≧0.05. (Item 10) The method for producing a solid electrolyte according to any one of items 1 to 9, wherein the calcination step involves calcining the mixed raw materials 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 the calcination step involves calcining the mixed raw materials in an atmosphere having the relationship Vin / (Vout×Dp)≦50. (Item 12) The method for producing a solid electrolyte according to item 5, wherein the container is made of at least one of the materials platinum, copper, and Al2O3. (Item 13) The method for producing a solid electrolyte according to item 12, wherein the container is at least one of a crucible made of platinum, copper, or Al2O3, or a container made of metal foil 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 described in 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 crystal structure comprising a plurality of cations including a metal cation, a halogen element, and a defect structure, A mixing step (S16) to produce a mixed raw material by mixing the precursor of the solid electrolyte or the raw material of the precursor with a halogen-containing raw material containing the halogen element, The system includes a firing step (S17) for firing the mixed raw materials, In the firing process, 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. A method for producing a solid electrolyte, comprising the firing step, in which the mixed raw materials are fired in an atmosphere having the relationship Vin / (Vout × Dp) ≥ 0.015, where Dp is the particle size which is the median diameter of the solid electrolyte particles.

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. A 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 that can be substituted for an O atom constituting the solid electrolyte, in the composition formula, α is in the range of 0.6 < α < 2.0, β is in the range of 0 < β ≤ 1, γ is in 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 the calcination step involves calcining the mixed raw materials 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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