Positive electrode active material for fluoride ion battery, and fluoride ion battery

Abstract

To provide a positive electrode active material for a fluoride ion battery having a large capacity, particularly a large capacity in a noble potential region, and a fluoride ion battery including such a positive electrode active material.SOLUTION: A positive electrode active material for a fluoride ion battery according to the present disclosure is calcium carbide. A positive electrode mixture according to the present disclosure includes the positive electrode active material according to the present disclosure. The fluoride ion battery according to the present disclosure has a positive electrode active material layer, and the positive electrode active material layer includes the positive electrode active material according to the present disclosure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode active material for a fluoride ion battery and a fluoride ion battery. [Background technology]

[0002] Patent Document 1 describes a positive electrode active material used in a fluoride ion battery, which contains Pb 2-x Cu 1+x The document discloses a positive electrode active material having a first active material having a composition represented by F6 (0≦x<2) and a second active material containing Bi and F elements. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-200852 Summary of the Invention [Problem to be solved by the invention]

[0004] There is a need to increase the capacity of fluoride ion batteries, especially in the noble potential region.

[0005] The fluoride ion battery of Patent Document 1 has a capacity of about 150 mAh / g that can be reversibly used for two or more cycles at a discharge voltage of about 0.6 V.

[0006] An object of the present disclosure is to provide a positive electrode active material for a fluoride ion battery that has a large capacity, particularly a large capacity in a noble potential region, and a fluoride ion battery that includes such a positive electrode active material. [Means for solving the problem]

[0007] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> Calcium carbide, a positive electrode active material for fluoride-ion batteries. <Aspect 2> 2. The cathode active material of embodiment 1, having peaks at 27.9°±0.5°, 32.3°±0.5°, 37.4°±0.5°, 46.1°±0.5°, and 54.1°±0.5° in X-ray diffraction measurement using Cukα radiation. <Aspect 3> A positive electrode mixture comprising the positive electrode active material according to aspect 1 or 2. <Aspect 4> A positive electrode active material layer is provided. The positive electrode active material layer contains the positive electrode mixture according to aspect 3. Fluoride-ion battery. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a positive electrode active material for a fluoride ion battery having a large capacity, particularly a large capacity in a noble potential region, and a fluoride ion battery including such a positive electrode active material. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a graph showing the results of XRD measurements on calcium carbide. [Figure 2] FIG. 2 is a graph showing the charge / discharge curve of the evaluation battery of Example 1. [Figure 3] FIG. 3 is a graph showing the discharge capacity down to 0.5 V in the second cycle of the test batteries of each example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the present disclosure.

[0011] <Positive electrode active material for fluoride ion batteries> The positive electrode active material for a fluoride ion battery of the present disclosure is calcium carbide.

[0012] The present inventors have unexpectedly discovered that calcium carbide (particularly represented by CaC2) can be used as a positive electrode active material for fluoride ion batteries.

[0013] In the present disclosure, calcium carbide may be a commercially available product or one prepared by a conventional method. As a commercially available product, calcium carbide manufactured by Sigma-Aldrich can be used.

[0014] The positive electrode active material of the present disclosure may have peaks at 27.9°±0.5°, 32.3°±0.5°, 37.4°±0.5°, 46.1°±0.5°, and 54.1°±0.5° in X-ray diffraction (XRD) measurement using Cukα radiation. The width of these peak positions may be ±0.3° or ±0.1°.

[0015] XRD measurement can be performed on the positive electrode active material using, for example, an Ultima III (manufactured by Rigaku) ​​CuKα radiation source under conditions of a measurement range of 20° to 70°, a scan rate of 2° / min, and a measurement interval of 0.02° in an argon (Ar) atmosphere.

[0016] <Positive electrode mixture> The cathode mixture of the present disclosure includes the cathode active material of the present disclosure. The cathode mixture of the present disclosure optionally includes a solid electrolyte, a conductive material, and a binder.

[0017] In the present disclosure, the term "cathode mixture" refers to a composition that can constitute a cathode active material layer either as is or by further containing other components. In the present disclosure, the term "cathode mixture slurry" refers to a slurry that contains a dispersion medium in addition to a "cathode mixture" and that can be applied and dried to form a cathode active material layer.

[0018] <Cathode active material> For the positive electrode active material, reference can be made to the above description regarding the positive electrode active material for a fluoride ion battery of the present disclosure.

[0019] From the viewpoint of capacity, the content of the positive electrode active material in the positive electrode mixture is preferably as high as possible. The ratio of the mass of the positive electrode active material to the total mass of the positive electrode mixture may be 10 to 90 mass%, and preferably 20 to 80 mass%.

[0020] <Solid electrolyte> Examples of the solid electrolyte include fluorides of lanthanoid elements such as La and Ce, fluorides of alkali metal elements such as Li, Na, K, Rb, and Cs, and fluorides of alkaline earth elements such as Ca, Sr, and Ba. The solid electrolyte may also be a fluoride containing multiple lanthanoid elements, alkali metal elements, and alkaline earth elements.

[0021] Specific examples of solid electrolytes include La (1-x) Ba x F (3-x) (0≦x≦2), Pb (2-x) Sn x F4(0≦x≦2), Ca (2-x) Ba x F4(0≦x≦2) and Ce (1-x) Ba x F (3-x) (0≦x≦2). Each of the x's may be greater than 0, 0.3 or greater, 0.5 or greater, or 0.9 or greater. Also, each of the x's may be smaller than 1, 0.9 or less, 0.5 or less, or 0.3 or less.

[0022] The proportion of the mass of the solid electrolyte to the total mass of the positive electrode mixture may be 10 to 90 mass %, and is preferably 20 to 80 mass %.

[0023] <Conductive materials> The conductive material is not particularly limited as long as it has the desired electronic conductivity, and examples of the conductive material include carbon materials, such as carbon blacks such as acetylene black, ketjen black, furnace black, and thermal black.

[0024] The proportion of the mass of the conductive material to the total mass of the positive electrode mixture may be 0.1 to 20 mass %, and is preferably 1 to 10 mass %.

[0025] <binder> The binder is not particularly limited as long as it is chemically and electrically stable, and examples thereof include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0026] Fluoride-ion battery The fluoride ion battery of the present disclosure has a positive electrode active material layer, and the positive electrode active material layer contains the positive electrode mixture of the present disclosure.

[0027] The fluoride ion battery of the present disclosure may have, in this order, a positive electrode current collector, a positive electrode active material layer containing the positive electrode mixture of the present disclosure, an electrolyte layer, a negative electrode active material layer, and a negative electrode current collector.

[0028] The fluoride ion battery of the present disclosure may have a battery case that houses these components.

[0029] The fluoride ion battery of the present disclosure may be a liquid-based battery or a solid-state battery. In the context of the present disclosure, a "solid-state battery" refers to a battery that uses at least a solid electrolyte as an electrolyte, and therefore a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte. Alternatively, the solid-state battery of the present disclosure may be an all-solid-state battery, i.e., a battery that uses only a solid electrolyte as an electrolyte.

[0030] The fluoride ion battery in the present disclosure may be a primary battery or a secondary battery.

[0031] The shape of the fluoride ion battery in the present disclosure may be, for example, a coin type, a laminate type, a cylindrical type, or a prismatic type.

[0032] <Positive electrode current collector> The material for the positive electrode current collector is not particularly limited as long as it has the desired electronic conductivity and does not undergo a significant change in volume or shape during charging and discharging. Examples of the material include stainless steel (SUS), aluminum, titanium, iron, nickel, copper, silver, platinum, gold, and carbon.

[0033] The positive electrode current collector may be in the form of, for example, a foil, a mesh, a pellet, or a porous material.

[0034] <Cathode active material layer> The positive electrode active material layer contains the positive electrode mixture of the present disclosure.

[0035] For the positive electrode mixture, reference can be made to the above description regarding the positive electrode mixture of the present disclosure.

[0036] The thickness of the positive electrode active material layer varies greatly depending on the configuration of the battery, and is not particularly limited.

[0037] The positive electrode active material layer can be formed, for example, by depositing a positive electrode mixture containing a positive electrode active material and an optional solid electrolyte, a conductive additive, and a binder on a positive electrode current collector as a substrate.

[0038] More specifically, for example, a positive electrode active material, an optional solid electrolyte, a conductive additive, and a binder are mixed in a ball mill to prepare a powder of a positive electrode composite, and a compact of the powder of the positive electrode composite is formed on a positive electrode current collector. Alternatively, for example, a positive electrode active material, an optional solid electrolyte, a conductive additive, and a binder may be dispersed in a dispersion medium to prepare a slurry, and the slurry may be applied to a positive electrode current collector and dried to form the positive electrode composite.

[0039] <Electrolyte layer> When the fluoride ion battery of the present disclosure is a liquid battery, the electrolyte layer may be composed of, for example, an electrolyte solution and an optional separator.

[0040] (electrolyte) The electrolyte may contain, for example, a fluoride salt and an organic solvent. Examples of the fluoride salt include inorganic fluoride salts, organic fluoride salts, and ionic liquids. An example of the inorganic fluoride salt is XF (X is Li, Na, K, Rb, or Cs). An example of the cation of the organic fluoride salt is an alkylammonium cation such as a tetramethylammonium cation.

[0041] The concentration of the fluoride salt in the electrolytic solution is, for example, 0.1 mol % or more and 40 mol % or less, and preferably 1 mol % or more and 10 mol % or less.

[0042] 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). An ionic liquid may also be used as the organic solvent.

[0043] (separator) The separator is not particularly limited as long as it has a composition that can withstand the range of uses of a fluoride ion battery, and examples of the separator include polymer nonwoven fabrics such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics, and microporous fillers of olefin resins such as polyethylene and polypropylene.

[0044] When the fluoride ion battery of the present disclosure is a solid-state battery, the electrolyte layer may be, for example, a layer of a solid electrolyte. The solid electrolyte may be any solid electrolyte that can be used in a fluoride ion battery.

[0045] (solid electrolyte) For the solid electrolyte, reference can be made to the above description regarding the positive electrode mixture of the present disclosure.

[0046] <Negative electrode active material layer> The negative electrode active material layer contains a negative electrode active material, and optionally a solid electrolyte, a conductive material, and a binder.

[0047] (Negative electrode active material) The negative electrode active material may be any active material having a lower potential than the positive electrode active material. Examples of the negative electrode active material include simple metals, alloys, and fluorides of metal oxides. Examples of metal elements contained in the negative electrode active material include La, Ca, Al, Eu, Li, Si, Ge, Sn, In, V, Cd, Cr, Fe, Zn, Ga, Ti, Nb, Mn, Yb, Zr, Sm, Ce, Mg, and Pb. Among these, the negative electrode active material is preferably MgF x , AlF x , LaF x , CeF x , CaF x , or PbF x It is preferable that x is a real number greater than 0.

[0048] The content of the negative electrode active material in the negative electrode active material layer is preferably as high as possible from the viewpoint of capacity. The ratio of the mass of the negative electrode active material to the total mass of the negative electrode active material layer may be 10 to 90 mass %, and preferably 20 to 80 mass %.

[0049] (Solid electrolyte, conductive material, and binder) For the solid electrolyte, the conductive material, and the binder, reference can be made to the above descriptions regarding the positive electrode mixture of the present disclosure.

[0050] <Negative electrode current collector> The material for the negative electrode current collector is not particularly limited as long as it has the desired electronic conductivity and does not undergo a significant change in volume or shape during charging and discharging. Examples of the material include stainless steel (SUS), aluminum, titanium, iron, nickel, copper, silver, platinum, gold, and carbon.

[0051] The negative electrode current collector may be in the form of, for example, a foil, a mesh, a pellet, or a porous material. [Example]

[0052] 《Fabrication of fluoride-ion batteries》 Example 1 Calcium carbide (CaC2) powder (Sigma-Aldrich) as the positive electrode active material, solid electrolyte (Ca 0.5 Ba 0.5 The cathode composite was obtained by mixing CaF2 (manufactured by Kojundo Chemical Co., Ltd.) and BaF2 (manufactured by Kojundo Chemical Co., Ltd.) in a weight ratio of 19:19:2 using a ball mill (rotation speed: 200 rpm). The cathode composite and the solid electrolyte (CaF2) that forms the solid electrolyte layer were then mixed. 0.5 Ba 0.5 A counter electrode composite prepared by mixing PbF2, PbF2, and a conductive material (acetylene black) at a ratio of 95:5, and Pb foil were laminated in this order and compacted to prepare the evaluation battery of Example 1.

[0053] Comparative Example 1 An evaluation battery for Comparative Example 1 was prepared in the same manner as in Example 1, except that lanthanide carbide (LaC2) powder (manufactured by Rare Metallic), which has the same MC2 composition (M is a metal element) as CaC2, was used instead of CaC2 powder as the positive electrode active material.

[0054] "evaluation" <XRD measurement> XRD measurement was performed on the positive electrode active material (CaC2) using, for example, an Ultima III (manufactured by Rigaku) ​​with a CuKα radiation source under conditions of a measurement range of 20° to 70°, a scan rate of 2° / min, and a measurement interval of 0.02° in an argon (Ar) atmosphere.

[0055] <Charge / Discharge Test> A charge-discharge test was carried out on the prepared evaluation battery. The conditions for the charge-discharge test were a temperature of 200°C, a cut-off potential of the positive electrode of -2.5V (vs. Pb / PbF2) to 3V (vs. Pb / PbF2), and a current of 50 μA / cm 2 It was decided.

[0056] "result" <XRD measurement> The results of XRD measurements on CaC2 are shown in Figure 1. As shown in Figure 1, XRD measurements on CaC2 using Cukα radiation showed peaks at 27.9°, 32.3°, 37.4°, 46.1°, and 54.1°.

[0057] <Charge / Discharge Test> The charge-discharge curve of the evaluation battery of Example 1 is shown in Figure 2. As shown in Figure 2, the discharge capacity at the second cycle of the battery of Example 1 containing CaC2 as the positive electrode active material was equivalent to the discharge capacity at the first cycle.

[0058] The discharge capacity up to 0.5 V in the second cycle of the evaluation batteries of each example is shown in Figure 3. As shown in Figure 3, the discharge capacity of the battery of Example 1 containing CaC2 as the positive electrode active material was about 4.5 times larger than the discharge capacity of the battery of Comparative Example 1.

Claims

1. Calcium carbide, a positive electrode active material for fluoride-ion batteries.

2. 2. The positive electrode active material according to claim 1, which has peaks at 27.9°±0.5°, 32.3°±0.5°, 37.4°±0.5°, 46.1°±0.5°, and 54.1°±0.5° in X-ray diffraction measurement using Cukα radiation.

3. A positive electrode mixture comprising the positive electrode active material according to claim 1 or 2.

4. A positive electrode active material layer is provided. The positive electrode active material layer contains the positive electrode mixture according to claim 3. Fluoride-ion battery.

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