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

Abstract

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. [Solution] The process involves crushing and mixing raw materials to produce a raw material mixture 1, placing the raw material mixture 1 in a firing container and firing it at 800-1200°C to produce an oxide, adding two raw materials, LiF and LaF3, to the oxide, crushing and mixing them to produce a raw material mixture 2, and firing the raw material mixture 2 at 850-1000°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: producing an acid fluoride-based solid electrolyte having a lattice constant of 10.436 Å or greater, represented by the formula M2O6F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0).

Description

[Technical Field]

[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. [Background technology]

[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 with 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] Also, regarding conventional fluoride-based solid electrolytes, for example, in Patent Document 1, a solid electrolyte for a secondary battery containing an oxide-based solid electrolyte having a pyrochlore structure represented by the composition formula Aa 2-α Ab (1+α) / 3 B2O 7-β X β is disclosed. In the formula, 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 in the range of 0.6 < α < 2.0, β is in the range of 0 < β ≤ 1, and a solid electrolyte for a secondary battery containing a defect structure and a method for manufacturing the same are disclosed.

[0007] Also, 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 is composed of one or more phases. The constituent material of the core phase contains a pyrochlore-type solid electrolyte represented by the 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). The constituent material of the shell phase has a chemical composition different from that of the pyrochlore-type solid electrolyte, has a chemical composition containing Li, and contains a material having a lower melting point than the pyrochlore-type solid electrolyte. In the pyrochlore-type solid electrolyte, in the composition formula, α is in the range of 0.6 < α < 2.0, β is in the range of 0 < β ≤ 1, and the sum of the valences of the cations composed of Aa, Ab, and B and the anions composed of O and X is negative, and a solid electrolyte for a secondary battery containing a defect structure is disclosed.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

[0009] Traditionally, the chemical formula was Li 2-x La (1+x) / 3 When synthesizing an oxyfluoride-based 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 oxyfluoride-based solid electrolyte reacts with moisture in the atmosphere, reducing the lattice constant and lowering the 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. [Means for solving the problem]

[0011] Based on the above findings, the present invention is defined as follows. (1) A process of crushing and mixing raw materials to produce a raw material mixture 1, The process involves placing the raw material mixture 1 into a firing container and firing it at 800-1200°C to produce an oxide, The process involves adding two raw materials, LiF and LaF3, to the aforementioned oxide, then grinding and mixing them to produce a raw material mixture 2. The raw material mixture 2 is calcined at 850-1000°C in a calcination vessel containing SiC, Si3N4, ZrO2, or C as the main components, thereby producing a composition formula: Li 2-x La (1+x) / 3 M2O6F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0). A step of manufacturing an oxyfluoride-based solid electrolyte having a lattice constant represented by 10.436 Å or more, and A method for manufacturing an oxyfluoride-based solid electrolyte having (2) The method for manufacturing an oxyfluoride-based solid electrolyte according to (1) above, wherein the firing container for the raw material mixture 2 contains SiC as a main component. (3) The method for manufacturing an oxyfluoride-based solid electrolyte according to (1) or (2) above, 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. (4) A method for manufacturing an all-solid-state lithium-ion battery including a solid electrolyte layer, a positive electrode layer, and a negative electrode layer, using the oxyfluoride-based solid electrolyte produced by the method for manufacturing an oxyfluoride-based solid electrolyte according to any one of (1) to (3) above.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a method for manufacturing an oxyfluoride-based solid electrolyte having good ionic conductivity (bulk ionic conductivity) and a method for manufacturing an all-solid-state lithium-ion battery. Here, the ionic conductivity is roughly divided into "bulk conductivity" and "grain boundary conductivity". "Bulk conductivity" does not vary significantly if a high-quality material can be produced because it is inherent to the material. However, "grain boundary conductivity" may vary significantly depending on the method and accuracy of producing the sintered body. In the present invention, "ionic conductivity" means "bulk conductivity".

Brief Description of the Drawings

[0013] [Figure 1] It is a schematic diagram of an all-solid-state lithium-ion battery according to the present embodiment.

Embodiments for Carrying Out the Invention

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

[0015] <Acid fluoride solid electrolyte> The acid-fluoride solid electrolyte of this embodiment has the compositional 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 oxyfluoride-based solid electrolyte of this embodiment has a lattice constant of 10.436 Å or higher. When the lattice constant of the oxyfluoride-based 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 oxyfluoride-based solid electrolyte is 10.440 Å or higher.

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

[0021] Next, the raw materials are crushed and mixed to produce 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, as it eliminates the need for gas adjustment in a continuous furnace, it is also preferable to carry out the firing in an atmosphere other than an inert atmosphere. 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 850-1000°C for 2-6 hours in a calcination vessel mainly containing SiC, Si3N4, ZrO2, or C to induce a fluorination reaction, thereby producing a Li-based compound. 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 850-1000°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] As mentioned above, the firing container mainly contains SiC, Si3N4, ZrO2, or C, but among these, a container mainly containing SiC is particularly preferred from the viewpoint of being usable in air and its processability.

[0028] The atmosphere for calcining the raw material mixture 2 is not particularly limited, but it is preferable to carry it out under an inert gas atmosphere such as argon. Furthermore, from the viewpoint of improving manufacturing efficiency, it is also preferable to carry out the calcination in an atmospheric atmosphere, especially since it eliminates the need for gas adjustment in a continuous furnace.

[0029] <All-solid-state lithium-ion battery> An all-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 all-solid-state lithium-ion battery according to an embodiment of the present invention can be configured as shown in Figure 1 using the solid electrolyte layer, the positive electrode layer, and the negative electrode layer.

[0030] (solid electrolyte layer) The solid electrolyte layer of this embodiment is formed by the acid-fluoride-based solid electrolyte of this embodiment described above. The average thickness of the solid electrolyte layer is not particularly limited and can be designed as appropriate depending on the purpose. The average thickness of the solid electrolyte layer in this embodiment may be, for example, 50 μm to 500 μm, or 50 μm to 100 μm.

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

[0032] (Positive electrode layer) The positive electrode layer of this embodiment is formed in layers by mixing a known positive electrode active material for lithium-ion batteries with the above-described acid fluoride-based solid electrolyte 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] Known positive electrode active materials for lithium-ion batteries include, for example, Li, with composition formula 2:Li a Ni b Co c Mn dThe positive electrode active material is represented by O2 (in composition formula 2, 1.00 ≤ a ≤ 1.08, 0.60 ≤ b ≤ 0.90, and b + c + d = 1.0). When the positive electrode active material of this embodiment is a high-nickel NCM positive electrode active material with a high Ni ratio of 0.60 to 0.90 as shown in composition formula 2, the capacity of the all-solid-state lithium-ion battery is generally higher. Furthermore, from this viewpoint, it is more preferable that 0.80 ≤ b ≤ 0.90 is set in composition formula 2.

[0034] The positive electrode composite may further contain a conductive additive. This conductive additive may be a carbon material, a metallic material, or a mixture thereof. The conductive additive may include, 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, osnium, rhodium, tungsten, and zinc. The conductive additive is preferably a highly conductive element of carbon, a metallic element containing carbon, nickel, copper, silver, cobalt, magnesium, lithium, gold, ruthenium, platinum, niobium, osnium, or rhodium, or a mixture or compound thereof. As carbon materials, for example, carbon black such as Ketjenblack, acetylene black, Denka black, thermal black, and channel black, graphite, carbon fiber, activated carbon, etc., can be used.

[0035] The average thickness of the positive 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 positive 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.

[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 creating layers of known negative electrode active materials for all-solid-state lithium-ion batteries. Alternatively, the negative electrode layer may be formed by creating layers of 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, for example, 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, 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, can be used. 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. Possible shapes for the positive electrode current collector include foil-like, plate-like, and mesh-like forms. 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 negative electrode current collector shapes include foil-like, plate-like, and mesh-like shapes. 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 selected as appropriate depending on the purpose. Examples include known laminate films that can be used with conventional 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 selected as appropriate depending on the purpose. Examples include cylindrical, rectangular, button-shaped, coin-shaped, and flat-shaped batteries. [Examples]

[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-based 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 match the stoichiometric composition of the target compound, and the raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, the raw material mixture 1 was placed in an Al2O3 crucible and calcined at 1200°C (intermediate synthesis temperature) for 4 hours under an atmospheric environment to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide, and the mixture was crushed and mixed using an automatic mortar and pestle to produce raw material mixture 2. Next, the raw material mixture 2 was calcined in a crucible containing SiC as the main component in the proportions shown in Table 1, under a nitrogen atmosphere, at 1000°C (fluorination temperature) for 6 hours to induce a fluorination reaction, thereby producing an acid-fluoride-based solid electrolyte.

[0047] (Example 2) In a glove box under an argon atmosphere, Li2CO3, La2O3, and Ta2O5 were weighed out so that the raw material composition would match the stoichiometric composition of the target compound, and raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, the raw material mixture 1 was placed in an Al2O3 crucible and calcined at 1200°C (intermediate synthesis temperature) for 4 hours under an atmospheric environment to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide, and the mixture was crushed and mixed using an automatic mortar and pestle to produce raw material mixture 2. Next, the raw material mixture 2 was calcined in a crucible containing SiC as the main component in the proportions shown in Table 1, under a nitrogen atmosphere, at 900°C (fluorination temperature) for 6 hours to induce a fluorination reaction, thereby producing an acid-fluoride-based solid electrolyte.

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

[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 match the stoichiometric composition of the target compound, and the raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, the raw material mixture 1 was placed in an Al2O3 crucible and calcined at 1200°C (intermediate synthesis temperature) for 4 hours under an atmospheric environment to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide, and the mixture was crushed and mixed using an automatic mortar and pestle to produce raw material mixture 2. Next, the raw material mixture 2 was calcined in a crucible containing ZrO2 as the main component in the proportions shown in Table 1, under a nitrogen atmosphere, at 1000°C (fluorination temperature) for 6 hours to induce a fluorination reaction, thereby producing an acid-fluoride-based solid electrolyte.

[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 match the stoichiometric composition of the target compound, and the raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, the raw material mixture 1 was placed in an Al2O3 crucible and calcined at 1200°C (intermediate synthesis temperature) for 4 hours under an atmospheric environment to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide, and the mixture was crushed and mixed using an automatic mortar and pestle to produce raw material mixture 2. Next, the raw material mixture 2 was calcined in a crucible containing carbon (C) as the main component in the proportions shown in Table 1, under an argon atmosphere, at 1000°C (fluorination temperature) for 6 hours to induce a fluorination reaction, thereby producing 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 match the stoichiometric composition of the target compound, and the raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, the raw material mixture 1 was placed in an Al2O3 crucible and calcined at 1200°C (intermediate synthesis temperature) for 4 hours under an atmospheric environment to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide, and the mixture was crushed and mixed using an automatic mortar and pestle to produce raw material mixture 2. Next, the raw material mixture 2 was calcined in a crucible containing Al2O3 as the main component in the proportions shown in Table 1, under a nitrogen atmosphere, at 1000°C (fluorination temperature) for 6 hours to induce a fluorination reaction, thereby producing 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 match the stoichiometric composition of the target compound, and the raw material mixture 1 was prepared by mixing them using an automatic mortar and pestle. Next, the 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 the mixture was crushed and mixed using an automatic mortar and pestle to produce raw material mixture 2. Next, the raw material mixture 2 was calcined in a crucible containing Al2O3 as the main component in the proportions shown in Table 1, under a nitrogen atmosphere, at 1000°C (fluorination temperature) for 6 hours to induce a fluorination reaction, thereby producing an acid-fluoride-based solid electrolyte.

[0054] <2. Composition 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 a Hitachi High-Tech Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-OES) "PS7800". 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 1-6 and Comparative Examples 1-2 under the conditions described below. • X-ray diffractometer: SmartLab manufactured by Rigaku Corporation ·Light source: CuKα line Voltage: 40kV ·Current: 30mA • Detector: One-dimensional detector • Measurement range: 2θ = 5 to 100 degrees Step width: 0.1 degree • Scan rate: 10 degrees / min The lattice constants for each sample were calculated by performing Rietveld analysis on the X-ray diffraction patterns obtained for Examples 1-8 and Comparative Examples 1-2. The evaluation results are shown in Table 1.

[0056] <3. Evaluation of bulk ion conductivity of oxyfluoride-based solid electrolytes> 0.5 g of each acid-fluoride-based solid electrolyte powder 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 Li ion migration resistance 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 / [(Li ion migration resistance (Ω)) × (Area of ​​the solid electrolyte portion of the pellet (cm) 2 )) The evaluation results are shown in Table 1.

[0057] <4. Evaluation of the relative density of oxyfluoride-based 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 )) × 100 The evaluation results are shown in Table 1.

[0058] [Table 1]

[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 both exhibited 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 process of crushing and mixing raw materials to produce raw material mixture 1, The process involves placing the raw material mixture 1 into a firing container and firing it at 800 to 1200°C to produce an oxide, The oxide contains LiF and LaF 3 The process involves adding two types of raw materials, crushing and mixing them to produce a raw material mixture 2, The raw material mixture 2 is SiC, Si 3 N 4 , ZrO 2 Alternatively, by firing at 850-1000°C in a firing container containing C as the main component, the composition formula: Li 2-x La (1+x) / 3 M 2 O 6 F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0.) A step to produce an acid fluoride-based solid electrolyte with a lattice constant of 10.436 Å or higher, A method for producing an acid fluoride-based solid electrolyte having [the specified characteristic].

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. A 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.

Images