Oxyfluoride-based solid electrolyte production method and all-solid-state lithium ion battery production method

Abstract

This oxyfluoride-based solid electrolyte production method comprises a step for preparing an oxide by calcining a raw material mixture 1 placed in a calcining vessel 1, a step for preparing a raw material mixture 2 by adding an alkali metal fluoride and a lanthanide fluoride to the oxide, followed by pulverizing and mixing, and a step for preparing an oxyfluoride-based solid electrolyte by calcining the raw material mixture 2 in a calcining vessel 2. A material J of the calcining vessel 2 is such that, when a heating simulation is performed using a thermodynamic equilibrium calculation with the initial molar amount set to A mol for each of the alkali metal fluoride, the material J, and nitrogen, the molar amount B mol of the alkali metal fluoride in a liquid that remains unreacted is not less than 99.90% of the initial molar amount A mol at a temperature 50°C higher than the melting point of the alkali metal fluoride, and is not less than 99.70% of the initial molar amount A mol at a temperature 150°C higher than the melting point of the alkali metal fluoride.

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-based solid electrolyte material having a pyrochlore 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-based 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 solid electrolyte for a secondary battery comprising a pyrochlore-structure oxide-based solid electrolyte represented by the formula, wherein Aa is an alkali metal, Ab contains at least one lanthanoid, B is a cationic metal different from Aa and Ab, X is an anion substitutable for an O atom constituting the pyrochlore structure, in the composition formula, α is in the range of 0.6 < α < 2.0, and β is in the range of 0 < β ≤ 1. Disclosed are a solid electrolyte for a secondary battery containing a defect structure and a method for producing the same.

[0007] Further, Patent Document 2 discloses a solid electrolyte comprising a particulate core phase (101) and a shell phase (102) covering at least a part of the core phase, wherein the shell phase consists of one or more phases, and the constituent material of the core phase is represented by the composition formula Aa 2-α Ab (1+α) / 3 B₂O 7-β X β (Aa: alkali metal, Ab: lanthanoid, B: cationic metal, X: anion substitutable for O) which comprises a pyrochlore-type solid electrolyte represented by, and the constituent material of the shell phase has a chemical composition different from that of the pyrochlore-type solid electrolyte and has a chemical composition containing Li, and comprises a material having a lower melting point than the pyrochlore-type solid electrolyte; in the composition formula of the pyrochlore-type solid electrolyte, 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 cations consisting of Aa, Ab and B and anions consisting of O and X is negative. A solid electrolyte for a secondary battery 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 the formula 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 alumina-containing crucible results in a reaction between the alumina component and the material. When calcined under such conditions, by-reaction products from the alumina crucible or alumina-containing crucible are mixed into the acid-fluoride solid electrolyte. Furthermore, the reaction between the acid-fluoride solid electrolyte and the calcination vessel can cause cracks in the crucible, leading to the volatilization of Li and F in the reaction system, or the reaction of the acid-fluoride solid electrolyte with moisture in the atmosphere. As a result, there is a problem of decreased 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 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 1 and firing it at 800 to 1200°C to produce an oxide; a step of adding alkali metal fluoride and lanthanide fluoride 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 2 at 800 to 1000°C to produce a material with composition formula: Aa 2-x Ab (1+x) / 3A method for producing an acid fluoride-based solid electrolyte, comprising the steps of: producing an acid fluoride-based solid electrolyte represented by the formula B2O6F (wherein Aa is an alkali metal, Ab contains at least a lanthanide, B is a metal selected from transition metals or Group 15 elements, and 0 ≤ x ≤ 1.0); wherein the firing container 2 has at least its inner surface composed of material J, and the material J of the firing container 2 is a material that, when an initial amount Amol of alkali metal fluoride, the material J, and nitrogen are provided, and a thermodynamic equilibrium simulation is performed at temperatures 50°C higher and 150°C higher than the melting point of the alkali metal fluoride, the amount of substance Bmol of liquid alkali metal fluoride remaining unreacted is 99.90% or more of the initial amount Amol at temperatures 50°C higher than the melting point of the alkali metal fluoride, and 99.70% or more at temperatures 150°C higher than the melting point of the alkali metal fluoride. (2) The method for producing an acid fluoride-based solid electrolyte according to (1), wherein the firing container 2 has the material J on at least the inner surface of the firing container 2 to a thickness of 0.15 mm or more. (3) The method for producing an acid fluoride-based solid electrolyte according to (1) or (2), wherein the firing container 2 is composed only of the material J. (4) The method for producing an acid fluoride-based solid electrolyte according to any one of (1) to (3), wherein the material J includes SiC, Si3N4, BN, ZrO2, or C. (5) In the step of producing the acid fluoride-based solid electrolyte, the raw material mixture 2 is fired 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 according to any one of (1) to (4) above, wherein an acid fluoride-based solid electrolyte represented by M2O6F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0) is produced. (6) A method for producing an all-solid-state lithium-ion battery including 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 (5) above.

[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: Aa 2-x Ab (1+x) / 3 It is represented as B2O6F (wherein Aa is an alkali metal, Ab contains at least a lanthanide, B is a transition metal or a metal selected from Group 15 elements, and 0 ≤ x ≤ 1.0).

[0016] In the above compositional formula, any of Li, Na, or K can be used as the alkali metal represented by Aa.

[0017] In the above compositional formula, Ab contains at least one lanthanide. At least one of La, Ce, Nd, and Sm can be used as the lanthanide represented by Ab. The basic composition of Ab consists of lanthanides, and some of the lanthanides constituting Ab may be substituted with alkaline earth metals (Ca, Mg, Sr, etc.). Ab may consist of lanthanides.

[0018] In the above compositional formula, B is a metal selected from transition metals or Group 15 elements. Furthermore, B is a different metal from Ab. In the crystal, B forms an octahedron surrounded by six oxygen atoms. As the transition metal represented by B, a Group 4 or Group 5 transition metal can be used; more specifically, at least one of Nb, Ta, Ti, Zr, Hf, or V can be used. As the Group 15 element represented by B, Sb or Bi can be used.

[0019] The acid-fluoride-based solid electrolyte of this embodiment has the composition formula: Li 2-x La (1+x) / 3 It may also be expressed as M2O6F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0).

[0020] 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.

[0021] 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.

[0022] 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.

[0023] <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 to obtain a predetermined composition. Examples of the raw materials used here include Li2CO3, La2O3, Nb2O5, etc.

[0024] Next, the raw materials are pulverized and mixed to prepare raw material mixture 1. The pulverization and mixing of the raw materials are not particularly limited, but are preferably performed with a planetary ball mill, for example. By placing the raw materials and zirconia beads having a diameter of 1 mm or less into a jar of the planetary ball mill, and rotating the jar on its own axis while revolving the jar around a common axis, the raw materials can be pulverized and mixed. The revolution speed of the planetary ball mill is preferably in the range of 100 rpm to 500 rpm.

[0025] Next, the raw material mixture 1 is placed into a firing container 1 and fired at 800 to 1200°C for 2 to 6 hours to prepare an oxide. The firing atmosphere for raw material mixture 1 is not particularly limited, but firing is preferably performed under an inert gas atmosphere such as argon. Furthermore, from the viewpoint of eliminating the need for gas adjustment particularly in a continuous furnace and improving production efficiency, it is also preferable to perform firing in an atmosphere other than an inert atmosphere. As an atmosphere other than an inert atmosphere, firing can be performed, for example, in an air atmosphere.

[0026] The material of the firing container 1 is not particularly limited, and for example, Al₂O₃, ZrO₂, Al₆SiO₂, MgO, CaO, and the like can be used. Further, as the material of the firing container 1, the content of these Al₂O₃, ZrO₂, Al₆SiO₂, MgO, CaO and the like may be 50% by mass or more, 70% by mass or more, or 90% by mass or more.

[0027] Next, an alkali metal fluoride and a lanthanoid fluoride are added to the oxide, followed by pulverization and mixing to prepare raw material mixture 2. Examples of the alkali metal fluoride include LiF, NaF, KF, and the like. Examples of the lanthanoid fluoride include LaF₃, CeF₃, PrF₃, NdF₃, DyF₃, and the like. The alkali metal fluoride may contain one type of alkali metal or may contain two or more types of alkali metals. The raw material mixture 2 may contain one type of lanthanoid fluoride or may contain two or more types of lanthanoid fluoride. The pulverization and mixing of raw material mixture 2 are not particularly limited, but, similarly to raw material mixture 1, are preferably performed with a planetary ball mill, for example.

[0028] Next, the raw material mixture 2 is calcined in the calcination container 2 at 800 to 1000°C to induce a fluorination reaction, resulting in the composition formula: Aa 2-x Ab (1+x) / 3 An acid-fluoride-based solid electrolyte represented by B2O6F (wherein Aa is an alkali metal, Ab contains at least a lanthanide, B is a transition metal or a metal selected from Group 15 elements, and 0 ≤ x ≤ 1.0) is prepared.

[0029] The firing temperature is preferably 850 to 1000°C, and more preferably 900 to 1000°C. The firing time is preferably 1 to 8 hours, and more preferably 2 to 6 hours.

[0030] The firing container 2 has at least an inner surface made of material J, and the material J of the firing container 2 is a material that satisfies the following conditions when heating simulations are performed in thermodynamic equilibrium calculations with an initial amount Amol of alkali metal fluoride, material J, and nitrogen, and the amount Bmol of liquid alkali metal fluoride remaining unreacted is 99.90% or more of the initial amount Amol at a temperature 50°C above the melting point of alkali metal fluoride, and 99.70% or more at a temperature 150°C above the melting point of alkali metal fluoride. When the alkali metal fluoride is LiF, the temperature 50°C above the melting point of alkali metal fluoride is 900°C, and the temperature 150°C above the melting point of alkali metal fluoride is 1000°C.

[0031] Composition formula: Aa 2-x Ab (1+x) / 3In the acid fluoride-based solid electrolyte represented by B2O6-xF2x (wherein Aa is an alkali metal, Ab contains at least a lanthanoid, B is a metal selected from transition metals or Group 15 elements, and 0≤x≤1.0), when an alumina crucible or an alumina-containing crucible, which is a common firing container, is used for synthesizing the acid fluoride-based solid electrolyte, the alumina component reacts with the material, causing small cracks in the crucible. In contrast, in the embodiment of the present invention, as described above, at least the inner surface of the firing container 2 is composed of material J. For material J of the firing container 2, when an initial amount A mol of each of an alkali metal fluoride, material J, and nitrogen is provided, and a heating simulation is performed by thermodynamic equilibrium calculation at a temperature 50°C higher than the melting point of the alkali metal fluoride and a temperature 150°C higher than the melting point of the alkali metal fluoride, the amount B mol of the remaining unreacted liquid alkali metal fluoride, relative to the initial amount A mol, satisfies 99.90% or more at the temperature 50°C higher than the melting point of the alkali metal fluoride, and 99.70% or more at the temperature 150°C higher than the melting point of the alkali metal fluoride. As described above, in the embodiment of the present invention, in the fluorination reaction of the raw material mixture 2 in the firing container 2, the decrease of liquid alkali metal fluoride in the reactant is effectively suppressed. This indicates that material J, which constitutes the inner surface of the firing container 2 in contact with the raw material mixture 2, is unlikely to react with the alkali metal fluoride. Therefore, the generation of impurity phases in the product obtained from the fluorination reaction of the raw material mixture 2 and the cracking of the firing container can be effectively suppressed. Accordingly, the volatilization of the alkali metal component and the F component, and further the reaction between the acid fluoride-based solid electrolyte and moisture in the atmosphere can be suppressed. As a result, an acid fluoride-based solid electrolyte having good ionic conductivity can be obtained.

[0032] The firing container 2 preferably has material J on at least its inner surface to a thickness of 0.15 mm or more. By making the thickness of material J on at least its inner surface to 0.15 mm or more, the penetration of alkali metal fluoride present as liquid into the firing container substrate can be reliably prevented, and the reaction with the firing container substrate can be reliably suppressed. Therefore, in the fluorination reaction of the raw material mixture 2 in the firing container 2, the reduction of liquid alkali metal fluoride in the reactant can be more reliably suppressed. The firing container 2 more preferably has material J on at least its inner surface to a thickness of 0.3 mm or more, and even more preferably to a thickness of 0.5 mm or more.

[0033] It is preferable that the firing container 2 is composed solely of material J. With such a configuration, the penetration of alkali metal fluoride, which exists as a liquid, into the firing container substrate can be prevented more reliably, and the reaction with the firing container substrate can be more reliably suppressed. Therefore, in the fluorination reaction of the raw material mixture 2 inside the firing container 2, the reduction of liquid alkali metal fluoride in the reactant can be suppressed even more reliably.

[0034] Furthermore, it is preferable that the material J of the firing container 2 is a material that satisfies the following conditions when heating simulations are performed in thermodynamic equilibrium calculations with an initial amount Amol of alkali metal fluoride, material J, and nitrogen, and the heating simulations are performed at temperatures 50°C higher and 150°C higher than the melting point of the alkali metal fluoride. The amount of Bmol of liquid alkali metal fluoride that remains unreacted is 99.95% or more of the initial amount Amol at a temperature 50°C higher than the melting point of the alkali metal fluoride, and 99.75% or more at a temperature 150°C higher than the melting point of the alkali metal fluoride (i.e., (Bmol / Amol) × 100 is 99.95% or more at a temperature 50°C higher than the melting point of the alkali metal fluoride, and 99.75% or more at a temperature 150°C higher than the melting point of the alkali metal fluoride). Furthermore, it is more preferable that the material J of the firing container 2 is such that, when an initial amount Amol of alkali metal fluoride, material J, and nitrogen are provided, and a thermodynamic equilibrium simulation is performed at temperatures 50°C higher than the melting point of alkali metal fluoride and 150°C higher than the melting point of alkali metal fluoride, the amount Bmol of liquid alkali metal fluoride remaining unreacted is 99.98% or more of the initial amount Amol at temperatures 50°C higher than the melting point of alkali metal fluoride, and 99.90% or more at temperatures 150°C higher than the melting point of alkali metal fluoride.

[0035] As described above, material J is not particularly limited as long as the amount of substance B mol of the alkali metal fluoride in the liquid remaining in the firing container 2 satisfies the conditions that, relative to the initial amount of substance A mol, B mol is 99.90% or more at a temperature 50°C higher than the melting point of the alkali metal fluoride, and 99.70% or more at a temperature 150°C higher than the melting point of the alkali metal fluoride. For example, a material containing SiC, Si3N4, BN, ZrO2, or C in a proportion of 90% by mass or more can be used. Furthermore, in embodiments of the present invention, material J preferably contains SiC, Si3N4, BN, ZrO2, or C in a proportion of 95% by mass or more, and particularly preferably contains 99% by mass or more.

[0036] As described above, the material of the main body of the firing container 2 is not limited as long as at least the inner surface is made of material J. For example, Al2O3, ZrO2, Al6SiO2, MgO, CaO, etc. can be used as the material of the main body of the firing container 2. Furthermore, the main body of the firing container 2 may contain these Al2O3, ZrO2, Al6SiO2, MgO, CaO, etc. in a proportion of 50% by mass or more, 70% by mass or more, or 90% by mass or more.

[0037] The firing containers 1 and 2 may be crucibles, saggars, setters, or tammann tubing.

[0038] 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 or nitrogen. 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.

[0039] <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. An 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.

[0040] (Solid Electrolyte Layer) The solid electrolyte layer of this embodiment is formed from 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 of this embodiment may be, for example, 50 μm to 500 μm, or 50 μm to 100 μm.

[0041] 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.

[0042] (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 oxyfluoride-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.

[0043] Known positive electrode active materials for lithium-ion batteries include, for example, composition formula 2: Li a Ni b Co c Mn d The material contains a positive electrode active material 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] (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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] The following examples are provided to better understand the present invention and its advantages, but the present invention is not limited to these examples.

[0056] <1. Simulation of Material J Selection for Firing Container 2> (Example 1) Thermodynamic equilibrium calculations were performed using the calculation software FactSage 8.3. The calculations were performed under the following conditions to calculate the amount of LiF (liquid) present at 900°C and 1000°C. 900°C is 50°C higher than the melting point of LiF, and 1000°C is 150°C higher than the melting point of LiF. In this example, LiF was used as the alkali metal fluoride, but it is not limited to this, and other alkali metal fluorides may be used. • Calculation mode: Equilib • Database used: FactPS, FToxide • Calculation conditions: - Reactions window: N2 (gas) + LiF (liquid) + ZrO2 (solid) (calculated assuming each composition is 1 mol) - Compound species: gas ideal, pure solids - Solution phases: Select all solution - Final conditions: T (°C): 500 1500 100 (100-degree increments from 500 to 1500) P (atm): 1 - Volume and physical prop data: assume molar volume of solids and liquids - Equilibrium: normal

[0057] (Example 2) The procedure was carried out in the same manner as in Example 1, except that the Reactions window in the calculation conditions was set to N2 (gas) + LiF (liquid) + SiC (solid).

[0058] (Example 3) The procedure was carried out in the same manner as in Example 1, except that the Reactions window in the calculation conditions was set to N2 (gas) + LiF (liquid) + BN (solid).

[0059] (Example 4) The procedure was carried out in the same manner as in Example 1, except that the Reactions window in the calculation conditions was set to N2 (gas) + LiF (liquid) + C (solid).

[0060] (Example 5) The procedure was carried out in the same manner as in Example 1, except that the Reactions window in the calculation conditions was set to N2 (gas) + LiF (liquid) + Si3N4 (solid).

[0061] (Comparative Example 1) The procedure was carried out in the same manner as in Example 1, except that the Reactions window in the calculation conditions was set to N2 (gas) + LiF (liquid) + Al2O3 (solid).

[0062] (Comparative Example 2) The procedure was carried out in the same manner as in Example 1, except that the Reactions window in the calculation conditions was set to N2 (gas) + LiF (liquid) + SiO2 (solid).

[0063] (Comparative Example 3) Reactions window in the calculation conditions is N2 (gas) + LiF (liquid) + Al6Si2O 13 The procedure was carried out in the same manner as in Example 1, except that the material was solid.

[0064] (Comparative Example 4) The procedure was carried out in the same manner as in Example 1, except that the Reactions window in the calculation conditions was set to N2 (gas) + LiF (liquid) + MgO (solid).

[0065] (Comparative Example 5) The procedure was carried out in the same manner as in Example 1, except that the Reactions window in the calculation conditions was set to N2 (gas) + LiF (liquid) + CaO (solid).

[0066] Based on the results of the heating simulations described above for Examples 1 to 5 and Comparative Examples 1 to 5, the ratio of the amount of substance B mol of LiF remaining unreacted to the initial amount A mol was calculated. The calculation results are shown in Table 1.

[0067] <2. Preparation of Acid Fluoride Solid Electrolytes> (Example 6) Each of the raw materials, Li2CO3, La2O3, and Nb2O5, was weighed 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 atmospheric atmosphere to produce an oxide. Next, two raw materials, LiF and LaF3, were added to the oxide, and raw material mixture 2 was prepared by grinding and mixing them using an automatic mortar and pestle. Next, 40 g of raw material mixture 2 was placed in a crucible containing Al2O3 as the main component (Al2O3 in a proportion of 90% by mass or more), which had been coated with ZrO2 to a thickness of about 1 mm on the inside, and calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere to induce a fluorination reaction, thereby producing an acid-fluoride-based solid electrolyte.

[0068] (Example 7) Li2CO3, La2O3, and Nb2O5 were weighed 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, 40 g of raw material mixture 2 was placed in a crucible that contained Al2O3 as the main component (containing Al2O3 in a proportion of 90% by mass or more) and coated on the inside of the crucible with SiC to a thickness of about 1 mm, and calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere to produce a fluorination reaction, thereby producing an acid fluoride-based solid electrolyte.

[0069] (Example 8) Li2CO3, La2O3, and Nb2O5 were weighed 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 1100°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 crushed and mixed using an automatic mortar and pestle to prepare raw material mixture 2. Next, 40 g of raw material mixture 2 was placed in a crucible that contained Al2O3 as the main component (containing Al2O3 in a proportion of 90% by mass or more) and coated on the inside of the crucible with BN to a thickness of about 0.15 mm, and calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere to produce a fluorination reaction, thereby producing an acid fluoride-based solid electrolyte.

[0070] (Example 9) 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 atmospheric environment 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, 100g of raw material mixture 2 was placed in a crucible containing ZrO2 as the main component (containing ZrO2 in a proportion of 90% by mass or more), and calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere to induce a fluorination reaction and produce an acid fluoride-based solid electrolyte.

[0071] (Example 10) The raw materials Li2CO3, La2O3, and Nb2O5 were weighed 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 atmospheric environment 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, 100 g of raw material mixture 2 was placed in a crucible containing SiC as the main component (containing SiC in a proportion of 90% by mass or more), and calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere to induce a fluorination reaction and produce an acid fluoride-based solid electrolyte.

[0072] (Example 11) The raw materials Li2CO3, La2O3, and Nb2O5 were weighed 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 atmospheric environment 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, 100g of raw material mixture 2 was placed in a crucible containing SiC as the main component (containing SiC in a proportion of 90% by mass or more), and calcined at 900°C (fluorination temperature) for 6 hours under a nitrogen atmosphere to induce a fluorination reaction and produce an acid fluoride-based solid electrolyte.

[0073] (Example 12) The raw materials Li2CO3, La2O3, and Nb2O5 were weighed 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, 100 g of raw material mixture 2 was placed in a crucible containing C as the main component (containing C in a proportion of 90% by mass or more), and calcined at 800°C (fluorination temperature) for 6 hours under an argon atmosphere to produce a fluorination reaction, thereby preparing an acid fluoride-based solid electrolyte.

[0074] (Comparative Example 6) Li2CO3, La2O3, and Nb2O5 were weighed 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 atmospheric environment 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, 100g of raw material mixture 2 was placed in a crucible containing Al2O3 as the main component (containing Al2O3 in a proportion of 90% by mass or more), and calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere to induce a fluorination reaction and produce an acid fluoride-based solid electrolyte.

[0075] (Comparative Example 7) Li2CO3, La2O3, and Nb2O5 were weighed 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 atmospheric environment 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, 40 g of raw material mixture 2 was placed in a crucible containing Al2O3 as the main component (containing Al2O3 in a proportion of 90% by mass or more) coated with AlPO4 to a thickness of about 0.15 mm, and calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere to produce a fluorination reaction, thereby producing an acid fluoride-based solid electrolyte.

[0076] (Comparative Example 8) Li2CO3, La2O3, and Nb2O5 were weighed 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 atmospheric environment 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, 100g of raw material mixture 2 was placed in a crucible containing MgO as the main component (containing MgO in a proportion of 90% by mass or more), and calcined at 1000°C (fluorination temperature) for 6 hours under a nitrogen atmosphere to induce a fluorination reaction and produce an acid fluoride-based solid electrolyte.

[0077] <3. Compositional Evaluation of Acid-Fluoride Solid Electrolytes> 0.5 g of each acid-fluoride solid electrolyte obtained in Examples 6-12 and Comparative Examples 6-8 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 2.

[0078] <4. Evaluation of Bulk Ion Conductivity of Acid-Fluoride Solid Electrolytes> 0.5 g of powder of each acid-fluoride solid electrolyte obtained in Examples 6-12 and Comparative Examples 6-8 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 2.

[0079] <5. 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 2.

[0080]

[0081]

[0082] (Evaluation Results) In the simulation results for Examples 1 to 5, the amount of substance B mol of liquid LiF that remains unreacted was 99.90% or more at 900°C and 99.70% or more at 1000°C relative to the initial amount A mol, and it is expected that these materials are suitable as the inner surface material for the firing container 2. On the other hand, in Comparative Examples 1 to 5, the amount of substance B mol of liquid LiF that remains unreacted did not meet the requirements of 99.90% or more at 900°C and 99.70% or more at 1000°C relative to the initial amount A mol, and it is presumed that there is a high possibility that these materials will react with oxide-based solid electrolytes. In Examples 6 to 12, in which materials expected to be suitable as the inner surface material for the firing container 2 based on the results of Examples 1 to 5 were used, acid-fluoride-based solid electrolytes with good ionic conductivity were obtained in all cases. On the other hand, based on the results of Comparative Examples 1 to 5, the acid-fluoride solid electrolytes in Comparative Examples 6 to 8, which used a material as a firing container that was presumed to be highly likely to react with the acid-fluoride solid electrolyte, all had poor ionic conductivity (Comparative Examples 6 and 7) or exceeded the measurement limit of ionic conductivity due to the presence of phases other than the acid-fluoride solid electrolyte or the volatilization of Li and F, or the resistance value in impedance measurement being too high (Comparative Example 8).

[0083] 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 1 and firing it at 800 to 1200°C to produce an oxide; a step of adding alkali metal fluoride and lanthanide fluoride to the oxide, crushing and mixing it to produce a raw material mixture 2; and a step of firing the raw material mixture 2 in a firing container 2 at 800 to 1000°C to produce a material with the composition formula: Aa 2-x Ab (1+x) / 3 A method for producing an acid fluoride-based solid electrolyte, comprising the steps of: producing an acid fluoride-based solid electrolyte represented by the formula B2O6F (wherein Aa is an alkali metal, Ab contains at least a lanthanide, B is a metal selected from transition metals or Group 15 elements, and 0 ≤ x ≤ 1.0); wherein the firing container 2 has at least its inner surface composed of material J, and the material J of the firing container 2 is a material that, when an initial amount Amol of alkali metal fluoride, the material J, and nitrogen are provided, and a thermodynamic equilibrium simulation is performed at temperatures 50°C higher and 150°C higher than the melting point of the alkali metal fluoride, the amount of substance Bmol of liquid alkali metal fluoride remaining unreacted is 99.90% or more of the initial amount Amol at temperatures 50°C higher than the melting point of the alkali metal fluoride, and 99.70% or more at temperatures 150°C higher than the melting point of the alkali metal fluoride.

2. The method for producing an acid fluoride-based solid electrolyte according to claim 1, wherein the firing container 2 has the material J on at least the inner surface of the firing container 2 with a thickness of 0.15 mm or more.

3. The method for producing an acid fluoride-based solid electrolyte according to claim 1, wherein the firing container 2 is composed solely of the material J.

4. The method for producing an acid fluoride-based solid electrolyte according to claim 1, wherein the material J comprises SiC, Si3N4, BN, ZrO2, or C.

5. In the process of producing the acid fluoride-based solid electrolyte, the raw material mixture 2 is calcined to produce a compound formula: Li 2-x La (1+x) / 3 A method for producing an acid fluoride-based solid electrolyte according to claim 1, comprising producing an acid fluoride-based solid electrolyte represented by M2O6F (wherein M is at least one of Nb and Ta, and 0 ≤ x ≤ 1.0).

6. 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 5.

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