Method for producing oxyfluoride-based solid electrolyte and method for producing all-solid-state lithium-ion battery

Abstract

Provided is a method for producing an oxyfluoride-based solid electrolyte, the method comprising: a step for preparing a raw material mixture 1 by crushing and mixing raw materials; a step for preparing an oxide by inserting the raw material mixture 1 into a firing container and firing at 800-1200ºC; a step for preparing a raw material mixture 2 by adding two types of raw materials including LiF and LaF3 to the oxide and crushing and mixing the raw materials and the oxide; and a step for, by firing the raw material mixture 2 at 850-1000ºC in a firing container containing SiC, Si3N4, ZrO2, or C as a main component thereof, preparing an oxyfluoride-based solid electrolyte having a lattice constant of 10.436 Å and being represented by the compositional formula Li2-xLa(1+x) / 3M2O6F (wherein, M is Nb and / or Ta, and 0 ≤ x ≤ 1.0).

Description

Method for producing an acid fluoride-based solid electrolyte and a method for producing an all-solid-state lithium-ion battery

[0001] The present invention relates to a method for producing an acid fluoride-based solid electrolyte and a method for producing an all-solid-state lithium-ion battery.

[0002] In recent years, with the rapid proliferation of information-related devices and communication equipment such as personal computers, video cameras, and mobile phones, the development of batteries used as power sources has become increasingly important. Among these batteries, lithium-ion batteries are attracting attention due to their high energy density. Furthermore, improvements in energy density and battery characteristics are also required for large-scale applications such as automotive power sources and load leveling lithium secondary batteries.

[0003] Furthermore, from the perspective of improving safety, lithium-ion batteries that do not use organic solvents as electrolytes, and in which the entire battery is solidified using a solid electrolyte, are attracting attention. Acid fluoride-based solid electrolytes have been proposed as solid electrolytes to be used in such lithium-ion batteries.

[0004] Oxyfluoride-based solid electrolytes used in all-solid-state lithium-ion batteries are non-flammable, highly stable in the atmosphere, and have higher ionic conductivity than general oxide-based solid electrolytes. Therefore, they are attracting attention as a component of next-generation batteries that offer high reliability, high power output, and high cycle characteristics.

[0005] In particular, Li, an acid fluoride solid electrolyte material having a pyrochlore-type structure 2-x La (1+x) / 3 M2O6F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0) is attracting attention as a material that exhibits extremely high ionic conductivity. While the most well-known oxide-based solid electrolyte material, the garnet-type structural material, has an ionic conductivity of up to about 1 mS / cm at room temperature, the above-mentioned oxyfluoride solid electrolyte material exhibits an extremely high ionic conductivity of up to 8 mS / cm.

[0006] Furthermore, regarding conventional acid fluoride-based solid electrolytes, for example, Patent Document 1 describes one with the composition formula Aa 2-α Ab (1+α) / 3 B2O 7-βX β A secondary battery solid electrolyte containing an oxide-based solid electrolyte having a pyrochlore structure represented by, wherein Aa is an alkali metal, Ab contains at least a lanthanoid, B is a cation metal different from Aa and Ab, X is an anion capable of substituting for an O atom constituting the pyrochlore structure, in the composition formula, α is within the range of 0.6 < α < 2.0, β is within the range of 0 < β ≤ 1, and a secondary battery solid electrolyte containing a defect structure and a method for producing the same are disclosed.

[0007] Further, in Patent Document 2, a particulate core phase (101) and a shell phase (102) covering at least a part of the core phase are provided, the shell phase consists of one or more phases, and the constituent material of the core phase has a composition formula Aa 2-α Ab (1+α) / 3 B2O 7-β X β (Aa: alkali metal, Ab: lanthanoid, B: cation metal, X: anion capable of substituting for O) and contains a pyrochlore-type solid electrolyte, the constituent material of the shell phase has a chemical composition different from the pyrochlore-type solid electrolyte and has a chemical composition containing Li, and contains a material having a melting point lower than that of the pyrochlore-type solid electrolyte. The pyrochlore-type solid electrolyte is such that in the composition formula, α is within the range of 0.6 < α < 2.0, β is within the range of 0 < β ≤ 1, and the total valence of the cations composed of Aa, Ab and B and the anions composed of O and X is negative, and a secondary battery solid electrolyte containing a defect structure is disclosed.

[0008] Japanese Patent No. 7334813 Japanese Patent No. 7338805

[0009] Conventionally, the composition formula: Li 2-x La (1+x) / 3When synthesizing an acid-fluoride solid electrolyte represented by M2O6F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0), using a common calcination vessel such as an alumina crucible or an alumina-containing crucible causes the alumina component to react with the material, resulting in small cracks in the crucible. As a result, Li and F in the reaction system volatilize, and the lattice constant decreases due to the reaction of the acid-fluoride solid electrolyte with moisture in the atmosphere, leading to a decrease in ionic conductivity.

[0010] The present invention was made to solve the above-mentioned problems, and aims to provide a method for producing an acid fluoride-based solid electrolyte having good ionic conductivity (bulk ionic conductivity) and a method for producing an all-solid-state lithium-ion battery.

[0011] The present invention, completed based on the above findings, is defined as follows: (1) A step of preparing a raw material mixture 1 by crushing and mixing raw materials; a step of preparing an oxide by placing the raw material mixture 1 in a firing container and firing it at 800 to 1200°C; a step of adding two raw materials, LiF and LaF3, to the oxide, crushing and mixing them to prepare a raw material mixture 2; and a step of firing the raw material mixture 2 at 850 to 1000°C in a firing container mainly containing SiC, Si3N4, ZrO2, or C, thereby producing a material with the composition formula: Li 2-x La (1+x) / 3 A method for producing an acid fluoride-based solid electrolyte, comprising the steps of: (2) producing an acid fluoride-based solid electrolyte having a lattice constant of 10.436 Å or more, represented by the formula M2O6F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0); (3) a method for producing an acid fluoride-based solid electrolyte according to (1), wherein the firing vessel for the raw material mixture 2 contains SiC as the main component; (4) a method for producing an acid fluoride-based solid electrolyte according to (1) or (2), wherein the firing of the raw material mixture 1 and / or the firing of the raw material mixture 2 is carried out in an atmosphere other than an inert atmosphere; and (5) a method for producing an all-solid-state lithium-ion battery comprising a solid electrolyte layer, a positive electrode layer and a negative electrode layer, using an acid fluoride-based solid electrolyte produced by the method for producing an acid fluoride-based solid electrolyte according to any one of (1) to (3).

[0012] The present invention provides a method for producing an acid-fluoride-based solid electrolyte having good ionic conductivity (bulk ionic conductivity) and a method for producing an all-solid-state lithium-ion battery. Here, ionic conductivity can be broadly divided into "bulk conductivity" and "grain boundary conductivity." "Bulk conductivity" is material-specific and does not fluctuate much if high-quality materials are produced, but "grain boundary conductivity" can fluctuate greatly depending on the method and precision of producing the sintered body. In the present invention, "ionic conductivity" refers to "bulk conductivity."

[0013] This is a schematic diagram of an all-solid-state lithium-ion battery according to this embodiment.

[0014] Next, embodiments for carrying out the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and it should be understood that appropriate design changes, improvements, etc., can be made based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the invention.

[0015] <Oxygen Fluoride Solid Electrolyte> The acid fluoride solid electrolyte of this embodiment has the composition formula: Li 2-x La (1+x) / 3 It is represented by the formula M2O6F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0).

[0016] The oxyfluoride-based solid electrolyte of this embodiment has a pyrochlore structure. The pyrochlore structure has a crystalline structure in which metal atoms are arranged at the vertices of a tetrahedron, and each vertex of the tetrahedron is shared. In the oxyfluoride-based solid electrolyte of this embodiment, the inclusion of the lanthanide La in the pyrochlore structure creates defects in the crystalline structure, improving the ionic conductivity.

[0017] In this embodiment, the acid-fluoride-based solid electrolyte has a composition formula where 0 ≤ x ≤ 1.0. Therefore, single-phase synthesis is facilitated. Furthermore, defects are generated in the crystal structure, which can improve ionic conductivity. In this embodiment, it is preferable that the acid-fluoride-based solid electrolyte has a composition formula where 0.5 ≤ x ≤ 0.8.

[0018] The average particle size D50 (50% cumulative volume particle size D50) of the acid fluoride-based solid electrolyte in this embodiment is not particularly limited, but may be 0.01 to 100 μm, 0.1 to 100 μm, or 0.1 to 50 μm.

[0019] The acid-fluoride solid electrolyte of this embodiment has a lattice constant of 10.436 Å or higher. When the lattice constant of the acid-fluoride solid electrolyte is 10.436 Å or higher, sufficient Li conduction pathways are ensured, and good ionic conductivity is obtained. It is more preferable that the lattice constant of the acid-fluoride solid electrolyte is 10.440 Å or higher.

[0020] <Method for producing acid-fluoride solid electrolytes> The method for producing the acid-fluoride solid electrolyte of this embodiment will be described in detail below. First, the raw materials for the acid-fluoride solid electrolyte are weighed in a glove box under an inert gas atmosphere such as argon or nitrogen gas to obtain a predetermined composition. Examples of the raw materials used here include Li2CO3, La2O3, Nb2O5, etc.

[0021] Next, the raw materials are crushed and mixed to produce a raw material mixture 1. The crushing and mixing of the raw materials is not particularly limited, but it is preferable to do so using a planetary ball mill, for example. The raw materials and zirconia beads with a diameter of 1 mm or less are placed in the container (jar) of the planetary ball mill, and the raw materials can be crushed and mixed by rotating and revolving the container. The rotational speed of the planetary ball mill is preferably in the range of 100 rpm to 500 rpm.

[0022] Next, the raw material mixture 1 is placed in a firing container and fired at 800 to 1200°C for 2 to 6 hours to produce an oxide. The firing atmosphere for the raw material mixture 1 is not particularly limited, but it is preferable to carry it out in an inert gas atmosphere such as argon. Furthermore, from the viewpoint of improving manufacturing efficiency, it is also preferable to carry out the firing in an atmosphere other than an inert atmosphere, as this eliminates the need for gas adjustment in a continuous furnace. An atmosphere other than an inert atmosphere can be, for example, air.

[0023] Next, two raw materials, LiF and LaF3, are added to the oxide, and the mixture is crushed and mixed to produce raw material mixture 2. The crushing and mixing of raw material mixture 2 is not particularly limited, but it is preferable to do so in the same way as raw material mixture 1, for example, using a planetary ball mill.

[0024] Next, the raw material mixture 2 is calcined at 850 to 1000°C for 2 to 6 hours in a calcination vessel mainly containing SiC, Si3N4, ZrO2, or C to induce a fluorination reaction, thereby producing a composition formula: Li 2-x La (1+x) / 3 An acid-fluoride-based solid electrolyte with a lattice constant of 10.436 Å or higher, represented by the formula M2O6F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0), can be prepared.

[0025] In embodiments of the present invention, a firing container mainly composed of SiC, Si3N4, ZrO2, or C means a firing container containing SiC, Si3N4, ZrO2, or C in a proportion of 90% by mass or more. Furthermore, in embodiments of the present invention, it is preferable that the firing container contains SiC, Si3N4, ZrO2, or C in a proportion of 95% by mass or more, and particularly preferable that it contains 99% by mass or more.

[0026] Composition formula: Li 2-x La (1+x) / 3 When synthesizing an acid-fluoride solid electrolyte represented by M2O6F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0), using a common calcination vessel such as an alumina crucible or an alumina-containing crucible results in small cracks forming in the crucible due to a reaction between the alumina component and the material. In contrast, in this embodiment, the fluorination reaction is induced by calcining the raw material mixture 2 in a calcination vessel such as a crucible or sheath containing SiC, Si3N4, ZrO2, or C as the main component. Calcination vessels containing SiC, Si3N4, ZrO2, or C as the main component do not crack even when calcined at 850 to 1000°C. Therefore, it is possible to suppress the volatilization of Li and F in the reaction system, and the decrease in lattice constant and subsequent decrease in ionic conductivity caused by the reaction of the acid-fluoride solid electrolyte with moisture in the atmosphere.

[0027] The firing container contains SiC, Si3N4, ZrO2, or C as a main component as described above. Among these, in particular, the one containing SiC as a main component is preferable because it can be used even in the atmosphere and from the viewpoint of workability.

[0028] The firing atmosphere of the raw material mixture 2 is not particularly limited, but it is preferably carried out in an inert gas atmosphere such as argon. Also, from the viewpoint of improving the production efficiency by eliminating the need for gas adjustment in a continuous furnace in particular, it is also preferable to carry out the firing in an air atmosphere.

[0029] <Full solid-state lithium-ion battery> The full solid-state lithium-ion battery according to an embodiment of the present invention includes a solid electrolyte layer, a positive electrode layer, and a negative electrode layer. The full solid-state lithium-ion battery according to an embodiment of the present invention can have a configuration as shown in FIG. 1 using a solid electrolyte layer, a positive electrode layer, and a negative electrode layer.

[0030] (Solid electrolyte layer) The solid electrolyte layer of the present embodiment is formed by the fluoride-based solid electrolyte of the present embodiment described above. The average thickness of the solid electrolyte layer is not particularly limited and can be appropriately designed according to the purpose. The average thickness of the solid electrolyte layer of the present embodiment may be, for example, 50 μm to 500 μm, or may be 50 μm to 100 μm.

[0031] The method for forming the solid electrolyte layer of the present embodiment is not particularly limited and can be appropriately selected according to the purpose. Examples of the method for forming the solid electrolyte layer of the present embodiment include sputtering using the target material of the solid electrolyte of the present embodiment described above, or a method of compression molding the solid electrolyte of the present embodiment described above.

[0032] (Positive electrode layer) The positive electrode layer of the present embodiment is formed by laminating a positive electrode composite material obtained by mixing a known positive electrode active material for a lithium-ion battery and the fluoride-based solid electrolyte of the present embodiment described above or another solid electrolyte. The content of the positive electrode active material in the positive electrode layer is preferably, for example, 50% by mass or more and 99% by mass or less, and more preferably 60% by mass or more and 90% by mass or less.

[0033] As a known cathode active material for a lithium ion battery, for example, the composition formula 2: Li a Ni b Co c Mn d O2 (in the composition formula 2, 1.00 ≤ a ≤ 1.08, 0.60 ≤ b ≤ 0.90, and b + c + d = 1.0).) includes a cathode active material represented by. When the cathode active material of the present embodiment is a high nickel NCM cathode active material having a high Ni ratio of 0.60 to 0.90 as shown in the above composition formula 2, the capacity of the all-solid-state lithium ion battery generally increases. Further, from such a viewpoint, in the above composition formula 2, it is more preferable that 0.80 ≤ b ≤ 0.90.

[0034] The cathode composite material may further contain a conductive aid. As the conductive aid, a carbon material, a metal material, or a mixture thereof can be used. The conductive aid may contain, for example, at least one element selected from the group consisting of carbon, nickel, copper, aluminum, indium, silver, cobalt, magnesium, lithium, chromium, gold, ruthenium, platinum, beryllium, iridium, molybdenum, niobium, osmium, rhodium, tungsten, and zinc. The conductive aid is preferably a simple carbon having high conductivity, carbon, or a simple metal containing nickel, copper, silver, cobalt, magnesium, lithium, gold, ruthenium, platinum, niobium, osmium, or rhodium, or a mixture or compound thereof. As the carbon material, for example, carbon black such as Ketjen black, acetylene black, Denka black, thermal black, channel black, graphite, carbon fiber, activated carbon, etc. can be used.

[0035] The average thickness of the cathode layer of the all-solid-state lithium ion battery is not particularly limited and can be appropriately designed according to the purpose. The average thickness of the cathode layer of the all-solid-state lithium ion battery may be, for example, 1 μm to 100 μm, or may be 1 μm to 10 μm.

[0036] The method for forming the positive electrode layer of an all-solid-state lithium-ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of methods for forming the positive electrode layer of an all-solid-state lithium-ion battery include a method of compression molding the positive electrode active material for the all-solid-state lithium-ion battery.

[0037] (Negative electrode layer) The negative electrode layer of an all-solid-state lithium-ion battery may be formed by layering known negative electrode active materials for all-solid-state lithium-ion batteries. Alternatively, the negative electrode layer may be formed by layering a negative electrode composite material obtained by mixing a known negative electrode active material for all-solid-state lithium-ion batteries with a solid electrolyte. The content of the negative electrode active material in the negative electrode layer is preferably 10% by mass or more and 99% by mass or less, and more preferably 20% by mass or more and 90% by mass or less.

[0038] The negative electrode layer, like the positive electrode layer, may contain a conductive additive. The conductive additive may be the same material as the material described for the positive electrode layer. As the negative electrode active material, for example, carbon materials can be used, specifically artificial graphite, graphite carbon fiber, resin-calcined carbon, pyrolysis vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-calcined carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and non-graphitizable carbon, or mixtures thereof. Furthermore, as the negative electrode material, for example, metallic lithium, metallic indium, metallic aluminum, metallic silicon, or alloys combined with other elements or compounds can be used.

[0039] The average thickness of the negative electrode layer of an all-solid-state lithium-ion battery is not particularly limited and can be designed appropriately depending on the purpose. The average thickness of the negative electrode layer of an all-solid-state lithium-ion battery may be, for example, 1 μm to 100 μm, or 1 μm to 10 μm.

[0040] The method for forming the negative electrode layer of an all-solid-state lithium-ion battery is not particularly limited and can be appropriately selected depending on the purpose. Examples of methods for forming the negative electrode layer of an all-solid-state lithium-ion battery include a method of compression molding of negative electrode active material particles and a method of vapor deposition of negative electrode active material.

[0041] Other components constituting the lithium-ion battery are not particularly limited and can be appropriately selected depending on the purpose. Examples include a positive electrode current collector, a negative electrode current collector, and a battery case.

[0042] The size and structure of the positive electrode current collector are not particularly limited and can be appropriately selected according to the purpose. Examples of materials for the positive electrode current collector include die steel, stainless steel, aluminum, aluminum alloy, titanium alloy, copper, gold, and nickel. Examples of shapes for the positive electrode current collector include foil, plate, and mesh. The average thickness of the positive electrode current collector may be, for example, 10 μm to 500 μm, or 50 μm to 100 μm.

[0043] The size and structure of the negative electrode current collector are not particularly limited and can be appropriately selected according to the purpose. Examples of materials for the negative electrode current collector include die steel, gold, indium, nickel, copper, and stainless steel. Examples of shapes for the negative electrode current collector include foil, plate, and mesh. The average thickness of the negative electrode current collector may be, for example, 10 μm to 500 μm, or 50 μm to 100 μm.

[0044] The battery case is not particularly limited and can be appropriately selected depending on the purpose, for example, known laminate films that can be used with conventional all-solid-state batteries. Examples of laminate films include resin laminate films and films in which metal has been vapor-deposited onto a resin laminate film. The shape of the battery is not particularly limited and can be appropriately selected depending on the purpose, for example, cylindrical, rectangular, button-shaped, coin-shaped, and flat-shaped batteries.

[0045] The following examples are provided to better understand the present invention and its advantages, but the present invention is not limited to these examples.

[0046] <1. Preparation of Acid Fluoride Solid Electrolytes> (Example 1) In a glove box under an argon atmosphere, Li2CO3, La2O3, and Nb2O5 were weighed out so that the raw material composition would be the stoichiometric composition of the target compound, and raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, raw material mixture 1 was placed in an Al2O3 crucible and calcined at 1200°C (intermediate synthesis temperature) for 4 hours under an air atmosphere to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide and crushed and mixed using an automatic mortar and pestle to prepare raw material mixture 2. Next, raw material mixture 2 was calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere in a crucible containing SiC as the main component in the proportions shown in Table 1 to induce a fluorination reaction and prepare an acid fluoride solid electrolyte.

[0047] (Example 2) In a glove box under an argon atmosphere, Li2CO3, La2O3, and Nb2O5 were weighed out so that the raw material composition would be the stoichiometric composition of the target compound, and raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, raw material mixture 1 was placed in an Al2O3 crucible and calcined at 1200°C (intermediate synthesis temperature) for 4 hours under an air atmosphere to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide and crushed and mixed using an automatic mortar and pestle to prepare raw material mixture 2. Next, raw material mixture 2 was calcined at 900°C (fluorination temperature) for 6 hours under a nitrogen atmosphere in a crucible containing SiC as the main component in the proportions shown in Table 1 to produce an acid fluoride-based solid electrolyte by inducing a fluorination reaction.

[0048] (Example 3) In a glove box under an argon atmosphere, Li2CO3, La2O3, and Nb2O5 were weighed out so that the raw material composition would be the stoichiometric composition of the target compound, and raw material mixture 1 was prepared by mixing them using a planetary ball mill. Next, raw material mixture 1 was placed in an Al2O3 crucible and calcined at 1000°C (intermediate synthesis temperature) for 4 hours under an air atmosphere to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide and crushed and mixed using an automatic mortar and pestle to prepare raw material mixture 2. Next, raw material mixture 2 was calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere in a crucible containing SiC as the main component in the proportions shown in Table 1 to induce a fluorination reaction and produce an acid fluoride-based solid electrolyte.

[0049] (Example 4) In a glove box under an argon atmosphere, Li2CO3, La2O3, and Nb2O5 were weighed out so that the raw material composition would be the stoichiometric composition of the target compound, and raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, raw material mixture 1 was placed in an Al2O3 crucible and calcined at 800°C (intermediate synthesis temperature) for 4 hours under an air atmosphere to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide and crushed and mixed using an automatic mortar and pestle to prepare raw material mixture 2. Next, raw material mixture 2 was calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere in a crucible containing SiC as the main component in the proportions shown in Table 1 to produce an acid fluoride-based solid electrolyte by inducing a fluorination reaction.

[0050] (Example 5) In a glove box under an argon atmosphere, Li2CO3, La2O3, and Nb2O5 were weighed out so that the raw material composition would be the stoichiometric composition of the target compound, and raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, raw material mixture 1 was placed in an Al2O3 crucible and calcined at 1200°C (intermediate synthesis temperature) for 4 hours under an air atmosphere to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide and crushed and mixed using an automatic mortar and pestle to prepare raw material mixture 2. Next, raw material mixture 2 was calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere in a crucible containing ZrO2 as the main component in the proportions shown in Table 1 to produce an acid fluoride-based solid electrolyte by inducing a fluorination reaction.

[0051] (Example 6) In a glove box under an argon atmosphere, Li2CO3, La2O3, and Nb2O5 were weighed out so that the raw material composition would be the stoichiometric composition of the target compound, and raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, raw material mixture 1 was placed in an Al2O3 crucible and calcined at 1200°C (intermediate synthesis temperature) for 4 hours under an air atmosphere to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide and crushed and mixed using an automatic mortar and pestle to prepare raw material mixture 2. Next, raw material mixture 2 was calcined at 1000°C (fluorination temperature) for 6 hours under an argon atmosphere in a crucible containing carbon (C) as the main component in the proportions shown in Table 1 to induce a fluorination reaction and produce an acid fluoride-based solid electrolyte.

[0052] (Comparative Example 1) In a glove box under an argon atmosphere, Li2CO3, La2O3, and Nb2O5 were weighed out so that the raw material composition would be the stoichiometric composition of the target compound, and raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, raw material mixture 1 was placed in an Al2O3 crucible and calcined at 1200°C (intermediate synthesis temperature) for 4 hours under an air atmosphere to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide and crushed and mixed using an automatic mortar and pestle to prepare raw material mixture 2. Next, raw material mixture 2 was calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere in a crucible containing Al2O3 as the main component in the proportions shown in Table 1 to induce a fluorination reaction and produce an acid fluoride-based solid electrolyte.

[0053] (Comparative Example 2) In a glove box under an argon atmosphere, Li2CO3, La2O3, and Nb2O5 were weighed out so that the raw material composition would be the stoichiometric composition of the target compound, and raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, raw material mixture 1 was placed in an Al2O3 crucible and calcined at 800°C (intermediate synthesis temperature) for 4 hours under an air atmosphere to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide and crushed and mixed using an automatic mortar and pestle to prepare raw material mixture 2. Next, raw material mixture 2 was calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere in a crucible containing Al2O3 as the main component in the proportions shown in Table 1 to induce a fluorination reaction and produce an acid fluoride-based solid electrolyte.

[0054] <2. Compositional Evaluation of Acid-Fluoride Solid Electrolytes> 0.5 g of each acid-fluoride solid electrolyte obtained in Examples 1-6 and Comparative Examples 1-2 was weighed out, dissolved in various acids, and then its composition was analyzed using an inductively coupled plasma atomic emission spectrometer (ICP-OES) "PS7800" manufactured by Hitachi High-Tech Corporation. The analysis results are shown in Table 1.

[0055] <3. XRD Evaluation of Solid Electrolytes (Lattice Constant Evaluation)> XRD evaluation was performed on each solid electrolyte sample obtained in Examples 1 to 6 and Comparative Examples 1 to 2 under the following conditions: ・X-ray diffractometer: SmartLab manufactured by Rigaku Corporation ・Light source: CuKα rays ・Voltage: 40kV ・Current: 30mA ・Detector: One-dimensional detector ・Measurement range: 2θ = 5 to 100 degrees ・Step width: 0.1 degrees ・Scan rate: 10 degrees / min Rietveld analysis was performed on the X-ray diffraction patterns obtained for Examples 1 to 6 and Comparative Examples 1 to 2 to calculate the lattice constant of each sample. The evaluation results are shown in Table 1.

[0056] <3. Evaluation of Bulk Ion Conductivity of Acid-Fluoride Solid Electrolytes> 0.5 g of powder of each acid-fluoride solid electrolyte obtained in Examples 1-6 and Comparative Examples 1-2 was pressed at a pressure of 370 MPa to form a plate. The formed plate was then placed in an Al2O3 or SiC crucible and fired at 1000°C for 6 hours under a nitrogen atmosphere to produce a sintered body for measurement. Gold was sputtered onto both sides of the aforementioned sintered body to produce a pellet with a gold electrode slightly less than 10 mm in diameter. Using this pellet, AC impedance measurements from 20 Hz to 100 MHz were performed at 30°C with an applied voltage of 100 mV using a Keysight E4990A with open-short correction. The arc appearing on the high-frequency side of the Cole-Cole plot obtained from the AC impedance measurement was analyzed to determine the bulk Li ion migration resistance of the sample. Next, the ionic conductivity (bulk ionic conductivity) was determined from the migration resistance of the Li ions and the thickness and area of ​​the solid electrolyte portion of the pellet used for measurement, based on the following formula: Ionic conductivity (mS / cm) = Thickness of the solid electrolyte portion of the pellet (cm) × 1000 / [(Migration resistance of Li ions (Ω)) × (Area of ​​the solid electrolyte portion of the pellet (cm) 2 The evaluation results are shown in Table 1.

[0057] <4. Evaluation of Relative Density of Acid-Fluoride Solid Electrolytes> Using the thickness and area of ​​the solid electrolyte portion of the pellets prepared in the "Evaluation of Bulk Ion Conductivity of Acid-Fluoride Solid Electrolytes" described above, and the mass of the pellets, the relative density was determined from the following formula: Dimensional density (g / cm³) 3 ) = Mass of pellet (g) / [(Thickness of solid electrolyte portion of pellet (cm)) × (Area of ​​solid electrolyte portion of pellet (cm)) 2 )) ] Relative density (%) = ( Dimensional density (g / cm³) 3 )) / (Theoretical density of acid-fluoride solid electrolytes (g / cm³) 3 The evaluation results are shown in Table 1.

[0058]

[0059] (Evaluation Results) In Examples 1 to 6, acid-fluoride-based solid electrolytes with good ionic conductivity were obtained in all cases. On the other hand, the acid-fluoride-based solid electrolytes in Comparative Examples 1 and 2 all had poor ionic conductivity because the raw material mixture 2 was calcined in an Al2O3 crucible.

[0060] One embodiment of the present invention provides a method for producing an acid fluoride-based solid electrolyte having good ionic conductivity and a method for producing an all-solid-state lithium-ion battery. This could lead to the widespread adoption of non-fossil energy, reduce the use of fossil energy sources such as oil and gas which currently account for a large portion of energy production, and potentially contribute to mitigating global warming. Furthermore, since the main materials used are substances with low environmental impact, such as lithium, carbon, manganese, nickel, and cobalt, and do not contain harmful substances such as cadmium, lead, or mercury, it has the potential to reduce environmental impact. For this reason, one embodiment of the present invention could potentially contribute to the United Nations-led Sustainable Development Goals (SDGs), specifically Goal 7, "Ensure access to affordable, reliable, sustainable, and modern energy for all," Goal 9, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation," and Goal 12, "Ensure sustainable consumption and production patterns."

Claims

1. A step of crushing and mixing raw materials to produce a raw material mixture 1; a step of placing the raw material mixture 1 in a firing container and firing it at 800 to 1200°C to produce an oxide; a step of adding two raw materials, LiF and LaF3, to the oxide, crushing and mixing them to produce a raw material mixture 2; and a step of firing the raw material mixture 2 in a firing container containing SiC, Si3N4, ZrO2, or C as the main component at 850 to 1000°C to produce a material with the composition formula: Li 2-x La (1+x) / 3 A method for producing an acid fluoride-based solid electrolyte, comprising the steps of: producing an acid fluoride-based solid electrolyte having a lattice constant of 10.436 Å or more, represented by the formula M2O6F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0); and 2. The method for producing an acid fluoride-based solid electrolyte according to claim 1, wherein the firing container for the raw material mixture 2 contains SiC as the main component.

3. The method for producing an acid fluoride-based solid electrolyte according to claim 1, wherein the calcination of the raw material mixture 1 and / or the raw material mixture 2 is carried out in an atmosphere other than an inert atmosphere.

4. A method for producing an all-solid-state lithium-ion battery comprising a solid electrolyte layer, a positive electrode layer, and a negative electrode layer, using an acid-fluoride-based solid electrolyte produced by the method for producing an acid-fluoride-based solid electrolyte described in any one of claims 1 to 3.

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