JP7088126B2 - Fluoride ion battery - Google Patents

Description

The present disclosure relates to a fluoride ion battery having good capacity characteristics.

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

For example, Patent Document 1 discloses a fluoride ion battery using a positive electrode active material and a solid electrolyte represented by PbF ₂ or PbMF _x in the positive electrode active material layer.

Japanese Unexamined Patent Publication No. 2019-029206

Fluoride ion batteries are required to have good capacity characteristics. The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a fluoride ion battery having good capacity characteristics.

In order to achieve the above object, in the present disclosure, a fluoride ion having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer. A fluoride ion battery in which at least one of the positive electrode active material layer and the negative electrode active material layer contains a metal oxide having a Bixubi ore type crystal structure and containing an In element as an active material. offer.

According to the present disclosure, since at least one of the positive electrode active material layer and the negative electrode active material layer contains a predetermined active material, a fluoride ion battery having good capacity characteristics can be obtained.

The present disclosure has an effect that a fluoride ion battery having good capacity characteristics can be obtained.

It is a schematic sectional drawing which shows an example of the fluoride ion battery in this disclosure. It is the result of the XRD measurement of the metal oxide used in Example 1. It is the result of the charge / discharge test of the evaluation battery obtained in Example 1. It is the result of the charge / discharge test of the evaluation battery obtained in Example 2. It is the result of the charge / discharge test of the evaluation battery obtained in Comparative Example 1.

Hereinafter, the fluoride ion battery in the present disclosure will be described in detail.
FIG. 1 is a schematic cross-sectional view showing an example of a fluoride ion battery in the present disclosure. The fluoride ion battery 10 shown in FIG. 1 has a positive electrode active material layer 1, a negative electrode active material layer 2, and an electrolyte layer 3 formed between the positive electrode active material layer 1 and the negative electrode active material layer 2. Further, at least one of the positive electrode active material layer 1 and the negative electrode active material layer 2 contains a metal oxide having a Bixubi ore type crystal structure and containing an In element as an active material. Further, the fluoride ion battery 10 shown in FIG. 1 includes a positive electrode current collector 4 that collects electricity from the positive electrode active material layer 1 and a negative electrode current collector 5 that collects electricity from the negative electrode active material layer 2. It has a battery case 6 for accommodating members.

According to the present disclosure, since at least one of the positive electrode active material layer and the negative electrode active material layer contains a predetermined active material, a fluoride ion battery having good capacity characteristics can be obtained. In the present disclosure, only the positive electrode active material layer may contain the above active material, or only the negative electrode active material layer may contain the above active material. Further, both the positive electrode active material layer and the negative electrode active material layer may contain the above active material, but in that case, the active material having a high reaction potential is used as the positive electrode active material among the above active materials. , An active material having a low reaction potential is used as the negative electrode active material.

The reason why the capacity characteristics of the fluoride ion battery in the present disclosure are good is presumed as follows. For example, as disclosed in Patent Document 1, it is known that a metal material is used as an active material for a fluoride ion battery. However, when such a metal material is used for a positive electrode, for example, if the fluoride reaction of the active material proceeds in the charging process, the surface of the active material may be covered with the metal fluoride. Since this metal fluoride has very low electron conductivity and is almost an insulator, it can react only near the surface of the active material. Further, when the metal fluoride grows to a certain thickness, the resistance increases and the reversible charge / discharge reaction may be hindered. Here, a metal oxide having a Bixubi ore-type crystal structure and containing an In element becomes a semiconductor exhibiting high conductivity by being doped with a trace amount of an element. Therefore, it is presumed that the electron conductivity is improved by doping with fluorine ions in the charging process, and the reaction can proceed to the inside of the active material particles. As a result, the capacity characteristics of the fluoride ion battery are improved. Inferred.
Hereinafter, the fluoride ion battery in the present disclosure will be described separately for each configuration.

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

The positive electrode active material layer preferably contains a metal oxide having a Bixubi ore type crystal structure and containing an In element as the active material (positive electrode active material). In this case, in the negative electrode active material layer described later, any active material having a lower reaction potential than this active material can be used as the negative electrode active material. Further, the positive electrode active material may contain only the above-mentioned active material, or may also contain other positive electrode active materials, but the former is preferable.

The metal oxide in the present disclosure contains at least the In element. The composition of the metal oxide in the present disclosure is not particularly limited as long as it contains at least In and has a crystal structure of the _Bixubi ore type described later, and examples thereof include a composition represented by In _x My _Oz . In the formula, x is, for example, 1.5 or more, and may be 1.8 or more. On the other hand, x is, for example, 2.5 or less, may be 2.3 or less, or may be 2.0 or less. Further, y in the formula may be 0 or may be larger than 0. In the latter case, y may be, for example, 0.3 or more. On the other hand, y is, for example, 1 or less, 0.7 or less, or 0.5 or less. Further, z in the formula is, for example, 2 or more, and may be 3 or more. On the other hand, z is, for example, 6 or less, and may be 4 or less. Further, M in the formula represents a metal element other than In, and is, for example, at least one of Sn, Ga, and V.

The metal oxide in the present disclosure has a Bixubi ore type crystal structure. It can be confirmed that the metal oxide has a Bixubi ore type crystal structure, for example, by performing X-ray structure analysis measurement (XRD measurement). The crystal phase having a Bixubi ore type crystal structure was 2θ = 21.5 °, 30.6 °, 35.5 °, 51.0 °, 60.7 ° in XRD measurement using Cu-Kα ray. It is preferable to have a typical peak. In addition, each of these peaks may be before and after in the range of ± 3.0 °. The above range may be ± 1.0 ° or ± 0.5 °.

The metal oxide in the present disclosure preferably has a crystal phase having a Bixubi ore type crystal structure as a main phase. The ratio of the crystal phase to the total crystal phase of the active material is, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. In particular, the metal oxide in the present disclosure preferably has the above crystal phase as a single phase.

Examples of the shape of the active material in the present disclosure include particulate matter. The average primary particle size (D ₅₀ ) of the active material is, for example, 10 nm or more and 100 nm or less, and may be 20 nm or more and 60 nm or less. The average primary particle size can be determined, for example, by observation with a scanning electron microscope (SEM). The number of samples is preferably large, for example, 20 or more, 50 or more, or 100 or more. The particle size of the active material can be appropriately adjusted, for example, by appropriately changing the production conditions of the active material or performing a classification treatment.

The proportion of the active material in the positive electrode active material layer is preferably higher from the viewpoint of capacity. The ratio of the active substance is, for example, 60% by weight or more, and may be 70% by weight or more. On the other hand, the ratio of the active substance is, for example, 99% by weight or less, and may be 95% by weight or less.

Examples of the conductive material include a carbon material. Specific examples of the carbon material include acetylene black, ketjen black, VGCF, and graphite. The proportion of the conductive material in the positive electrode active material layer is, for example, 1% by weight or more, and may be 5% by weight or more. On the other hand, the proportion of the conductive material is, for example, 30% by weight or less, and may be 20% by weight or less. If the proportion of the conductive material is too small, the electron conduction path is not formed and the electrode resistance may increase. If the ratio of the conductive material is too large, the ratio of the positive electrode active material is relatively low, which may lower the energy density.

Examples of the binder include rubber-based binders and fluoride-based binders. The proportion of the binder in the positive electrode active material layer is, for example, 1% by weight or more and 30% by weight or less.

Examples of the solid electrolyte include an inorganic solid electrolyte. Examples of the inorganic solid electrolyte include fluorides containing lanthanoid elements such as La and Ce, fluorides containing alkaline elements such as Li, Na, K, Rb and Cs, and alkaline earths such as Ca, Sr and Ba. Fluorine containing an element can be mentioned. Specific examples of the inorganic solid electrolyte include fluoride containing La and Ba, fluoride containing Pb and Sn, and fluoride containing Bi and Sn. Specific examples of the solid electrolyte include La _0.9 Ba _0.1 F _2.9 .

The thickness of the positive electrode active material layer is not particularly limited and can be appropriately adjusted according to the configuration of the battery.

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

The negative electrode active material layer preferably contains the active material described in the above "1. Positive electrode active material layer" as the active material (negative electrode active material). In this case, any active material having a higher reaction potential than the above-mentioned active material can be used as the positive electrode active material.

The proportion of the negative electrode active material in the negative electrode active material layer is preferably higher from the viewpoint of capacity. The ratio of the negative electrode active material is, for example, 60% by weight or more, and may be 70% by weight or more. On the other hand, the proportion of the negative electrode active material is, for example, 99% by weight or less, and may be 95% by weight or less.

The types and proportions of the solid electrolyte, the conductive material, and the binder used in the negative electrode active material layer can be the same as those described in "1. Positive electrode active material layer" described above. The description is omitted.

The thickness of the negative electrode active material layer is not particularly limited and can be appropriately adjusted according to the configuration of the battery.

3. 3. Electrolyte layer The electrolyte layer is a layer formed between the positive electrode active material layer and the negative electrode active material layer. The electrolyte constituting the electrolyte layer may be a liquid electrolyte (electrolyte solution) or a solid electrolyte. That is, the electrolyte layer may be a liquid electrolyte layer or a solid electrolyte layer, but the latter is preferable.

The electrolytic solution in the present disclosure contains, for example, a fluoride salt and an organic solvent. Examples of the fluoride salt include an inorganic fluoride salt, an organic fluoride salt, and an ionic liquid. As an example of the inorganic fluoride salt, XF (X is Li, Na, K, Rb or Cs) can be mentioned. As an example of the cation of the organic fluoride salt, an alkylammonium cation such as a tetramethylammonium cation can be mentioned. 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.

The organic solvent of the electrolytic solution is usually a solvent that dissolves a fluoride salt. Examples of the organic solvent include glyme such as triethylene glycol dimethyl ether (G3) and tetraethylene glycol dimethyl ether (G4), ethylene carbonate (EC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and propylene carbonate (PC). ), Cyclic carbonate such as butylene carbonate (BC), and chain carbonate such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylmethyl carbonate (EMC). Moreover, you may use an ionic liquid as an organic solvent.

On the other hand, since the solid electrolyte can be the same as the content described in "1. Positive electrode active material layer" described above, the description here is omitted.

The thickness of the electrolyte layer is not particularly limited and can be appropriately adjusted according to the battery configuration.

4. Other Configurations The fluoride ion battery in the present disclosure usually has a positive electrode current collector that collects electricity from the positive electrode active material layer and a negative electrode current collector that collects electricity from the negative electrode active material layer. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of the material of the negative electrode current collector include SUS, copper, nickel, and carbon. Examples of the shapes of the positive electrode current collector and the negative electrode current collector include a foil shape, a mesh shape, and a porous shape, respectively. Further, the fluoride ion battery in the present disclosure may have a battery case for accommodating a battery member. As the battery case, a battery case of a general battery 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 a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful as an in-vehicle battery, for example. The secondary battery also includes the use of the secondary battery as a primary battery (use for the purpose of discharging only once after charging). Further, examples of the shape of the fluoride ion battery of the present disclosure include a coin type, a laminated type, a cylindrical type and a square type.

The present disclosure is not limited to the above embodiment. The above embodiment is an example, and any object having substantially the same structure as the technical idea described in the claims of the present disclosure and having the same effect and effect is the present invention. Included in the technical scope of the disclosure.

[Example 1]
The weight ratio of the negative electrode active material (In ₂ O ₃ , manufactured by Aldrich), the solid electrolyte (La _0.9 Ba _0.1 F _2.9 ), and the conductive material (acetylene black) is 30:60:10. The negative electrode mixture was obtained by mixing using a ball mill (working electrode). The positive electrode active material (PbF ₂ ) and the conductive material (acetylene black) were mixed at a weight ratio of 95: 5 to obtain a positive electrode mixture. The obtained negative electrode mixture, the solid electrolyte (La _0.9 Ba _0.1 F _2.9 ) forming the solid electrolyte layer, the positive electrode mixture, and the Pb foil (counter electrode) are laminated and powder molded. By doing so, a battery for evaluation was produced.

[Example 2]
An evaluation battery was produced in the same manner as in Example 1 except that In _1.8 Sn _0.1 O _2.9 was used as the negative electrode active material contained in the negative electrode mixture.

[Comparative Example 1]
An evaluation battery was produced in the same manner as in Example 1 except that a Cu ₂₃ Al ₆₅ Fe ₁₂ alloy was used as the negative electrode active material contained in the negative electrode mixture.

[evaluation]
(XRD measurement)
XRD measurement (using CuKα ray) was performed on the negative electrode active material (In ₂ O ₃ ) in Example 1. The results are shown in FIG. As shown in FIG. 2, in the negative electrode active material, characteristic peaks were confirmed at the positions of 2θ = 21.5 °, 30.6 °, 35.5 °, 51.0 ° and 60.7 °. It was confirmed that the crystal phase of the Bixubi ore type was almost monophasic.

(Charging / discharging test)
The evaluation batteries obtained in Examples 1 and 2 and Comparative Example 1 were subjected to a charge / discharge test. The charge / discharge test was performed under the conditions of a current of 50 μA / cm ² and a terminal potential of the working electrode of -2.6 V (vs Pb / PbF ₂ ) to 0 V (vs Pb / PbF ₂ ) in an environment of 140 ° C. In Example 1, 3 cycles of charging and 2 cycles of discharging were performed, and in Example 2 and Comparative Example 1, 3 cycles of charging and discharging were performed, respectively. The results are shown in FIGS. 3 to 5.

As shown in FIG. 3, in Example 1 (In ₂ O ₃ ), from the start of charging to the potential at which the electrolyte is reduced and decomposed (central potential-2.4V (vs Pb / PbF ₂ )) up to the second cycle. A charging capacity of 82 mAh / g was obtained, and a charging capacity of about 60 mAh / g was obtained even in the third cycle. Further, as shown in FIG. 4, in Example 2 (In _1.8 Sn _0.1 O _2.9 ) as in Example 1, the second cycle from the start of charging to the potential at which the electrolyte is reduced and decomposed. Up to, a charging capacity of 63 mAh / g was obtained, and a charging capacity of about 50 mAh / g was obtained even in the third cycle. On the other hand, in Comparative Example 1 (Cu ₂₃ Al ₆₅ Fe ₁₂ ), only a charge capacity of 14 mAh / g was obtained from the start of charging to the potential for reduction and decomposition of the electrolyte. As described above, in Examples 1 and 2, the volume derived from the active material was large and the volume characteristics were good as compared with Comparative Example 1.

1 ... Positive electrode active material layer 2 ... Electrolyte layer 3 ... Negative electrode active material layer 4 ... Positive electrode current collector 5 ... Negative electrode current collector 6 ... Battery case 10 ... Fluoride ion battery

Claims (1)

A fluoride ion battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer.
A fluoride ion battery in which at least one of the positive electrode active material layer and the negative electrode active material layer contains a metal oxide having a Bixubi ore type crystal structure and containing an In element as an active material.

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