Solid electrolyte material for fluoride ion batteries and production method for solid electrolyte material for fluoride ion batteries

Abstract

Provided is a solid electrolyte material for fluoride ion batteries that has high fluoride ion conduction. According to the present invention, a solid electrolyte material for fluoride ion batteries includes a metal fluoride complex that has, as a principal phase, a crystal structure that contains adduct ions in a fluorite structure that includes fluoride ions, lanthanoid metal ions, and alkali earth metal ions. The ion radius of the adduct ions is greater than the ion radius of the alkali earth metal ions. The composition of the metal fluoride complex is such that the ratio of the number of moles of the fluoride ions to the total number of moles of the lanthanoid metal ions, the alkali earth metal ions, and the adduct ions is greater than 1.87 but less than 3 and such that the ratio of the number of moles of the adduct ions to the number of moles of the alkali earth metal ions is less than 1.

Description

Solid electrolyte material for fluoride ion batteries and its manufacturing method

[0001] The present disclosure relates to a solid electrolyte material for a fluoride ion battery and a method for producing the same.

[0002] Fluoride ion solid-state batteries, which utilize the reaction of fluoride ions, are known as batteries with high voltage and high energy density. While fluoride ion batteries operate at high temperatures, such as 150°C or higher, they have the problem of not functioning at low temperatures due to the low ionic conductivity of the solid electrolyte. In relation to this, for example, Japanese Patent Application Laid-Open No. 2018-77992 proposes a solid electrolyte material having a Tysonite structure.

[0003] An object of one aspect of the present disclosure is to provide a solid electrolyte material for a fluoride ion battery having high ionic conductivity of fluoride ions.

[0004] The first aspect is a solid electrolyte material for a fluoride ion battery, which includes a metal composite fluoride having, as a main phase, a crystalline structure containing additional ions in a fluorite structure containing fluoride ions, lanthanoid metal ions, and alkaline earth metal ions. In the solid electrolyte material, the additional ions have a larger ionic radius than the alkaline earth metal ions. The metal composite fluoride has a composition in which the ratio of the number of moles of fluoride ions to the total number of moles of lanthanoid metal ions, alkaline earth metal ions, and additional ions is greater than 1.87 and less than 3, and the ratio of the number of moles of additional ions to the number of moles of alkaline earth metal ions is less than 1.

[0005] A second aspect is a solid electrolyte layer for a fluoride ion battery containing the solid electrolyte material of the first aspect. A third aspect is a fluoride ion battery including a solid electrolyte layer containing the solid electrolyte material of the first aspect, a positive electrode, and a negative electrode.

[0006] A fourth aspect is a method for producing a solid electrolyte for a fluoride ion battery, comprising: preparing a mixture containing a lanthanoid metal fluoride, an alkaline earth metal fluoride, and a fluoride of an additional ion; and heat-treating the mixture at a temperature of 200°C to 1000°C to obtain a metal composite fluoride. The mixture contains the lanthanoid metal fluoride, the alkaline earth metal fluoride, and the fluoride of the additional ion in a content ratio satisfying 1.87<(3p+2q+nr) / (p+q+r)<3, where pmol is the content of the lanthanoid metal ion in the lanthanoid metal fluoride, qmol is the content of the alkaline earth metal ion in the alkaline earth metal fluoride, rmol is the content of the additional ion in the fluoride of the additional ion, and n is the valence of the additional ion. The additional ion has a larger ionic radius than the alkaline earth metal ion. The metal composite fluoride has a crystal structure containing the additional ion in a fluorite structure as a main phase.

[0007] According to one aspect of the present disclosure, it is possible to provide a solid electrolyte material for a fluoride ion battery having high ionic conductivity of fluoride ions.

[0008] 1 is an example of X-ray diffraction spectra of solid electrolyte materials according to Examples 1 to 3 and Comparative Examples 1 to 4. FIG. 2 is an example of X-ray diffraction spectra of solid electrolyte materials according to Comparative Example 1, Comparative Example 2, and Examples 4 to 6. FIG. 3 is an example of X-ray diffraction spectra of solid electrolyte materials according to Comparative Example 1, Comparative Example 2, Example 1, and raw material compounds. FIG. 4 is an example of X-ray diffraction spectra of solid electrolyte materials according to Comparative Example 1 and Comparative Examples 5 to 7. FIG. 5 is an example of X-ray diffraction spectra of solid electrolyte materials according to Comparative Example 1 and Comparative Examples 8 to 10.

[0009] In this specification, the term "process" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, the content of each component in a composition refers to the total amount of the multiple substances present in the composition, unless otherwise specified, when multiple substances corresponding to each component are present in the composition. Furthermore, the upper and lower limits of the numerical ranges described in this specification can be arbitrarily selected and combined from the numerical values ​​exemplified as numerical ranges. Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments described below exemplify solid electrolyte materials for fluoride ion batteries and methods for producing the same in order to embody the technical concept of the present invention, and the present invention is not limited to the solid electrolyte materials for fluoride ion batteries and methods for producing the same described below.

[0010] Solid Electrolyte Material The solid electrolyte material may include a metal composite fluoride having, as a main phase, a crystal structure containing additional ions having a larger ionic radius than the alkaline earth metal ions in a fluorite structure containing fluoride ions, lanthanoid metal ions, and alkaline earth metal ions. The metal composite fluoride may have a composition in which the ratio of the number of moles of fluoride ions to the total number of moles of lanthanoid metal ions, alkaline earth metal ions, and additional ions is, for example, more than 1.87 and less than 3, and the ratio of the number of moles of additional ions to the number of moles of alkaline earth metal ions is less than 1. The solid electrolyte material may be, for example, a material constituting a solid electrolyte layer included in a fluoride ion battery.

[0011] The metal composite fluoride constituting the solid electrolyte material further contains additional ions in a fluorite structure containing fluoride ions, lanthanoid metal ions, and alkaline earth metal ions. The additional ions may be solid-solved in the fluorite structure. Generally, the fluorite structure is an ionic crystal structure composed of alkaline earth metal ions and fluoride ions in a ratio of 1:2. In the fluorite structure of the metal composite fluoride, lanthanoid metal ions are solid-solved in addition to alkaline earth metal ions and fluoride ions. The solid solution of lanthanoid metal ions in the fluorite structure improves ionic conductivity. This can be explained, for example, as follows: The solid solution of lanthanoid metal ions increases the fluoride ion content in the fluorite structure, and fluoride ions are present in interstitial sites. This can be explained by the domino effect of the fluoride ions present in the interstitial sites and the fluoride ions present in the normal sites, causing the fluoride ions to conduct between the lattices through a conduction mechanism known as quasi-lattice diffusion.

[0012] The metal complex fluoride can exhibit higher ionic conductivity by having a crystal structure (hereinafter also referred to as a "specific crystal structure") containing additional ions having an ionic radius larger than that of alkaline earth metal ions in a fluorite structure containing fluoride ions, lanthanoid metal ions, and alkaline earth metal ions as a main phase. This can be considered to be because, for example, the inclusion of additional ions having an ionic radius larger than that of alkaline earth metal ions in the crystal structure increases the lattice constant of the crystal of the metal complex fluoride, thereby facilitating the movement of fluoride ions responsible for ionic conduction within the crystal.

[0013] The metal composite fluoride has a specific crystal structure as a main phase. The content of the specific crystal structure in the crystal phase of the metal composite fluoride may be, for example, 60 mol% or more. The content of the specific crystal structure in the crystal phase of the metal composite fluoride may be preferably 80 mol% or more, or 100 mol%.

[0014] The fact that a metal complex fluoride contains lanthanoid metal ions, alkaline earth metal ions, and additional ions in its composition can be confirmed, including their content ratios, by, for example, subjecting the metal complex fluoride to inductively coupled plasma (ICP) optical emission spectroscopy. Since a fluorite structure is generally an ionic crystal, the detection of lanthanoid metal ions, alkaline earth metal ions, and additional ions by ICP optical emission spectroscopy can be considered to indicate that these ions are present as ions in the crystal structure of the metal complex fluoride.

[0015] In the composition of the metal complex fluoride, the ratio of the number of moles of fluoride ions to the total number of moles of lanthanoid metal ions, alkaline earth metal ions, and adduct ions (hereinafter also referred to as the "total number of moles of cations") may be more than 1.87 and less than 3. The ratio of the number of moles of fluoride ions to the total number of moles of cations in the composition of the metal complex fluoride may preferably be 1.9 or more, or 2 or more, and more preferably greater than 2. It may also preferably be 2.8 or less, or 2.6 or less, and more preferably 2.3 or less, 2.2 or less, or 2.1 or less. When the ratio of the number of moles of fluoride ions is within the above range, ionic conductivity tends to be further improved. Note that the number of moles of fluoride ions contained in the composition of the metal complex fluoride is calculated based on the amount of metal ions quantified by ICP atomic emission spectroscopy, taking into account the valence of each, with the total number of moles of lanthanoid metal ions, alkaline earth metal ions, and adduct ions being 1.

[0016] For example, the lanthanide metal ion La ３＋ , alkaline earth metal ions Ba ２＋ and the adduct ion Cs ＋are detected in a molar ratio of 1:1:1, respectively. In this case, if the total number of moles of lanthanum ions, barium ions, and cesium ions is 1, the detected amounts of lanthanum ions, barium ions, and cesium ions are each 1 / 3 on a molar basis. If the valence of lanthanum ions is 3, the valence of barium ions is 2, and the valence of cesium ions is 1, the number of moles of fluoride ions contained in the composition of the metal complex fluoride is calculated to be (1 / 3) x 3 + (1 / 3) x 2 + (1 / 3) x 1 = 2.

[0017] Examples of lanthanoid metals that provide the lanthanoid metal ions contained in the metal composite fluoride include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), and samarium (Sm). The lanthanoid metal preferably contains at least lanthanum and may further contain cerium, samarium, or the like, and more preferably may contain at least lanthanum. The ratio of the number of moles of lanthanum ions to the total number of moles of lanthanoid metal ions contained in the metal composite fluoride may be, for example, 0.5 or more, preferably 0.7 or more, or 0.9 or more. The upper limit of the ratio of the number of moles of lanthanum ions may be, for example, 1.

[0018] The ratio of the number of moles of lanthanoid metal ions in the composition of the metal composite fluoride to the total number of moles of lanthanoid metal ions, alkaline earth metal ions, and additional ions may be, for example, more than 0 and less than 0.8. The ratio of the number of moles of lanthanoid metal ions may be preferably 0.05 or more, 0.1 or more, 0.2 or more, or 0.28 or more, and may be preferably 0.6 or less, 0.4 or less, 0.34 or less, 0.32 or less, or 0.3 or less. When the ratio of the number of moles of lanthanoid metal ions is within the above range, the main phase of the metal composite fluoride can have a fluorite structure.

[0019] Examples of alkaline earth metals that provide the alkaline earth metal ions contained in the metal complex fluoride include calcium (Ca), strontium (Sr), barium (Ba), etc. The alkaline earth metal preferably contains at least barium, and may further contain strontium, calcium, etc., and more preferably may contain at least barium. The ratio of the number of moles of barium ions to the total number of moles of alkaline earth metal ions contained in the metal complex fluoride may be, for example, 0.5 or more, preferably 0.7 or more, or 0.9 or more. The upper limit of the ratio of the number of moles of barium ions may be, for example, 1.

[0020] The ratio of the number of moles of alkaline earth metal ions in the composition of the metal composite fluoride to the total number of moles of lanthanoid metal ions, alkaline earth metal ions, and additional ions may be, for example, 0.2 or more and less than 1. The ratio of the number of moles of alkaline earth metal ions may be preferably 0.4 or more, or 0.45 or more, and may also be preferably 0.8 or less, 0.6 or less, 0.55 or less, or 0.5 or less. When the ratio of the number of moles of alkaline earth metal ions is within the above range, the main phase of the metal composite fluoride can have a fluorite structure.

[0021] The ratio of the number of moles of lanthanoid metal ions to the number of moles of alkaline earth metal ions in the composition of the metal complex fluoride may be, for example, more than 0 and not more than 4. The ratio of the number of moles of lanthanoid metal ions to the number of moles of alkaline earth metal ions may be preferably not less than 0.1, not less than 0.3, not less than 0.5, or not less than 0.55, and may be preferably not more than 1.5, not more than 1.0, not more than 0.8, or not more than 0.7.

[0022] The additional ions contained in the metal composite fluoride may be solid-dissolved in the crystal structure contained as a main phase of the metal composite fluoride, or may be distributed approximately uniformly throughout the crystal structure contained as a main phase of the metal composite fluoride. Here, the additional ions being solid-dissolved in the crystal structure contained as a main phase of the metal composite fluoride means that some of the cations constituting the crystal structure contained as a main phase of the metal composite fluoride are substituted with the additional ions.

[0023] The adduct ions contained in the metal composite fluoride may be cations having an ionic radius larger than that of the alkaline earth metal ions constituting the fluorite structure contained in the metal composite fluoride. The cations may be inorganic ions such as metal ions or organic cations. Here, for metal ions, the ionic radius of the cations can be values ​​known in the literature. For example, the ionic radius of calcium ions is 0.114 nm to 0.126 nm, the ionic radius of strontium ions is 0.132 nm to 0.140 nm, and the ionic radius of barium ions is 0.149 nm to 0.175 nm. The ionic radius of organic cations can be calculated by simulation calculations such as density functional theory (DFT). For example, the ionic radius of tetramethylammonium ions calculated using this method is approximately 0.18 nm to 0.27 nm.

[0024] Specific examples of the adduct ion include inorganic ions such as cesium (Cs) ions (ionic radius: 0.181 nm to 0.202 nm), rubidium (Rb) ions (ionic radius: 0.166 nm to 0.175 nm), and ammonium ions (ionic radius: 0.175 nm), and organic cations such as methylammonium ions, dimethylammonium ions, trimethylammonium ions, tetramethylammonium ions, ethylammonium ions, diethylammonium ions, triethylammonium ions, and tetraethylammonium ions. The adduct ion may include at least one selected from the group consisting of cesium ions, methylammonium ions, dimethylammonium ions, trimethylammonium ions, tetramethylammonium ions, ethylammonium ions, diethylammonium ions, triethylammonium ions, and tetraethylammonium ions, and preferably includes at least a cesium ion.

[0025] The ratio of the number of moles of cesium ions to the total number of moles of additional ions contained in the metal complex fluoride may be, for example, 0.5 or more, preferably 0.6 or more, 0.8 or more, 0.9 or more, or 0.98 or more. The upper limit of the ratio of the number of moles of cesium ions may be, for example, 1.

[0026] The adduct ion has a larger ionic radius than the alkaline earth metal ion. The ratio of the ionic radius of the adduct ion to the ionic radius of the alkaline earth metal ion may be, for example, greater than 1 and not greater than 3. The ratio of the ionic radius of the adduct ion to the alkaline earth metal ion may preferably be 1.05 or greater, 1.06 or greater, 1.08 or greater, 1.09 or greater, or 1.1 or greater, and may preferably be 2 or less, 1.6 or less, 1.2 or less, or 1.15 or less.

[0027] The ratio of the number of moles of additional ions in the composition of the metal complex fluoride to the total number of moles of lanthanoid metal ions, alkaline earth metal ions, and additional ions may be, for example, more than 0 and less than 0.38. The ratio of the number of moles of additional ions may be preferably 0.05 or more, 0.2 or more, or 0.25 or more, and may be preferably 0.35 or less, 0.3 or less, or 0.28 or less.

[0028] The ratio of the number of moles of additional ions in the composition of the metal complex fluoride to the number of moles of alkaline earth metal ions may be, for example, greater than 0 and less than 1. The ratio of the number of moles of additional ions to the number of moles of alkaline earth metal ions may be preferably 0.1 or more, 0.2 or more, or 0.4 or more, and may also be preferably 0.9 or less, 0.7 or less, 0.6 or less, or 0.5 or less. Furthermore, the ratio of the number of moles of additional ions in the composition of the metal complex fluoride to the number of moles of lanthanoid metal ions may be, for example, greater than 0 and 1.5 or less. The ratio of the number of moles of additional ions to the number of moles of lanthanoid metal ions may be preferably 0.1 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, or 0.7 or more, and may also be preferably 1.2 or less, or 1.0 or less.

[0029] The metal complex fluoride may have a composition represented by the following formula (1): １－ｘ―ｙ M ｘ A ｙ F ｚ (1)

[0030] In formula (1), Ln represents a lanthanoid metal ion, M represents an alkaline earth metal ion, and A represents an adduct ion. x, y, and z may satisfy 0<x<1, 0<y<1, 0<x+y<1, and 1.87<z<3. x and y may preferably satisfy 0.4≦x<1, 0.4<x+y<1, and 0<y<0.38. z may preferably satisfy 2≦z≦2.6. x and y may more preferably satisfy 0.4≦x<0.8, 0.4<x+y<1, and 0.05<y≦0.35. z may preferably satisfy 2<z≦2.3.

[0031] The details of the lanthanoid metal ion, alkaline earth metal ion and additional ion in formula (1) are as described above.

[0032] In X-ray diffraction (XRD) measurement using CuKα radiation, the solid electrolyte material may have peaks at positions such as 2θ=25.3°±1°, 29.3°±1°, 41.9°±1°, and 49.6°±1°. Preferably, at least two of these peaks may be present simultaneously, more preferably at least three of these peaks may be present simultaneously, and even more preferably four of these peaks may be present simultaneously. When the solid electrolyte material has peaks at the above positions, it can be considered that it contains a fluorite structure.

[0033] The volume average particle size of the solid electrolyte material may be, for example, 1 nm or more and 100 μm or less, and preferably 20 nm or more and 10 μm or less. The volume average particle size of the solid electrolyte material is determined as the particle size corresponding to 50% of the cumulative volume from the small diameter side in the volume-based cumulative particle size distribution. The volume-based cumulative particle size distribution is measured, for example, using a laser diffraction particle size distribution analyzer.

[0034] 1. Method for Producing a Solid Electrolyte for a Fluoride Ion Battery A method for producing a solid electrolyte for a fluoride ion battery may include a preparation step of preparing a mixture containing a lanthanoid metal ion source, an alkaline earth metal ion source, and an additional ion source, and a heat treatment step of heat-treating the mixture at a predetermined temperature to obtain a metal composite fluoride. The obtained metal composite fluoride may have, as a main phase, a crystal structure containing additional ions in a fluorite structure containing lanthanoid metal ions, alkaline earth metal ions, and fluoride ions. The additional ions may have a larger ionic radius than the alkaline earth metal ions. At least one of the lanthanoid metal ion source, alkaline earth metal ion source, and additional ion source may contain fluoride ions.

[0035] In the preparation step, a mixture containing a lanthanoid metal ion source, an alkaline earth metal ion source, and an additional ion source is prepared. Details of the lanthanoid metal contained in the lanthanoid metal ion source, the alkaline earth metal contained in the alkaline earth metal ion source, and the additional ions contained in the additional ion source are as described above.

[0036] In one embodiment, the lanthanoid metal ion source may include a lanthanoid metal fluoride, the alkaline earth metal ion source may include an alkaline earth metal fluoride, and the additional ion source may include a fluoride of the additional ion. The content ratio of the lanthanoid metal fluoride, alkaline earth metal fluoride, and fluoride of the additional ion in the mixture may satisfy the relationship 1.87<(3p+2q+nr) / (p+q+r)<3, where pmol is the content of the lanthanoid metal ion contained in the lanthanoid metal fluoride, qmol is the content of the alkaline earth metal ion contained in the alkaline earth metal fluoride, rmol is the content of the additional ion contained in the fluoride of the additional ion, and n is the valence of the additional ion. When the mixture contains the lanthanoid metal fluoride, alkaline earth metal fluoride, and fluoride of the additional ion in such a content ratio, the ratio of the number of moles of fluoride ions in the composition of the obtained metal complex fluoride to the total number of moles of the lanthanoid metal ion, alkaline earth metal ion, and additional ion is more than 1.87 and less than 3. The (3p + 2q + nr) / (p + q + r) may preferably be 1.9 or more, or 2 or more, and more preferably exceed 2. It may also preferably be 2.8 or less, or 2.6 or less, and more preferably 2.3 or less.

[0037] In one embodiment, the mixture may have a composition in which, when the sum of the number of moles of lanthanoid metal ions contained in the lanthanoid metal source, the number of moles of alkaline earth metal ions contained in the alkaline earth metal source, and the number of moles of additional ions contained in the additional ion source is taken as 1, the ratio of the number of moles of fluoride ions contained in the mixture is greater than 1.87 and less than 3. The ratio of the number of moles of fluoride ions in the mixture may preferably be 1.9 or greater, or 2 or greater, and more preferably greater than 2. It may also preferably be 2.8 or less, or 2.6 or less, and more preferably 2.3 or less.

[0038] Examples of the lanthanoid metal ion source contained in the mixture include lanthanoid metal fluorides, lanthanoid metal chlorides, lanthanoid metal hydroxides, and lanthanoid metal oxides. The lanthanoid metal ion source may be a hydrate. The lanthanoid metal ion source may preferably contain at least a lanthanoid metal fluoride. The ratio of the number of moles of lanthanoid metal fluoride to the total number of moles of the lanthanoid metal ion source may be, for example, 0.2 or more, preferably 0.8 or more, based on the number of moles of the lanthanoid metal. The upper limit of the ratio of the number of moles of lanthanoid metal fluoride may be, for example, 1.

[0039] The purity of the lanthanoid metal ion source may be, for example, 50% or more, preferably 80% or more, and the upper limit of the purity of the lanthanoid metal ion source may be, for example, 100%.

[0040] Examples of the alkaline earth metal ion source contained in the mixture include alkaline earth metal fluorides, alkaline earth metal chlorides, alkaline earth metal hydroxides, and alkaline earth metal oxides. The alkaline earth metal ion source may be a hydrate. The alkaline earth metal ion source may preferably contain at least an alkaline earth metal fluoride. The ratio of the number of moles of alkaline earth metal fluoride to the total number of moles of alkaline earth metal ion sources may be, for example, 0.2 or more, preferably 0.8 or more, based on the number of moles of alkaline earth metal. The upper limit of the ratio of the number of moles of alkaline earth metal fluoride may be, for example, 1.

[0041] The purity of the alkaline earth metal ion source may be, for example, 50% or more, preferably 80% or more, and the upper limit of the purity of the alkaline earth metal ion source may be, for example, 100%.

[0042] Examples of the adduct ion source contained in the mixture include fluorides of the adduct ions, chlorides of the adduct ions, hydroxides of the adduct ions, and oxides of the adduct ions. The adduct ion source may be a hydrate. The adduct ion source may preferably contain at least fluorides of the adduct ions. The ratio of the number of moles of fluorides of the adduct ions to the total number of moles of the adduct ion source may be, for example, 0.2 or more, preferably 0.8 or more, based on the number of moles of the adduct ions. The upper limit of the ratio of the number of moles of fluorides of the adduct ions may be, for example, 1.

[0043] The purity of the additional ion source may be, for example, 50% or more, preferably 80% or more, and the upper limit of the purity of the additional ion source may be, for example, 100%.

[0044] Regarding the mixing ratio of the lanthanoid metal ion source, alkaline earth metal ion source, and additional ion source in the mixture, the ratio of the number of moles of lanthanoid metal ions contained in the lanthanoid metal ion source to the total number of moles of lanthanoid metal ions contained in the lanthanoid metal ion source, alkaline earth metal ions contained in the alkaline earth metal ion source, and additional ions contained in the additional ion source (total number of moles of cations) may be, for example, greater than 0 and less than 0.8 moles. The ratio of the number of moles of lanthanoid metal ions to the total number of moles of cations may preferably be 0.05 or greater, or 0.1 or greater, and may preferably be 0.6 or less, or 0.4 or less. The ratio of the number of moles of alkaline earth metal ions to the total number of moles of cations may, for example, be 0.2 or greater but less than 1. The ratio of the number of moles of alkaline earth metal ions to the total number of moles of cations may preferably be 0.4 or greater, or preferably 0.8 or less. The ratio of the number of moles of additional ions to the total number of moles of cations may, for example, be greater than 0 and less than 0.38. The ratio of the number of moles of additional ions to the number of moles of total cations may preferably be 0.05 or more, or 0.2 or more, and may preferably be 0.35 or less, or 0.3 or less.

[0045] The ratio of the content of lanthanoid metal ions to the content of alkaline earth metal ions in the mixture may be, for example, more than 0 and not more than 4. The ratio of the content of lanthanoid metal ions to the content of alkaline earth metal ions may be preferably not less than 0.1, or not less than 0.3, and may be preferably not more than 1.5, or not more than 1.0.

[0046] The mixture can be prepared by weighing the lanthanoid metal ion source, alkaline earth metal ion source, and additional ion source to a desired blending ratio, and then mixing them by a mixing method using a ball mill or the like, or a mixing method using a mixer such as a Henschel mixer or a V-type blender. The mixing may be performed by dry mixing, or by wet mixing with the addition of a solvent or the like. The mixture may be dried. Drying may be performed by, for example, heat drying, vacuum drying, freeze drying, or the like, or a combination of these methods. The heat drying conditions may be, for example, 30°C to 200°C for 0.5 hours to 24 hours.

[0047] The mixture may preferably be a product of mechanical milling of a lanthanoid metal ion source, an alkaline earth metal ion source, and an additional ion source. That is, the mixture may be obtained by mixing the lanthanoid metal ion source, the alkaline earth metal ion source, and the additional ion source by mechanical milling. The mechanical milling may be performed using, for example, a planetary ball mill, a bead mill, a ball mill, a jet mill, or the like. When using a planetary ball mill, the mechanical milling may be performed for 0.5 hours to 48 hours, preferably 5 hours to 24 hours.

[0048] In the heat treatment step, the prepared mixture is heat-treated at a predetermined temperature to obtain a metal composite fluoride. The metal composite fluoride obtained in the heat treatment step may be a solid electrolyte for a fluoride ion battery. The heat treatment temperature in the heat treatment step is, for example, 200°C or higher and 1000°C or lower, preferably 300°C or higher or 400°C or higher, and preferably 700°C or lower or 600°C or lower.

[0049] The heat treatment may include raising the temperature to a predetermined heat treatment temperature, maintaining the heat treatment temperature, and lowering the temperature from the heat treatment temperature. The temperature increase rate to the heat treatment temperature may be, for example, from room temperature, from 1°C / min to 20°C / min, preferably from 5°C / min to 10°C / min. The heat treatment time for maintaining the heat treatment temperature may be, for example, 1 hour or more, preferably from 5 hours to 10 hours. The heat treatment time may be, for example, 48 hours or less, preferably from 20 hours or less, or from 10 hours or less. The temperature decrease rate from the heat treatment temperature to room temperature may be, for example, from 1°C / min to 20°C / min.

[0050] The atmosphere in the heat treatment step may be, for example, an inert gas atmosphere. Examples of inert gases include nitrogen gas and rare gases such as argon. The inert gas atmosphere may have an inert gas content of, for example, 90% by volume or more, preferably 95% by volume or more, or 98% by volume or more, and may be substantially 100% by volume of inert gas. Here, "substantially" means that the presence of gases other than the inert gas that are inevitably mixed in is not excluded. The content of gases other than the inert gas may be, for example, 1% by volume or less.

[0051] The pressure in the atmosphere in the heat treatment step may be, for example, 0 MPa or more and 1 MPa or less in terms of gauge pressure. The heat treatment of the mixture can be carried out using, for example, a tubular furnace, a hearth lifting furnace, or the like.

[0052] The metal composite fluoride obtained by the heat treatment step may have a composition in which the ratio of the number of moles of lanthanoid metal ions to the total number of moles of lanthanoid metal ions, the alkaline earth metal ions, and the additional ions is more than 0 and less than 0.6, the ratio of the number of moles of alkaline earth metal ions is 0.4 or more and less than 1.0, and the ratio of the number of moles of additional ions is more than 0 and less than 0.38.

[0053] Solid Electrolyte Layer The solid electrolyte layer contains at least the solid electrolyte material described above. The solid electrolyte layer can be prepared, for example, by pressure molding the solid electrolyte material. The pressure used in pressure molding can be, for example, 10 MPa or more and 1000 MPa or less.

[0054] The solid electrolyte layer may also contain other components besides the solid electrolyte material as needed. Examples of other components include binders. Examples of binders include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), rubber-based binders such as styrene butadiene rubber (SBR), olefin-based binders such as polypropylene (PP) and polyethylene (PE), and cellulose-based binders such as carboxymethyl cellulose (CMC).

[0055] Fluoride ion battery A fluoride ion battery includes a solid electrolyte layer, a positive electrode, and a negative electrode. The fluoride ion battery may be an all-solid-state battery. The solid electrolyte layer included in the fluoride ion battery has been described above. By including a solid electrolyte layer containing a specific solid electrolyte material and having high ionic conductivity, the battery can function as a fluoride ion battery even at relatively low temperatures.

[0056] The positive electrode constituting the fluoride ion battery may be a positive electrode layer containing at least a positive electrode active material, and may further include a current collector in addition to the positive electrode layer. The positive electrode layer may further include a conductive material, a binder, etc. in addition to the positive electrode active material, as necessary.

[0057] Examples of the positive electrode active material include simple metals, alloys, metal oxides, and fluorides thereof. Examples of metal elements contained in the positive electrode active material include Cu, Ag, Ni, Co, Pb, Ce, Mn, Au, Pt, Rh, V, Os, Ru, Fe, Cr, Bi, Nb, Sb, Ti, Sn, and Zn. Among these, the positive electrode active material includes Cu, CuF ｍ , Fe, FeF ｍ , Ag and AgF ｍIt is preferable that the positive electrode active material contains at least one selected from the group consisting of: wherein m is independently a real number greater than 0. Other examples of the positive electrode active material include carbon materials and fluorides thereof. Examples of carbon materials include graphite, coke, and carbon nanotubes. Still other examples of the positive electrode active material include polymer materials. Examples of polymer materials include polyaniline, polypyrrole, polyacetylene, and polythiophene.

[0058] Examples of conductive materials include carbon materials, such as carbon blacks including acetylene black, ketjen black, furnace black, and thermal black, and examples of binders include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0059] The negative electrode constituting the fluoride ion battery may be a negative electrode layer containing at least a negative electrode active material, and may further include a current collector in addition to the negative electrode layer. The negative electrode layer may further include a conductive material, a binder, etc., in addition to the negative electrode active material, as necessary.

[0060] Any active material having a lower potential than the positive electrode active material can be selected as the negative electrode active material. Therefore, the above-mentioned positive electrode active material may be used as the negative electrode active material. Examples of the negative electrode active material include simple metals, alloys, metal oxides, and fluorides thereof. Examples of metal elements contained in the negative electrode active material include La, Ca, Al, Eu, Li, Si, Ge, Sn, In, V, Cd, Cr, Fe, Zn, Ga, Ti, Nb, Mn, Yb, Zr, Sm, Ce, Mg, and Pb. Among these, the negative electrode active material may include Mg, MgF ｎ , Al, AlF ｎ , Ce, CeF ｎ , Ca, CaF ｎ , Pb and PbF ｎIt is preferable that the negative electrode active material contains at least one selected from the group consisting of: wherein n is independently a real number greater than 0. The negative electrode active material can also be the carbon material and polymer material described above. The conductive material and binder can also be the same materials as those used in the positive electrode layer described above.

[0061] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The compositions of the solid electrolyte materials in each example and comparative example are shown as the results of composition analysis described below.

[0062] Example 1 (Cs ０．０９ Ba ０．５６ La ０．３６ F ２．２７ Synthesis of CsF and BaF ２ and LaF ３ were weighed out so as to have a molar ratio of 1:5.4:3.6. The weighed materials were heated and dried at 120°C for 2 hours, and then pulverized and mixed using a planetary ball mill at 600 rpm for 10 hours to obtain a mixture. The obtained mixture was heat-treated at 600°C for 10 hours in an argon atmosphere to obtain a solid electrolyte material of Example 1 as a metal composite fluoride.

[0063] Example 2 (Cs ０．２２ Ba ０．４８ La ０．３０ F ２．０９ Synthesis of CsF and BaF ２ and LaF ３ A solid electrolyte material of Example 2 was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 2:4.8:3.2.

[0064] Example 3 (Cs ０．２７ Ba ０．４５ La ０．２８ F ２．０１ Synthesis of CsF and BaF ２ and LaF ３ A solid electrolyte material of Example 3 was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 3:4.2:2.8.

[0065] Example 4 (Cs ０．０９ Ba ０．５６ La０．３５ F ２．２７ A solid electrolyte material of Example 4 was obtained in the same manner as in Example 1, except that the temperature of the heat treatment was changed to 400°C.

[0066] Example 5 (Cs ０．２２ Ba ０．４８ La ０．３０ F ２．０９ A solid electrolyte material of Example 5 was obtained in the same manner as in Example 2, except that the temperature of the heat treatment was changed to 400°C.

[0067] Example 6 (Cs ０．２９ Ba ０．４４ La ０．２８ F １．９９ A solid electrolyte material of Example 6 was obtained in the same manner as in Example 3, except that the temperature of the heat treatment was changed to 400°C.

[0068] Comparative Example 1 (Ba ０．６１ La ０．３９ F ２．３７ Synthesis of BaF ２ and LaF ３ A solid electrolyte material of Comparative Example 1 was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 6:4.

[0069] Comparative Example 2 (Ba ０．６１ La ０．３９ F ２．３７ A solid electrolyte material of Comparative Example 2 was obtained in the same manner as in Comparative Example 1, except that the temperature of the heat treatment was changed to 400°C.

[0070] Comparative example 3 (Cs ０．３８ Ba ０．３８ La ０．２４ F １．８７ Synthesis of CsF and BaF ２ and LaF ３ A solid electrolyte material of Comparative Example 3 was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 4:3.6:2.4.

[0071] Comparative example 4 (Cs ０．４７ Ba ０．３３ La ０．２０ F １．７４ Synthesis of CsF and BaF ２ and LaF ３A solid electrolyte material of Comparative Example 4 was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 5:3:2.

[0072] Comparative Example 5 (Sr ０．１２ Ba ０．５４ La ０．３５ F ２．３５ Synthesis of SrF ２ and BaF ２ and LaF ３ A solid electrolyte material of Comparative Example 5 was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 1:5.4:3.6.

[0073] Comparative Example 6 (Sr ０．２２ Ba ０．４７ La ０．３０ F ２．３０ Synthesis of SrF ２ and BaF ２ and LaF ３ A solid electrolyte material of Comparative Example 6 was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 2:4.8:3.2.

[0074] Comparative Example 7 (Sr ０．３３ Ba ０．４１ La ０．２６ F ２．２６ Synthesis of SrF ２ and BaF ２ and LaF ３ A solid electrolyte material of Comparative Example 7 was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 3:4.2:2.8.

[0075] Comparative Example 8 (Y ０．１０ Ba ０．５５ La ０．３５ F ２．４５ Synthesis of YF ３ and BaF ２ and LaF ３ A solid electrolyte material of Comparative Example 8 was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 1:5.4:3.6. The ionic radius of the yttrium ion was 0.104 nm or more and 0.116 nm or less.

[0076] Comparative Example 9 (Y ０．２０ Ba ０．４９ La ０．３１ F ２．５１Synthesis of YF ３ and BaF ２ and LaF ３ A solid electrolyte material of Comparative Example 9 was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 2:4.8:3.2.

[0077] Comparative Example 10 (Y ０．３０ Ba ０．４３ La ０．２７ F ２．５７ Synthesis of YF ３ and BaF ２ and LaF ３ A solid electrolyte material of Comparative Example 10 was obtained in the same manner as in Example 1, except that the components were weighed out so as to have a molar ratio of 3:4.2:2.8.

[0078] Evaluation 1. Composition Analysis The composition of the solid electrolyte material obtained above was determined by inductively coupled plasma (ICP) atomic emission spectroscopy. Specifically, as a pretreatment method, the solid electrolyte material was melted in an alkali, then heated and dissolved in hydrochloric acid, and the composition amount of metal ions was measured using an inductively coupled plasma (ICP) atomic emission spectroscopy analyzer (ICP-AES; Optima 8300: manufactured by Perkin Elmer). The molar ratio of fluoride ions in the composition was determined, with the total composition amount of metal ions being 1.

[0079] 2. Ion Conductivity Measurement A solid electrolyte layer sample was prepared from the solid electrolyte material obtained above as follows: 200 mg of the solid electrolyte material was weighed and pressed at 380 MPa to obtain a solid electrolyte layer sample.

[0080] The obtained solid electrolyte layer sample was measured by an AC impedance method (measurement temperature: 25°C, applied voltage: 500 mV, measurement frequency range: 120 MHz to 20 Hz) using a high frequency impedance measurement system (Keysight Impedance Analyzer Model E4990A), and the ionic conductivity of fluoride ions was calculated from the thickness of the solid electrolyte layer sample and the resistance value on the real axis of the Cole-Cole plot.

[0081] The solid electrolyte material obtained above was packed in an XRD glass folder and subjected to powder XRD measurement using an X-ray diffraction measurement device (Miniflex 600 manufactured by Rigaku Corporation). Specifically, using CuKα radiation (λ = 0.154 nm), the measurement was performed at a scan speed of 10° / min and a step width of 0.02° from 2θ = 20° to 60°.

[0082] The lattice spacing d was calculated from the angle θ of the peak position (111 plane) around 25°, which was the highest intensity in the diffraction pattern, using the Bragg formula (2d sin θ=nλ). Cubic Miller indices d ｈｋｌ = a / √(h ２ +k ２ +l ２ ) was used to calculate the lattice constant a (nm).

[0083]

[0084] In Examples 1 to 3, the lattice constant increased with an increase in the Cs content, resulting in an improvement in the ionic conductivity of fluoride ions. This is thought to be due to the increased crystal size contributing to the ionic conductivity. On the other hand, in Comparative Examples 3 and 4, although the lattice constant increased, the ionic conductivity significantly decreased. This is thought to be due to the fact that the ratio of the number of moles of fluorine ions to the total number of moles of metal ions decreased, resulting in the disappearance of F2 sites (excess fluorine sites), and thus a change in the ionic conduction mechanism. In Comparative Examples 5 to 10, the ionic conductivity also decreased in response to the decrease in the lattice constant.

[0085] The XRD spectra of the solid electrolyte materials obtained above are shown in Figures 1 to 5. The peaks observed in each solid electrolyte material are summarized below.

[0086] It was confirmed that the solid electrolyte material of Example 1 had peaks at 2θ=25.247°, 29.234°, 41.831°, 49.501°, and 51.854°. It was also confirmed that the solid electrolyte material of Example 1 had a fluorite structure because it had peaks at four positions of 2θ=25.3°±1°, 29.3°±1°, 41.9°±1°, and 49.6°±1°.

[0087] It was confirmed that the solid electrolyte material of Example 2 had peaks at 2θ=25.226°, 29.208°, 41.786°, 49.437°, and 51.794°.

[0088] It was confirmed that the solid electrolyte material of Example 3 had peaks at 2θ=25.156°, 29.133°, 41.700°, 49.344°, and 51.191°.

[0089] It was confirmed that the solid electrolyte material of Example 4 had peaks at 2θ=25.230°, 29.215°, 41.818°, 49.483°, and 51.851°.

[0090] It was confirmed that the solid electrolyte material of Example 5 had peaks at 2θ=25.207°, 29.186°, 41.747°, 49.372°, and 51.768°.

[0091] It was confirmed that the solid electrolyte material of Example 6 had peaks at 2θ=25.154°, 29.110°, 41.653°, 49.277°, and 51.666°.

[0092] It was confirmed that the solid electrolyte material of Comparative Example 1 had peaks at 2θ=25.299°, 29.302°, 41.946°, 49.647°, and 52.021°.

[0093] It was confirmed that the solid electrolyte material of Comparative Example 2 had peaks at 2θ=25.327°, 29.294°, 41.982°, 49.683°, and 52.070°.

[0094] It was confirmed that the solid electrolyte material of Comparative Example 3 had peaks at 2θ=25.121°, 29.092°, 41.615°, 49.238°, and 51.574°.

[0095] It was confirmed that the solid electrolyte material of Comparative Example 4 had peaks at 2θ=24.953°, 25.271°, 28.923°, 41.359°, 48.938°, and 51.278°.

[0096] In the solid electrolyte materials of Examples 1 to 3 and Comparative Examples 3 and 4, all peaks are shifted to the lower angle side compared to the solid electrolyte material of Comparative Example 1, and the peaks of CsF at 25.590°, 29.663°, 42.419°, 50.231°, and 52.607° cannot be confirmed. This indicates that Cs is a fluorite-structured Ba ０．６１ La ０．３９ F ２．３７ It can be seen that the solid electrolyte materials of Examples 4 to 6 also have all peaks shifted to lower angles compared to the solid electrolyte material of Comparative Example 2.

[0097] It was confirmed that the solid electrolyte material of Comparative Example 5 had peaks at 2θ=25.421°, 29.445°, 42.166°, 49.907°, and 52.306°.

[0098] It was confirmed that the solid electrolyte material of Comparative Example 6 had peaks at 2θ=25.588°, 29.629°, 42.434°, 50.219°, and 52.634°.

[0099] It was confirmed that the solid electrolyte material of Comparative Example 7 had peaks at 2θ=25.725°, 29.804°, 42.665°, 50.501°, and 52.916°.

[0100] In the solid electrolyte materials of Comparative Examples 5 to 7, all peaks are shifted to the higher angle side compared to the solid electrolyte material of Comparative Example 1. ２Since the peaks at 26.571°, 30.777°, 44.090°, 52.232°, and 54.750°, which are the peaks of the fluorite structure, cannot be confirmed, it is considered that Sr is not a ０．６１ La ０．３９ F ２．３７ It can be seen that it is dissolved in the crystal structure.

[0101] It was confirmed that the solid electrolyte material of Comparative Example 8 had peaks at 2θ=25.510°, 29.530°, 42.298°, 50.074°, and 52.483°.

[0102] It was confirmed that the solid electrolyte material of Comparative Example 9 had peaks at 2θ=27.581°, 29.811°, 42.685°, 50.524°, and 52.970°.

[0103] It was confirmed that the solid electrolyte material of Comparative Example 10 had peaks at 2θ=25.884°, 29.979°, 42.960°, 50.836°, and 53.286°.

[0104] In the solid electrolyte material of Comparative Example 8, all peaks are shifted to the higher angle side compared to the solid electrolyte material of Comparative Example 1. ３ The peaks at 23.963°, 24.537°, 27.809°, 30.925°, 34.779°, 35.994°, 37.189°, 38.546°, 40.958°, 43.849°, 45.553°, 46.924°, 47.528°, 48.982°, 49.41°, 52.212°, 53.344°, 54.935°, 57.872°, and 59.581°, which are the peaks of ０．６１ La ０．３９ F ２．３７ In the solid electrolyte materials of Comparative Examples 9 and 10, the above YF ３ Some peaks can be seen, but the Ba in the fluorite structure ０．６１ La ０．３９ F ２．３７ The peak of γ shifts to the high angle side, which indicates that Y is not completely dissolved in the Ba fluorite structure. ０．６１ La ０．３９ F２．３７ It is thought that it is solid-dissolved in

[0105] The disclosure of Japanese Patent Application No. 2021-196398 (filing date: December 2, 2021) is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. The present invention includes a metal complex fluoride having, as a main phase, a crystal structure containing additional ions in a fluorite structure containing fluoride ions, lanthanoid metal ions, and alkaline earth metal ions, the adduct ion has a larger ionic radius than the alkaline earth metal ion; the metal complex fluoride has a ratio of the number of moles of the fluoride ions to the total number of moles of the lanthanoid metal ions, the alkaline earth metal ions, and the additional ions of more than 1.87 and less than 3; A solid electrolyte material for a fluoride ion battery having a composition in which the ratio of the number of moles of the additional ions to the number of moles of the alkaline earth metal ions is less than 1.

2. The metal complex fluoride has a molar ratio of the lanthanoid metal ion, the alkaline earth metal ion, and the additional ion to the total molar number of the lanthanoid metal ion, the alkaline earth metal ion, and the additional ion, the ratio of the number of moles of the lanthanoid metal ions is greater than 0 and less than 0.6; the ratio of the number of moles of the alkaline earth metal ions is 0.4 or more and less than 1.0, The solid electrolyte material according to claim 1, having a composition in which the ratio of the number of moles of the additional ions is greater than 0 and less than 0.

38.

3. The solid electrolyte material according to claim 1 , wherein the metal composite fluoride has a composition represented by the following formula (1): Ln １－ｘ―ｙ M ｘ A ｙ F ｚ (1) (In formula (1), Ln represents a lanthanoid metal ion, M represents an alkaline earth metal ion, and A represents an adduct ion. x, y, and z satisfy the following conditions: 0<x<1, 0<y<1, 0<x+y<1, and 1.87<z<3.)

4. The solid electrolyte material according to claim 3, wherein x and y in the formula (1) satisfy 0.4≦x<1, 0.4<x+y<1, and 0<y<0.

38.

5. 2. The solid electrolyte material according to claim 1, wherein the lanthanoid metal ions include lanthanum ions.

6. The solid electrolyte material according to claim 1 , wherein the alkaline earth metal ions include barium ions.

7. The solid electrolyte material according to claim 1 , wherein the additional ions include cesium ions.

8. A solid electrolyte layer for a fluoride ion battery containing the solid electrolyte material described in claim 1.

9. A fluoride ion battery comprising the solid electrolyte layer according to claim 8, a positive electrode, and a negative electrode.

10. preparing a mixture containing a lanthanoid metal fluoride, an alkaline earth metal fluoride, and a fluoride of an adduct ion in a content ratio that satisfies 1.87<(3p+2q+nr) / (p+q+r)<3, where pmol is the content of the lanthanoid metal ion contained in the lanthanoid metal fluoride, qmol is the content of the alkaline earth metal ion contained in the alkaline earth metal fluoride, rmol is the content of the adduct ion contained in the fluoride of the adduct ion, and n is the valence of the adduct ion; heat-treating the mixture at a temperature of 200°C or higher and 1000°C or lower to obtain a metal complex fluoride; the adduct ion has a larger ionic radius than the alkaline earth metal ion; The metal composite fluoride has a crystal structure containing additional ions in a fluorite structure as a main phase.

11. 11. The method for producing a solid electrolyte according to claim 10, wherein the mixture has a ratio of the content of the lanthanoid metal ions to the content of the alkaline earth metal ions of more than 0 and not more than 1.

5.

12. 11. The method for producing a solid electrolyte according to claim 10, wherein the mixture has a ratio of the content of the additional ions to the total content of the lanthanoid metal ions, the alkaline earth metal ions, and the additional ions that is greater than 0 and less than 0.

4.

13. 11. The method for producing a solid electrolyte according to claim 10, wherein the mixture is a mechanically milled product of a lanthanoid metal fluoride, an alkaline earth metal fluoride, and a fluoride of an additional ion.

14. The metal complex fluoride has a molar ratio of the lanthanoid metal ion, the alkaline earth metal ion, and the additional ion to the total molar number of the lanthanoid metal ion, the alkaline earth metal ion, and the additional ion, the ratio of the number of moles of the lanthanoid metal ions is greater than 0 and less than 0.6; the ratio of the number of moles of the alkaline earth metal ions is 0.4 or more and less than 1.0, The method for producing a solid electrolyte according to any one of claims 10 to 13, wherein the composition has a ratio of the number of moles of the additional ions that is greater than 0 and less than 0.38.