Method for producing solid electrolytes

Abstract

A method for producing a solid electrolyte having a pyrochlore-type crystal structure containing alkali metals, lanthanides, at least one specific element from transition elements, group 13 elements, group 14 elements, or group 15 elements, and halogen elements, comprising a mixing step (S11, S14, S21) for mixing a plurality of raw materials for the solid electrolyte to produce a raw material mixture, and a firing step (S12, S15, S22) for heating and firing the raw material mixture at a predetermined temperature. The raw materials include alkali metal compounds, lanthanide compounds, and specific element compounds. 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.

Description

Cross - reference to related applications

[0001] This application is based on Japanese Patent Application No. 2024 - 225700 filed on December 20, 2024, the content of which is incorporated herein by reference.

Technical Field

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

Background Art

[0003] In Patent Document 1, a pyrochlore - type solid electrolyte with the composition formula Aa 2-α Ab (1+α) / 3 B2O 7-β X γ (Aa: alkali metal, Ab: lanthanoid, B: cation metal, X: halogen replaceable 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 replaced by a halogen element, and high ionic conductivity is obtained.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] Due to characteristics such as the volatile nature of the contained alkali metal and halogen elements and the fact that it is a complex oxide composed of multiple metal components, the above - mentioned pyrochlore - type solid electrolyte is likely to generate impurities in the product during the manufacturing process.

[0006] The object of the present invention is to suppress the generation of impurities in a method for manufacturing 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 crystalline 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, then S1 / S2 ≤ 12 and S3 / S2 ≥ 0.08 They have a relationship.

[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. [Brief explanation of the drawing]

[0009] [Figure 1] This is a cross-sectional view showing the configuration of a secondary battery according to an embodiment of the present disclosure. [Figure 2] This figure shows the crystal structure of a pyrochlore-type solid electrolyte. [Figure 3] This diagram shows the manufacturing process for pyrochlore-type solid electrolytes when synthesized in two steps. [Figure 4] This diagram shows the manufacturing process for producing pyrochlore-type solid electrolytes in a single step. [Figure 5] This figure shows examples and comparative examples of pyrochlore-type solid electrolytes produced under various different conditions. [Figure 6] This figure shows examples and comparative examples of pyrochlore-type solid electrolytes produced under various different conditions. [Modes for carrying out the invention]

[0010] Hereinafter, embodiments of applying the ion conductor of this disclosure to a solid electrolyte for a secondary battery will be described with reference to the drawings. The secondary battery 10 of this embodiment is a lithium-ion battery in which charging and discharging are performed by the movement of lithium ions between the negative electrode 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. The positive electrode layer 14 and the electrolyte layer 15 are in contact. The negative electrode layer 12 and the positive electrode layer 14 are connected via the electrolyte layer 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 layer 12 and the positive electrode layer 14 via the electrolyte layer 15.

[0013] A laminate containing the negative electrode layer 12, the positive electrode layer 14, and the 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. The positive electrode current collector 13 and the positive electrode layer 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 suitable for use as a current collector in a lithium-ion battery. In this embodiment, Cu is used as the negative electrode current collector 11 and Al is used as the positive electrode current collector 13.

[0015] The negative electrode material constituting the negative electrode layer 12 can be any material usable as a negative electrode active material for lithium-ion batteries, such as carbon-based negative electrode materials, oxide-based negative electrode materials, or metal-based negative electrode materials. These negative electrode materials may be used individually or in combination.

[0016] As the carbon-based negative electrode material, for example, natural graphite, artificial graphite, and hard carbon can be used. As the oxide-based negative electrode material, for example, Li4Ti5O 12 , TiO2(B), and TiNb2O7 can be used. As the metal-based negative electrode material, for example, silicon-based negative electrode material and 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 aid, a binder, and a polymer. As the conductive aid, for example, a carbon material such as carbon black can be used. As the binder, for example, an aqueous binder such as a mixture of SBR (styrene-butadiene rubber) and CMC (carboxymethyl cellulose) can be used. Further, 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 that can be used as a positive electrode active material for a lithium-ion battery. As the positive electrode material, for example, a layered rock salt type active material, an olivine type active material, and 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.

[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 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 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, 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.

[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 (2-α) of Aa 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, 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.

[0027] 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.

[0028] 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.

[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 forms an octahedron surrounded by six oxygen atoms. As the transition element represented by B, a group 4 or 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 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.

[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 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.

[0033] 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.

[0034] 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.

[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 contained in the pyrochlore structure. Because the anion represented by X is present in the BO6 octahedron structure, the alkali metal Aa can be located in the center of the space between the BO6 octahedron and the BO6 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, 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 Ta2O6F, Li 1.25 La 0.58 Nb2O6F, Li 1.25 La 0.58 TaNbO6F, Li 1.25 La 0.58 Nb2O6Cl can be used as an example. Below, "Li 1.25 La 0.58 Ta2O6F is "LLTOF", Li 1.25 La 0.58 Nb2O6F" is "LLNOF", "Li 1.25 La 0.58 TaNbO6F is "LLTNOF", Li 1.25 La 0.58 Nb2O6Cl 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 the 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 the 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 the 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] Alkali metal compounds include alkali metal non-halides, which do not contain halogen elements, and alkali metal halides, which do contain halogen elements. Lanthanide compounds include lanthanide non-halides, which do not contain halogen elements, and lanthanide halides, which do contain halogen elements.

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

[0042] For example, lithium compounds such as LiF, LiCl, and Li2CO3 can be used. LiF and LiCl are alkali metal halides, while Li2CO3 is an alkali metal non-halide. For example, lanthanum compounds such as LaF3, LaCl3, and La2O3 can be used. LaF3 and LaCl3 are lanthanide halides, while La2O3 is a lanthanide non-halide. Alkali metal non-halides and lanthanide non-halides contain oxygen. For example, tantalum compounds such as Ta2O5 can be used. For example, niobium compounds such as Nb2O5 can be used.

[0043] In this embodiment, Li2CO3, LiF, Ta2O5, La2O3, and LaF3 are used as raw materials for LLTOF. Li2CO3, LiF, Nb2O5, La2O3, and LaF3 are used as raw materials for LLNOF. Li2CO3, LiF, Ta2O5, Nb2O5, La2O3, and LaF3 are used as raw materials for LLTNOF. Li2CO3, LiCl, Nb2O5, La2O3, and LaCl3 are used as raw materials for LLNOCl.

[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 the alkali metal compound with the specific element compound. Also, since the alkali metal is volatile, it is desirable to suppress volatilization. For this reason, the specific surface area S1 of the alkali metal compound is made smaller than the specific surface area S2 of the specific element 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 element compound is desirably S1 / S2 ≦ 50, more desirably S1 / S2 ≦ 10, and even more desirably S1 / S2 ≦ 1.

[0049] Also, it is desirable to promote the reaction of the lanthanoid compound with the specific element compound. For this reason, the specific surface area S3 of the lanthanoid compound is made larger than the specific surface area S2 of the specific element compound to promote the reaction of the lanthanoid compound. The ratio of the specific surface area S3 of the lanthanoid compound to the specific surface area S2 of the specific element compound is desirably S3 / S2 ≧ 0.01, more desirably S3 / S2 ≧ 0.1, and even more desirably S3 / S2 ≧ 1.

[0050] Also, it is desirable to promote the halogenation reaction by promoting the reaction of the alkali metal halide with the specific element compound more than the reaction of the alkali metal non-halide with the specific element compound. For this reason, 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, it is desirable to have the relationship S1A < S1B.

[0051] Also, it is desirable to promote the halogenation reaction by promoting the reaction of the lanthanoid halide with the specific element compound more than the reaction of the lanthanoid non-halide with the specific element compound. For this reason, when the specific surface area of the lanthanoid non-halide is S3A and the specific surface area of the lanthanoid halide is S3B, it is desirable to have the relationship S3A < 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 This shows the process for manufacturing Ta2O6F(LLTOF). Figure 3 shows a two-step synthesis in which the mixing steps S11 and S13, in which the raw materials are mixed, and the calcination steps S12 and S14, in which the mixture is calcined, are performed twice each. Figure 4 shows a one-step synthesis in which the mixing step S21, in which the raw materials are mixed, and the calcination step S22, in which the mixture is calcined, are performed once each.

[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. Metal oxides and metal carbon oxides can be used as the lanthanum source, lithium source, and tantalum source. In the example shown in Figure 3, Li2CO3 is used as the lithium source, La2O3 is used as the lanthanum source, and Ta2O5 is used as the tantalum source. When producing LLNOF and LLNOCl, Nb2O5 can be used as the niobium source instead of the tantalum source. When producing LLTNOF, Ta2O5 and Nb2O5 can be used.

[0057] Next, the raw materials (Li2CO3, La2O3, Ta2O5) prepared in S10 are weighed, mixed in a predetermined ratio, and crushed to produce a raw material mixture in the first mixing step S11.

[0058] The specific surface area of ​​the raw materials used in the first mixing step S11 is adjusted according to their type. Specifically, the ratio of the specific surface area S1A of Li2CO3 (alkali metal non-halide) to the specific surface area S2 of Ta2O5 (specific element compound) is set to S1A / S2 ≤ 50, and the ratio of the specific surface area S3A of La2O3 (lanthanide non-halide) to the specific surface area S2 of Ta2O5 (specific element compound) 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 Ta2O6(LLTO) is obtained.

[0060] Next, a second raw material preparation step S13 of preparing a halogen source as a raw material for the pyrochlore-type solid electrolyte is performed. The halogen source is a halogen-containing raw material containing a halogen element, and LiF and LaF3 are used in this embodiment. LiF is an alkali metal halide, and LaF3 is a lanthanoid halide. When manufacturing LLNOCl, for example, LiCl and LaCl3 may be used as the halogen source.

[0061] Next, a second mixing step S14 is performed in which the raw materials (LLTO, LiF, LaF3) prepared in S13 are weighed, mixed at a predetermined ratio, and pulverized to produce a raw material mixture.

[0062] The specific surface areas of the raw materials used in the second mixing step S14 are adjusted according to the type. Specifically, the ratio of the specific surface area S1B of LiF (alkali metal halide) to the specific surface area S2 of Ta2O5 (specific element compound) is set to S1B / S2 ≤ 50. Further, the specific surface area S1A of Li2CO3 (alkali metal non-halide) and the specific surface area S1B of LiF (alkali metal halide) have the relationship of S1A < S1B.

[0063] Similarly, the ratio of the specific surface area S3B of LaF3 (lanthanoid halide) to the specific surface area S2 of Ta2O5 (specific element compound) is set to S3B / S2 ≥ 0.01. Further, the specific surface area S3A of La2O3 (lanthanoid non-halide) and the specific surface area S3B of LaF3 (lanthanoid halide) have the relationship of S3A < S3B.

[0064] Next, a second firing step S15 of firing the raw material mixture is performed. In the second firing step S15, the mixture is placed in a firing furnace and heated at 1200 °C for 5 hours for firing. The firing can be performed in an inert atmosphere such as nitrogen or argon or in the air. By cooling the product of the second firing step S15, the target product Li 1.25 Ta 0.58 Ta2O6F (LLTOF) is obtained.

[0065] Next, the one-step synthesis shown in FIG. 4 will be described. First, a raw material preparation step S20 of preparing a lanthanum source, a lithium source, a tantalum source, and a halogen source as raw materials for LLTOF is performed. In the example shown in FIG. 4, Li2CO3 is used as the lithium source, La2O3 is used as the lanthanum source, Ta2O5 is used as the tantalum source, and LiF and LaF3 are used as the halogen sources.

[0066] Next, a mixing step S21 is performed in which the raw materials (LiF, LaF3, Li2CO3, La2O3, Ta2O5) prepared in S20 are weighed, mixed at a predetermined ratio, and pulverized to produce a raw material mixture. The raw materials used in the mixing step S21 have their specific surface areas adjusted according to the type, similar to the first mixing step S12 and the second mixing step S14 described above.

[0067] Next, a firing step S22 of firing the raw material mixture is performed. In the firing step S12, the raw material mixture is placed in a firing furnace and heated at 1200 ° C for 5 hours for firing. The firing can be performed in an inert atmosphere such as nitrogen or argon or in the air. By cooling the product of the firing step S22, the target product Li 1.25 La 0.58 Ta2O6F (LLTOF) is obtained.

[0068] Next, the cases where a pyrochlore-type solid electrolyte is produced with different various conditions will be described using the examples and comparative examples shown in FIGS. 5 and 6.

[0069] Example 1-1 1 is such that 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 lanthanoid compound to the specific surface area S2 of the specific element compound is S3 / S2≥0.01.

[0070] Examples 6, 9, 1 1 are such that the specific surface area S1A of the alkali metal non-halide and the specific surface area S1B of the alkali metal halide have a relationship of S1A <S1B. Furthermore, Examples 6, 9, 1 1The specific surface area S3A of the lanthanoid non-halide and the specific surface area S3B of the lanthanoid halide have a relationship of 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 lanthanoid 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 lanthanoid compound to the specific surface area S2 of the specific element compound is S3 / S2 < 0.01.

[0072] Example 1~1 1 The specific surface areas of each raw material in Examples 1 and Comparative Examples 1 and 2 were measured by the gas adsorption method using nitrogen gas using TriStarII manufactured by Shimadzu Corporation as the specific surface area measuring device after removing moisture and the like 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 analysis by XRD, it was determined that there were impurities when crystal peaks other than the desired pyrochlore-type solid electrolyte appeared, and it was determined that there were no impurities when they did not appear. The moisture content of the raw material mixture before the firing treatment was measured by applying the Karl Fischer method of coulometric titration and using ADP-611 manufactured by Kyoto Electronics Industry Co., Ltd. as the moisture vaporization device and MKC-610 as the moisture meter.

[0073] In Example 1, LLTOF was produced as the pyrochlore-type solid electrolyte. In Example 1, Li2CO3 was used as the alkali metal non-halide, LiF was used as the alkali metal halide, Ta2O5 was used as the specific element compound, La2O3 was used as the lanthanoid non-halide, and LaF3 was used as the lanthanoid halide.

[0074] In Example 1, the specific surface areas S1A and S1B of the alkali metal non-halide and the alkali metal halide were 6m 2 / g, and the specific surface area S2 of the specific element compound was 5m 2 / g, the specific surface area S3A and S3B of lanthanide nonhalides and lanthanide halides is 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 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 were 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 were increased by 20 m² 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 was larger than in Example 1, making the reaction of La easier 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 the reaction of La less viable and requiring longer calcination times. Therefore, in Example 5, the first and second calcination steps in the two-step synthesis were each performed by heating 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 1m² 2 / g, the specific surface area S3B of lanthanide nonhalides is 5m² 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、S3A<S3Bとなっている。

[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-step 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 elemental 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 area S3A and S3B of lanthanide nonhalides and lanthanide halides is 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 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] Example 9 differs from Example 1 in that the alkali metal halide is LiCl, the lanthanide halide is LaCl3, the specific element compound is Nb2O5, and 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 2m² / g. 2 The specific surface area S3B of lanthanide halides is 5 m² / g. 2The ratio of specific surface area in Example 9 was S1A / S2=1.5, S1B / S2=2.5, S3A / S2=0.5, and S3B / S2=1.25. Furthermore, in Example 9, S1A <S1B、S3A<S3Bとなっている。

[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 elemental compounds are Nb2O5 and Ta2O5, and 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 10m² 2 / g, the specific surface area S3A of lanthanide nonhalides is 1m² 2 / g, the specific surface area S3B of lanthanide nonhalides is 5m² 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、S3A<S3Bとなっている。

[0105] Furthermore, Example 11 differs from Example 1 in that it synthesizes a pyrochlore-type solid electrolyte in a single step, involving only one mixing and calcination of the raw materials. The single calcination 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 comparison of Example 1, where the specific surface areas S1A and S1B of the alkali metal non-halide and alkali metal halide are 300 m². 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 excessively large, causing Li to volatilize during the manufacturing process of the pyrochlore-type solid electrolyte, resulting in the generation of LaTaO4 as an impurity.

[0109] Comparative Example 2 shows that the specific surface areas S3A and S3B of the lanthanide non-halogen and lanthanide halide are 0.04 m², respectively, compared to Example 1. 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, resulting in the generation of LiTaO3 as an impurity.

[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] In addition, in the present 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. Thereby, in the firing steps S12, S15, and S22, volatilization of the alkali metal can be suppressed, and impurities contained in the product can be reduced as much as possible. Furthermore, by reducing the specific surface area of the alkali metal halide, volatilization of the halogen element can be suppressed, and impurities contained in the product can be reduced as much as possible.

[0113] In addition, in the present embodiment, the ratio of the specific surface area S3 of the lanthanoid compound to the specific surface area S2 of the specific element compound is set to S3 / S2 ≧ 0.01. Thereby, in the firing steps S12, S15, and S22, the reaction of the lanthanoid can be promoted, and impurities contained in the product can be reduced as much as possible. Also, since the lanthanoid becomes more likely to react, the firing treatment can be performed in a short time.

[0114] In addition, in the present 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. Thereby, the halogenation reaction in the production process of the pyrochlore-type solid electrolyte can be promoted, and the synthesis of the pyrochlore-type solid electrolyte can be promoted.

[0115] In addition, in the present embodiment, the relationship between the specific surface area S3A of the lanthanoid non-halide and the specific surface area S3B of the lanthanoid halide is set to S3A < S3B. Thereby, the halogenation reaction in the production process of the pyrochlore-type solid electrolyte can be promoted, and the synthesis of the pyrochlore-type solid electrolyte can be promoted.

[0116] In addition, in the present embodiment, the moisture content of the raw material mixture is set to 10,000 ppm or less. Thereby, the firing time in the production process of the pyrochlore-type solid electrolyte can be shortened.

[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 solid electrolytes 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 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 having the relationship S1 / S2 ≤ 50 and S3 / S2 ≥ 0.01, where 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. (Item 2) 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. The method for producing a solid electrolyte according to item 1, wherein 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, S1A < S1B. (Item 3) The lanthanoid compound includes a lanthanoid non-halide that does not contain the halogen element and a lanthanoid halide that contains the halogen element. The method for producing a solid electrolyte according to item 1 or 2, wherein when the specific surface area of the lanthanoid non-halide is S3A and the specific surface area of the lanthanoid halide is S3B, S3A < S3B. (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 lanthanoid is at least one of La, Ce, Nd, and Sm. (Item 6) The method for producing a solid electrolyte according to any one of items 1 to 5, wherein the specific element is at least one of Nb, Ta, Ti, Zr, Hf, V, Al, Ga, In, Ge, Sn, Sb, and Bi. (Item 7) The 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) The method for producing a solid electrolyte according to any one of items 1 to 7, wherein the mixing step and the firing step are each performed once.

[0120] Although the present disclosure has been described based on examples, it should be understood that the present disclosure is not limited to such examples or structures. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, although various combinations and forms are shown in the present disclosure, other combinations and forms that include only one element, more than one element, or less than one element thereof are also within the scope and spirit of the present disclosure.

Claims

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 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 mix multiple raw materials of the solid electrolyte to produce a raw material mixture, 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 ≤ 12 and S3 / S2 ≥ 0.

08.

2. 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. The 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.

3. 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 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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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