JP2020194697A - Fluoride ion battery - Google Patents

Abstract

To provide a fluoride ion battery having good capacitance characteristics.SOLUTION: A fluoride ion battery disclosed herein includes 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, and at least one of the positive electrode active material layer and the negative electrode active material layer contains a transition metal oxide having a rock salt type crystal structure as an active material.SELECTED DRAWING: Figure 1

Description

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

As a battery having a high voltage and a high energy density, for example, a Li ion battery is known. A Li-ion battery is a cation-based battery that uses Li ions as a carrier. 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 in which a positive electrode active material and a solid electrolyte represented by PbF ₂ or PbMF _x are used 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 circumstances, 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. Provided is a fluoride ion battery, wherein at least one of the positive electrode active material layer and the negative electrode active material layer contains a transition metal oxide having a rock salt type crystal structure as an active material.

According to the present disclosure, at least one of the positive electrode active material layer and the negative electrode active material layer contains a transition metal oxide having a rock salt type crystal structure as an active material, so that a fluoride ion battery having good capacity characteristics is obtained. be able to.

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

It is the schematic sectional drawing which shows an example of the fluoride ion battery in this disclosure. It is a result of XRD measurement of the transition 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 Example 3. It is the result of the charge / discharge test of the evaluation battery obtained in Example 4. It is the result of the charge / discharge test of the evaluation battery obtained in Example 5. This 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 transition metal oxide having a rock salt type crystal structure 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 storing members.

According to the present disclosure, at least one of the positive electrode active material layer and the negative electrode active material layer contains a transition metal oxide having a rock salt type crystal structure as an active material, so that a fluoride ion battery having good capacity characteristics is obtained. be able to. In the present disclosure, only the positive electrode active material layer may contain the above active material, and 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. On the other hand, the rock salt type transition metal oxide, even if it is an insulator in the initial state, is doped with holes and donors due to fluctuations in the valence of the transition metal, and the electron conductivity is improved. Therefore, for example, in the process of charging the positive electrode, it is presumed that the electron conductivity is improved when fluorine ions are doped, and the reaction can proceed to the inside of the active material particles, and as a result, the capacity characteristics of the fluoride ion battery. Is presumed to be good.
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 an electrolyte, a conductive material and a binder, if necessary.

The positive electrode active material layer preferably contains a transition metal oxide having a rock salt type crystal structure 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 a transition metal oxide having a rock salt type crystal structure, or may also contain other positive electrode active materials, but the former is preferable.

Examples of the transition metal element in the transition metal oxide include Fe, Co, Ni, Ti, Nb and Mn. The transition metal oxide may contain only one type of transition metal element, or may contain two or more types of transition metal elements. The composition of the transition metal oxide is not particularly limited as long as it has a rock salt type crystal structure described later, and examples thereof include a composition represented by MO (M is the transition metal element). In the present disclosure, the transition metal oxide is preferable because NbO has particularly good capacitance characteristics.

The transition metal oxide in the present disclosure has a rock salt type crystal structure. It can be confirmed that the transition metal oxide has a rock salt type crystal structure, for example, by performing X-ray structure analysis measurement (XRD measurement). The crystal phase having a rock salt type crystal structure has the following peaks in XRD measurement using Cu-Kα rays, for example. In the case of a transition metal oxide containing Fe as a transition metal element, it has typical peaks at, for example, 2θ = 36.1 °, 41.9 °, 60.7 °, and 72.7 °, and as a transition metal element. In the case of a transition metal oxide containing Co, it has typical peaks at, for example, 2θ = 36.5 °, 41.9 °, 61.5 °, and 73.6 °, and contains Ni as a transition metal element. In the case of a transition metal oxide, for example, a transition metal oxide having typical peaks at 2θ = 37.2 °, 43.3 °, 62.9 °, and 75.4 ° and containing Ti as a transition metal element. In the case of a transition metal oxide having typical peaks at 2θ = 37.8 °, 43.8 °, 62.4 °, 76.0 ° and containing Nb as a transition metal element, for example. It has typical peaks at 2θ = 37.5 °, 43.5 °, 62.9 ° and 71.3 °. It should be noted that these peaks may be before and after in the range of ± 0.5 °, may be before and after in the range of ± 0.3 °, and may be before and after in the range of ± 0.1 °. You may. Further, for example, by referring to ICSD (Crystal Structure Database), it is possible to determine whether or not the crystal structure is rock salt type.

The transition metal oxide in the present disclosure preferably has a crystal phase having a rock salt 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 transition 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 10 μm or less, and may be 20 nm or more and 1 μm or less. The average primary particle size can be determined by, for example, 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 proportion of the 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 active material 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 lowered, 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.

The electrolyte has the same contents as “3. Electrolyte layer” described later.

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 an 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. On the other hand, when the positive electrode active material layer contains the above-mentioned active material, the negative electrode active material layer preferably contains an active material containing an F element. Examples of the active material containing the F element include PbF ₂ .

The proportion of the negative electrode active material in the negative electrode active material layer is preferably higher from the viewpoint of capacity. The proportion 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 electrolyte, the conductive material and the binder used in the negative electrode active material layer can be the same as those described in the positive electrode active material layer described above, and thus the description thereof is omitted here.

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 glime 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 ethyl methyl carbonate (EMC). Moreover, you may use an ionic liquid as an organic solvent.

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. Fluoride containing an element can be mentioned. Specific examples of the inorganic solid electrolyte include fluorides containing La and Ba, fluorides containing Pb and Sn, and fluorides containing Bi and Sn. Specific examples of the solid electrolyte include La _0.9 Ba _0.1 F _2.9 .

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

4. Other Configurations The fluoride ion battery in the present disclosure usually includes 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, and among them, 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 as a primary battery of the secondary battery (use for the purpose of discharging only once after charging). Further, examples of the shape of the fluoride ion battery in 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 exhibiting the same effect and effect is the present invention. Included in the technical scope of the disclosure.

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

[Example 2]
An evaluation battery was produced in the same manner as in Example 1 except that CoO was used as the positive electrode active material contained in the positive electrode mixture.

[Example 3]
An evaluation battery was produced in the same manner as in Example 1 except that NiO was used as the positive electrode active material contained in the positive electrode mixture.

[Example 4]
An evaluation battery was produced in the same manner as in Example 1 except that TiO was used as the positive electrode active material contained in the positive electrode mixture.

[Example 5]
An evaluation battery was produced in the same manner as in Example 1 except that NbO was used as the positive electrode active material contained in the positive 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 positive electrode active material contained in the positive electrode mixture.

[Evaluation]
(XRD measurement)
XRD measurement (using CuKα ray) was performed on the positive electrode active material (FeO) in Example 1. The result is shown in FIG. As shown in FIG. 2, in the positive electrode active material, characteristic peaks were confirmed at the positions of 2θ = 36.1 °, 41.9 °, 60.7 °, and 72.7 °, and the crystal phase of the rock salt structure. Was confirmed to have almost a single phase.

(Charge / discharge test)
A charge / discharge test was performed on the evaluation batteries obtained in Examples 1 to 5 and Comparative Example 1. The charge / discharge test was performed under the conditions of a current of 50 μA / cm ² and a final potential of the working electrode of −1.5 V (vs Pb / PbF ₂ ) to 3.0 V (vs Pb / PbF ₂ ) in an environment of 140 ° C. .. The results are shown in FIGS. 3 to 8. Since the reduction decomposition potential of the solid electrolyte (La _0.9 Ba _0.1 F _2.9 ) used for the positive electrode mixture is -2.4 V (vs Pb / PbF ₂ ), it can be obtained in the above potential range. It can be said that all the capacities are derived from the positive electrode active material.

As shown in FIG. 3, in Example 1 (FeO), a flat potential portion was confirmed on both the charging side and the discharging side, and a charging / discharging capacity of about 35 mAh / g was obtained. As shown in FIG. 4, in Example 2 (CoO), a flat potential portion was confirmed in the vicinity of 2V and -1V, and a discharge capacity of about 100 mAh / g was obtained. As shown in FIG. 5, in Example 3 (NiO), a discharge capacity of about 10 mAh / g was obtained. As shown in FIG. 6, in Example 4 (TiO), a two-stage potential flat portion was confirmed centering on the vicinity of -1V and 0V, and a discharge capacity of about 17 mAh / g was obtained. As shown in FIG. 7, in Example 5 (NbO), a discharge capacity of about 500 mAh / g was obtained centering on 0 V. On the other hand, as shown in FIG. 8, in Comparative Example 1 (Cu ₂₃ Al ₆₅ Fe ₁₂ ), only a very low discharge capacity of 2 mAh / g or less was obtained. As described above, it was confirmed that all of Examples 1 to 5 exhibited better capacitance characteristics than Comparative Example 1.

1 ... Positive electrode active material layer 2 ... Negative electrode active material layer 3 ... Electrolyte 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 transition metal oxide having a rock salt type crystal structure as an active material.