Electrode active material for fluoride-ion batteries, electrodes for fluoride-ion batteries, and fluoride-ion batteries

Abstract

To provide an electrode active material for a fluorine ion battery.SOLUTION: The present invention relates to an electrode active material including a composite oxide containing a melilite-type crystal structure. The composite oxide may include a first metallic atom including at least one type selected from a first metallic atom group, a second metallic atom including at least one type selected from a second metallic atom group, and a specific non-metallic atom including at least one type selected from a specific non-metallic atom group. The specific non-metallic atom may include O. The first metallic atom group includes Li, Be, Na, Mg, K, Ca, Rb, Sr, Y, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Bi. The second metallic atom group includes Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Hf, Ta, W, Re, Os, Ir, Pt, Au. The specific non-metallic atom group includes O, F, N, S, and Cl.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to an electrode active material for a fluoride ion battery, an electrode for a fluoride ion battery, and a fluoride ion battery.

Background Art

[0002] Lithium ion batteries are known as secondary batteries having a high energy density. As a battery capable of achieving a higher energy density than a lithium ion battery, a fluoride ion battery has been proposed. For example, in Patent Document 1, an active material having a layered perovskite structure and a crystal phase with a specific composition has been proposed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] One aspect of the present disclosure aims to provide an electrode active material for a fluoride ion battery.

Means for Solving the Problems

[0005] The first aspect is an electrode active material for a fluoride ion battery including a composite oxide containing a melilite-type crystal structure. The second aspect is an electrode for a fluoride ion battery including the electrode active material for a fluoride ion battery of the first aspect. The third aspect is a fluoride ion battery including the electrode for a fluoride ion battery of the second aspect and an electrolyte.

Effects of the Invention

[0006] According to one aspect of the present disclosure, an electrode active material for a fluoride ion battery can be provided.

Brief Description of the Drawings

[0007] [Figure 1] This figure shows an example of the X-ray diffraction spectrum of a composite oxide according to the example. [Figure 2] This figure shows an example of a charge / discharge curve for an evaluation battery. [Modes for carrying out the invention]

[0008] In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as their intended purpose is achieved. Furthermore, the content of each component in a composition refers to the total amount of multiple substances present in the composition, unless otherwise specified, when multiple substances corresponding to each component exist in the composition. In addition, the upper and lower limits of the numerical ranges described herein can be arbitrarily selected and combined from the numerical values ​​exemplified as numerical ranges. Embodiments of the present invention will now be described in detail. However, the embodiments shown below are examples of electrode active materials for fluoride-ion batteries, electrodes for fluoride-ion batteries, and fluoride-ion batteries that embody the technical concept of the present invention, and the present invention is not limited to the electrode active materials for fluoride-ion batteries, electrodes for fluoride-ion batteries, and fluoride-ion batteries shown below.

[0009] Electrode active material for fluoride-ion batteries Electrode active materials for fluoride-ion batteries (hereinafter also simply referred to as "electrode active materials") include composite oxides containing a melilite-type crystal structure. Many conventionally known electrode active materials for fluoride-ion batteries are metallic active materials, which function as active materials through the fluorination and defluorination reaction of metals. The fluorination and defluorination reaction of metals is a reaction that involves a large change in crystal structure, resulting in a large volume change. Therefore, resistance tends to be high, and cycle characteristics and rate characteristics tend to be low. On the other hand, compounds with a layered crystal structure exhibit their function as active materials through the insertion and deinsertion of carrier ions into and out of the interlayer space. Since the crystal structure of the active material does not change, the volume change is small, and a reduction in resistance and improvement in cycle characteristics and rate characteristics can be expected. Composite oxides with a melilite-type crystal structure also have a layered structure, so these advantages can be expected.

[0010] Generally, composite oxides containing a melilite-type crystal structure are, for example, M 1 2M 2 It has a theoretical composition represented by 3X7. Here M 1 This represents alkali metals, alkaline earth metals, lanthanides, etc. 2 represents transition metals such as Al, Si, Zn, Ge, etc. X represents O, N, F, S, Cl, etc. In the melilite crystal structure, M 2 - The X4 tetrahedron takes on a two-dimensional network structure, M 1 It forms a layered structure with sites in between. For information on the composition of the melilite-type crystal structure, see, for example, International Publication No. 2019 / 065285. In the melilite-type crystal structure, excellent cycle and rate characteristics are expected due to the two-dimensional diffusion of fluoride ions. Also, M 2 Increased capacity is expected through redox reactions of anions coordinated to the site.

[0011] The composite oxide containing the melilite-type crystal structure according to this disclosure (hereinafter also simply referred to as "composite oxide") may contain in its composition a first metal atom containing at least one selected from a first group of metal atoms, a second metal atom containing at least one selected from a second group of metal atoms, and a specific nonmetal atom containing at least one selected from a specific nonmetal atom group, including at least an oxygen atom. The composition of the composite oxide may contain only one first metal atom, or a combination of two or more first metal atoms. Furthermore, the composition of the composite oxide may contain only one second metal atom, or a combination of two or more second metal atoms. In addition, the composition of the composite oxide may contain only an oxygen atom as the specific nonmetal atom, or a combination of an oxygen atom and other specific nonmetal atoms.

[0012] The first group of metal atoms may consist of at least one metal atom selected from the group consisting of Li, Be, Na, Mg, K, Ca, Rb, Sr, Y, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Bi, etc. The first group of metal atoms may contain at least one metal selected from the group consisting of Ca, Sr, Y, Ba, and La, and may contain at least Sr.

[0013] Furthermore, the first metal atom may contain at least one selected from the group consisting of Ca, Sr, Y, Ba, and La, and may further contain at least one selected from the group consisting of Li, Be, Na, Mg, K, Rb, Y, Cs, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Bi. If the first metal atom contains at least one selected from the group consisting of Ca, Sr, Y, Ba, and La, the total content of Ca, Sr, Y, Ba, and La in the first metal atom may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. The total content of Ca, Sr, Y, Ba, and La in the first metal atom may be, for example, 100 mol% or less, or less than 100 mol%.

[0014] Furthermore, the first metal atom may contain Sr and further contain at least one selected from the group consisting of Li, Be, Na, Mg, K, Ca, Rb, Y, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Bi. If the first metal atom contains Sr, the Sr content in the first metal atom may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. The Sr content in the first metal atom may be, for example, 100 mol% or less, or less than 100 mol%.

[0015] The second group of metal atoms may consist of at least one metal atom selected from the group consisting of Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Hf, Ta, W, Re, Os, Ir, Pt, Au, etc. The second group of metal atoms may contain at least one metal selected from the group consisting of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge, may contain at least one metal selected from the group consisting of Fe and Ge, and may contain at least Fe and Ge.

[0016] Furthermore, the second metal atom may contain at least one selected from the group consisting of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge, and may further contain at least one selected from the group consisting of Sc, Ti, V, Cr, Zn, Ga, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Hf, Ta, W, Re, Os, Ir, Pt, and Au. If the second metal atom contains at least one selected from the group consisting of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge, the total content of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge in the second metal atom may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. The total content of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge in the second metal atom may be, for example, 100 mol% or less, or less than 100 mol%.

[0017] Furthermore, the second metal atom may contain at least one selected from the group consisting of Fe and Ge, and may further contain at least one selected from the group consisting of Al, Si, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Hf, Ta, W, Re, Os, Ir, Pt, and Au. If the second metal atom contains at least one selected from the group consisting of Fe and Ge, the total content of Fe and Ge in the second metal atom may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. The total content of Fe and Ge in the second metal atom may be, for example, 100 mol% or less, or less than 100 mol%.

[0018] The specified nonmetallic atom group may contain at least O, N, F, S, and Cl. The specified nonmetallic atom may contain at least O and at least one other specified nonmetallic atom (e.g., N, F, S, Cl, etc.) selected from the specified nonmetallic atom group. The O content in the specified nonmetallic atom may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more.

[0019] The composition of the composite oxide may have a ratio of the total number of moles of the second metal atom to the total number of moles of the first metal atom, for example, between 1.4 and 1.6, between 1.45 and 1.55, or between 1.55. Furthermore, the composition of the composite oxide may have a ratio of the total number of moles of specific nonmetal atoms to the total number of moles of the first and second metal atoms, for example, between 1.3 and 1.5, between 1.35 and 1.45, or between 1.45. The composition of the composite oxide, when the total number of moles of specific nonmetal atoms is 7, may have a ratio of the total number of moles of the first metal atom greater than 1.9 and less than 2.1, between 1.95 and 2.05, or between 2.05. The composition of the composite oxide, when the total number of moles of specific nonmetal atoms is 7, may have a ratio of the total number of moles of the second metal atom greater than 2.9 and less than 3.1, between 2.95 and 3.05, or between 3.05.

[0020] The composite oxide may have a composition represented by, for example, the following formula (1). M 1b M 2 c X d (1)

[0021] In formula (1), b and c may satisfy, for example, 1.9 < b < 2.1, 2.9 < c < 3.1, 6.8 < d < 7.2, and may satisfy 1.95 ≦ b ≦ 2.05, 2.95 ≦ c ≦ 3.05, 6.9 < d < 7.1.

[0022] M 1 may contain at least one selected from the group consisting of, for example, Li, Be, Na, Mg, K, Ca, Rb, Sr, Y, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Bi. M 1 may contain at least one selected from the group consisting of Ca, Sr, Y, Ba, and La, and may contain at least Sr.

[0023] M 1 contains at least one selected from the group consisting of Ca, Sr, Y, Ba, and La, and may further contain at least one selected from the group consisting of Li, Be, Na, Mg, K, Rb, Y, Cs, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Bi. M 1 When M contains at least one selected from the group consisting of Ca, Sr, Y, Ba, and La, M 1 the total content of Ca, Sr, Y, Ba, and La in may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. M 1 the total content of Ca, Sr, Y, Ba, and La in may be, for example, 100 mol% or less, or less than 100 mol%.

[0024] M 1 contains Sr and may further contain at least one selected from the group consisting of Li, Be, Na, Mg, K, Ca, Rb, Y, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Bi. M 1If it contains Sr, M 1 The Sr content in may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. 1 The Sr content in this product may be, for example, 100 mol% or less, or less than 100 mol%.

[0025] M 2 This may include at least one selected from the group consisting of, for example, Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Hf, Ta, W, Re, Os, Ir, Pt, and Au. 2 It may contain at least one selected from the group consisting of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge, and may contain at least one selected from the group consisting of Fe and Ge, and may contain at least Fe and Ge.

[0026] M 2 It comprises at least one selected from the group consisting of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge, and may further comprise at least one selected from the group consisting of Sc, Ti, V, Cr, Zn, Ga, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Hf, Ta, W, Re, Os, Ir, Pt, and Au. 2 If it includes at least one selected from the group consisting of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge, 2 The total content of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge in the mixture may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. 2 The total content of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge in the mixture may be, for example, 100 mol% or less, or less than 100 mol%.

[0027] M 2It comprises at least one selected from the group consisting of Fe and Ge, and may further comprise at least one selected from the group consisting of Al, Si, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Hf, Ta, W, Re, Os, Ir, Pt, and Au. 2 If it includes at least one selected from the group consisting of Fe and Ge, 2 The total content of Fe and Ge in this may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. 2 The total content of Fe and Ge in this mixture may be, for example, 100 mol% or less, or less than 100 mol%.

[0028] X contains O and may further contain at least one specific nonmetallic atom selected from the group consisting of N, F, S, and Cl. The O content in X may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more.

[0029] The number of moles of oxygen atoms in the composition of a composite oxide is calculated based on the amount of metal ions quantified by ICP emission spectrometry, assuming a total of 5 moles of the first and second metal atoms, and taking into account the valence of each metal. The number of moles of N, F, S, and Cl in the composition of the composite oxide is calculated in the same manner.

[0030] For example, suppose that ICP emission spectroscopy detects the primary metal atom Sr (divalent), and the secondary metal atoms Fe (trivalent) and Ge (tetravalent) in a molar ratio of 2:2:1, respectively. In this case, the detected amounts of strontium ions, iron ions, and germanium ions are 2, 2, and 1, respectively, on a molar basis. Assuming the valency of the strontium ion is 2, the valency of the iron ion is 3, and the valency of the germanium ion is 4, the number of moles of oxygen atoms contained in the composition of the composite oxide can be calculated as (2×2+3×2+1×4) / 2=7.

[0031] The presence of a melilite-type crystal structure in a composite oxide can be confirmed by measuring its X-ray diffraction (XRD) spectrum. Specifically, if the XRD spectrum of an inorganic crystal with a composition corresponding to the composite oxide and shown to have a melilite-type crystal structure in the Inorganic Crystal Structure Database (ICSD) is similar to that of the composite oxide, then the composite oxide can be identified as having a melilite-type crystal structure.

[0032] For example, if a composite oxide has the theoretical composition Sr2Fe2GeO7, the composite oxide can be identified as having a melilite crystal structure if the XRD data of the composite oxide has corresponding peaks for multiple high-intensity peaks (e.g., four) in the XRD data of Sr2CoGe2O7 in ICSD. Specifically, for example, if the 2θ of the XRD data of Sr2Fe2GeO7 is located at 27.44°±2°, 29.60°±2°, 34.80°±2°, and 49.06°±2°, it can be identified as having a melilite crystal structure.

[0033] The shape of the composite oxide can be appropriately selected from, for example, particulate or bulk. The volume-average particle size of the composite oxide may be, for example, 1 nm to 100 μm. The volume-average particle size of the composite oxide may be 20 nm or more, or 10 μm or less. The volume-average particle size of the composite oxide is determined as the particle size corresponding to 50% of the volume accumulation 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] The composite oxide constituting the electrode active material may be a single type or a combination of two or more types. Furthermore, the electrode active material may be either a positive electrode active material or a negative electrode active material, depending on the active material constituting the counter electrode. That is, when constructing a fluoride ion battery, the composite oxide can be used as a positive electrode active material by constructing the counter electrode with an active material having a lower potential than the composite oxide. On the other hand, the composite oxide can be used as a negative electrode active material by constructing the counter electrode with an active material having a higher potential than the composite oxide.

[0035] When an electrode active material is used as the positive electrode active material, any active material having a lower potential than the positive electrode active material can be selected as the negative electrode active material. Examples of negative electrode active materials include elemental metals, alloys, metal oxides, and fluorides thereof. Examples of metal atoms 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, Pb, etc. Among these, Mg and MgF are particularly suitable as negative electrode active materials. x , Al, AlF x , Sn, SnF x Ce, CeF x Ca, CaF x , Pb and PbF x It is preferable to include at least one selected from the group consisting of the following. Note that x is a real number greater than 0. In addition, carbon materials and their fluorides can also be given as a negative electrode active material. Examples of carbon materials include graphite, coke, and carbon nanotubes. Further examples of negative electrode active materials include polymer materials. Examples of polymer materials include polyaniline, polypyrrole, polyacetylene, and polythiophene.

[0036] When an electrode active material is used as the negative electrode active material, any active material having a higher potential than the negative electrode active material can be selected as the positive electrode active material. Examples of positive electrode active materials include elemental metals, alloys, metal oxides, and fluorides thereof. Examples of metal atoms 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, Zn, etc. Among these, Cu and CuF are used as positive electrode active materials. x Fe, FeF x Preferably, the material includes at least one selected from the group consisting of Bi and BiFx, where x is a real number greater than 0. Furthermore, the carbon material and polymer material described above can also be used as the positive electrode active material.

[0037] The content of the composite oxide in the electrode active material may be, for example, 50% by mass or more, 70% by mass or more, or 90% by mass or more relative to the electrode active material. The upper limit of the composite oxide content may be, for example, 100% by mass or less.

[0038] Methods for producing composite oxides can be used for manufacturing ceramic materials. For example, liquid-phase methods such as complex polymerization, hydrothermal synthesis, and coprecipitation, as well as solid-phase methods such as sintering and mechanochemical methods, can be used. Of these, liquid-phase methods can produce composite oxides with high chemical uniformity.

[0039] Complex oxides can also be synthesized, for example, by complex polymerization. This method allows for higher chemical uniformity of the resulting complex oxide compared to the solid-phase method. In this method, first, a metal source containing the metals constituting the complex oxide is weighed out in a manner similar to the stoichiometric ratio of the metals contained in the target complex oxide to obtain a metal source mixture. Next, the metal source mixture is mixed with pure water and citric acid, and ethylene glycol is added as needed to obtain a raw material solution. The raw material solution is heated and concentrated to obtain a powdered precursor. After grinding the precursor as needed, the precursor is heat-treated to obtain the desired complex oxide. For details on complex polymerization, see, for example, International Publication No. 2019 / 065285.

[0040] The metal source used in the production of complex oxides can be appropriately selected from, for example, nitrates, acetates, oxides, etc., containing the desired metal.

[0041] Electrode composition for fluoride ion batteries The electrode composition for fluoride-ion batteries (hereinafter also simply referred to as "electrode composition") contains a composite oxide having a melilite-type crystal structure. The composite oxide may constitute the electrode composition as an electrode active material. Details of the composite oxide are as previously described. The content of the composite oxide in the electrode composition may be, for example, 30% to 99% by mass, 50% to 80% by mass, or 80% by mass, relative to the electrode composition. The electrode composition may contain one type of composite oxide alone, or two or more types in combination.

[0042] In addition to the composite oxide, the electrode composition may further contain at least one other component selected from the group consisting of conductive additives, binders, solid electrolytes, dispersants, and the like.

[0043] Any conductive additive with the desired electronic conductivity can be used, such as carbon materials. Examples of carbon materials include fibrous carbon, acetylene black, Ketjen black, furnace black, thermal black, graphene, fullerene, and carbon nanotubes. Examples of binders include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0044] Examples of solid electrolytes include fluorides of lanthanides such as La and Ce, fluorides of alkali metals such as Li, Na, K, Rb, and Cs, and fluorides of alkaline earth metals such as Ca, Sr, and Ba. Specifically, fluorides of La and Ba (for example, La 0.9 Ba 0.1 F 2.9 Examples include fluorides of Pb and Sn (e.g., PbSnF4).

[0045] If the electrode composition contains other components in addition to the composite oxide, the content of the other components in the electrode composition may be, for example, 1% by mass or more and 80% by mass or less, 20% by mass or more, or 50% by mass or less, relative to the electrode composition.

[0046] The electrode composition can be used to form the electrode active material layer that constitutes the electrode. Depending on the active material that constitutes the counter electrode, the electrode composition may be a positive electrode composition that constitutes the positive electrode active material layer, or a negative electrode composition that constitutes the negative electrode active material layer.

[0047] electrodes for fluoride-ion batteries An electrode for a fluoride-ion battery (hereinafter also simply referred to as "the electrode") includes an electrode composition for a fluoride-ion battery. The electrode may comprise a current collector and an electrode active material layer disposed on the current collector. Examples of materials for the current collector include gold, platinum, stainless steel, aluminum, nickel, iron, titanium, and carbon. The material of the current collector can be appropriately selected according to the potential of the electrode. Examples of shapes for the current collector include foil, mesh, and porous shapes.

[0048] The electrode active material layer placed on the current collector may be composed of the electrode composition described above. The content of the composite oxide in the electrode active material layer may be, for example, 20% by mass or more, 50% by mass or more, 70% by mass or more, or 90% by mass or more, relative to the electrode active material layer. The content of the composite oxide in the electrode active material layer may be, for example, 99% by mass or less.

[0049] The electrode active material layer may further contain, in addition to the composite oxide, at least one selected from the group consisting of conductive additives, binders, solid electrolytes, dispersants, etc. The content of the conductive additive in the electrode active material layer may be, for example, 1% to 20% by mass, 5% to 10% by mass, or 10% by mass or less, relative to the electrode active material layer. The content of the binder in the electrode active material layer may be, for example, 1% to 30% by mass, relative to the electrode active material layer.

[0050] The electrodes for a fluoride battery may be a positive electrode for a fluoride battery having a positive electrode active material layer, or a negative electrode for a fluoride battery having a negative electrode active material layer, depending on the active material constituting the counter electrode active material layer.

[0051] The electrode may be constructed by pressurizing a powdered electrode composition to form an electrode active material layer, and then connecting the electrode active material layer to a current collector. Alternatively, the electrode may be constructed by applying an electrode composition containing a solvent onto a current collector, drying it as needed, and then press-molding it to form an electrode active material layer on the current collector.

[0052] Fluoride ion battery A fluoride-ion battery comprises a fluoride-ion battery electrode, an electrolyte, and a counter electrode. The fluoride-ion battery electrode may be configured as a positive electrode with the counter electrode as the negative electrode, or as a negative electrode with the counter electrode as the positive electrode. A separator may be provided between the positive and negative electrodes of the fluoride-ion battery. A fluoride-ion battery may be a primary battery or a secondary battery, preferably a secondary battery. Note that primary batteries also include secondary batteries used as primary batteries (used for a single discharge after charging). Examples of fluoride-ion battery shapes include coin type, laminate type, cylindrical type, and prismatic type.

[0053] The electrodes for a fluoride-ion battery are as previously described. The electrolyte is placed between the electrodes for the fluoride-ion battery and the counter electrode. The electrolyte may be a liquid electrolyte (electrolyte solution) or a solid electrolyte.

[0054] The electrolyte may be, for example, a non-aqueous electrolyte containing a fluoride salt and an organic solvent. Examples of fluoride salts include inorganic fluoride salts, organic fluoride salts, and ionic liquids. An example of an inorganic fluoride salt is XF, where X may contain at least one alkali metal selected from the group consisting of Li, Na, K, Rb, and Cs. Examples of cations of organic fluoride salts include alkylammonium cations such as tetramethylammonium cations. The concentration of the fluoride salt in the electrolyte may be, for example, 0.1 mol% to 40 mol%, 1 mol% or more, or 10 mol% or less.

[0055] The organic solvent constituting the electrolyte can be any solvent that dissolves fluoride salts. Examples of organic solvents include glyces such as triethylene glycol dimethyl ether (G3) and tetraethylene glycol dimethyl ether (G4), cyclic carbonates such as ethylene carbonate (EC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), propylene carbonate (PC), and butylene carbonate (BC), and linear carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Ionic liquids may also be used as organic solvents.

[0056] Examples of solid electrolytes include fluorides of lanthanides such as La and Ce, fluorides of alkali metals such as Li, Na, K, Rb, and Cs, and fluorides of alkaline earth metals such as Ca, Sr, and Ba. Specifically, fluorides of La and Ba (for example, La 0.9 Ba 0.1 F 2.9 Examples include fluorides of Pb and Sn (e.g., PbSnF4).

[0057] The counter electrode may comprise a current collector and an electrode active material layer placed on the current collector. The material of the current collector may be appropriately selected according to the potential of the counter electrode. For example, when the counter electrode is used as a negative electrode, the material of the current collector can be gold, platinum, stainless steel, copper, nickel, carbon, etc. The shape of the current collector can be foil-shaped, mesh-shaped, porous, etc.

[0058] When a fluoride ion battery is constructed using an electrode for fluoride ion batteries as the positive electrode, the negative electrode active material constituting the negative electrode active material layer of the counter electrode (the negative electrode) may be any active material having a lower potential than the composite oxide that is the positive electrode active material. Specific examples of negative electrode active materials are as previously described. The content of the negative electrode active material in the negative electrode active material layer may be, for example, 30% by mass or more, 50% by mass or more, 70% by mass or more, or 90% by mass or more relative to the negative electrode active material layer. The upper limit of the content of the negative electrode active material in the negative electrode active material layer may be, for example, 99% by mass or less.

[0059] When a fluoride ion battery is constructed using an electrode for fluoride ion batteries as the negative electrode, the positive electrode active material constituting the positive electrode active material layer of the counter electrode, which serves as the positive electrode, should be an active material having a higher potential than the composite oxide that serves as the negative electrode active material. Specific examples of positive electrode active materials are as previously described. The content of the positive electrode active material in the positive electrode active material layer may be, for example, 30% by mass or more, 50% by mass or more, 70% by mass or more, or 90% by mass or more relative to the positive electrode active material layer. The content of the positive electrode active material in the positive electrode active material layer may be, for example, 99% by mass or less.

[0060] The counter electrode active material layer may further contain, in addition to the electrode active material, at least one selected from the group consisting of conductive additives, binders, solid electrolytes, dispersants, etc. The content of the conductive additive in the counter electrode active material layer may be, for example, 1% by mass or more and 20% by mass or less, 5% by mass or more, or 10% by mass or less, relative to the electrode active material layer. The content of the binder in the electrode active material layer may be, for example, 1% by mass or more and 30% by mass or less, relative to the electrode active material layer.

[0061] The inventions described herein may encompass, for example, the following embodiments: [1] Electrode active material for fluoride-ion batteries containing a composite oxide with a melilite-type crystal structure.

[0062] [2] The composite oxide comprises a first metal atom including at least one selected from the following first group of metal atoms, a second metal atom including at least one selected from the following second group of metal atoms, and a specific nonmetal atom including at least one selected from the following specific nonmetal atom group, wherein the specific nonmetal atom comprises at least an oxygen atom, as described in [1]. First metal atomic group: Li, Be, Na, Mg, K, Ca, Rb, Sr, Y, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Bi. Second metal atomic group: Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Hf, Ta, W, Re, Os, Ir, Pt, Au. Specific nonmetallic atomic groups: O, F, N, S, Cl.

[0063] [3] The composite oxide has a composition in which the ratio of the total number of moles of the second metal atoms to the total number of moles of the first metal atoms is 1.4 or more and 1.6 or less, and the ratio of the total number of moles of the specified nonmetal atoms to the total number of moles of the first metal atoms and the second metal atoms is 1.3 or more and 1.5 or less. [2] Electrode active material for fluoride ion battery.

[0064] [4] The composite oxide comprises at least one selected from the group consisting of Ca, Sr, Y, Ba and La as the first metal atom, according to either [2] or [3].

[0065] [5] The composite oxide comprises at least one selected from the group consisting of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge as the second metal atom, according to any one of [2] to [4].

[0066] [6] The composite oxide comprises at least Sr as the first metal atom, according to any one of [2] to [5], an electrode active material for a fluoride ion battery.

[0067] [7] The composite oxide is the electrode active material for a fluoride ion battery according to any one of [2] to [6], including at least one selected from the group consisting of Fe and Ge as the second metal atom.

[0068] [8] The composite oxide is the electrode active material for a fluoride ion battery according to any one of [1] to [7], having a volume average particle diameter of 20 nm or more and 10 μm or less.

[0069] [9] The composite oxide is the electrode active material for a fluoride ion battery according to [1], having a composition represented by the following formula (1). M 1 b M 2 c X d (1) (In formula (1), 1.9 < b < 2.1, 2.9 < c < 3.1, 6.8 < d < 7.2 are satisfied, M 1 includes at least one selected from the group consisting of Li, Be, Na, Mg, K, Ca, Rb, Sr, Y, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Bi, and M 2 includes at least one selected from the group consisting of Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Hf, Ta, W, Re, Os, Ir, Pt, and Au, X includes O, and may further include at least one selected from the group consisting of N, F, S, and Cl.)

[0070]

[10] In the formula (1), the M 1 includes at least one selected from the group consisting of Ca, Sr, Y, Ba, and La, which is the electrode active material for a fluoride ion battery according to [9].

[0071]

[11] In the formula (1), the M 2The electrode active material for a fluoride ion battery according to [9] or

[10] , comprising at least one selected from the group consisting of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge.

[0072]

[12] In formula (1) above, M 1 The electrode active material for fluoride-ion batteries according to any one of [9] to

[11] , comprising at least Sr.

[0073]

[13] In formula (1) above, M 2 The electrode active material for a fluoride ion battery according to any one of [9] to

[12] , comprising at least one selected from the group consisting of Fe and Ge.

[0074]

[14] The composite oxide is an electrode active material for a fluoride ion battery according to any one of [9] to

[13] , wherein the volume average particle size is 20 nm or more and 10 μm or less.

[0075] Electrode for a fluoride-ion battery comprising the electrode active material for fluoride-ion batteries described in any of

[15] , [1] to

[14] .

[0076] A fluoride-ion battery comprising electrodes for fluoride-ion batteries and an electrolyte as described in

[16]

[15] . [Examples]

[0077] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0078] Example 1 Synthesis of complex oxides Sr(NO3)2 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), Fe(NO3)2·9H2O (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and GeO2 (manufactured by Kojunsei Chemical Laboratory Co., Ltd.) were weighed in a molar ratio of 2:2:1. Pure water, citric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in an amount equal to 5 molars of the total cations, and ethylene glycol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in an amount equal to the total cations were added and stirred until homogeneous to obtain the raw material solution. The raw material solution was left to stand in a constant temperature bath set to 150°C and heated to concentrate a powdered precursor. The obtained precursor was pulverized and heat-treated in a box furnace at 1000°C in air for 10 hours to obtain a composite oxide.

[0079] Composition analysis The composition of the composite oxide obtained above was determined by inductively coupled plasma (ICP) emission spectroscopy. Specifically, after alkali melting as a pretreatment, the oxide was heated and dissolved in hydrochloric acid, and the amount of metal ions was measured using an inductively coupled plasma (ICP) emission spectrometer (ICP-AES; Optima8300: Perkin Elmer). The molar ratio of oxygen atoms in the composition was determined by setting the total amount of metal ions to 5. The obtained composite oxide was Sr 2.00 Fe 2.04 Ge 0.96 O 6.98 It had a composition represented by [formula].

[0080] Preparation of solid electrolytes BaF2 (manufactured by Kojun Chemical Laboratory Co., Ltd.) and LaF3 (manufactured by Kojun Chemical Laboratory Co., Ltd.) were weighed in a molar ratio of 1:9. The weighed materials were heated and dried at 120°C for 2 hours, and then ground 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 under an argon atmosphere, and LaF3 was added. 0.9 Ba 0.1 F 2.9 A solid electrolyte having the composition represented by was obtained.

[0081] Preparation of cathode composition 150 mg of the composite oxide obtained above as the electrode active material, 300 mg of the solid electrolyte obtained above, and VGCF as the conductive additive. (R) -50 mg of H (manufactured by Showa Denko) was prepared and mixed in a mortar for 15 minutes. 15 g of zirconia (ZrO2) balls (Φ3 mm) were added as a mixing medium, and the mixture was homogenized to obtain the cathode composition. This entire process was carried out in a glove box under an argon atmosphere.

[0082] Preparation of negative electrode composition 150 mg of SnF2 (Sigma-Aldrich) as the negative electrode active material, 300 mg of the solid electrolyte obtained above, and VGCF as a conductive additive. (R) -50 mg of H was prepared and mixed in a mortar for 15 minutes. 15 g of ZrO2 balls (Φ3 mm) were added as a mixing medium and mixed in a homogenizer to obtain the negative electrode composition. This entire process was carried out in a glove box under an argon atmosphere.

[0083] Fabrication of evaluation batteries The positive electrode composition (10 mg), solid electrolyte (175 mg), and negative electrode composition (50 mg) obtained above were layered in this order and compacted. Gold foil was attached to both ends as current collectors to fabricate an evaluation battery. This entire process was carried out in a glove box under an argon atmosphere.

[0084] [evaluation] XRD measurement The composite oxide (Sr) obtained above 2.00 Fe 2.04 Ge 0.96 O 6.98 The sample was packed into an XRD glass folder, and powder XRD measurements were performed using an X-ray diffraction analyzer (Miniflex600, Rigaku). Specifically, measurements were performed using CuKα rays (λ=0.154nm) from 2θ=20° to 80° with a scan speed of 10° / min and a step size of 0.02°. The results are shown in Figure 1. The lower panel shows the XRD spectrum of a melilite-type composite oxide with a composition represented by Sr2CoGe2O7 as a standard sample.

[0085] In the XRD spectra of the composite oxides obtained above, four high-intensity peaks were observed at 2θ = 27.44°, 29.60°, 34.80°, and 49.08°.

[0086] The observation of peaks corresponding to four peaks in the ICSD XRD data at 2θ = 27.44°±2°, 29.60°±2°, 34.80°±2°, and 49.06°±2° indicates that the composite oxide obtained above has a melilite-type crystal structure.

[0087] Charge / Discharge Test A constant current charge-discharge test was performed on the evaluation battery obtained in Example 1. The charge-discharge test was conducted at 140°C with a current of 6.7 mA / g and charge / discharge termination potentials of -1.5 V and 2.5 V (vs. Sn / SnF2), performing 11 charge-discharge cycles. The charge-discharge curve after the 11th cycle is shown in Figure 2.

[0088] In the charging curve, a first plateau region was observed around -1.0 to 0.5V (vs.Sn / SnF2), and a second plateau region was observed around 1.5 to 2.0V (vs.Sn / SnF2). The theoretical capacity of Sr2Fe2GeO7 is 56.9mAh / g per electron. Since the capacity obtained in the first plateau region corresponds to a two-electron reaction, Fe 3+ / Fe 4+ It is thought that charge compensation is being performed in this reaction. In the second plateau region, a capacity exceeding the number of reaction electrons due to the redox of the metal atoms is observed, suggesting that charge compensation is being performed by oxygen redox.

Claims

1. Electrode active material for fluoride-ion batteries containing a composite oxide with a melilite-type crystal structure.

2. The composite oxide comprises a first metal atom comprising at least one selected from the following first group of metal atoms, a second metal atom comprising at least one selected from the following second group of metal atoms, and a specific nonmetal atom comprising at least one selected from the following specific nonmetal atom group, wherein the specific nonmetal atom comprises at least an oxygen atom, as described in claim 1. Group 1 of metal atoms: Li, Be, Na, Mg, K, Ca, Rb, Sr, Y, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Bi. Second metal atomic group: Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Hf, Ta, W, Re, Os, Ir, Pt, Au. Specific nonmetallic atomic groups: O, F, N, S, Cl.

3. The electrode active material for a fluoride ion battery according to claim 2, wherein the composite oxide has a composition in which the ratio of the total number of moles of the second metal atoms to the total number of moles of the first metal atoms is 1.4 or more and 1.6 or less, and the ratio of the total number of moles of the specified nonmetal atoms to the total number of moles of the first metal atoms and the second metal atoms is 1.3 or more and 1.5 or less.

4. The electrode active material for a fluoride ion battery according to claim 2 or claim 3, wherein the composite oxide comprises at least one selected from the group consisting of Ca, Sr, Y, Ba, and La as the first metal atom.

5. The electrode active material for a fluoride ion battery according to claim 2 or claim 3, wherein the composite oxide comprises at least one selected from the group consisting of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge as the second metal atom.

6. The electrode active material for a fluoride ion battery according to claim 2 or claim 3, wherein the composite oxide comprises at least Sr as the first metal atom.

7. The electrode active material for a fluoride ion battery according to claim 2 or claim 3, wherein the composite oxide comprises at least one selected from the group consisting of Fe and Ge as the second metal atom.

8. The electrode active material for a fluoride ion battery according to claim 7, wherein the composite oxide has a volume-average particle size of 20 nm or more and 10 μm or less.

9. The electrode active material for a fluoride ion battery according to claim 1, wherein the composite oxide has a composition represented by the following formula (1). M １ ｂ M ２ ｃ X ｄ (1) (In equation (1), 1.9 < b < 2.1, 2.9 < c < 3.1, and 6.8 < d < 7.2 are satisfied, M １ It includes at least one selected from the group consisting of Li, Be, Na, Mg, K, Ca, Rb, Sr, Y, Cs, Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Bi, M ２ X includes at least one element selected from the group consisting of Al, Si, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Sn, Hf, Ta, W, Re, Os, Ir, Pt, and Au, and X includes O and may further include at least one element selected from the group consisting of N, F, S, and Cl.

10. In formula (1) above, M １ The electrode active material for a fluoride ion battery according to claim 9, comprising at least one selected from the group consisting of Ca, Sr, Y, Ba, and La.

11. In the above formula (1), the M ２ The electrode active material for a fluoride ion battery according to claim 9, comprising at least one selected from the group consisting of Al, Si, Mn, Fe, Co, Ni, Cu, and Ge.

12. In formula (1) above, M １ The electrode active material for a fluoride ion battery according to claim 9, comprising at least Sr.

13. In formula (1) above, M ２ The electrode active material for a fluoride ion battery according to claim 9, comprising at least one selected from the group consisting of Fe and Ge.

14. The electrode active material for a fluoride ion battery according to claim 13, wherein the composite oxide has a volume-average particle size of 20 nm or more and 10 μm or less.

15. An electrode for a fluoride-ion battery comprising the electrode active material for a fluoride-ion battery described in any one of claims 1 to 3 and claims 9 to 14.

16. A fluoride-ion battery comprising an electrode for a fluoride-ion battery and an electrolyte as described in claim 15.

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