Fluoride ion conductor and fluoride ion battery

Abstract

To provide a technology for decreasing porosity while avoiding a decrease in fluoride ion conductivity in a fluoride ion conductor.SOLUTION: A fluoride ion conductor is composed of a sintered body including fluorine, yttrium, and barium.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fluoride ion conductor and a fluoride ion battery. [Background technology]

[0002] Fluoride ion conductors in which fluoride ions can move have been known (for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2023 / 100599 [Patent Document 2] Japanese Patent Application Publication No. 2018-77986 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even with the prior art such as Patent Documents 1 and 2, there is still room for improvement in the technology for reducing the porosity of a fluoride ion conductor while suppressing the decrease in fluoride ion conductivity.

[0005] An object of the present invention is to provide a technique for reducing the porosity of a fluoride ion conductor while suppressing a decrease in fluoride ion conductivity. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following aspects.

[0007] (1) According to one aspect of the present invention, there is provided a fluoride ion conductor, which is made of a sintered body containing fluorine, yttrium, and barium.

[0008] According to this configuration, the fluoride ion conductor is made of a sintered body containing fluorine, yttrium, and barium. The sintered body containing fluorine, yttrium, and barium has excellent sinterability, so pores are less likely to form. This provides a relatively large number of conduction paths for fluoride ions, thereby suppressing a decrease in fluoride ion conductivity. Therefore, in the fluoride ion conductor, it is possible to reduce the porosity while suppressing a decrease in fluoride ion conductivity.

[0009] (2) In the fluoride ion conductor of the above embodiment, the fluorine content may be 69 mol% or more. According to this configuration, the sintered body that is the fluoride ion conductor contains fluorine, yttrium, and barium, and contains 69 mol% or more of fluorine. This makes it possible to increase the fluoride ion conductivity of the fluoride ion conductor.

[0010] (3) In the fluoride ion conductor of the above embodiment, the porosity may be 5% or less. With this configuration, since the porosity is 5% or less, the sintered body that is the fluoride ion conductor has a relatively large number of conduction paths for fluoride ions. This makes it possible to suppress a decrease in the fluoride ion conductivity in the fluoride ion conductor.

[0011] (4) In the fluoride ion conductor of the above embodiment, the fluoride ion conductivity is 0.5 × 10 -7 According to this configuration, the sintered body that is a fluoride ion conductor contains fluorine, yttrium, and barium, and the fluoride ion conductivity may be 0.5×10 S / cm or more. -7 This allows the fluoride ion conductor to be applied to various technical fields that use fluoride ions as a charge carrier.

[0012] (5) According to another aspect of the present invention, there is provided a fluoride ion battery. The fluoride ion battery includes the fluoride ion conductor having the above-described configuration. According to this configuration, the fluoride ion battery includes the fluoride ion conductor made of a sintered body containing fluorine, yttrium, and barium. This reduces the porosity of the fluoride ion conductor, which serves as a conduction path for fluoride ions in the fluoride ion battery, thereby suppressing deterioration in the charge / discharge characteristics of the fluoride ion battery.

[0013] The present invention can be realized in various forms, for example, a method for manufacturing a fluoride ion conductor, a method for manufacturing a fluoride ion battery, a device and a system including a fluoride ion conductor, a method for controlling these devices and systems, a computer program for supplying power in these devices and systems, etc. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of a fluoride ion battery according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating the evaluation results of the fluoride ion conductor of the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] First Embodiment Fig. 1 is a schematic diagram illustrating the configuration of a fluoride ion battery of the first embodiment. As shown in Fig. 1, the fluoride ion battery 10 of this embodiment includes a positive electrode 11, a negative electrode 12, and a fluoride ion conductor 1. The fluoride ion battery 10 of this embodiment is charged and discharged by the movement of fluoride ions as charge carriers between the positive electrode 11 and the negative electrode 12 in accordance with the operating state of an electric device 5 such as a motor. Note that, for convenience of explanation, the thickness relationships between the positive electrode 11, the negative electrode 12, and the fluoride ion conductor 1 in Fig. 1 are illustrated to differ from the actual thickness relationships.

[0016] The positive electrode 11 includes a positive electrode active material layer 11a and a positive electrode current collector 11b. The positive electrode active material layer 11a is a layer containing a positive electrode active material. The positive electrode active material is, for example, a metal element, an alloy, a metal oxide, or a metal fluoride. The positive electrode active material layer 11a may further contain at least one of a conductive material and a binder in addition to the positive electrode active material. The positive electrode current collector 11b has, for example, a foil, mesh, or porous shape. The positive electrode current collector 11b supports the positive electrode active material layer 11a and collects current from the positive electrode active material layer 11a. In the positive electrode 11, fluoride ions (F - During charging, a defluorination reaction occurs in which fluoride ions are bonded to the electrolyte.

[0017] The negative electrode 12 includes a negative electrode active material layer 12a and a negative electrode current collector 12b. The negative electrode active material layer 12a is a layer containing a negative electrode active material. The negative electrode active material has a lower potential than the positive electrode active material. The negative electrode active material is, for example, a metal element, an alloy, a metal oxide, or a metal fluoride. The negative electrode active material layer 12a may further contain at least one of a conductive material and a binder in addition to the negative electrode active material. The negative electrode current collector 12b has, for example, a foil, mesh, or porous shape. The negative electrode current collector 12b supports the negative electrode active material layer 12a and collects current from the negative electrode active material layer 12a. In the negative electrode 12, a defluorination reaction proceeds in the negative electrode active material layer 12a during charging, and a fluorination reaction proceeds during discharging.

[0018] The fluoride ion conductor 1 is disposed between the positive electrode active material layer 11a of the positive electrode 11 and the negative electrode active material layer 12a of the negative electrode 12. The fluoride ion conductor 1 is a solid electrolyte, and allows fluoride ions to move between the positive electrode active material layer 11a and the negative electrode active material layer 12a.

[0019] The fluoride ion conductor 1 of this embodiment is a sintered body containing fluorine (F), yttrium (Y), and barium (Ba). The composition formula of the sintered body that is the fluoride ion conductor 1 of this embodiment can be expressed as the following formula (1). Ba (1-x) Y(1+x) F (5+x) ···(1) In formula (1), -0.4≦x≦0.4. The composition formula of the sintered body that is the fluoride ion conductor 1 of this embodiment is Ba 0.9 Y 1.1 F 5.1 The sintered body that is the fluoride ion conductor 1 may contain trace amounts of elements other than fluorine, yttrium, and barium, provided that the total amount of fluorine, yttrium, and barium is, for example, 99.5 mol % or more.

[0020] In the fluoride ion conductor 1 of this embodiment, the fluorine content is 69 mol% or more and 73 mol% or less. In the fluoride ion conductor 1, the fluorine content of 69 mol% or more and 73 mol% or less makes it possible to increase the fluoride ion conductivity, as described below. When the fluorine content in the sintered body that is the fluoride ion conductor 1 is 71.0 mol% or more, the fluoride ion conductivity can be further increased. The fluorine content of the fluoride ion conductor 1 of this embodiment is 71.8 mol%.

[0021] The fluoride ion conductor 1 of this embodiment has a porosity of 5% or less. When the porosity of the fluoride ion conductor 1 is 5% or less, the density becomes relatively large, and a relatively large number of paths through which fluoride ions can be conducted are formed in the fluoride ion conductor 1. This facilitates the movement of fluoride ions between the positive electrode active material layer 11a and the negative electrode active material layer 12a, and the charge / discharge characteristics of the fluoride ion battery 10 including the fluoride ion conductor 1 are improved. The smaller the porosity of the fluoride ion conductor 1, the more likely it is to become a dense body, and more paths through which fluoride ions can be conducted are formed. In other words, the denser the fluoride ion conductor 1, the higher the fluoride ion conductivity. The porosity of the fluoride ion conductor 1 is calculated by imaging a cross section using a scanning electron microscope (SEM) and performing image analysis on the image of the captured cross section. The porosity of the fluoride ion conductor 1 of this embodiment is 2.5%.

[0022] In the fluoride ion conductor 1 of this embodiment, the fluoride ion conductivity is 0.5 × 10 -7 The fluoride ion conductivity of the fluoride ion conductor 1 refers to the fluoride ion conductivity within the crystal grains contained in the sintered body. The fluoride ion conductivity of the fluoride ion conductor 1 is 0.5×10 -7 S / cm or more, the fluoride ion battery 10 can be charged and discharged in a relatively short time. The fluoride ion conductivity of the fluoride ion conductor 1 is measured by an AC impedance method (measurement temperature: 25°C, applied voltage 10 mV, measurement frequency range: 7 MHz to 0.1 Hz) using a high-frequency impedance measurement system, and calculated from the thickness of the fluoride ion conductor 1 and the resistance value on the real axis of the Cole-Cole plot. As described above, when the porosity of the sintered body is relatively small, fluoride ions move easily, and therefore the fluoride ion conductivity increases. The fluoride ion conductivity of the fluoride ion conductor 1 of this embodiment is 5×10 -7 S / cm.

[0023] Next, a method for producing the fluoride ion conductor 1 will be described. First, a BaF2 sample (manufactured by Hakushin Chemical Co., Ltd.) and a YF3 sample (manufactured by Nippon Yttrium Co., Ltd.) are prepared as raw materials. Next, a sintered body having the composition formula BaF3, which is the fluoride ion conductor 1, is prepared. 0.9 Y 1.1 F 5.1 The weighed BaF2 sample and YF3 sample are uniformly mixed by dry mixing to prepare a mixed powder. Next, the prepared mixed powder is set in a mold and pressed, and then subjected to cold isostatic pressing (CIP) to prepare a molded body. The load in CIP is, for example, 1.5 tons. Finally, the prepared molded body is fired to complete a sintered body that will become the fluoride ion conductor 1. The firing conditions for the molded body are, for example, an argon atmosphere at 9 atmospheres, a firing temperature of 1025°C, and a holding time of 2 hours.

[0024] Next, an evaluation test performed on the fluoride ion conductor will be described. In this evaluation test, the effects of the composition and the firing temperature on the properties of the sintered body, which is a fluoride ion conductor, were evaluated.

[0025] FIG. 2 is a diagram illustrating the evaluation results of fluoride ion conductors. In this evaluation test, ten types of sintered bodies (hereinafter simply referred to as "samples") manufactured by a method similar to the manufacturing method of the fluoride ion conductor 1 of this embodiment described above were prepared. Of Samples 1 to 10 shown in FIG. 2, Samples 1 to 8 were manufactured using BaF2 and YF3 samples, similar to the fluoride ion conductor 1 of this embodiment, and contained fluorine, yttrium, and barium. Sample 9 was manufactured using LaF3 instead of the YF3 sample, and contained fluorine, barium, and lanthanum (La). Sample 10 was manufactured using CaF2 instead of the BaF2 sample, and contained fluorine, yttrium, and calcium (Ca). Samples 9 and 10 were both fired at a temperature of 1300°C, which was set higher than Samples 1 to 8 (fired at temperatures of 950°C to 1025°C).

[0026] FIG. 2 shows the "fluoride ion conductivity" (unit: S / cm) and "porosity" (unit: %) for each of Samples 1 to 10. The "fluoride ion conductivity" was measured by an AC impedance method (measurement temperature: 25°C, applied voltage: 10 mV, measurement frequency range: 7 MHz to 0.1 Hz) using a high-frequency impedance measurement system, similar to the method for measuring the fluoride ion conductivity of the fluoride ion conductor 1 of this embodiment, and calculated from the sample thickness and the resistance value on the real axis of the Cole-Cole plot. The "porosity" was calculated by imaging a cross section of the sample using a scanning electron microscope (SEM) and performing image analysis on the image of the cross section.

[0027] As shown in FIG. 2, Samples 1 to 8, which contain fluorine, yttrium, and barium, were confirmed to have fluoride ion conductivities comparable to those of Sample 9, which contains fluorine, lanthanum, and barium, and Sample 10, which contains fluorine, yttrium, and calcium. Meanwhile, the "porosity" of Samples 1 to 8 was confirmed to be smaller than that of Samples 9 and 10. It is believed that the relatively low melting point of the raw material YF3 in Samples 1 to 8 facilitates efficient sintering during firing, resulting in relatively low porosity. When the porosity of a sintered body decreases, the degree of packing of crystal particles increases, leading to increased density. Furthermore, the small number of pores provides a relatively large number of conduction paths for fluoride ions, making it difficult for the fluoride ion conductivity to decrease.

[0028] Fluoride ion batteries often use a fluoride ion conductor, which is made of an alkaline earth metal such as calcium, a lanthanoid metal such as lanthanum, and fluorine, as a solid electrolyte. Such fluoride ion conductors are manufactured by mechanochemical and heat treatment processes, but they tend to form pores internally. Therefore, fluoride ion conductors made of an alkaline earth metal, a lanthanoid metal, and fluorine have a relatively low density, making it difficult to improve the charge / discharge characteristics of fluoride ion batteries.

[0029] The fluoride ion conductor 1 of this embodiment, which is a sintered body containing fluorine, yttrium, and barium, can be fired at a relatively low temperature, and therefore has excellent sinterability and is less likely to form pores inside. This makes it possible to obtain a solid electrolyte with a relatively small porosity without significantly reducing the fluoride ion conductivity.

[0030] According to the fluoride ion conductor 1 of the present embodiment described above, the fluoride ion conductor 1 is made of a sintered body containing fluorine, yttrium, and barium. A sintered body containing fluorine and yttrium has excellent sinterability, and therefore pores are less likely to form. This provides a relatively large number of conduction paths for fluoride ions, thereby suppressing a decrease in fluoride ion conductivity. Therefore, in the fluoride ion conductor, it is possible to reduce the porosity while suppressing a decrease in fluoride ion conductivity.

[0031] Furthermore, according to the fluoride ion conductor 1 of this embodiment, the sintered body that is the fluoride ion conductor 1 contains fluorine, yttrium, and barium, and contains 69 mol % or more of fluorine, which makes it possible to increase the fluoride ion conductivity of the fluoride ion conductor 1.

[0032] Furthermore, according to the fluoride ion conductor 1 of this embodiment, the porosity of the fluoride ion conductor 1 is 5% or less. This allows the sintered body that is the fluoride ion conductor 1 to have a relatively large number of conduction paths for fluoride ions. Therefore, it is possible to suppress a decrease in the fluoride ion conductivity of the fluoride ion conductor 1.

[0033] Furthermore, according to the fluoride ion conductor 1 of this embodiment, the sintered body that is the fluoride ion conductor 1 contains fluorine, yttrium, and barium, and has a fluoride ion conductivity of 0.5×10 -7 S / cm or more, which allows the fluoride ion conductor 1 to be applied to various technical fields that use fluoride ions as a charge carrier.

[0034] Furthermore, the fluoride ion battery 10 of this embodiment includes the fluoride ion conductor 1 made of a sintered body containing fluorine, yttrium, and barium. This reduces the porosity of the fluoride ion conductor, which serves as a conduction path for fluoride ions in the fluoride ion battery 10, and therefore can suppress deterioration in the charge / discharge characteristics of the fluoride ion battery.

[0035] <Modification of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0036] [Variation 1] In the above-described embodiment, the fluoride ion conductor 1 is provided in the fluoride ion battery 10. However, the technical field to which the fluoride ion conductor is applied is not limited to this. The fluoride ion conductor may be applied to a sensor for detecting a fluoride ion concentration or an oxygen concentration.

[0037] [Variation 2] In the above-described embodiment, the fluorine content of the fluoride ion conductor 1 is set to 69 mol % or more and 73 mol % or less. Although the upper and lower limits of the fluorine content are not limited to these, the fluorine content of 69 mol % or more and 73 mol % or less can increase the fluoride ion conductivity.

[0038] [Variation 3] In the above-described embodiment, the porosity of the fluoride ion conductor 1 is set to 5% or less. Although the upper limit of the porosity is not limited to this, by setting the porosity to 5% or less, a sintered body in which fluoride ions can easily move is obtained.

[0039] [Variation 4] In the above embodiment, the fluoride ion conductivity of the fluoride ion conductor 1 is 0.5×10 -7 The fluoride ion conductivity was 0.5×10 -7 Although the fluoride ion conductivity may be less than S / cm, a higher fluoride ion conductivity is preferred.

[0040] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0041] (Application example 1) A fluoride ion conductor, A sintered body comprising fluorine, yttrium, and barium. Fluoride ion conductor. (Application example 2) The fluoride ion conductor according to Application Example 1, The fluorine content is 69 mol% or more. Fluoride ion conductor. (Application example 3) The fluoride ion conductor according to Application Example 1 or Application Example 2, The porosity is 5% or less. Fluoride ion conductor. (Application example 4) The fluoride ion conductor according to any one of Application Examples 1 to 3, Fluoride ionic conductivity is 0.5×10 -7 S / cm or more, Fluoride ion conductor. (Application example 5) 1. A fluoride ion battery, comprising: The fluoride ion conductor according to any one of Application Examples 1 to 4 is provided. Fluoride-ion battery. [Explanation of symbols]

[0042] 1...Fluoride ion conductor 10...Fluoride-ion battery

Claims

1. A fluoride ion conductor, A sintered body comprising fluorine, yttrium, and barium. Fluoride ion conductor.

2. 2. The fluoride ion conductor of claim 1, The fluorine content is 69 mol% or more. Fluoride ion conductor.

3. 3. The fluoride ion conductor according to claim 1 or claim 2, The porosity is 5% or less. Fluoride ion conductor.

4. 3. The fluoride ion conductor according to claim 1 or claim 2, Fluoride ion conductivity is 0.5 × 10 -7 S / cm or more, Fluoride ion conductor.

5. 1. A fluoride ion battery, comprising: The fluoride ion conductor according to claim 1 or 2 is provided. Fluoride-ion battery.

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