Fluoride ion battery

Abstract

To provide a high capacity fluoride ion battery.SOLUTION: A fluoride ion battery includes a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, and the negative electrode layer contains, as a negative electrode active material, a transition metal oxide having a layered structure and represented by MxOy, and M in MxOy is at least one selected from the group consisting of Ti, Zr, and Ta, x / y is 2 to 6, and y / (x+y)≥0.1 is satisfied.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present disclosure relates to fluoride-ion batteries. [Background technology]

[0002] Patent Document 1 discloses a fluoride ion battery having, as an active material, a transition metal oxide having a rock salt type crystal structure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-194697 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a demand for high-capacity fluoride-ion batteries.

[0005] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a high-capacity fluoride ion battery. [Means for solving the problem]

[0006] [1] 1. A fluoride ion battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the negative electrode layer contains, as a negative electrode active material, a transition metal oxide having a layered structure and represented by MxOy, A fluoride ion battery, wherein in the MxOy, M is at least one selected from the group consisting of Ti, Zr, and Ta, x / y is 2 to 6, and y / (x+y)≧0.1 is satisfied.

[0007] [2] The fluoride ion battery according to [1], wherein the transition metal oxide satisfies A / B≦0.1, where A is the maximum peak intensity between 2θ=15° and 30°, and B is the maximum peak intensity between 2θ=30° and 40° in X-ray diffraction measurement using CuKα rays.

[0008] [3] The fluoride ion battery according to [1], wherein the transition metal oxide is at least one selected from the group consisting of TiO, TiO, and TiO.

[0009] [4] The fluoride ion battery according to [1], wherein the electrolyte layer is a solid electrolyte layer containing a solid electrolyte.

[0010] [5] The solid electrolyte is Ca 0.5 Ba 0.5 [4] The fluoride ion battery according to [4], wherein F2. [Effects of the Invention]

[0011] The present disclosure can provide a high capacity fluoride ion battery. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an example of a fluoride ion battery according to the present disclosure. [Figure 2] FIG. 2 shows the results of XRD measurement of Example 1. [Figure 3] FIG. 3 shows the results of XRD measurement of Example 2. [Figure 4] FIG. 4 shows the results of XRD measurement of Example 3. [Figure 5] FIG. 5 shows the results of XRD measurement of Comparative Example 1. [Figure 6] FIG. 6 shows the results of XRD measurement of Comparative Example 2. [Figure 7] FIG. 7 is a graph showing the results of the charge-discharge test of Example 1. [Figure 8]FIG. 8 is a graph showing the results of the charge-discharge test of Example 2. [Figure 9] FIG. 9 is a graph showing the results of the charge-discharge test of Example 3. [Figure 10] FIG. 10 is a graph showing the results of the charge-discharge test of Comparative Example 1. [Figure 11] FIG. 11 is a graph showing the results of the charge-discharge test of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of a fluoride ion battery that do not characterize the present disclosure) can be understood as design matters of a person skilled in the art based on prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field. The dimensional relationships (length, width, thickness, etc.) in the figure do not reflect the actual dimensional relationships. Figure 1 also shows the directions of a three-dimensional Cartesian coordinate system. Here, the xy plane is the horizontal plane, the z-axis direction is the vertical direction, and the larger dimension in the z-axis direction is the top. Furthermore, in this specification, when expressing the manner in which another component is placed relative to a certain component, the terms "above" or "below" are used, unless otherwise specified, and include both cases in which another component is placed directly above or below a certain component so as to be in contact with the component, and cases in which another component is placed above or below a certain component via another component.

[0014] The present disclosure provides a fluoride ion battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the negative electrode layer contains, as a negative electrode active material, a transition metal oxide having a layered structure and represented by MxOy, The present invention provides a fluoride ion battery, wherein in the MxOy, M is at least one selected from the group consisting of Ti, Zr, and Ta, x / y is 2 to 6, and y / (x+y)≧0.1 is satisfied.

[0015] To effectively use transition metal oxides as negative electrode active materials in fluoride-ion batteries, it is important to achieve both a low reaction potential and a high charge / discharge capacity. The capacity of a fluoride-ion battery is determined by the amount of fluoride ions absorbed during charging and discharging. Furthermore, since the reaction potential is dominated by the redox potential of the metal element, metal elements with a lower redox potential than tin and lead are desirable. In this disclosure, a layered compound capable of absorbing a sufficient amount of fluoride ions in its crystal structure is used as a transition metal oxide, and a metal element with a low redox potential is used as a reactive element of the active material. The transition metal oxide used in this disclosure has sufficient voids in its layered crystal structure for fluorine to penetrate, enabling high capacity and stable charge / discharge. In addition, because it contains transition metal elements with lower redox potentials than tin and lead, it is possible for fluorination and defluorination reactions to occur at lower potentials.

[0016] The fluoride ion battery of the present disclosure has a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer. Fig. 1 is a schematic cross-sectional view showing an example of a fluoride ion battery according to the present disclosure. The fluoride ion battery 10 shown in Fig. 1 includes a positive electrode layer 1, a negative electrode layer 2, an electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 2, a positive electrode current collector 4 that collects current from the positive electrode layer 1, and a negative electrode current collector 5 that collects current from the negative electrode layer 2.

[0017] [Positive electrode layer] The positive electrode layer in the present disclosure is a layer containing at least a positive electrode active material. The positive electrode layer may also contain at least one of an electrolyte, a conductive material, and a binder, as needed. The thickness of the positive electrode layer is not particularly limited and can be adjusted appropriately depending on the battery configuration.

[0018] The positive electrode active material is any active material that has a higher potential than the negative electrode active material described below. In the positive electrode active material, a defluorination reaction typically occurs during discharge. Examples of the positive electrode active material include a metal, an alloy, and a metal oxide. The positive electrode active material may be a fluoride of a metal, a fluoride of an alloy, or a fluoride of a metal oxide. Examples of metal elements contained in the positive electrode active material include Cu, Ag, Ni, Co, Pb, Ce, Mn, Au, Pt, Rh, V, Os, Ru, Fe, Cr, Bi, Ni, Sb, Ti, Sn, and Zn. Examples of the positive electrode active material include a carbon material. Examples of the carbon material include graphite, coke, and carbon nanotubes. The positive electrode active material may also be a fluoride of a carbon material. Examples of the positive electrode active material include a polymer material. Examples of the polymer material include polyaniline, polypyrrole, polyacetylene, and polythiophene. The positive electrode active material may also be a fluoride of a polymer material. The positive electrode active material may be PbF2 or the like. The content of the positive electrode active material in the positive electrode layer is not particularly limited, but is, for example, 30% by weight or more, or may be 50% by weight or more, or may be 70% by weight or more.

[0019] Known conductive materials can be used, such as carbon materials and metal particles. Examples of carbon materials include acetylene black (AB), furnace black, VGCF, carbon nanotubes, and carbon nanofibers. Among them, from the viewpoint of electron conductivity, at least one selected from the group consisting of VGCF, carbon nanotubes, and carbon nanofibers may be used. Examples of metal particles include particles of Ni, Cu, Fe, and SUS. The content of the conductive material in the positive electrode layer is not particularly limited.

[0020] Examples of binders include rubber-based binders and fluoride-based binders. Examples of rubber-based binders include butadiene rubber, hydrogenated butadiene rubber, styrene butadiene rubber (SBR), hydrogenated styrene butadiene rubber, nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, and ethylene propylene rubber. Examples of fluoride-based binders include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene, and fluororubber. The content of the binder in the positive electrode layer is not particularly limited.

[0021] The electrolyte is the same as that described in the "electrolyte layer" below. The content of the electrolyte in the positive electrode layer is, for example, 5% by weight or more, and may be 10% by weight or more. On the other hand, the content of the electrolyte is, for example, 70% by weight or less, and may be 40% by weight or less. If the proportion of the electrolyte is too low, it may be impossible to diffuse fluoride ions deep into the positive electrode layer with low resistance. If the proportion of the electrolyte is too high, the proportion of the active material will be relatively low, and the energy density may decrease.

[0022] [Negative electrode layer] The negative electrode layer in the present disclosure is a layer containing at least a negative electrode active material, and may also contain at least one of an electrolyte, a conductive material, and a binder, as necessary.

[0023] The negative electrode layer contains, as a negative electrode active material, a transition metal oxide having a layered structure and represented by MxOy. In the MxOy, M is at least one element selected from the group consisting of Ti, Zr, and Ta. In the above MxOy, x / y is 2 to 6, and may be 2 to 3. The MxOy satisfies y / (x+y)≧0.1, that is, the oxygen concentration of the transition metal oxide is 10 atom % or more, and the y / (x+y) may be 0.14 to 0.33.

[0024] Whether or not a transition metal oxide has a layered structure can be determined by X-ray diffraction (XRD) measurement using CuKα radiation. In X-ray diffraction measurement using CuKα radiation, the transition metal oxide may satisfy A / B≦0.1 or A / B≦0.03, where A is the maximum peak intensity between 2θ=15° and 30° and B is the maximum peak intensity between 2θ=30° and 40°. The transition metal oxide may be a single-phase material having only the crystalline phase having the layered structure described above, or may be a multi-phase material having a crystalline phase having a layered structure and a crystalline phase having another structure. In the latter case, it is preferable that the crystalline phase having the layered structure described in the present disclosure be the main phase. The "main phase" refers to the crystalline phase containing the most intense peak in the XRD chart. When the transition metal oxide has the crystalline phase having the layered structure described in the present disclosure as the main phase, the proportion of the crystalline phase having the layered structure described in the present disclosure to all crystalline phases is, for example, 50% by weight or more, 70% by weight or more, 90% by weight or more, or even 99% by weight or more.

[0025] Examples of transition metal oxides include Ti oxides such as Ti2O, Ti3O, and Ti6O, Zr oxides such as Zr4O, and Ta oxides such as Ta4O.

[0026] The shape of the negative electrode active material is not particularly limited, but may be, for example, particulate. 50 ) is, for example, 1 nm or more and 100 μm or less. 50 ) can be calculated, for example, from measurements using a laser diffraction particle size distribution analyzer or a scanning electron microscope (SEM). The content of the negative electrode active material in the negative electrode layer is not particularly limited, but is, for example, 30% by weight or more, or may be 50% by weight or more, or may be 70% by weight or more.

[0027] The electrolyte, conductive material, and binder are the same as those described above in the "positive electrode layer," and therefore will not be described here. The content of the electrolyte in the negative electrode layer is, for example, 5% by weight or more, and may be 10% by weight or more. On the other hand, the content of the electrolyte is, for example, 70% by weight or less, and may be 40% by weight or less. If the proportion of the electrolyte is too low, fluoride ions may not be able to diffuse deep into the negative electrode layer with low resistance. If the proportion of the electrolyte is too high, the proportion of the active material may be relatively low, and the energy density may decrease. In addition, the thickness of the negative electrode layer is not particularly limited and can be adjusted appropriately depending on the configuration of the battery.

[0028] [Electrolyte layer] The electrolyte layer in the present disclosure is a layer disposed between the positive electrode layer and the negative electrode layer, and contains at least an electrolyte. The electrolyte layer may further contain a binder, if necessary. The type of binder is the same as that described above for the "positive electrode layer," and therefore will not be described here. The electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0029] The electrolyte solution may, for example, contain a fluoride salt and an organic solvent. The fluoride salt may, for example, be an inorganic fluoride salt, an organic fluoride salt, or an ionic liquid. An example of an inorganic fluoride salt is XF (where X is Li, Na, K, Rb, or Cs). An example of a cation of an organic fluoride salt is an alkylammonium cation such as a tetramethylammonium cation. The concentration of the fluoride salt in the electrolyte solution may, for example, be 0.1 mol% or more and 40 mol% or less, or may be 1 mol% or more and 10 mol% or less.

[0030] The organic solvent of the electrolyte is usually a solvent that dissolves a fluoride salt. Examples of the organic solvent include glymes 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 chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). In addition, an ionic liquid may be used as the organic solvent.

[0031] The solid electrolyte may be, for example, an inorganic solid electrolyte. Examples of the inorganic solid electrolyte include fluorides containing lanthanoid elements such as La and Ce, fluorides containing alkali elements such as Li, Na, K, Rb and Cs, and fluorides containing alkaline earth elements such as Ca, Sr and Ba. Specifically, fluorides containing Ca and Ba (for example, Ca 0.5 Ba 0.5 F2), fluorides containing La and Ba (e.g., La 0.9 Ba 0.1 F 2.9 ), and fluorides containing Pb and Sn. The thickness of the electrolyte layer is not particularly limited and can be adjusted appropriately depending on the configuration of the battery.

[0032] [Other configurations] The fluoride ion battery according to the present disclosure may have a positive electrode current collector that collects current from the positive electrode layer, a negative electrode current collector that collects current from the negative electrode layer, and a battery case that houses these components. Examples of materials for the positive electrode current collector include SUS, aluminum, nickel, lead, iron, titanium, platinum, and carbon. Examples of materials for the negative electrode current collector include SUS, copper, nickel, lead, platinum, and carbon. The current collector may be in the form of, for example, a foil, a mesh, or a porous material. As the battery case, a conventionally known battery case can be used. Furthermore, the fluoride ion battery may have a separator between the positive electrode layer and the negative electrode layer, because this allows for a safer battery to be obtained.

[0033] [Fluoride-ion battery] The fluoride ion battery in the present disclosure may be a primary battery or a secondary battery, but is preferably a secondary battery. This is because it can be repeatedly charged and discharged, making it useful, for example, as an in-vehicle battery. Note that secondary batteries also include those used like primary batteries (used only for one discharge after charging). Fluoride ion batteries may be shaped, for example, as coin-type, laminated, cylindrical, or rectangular. The fluoride ion battery in the present disclosure may be a liquid-based battery containing an electrolyte solution, or may be a solid-state battery. Note that in the present disclosure, a solid-state battery refers to a battery containing a solid electrolyte. The solid-state battery may be a semi-solid-state battery, which is a solid-state battery containing a solid electrolyte and a liquid-based material, or an all-solid-state battery, which is a solid-state battery not containing a liquid-based material.

[0034] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0035] (Examples 1 to 3) [Synthesis of titanium oxide] Titanium (Ti) (manufactured by Sigma-Aldrich) and titanium dioxide (TiO) (manufactured by Kojundo Chemical) were weighed to achieve molar compositions of Ti:O = 0.67:0.33 (Example 1), 0.75:0.25 (Example 2), and 0.86:0.14 (Example 3), and titanium oxides with a layered rock salt structure (TiO: Example 1, TiO: Example 2, TiO: Example 3) were synthesized as negative electrode active materials by arc melting. The synthesized titanium oxides as negative electrode active materials were pulverized in a mortar.

[0036] (Comparative Examples 1 and 2) Instead of the titanium oxide, titanium (Ti): Comparative Example 1 and titanium dioxide (TiO2): Comparative Example 2, which were used in synthesizing the titanium oxide, were used as the negative electrode active material.

[0037] [XRD measurement] Using a Miniflex CuKα radiation source (manufactured by Rigaku), X-ray diffraction measurements were performed on each of the negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 and 2 under an argon (Ar) atmosphere under the conditions of a measurement range of 2θ = 10° to 80°, a scan rate of 2° / min, and a measurement interval of 0.02°. Figure 2 shows the results of Example 1, Figure 3 shows the results of Example 2, Figure 4 shows the results of Example 3, Figure 5 shows the results of Comparative Example 1, and Figure 6 shows the results of Comparative Example 2. Table 1 shows the values ​​of A / B. 2 to 5, in Examples 1 to 3 and Comparative Example 1, almost no peaks appear at 2θ=10° to 30°, whereas three clear peaks appear at 2θ=30° to 40°. These are XRD peaks derived from the layered structure. On the other hand, as shown in FIG. 6, in Comparative Example 2, the strongest peak appears at 2θ=10° to 30°, whereas a peak appears at 2θ=30° to 40°, but it is not strong, indicating a structure other than a layered structure.

[0038] [Fabrication of all-solid-state fluoride-ion batteries] The negative electrode active materials of Examples 1 to 3 and Comparative Examples 1 and 2 were used as the negative electrode active materials, and calcium barium fluoride (Ca 0.5 Ba 0.5 F2) and vapor-grown carbon fiber (VGCF) (Showa Denko) as a conductive material were provided in a weight ratio of 30:60:10 and mixed in a ball mill at 100 rpm for 10 hours to prepare a negative electrode layer composite. The negative electrode layer composite was placed on Pt foil as a negative electrode current collector to obtain a negative electrode having a negative electrode layer on the negative electrode current collector. The calcium barium fluoride was prepared by mixing calcium fluoride (CaF2) (manufactured by Kojundo Chemical Co., Ltd.) and barium fluoride (BaF2) (manufactured by Kojundo Chemical Co., Ltd.) in a ball mill at 600 rpm for 20 hours. The solid electrolyte layer used the above-mentioned calcium barium fluoride as the solid electrolyte. The positive electrode layer was prepared by weighing lead fluoride (PbF) (manufactured by Kojundo Chemical Co., Ltd.) as the positive electrode active material and acetylene black (manufactured by Denka) as the conductive material in a weight ratio of 95:5 and mixing them in a ball mill at 600 rpm for 3 hours. The positive electrode layer composite was placed on Pb foil as a positive electrode current collector to obtain a positive electrode having a positive electrode layer on the positive electrode current collector. The batteries (all-solid-state fluoride ion batteries) of Examples 1 to 3 and Comparative Examples 1 and 2 were fabricated by laminating an anode current collector, an anode layer, a solid electrolyte layer, a cathode layer, and a cathode current collector in this order.

[0039] [Charge / discharge test] For each of the batteries of Examples 1 to 3 and Comparative Examples 1 and 2, a charge-discharge test was carried out under conditions of a voltage range of 0 V to -2.7 V (vs. Pb / PbF2), a current of 50 μA, and a temperature of 200°C. Fig. 7 shows the results of Example 1, Fig. 8 shows the results of Example 2, Fig. 9 shows the results of Example 3, Fig. 10 shows the results of Comparative Example 1, and Fig. 11 shows the results of Comparative Example 2. In Figs. 7 to 11, the solid and dashed lines represent the charge / discharge curves for the first and second cycles, respectively. Table 1 shows the initial charge capacity and initial discharge capacity of each battery of Examples 1 to 3 and Comparative Examples 1 and 2.

[0040] [Table 1]

[0041] 7 to 9, it is clear that high capacity was obtained and charge / discharge reactions were progressing in Examples 1 to 3. On the other hand, as shown in Figures 10 and 11, it is clear that almost no capacity was obtained and charge / discharge reactions were not progressing in Comparative Examples 1 and 2. [Explanation of symbols]

[0042] 1...Positive electrode layer 2...Anode layer 3...electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...Fluoride-ion battery

Claims

1. 1. A fluoride ion battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the negative electrode layer contains, as a negative electrode active material, a transition metal oxide having a layered structure and represented by MxOy, In the MxOy, M is at least one element selected from the group consisting of Ti, Zr, and Ta, x / y is 2 to 6, and y / (x+y)≧0.1 is satisfied.

2. The transition metal oxide satisfies A / B≦0.1 when the maximum peak intensity between 2θ = 15° and 30° is defined as A and the maximum peak intensity between 2θ = 30° and 40° is defined as B in X-ray diffraction measurement using CuKα rays. Fluoride ion battery according to claim 1.

3. The transition metal oxide is Ti ２ O, Ti ３ O and Ti ６ 2. The fluoride ion battery according to claim 1, wherein the fluoride ion battery is at least one selected from the group consisting of O.

4. 2. The fluoride ion battery according to claim 1, wherein the electrolyte layer is a solid electrolyte layer containing a solid electrolyte.

5. The solid electrolyte is Ca ０．５ Ba ０．５ F ２ 5. The fluoride ion battery according to claim 4, wherein

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