Method for producing solid electrolyte

Abstract

A method for producing a solid electrolyte that has a pyrochlore-type crystal structure and contains an alkali metal, a lanthanoid, at least one specific element selected from transition elements, group 13 elements, group 14 elements, and group 15 elements, and a halogen element, the method comprising: mixing steps (S11, S14, S21) for mixing a plurality of raw materials of the solid electrolyte to produce a raw material mixture; and firing steps (S12, S15, S22) for heating the raw material mixture at a prescribed temperature to fire the mixture. The raw materials include an alkali metal compound, a lanthanoid compound, and a specific element compound. When S1 is defined as the specific surface area of the alkali metal compound, S2 is defined as the specific surface area of the specific element compound, and S3 is defined as the specific surface area of the lanthanoid compound, the relationships S1 / S2 ≤ 50 and S3 / S2 ≥ 0.01 hold true.

Description

Method for producing solid electrolytes Cross-reference of related applications

[0001] This application is based on Japanese Patent Application No. 2024-225700, filed on December 20, 2024, and its contents are incorporated herein by reference.

[0002] This disclosure relates to a method for producing a solid electrolyte.

[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 have been proposed (Aa: alkali metal, Ab: lanthanide, B: cationic metal, X: halogen substitutable for oxygen). 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.

[0004] Patent No. 7334813

[0005] The pyrochlore-type solid electrolytes described above tend to generate impurities in the product during the manufacturing process due to characteristics such as the volatilization of alkali metals and halogen elements they contain, and their composition as complex oxides made of multiple metal components.

[0006] The present invention aims to suppress the generation of impurities in a method for producing a solid electrolyte having a pyrochlore-type crystal structure.

[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 comprising an alkali metal, a lanthanide, at least one specific element from a transition element, a group 13 element, a group 14 element, or a group 15 element, and a halogen element, comprising a mixing step of mixing a plurality of raw materials for the solid electrolyte to produce a raw material mixture, and a firing step of heating the raw material mixture at a predetermined temperature to calcine it. The raw materials include an alkali metal compound containing an alkali metal, a lanthanide compound containing a lanthanide, and a specific element compound containing a specific element. When the specific surface area of ​​the alkali metal compound is S1, the specific surface area of ​​the specific element compound is S2, and the specific surface area of ​​the lanthanide compound is S3, the relationships S1 / S2 ≤ 50 and S3 / S2 ≥ 0.01 exist.

[0008] According to this method, by setting the specific surface area for each raw material according to the type of raw material used in the pyrochlore-type solid electrolyte, the reaction of each raw material particle can be controlled during the production of the pyrochlore-type solid electrolyte. As a result, the generation of impurities can be suppressed, and the synthesis of the pyrochlore-type solid electrolyte can be promoted.

[0009] This is a cross-sectional view showing the configuration of a secondary battery according to an embodiment of the present disclosure. This is a diagram showing the crystal structure of a pyrochlore-type solid electrolyte. This is a diagram showing the manufacturing process when a pyrochlore-type solid electrolyte is produced by a two-step synthesis. This is a diagram showing the manufacturing process when a pyrochlore-type solid electrolyte is produced by a one-step synthesis. This is a diagram showing examples and comparative examples when a pyrochlore-type solid electrolyte is produced under various different conditions. This is a diagram showing examples and comparative examples when a pyrochlore-type solid electrolyte is produced under various different conditions.

[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 layer 12 and the positive electrode layer 14.

[0011] As shown in Figure 1, the secondary battery 10 comprises a negative electrode current collector 11, a negative electrode layer 12, a positive electrode current collector 13, a positive electrode layer 14, and an electrolyte layer 15.

[0012] An electrolyte layer 15 is sandwiched between the positive electrode layer 14 and the negative electrode layer 12. The negative electrode layer 12 and the electrolyte layer 15 are in contact with each other. The positive electrode layer 14 and the electrolyte layer 15 are in contact with each other. The negative electrode layer 12 and the positive electrode layer 14 are connected via the electrolyte layer 15. The secondary battery 10 of the present embodiment is a lithium-ion battery in which charge and discharge are performed by lithium ions moving between the negative electrode layer 12 and the positive electrode layer 14 through the electrolyte layer 15.

[0013] A laminate including these negative electrode layer 12, positive electrode layer 14, and electrolyte layer 15 is provided between the negative electrode current collector 11 and the positive electrode current collector 13. The negative electrode current collector 11 and the negative electrode layer 12 are in contact with each other. The positive electrode current collector 13 and the positive electrode layer 14 are in contact with each other. 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 the present 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 layer 12 can be any material that can be used as a negative electrode active material for a lithium-ion battery, and for example, a carbon-based negative electrode material, an oxide-based negative electrode material, a metal-based negative electrode material, etc. can be used. These negative electrode materials can be used alone or in combination.

[0016] As the carbon-based negative electrode material, for example, natural graphite, artificial graphite, hard carbon can be used. As the oxide-based negative electrode material, for example, Li ４ Ti ５ O １２ 、TiO ２ (B)、TiNb ２ O ７ can be used. As the metal-based negative electrode material, for example, a silicon-based negative electrode material, lithium metal can be used.

[0017] In this embodiment, graphite is used as the negative electrode material. The negative electrode layer 12 may contain a conductive additive, a binder, and a polymer. As the conductive additive, a carbon material such as carbon black can be used. As the binder, an aqueous binder such as a mixture of SBR (styrene-butadiene rubber) and CMC (carboxymethylcellulose) can be used. Furthermore, the negative electrode layer 12 may contain a solid electrolyte.

[0018] The positive electrode material constituting the positive electrode layer 14 can be any material usable as a positive electrode active material for lithium-ion batteries. Examples of positive electrode materials include layered rock salt type active materials, olivine type active materials, and spinel type active materials. Examples of layered rock salt type active materials include LiNi ｘ Co ｙ Mn ｚ O ２ (NCM), LiNi ｘ Co ｙ Al ｚ O ２ A ternary cathode material such as (NCA) can be used. As an olivine-type active material, for example, LiFePO ４ (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.

[0019] The positive electrode layer 14 may contain a conductive additive, a binder, and a polymer. The conductive additive can be, for example, a carbon material such as carbon black. As the binder, for example, polyvinylidene fluoride (PVdF) can be used. Furthermore, the positive electrode layer 14 may contain a solid electrolyte.

[0020] The electrolyte layer 15 is ionic conductive and can move lithium ions between the negative electrode layer 12 and the positive electrode layer 14. A solid electrolyte is used as the electrolyte material for the electrolyte layer 15. The electrolyte layer 15 may contain a binder. Furthermore, the electrolyte layer 15 may contain an electrolyte solution and a polymer. For example, ethylene carbonate can be used as the electrolyte solution. The electrolyte solution may also be an ionic liquid. For example, polyethylene oxide can be used as the polymer.

[0021] In this embodiment, a pyrochlore-type oxide solid electrolyte having a pyrochlore-type crystal structure is used as the solid electrolyte constituting the electrolyte layer 15. Hereinafter, the pyrochlore-type oxide solid electrolyte will also be referred to as a pyrochlore-type solid electrolyte.

[0022] 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 element 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.

[0023] 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. ６ In 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] Cation B is a cation distinct from Aa and Ab, and is an element selected from transition elements or elements of groups 13 to 15. In the crystal, B constitutes an octahedron surrounded by six oxygen atoms. As the transition element represented by B, a group 4 transition element or a group 5 transition element 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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 octahedron structure, alkali metals Aa are BO ６ Without relying on an octahedron, BO ６ It can be positioned in the center of the space between the octahedron and the solid electrolyte. 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.

[0036] 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.

[0037] Examples of pyrochlore-type solid electrolytes include Li １．２５ La ０．５８ Ta ２ O ６ F, Li １．２５ La ０．５８ Nb ２ O ６ F, Li １．２５ La ０．５８ TaNbo 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 Ta ２ O ６ "F" is "LLTOF", "Li １．２５ La ０．５８ Nb ２ O ６ F" to "LLNOF", Li １．２５ La ０．５８ TaNbo ６ F" to "LLTNOF", Li １．２５ La ０．５８ Nb ２ O ６ "Cl" is also referred to as "LLNOCl".

[0038] The raw materials used in the manufacture of pyrochlore-type solid electrolytes include alkali metal compounds containing alkali metals, lanthanide compounds containing lanthanides, and specific element compounds containing any of the following elements: transition elements, group 13 elements, group 14 elements, or group 15 elements.

[0039] The alkali metal contained in alkali metal compounds is cation Aa in the composition formula of pyrochlore-type solid electrolytes, and is at least one of Li, Na, or K. The lanthanide contained in lanthanide compounds is cation Ab in the composition formula of pyrochlore-type solid electrolytes, and is at least one of La, Ce, Nd, or Sm. The specific element contained in specific element compounds is cation B in the composition formula of pyrochlore-type solid electrolytes, and is at least one of Nb, Ta, Ti, Zr, Hf, V, Al, Ga, In, Ge, Sn, Sb, or Bi.

[0040] The alkali metal compounds include alkali metal non-halides that do not contain halogen elements and alkali metal halides that contain halogen elements. The lanthanoid compounds include lanthanoid non-halides that do not contain halogen elements and lanthanoid halides that contain halogen elements.

[0041] In this embodiment, a lithium compound containing Li is used as the alkali metal compound, and a lanthanum compound containing La is used as the lanthanoid compound. Further, a niobium compound containing Nb or a tantalum compound containing Ta is used as the specific element compound, and a fluoride containing F or a chloride containing Cl is used as the halogen compound.

[0042] As the lithium compound, for example, LiF, LiCl, Li ２ CO ３ can be used. LiF and LiCl are alkali metal halides, and Li ２ CO ３ is an alkali metal non-halide. As the lanthanum compound, for example, LaF ３ , LaCl ３ , La ２ O ３ can be used. LaF ３ , LaCl ３ are lanthanoid halides, and La ２ O ３ is a lanthanoid non-halide. The alkali metal non-halide and the lanthanoid non-halide contain O. As the tantalum compound, for example, Ta ２ O ５ can be used. As the niobium compound, for example, Nb ２ O ５ can be used.

[0043] In this embodiment, as the raw materials of LLTOF, Li ２ CO ３ , LiF, Ta ２ O ５ , La ２ O ３ , LaF３ It uses Li as a raw material for LLNOF. ２ CO ３ LiF, Nb ２ O ５ La ２ O ３ LaF ３ It uses Li as a raw material for LLTNOF. ２ CO ３ LiF, Ta ２ O ５ , Nb ２ O ５ La ２ O ３ LaF ３ It uses Li as a raw material for LLNOCl. ２ CO ３ LiCl, Nb ２ O ５ La ２ O ３ LaCl ３ It uses this.

[0044] According to our research, in the manufacturing process of pyrochlore-type solid electrolytes, the reactivity of elements contained in the raw materials tends to be as follows, resulting in the easy generation of impurities in the product.

[0045] Alkali metals and halogen elements are highly volatile. Alkali metals react readily with certain elements. Lanthanides do not react readily with certain elements. Furthermore, halogenation reactions during the manufacturing process are less likely to occur than oxidation reactions. In other words, lanthanide halides are less reactive than lanthanide non-halides, and alkali metal halides are less reactive than alkali metal non-halides.

[0046] In this embodiment, based on the above-mentioned findings, the specific surface area of ​​raw material particles containing alkali metal compounds, lanthanide compounds, and specific elemental compounds is set according to the type of raw material particle, thereby suppressing the generation of impurities during the manufacturing process of pyrochlore-type solid electrolytes.

[0047] Specifically, the specific surface area of ​​raw material particles whose reaction is to be promoted is increased, while the specific surface area of ​​raw material particles whose reaction is to be suppressed is decreased. In this embodiment, the ratio of the specific surface area S1 of the alkali metal compound to the specific surface area S2 of the specific element compound and the ratio of the specific surface area S3 of the lanthanide compound to the specific surface area S2 of the specific element compound are set based on the specific surface area S2 of the specific element compound.

[0048] It is desirable to suppress the reaction of alkali metal compounds with specific elemental compounds. Furthermore, since alkali metals are highly volatile, it is desirable to suppress their volatilization. For this reason, the specific surface area S1 of the alkali metal compound is reduced relative to the specific surface area S2 of the specific elemental compound to suppress the reaction and volatilization of the alkali metal compound. The ratio of the specific surface area S1 of the alkali metal compound to the specific surface area S2 of the specific elemental compound is preferably S1 / S2 ≤ 50, more preferably S1 / S2 ≤ 10, and even more preferably S1 / S2 ≤ 1.

[0049] Furthermore, it is desirable for lanthanide compounds to promote reactions with specific element compounds. For this reason, the specific surface area S3 of the lanthanide compound is increased relative to the specific surface area S2 of the specific element compound to promote the reaction of the lanthanide compound. The ratio of the specific surface area S3 of the lanthanide compound to the specific surface area S2 of the specific element compound is preferably S3 / S2 ≥ 0.01, more preferably S3 / S2 ≥ 0.1, and even more preferably S3 / S2 ≥ 1.

[0050] Furthermore, it is desirable to accelerate the halogenation reaction by promoting the reaction between alkali metal halides and specific element compounds more than the reaction between alkali metal non-halides and specific element compounds. For this reason, it is desirable that the relationship S1A < S1B exists when the specific surface area of ​​the alkali metal non-halide is S1A and the specific surface area of ​​the alkali metal halide is S1B.

[0051] Furthermore, it is desirable to accelerate the halogenation reaction by promoting the reaction between lanthanide halides and specific element compounds more than the reaction between lanthanide non-halides and specific element compounds. For this reason, it is desirable that the relationship S3A < S3B exists when the specific surface area of ​​the lanthanide non-halide is S3A and the specific surface area of ​​the lanthanide halide is S3B.

[0052] Furthermore, if the raw material mixture for pyrochlore-type solid electrolytes contains a large amount of water, the synthesis time for the pyrochlore-type solid electrolyte will be prolonged. In addition, water and halogen components may react during the synthesis reaction, promoting the generation of toxic hydrogen halides. For this reason, it is desirable to reduce the water content of the raw material mixture. For example, a raw material mixture with a low water content can be obtained by pre-drying the raw material mixture for pyrochlore-type solid electrolytes.

[0053] The moisture content of the raw material mixture is preferably ≤ 10,000 ppm, more preferably ≤ 5,000 ppm, and even more preferably ≤ 1,000 ppm. The moisture content of the raw material mixture can be measured by the Karl Fischer method.

[0054] Next, the method for producing the pyrochlore-type solid electrolyte of this embodiment will be explained using Figures 3 and 4. Figures 3 and 4 show Li １．２５ La ０．５８ Ta ２ O ６ This shows the manufacturing process for F (LLTOF). Figure 3 shows a two-stage synthesis in which the mixing steps S11 and S13, in which the raw materials are mixed, and the firing steps S12 and S14, in which the mixture is fired, are each performed twice. Figure 4 shows a one-stage synthesis in which the mixing step S21, in which the raw materials are mixed, and the firing step S22, in which the mixture is fired, are each performed once.

[0055] The moisture content of the raw material mixture for the pyrochlore-type solid electrolyte is measured before the second calcination step S15 if a two-step synthesis is performed, and before the calcination step S22 if a one-step synthesis is performed.

[0056] First, the two-step synthesis shown in Figure 3 will be explained. First, a raw material preparation step S10 is performed to prepare a lanthanum source, a lithium source, and a tantalum source as raw materials for LLTOF. As the lanthanum source, lithium source, and tantalum source, metal oxides and metal carbon oxides can be used. In the example shown in Figure 3, Li is used as the lithium source. ２ CO ３ Using La as the lantern source ２ O ３ Using Ta as the tantalum source ２ O ５ This is used. Furthermore, when manufacturing LLNOF and LLNOCl, Nb is used as the niobium source instead of the tantalum source. ２ O ５ You can use this. When manufacturing LLTNOF, Ta ２ O ５ and Nb ２ O ５ You can use it.

[0057] Next, the raw materials (Li) prepared in S10 ２ CO ３ La ２ O ３ Ta ２ O ５ A first mixing step S11 is performed, in which the ingredients are weighed, mixed in a predetermined ratio, and crushed to produce a raw material mixture.

[0058] The raw materials used in the first mixing step S11 have their specific surface area adjusted according to their type. Specifically, Ta ２ O ５ Li (as a specific element compound) ２ CO ３ The ratio of the specific surface areas S1A of (alkali metal non-halide) is set to S1A / S2 ≤ 50, and Ta ２ O ５ La relative to the specific surface area S2 of (specific element compound) ２ O ３ The ratio of the specific surface area S3A of (lanthanide non-halogenated) is set to S3A / S2 ≥ 0.01.

[0059] Next, a first calcination step S12 is performed to calcine the raw material mixture. In the first calcination step S12, the raw material mixture is placed in a calcination furnace and calcined by heating at 1200°C for 5 hours. Calcination can be performed in an inert atmosphere such as nitrogen or argon, or in the atmosphere. By cooling the product of the first calcination step S12, Li, a precursor of the target product LLTOF, is obtained. ０．５ La ０．５ Ta ２ O ６ (LLTO) is obtained.

[0060] Next, a second raw material preparation step S13 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 halogen elements, and in this embodiment, LiF and LaF ３ It uses LiF, which is an alkali metal halide, and LaF ３ It is a lanthanide halide. When producing LLNOCl, for example, LiCl and LaCl are used as halogen sources. ３ You can use it.

[0061] Next, the raw materials prepared in S13 (LLTO, LiF, LaF) ３ A second mixing step S14 is performed, in which the ingredients are weighed, mixed in a predetermined ratio, and crushed to produce a raw material mixture.

[0062] The raw materials used in the second mixing step S14 have their specific surface area adjusted according to their type. Specifically, Ta ２ O ５ The ratio of the specific surface area S1B of LiF (alkali metal halide) to the specific surface area S2 of (specific element compound) is set to S1B / S2 ≤ 50. Furthermore, Li ２ CO ３ The specific surface area S1A of an alkali metal non-halide and the specific surface area S1B of LiF (alkali metal halide) have the relationship S1A < S1B.

[0063] Similarly, Ta ２ O ５ LaF (of a specific element compound) relative to the specific surface area S2 ３ The ratio of the specific surface area S3B of (lanthanide halides) is set to S3B / S2 ≥ 0.01. Furthermore, La２ O ３ Specific surface area S3A and LaF of (lanthanide non-halogenated) ３ The specific surface area S3B of a lanthanide halide has the relationship S3A < S3B.

[0064] Next, a second calcination step S15 is performed to calcine the raw material mixture. In the second calcination step S15, the mixture is placed in a calcination furnace and calcined by heating at 1200°C for 5 hours. Calcination can be performed in an inert atmosphere such as nitrogen or argon, or in the atmosphere. By cooling the product of the second calcination step S15, the target product Li is obtained. １．２５ Ta ０．５８ Ta ２ O ６ F(LLTOF) is obtained.

[0065] Next, we will explain the one-step synthesis shown in Figure 4. First, a raw material preparation step S20 is performed to prepare lanthanum source, lithium source, tantalum source, and halogen source as raw materials for LLTOF. In the example shown in Figure 4, Li is used as the lithium source. ２ CO ３ Using La as the lantern source ２ O ３ Using Ta as the tantalum source ２ O ５ Using LiF and LaF as halogen sources, ３ It uses this.

[0066] Next, the raw materials (LiF, LaF) prepared in S20 ３ Li ２ CO ３ La ２ O ３ Ta ２ O ５ Mixing step S21 is performed in which the raw materials are weighed, mixed in a predetermined ratio, and crushed to produce a raw material mixture. The raw materials used in mixing step S21 have their specific surface area adjusted according to their type, similar to the first mixing step S12 and the second mixing step S14 described above.

[0067] Next, a calcination process S22 is performed to calcine the raw material mixture. In calcination process S12, the raw material mixture is placed in a calcination furnace and calcined by heating at 1200°C for 5 hours. Calcination can be performed in an inert atmosphere such as nitrogen or argon, or in the atmosphere. By cooling the product of calcination process S22, the target product Li is obtained. １．２５ La ０．５８ Ta ２ O ６ F(LLTOF) is obtained.

[0068] Next, we will explain the cases in which pyrochlore-type solid electrolytes are produced under various different conditions, using the examples and comparative examples shown in Figures 5 and 6.

[0069] In Examples 1 to 10, the ratio of the specific surface area S1 of the alkali metal compound to the specific surface area S2 of the specific element compound is S1 / S2 ≤ 50, and the ratio of the specific surface area S3 of the lanthanide compound to the specific surface area S2 of the specific element compound is S3 / S2 ≥ 0.01.

[0070] Examples 6, 9, and 10 show that the specific surface area S1A of the alkali metal non-halide and the specific surface area S1B of the alkali metal halide have the relationship S1A < S1B. Furthermore, in Examples 6, 9, and 10, the specific surface area S3A of the lanthanide non-halide and the specific surface area S3B of the lanthanide halide have the relationship S3A < S3B.

[0071] In Comparative Example 1, the ratio of the specific surface area S1 of the alkali metal compound to the specific surface area S2 of the specific element compound is S1 / S2 > 50, and the ratio of the specific surface area S3 of the lanthanide compound to the specific surface area S2 of the specific element compound is S3 / S2 ≥ 0.01. In Comparative Example 2, the ratio of the specific surface area S1 of the alkali metal compound to the specific surface area S2 of the specific element compound is S1 / S2 ≤ 50, and the ratio of the specific surface area S3 of the lanthanide compound to the specific surface area S2 of the specific element compound is S3 / S2 < 0.01.

[0072] The specific surface area of ​​each raw material in Examples 1-10 and Comparative Examples 1 and 2 was measured using a gas adsorption method with nitrogen gas, using a TriStar II specific surface area measuring device manufactured by Shimadzu Corporation, after removing any moisture adhering to the raw materials. Furthermore, the presence or absence of impurities in the product was confirmed using an X-ray diffractometer (XRD). In the XRD analysis, the presence of impurities was determined if a crystalline peak other than the desired pyrochlore-type solid electrolyte appeared, and the absence of impurities was determined if no such peak appeared. The moisture content of the raw material mixture before calcination treatment was measured using the Karl Fischer coulometric titration method, with an ADP-611 water vaporizer manufactured by Kyoto Electronics Manufacturing Co., Ltd. and an MKC-610 moisture meter.

[0073] In Example 1, LLTOF was prepared as a pyrochlore-type solid electrolyte. In Example 1, Li was used as the alkali metal nonhalide. ２ CO ３ LiF as an alkali metal halide, and Ta as a specific element compound. ２ O ５ , as a lanthanide nonhalogenate La ２ O ３ , as a lanthanide halide, LaF ３ I used it.

[0074] In Example 1, the specific surface areas S1A and S1B of the alkali metal non-halide and alkali metal halide were 6 m². ２ / g, the specific surface area S2 of the compound of a specific element is 5m² ２ / g, the specific surface areas S3A and S3B of lanthanide non-halides and lanthanide halides are 2m². ２ The values ​​were / g. In Example 1, the specific surface area ratios were S1A / S2 = S1B / S2 = 1.2 and S3A / S2 = S3B / S2 = 0.4.

[0075] In Example 1, the moisture content of the raw material mixture was 3000 ppm. In Example 1, a pyrochlore-type solid electrolyte was synthesized by a two-step synthesis method involving two mixing and calcination steps of the raw materials. The first and second calcination steps were each performed by heating at 1200°C for 5 hours.

[0076] Analysis of the pyrochlore-type solid electrolyte produced in Example 1 revealed no evidence of impurity formation.

[0077] In Example 2, the specific surface areas S1A and S1B of the alkali metal non-halide and alkali metal halide are 1 m², respectively, compared to Example 1. ２ The difference is that it is expressed as / g. In Example 2, the specific surface area ratio is S1A / S2 = S1B / S2 = 0.2.

[0078] In Example 2, the specific surface area of ​​the alkali metal compound is smaller than in Example 1, making it less likely for Li and F to volatilize, thus enabling high-temperature, short-time firing. For this reason, in Example 2, the first and second firing steps in the two-step synthesis were each performed at 1300°C for 2 hours.

[0079] Analysis of the pyrochlore-type solid electrolyte produced in Example 2 revealed no evidence of impurity formation.

[0080] In Example 3, the specific surface areas S1A and S1B of the alkali metal non-halide and alkali metal halide were 60 m², respectively, compared to Example 1. ２ The difference is that it is expressed as / g. In Example 3, the specific surface area ratio is S1A / S2 = S1B / S2 = 12.

[0081] In Example 3, the specific surface area of ​​the alkali metal compound was larger than in Example 1, making Li and F more easily volatile, thus requiring low-temperature, long-duration firing. For this reason, in Example 3, the first and second firing steps in the two-step synthesis were each performed at 1100°C for 10 hours.

[0082] Analysis of the pyrochlore-type solid electrolyte produced in Example 3 revealed no evidence of impurity formation.

[0083] In Example 4, the specific surface areas S3A and S3B of the lanthanide non-halogen and lanthanide halide are 20 m², respectively, compared to Example 1. ２ The difference is that it is expressed as / g. In Example 4, the specific surface area ratio is S3A / S2 = S3B / S2 = 4.

[0084] In Example 4, the specific surface area of ​​the lanthanide compound is larger than in Example 1, making La more reactive and allowing for shorter calcination times. Therefore, in Example 4, the first and second calcination steps in the two-step synthesis were each performed by heating at 1200°C for 3 hours.

[0085] Analysis of the pyrochlore-type solid electrolyte produced in Example 4 revealed no evidence of impurity formation.

[0086] In Example 5, the specific surface areas S3A and S3B of the lanthanide non-halogen and lanthanide halide were 0.4 m², respectively, compared to Example 1. ２ The difference is that it is expressed as / g. In Example 5, the specific surface area ratio is S3A / S2 = S3B / S2 = 0.08.

[0087] In Example 5, the specific surface area of ​​the lanthanide compound was smaller than in Example 1, making it more difficult for La to react, thus requiring longer calcination times. For this reason, in Example 5, the first and second calcination steps in the two-step synthesis were each performed at 1200°C for 10 hours.

[0088] Analysis of the pyrochlore-type solid electrolyte produced in Example 5 revealed no evidence of impurity formation.

[0089] In Example 6, compared to Example 1, the specific surface area S3A of the alkali metal non-halide was 3 m² / g, and the specific surface area S3B of the alkali metal non-halide was 10 m² / g. ２ / g, the specific surface area S3A of lanthanide nonhalides is 1 m² ２ / g, the specific surface area S3B of the lanthanide nonhalide is 5 m² ２ The difference is that it is expressed as / g. In Example 6, the specific surface area ratios are S1A / S2 = 0.6, S1B / S2 = 2, S3A / S2 = 0.2, and S3B / S2 = 1. Furthermore, in Example 6, S1A < S1B and S3A < S3B.

[0090] In Example 6, the specific surface area of ​​the alkali metal non-halides is smaller and the specific surface area of ​​the alkali metal halides is larger than in Example 1, while the specific surface area of ​​the lanthanide non-halides is smaller and the specific surface area of ​​the lanthanide halides is larger. Therefore, in Example 6, F reacts more easily, and calcination at low temperatures and for a short time is possible. In Example 6, the first and second calcination steps in the two-step synthesis were each performed by heating at 1100°C for 3 hours.

[0091] Analysis of the pyrochlore-type solid electrolyte produced in Example 6 revealed no evidence of impurity formation.

[0092] Example 7 differs from Example 1 in that the moisture content of the raw material mixture is 500 ppm. Because the moisture content of the raw material mixture in Example 7 is lower than in Example 1, the firing time can be shortened. Therefore, in Example 7, the first and second firing steps in the two-stage synthesis were each performed at 1200°C for 3 hours.

[0093] Analysis of the pyrochlore-type solid electrolyte produced in Example 7 revealed no evidence of impurity formation.

[0094] Example 8 differs from Example 1 in that the specific element compound is Nb2O5 and the pyrochlore-type solid electrolyte produced is LLNOF.

[0095] In Example 8, the specific surface areas S1A and S1B of the alkali metal non-halide and alkali metal halide were 6 m². ２ / g, the specific surface area S2 of the compound of a specific element is 4m² ２ / g, the specific surface areas S3A and S3B of lanthanide non-halides and lanthanide halides are 2m². ２ The values ​​were / g. In Example 8, the specific surface area ratios were S1A / S2 = S1B / S2 = 1.5 and S3A / S2 = S3B / S2 = 0.5.

[0096] In Example 8, the moisture content of the raw material mixture was 3000 ppm. In Example 8, a pyrochlore-type solid electrolyte was synthesized by a two-step synthesis method involving two mixing and calcination steps of the raw materials. The first and second calcination steps were each performed by heating at 1000°C for 5 hours.

[0097] Analysis of the pyrochlore-type solid electrolyte produced in Example 8 revealed no evidence of impurity formation.

[0098] In Example 9, the alkali metal halide is LiCl and the lanthanide halide is LaCl, compared to Example 1. ３ The specific element compound is Nb ２ O ５ The difference lies in the fact that the pyrochlore-type solid electrolyte produced is LLNOCl.

[0099] In Example 9, the specific surface area S1A of the alkali metal nonhalide was 6 m². ２ The specific surface area S1B of alkali metal halides is 10 m² / g. ２ / g, the specific surface area S2 of the compound of a specific element is 4m² ２ The specific surface area S3A of lanthanide nonhalides is 2 m² / g. ２ The specific surface area S3B of the lanthanide halide is 5 m² / g. ２ The values ​​were / g. In Example 9, the specific surface area ratios were S1A / S2 = 1.5, S1B / S2 = 2.5, S3A / S2 = 0.5, and S3B / S2 = 1.25. Furthermore, in Example 9, S1A < S1B and S3A < S3B.

[0100] In Example 9, the moisture content of the raw material mixture was 4000 ppm. In Example 9, a pyrochlore-type solid electrolyte was synthesized by a two-step synthesis method involving two mixing and calcination steps of the raw materials. The first and second calcination steps were each performed by heating at 800°C for 5 hours.

[0101] Analysis of the pyrochlore-type solid electrolyte produced in Example 9 revealed no evidence of impurity formation.

[0102] Example 10 differs from Example 1 in that the specific element compound is Nb ２ O ５ and Ta ２ O５ The difference lies in the fact that the pyrochlore-type solid electrolyte produced is LLTNOF.

[0103] Analysis of the pyrochlore-type solid electrolyte produced in Example 10 revealed no evidence of impurity formation.

[0104] In Example 11, the specific surface area S3A of the alkali metal nonhalide was 3 m² compared to Example 1. ２ / g, the specific surface area S3B of alkali metal nonhalides is 10 m² ２ / g, the specific surface area S3A of lanthanide nonhalides is 1 m² ２ / g, the specific surface area S3B of the lanthanide nonhalide is 5 m² ２ The difference is that it is expressed as / g. In Example 11, the specific surface area ratios are S1A / S2 = 0.6, S1B / S2 = 2, S3A / S2 = 0.2, and S3B / S2 = 1. Furthermore, in Example 11, S1A < S1B and S3A < S3B.

[0105] Furthermore, Example 11 differs from Example 1 in that it synthesizes a pyrochlore-type solid electrolyte in a single-step synthesis, involving only one mixing and firing of the raw materials. The single firing step in Example 11 involved heating at 1100°C for 4 hours.

[0106] Analysis of the pyrochlore-type solid electrolyte produced by the one-step synthesis in Example 11 revealed no evidence of impurity formation.

[0107] Comparative Example 1 is a comparative example in which the specific surface areas S1A and S1B of the alkali metal non-halide and alkali metal halide are 300 m², compared to Example 1. ２ The difference lies in the fact that it is expressed as / g. In Comparative Example 1, the specific surface area ratio is S1A / S2 = S1B / S2 = 60. In Comparative Example 1, S1A / S2 = S1B / S2 > 50.

[0108] In Comparative Example 1, the specific surface area of ​​the alkali metal compound was excessive, and Li volatilized during the manufacturing process of the pyrochlore-type solid electrolyte, resulting in LaTaO as an impurity. ４ An incident occurred.

[0109] Comparative Example 2 shows that, compared to Example 1, the specific surface areas S3A and S3B of the lanthanide non-halogen and lanthanide halide are 0.04 m². ２ The difference lies in the fact that it is expressed as / g. In Comparative Example 2, the specific surface area ratio is S3A / S2 = S3B / S2 = 0.008. In Comparative Example 2, S3A / S2 = S3B / S2 < 0.01.

[0110] In Comparative Example 2, the specific surface area of ​​the lanthanide compound was insufficient, making it difficult for La to react during the production process of the pyrochlore-type solid electrolyte, and resulting in LiTaO as an impurity. ３ An incident occurred.

[0111] According to the embodiment described above, when manufacturing a pyrochlore-type solid electrolyte, the specific surface area is set for each raw material according to the type of raw material for the pyrochlore-type solid electrolyte. This allows for control of the reaction of each raw material particle during the calcination process, minimizing impurities in the product and promoting the synthesis of the pyrochlore-type solid electrolyte.

[0112] Furthermore, in this embodiment, the ratio of the specific surface area S1 of the alkali metal compound to the specific surface area S2 of the specific element compound is set to S1 / S2 ≤ 50. This suppresses the volatilization of alkali metals in the calcination steps S12, S15, and S22, and reduces impurities in the product as much as possible. In addition, by reducing the specific surface area of ​​the alkali metal halide, the volatilization of halogen elements can be suppressed, and impurities in the product can be reduced as much as possible.

[0113] Furthermore, in this embodiment, the ratio of the specific surface area S3 of the lanthanide compound to the specific surface area S2 of the specific element compound is set to S3 / S2 ≥ 0.01. This allows the reaction of the lanthanide to be promoted in the calcination steps S12, S15, and S22, and the amount of impurities in the product can be reduced as much as possible. In addition, because the lanthanide reacts more easily, the calcination process can be performed in a shorter time.

[0114] Furthermore, in this embodiment, the relationship between the specific surface area S1A of the alkali metal non-halide and the specific surface area S1B of the alkali metal halide is set to S1A < S1B. This promotes the halogenation reaction in the manufacturing process of pyrochlore-type solid electrolytes and accelerates the synthesis of pyrochlore-type solid electrolytes.

[0115] Furthermore, in this embodiment, the relationship between the specific surface area S3A of the lanthanide non-halide and the specific surface area S3B of the lanthanide halide is set to S3A < S3B. This promotes the halogenation reaction in the manufacturing process of pyrochlore-type solid electrolytes and accelerates the synthesis of pyrochlore-type solid electrolytes.

[0116] Furthermore, in this embodiment, the moisture content of the raw material mixture is set to 10,000 ppm or less. This makes it possible to shorten the calcination time in the manufacturing process of pyrochlore-type solid electrolytes.

[0117] 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.

[0118] 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.

[0119] Furthermore, 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 an alkali metal, a lanthanide, at least one specific element from a transition element, a group 13 element, a group 14 element, or a group 15 element, and a halogen element, comprising: a mixing step (S11, S14, S21) of mixing a plurality of raw materials for the solid electrolyte to produce a raw material mixture; and a firing step (S12, S15, S22) of heating and firing the raw material mixture at a predetermined temperature, wherein the raw materials include an alkali metal compound containing the alkali metal, a lanthanide compound containing the lanthanide, and a specific element compound containing the specific element, and the relationship S1 / S2 ≤ 50 and S3 / S2 ≥ 0.01 when the specific surface area of ​​the alkali metal compound is S1, the specific surface area of ​​the specific element compound is S2, and the specific surface area of ​​the lanthanide compound is S3. (Item 2) The method for producing a solid electrolyte according to Item 1, wherein the alkali metal compound comprises an alkali metal non-halide that does not contain the halogen element and an alkali metal halide that contains the halogen element, and when the specific surface area of ​​the alkali metal non-halide is S1A and the specific surface area of ​​the alkali metal halide is S1B, the relationship S1A < S1B exists. (Item 3) The method for producing a solid electrolyte according to Item 1 or 2, wherein the lanthanide compound comprises a lanthanide non-halide that does not contain the halogen element and a lanthanide halide that contains the halogen element, and when the specific surface area of ​​the lanthanide non-halide is S3A and the specific surface area of ​​the lanthanide halide is S3B, the relationship S3A < S3B exists. (Item 4) The method for producing a solid electrolyte according to any one of Items 1 to 3, wherein the alkali metal is at least one of Li, Na, and K. (Item 5) The method for producing a solid electrolyte according to any one of Items 1 to 4, wherein the lanthanide is at least one of La, Ce, Nd, and Sm.(Item 6) A method for producing a solid electrolyte according to any one of items 1 to 5, wherein the specified element is at least one of Nb, Ta, Ti, Zr, Hf, V, Al, Ga, In, Ge, Sn, Sb, and Bi. (Item 7) A method for producing a solid electrolyte according to any one of items 1 to 6, wherein the moisture content of the raw material mixture measured by the Karl Fischer method is 10,000 ppm or less. (Item 8) A method for producing a solid electrolyte according to any one of items 1 to 7, wherein the mixing step and the calcination step are each performed once.

[0120] 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

A method for producing a solid electrolyte having a pyrochlore-type crystal structure, comprising an alkali metal, a lanthanide, at least one specific element from the transition elements, group 13 elements, group 14 elements, or group 15 elements, and a halogen element, A mixing step (S11, S14, S21) is performed to prepare a raw material mixture by mixing multiple raw materials of the solid electrolyte, A firing process (S12, S15, S22) in which the raw material mixture is heated and fired at a predetermined temperature, Equipped with, The raw materials include an alkali metal compound containing the alkali metal, a lanthanide compound containing the lanthanide, and a specific element compound containing the specific element. A method for producing a solid electrolyte, wherein S1 is the specific surface area of ​​the alkali metal compound, S2 is the specific surface area of ​​the specific element compound, and S3 is the specific surface area of ​​the lanthanide compound, and S1 / S2 ≤ 50 and S3 / S2 ≥ 0.

01. The alkali metal compound comprises an alkali metal non-halide that does not contain the halogen element and an alkali metal halide that contains the halogen element. A method for producing a solid electrolyte according to claim 1, wherein the relationship S1A < S1B is obtained when the specific surface area of ​​the alkali metal non-halide is S1A and the specific surface area of ​​the alkali metal halide is S1B. 　 The lanthanide compound comprises a lanthanide non-halogenate that does not contain the halogen element and a lanthanide halide that contains the halogen element. The method for producing a solid electrolyte according to claim 1, wherein when the specific surface area of ​​the lanthanide non-halide is S3A and the specific surface area of ​​the lanthanide halide is S3B, the relationship S3A < S3B is met. 　 The method for producing a solid electrolyte according to any one of claims 1 to 3, wherein the alkali metal is at least one of Li, Na, and K. 　 The method for producing a solid electrolyte according to any one of claims 1 to 3, wherein the lanthanide is at least one of La, Ce, Nd, and Sm. 　 A method for producing a solid electrolyte according to any one of claims 1 to 3, wherein the specified element is at least one of Nb, Ta, Ti, Zr, Hf, V, Al, Ga, In, Ge, Sn, Sb, and Bi. 　 A method for producing a solid electrolyte according to any one of claims 1 to 3, wherein the moisture content of the raw material mixture, as measured by the Karl Fischer method, is 10,000 ppm or less. 　 A method for producing a solid electrolyte according to any one of claims 1 to 3, wherein the mixing step and the firing step are each performed once.

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