Positive electrode active material for fluoride ion batteries, fluoride ion batteries, and methods for manufacturing the same.

Abstract

To provide a positive electrode active material for fluoride-ion batteries that enables low-temperature operation and has excellent cycle characteristics. [Solution] A positive electrode active material for a fluoride ion battery, which is an alloy containing an intermetallic compound of a first metal, Sn, and a second metal, which is Co, Cu, Ni, Fe, Sb, or a combination thereof.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a fluoride ion battery, a fluoride ion battery, and methods for manufacturing them.

Background Art

[0002] Fluoride ion batteries can be expected to have a high energy density and theoretically have a mass energy density more than five times that of current lithium ion batteries. In addition, fluoride ion batteries can use a non-flammable solid electrolyte and can be expected to have high safety. For these reasons, research and development towards practical application have been carried out (Non-Patent Documents 1 to 4). If fluoride ion batteries are put into practical use, further development in the fields of mobile devices, electric vehicles, renewable energy, etc. is expected.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Non-Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] Fluoride-ion batteries operate at relatively high temperatures, and while there is active development of solid electrolytes for lower-temperature operation, the development of active materials remains insufficient, posing a significant challenge. Conventional cathode active materials using pure metals have low ionic conductivity, making low-temperature operation difficult. Furthermore, irreversible structural changes that occur during charge-discharge reactions lead to severe cycle degradation. Therefore, the development of novel cathode active materials that balance ionic conductivity and cycle characteristics is an urgent task. [Means for solving the problem]

[0005] The gist of this invention is as follows: (1) A positive electrode active material for a fluoride ion battery, which is an alloy containing an intermetallic compound of a first metal, Sn, and a second metal, Co, Cu, Ni, Fe, Sb, or a combination thereof. (2) The positive electrode active material according to (1) above, wherein the alloy includes a network of fluorides of the Sn, a network of fluorides of the second metal, or a network of a combination thereof. (3) The positive electrode active material according to (1) or (2) above, wherein the molar ratio of Sn contained in the alloy is 40% or more. (4) The positive electrode active material according to any one of (1) to (3) above, wherein the intermetallic compound includes an intermetallic compound of Sn and Co, an intermetallic compound of Sn and Cu, or a combination thereof. (5) The positive electrode active material according to any one of (1) to (4) above, wherein the intermetallic compound includes CoSn2, CoSn, Cu6Sn5, or a combination thereof. (6) A positive electrode active material for a fluoride-ion battery, which is an alloy comprising a network of fluorides of a first metal, Sn, and a network of fluorides of a second metal, Co, Cu, Ni, Fe, Sb, or a combination thereof. (7) A fluoride ion battery containing the positive electrode active material described in any of (1) to (6) above. (8) A fluoride ion battery comprising a negative electrode current collector, a negative electrode layer, a fluorine-based electrolyte layer, a positive electrode layer containing the positive electrode active material according to any one of (1) to (6) above, and a positive electrode current collector, wherein the negative electrode layer contains a Pb-Zr-F ternary solid solution as a negative electrode active material. (9) The Pb-Zr-F ternary solid solution is Pb 1-x Zr x F 2+2x (0 < x ≦ 0.18), the fluoride ion battery according to (8) above. (10) A method for producing a positive electrode active material for a fluoride ion battery, comprising melting a first metal Sn and a second metal of Co, Cu, Ni, Fe, Sb, or a combination thereof to form an alloy containing an intermetallic compound of the Sn and the second metal. (11) The method according to (10) above, comprising subjecting the alloy to a fluorination treatment to decompose at least a part of the intermetallic compound to generate a network of Sn fluoride, a network of the second metal fluoride, or a combination thereof. (12) The method according to (10) or (11) above, wherein the melting treatment comprises melting a mixture of the Sn and the second metal containing the Sn in a molar ratio of 40% or more with respect to the total of the Sn and the second metal. (13) The method according to any one of (10) to (12) above, wherein the intermetallic compound contains an intermetallic compound of Sn and Co, an intermetallic compound of Sn and Cu, or a combination thereof. (14) The method according to any one of (10) to (13) above, wherein the intermetallic compound contains CoSn2, CoSn, Cu6Sn5, or a combination thereof. (15) A method for producing a fluoride ion battery, comprising obtaining a laminate including a negative electrode current collector, a negative electrode layer, a fluorine-based electrolyte layer, a positive electrode layer containing the positive electrode active material obtained by the production method according to any one of (10) to (14) above, and a positive electrode current collector. (16) The method for producing a fluoride ion battery according to (15) above, wherein the negative electrode layer contains a Pb-Zr-F ternary solid solution as a negative electrode active material. (17) The Pb-Zr-F ternary solid solution is Pb 1-x Zr x F 2+2x The method for manufacturing a fluoride ion battery according to (16) above, where (0 < x ≤ 0.18).

Advantages of the Invention

[0006] According to the present invention, it is possible to provide a positive electrode active material for a fluoride ion battery that enables low-temperature operation and has excellent cycle characteristics.

Brief Description of the Drawings

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view of the structure of an intermetallic compound contained in the positive electrode active material of the present disclosure during (A) the initial charging process, (B) the regenerated state, and (C) the re-crystallization. [Figure 2] FIG. 2 is a schematic cross-sectional view of a all-solid-state fluoride ion battery 100 including a fabricated negative electrode current collector 70, a negative electrode layer 50, a fluorine-based solid electrolyte layer 40, a positive electrode layer 30, and a positive electrode current collector 60. [Figure 3] FIG. 3 is a graph of (A) charge-discharge curves and (B) cycle characteristics measured at a temperature of 140°C and a current density of 20 mA / g for the all-solid-state fluoride ion batteries fabricated in Examples 1 and 2. [Figure 4] FIG. 4 is a graph of cycle characteristics measured at a temperature of 140°C for the all-solid-state fluoride ion battery fabricated in Example 1 while increasing the current density from 20 mA / g to 10000 mA / g. [Figure 5] FIG. 33 is a graph of charge-discharge curves of the 5th cycle measured at 140°C, 80°C, 60°C, and 40°C at a current density of 20 mA / g for the all-solid-state fluoride ion battery fabricated in Example 1. [Figure 6] FIG. 6 is a graph of cycle characteristics at 140°C and 60°C for the all-solid-state fluoride ion battery fabricated in Example 1. [Figure 7] FIG. 7 is a graph explaining the structural changes of the positive electrode active material CoSn2 during the charge-discharge process of the all-solid-state fluoride ion battery fabricated in Example 1. [Figure 8] Figure 8 is a schematic diagram of the charge-discharge mechanism of CoSn2. [Figure 9] Figure 9 shows the results of scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) analysis of the charge state (0.5V) of CoSn2. [Figure 10] Figure 10 shows the STEM-EELS analysis results for the discharge state (-1.5V) of CoSn2 after one charge-discharge cycle. [Figure 11] Figure 11 is a graph of the cycle characteristics of the all-solid-state fluoride-ion battery fabricated in Example 3, measured at a temperature of 140°C while increasing the current density from 20 mA / g to 5000 mA / g. [Figure 12] Figure 12 is a graph of the cycle characteristics of the all-solid-state fluoride-ion battery fabricated in Example 3, measured at a temperature of 60°C and a current density of 20 mA / g. [Figure 13] Figure 13 shows the charge-discharge curves of the all-solid-state fluoride-ion batteries prepared in Example 3 and Example 4, measured at a temperature of 60°C and a current density of 20 mA / g. [Figure 14] Figure 14 is a graph comparing the cycle characteristics of the all-solid-state fluoride ion batteries prepared in Example 3 and Example 4. [Modes for carrying out the invention]

[0008] This disclosure relates to a positive electrode active material for fluoride-ion batteries, which is an alloy containing an intermetallic compound of a first metal, Sn, and a second metal, which is Co, Cu, Ni, Fe, Sb, or a combination thereof. The positive electrode active material of this disclosure enables the realization of a fluoride-ion battery that can operate at a lower temperature than conventional batteries, has excellent cycle characteristics, and a long lifespan.

[0009] The positive electrode active material of this disclosure is an alloy containing an intermetallic compound of Sn, which exhibits excellent ionic conductivity when fluorinated, and an element that exhibits high capacity due to multi-electron reactions during fluorination and defluorination. The positive electrode active material of this disclosure can achieve both low-temperature operation and high cycle characteristics in fluoride ion batteries. Furthermore, the positive electrode active material of this disclosure can be easily manufactured by melting alone.

[0010] A fluoride-ion battery containing the positive electrode active material of this disclosure in the positive electrode is preferably operable at a low temperature of 140°C or lower, more preferably 80°C or lower, and even more preferably 60°C or lower. The lower limit of the operating temperature of a fluoride-ion battery containing the positive electrode active material of this disclosure in the positive electrode is not particularly limited, but may be, for example, 50°C or higher or 55°C or higher.

[0011] A fluoride-ion battery containing the positive electrode active material of this disclosure in the positive electrode is preferably capable of operating for 40 cycles or more, more preferably 250 cycles or more, and even more preferably 1000 cycles or more.

[0012] "Operable" means that a fluoride-ion battery containing the positive electrode active material of this disclosure in its positive electrode exhibits a discharge capacity of greater than 0 mAh / g, preferably 50 mAh / g or more, more preferably 100 mAh / g or more, even more preferably 150 mAh / g or more, and even more preferably 200 mAh / g or more. The discharge capacity expressed in units of mAh / g is the discharge capacity per unit mass of the positive electrode active material (amount charged).

[0013] A fluoride-ion battery containing the positive electrode active material of this disclosure in the positive electrode can produce a fluoride-ion battery exhibiting a discharge capacity of 400 mAh / g or more, 450 mAh / g or more, 500 mAh / g or more, or 550 mAh / g or more at a low temperature of 140°C. Furthermore, a fluoride-ion battery containing the positive electrode active material of this disclosure in the positive electrode can produce a fluoride-ion battery exhibiting a discharge capacity of 200 mAh / g or more, 210 mAh / g, 220 mAh / g or more, or 230 mAh / g or more at a low temperature of 60°C.

[0014] A fluoride-ion battery containing the positive electrode active material of this disclosure in the positive electrode preferably exhibits a capacity retention rate of 80% or more, more preferably 90% or more, after 1000 cycles at 140°C. A fluoride-ion battery containing the positive electrode active material of this disclosure in the positive electrode preferably exhibits a capacity retention rate of 80% or more, more preferably 90% or more, after 250 cycles at 60°C. The capacity retention rate is the ratio of the discharge capacity based on the discharge capacity in the cycle that showed the maximum discharge capacity.

[0015] Sn can exhibit excellent ionic conductivity when fluorinated. Therefore, by using intermetallic compounds containing Sn as positive electrode active materials for fluoride-ion batteries, it is possible to operate fluoride-ion batteries at lower temperatures than conventional batteries. Elements that exhibit high ionic conductivity when fluorinated include Sn and the elements listed in Table 1. Among these, Sn / SnF2 has the highest oxidation-reduction potential and an ionic conductivity of 10 at 60°C when fluorinated. -5 It has excellent S / cm.

[0016] [Table 1]

[0017] Sn-based alloys exhibit excellent fluoride ion conductivity, enabling the creation of fluoride ion batteries that can operate even at low temperatures. By using an alloy containing an intermetallic compound of Sn and a second metal (described later) as the positive electrode active material for a fluoride ion battery, a fluoride ion battery exhibiting excellent discharge capacity at low temperatures can be obtained. The intermetallic compound can be obtained from Sn and the second metal by dissolution treatment.

[0018] The second metal that forms an intermetallic compound with Sn is Co, Cu, Ni, Fe, Sb, or a combination of these. At 140°C, the theoretical capacities are 694 mAh / g for CoF3, 528 mAh / g for CuF2, 554 mAh / g for NiF2, 713 mAh / g for FeF3, and 450 mAh / g for SbF3. As shown in Table 2, the second metal has a higher redox potential than Sn, and by using the intermetallic compound of Sn and the second metal as the positive electrode of a fluoride ion battery, it is possible to discharge at a high potential and obtain a high energy density.

[0019] [Table 2]

[0020] Although not bound by theory, since the redox potential of Sn is lower than that of the second metal, when an alloy containing an intermetallic compound of Sn and the second metal is fluorinated, Sn is fluorinated before the second metal, making it easier to form ion conduction paths within the positive electrode active material. This is thought to allow for better formation of ion conduction paths.

[0021] The second metal can exhibit high capacity through multi-electron reactions such as two-electron and three-electron reactions during fluoridation and defluoridation. For example, as shown in Table 2, Fe becomes FeF3 through fluoridation, and can therefore exhibit high capacity through the multi-electron reaction of formula (1). [ka] As shown in equation (1), Fe can be obtained in high volume by using a conversion reaction in which the structure changes when FeF3 is converted to Fe. The same multi-electron reaction and conversion reaction can be applied to Co, Cu, Ni, and Sb.

[0022] The second metal is preferably Co, Cu, Ni, Fe, or a combination thereof. Of the second metals, Co, Cu, Ni, and Fe have relatively small atomic numbers and can provide a higher discharge capacity per unit mass.

[0023] Preferably, the alloy includes a network of fluorides of the Sn, a network of fluorides of the second metal, or a network of a combination thereof.

[0024] In the initial stages of the first charge (first charge) of a fluoride-ion battery containing the positive electrode active material of this disclosure, the intermetallic compound of the positive electrode active material decomposes into microcrystals of Sn fluoride and microcrystals of a second metal. As a result, in the initial stages of the first charge, the Sn in the positive electrode active material fluorides, forming a nanoscale network of Sn fluoride and a nanoscale network of the second metal. The formation of a nanoscale network of Sn fluoride in the positive electrode active material improves ionic conductivity and enables low-temperature operation. The formation of a nanoscale network of the second metal allows for high discharge capacity.

[0025] A nanoscale network refers to a network in which the width of the Sn fluoride and the second metal fluoride constituting the network, in the direction perpendicular to the longitudinal direction of the network, is preferably 20 nm or less, more preferably 10 nm or less, and even more preferably 5 nm or less. The lower limit of the width is not particularly limited as long as the network is connected, but for example, it is 1 nm or more, 2 nm or more, or 3 nm or more.

[0026] Figure 1 shows schematic cross-sectional diagrams of the microstructure of the intermetallic compound contained in the positive electrode active material of this disclosure during (A) the initial charging process, (B) the regeneration state, and (C) the subsequent microcrystallization. Figure 1 is an example where the second metal is Co, but the same applies when the second metal is Cu, Ni, Fe, and Sb.

[0027] In the initial charging process shown in Figure 1(A), CoSn2 is decomposed into microcrystals of SnF2, a fluoride of Sn, and CoF2, a fluoride of a second metal, forming a network structure of SnF2 and a network structure of CoF2, the fluoride of the second metal. SnF2 has excellent ionic conductivity, and F - Conduction paths can be formed even within the active material. CoF2, a fluoride of the second metal, can have high capacity through multi-electron reactions. Thus, the positive electrode active material of this disclosure can form conduction paths for fluoride ions during the initial charging process, and can therefore exhibit high capacity even at low temperatures.

[0028] During the initial charging process, CoSn2 separates into SnF2 and CoF2. As charging continues, it fluorinated into SnF3 and CoF3, and then defluorinated during the subsequent discharge process to form SnF2 and CoF2, finally reversibly changing back to CoSn2. Thus, starting from the initial state of CoSn2, during the initial charging process shown in Figure 1(A), CoSn2 decomposes into microcrystals of SnF2 and CoF2. After one charge-discharge cycle, it returns to a state where the microcrystals aggregate, as shown in Figure 1(B).

[0029] In the initial charging process, a portion of CoSn2 is decomposed into microcrystals of SnF2, a fluoride of Sn, and CoF2, a fluoride of a second metal. The alloy then contains the intermetallic compound CoSn2, a network structure of SnF2, and a network structure of CoF2, the fluoride of the second metal. Similarly, in the final stage of discharge, the alloy contains the intermetallic compound CoSn2, a network structure of SnF2, and a network structure of CoF2, the fluoride of the second metal. In other words, depending on the fluoridation state (charge / discharge state), the alloy may contain only the intermetallic compound, the intermetallic compound, the fluoride of Sn, and the fluoride of a second metal, or the fluoride of Sn and the fluoride of a second metal.

[0030] The microcrystals of the fluoride of Sn and the fluoride of the second metal formed during the charging process are preferably microcrystals having a diameter of about 2 to 10 nm, more preferably about 3 to 7 nm. The intermetallic compound formed after discharging after being separated into the fluoride of Sn and the fluoride of the second metal during the charging process is preferably a microcrystal having a diameter of about 3 to 12 nm, more preferably about 5 to 10 nm.

[0031] Since the state of Fig. 1(B) is the same as or more microcrystallized than the initial CoSn2 state, when charging again, as shown in Fig. 1(C), a network structure of SnF2 similar to or finer than that in the first cycle and a network structure of CoF2, which is the fluoride of the second metal, are formed. Even if the subsequent charge-discharge cycles are repeated, the states of Fig. 1(B) and Fig. 1(C) are reversibly repeated, and irreversible structural changes are suppressed, so excellent cycle characteristics can be exhibited. The reversible changes and the formation of the network structure shown in Fig. 1(A) to Fig. 1(C) are the same for Fe, Cu, Ni, and Sb.

[0032] The molar ratio of Sn contained in the alloy, preferably in the intermetallic compound, is preferably 40% or more, more preferably 45% or more, still more preferably 50% or more, even more preferably 55% or more, and even more preferably 60% or more. The molar ratio of Sn contained in the alloy is the molar ratio of Sn to the total of Sn and the second metal contained in the alloy. When the molar ratio of Sn contained in the alloy is within the above preferred range, - a conduction path of F can be formed better in the active material.

[0033] The upper limit of the molar ratio of Sn contained in the alloy may be, for example, 80% or less, 75% or less, or 70% or less. By setting the upper limit of the molar ratio of Sn in the alloy within the above-exemplified range to ensure the content of the second metal, it becomes easier to obtain a high capacity by a multi-electron reaction.

[0034] Intermetallic compounds of Sn and Co can be CoSn2, CoSn, Co3Sn2, or combinations thereof. Intermetallic compounds of Sn and Cu can be Cu6Sn5, Cu3Sn, Cu 10 Sn3, Cu 41 Sn 11 These can be , or combinations thereof. Intermetallic compounds of Sn and Ni can be Ni3Sn, Ni3Sn2, Ni3Sn4, or combinations thereof. Intermetallic compounds of Sn and Fe can be Fe5Sn3, Fe3Sn2, FeSn, FeSn2, or combinations thereof. Intermetallic compounds of Sn and Sb can be SbSn, Sb2Sn3, or combinations thereof.

[0035] Preferably, the intermetallic compound includes an intermetallic compound of Sn and Co, an intermetallic compound of Sn and Cu, or a combination thereof. As mentioned above, Sn is preferred because it fluorides to form an excellent ion conduction path, and Co and Cu are preferred because they each have high redox potentials and large capacities.

[0036] Preferably, the intermetallic compound includes CoSn2, CoSn, Cu6Sn5, or a combination thereof. The above preferred intermetallic compound has a high content of Sn, which fluorides to form excellent ion conduction paths, and also contains Co and Cu, which have high oxidation-reduction potentials and high capacity, making it easier to achieve both low-temperature operation and good cycle characteristics.

[0037] The positive electrode active material of this disclosure before preparing the positive electrode mixture may be relatively coarse-grained, and its volume-average particle size (hereinafter also referred to as D50) can be preferably 1 to 50 μm, more preferably 2 to 30 μm, and even more preferably 3 to 10 μm. When preparing a positive electrode mixture using the positive electrode active material of this disclosure, the positive electrode active material, electrolyte, conductive additive, etc. can be mixed and crushed and / or pulverized, so the volume-average particle size (hereinafter also referred to as D50) of the positive electrode active material of this disclosure in the positive electrode mixture is preferably 0.005 to 10 μm, more preferably 0.01 to 1 μm, and even more preferably 0.02 to 0.1 μm. The positive electrode active material of this disclosure exhibits good charge-discharge characteristics even when incorporated into the positive electrode with the above preferred particle size, but it also exhibits good charge-discharge characteristics even when further refined and incorporated into the positive electrode.

[0038] A fluoride-ion battery can be obtained equipped with the positive electrode active material of this disclosure. Since the positive electrode active material of this disclosure has good ionic conductivity and high capacity, a fluoride-ion battery equipped with the positive electrode active material of this disclosure has good properties. The fluoride-ion battery is preferably a fluoride-ion secondary battery. The fluoride-ion battery comprises a negative electrode current collector, a negative electrode layer, a fluorine-based electrolyte layer, a positive electrode layer, and a positive electrode current collector.

[0039] The positive electrode layer is a layer containing the positive electrode active material of this disclosure. The positive electrode layer may contain other positive electrode active materials in addition to the positive electrode active material of this disclosure. The positive electrode layer may contain other components in addition to the positive electrode active material. The positive electrode layer may further contain at least one of a conductive additive, an electrolyte, and a binder in addition to the positive electrode active material.

[0040] The conductive additive is not particularly limited as long as it has the desired electronic conductivity, but examples include carbon materials. Examples of carbon materials include carbon black such as acetylene black, Ketjen black, furnace black, and thermal black, as well as graphene, fullerene, carbon nanofibers, or carbon nanotubes. The lower limit of the proportion of the conductive additive in the positive electrode active material layer may be, for example, 1% by weight or more, or 5% by weight or more, and a better electronic conduction path can be formed within this range. The upper limit of the proportion of the conductive additive in the positive electrode active material layer may be, for example, 20% by weight or less, or 15% by weight or less, and by setting it within this range, the proportion of active material in the positive electrode active material can be ensured, and a better energy density can be obtained.

[0041] The binder is not particularly limited as long as it is chemically and electrically stable, but examples of fluorine-based binders include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0042] The electrolyte can be one that has been conventionally used in fluoride-ion batteries, and preferably, an electrolyte used in a fluorine-based electrolyte layer can be used.

[0043] The content of the positive electrode active material in the positive electrode layer is, for example, 30% by weight or more, 50% by weight or more, or 70% by weight or more. The thickness of the positive electrode layer can be, for example, 0.1 μm to 1000 μm, 1 to 100 μm, or 20 to 40 μm.

[0044] The negative electrode layer is a layer containing the negative electrode active material. The negative electrode active material can be an active material conventionally used in fluoride ion batteries, such as PbF2, MgF2, CeF3, or a Pb-Zr-F ternary solid solution in which some of the lead in lead fluoride (PbF2) is replaced with zirconium (Zr).

[0045] The negative electrode active material is preferably a Pb-Zr-F ternary solid solution. Since the Pb-Zr-F ternary solid solution has excellent ionic conductivity, by using the positive electrode active material of the present disclosure for the positive electrode and the Pb-Zr-F ternary solid solution as the negative electrode active material for the negative electrode, a battery having more excellent high capacity and cycle characteristics at low temperature can be obtained.

[0046] The ternary solid solution of Pb-Zr-F preferably contains Pb 1-x Zr x F 2+2x (0 < x ≤ 0.18), more preferably contains Pb 1-x Zr x F 2+2x (0.05 ≤ x ≤ 0.15), still more preferably contains Pb 1-x Zr x F 2+2x (0.075 ≤ x ≤ 0.125), for example, contains Pb 0.9 Zr 0.1 F 2.2 . Pb 1-x Zr x F 2+2x can exhibit higher ionic conductivity when x is within the above range.

[0047] The negative electrode active material layer may contain other components in addition to the negative electrode active material. The negative electrode active material layer may further contain at least one of a conductive auxiliary material, an electrolyte, and a binder in addition to the negative electrode active material.

[0048] The content of the negative electrode active material in the negative electrode layer is, for example, 30% by weight or more, 50% by weight or more, or 70% by weight or more. The thickness of the negative electrode layer can be, for example, 0.1 μm to 1000 μm, 1 to 100 μm, or 20 to 50 μm.

[0049] The fluorine-based electrolyte layer is a layer containing a fluorine-based electrolyte formed between the positive electrode layer and the negative electrode layer. The fluorine-based electrolyte can be a conventional electrolyte used in fluoride ion batteries, for example, La 0.9 Sr 0.1 F 2.9 (LSF) 、 Ce 0.9 La0.05 Sr 0.05 F 2.95 Ba 0.6 La 0.4 F 2.4 The electrolyte constituting the fluorine-based electrolyte layer may be a solid electrolyte, a liquid electrolyte (electrolyte solution), or a polymer electrolyte. The thickness of the fluorine-based electrolyte layer can be, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 200 μm.

[0050] The positive electrode current collector and the negative electrode current collector can be current collectors conventionally used in fluoride-ion batteries, and can be foil-shaped, mesh-shaped, or porous.

[0051] This disclosure also relates to a positive electrode active material for a fluoride-ion battery, which is an alloy comprising a network of fluorides of a first metal, Sn, and a network of fluorides of a second metal, Co, Cu, Ni, Fe, Sb, or a combination thereof.

[0052] The positive electrode active material is preferably an alloy consisting of a network of Sn fluoride and a network of fluoride of a second metal, such as Co, Cu, Ni, Fe, Sb, or a combination thereof.

[0053] The configuration of the fluoride network of Sn and the fluoride network of the second metal are as described above.

[0054] This disclosure also relates to a method for producing a positive electrode active material for a fluoride-ion battery, comprising dissolving a first metal, Sn, and a second metal, Co, Cu, Ni, Fe, Sb, or a combination thereof, to form an alloy comprising an intermetallic compound of the Sn and the second metal.

[0055] The positive electrode active material of this disclosure can be easily prepared by dissolving a combination of a first metal, Sn, and a second metal.

[0056] The first metal, Sn, can be used in any shape, such as granular or lump form. While high purity is preferable for Sn, it may contain impurities.

[0057] The second metal can be in any shape, such as granular or lump form. While the second metal is preferably of high purity, it may contain impurities other than Co, Cu, Ni, Fe, and Sb.

[0058] The melting temperature is preferably 1500 to 2000°C. The melting time is preferably 1 to 30 minutes, more preferably 3 to 15 minutes, and even more preferably 5 to 10 minutes. The melting atmosphere can be a vacuum or an inert gas atmosphere. The melting method is preferably vacuum melting, arc melting, or plasma melting, and more preferably arc melting. An alloy can be produced by arc melting two or more metals together.

[0059] The alloy of the positive electrode active material of this disclosure can be produced by melting alone, but may also be further subjected to solution treatment. The solution treatment temperature can be, for example, 600 to 1200°C, depending on the alloy composition. The solution treatment time can be 100 to 500 hours. To prevent oxidation of the alloy, the heat treatment atmosphere can be a vacuum or an inert gas atmosphere. For example, the alloy can be sealed in quartz and solution treated in a vacuum atmosphere.

[0060] Preferably, the alloy is subjected to a fluoride treatment to decompose at least a portion of the intermetallic compound, thereby generating a network of Sn fluoride, a network of the second metal fluoride, or a network of a combination thereof. By subjecting the alloy to a fluoride treatment to decompose a portion of the intermetallic compound, a network of Sn, a network of the second metal fluoride, or a network of a combination thereof can be formed in the alloy. By subjecting the alloy to a fluoride treatment to decompose all of the intermetallic compound, the intermetallic compound disappears, and a network of Sn fluoride and a network of the second metal fluoride can be formed in the alloy.

[0061] Fluorination treatment includes charging, discharging, or repeatedly doing so, a battery constructed by arranging a positive electrode active material adjacent to a fluorine-based electrolyte, or chemically fluorinating the positive electrode active material.

[0062] By charging a battery constructed by placing the positive electrode active material adjacent to a fluorine-based electrolyte, fluoride ions are supplied from the fluorine-based electrolyte, allowing fluoridation treatment to be performed from the surface of the positive electrode active material in contact with the fluorine-based electrolyte toward the interior. During charging, the intermetallic compound may separate into fluoride of Sn and fluoride of a second metal. During charging, the intermetallic compound may separate into fluoride of Sn and a second metal, and then the second metal may be fluorinated. After charging and discharging, the fluoride of Sn and the fluoride of the second metal are defluorinated and return to an intermetallic compound of Sn and a second metal. If charged again from there, it may separate again into fluoride of Sn and fluoride of a second metal. Even if the separation of Sn fluoride and the second metal fluoride is not achieved in all of the positive electrode active material particles during the initial charge, the separation of Sn fluoride and the second metal fluoride may further progress within the positive electrode active material particles as charging and discharging are repeated.

[0063] The positive electrode active material may be fluorinated by chemical fluorination treatment without forming a battery. Chemical fluorination treatment can be carried out by immersing the positive electrode active material in a fluorinating agent. The fluorinating agent can be, for example, bis(2-methoxyethyl)aminosulfur trifluoride, diethylaminosulfur=trifluoride, or bis(2-methoxyethyl)aminosulfur trifluoride diluted with acetonitrile solution.

[0064] The positive electrode active material disclosed herein is for use in fluoride-ion batteries, but can be manufactured and sold in any form, such as as a standalone positive electrode active material, as a positive electrode mixture, as a positive electrode layer, or incorporated into a fluoride-ion battery. The positive electrode active material disclosed herein can be sold either before or after fluorination treatment. The positive electrode active material disclosed herein can be incorporated into a battery, charged, discharged, or repeatedly subjected to these processes, and then removed from the battery and sold in any form, such as positive electrode active material, positive electrode mixture, or positive electrode layer. The positive electrode active material disclosed herein can also be sold after being chemically fluorinated.

[0065] The aforementioned dissolution treatment preferably includes dissolving a mixture of Sn and the second metal, in which Sn is present at a molar ratio of 40% or more relative to the total amount of Sn and the second metal. This makes it possible to achieve a molar ratio of 40% or more of Sn in the alloy obtained by the dissolution treatment.

[0066] The intermetallic compound preferably includes an intermetallic compound of Sn and Co, an intermetallic compound of Sn and Cu, or a combination thereof. The intermetallic compound preferably includes CoSn2, CoSn, Cu6Sn5, or a combination thereof. The above description can be applied to other configurations of the positive electrode active material.

[0067] This disclosure also relates to a method for manufacturing a fluoride-ion battery, comprising obtaining a laminate comprising a negative electrode current collector, a negative electrode layer, a fluorine-based electrolyte layer, a positive electrode layer containing a positive electrode active material obtained by the above manufacturing method, and a positive electrode current collector.

[0068] The configuration of the negative electrode current collector, negative electrode layer, fluorine-based electrolyte layer, and positive electrode current collector can be adapted to the above-described method. The laminate including the negative electrode current collector, negative electrode layer, fluorine-based electrolyte layer, positive electrode layer, and positive electrode current collector can be manufactured by any method, such as pressure molding. For example, the laminate of the negative electrode layer, fluorine-based electrolyte layer, and positive electrode layer can be manufactured by any method, such as pressure molding, and then the current collector can be placed. When the laminate is pressure molded, the pressure of the pressure molding can be 10 to 600 MPa. The positive electrode current collector and negative electrode current collector can be formed by any method, such as lamination, coating, or vapor deposition. [Examples]

[0069] (Example 1) (Fabrication of positive electrode active material) 1.989 g of granular Co (99.97% purity, D50=4 mm) and 8.011 g of granular Sn (99.99% purity, D50=5 mm) were mixed so that the molar ratio of Co:Sn was 1:2. 10 g of the intermetallic compound CoSn2 was prepared by arc melting the mixture in an Ar atmosphere at 1500°C for 10 minutes using an arc melting apparatus.

[0070] (Preparation of solid electrolytes) La(NO3)3·6H2O reagent, Sr(NO3)2 reagent (manufactured by Fujifilm Wako Pure Chemical Industries), and NH4F reagent (manufactured by Sigma-Aldrich) were dissolved in purified water and mixed in a molar ratio of 0.9:0.1:2.9. The resulting precipitate was filtered and calcined at 800°C for 4 hours under an argon atmosphere to obtain La 0.9 Sr 0.1 F 2.9 (LSF) was prepared.

[0071] (Preparation of positive electrode mixture) Prepared CoSn2 powder and La 0.9 Sr 0.1 F 2.9 (LSF) was used as the positive electrode active material and the fluorine-based solid electrolyte, respectively. 0.12 g of CoSn2 was used as the positive electrode active material, and 0.24 g of La was used as the fluorine-based solid electrolyte. 0.9 Sr 0.1 F 2.9A cathode mixture was prepared by mixing (LSF) and 0.04 g of acetylene black (D50 = 48 nm) as a conductive additive, and mechanically milling it at 600 rpm for 3 hours using a ball mill. The D50 of the cathode active material in the cathode mixture was 0.05 μm. The D50 of the cathode active material was measured using a STEM.

[0072] (Preparation of negative electrode mixture) 0.12 g of PbF2 (high-purity chemical company, 99.9% purity) as the negative electrode active material, and 0.24 g of La as the fluorine-based solid electrolyte. 0.9 Sr 0.1 F 2.9 (LSF) and 0.04 g of acetylene black (D50=48 nm) as a conductive additive were mixed and mechanically milled at 100 rpm for 10 hours using a ball mill to prepare the negative electrode mixture.

[0073] (Battery construction) The electrolyte used in the electrolyte layer is a prepared fluorine-based solid electrolyte, La 0.9 Sr 0.1 F 2.9 Using (LSF), 50 mg of the prepared negative electrode mixture, 150 mg of the fluorine-based solid electrolyte, and 10 mg of the positive electrode mixture were pressure-molded at 392 MPa using a powder compacting cell to produce a pellet with a diameter of 11 mm, comprising a 30 μm thick positive electrode layer, a 150 μm thick fluorine-based solid electrolyte layer, and a 35 μm thick negative electrode layer.

[0074] A coin-cell type all-solid-state fluoride-ion battery was fabricated by placing a 20 μm thick Pt foil on the positive electrode layer as the positive electrode current collector, and a 200 μm thick Pb foil 71 and an 18 μm thick Al foil 72 on the negative electrode layer as the negative electrode current collectors. Figure 2 shows a schematic cross-sectional view of the all-solid-state fluoride-ion battery 100, which comprises the fabricated negative electrode current collector 70, negative electrode layer 50, fluorine-based solid electrolyte layer 40, positive electrode layer 30, and positive electrode current collector 60. The mixture, electrolyte, and all-solid-state fluoride-ion battery were all fabricated in an Ar gas atmosphere.

[0075] (Example 2) The cathode mixture and all-solid-state fluoride ion battery were prepared in the same manner as in Example 1, except that the raw material reagents were mixed so that the molar ratio of Co:Sn was 1:1.

[0076] (Example 3) The positive electrode mixture and the all-solid-state fluoride ion battery were prepared in the same manner as in Example 1, except that the raw material reagents were mixed so that the molar ratio of Cu:Sn was 6:5.

[0077] (Example 4) The negative electrode active material is Pb 0.9 Zr 0.1 F 2.2 Except for the above, an all-solid-state fluoride ion battery was fabricated using the same method as in Example 3. 0.9 Zr 0.1 F 2.2 This was prepared by mixing PbF2 and ZrF4 in a molar ratio of 9:1 and mechanically milling them at 600 rpm for 3 hours using a ball mill.

[0078] (Measurement of charge / discharge characteristics) The all-solid-state fluoride-ion batteries prepared in Examples 1-4 were subjected to a vacuum (10°C) using a VMP-300 multipotentiostat (BioLogic). -4 The charge-discharge characteristics were evaluated using a galvanostat mode while varying the temperature and current density at Pa. After confirming with a thermocouple that the temperature in the vacuum atmosphere containing the all-solid-state fluoride-ion battery was at the set temperature, the charge-discharge characteristics were measured 2 hours later.

[0079] (Charge / discharge curves and cycle characteristics) Figure 3 shows (A) the charge-discharge curve and (B) the cycle characteristics of the all-solid-state fluoride-ion batteries prepared in Examples 1 and 2, measured at a temperature of 140°C and a current density of 20 mA / g.

[0080] In the charge-discharge curves shown in Figure 3(A), both the all-solid-state fluoride-ion batteries fabricated in Examples 1 and 2 showed high discharge capacities. The all-solid-state fluoride-ion battery fabricated in Example 1 showed a discharge capacity of 591 mAh / g, and the all-solid-state fluoride-ion battery fabricated in Example 2 showed a discharge capacity of 579 mAh / g. In the cycle characteristics shown in Figure 3(B), after 40 cycles, the all-solid-state fluoride-ion battery fabricated in Example 1 showed a discharge capacity of 565 mAh / g, and the all-solid-state fluoride-ion battery fabricated in Example 2 showed a discharge capacity of 543 mAh / g.

[0081] (Cycle characteristics while varying current density) Figure 4 shows the cycle characteristics of the all-solid-state fluoride-ion battery fabricated in Example 1, measured at a temperature of 140°C while increasing the current density from 20 mA / g to 10,000 mA / g. Charge-discharge curves and discharge capacity were measured for three cycles at each current density. Figure 4(A) shows the charge-discharge curves for the first three cycles measured at a current density of 20 mA / g. Figure 4(B) is a graph evaluating the discharge capacity (rate characteristics) measured at 20 mA / g, after increasing the current density from 20 mA / g to 10,000 mA / g.

[0082] In the charge-discharge curves in Figure 4(A), the curves are almost identical in shape during the first three cycles, and plateaus are observed at the same potential, indicating that essentially the same fluorination and defluorination charge-discharge mechanisms occurred during the first three cycles.

[0083] In the cycle characteristics shown in Figure 4(B), although the discharge capacity decreases as the current density increases, the battery continues to operate as a secondary battery even when the current density is increased to 10,000 mA / g, indicating that it can operate even at high rates such as 10,000 mA / g.

[0084] (Charge-discharge characteristics when measurement temperature conditions are changed) Figure 5 shows the charge-discharge curves for the all-solid-state fluoride-ion battery fabricated in Example 1, measured at a current density of 20 mA / g at 140°C, 80°C, 60°C, and 40°C, after 5 cycles. Although the discharge capacity tends to decrease as the measurement temperature decreases from 140°C, it showed discharge capacities of 537 mAh / g at 140°C, 280 mAh / g at 80°C, and 221 mAh / g at 60°C, indicating that the increase in overvoltage was relatively suppressed above 60°C.

[0085] (Cycle characteristics at 140°C and 60°C) Figure 6 shows the cycle characteristics of the all-solid-state fluoride-ion battery fabricated in Example 1 at 140°C and 60°C. Figure 6(A) shows the cycle characteristics after 1000 cycles at a measurement temperature of 140°C and a current density of 1000 mA / g, and Figure 6(B) shows the cycle characteristics after 250 cycles at a measurement temperature of 60°C and a current density of 20 mA / g.

[0086] As shown in Figure 6(A), the discharge capacity increased from the first cycle to 35 cycles, reaching a discharge capacity of 308 mAh / g at 35 cycles. After that, the discharge capacity remained almost constant even after 1000 cycles, reaching 286 mAh / g at 1000 cycles, demonstrating a capacity retention rate of 92.9%. The capacity retention rate is the ratio of the discharge capacity relative to the maximum discharge capacity at 35 cycles.

[0087] As shown in Figure 6(B), the discharge capacity increased from the first cycle to 50 cycles, reaching a discharge capacity of 239 mAh / g at 50 cycles. Subsequently, the discharge capacity remained almost constant even after 250 cycles, reaching 229 mAh / g at 250 cycles, demonstrating a capacity retention rate of 95.8%.

[0088] (Structural changes of CoSn2 during the charge-discharge process) Figure 7 shows a graph illustrating the structural changes of the positive electrode active material CoSn2 during the charge-discharge process of the all-solid-state fluoride ion battery fabricated in Example 1. Figure 7(A) is the charge-discharge curve when charged and discharged at a temperature of 140°C and a current density of 20 mA / g. The horizontal axis represents the amount of F absorbed by CoSn2.- The quantity (mol) is shown, and the vertical axis represents the potential (vsPb / PbF2). Figure 7(B) shows the powder X-ray diffraction (XRD) patterns of the positive electrode mixture in five states: initial state, charged state (0.5V), charged state (1.5V), discharged state (0V), and discharged state (-1.5V) as shown in Figure 7(A). The XRD patterns of the positive electrode mixture were measured on the surface of the positive electrode mixture exposed by peeling off the positive electrode current collector.

[0089] In the powder XRD pattern in Figure 7(B), only the CoSn2 peak and the LSF peak are visible in the initial state. The LSF peak is detected as LSF contained in the cathode mixture. In the charged state (0.5V), the CoSn2 peak disappears, and the SnF2 and CoF2 peaks are visible. That is, Sn and Co are fluorinated in the divalent state. In the further charged state (1.5V), the SnF2 and CoF2 peaks disappear, and the SnF3 and CoF3 peaks are visible. That is, Sn and Co are fluorinated in the trivalent state. Next, in the discharge state (0V) during the discharge process, the SnF3 and CoF3 peaks disappear, and the SnF2 and CoF2 peaks are visible. In the further discharge state (-1.5V), the SnF2 and CoF2 peaks disappear, and the CoSn2 peak is visible. As shown in equation (2), it can be seen that CoSn2 underwent a reversible structural change during the charge-discharge process. [ka]

[0090] Figure 8 shows a schematic diagram of the charge-discharge mechanism of CoSn2. Starting from the initial state of CoSn2, charging begins, and in the charged state (0.5V), CoSn2 separates into divalent fluorides of SnF2 and CoF2. Further charging to the charged state (1.5V) forms trivalent fluorides of SnF3 and CoF3. Next, during discharge, in the discharged state (0V), it returns to the divalent fluorides of SnF2 and CoF2, and further discharge to the discharged state (-1.5V) returns it to CoSn2.

[0091] During the charging process in which CoSn2 separates into divalent fluorides of SnF2 and CoF2, and during the discharge process in which SnF2 and CoF2 return to CoSn2, the reaction shown in equation (3) occurs. [ka]

[0092] During the charging process in which SnF2 and CoF2 are converted to trivalent fluorides SnF3 and CoF3, and during the discharge process in which SnF3 and CoF3 are converted back to divalent fluorides SnF2 and CoF2, the reaction shown in equation (4) occurs. [ka]

[0093] In other words, theoretically, CoSn2 releases 9 moles of F per mole of CoSn2 during the charge-discharge process. - It absorbs and releases. On the other hand, from the results shown in Figure 7(A) obtained in practice, 1 mol of CoSn2 absorbs 7.9 mol of F during the charging process. - It absorbs 6.5 mol of F during the discharge process. - It was calculated that 88% of the CoSn2 was decomposed into fluoride during the actual charge-discharge process using CoSn2 as the positive electrode active material, and 82% of the fluoride was regenerated into CoSn2.

[0094] (Changes in microstructure) Figure 9 shows the results of scanning transmission electron microscopy-electron energy loss spectroscopy (STEM-EELS) analysis of CoSn2 in its charged state (0.5V). XRD analysis has shown that the initial state of CoSn2 separates into divalent fluorides of SnF2 and CoF2 in the charged state (0.5V), and the EELS spectrum shown in Figure 9(A) also detects peaks of Sn, Co, and F.

[0095] Based on the EELS spectrum, the spatial distributions of Sn, Co, and F were mapped. Figure 9(B) shows the spatial mapping image of F, Figure 9(C) shows the spatial mapping image of Co, and Figure 9(D) shows the spatial mapping image of Sn. As shown in Figure 9(B), the spatial distribution of F was relatively uniform, but as shown in Figures 9(C) and 9(D), the spatial distributions of Co and Sn were heterogeneous. In areas where the concentration of Sn was low, the concentration of Co was high and CoF2 was formed, and in areas where the concentration of Co was low, the concentration of Sn was high and SnF2 was formed. It was found that SnF2 and CoF2 are microcrystals with a diameter of about 5 nm. In other words, it can be seen that CoSn2 separated into microcrystals of CoF2 and SnF2 during the charging process.

[0096] (Changes in microstructure after one cycle) Figure 10 shows the STEM-EELS analysis results for the discharge state (-1.5V) of CoSn2 after one charge-discharge cycle. XRD analysis results have shown that after one charge-discharge cycle, the initial CoSn2 undergoes fluorination and defluorination to return to CoSn2, and the EELS spectrum shown in Figure 10(A) also detected only peaks for Sn and Co.

[0097] Based on the EELS spectra, the spatial distributions of Sn and Co were mapped. Figure 10(C) shows the spatial mapping image of Co, and Figure 10(D) shows the spatial mapping image of Sn. As shown in Figures 10(C) and 10(D), the spatial distributions of Co and Sn were relatively uniform.

[0098] ADF-STEM observations were performed on the regions enclosed by solid lines in the spatial mapping images of Co and Sn in Figures 10(C) and 10(D). Figure 10(B) shows the ADF-STEM observation image. In the region enclosed by the dashed line in the ADF-STEM image of Figure 10(B) (corresponding to the regions enclosed by the dashed lines in Figures 10(C) and 10(D)), lattice fringes of different orientations were observed, indicating the formation of CoSn2 microcrystals of approximately 5-10 nm.

[0099] From the above analysis results, it can be seen that CoSn2 separates into microcrystals of SnF2 and CoF2 during the charging process (fluorination process), and then returns to being CoSn2 microcrystals during the subsequent discharge process (defluorination process), while maintaining the morphology of the microcrystals formed during the charging process.

[0100] (Characteristic evaluation of Cu6Sn5) Figure 11 shows the cycle characteristics of the all-solid-state fluoride-ion battery fabricated in Example 3, measured at a temperature of 140°C while increasing the current density from 20 mA / g to 5000 mA / g. Charge-discharge curves and discharge capacity were measured for three cycles at each current density. Figure 11(A) shows the charge-discharge curve for the first three cycles measured at a current density of 20 mA / g. Figure 11(B) is a graph evaluating the discharge capacity (rate characteristics) measured at 20 mA / g, after increasing the current density from 20 mA / g to 5000 mA / g. Figure 11(C) shows the cycle characteristics of the all-solid-state fluoride-ion battery fabricated in Example 3, measured at a temperature of 140°C and a current density of 1000 mA / g for 1000 cycles.

[0101] In the charge-discharge curves shown in Figure 11(A), the curves are almost identical in shape during the first three cycles, indicating that, similar to CoSn2, Cu6Sn5 also underwent essentially the same fluorination and defluorination charge-discharge mechanisms during the first three cycles.

[0102] In the rate characteristics shown in Figure 11(B), although the discharge capacity decreases as the current density increases, the battery continues to operate as a secondary battery even when the current density is increased to 5000 mA / g, indicating that it can operate even at high rates such as 5000 mA / g.

[0103] As shown in Figure 11(C), the discharge capacity increased from the initial cycle to 45 cycles, reaching a discharge capacity of 179 mAh / g at 45 cycles. After that, the discharge capacity remained nearly constant even after 1000 cycles, reaching 167 mAh / g at 1000 cycles, demonstrating a capacity retention rate of 93.7%. The capacity retention rate is the ratio of the discharge capacity relative to the maximum discharge capacity at 45 cycles.

[0104] (Evaluation of cycle characteristics at low temperatures) Figure 12 shows the cycle characteristics of the all-solid-state fluoride-ion battery fabricated in Example 3, measured at a temperature of 60°C and a current density of 20 mA / g. From the charge-discharge curves for cycles 1 to 15 shown in Figure 12(A), it can be seen that a discharge capacity of approximately 150 mAh / g was obtained after 15 cycles. From the graph of the change in discharge capacity from cycles 1 to 67 in Figure 12(B), it can be seen that the battery exhibits excellent cycle characteristics even at 60°C.

[0105] Figure 13 shows the charge-discharge curves of the all-solid-state fluoride ion batteries prepared in Example 3 and Example 4, measured at a temperature of 60°C and a current density of 20 mA / g. It was confirmed that the battery prepared in Example 4 had improved capacity compared to the battery prepared in Example 3. The Pb used as the negative electrode active material in Example 4... 0.9 Zr 0.1 F 2.2 Because it has superior ion conductivity compared to PbF2, it can achieve high capacity at low temperatures. In Example 3, the negative electrode characteristics were a bottleneck for battery capacity, but in Example 4, it can be seen that the battery capacity was improved by improving the negative electrode characteristics.

[0106] Figure 14 shows a graph comparing the cycle characteristics of the all-solid-state fluoride-ion batteries prepared in Example 3 and Example 4. It was confirmed that the cycle characteristics were improved in Example 4 compared to Example 3. [Explanation of Symbols]

[0107] 30 positive electrode 40 Fluorine-based electrolyte layer 50 Negative electrode layer 60 Positive electrode current collector 70, 71, 72 Negative electrode current collector 100 All-solid-state fluoride-ion batteries

Claims

1. A positive electrode active material for a fluoride-ion battery, which is an alloy containing an intermetallic compound of a first metal, Sn, and a second metal, such as Co, Cu, Ni, Fe, Sb, or a combination thereof.

2. The positive electrode active material according to claim 1, wherein the alloy includes a network of fluorides of the Sn, a network of fluorides of the second metal, or a network of a combination thereof.

3. The positive electrode active material according to claim 1, wherein the molar ratio of Sn contained in the alloy is 40% or more.

4. The positive electrode active material according to claim 1, wherein the intermetallic compound includes an intermetallic compound of Sn and Co, an intermetallic compound of Sn and Cu, or a combination thereof.

5. The intermetallic compound is CoSn ２ CoSn, Cu ６ Sn ５ The positive electrode active material according to claim 1, including, or a combination thereof.

6. A positive electrode active material for a fluoride-ion battery, which is an alloy comprising a network of fluorides of a first metal, Sn, and a network of fluorides of a second metal, Co, Cu, Ni, Fe, Sb, or a combination thereof.

7. A fluoride ion battery comprising the positive electrode active material according to any one of claims 1 to 6.

8. A fluoride ion battery comprising a negative electrode current collector, a negative electrode layer, a fluorine-based electrolyte layer, a positive electrode layer containing a positive electrode active material according to any one of claims 1 to 6, and a positive electrode current collector, wherein the negative electrode layer contains a Pb-Zr-F ternary solid solution as the negative electrode active material.

9. The Pb-Zr-F ternary solid solution is Pb １－ｘ Zr ｘ F ２＋２ｘ The fluoride ion battery according to claim 8, wherein (0 < x ≤ 0.18).

10. A method for producing a positive electrode active material for a fluoride ion battery, comprising dissolving a first metal, Sn, and a second metal, which is Co, Cu, Ni, Fe, Sb, or a combination thereof, to form an alloy containing an intermetallic compound between Sn and the second metal.

11. The manufacturing method according to claim 10, comprising fluorinating the alloy to decompose at least a portion of the intermetallic compound to generate a network of Sn fluorides, a network of the second metal fluorides, or a network of a combination thereof.

12. The manufacturing method according to claim 10, wherein the dissolution treatment includes dissolving a mixture of Sn and a second metal, the Sn being present in a molar ratio of 40% or more of the total amount of the Sn and the second metal.

13. The manufacturing method according to claim 10, wherein the intermetallic compound includes an intermetallic compound of Sn and Co, an intermetallic compound of Sn and Cu, or a combination thereof.

14. The intermetallic compound is CoSn ２ , CoSn, Cu ６ Sn ５ , or a combination thereof, the manufacturing method according to claim 10.

15. A method for manufacturing a fluoride ion battery, comprising obtaining a laminate comprising a negative electrode current collector, a negative electrode layer, a fluorine-based electrolyte layer, a positive electrode layer containing a positive electrode active material obtained by the manufacturing method described in any one of claims 10 to 14, and a positive electrode current collector.

16. The method for producing a fluoride ion battery according to claim 15, wherein the negative electrode layer contains a Pb-Zr-F ternary solid solution as the negative electrode active material.

17. The Pb-Zr-F ternary solid solution is Pb １－ｘ Zr ｘ F ２＋２ｘ A method for manufacturing a fluoride ion battery according to claim 16, wherein (0 < x ≤ 0.18).

Images