JP2022132767A - Solid electrolyte and fluoride ion battery - Google Patents

Abstract

To provide a solid electrolyte having good fluoride ion conductivity in a room temperature region.SOLUTION: The above problem is solved by providing a solid electrolyte comprising a crystal phase represented by RbxSbF3+x (where x satisfies 1.6≤x≤2.4) in the disclosure hereof, which is to be used for a fluoride ion battery.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to solid electrolyte and fluoride ion batteries.

Li-ion batteries, for example, are known as high-voltage and high-energy-density batteries. A Li-ion battery is a cation-based battery that uses Li-ions as carriers. On the other hand, as an anion-based battery, a fluoride ion battery using fluoride ions as carriers is known.

For example, Patent Document 1 discloses a solid electrolyte having an A ₂ SiF ₆ crystal phase (A is at least one of K, Na and Li).

JP 2019-091572 A

The solid electrolyte described in Patent Document 1 has a high fluoride ion conductivity in a high temperature range of, for example, 80° C. or higher, but a low fluoride ion conductivity in a lower temperature range, that is, a room temperature range. The present disclosure has been made in view of the above circumstances, and a main object thereof is to provide a solid electrolyte having good fluoride ion conductivity in the room temperature range.

In order to solve the above problems, in the present disclosure, a crystal represented by Rb _x SbF _3+x (where x satisfies 1.6 ≤ x ≤ 2.4) is a solid electrolyte used in a fluoride ion battery A solid electrolyte is provided comprising a phase.

According to the present disclosure, a solid electrolyte having good fluoride ion conductivity in a room temperature range is obtained by including a predetermined crystal phase.

In the above disclosure, x may satisfy 1.8≦x≦2.4.

In the above disclosure, the solid electrolyte may be a single-phase material of the crystal phase.

Further, in the present disclosure, a fluoride ion battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer, the negative electrode layer and At least one of the solid electrolyte layers provides a fluoride ion battery containing the solid electrolyte described above.

According to the present disclosure, at least one of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer contains the solid electrolyte described above, thereby providing a fluoride ion battery with good output characteristics in the room temperature range.

The present disclosure has the effect of being able to provide a solid electrolyte having good fluoride ion conductivity in the room temperature range.

1 is a schematic cross-sectional view showing an example of a fluoride ion battery in the present disclosure; FIG. It is the result of XRD measurement of Examples 1-5. 4 is a graph showing the fluoride ion conductivity of Examples 1-5.

The solid electrolyte and fluoride ion battery according to the present disclosure will be described in detail below.

A. Solid Electrolyte The solid electrolyte in the present disclosure is a solid electrolyte used in fluoride ion batteries, and has a crystal phase represented by Rb _x SbF _3+x (where x satisfies 1.6≦x≦2.4).

According to the present disclosure, a solid electrolyte having good fluoride ion conductivity in a room temperature range is obtained by including a predetermined crystal phase. In the present disclosure, the "room temperature range" is, for example, 0°C or higher and 40°C or lower, typically 25°C.

In general, the fluoride ion conductivity of a solid electrolyte depends on temperature, and the higher the temperature, the higher the fluoride ion conductivity, and the lower the temperature, the lower the fluoride ion conductivity. For example, the solid electrolyte disclosed in Patent Document 1 (a solid electrolyte having a crystal phase containing the alkali metal elements A element, Si element and F element) is, for example, fluoride ion conductive in a high temperature range of 80 ° C. or higher. Although the temperature is high, the fluoride ion conductivity is low in the room temperature range, which is a lower temperature range. This is probably because the strong ionic bond between the alkali metal element and the F element inhibits the diffusion of F. On the other hand, in the present disclosure, since the lone electron pair of the 5s orbital of Sb ³⁺ repels F ⁻ , it is possible to suppress the trapping of F ⁻ by Rb ⁺ which is an alkali metal element. In other words, the Sb element contained in the crystal phase can weaken the ionic bonding force between Rb ⁺ and F ⁻ . As a result, the fluoride ion conductivity in the room temperature range is improved.

The solid electrolyte in the present disclosure includes a crystal phase (hereinafter also referred to as crystal phase A) represented by Rb _x SbF _3+x (where x satisfies 1.6≦x≦2.4). x may be 1.8 or more, or 1.9 or more. On the other hand, x may be 2.3 or less, or 2.2 or less.

The solid electrolyte in the present disclosure includes at least crystal phase A as the crystal phase. Among them, the solid electrolyte preferably has the crystalline phase A as a main phase. The main phase refers to the crystal phase to which the maximum peak observed by X-ray diffraction measurement belongs. In particular, the solid electrolyte is preferably a crystalline phase A single-phase material.

Crystalline phase A has a typical peak near 2θ=27° in X-ray diffraction measurement using CuKα rays.

Also, the solid electrolyte in the present disclosure preferably does not have a heterophasic peak appearing near 2θ=26°. The phrase "having no peaks of different phases" means that the diffraction intensity of peaks derived from different phases is so small that it cannot be distinguished from the surrounding noise.

Moreover, when the solid electrolyte in the present disclosure has a peak of a heterogeneous phase, it is preferable that the diffraction intensity of the peak is small. Here, when the diffraction intensity of the main peak of the crystalline phase A is Ia and the diffraction intensity of the peak of the heterogeneous phase is Ib, Ib/Ia is preferably 0.3 or less, and is 0.1 or less. is more preferable.

Examples of the shape of the solid electrolyte include particulate. Also, the average particle size (D ₅₀ ) of the solid electrolyte is, for example, 0.1 μm or more and 50 μm or less. The average particle size ( _D50 ) can be obtained from the results of particle size distribution measurement by a laser diffraction scattering method. Further, the fluoride ion conductivity (25° C.) of the solid electrolyte is, for example, 1×10 ⁻⁶ S/cm or more, preferably 1×10 ⁻⁵ S/cm or more.

The method for producing the solid electrolyte is not particularly limited, but for example, a raw material composition containing at least a fluoride of Rb and a fluoride of Sb is mixed while applying mechanical energy, and then heat-treated. . Examples of the method of applying mechanical energy include mechanical milling such as ball milling. The table rotation speed in the ball mill is, for example, 500 rpm or more and 700 rpm or less. The processing time of mechanical milling is, for example, 1 hour or more and 25 hours or less. The heat treatment temperature is, for example, 600° C. or higher, may be 700° C. or higher, or may be 800° C. or higher. On the other hand, the heat treatment temperature is, for example, 1200° C. or lower. Further, the heat treatment time is, for example, 1 hour or longer, may be 20 hours or longer, or may be 40 hours or longer. On the other hand, the heat treatment time is, for example, 100 hours or less. Also, the heat treatment may be performed in an inert gas atmosphere such as an Ar gas atmosphere.

Moreover, the solid electrolyte in the present disclosure is used in a fluoride ion battery, which will be described later.

B. Fluoride Ion Battery FIG. 1 is a schematic cross-sectional view showing an example of a fluoride ion battery in the present disclosure. Fluoride ion battery 10 shown in FIG. It has a current collector 4, a negative electrode current collector 5 that collects current from the negative electrode layer 2, and a battery case 6 that houses these members. In the present disclosure, at least one of the positive electrode layer 1, the negative electrode layer 2 and the solid electrolyte layer 3 contains the solid electrolyte described above. In addition, since the fluoride ion battery in the present disclosure has a solid electrolyte layer, it can also be referred to as an all-solid fluoride ion battery.

According to the present disclosure, at least one of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer contains the solid electrolyte described above, thereby providing a fluoride ion battery with good output characteristics in the room temperature range.

1. Positive Electrode Layer The positive electrode layer in the present disclosure is a layer containing at least a positive electrode active material. Moreover, the positive electrode layer may further contain at least one of a solid electrolyte, a conductive material and a binder, if necessary.

The positive electrode active material is generally an active material that defluorinates during discharge. Examples of positive electrode active materials include simple metals, alloys, metal oxides, and fluorides thereof. Metal elements contained in the positive electrode active material include, for example, Cu, Ag, Ni, Co, Pb, Ce, Mn, Au, Pt, Rh, V, Os, Ru, Fe, Cr, Bi, Nb, Sb, Ti , Sn and Zn. Among them, the positive electrode active material is preferably Cu, _CuFz , Fe, _FeFz , Ag, or _AgFz . Note that z is a real number greater than zero. Other examples of positive electrode active materials include carbon materials and fluorides thereof. Carbon materials include, for example, graphite, coke and carbon nanotubes. Still another example of the positive electrode active material is a polymer material. Polymer materials include, for example, polyaniline, polypyrrole, polyacetylene and polythiophene.

Examples of conductive materials include carbon materials. Specific examples of carbon materials include acetylene black, ketjen black, VGCF, and graphite. Examples of binders include rubber-based binders and fluoride-based binders. The solid electrolyte is the same as described later in "3. Solid electrolyte layer". In particular, the positive electrode layer preferably contains the solid electrolyte described in "A. Solid electrolyte". Moreover, the thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

2. Negative Electrode Layer The negative electrode layer in the present disclosure is a layer containing at least a negative electrode active material. Moreover, the negative electrode layer may further contain at least one of a solid electrolyte, a conductive material and a binder, if necessary.

The negative electrode active material is usually an active material that defluorinates during charging. Examples of negative electrode active materials include simple metals, alloys, metal oxides, and fluorides thereof. 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. Moreover, the above-described carbon materials and polymer materials can also be used as the negative electrode active material.

The conductive material, the binder, and the solid electrolyte are the same as those described in “1. In particular, the negative electrode layer preferably contains the solid electrolyte described in "A. Solid electrolyte". Moreover, the thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

3. Solid Electrolyte Layer The solid electrolyte layer in the present disclosure is a layer formed between the positive electrode layer and the negative electrode layer, and contains at least a solid electrolyte. Moreover, the solid electrolyte layer may further contain a binder as needed.

The solid electrolyte is not particularly limited as long as it is a material having fluoride ion conductivity, but it is usually an inorganic fluoride. Moreover, the solid electrolyte layer preferably contains the solid electrolyte described in "A. Solid electrolyte". Since the content of the binder is the same as described in "1. Positive electrode layer", the description thereof is omitted here. The thickness of the solid electrolyte layer is not particularly limited, and can be appropriately adjusted depending on the configuration of the battery.

4. Other Configurations The fluoride ion battery in the present disclosure preferably has 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 the above-described members. . Examples of the shape of the current collector include foil, mesh, and porous. As the battery case, a conventionally known battery case can be used.

5. 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 they can be repeatedly charged and discharged, and are useful, for example, as batteries for vehicles. The secondary battery also includes use as a primary battery (use for the purpose of discharging only once after charging). Moreover, examples of the shape of the fluoride ion include a coin shape, a laminate shape, a cylindrical shape, and a square shape.

Note that the present disclosure is not limited to the above embodiments. The above embodiment is an example, and any device that has substantially the same configuration as the technical idea described in the claims of the present disclosure and produces the same effect is the present invention. It is included in the technical scope of the disclosure.

[Example 1]
(Synthesis of solid electrolyte)
They were weighed so that RbF:SbF ₃ =2.4:1 (molar ratio) in an Ar atmosphere, and mixed in a planetary ball mill at 600 rpm for 10 hours. After that, the solid electrolyte (Rb _2.4 SbF _5.4 ) was obtained by firing at 400° C. for 4 hours in an Ar atmosphere.

[Example 2]
A solid electrolyte (Rb _2.2 SbF _5.2 ) was obtained in the same manner as in Example 1, except that RbF and SbF ₃ were weighed so that the molar ratio was 2.2:1.

[Example 3]
A solid electrolyte (Rb ₂ SbF ₅ ) was obtained in the same manner as in Example 1, except that RbF and SbF ₃ were weighed so as to be 2.0:1 (molar ratio).

[Example 4]
A solid electrolyte (Rb _1.8 SbF _4.8 ) was obtained in the same manner as in Example 1, except that RbF and SbF ₃ were weighed so that the molar ratio was 1.8:1.

[Example 5]
A solid electrolyte (Rb _1.6 SbF _4.6 ) was obtained in the same manner as in Example 1, except that RbF and SbF ₃ were weighed so that the molar ratio was 1.6:1.

[Comparative Example 1]
K ₂ SiF ₆ was used as a solid electrolyte.

[Comparative Example 2]
Li ₂ SiF ₆ was used as a solid electrolyte.

[evaluation]
(XRD measurement)
The solid electrolytes in Examples 1 to 5 were subjected to X-ray diffraction measurement (XRD measurement) using CuKα rays. Also, Ib/Ia was calculated from the XRD spectrum. The results are shown in FIG. 2 and Table 1.

As shown in FIG. 2, it was confirmed that all of the solid electrolytes in Examples 1 to 5 had the crystalline phase A. Further, as shown in FIG. 2 and Table 1, in Examples 1 to 4, it was confirmed that they were single-phase materials of the crystal phase A. On the other hand, Example 5 was confirmed to have a crystalline phase A and a heterophase.

(Fluoride ion conductivity measurement)
Measurement cells were prepared using the solid electrolytes obtained in Examples 1-5 and Comparative Examples 1-2, and the fluoride ion conductivity was measured by the AC impedance method. First, 200 mg of each solid electrolyte powder was placed in a ceramic cylinder made by Macor, and uniaxial pressure molding was performed at 1 ton/cm ² to form a pellet. Thereafter, acetylene black was layered on both sides of the pellet as a current collector, and then pressed at a pressure of 4 ton/cm ² . The pressed cell was bolted with a torque of 6 N·m. Thus, a measuring cell was produced. The measurement environment was a vacuum of 10 ^-3 Pa. The measurement temperature was room temperature (25° C.) for Examples 1 to 5, 200° C. for Comparative Example 1, and 80° C. for Comparative Example 2. The impedance measurement conditions were a frequency of 10 ⁶ Hz to 10 ⁻² Hz and a voltage amplitude of 50 mV. Fluoride ion conductivity was calculated from the ion conductivity resistance obtained by impedance measurement, the thickness of the sample, and the electrode area. Results are shown in Table 1 and FIG.

Examples 1-5 showed good fluoride ion conductivity at room temperature. In particular, the fluoride ion conductivity was high in Examples 1 to 4. This is because, as shown in FIG. 2 and Table 1, Examples 1-4 have a Rb _x SbF _3+x crystalline phase as a single phase, and Example 5 has a heterophasic phase in addition to the Rb _x SbF _3+x crystalline phase. It is thought that it was because it was equipped with On the other hand, the fluoride ion conductivity (200° C.) of Comparative Example 1 was comparable to the fluoride ion conductivity (25° C.) of Examples 1-5. In general, the fluoride ion conductivity has temperature dependence, and the lower the temperature, the lower the fluoride ion conductivity. Therefore, the fluoride ion conductivity of Comparative Example 1 in the room temperature range is It is lower than the fluoride ion conductivity of 5. In addition, the fluoride ion conductivity (80° C.) of Comparative Example 2 was significantly lower than the fluoride ion conductivity (25° C.) of Examples 1-5. Thus, it was confirmed that the solid electrolyte of the present disclosure has good fluoride ion conductivity in the room temperature range.

DESCRIPTION OF SYMBOLS 1... Positive electrode layer 2... Solid electrolyte layer 3... Negative electrode layer 4... Positive electrode collector 5... Negative electrode collector 6... Battery case 10... Fluoride ion battery

Claims (4)

A solid electrolyte used in a fluoride ion battery,
A solid electrolyte having a crystal phase represented by Rb _x SbF _3+x (where x satisfies 1.6≦x≦2.4). 2. The solid electrolyte according to claim 1, wherein said x satisfies 1.8≤x≤2.4. 3. The solid electrolyte according to claim 1, wherein said solid electrolyte is a single phase material of said crystalline phase. A fluoride ion battery having a positive electrode layer, a negative electrode layer, and a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer,
A fluoride ion battery, wherein at least one of the positive electrode layer, the negative electrode layer and the solid electrolyte layer contains the solid electrolyte according to any one of claims 1 to 3.

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