JP2021174774A - Negative electrode for fluoride ion battery and fluoride ion battery - Google Patents

Abstract

To provide means capable of sufficiently proceeding reversible battery reaction in a fluoride ion battery.SOLUTION: In a negative electrode for a fluoride ion battery having a negative electrode active material layer containing a negative electrode active material and a negative electrode current collector for collecting a current of the negative electrode active material layer, the negative electrode active material contains metal fluoride whose defluorination reaction potential is nobler than the reduction decomposition potential of an inert coating composed of oxides and fluorides formed on the surface of the negative electrode current collector; a constituent material of the negative electrode current collector is aluminum or magnesium or an alloy thereof; and the negative electrode active material layer does not contain a conductive auxiliary agent made of a carbon material.SELECTED DRAWING: Figure 1

Description

The present invention relates to a negative electrode for a fluoride ion battery and a fluoride ion battery.

A Li-ion battery (LIB) is known as a storage battery having a high voltage and a high energy density. ^{LIB is a cation-based battery that utilizes the reversible insertion / deinsertion reaction of Li +} ions into the positive and negative electrode host crystals, and is generated by the dissociation of the lithium salt dissolved in a non-aqueous solvent (organic electrolyte). The balance between the amount of charge and the amount of substance in the system is maintained by the movement of Li ^{+ ions between the two electrodes.}

In addition, as an innovative battery that greatly improves the energy density of the LIB, ^{the formation of polyvalent metal fluoride by the reaction of fluoride ion (F −} ) with a metal and its reverse reaction (fluoride of the metal fluoride). There are anion-based fluoride ion batteries that utilize reaction). ^{It is the lightest F-} ion (M = 19) among the halide ions that moves between the two electrodes in this battery, and in some cases 2-3 or more F ^- ions per metal atom. The involvement of (and the same number of electrons) in the electrode reaction is the largest factor that results in the high energy density described above.

The fluoride ion battery does not require a host grid, which is an essential member of the LIB. F ^- ions of this kind battery FIB (Fluoride Ion Battery) that play a leading role in both the charge transfer in the electrolyte and the electrode reaction or F ^- FSB that emphasizes the role of bi-directional movement of ions (Fluoride Shuttle Battery; Fluoride It is known by the abbreviation of (ion shuttle secondary battery).

Regarding the reduction (defluoride) reaction of metal fluoride, which is one of the basic elements of fluoride ion batteries, a considerable number of reports have already been made in the 1970s research, which attracted attention to solid electrolytes. However, it was only relatively recently that the significant reversibility of charge and discharge, which is essentially essential for secondary batteries, was confirmed, albeit incompletely, within the framework of all-solid-state batteries.

Also, in general, due to restrictions on the ionic conductivity of solid electrolytes and the electrochemical reactivity at the solid / solid interface, reports of room temperature operation of solid FIB batteries are only one of the most recently published examples.

In a wet battery that uses a non-aqueous electrolyte solution for transporting fluoride ions, the above restrictions are basically removed. There is no shortage of prior patents and academic papers on electrolytes that can be used for that purpose. As a typical example, there is a method using an ionic liquid that dissolves various fluoride salts relatively easily (Patent Document 1), and in addition, a so-called anion receptor (anion acceptor) in a high-boiling general-purpose organic solvent. A method of promoting the dissolution of fluoride by adding the above has also been reported.

Japanese Unexamined Patent Publication No. 2016-62221

Here, in Patent Document 1, A is used as a negative electrode active material used in a fluoride ion battery.
lF _x is illustrated. However, according to the studies by the present inventors, it has been found that it is difficult to reversibly proceed the battery reaction when _{aluminum trifluoride (AlF 3) is used as the active material of the fluoride ion battery.} bottom.

Further, Patent Document 1 discloses that a material having electron conductivity such as various carbon materials may be included in the negative electrode active material as a conductive material (conductive auxiliary agent). However, according to the study by the present inventors, if the negative electrode used in the fluoride ion battery contains a conductive material (conductive aid) made of a carbon material, the original battery reaction cannot proceed sufficiently. It turned out that.

Therefore, an object of the present invention is to provide a means capable of sufficiently advancing a reversible battery reaction in a fluoride ion battery.

In order to achieve the above-mentioned problems, the present inventors have conducted extensive research. As a result, the negative electrode active material is a metal fluoride in which the depolarization reaction potential satisfies a predetermined relationship with the reduction decomposition potential of the inert coating composed of oxide and fluoride formed on the surface of the negative electrode current collector. By including it in the negative electrode active material layer, the constituent material of the negative electrode current collector is aluminum or magnesium or an alloy thereof, and the negative electrode active material layer does not contain a conductive auxiliary agent made of a carbon material. We have found that a reversible battery reaction can proceed sufficiently, and have completed the present invention.

That is, according to one embodiment of the present invention, there is provided a negative electrode for a fluoride ion battery having a negative electrode active material layer containing a negative electrode active material and a negative electrode current collector that collects electricity from the negative electrode active material layer. .. Here, in the negative electrode, the negative electrode active material contains a metal fluoride, and the defluorination reaction potential of the metal fluoride is an inactive state composed of an oxide and a fluoride formed on the surface of the negative electrode current collector. The potential is noble than the reduction decomposition potential of the coating film, the constituent material of the negative electrode current collector is aluminum or magnesium or an alloy thereof, and the negative electrode active material layer does not contain a conductive auxiliary agent made of a carbon material. It has characteristics.

According to the present invention, the reversible progress of the battery reaction is ensured by using the negative electrode active material having the above-mentioned predetermined depolarization reaction potential, and the negative electrode current collector made of a specific constituent material is used and the carbon material is used. By not using a conductive material (conductive auxiliary agent) made of the above material, the progress of the reduction decomposition reaction of the electrolyte is suppressed. As a result, the reversible battery reaction can be sufficiently advanced.

It is a conceptual diagram which shows the principle of the fluoride ion battery which concerns on one form of this invention. (A) to (F) of FIG. 2 are cyclic voltammetrys obtained as a result of each cyclic voltammetry (CV) measurement of Reference Examples 1 to 6. (A) to (F) of FIG. 3 are chronopotencyograms obtained as a result of each chronopotency metric (CP) measurement of Reference Examples 1 to 6. (A) and (B) of FIG. 4 are cyclic voltammograms obtained as a result of performing CV measurement for each of the aluminum (Al) foil alone and the magnesium (Mg) foil alone. (A) to (C) of FIG. 5 are cyclic voltammetrys obtained as a result of cyclic voltammetry (CV) measurement of each of Example 1, Example 2 and Comparative Example 1. FIG. 6 is a chronopotencygram obtained as a result of the chronopotencymetry (CP) measurement of Example 2. (A) to (C) of FIG. 7 are chronopotencyograms obtained as a result of chronopotency metric (CP) measurement of each of Example 3, Comparative Example 2 and Comparative Example 3. (A) to (D) of FIG. 8 are charge / discharge curves for each of Comparative Example 4 and Examples 4-1 to 4-3. (A) and (B) of FIG. 9 are charge / discharge curves for each of Comparative Example 5 and Example 5. (A) to (C) of FIG. 10 are charge / discharge curves for each of Examples 6-1 to 6-3. (A) and (B) of FIG. 11 are charge / discharge curves for each of Example 7-1 and Example 7-2.

According to one embodiment of the present invention, the negative electrode is a negative electrode for a fluoride ion battery having a negative electrode active material layer containing a negative electrode active material and a negative electrode current collector that collects electricity from the negative electrode active material layer. The active material contains metal fluoride, and the defluorination reaction potential of the metal fluoride is noble than the reduction decomposition potential of the inert coating composed of oxide and fluoride formed on the surface of the negative electrode current collector. For a fluoride ion battery, which is a potential, the constituent material of the negative electrode current collector is aluminum or magnesium or an alloy thereof, and the negative electrode active material layer does not contain a conductive auxiliary agent made of a carbon material. A negative electrode is provided.

Hereinafter, embodiments of the negative electrode for a fluoride ion battery and the fluoride ion battery according to the present invention will be described in detail with reference to the drawings.

FIG. 1 is a conceptual diagram showing the principle of a fluoride ion battery according to an embodiment of the present invention. As shown in FIG. 1, the fluoride ion battery 1 has a positive electrode 10, a negative electrode 20, and an electrolyte layer 30 arranged between the positive electrode 10 and the negative electrode 20. In the embodiment shown in FIG. 1, the positive electrode 10 has a configuration in which the positive electrode active material layer 12 is arranged on one surface of a positive electrode current collector made of aluminum (Al) foil 11. The positive electrode active material layer 12 is a mixture layer containing a positive electrode active material 13 and a binder (not shown). On the other hand, the negative electrode 20 has a structure in which the negative electrode active material 21 is supported in the pores of the foamed aluminum 22 which is a conductive porous structure (conductive porous body). Here, the foamed aluminum 22 on the negative electrode 20 side functions as a negative electrode current collector. An electrolytic solution (liquid electrolyte) containing ^{fluoride ions (F −} ) is used in the electrolyte layer 30 of the present embodiment. The positive electrode current collector made of the aluminum (Al) foil 11 and the negative electrode current collector made of the foamed aluminum 22 are connected to the external load 40.

With such a configuration, when the fluoride ion battery 1 is discharged, a voltage is applied to the external load 40 and a current flows. At this time, the fluoride ions (F ⁻ ) contained in the electrolyte layer 30 mediate the battery reaction by moving the electrolyte layer 30 from the positive electrode 10 side to the negative electrode 20 side. On the other hand, when charging the fluoride ion battery 1, an external power source is connected to the positive electrode 10 and the negative electrode 20 instead of the external load 40, and fluoride ions (F ⁻ ) are forced from the negative electrode 20 to the positive electrode 10 via the electrolyte layer 30. Charging is achieved by moving the electrode.

<< Negative electrode for fluoride ion battery >>
Hereinafter, the main constituent members of the negative electrode for a fluoride ion battery according to this embodiment will be described. The negative electrode for a fluoride ion battery according to the present embodiment includes a negative electrode active material layer containing a negative electrode active material and a negative electrode current collector for collecting current from the negative electrode active material layer.

[Negative electrode active material layer]
The negative electrode active material layer contains a negative electrode active material. In the negative electrode according to this embodiment, the negative electrode active material contains metal fluoride. The defluorination reaction potential of the metal fluoride is characterized in that it is noble than the reduction decomposition potential of the inert film composed of oxide and fluoride formed on the surface of the negative electrode current collector. .. Here, the defluorination reaction potential of the metal fluoride contained in the negative electrode active material is a value peculiar to the negative electrode active material. For example, the _{defluorination reaction potentials of TiF 3} , Al _0.97 Ti _0.03 F ₃ and CeF ₃ are each 1.95 [V vs. SHE (Standard Hydrogen Electrode)], -2.10 [V vs. SHE] and -2.62 [V vs. SHE]. Therefore, the negative electrode current collector and the like so that these defluorination reaction potentials are more noble than the reductive decomposition potential of the inactive film composed of oxides and fluorides formed on the surface of the negative electrode current collector. You just have to decide the composition of. Whether or not the negative electrode for a fluoride ion battery satisfies the above-mentioned predetermined relationship is determined from the charge / discharge curve obtained by performing a charge / discharge test as described in the column of Examples described later. Is possible.

The specific type of the metal fluoride as the negative electrode active material is not particularly limited, and may satisfy the above-mentioned regulations with the passive film formed on the surface of the negative electrode current collector. As an example, the metal fluorides are Al _1-x (Ti) _x F ₃ (here, 0 <x ≦ 0.5), Ti _1-y (Al) _y F ₃ (here, 0 ≦ y). ≦ 0.5 at a) and preferably contains at least one selected from the group consisting of CeF _3. These negative electrode active materials can sufficiently proceed with a reversible battery reaction by satisfying the above-mentioned regulations with the passive film formed on the surface of the negative electrode current collector. Here, x is not particularly limited as long as it is a real number larger than 0 and 0.5 or less, but is preferably 0.01 or more and 0.1 or less, and more preferably 0.02 or more and 0.5 or less. .. Further, y is not particularly limited as long as it is a real number of 0 or more and 0.5 or less, but is preferably 0.01 or more and 0.1 or less, and more preferably 0.02 or more and 0.08 or less. Among them, from the viewpoint that a high-capacity fluoride ion battery can be constructed, the metal fluoride is Al _1-x (Ti) _x F ₃ (here, 0 <x ≦ 0.5). It is more preferable to include it. _{Regarding Al 1-x} (Ti) _x F ₃ and Ti _1-y (Al) _y F ₃ (y> 0) as the negative electrode active material, trifluoride is used in an inert atmosphere such as argon or nitrogen. It can be produced by weighing aluminum (AlF ₃ ) powder and titanium trifluoride (TiF ₃ ) powder at a desired mass ratio and performing a mixing treatment using a mixing device such as a ball mill.

The negative electrode active material layer may further contain a negative electrode active material other than the above-mentioned negative electrode active material. However, from the viewpoint of sufficiently obtaining the effects of the present invention, Al _1-x (Ti) _x F ₃ (0 <x ≦ 0.5) and Ti _1-y (Al) in the total amount of the negative electrode active material. the content of _{y F 3 (0 ≦ y ≦} 0.5) or CeF ₃ is preferably not less than 50 wt%, and more is preferably 70 mass% or more, still more preferably at least 80 wt%, more It is preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

Further, the negative electrode active material layer according to the present embodiment may further contain a binder. Examples of the binder include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), and polyimide (PI).

On the other hand, the negative electrode active material layer according to this embodiment is characterized in that it does not contain a conductive auxiliary agent made of a carbon material. As demonstrated in the column of Examples described later, this is because the negative electrode active material layer contains a conductive auxiliary agent made of a carbon material, so that a side reaction due to the reductive decomposition of the electrolytic solution proceeds, and a sufficient battery reaction occurs. Is not progressing, and sufficient charge / discharge characteristics cannot be obtained. The provision that "does not contain a conductive auxiliary agent made of carbon material" includes, for example, the case where a small amount of the conductive auxiliary agent made of carbon material is added for the purpose of avoiding patent infringement. For example, even when the blending amount of the conductive auxiliary agent made of carbon material in the negative electrode active material layer is 3% by mass or less, the condition of "does not contain the conductive auxiliary agent made of carbon material" is satisfied. Further, the negative electrode active material layer may contain a conductive auxiliary agent made of a material other than the carbon material (for example, metal), but it is preferable that the negative electrode active material layer is not contained as much as possible.

The blending ratio of each component contained in the negative electrode active material layer is not particularly limited, but when the negative electrode active material layer contains a negative electrode active material and a binder, the blending ratio of these components is preferably 70:30 to 99.5. : 0.5 (active material: binder (mass ratio)), more preferably 90: 10 to 99: 1 (active material: binder (mass ratio)).

[Negative electrode current collector]
The negative electrode current collector is a member that collects current from the negative electrode active material layer. Therefore, the negative electrode current collector needs to be made of a conductive material. In the negative electrode according to the present embodiment, the constituent material of the negative electrode current collector is aluminum (Al), magnesium (Mg), or an alloy thereof. Such a configuration has an advantage that the progress of side reactions due to the reductive decomposition of the electrolytic solution can be significantly suppressed, as demonstrated in the column of Examples described later. It is presumed that the mechanism by which such an effect is exerted is that the passivation film is stable in the reaction potential region of the active material on the surface of the negative electrode current collector made of Al or Mg.

The shape of the negative electrode current collector is not particularly limited as long as it can hold the above-mentioned negative electrode active material (or a mixture containing the negative electrode active material and an additive such as a binder). As an example of the shape of the negative electrode current collector, in addition to the foil shape, the shape of a conductive porous structure (conductive porous body) is also exemplified. A conductive porous body is a member having a porous structure (a large number of voids) inside and having conductivity, and here, a conductive porous body made of aluminum (Al) or magnesium (Mg) or an alloy thereof is used. Illustrated. Preferably, the conductive porous body constituting the negative electrode current collector is made of foamed metal, and more preferably made of foamed aluminum. As described above, the negative electrode according to the present embodiment is characterized in that it does not use a conductive auxiliary agent made of a carbon material (for example, carbon black such as acetylene black, graphite, carbon nanotubes, etc.), but is conductive made of a foamed metal. By constructing the negative electrode current collector using the porous body, it is possible to form a sufficiently good conductive path even in such a case.

《Fluoride ion battery》
According to another embodiment of the present invention, as shown in FIG. 1, a fluoride ion battery having a positive electrode, a negative electrode, and an electrolyte layer containing an electrolyte arranged between the positive electrode and the negative electrode. A fluoride ion battery, wherein the negative electrode is the negative electrode for a fluoride ion battery according to the above-described embodiment of the present invention, is also provided. The shape of the fluoride ion battery is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type. Hereinafter, components other than the negative electrode in the fluoride ion battery will be briefly described.

[Positive current collector]
The positive electrode current collector is a member that collects current from the positive electrode active material layer. Therefore, the positive electrode current collector needs to be made of a conductive material. In the positive electrode according to the present embodiment, the constituent material of the positive electrode current collector is not particularly limited, but the aluminum (Al) foil as shown in FIG. 1 and other metal current collectors used in conventionally known secondary batteries are used. , A resin current collector having a conductive resin layer and the like can be used.

[Positive electrode active material layer]
The positive electrode active material layer contains a positive electrode active material. Examples of the positive electrode active material that can be used for the positive electrode according to this embodiment include pure metals, alloys, metal oxides, and metal fluorides. The element contained in the positive electrode active material is, for example, one of Ag, Pt, Au, Cr, Mo, W, V, Fe, Co, Ni, Cu, Zn, S, Sb, Bi, Sn, Pb and C. The above can be mentioned. Further, among these, the positive electrode active material preferably contains any one of Fe, Co, Ni, Cu, Pb, Bi and Zn. In particular, the positive electrode active material more preferably contains Cu such as Cu metal, Cu alloy and Cu fluoride.

Further, the positive electrode active material layer constituting the positive electrode according to the present embodiment may further contain the binder and the conductive auxiliary agent described in the column of the negative electrode active material layer.

[Electrolyte layer]
The electrolyte layer is a member arranged between the positive electrode (positive electrode active material layer) and the negative electrode (negative electrode active material layer), and is a fluoride so that fluoride ions (F ⁻ ) can move back and forth during charging and discharging. It is a layer having conductivity to ions. In the fluoride ion battery according to this embodiment, the electrolyte contained in the electrolyte layer is usually a liquid electrolyte (electrolyte solution). When the electrolyte layer is a liquid electrolyte (electrolyte solution), a separator may be used for the electrolyte layer. The separator is not particularly limited as long as it has a composition that can withstand the range of use of the fluoride ion battery. Examples thereof include a microporous film made of an olefin resin. These may be used alone or in combination.

As the liquid electrolyte (electrolyte solution), conventionally known electrolytes for fluoride ion batteries may be used, but particularly preferably, ester-based or lactone-based (for example, γ-butyrolactone) having α-hydrogen. An organic electrolyte solution containing a single or mixed organic solvent (such as ε-caprolactone) and an alkali metal fluoride having an alkali metal cation and a fluoride ion (for example, cesium fluoride) is used. By using such an electrolytic solution as an electrolyte, excellent capacitance characteristics can be exhibited.

[Alkali metal fluoride]
Ion-conducting fluoride ions that directly contribute to the electrode reaction can be introduced into the electrolytic solution by dissolving organic fluoride, but they have a high capacity due to problems such as the electrochemical stability of coexisting organic cations. Not suitable for fluoride ion batteries. Considering the effect on the weight energy density of the secondary battery as another condition, the most desirable sources of fluoride ions are lithium fluoride (LiF), sodium fluoride (NaF), potassium fluoride (KF), and fluoride. It is an alkali metal fluoride such as rubidium fluoride (RbF) and cesium fluoride (CsF).

[Mixed lithium salt]
The fluoride ion conductive electrolytic solution in which only alkali metal fluoride is dissociated and dissolved at a concentration of 1 mM or more is likely to cause a side reduction reaction involving a fluoride ion-derived solvent in a negative high potential region, and is even more base than zinc. It competes with the fluorination reaction of various metals and interferes with the original battery operation. This problem can be easily solved by excessively mixing an arbitrary lithium salt co-dissolvable in the electrolytic solution of the present embodiment, represented by LiFSA (FSA: bis (fluorosulfonyl) amide), in the electrolytic solution. , It becomes possible to operate a battery utilizing the fluorination reaction of the most base metal species such as aluminum and lantern.

In the preparation of the above mixed electrolytic solution, the concentration of the lithium salt added in excess may be adjusted to be at least 3 times or more, preferably 5 times or more, more preferably about 10 times the concentration of the dissociated alkali metal fluoride. desirable. When the concentration (addition amount) of the lithium salt is 3 times or more, it is desirable that the fluoride ion concentration is not lowered because the fluoride ion and the lithium ion do not form an insoluble solid substance.

As the anion species of the lithium salt, TFSA ⁻ , BETA ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , and ClO ₄ ^{− may be used in addition to FSA −} . That is, the lithium salt to be added in excess _{is preferably any one of LiFSA, LiTFSA, LiBETA, LiBF 4} , LiPF ₆ , and LiClO ₄ or a mixture of two or more thereof.

[Mixed barium salt]
Although not as effective as a lithium salt, an irreversible reduction current in a negative high potential region can be suppressed by excessively mixing a barium salt typified by _{Ba (FSA) 2 with the electrolytic solution.} In the preparation of the above mixed electrolyte, the concentration of the barium salt added in excess may be adjusted to be at least 3 times or more, preferably 5 times or more, more preferably about 10 times the concentration of the dissociated alkali metal fluoride. desirable. When the concentration (addition amount) of this barium salt is 3 times or more, it is desirable that the fluoride ion concentration is not lowered because the fluoride ion and the barium ion do not form an insoluble solid substance. Examples of the anionic species of the barium salt, FSA ^- except the _{^{TFSA -, BETA -, BF 4}} - but no problem. That is, the barium salt to be added in excess is any one of Ba (FSA) ₂ , Ba (TFSA) ₂ , Ba (BETA) ₂ , Ba (BF ₄ ) ₂ , or a mixture of two or more thereof. Is preferable.

[Compounds containing boron]
In the fluoride ion battery according to the present embodiment, the electrolyte (electrolyte solution) can realize a higher reversible capacity by containing a compound containing boron as an additive. The type of the compound containing boron is not particularly limited, and conventionally known boron compounds can be mentioned, but among them, a compound having one boroxine structure (monocyclic boroxine compound) is preferable. "Boroxine" is _{a heterocyclic compound represented by the chemical formula of B 3} H ₃ O ₃ , and has a six-membered ring structure in which boron atoms bonded to one hydrogen atom and oxygen atoms are alternately arranged. .. Examples of the monocyclic boroxine compound having one such boroxine structure include 2,4,6-trimethoxyboroxine (TMBx), 2,4,6-triphenylboroxine (TPBx), 2,4. Examples thereof include 6-tris (4-fluorophenyl) boroxine (TFBPx) and 2,4,6-tris (m-terphenyl-5'-yl) boroxine (TTBx). In addition, monocyclic boroxine compounds disclosed in International Publication No. 2017/082268 pamphlet may be used.

When the electrolyte (electrolyte solution) contains a compound containing boron, its concentration is not particularly limited, but from the viewpoint of obtaining a high reversible capacity, it is preferably 0.8 M or less, more preferably 0.5 M or less. Yes, more preferably 0.05 to 0.5 M, particularly preferably 0.05 to 0.3 M, and most preferably 0.05 to 0.1 M.

The present invention will be described in more detail below by exemplifying experiments.

[Reference example 1]
A collector made of commercially available aluminum (Al) foil (thickness 20 μm) is cut to a size of 5 mm × 10 mm, and a metal surface other than the reaction surface is connected to the terminals so that the reaction surface has a size of 5 mm × 5 mm. The electrode of this reference example was produced by heat-sealing and masking with a polypropylene (PP) seal film so as to leave a part of the portion.

[Reference example 2]
The electrodes of this reference example were produced by the same method as in Reference Example 1 described above, except that a commercially available magnesium (Mg) foil was used as the current collector instead of the aluminum (Al) foil.

[Reference example 3]
The electrodes of this reference example were produced by the same method as in Reference Example 1 described above, except that a commercially available copper (Cu) foil was used as the current collector instead of the aluminum (Al) foil.

[Reference example 4]
The electrodes of this reference example were produced by the same method as in Reference Example 1 described above, except that a commercially available nickel (Ni) foil was used as the current collector instead of the aluminum (Al) foil.

[Reference Example 5]
A conductive auxiliary agent made of acetylene black (AB), which is a carbon material, and polyvinylidene fluoride (PVdF), which is a binder, are kneaded at a mass ratio of 50:50, and N-methyl-2-pyrrolidone (NMP) is further added. A slurry having an appropriate viscosity was prepared. The obtained slurry was applied to one surface of a current collector made of an aluminum (Al) foil similar to that in Reference Example 1, and vacuum dried at 120 ° C. Next, an electrode sheet was prepared by performing a press treatment so that the porosity was 40 to 50%. The obtained electrode sheet was cut into a size of 5 mm × 10 mm, and a part of the mixed material surface was peeled off so that the mixed material surface had a size of 5 mm × 5 mm to prepare an electrode of this reference example.

[Reference example 6]
The electrodes of this reference example were produced by the same method as in Reference Example 5 described above, except that carbon nanotubes (CNT), which is also a carbon material, was used as a conductive auxiliary agent in place of acetylene black (AB). ..

[Evaluation of reduction resistance of electrolytic solution]
The reduction resistance of the electrolytic solution to the electrodes prepared in each of the above-mentioned Reference Examples 1 to 6 was evaluated.

Specifically, first, an electrode sheet composed of activated carbon and polytetrafluoroethylene (PTFE), which is a binder, with the electrodes prepared in each of the above reference examples as working electrodes (activated carbon: PTFE = 70:30 (mass ratio)). ) Was used as the counter electrode, and the Ag line was used as the reference electrode to prepare a beaker cell. Here, as the electrolytic solution, one in which LiFSA (0.5 mol / L) and CsF (0.038 mol / L) were dissolved in γ-butyrolactone (GBL) was used (see JP-A-2021-36512). ..

Using each beaker cell prepared above, the reduction resistance of the electrolytic solution was evaluated by cyclic voltammetry (CV) measurement and chronopotencyometry (CP) measurement.

Cyclic voltammetry (CV) measurement was performed in an argon atmosphere at room temperature, and the sweep rate was 1 mV / sec. Cyclic voltammetrys obtained as a result of the cyclic voltammetry (CV) measurement of Reference Examples 1 to 6 are shown in FIGS. 2A to 2F, respectively. Further, based on each cyclic voltammogram, the reduction and decomposition current values of the electrolytic solutions up to the vicinity of the fluorinated defluorination reaction potential of _{Al / AlF 3 of -2.4 V (vs. Ag) were compared.} Then, what the current value thereof becomes 0.1 mA / cm ² or less and 〇 (OK), shown in Table 1 below what a 0.1 mA / cm ² than as × (NG).

The chronopotencyometry (CP) measurement was performed in an argon atmosphere at room temperature, and the current rate of the constant current test was 10 μA. The chronopotencygrams obtained as a result of the chronopotencymetry (CP) measurement of Reference Examples 1 to 6 are shown in FIGS. 3A to 3F, respectively. In addition, a reaction plateau in which the potential becomes constant was observed based on each chronopotensiogram, and the potential was around 2.4 V (vs. Ag), which is the fluorinated defluorination reaction potential of _{Al / AlF 3.} Table 1 below shows those with a lower potential as 〇 (OK) and those with a more noble potential as × (NG). As shown in Table 1, Reference Example 1
And Reference Example 2 was 〇 (OK).

Here, as can be seen from the results shown in FIGS. 2 (A) and 3 (A), and FIGS. 2 (B) and 3 (B), in Reference Example 1 and Reference Example 2, the secondary by reductive decomposition of the electrolytic solution is used. the reaction does not proceed unless become lower potential than Al / AlF ₃ reaction potential. Therefore, in the negative electrode for a fluoride ion battery using these materials as a current collector, the defluorination reaction from the negative electrode active material is prioritized over the side reaction due to the reductive decomposition of the electrolytic solution when the fluoride ion battery is charged. It is thought that it will proceed to.

On the other hand, as can be seen from the results shown in FIGS. 2 (C) and 3 (C), and FIGS. 2 (D) and 3 (D), in Reference Example 3 and Reference Example 4, -0.6 V ( A side reaction that seems to be a reductive decomposition of the electrolytic solution was observed from the vicinity of the standard hydrogen electrode (SHE). Therefore, in the negative electrode for a fluoride ion battery using these materials as a current collector, the side reaction by the reductive decomposition of the electrolytic solution is more than the defluorination reaction from the negative electrode active material when the fluoride ion battery is charged. It is considered that priority will be given to the progress.

Further, as can be seen from the results shown in FIGS. 2 (E) and 3 (E), and FIGS. 2 (F) and 3 (F), Reference Example 5 and Reference Example using a conductive aid made of a carbon material. In No. 6, a side reaction that seems to be a reductive decomposition of the electrolytic solution was observed from around −1.0 V (vs. SHE). _{In this way, the reducing decomposition of the electrolytic solution occurs at a potential noble than the Al / AlF 3} reaction potential on the surface of the conductive auxiliary agent made of carbon material, so that the defluorination reaction of the negative electrode active material, which is the original electrode reaction, occurs. Is considered to be inhibited.

[Example 1]
(Synthesis of active material)
_{Commercially available TiF 3} powder (Sigma-Aldrich) was added as an additive to commercially available AlF ₃ powder (Fuji Film Wako Pure Chemical Industries, Ltd.) at a predetermined ratio, and mixed treatment was performed with a ball mill under an argon atmosphere. the _Al 0.97 _{Ti 0.03} F ₃ example in which the active material was synthesized.

(Preparation of electrodes)
_{The active material (Al 0.97} Ti _0.03 F ₃ ) prepared above was pressure-bonded to one surface of a current collector made of a commercially available aluminum (Al) foil to prepare the electrodes of this example.

(Creation of cell)
Using the electrode prepared above as the working electrode, an electrode sheet (activated carbon: PTFE = 70:30 (mass ratio)) composed of activated carbon and the binder polytetrafluoroethylene (PTFE) was used as the counter electrode, and the Ag wire was used as the reference electrode. Was used to prepare the beaker cell of this example. As the electrolytic solution, one in which LiFSA (0.14 mol / L) and CsF (0.012 mol / L) were dissolved in γ-butyrolactone (GBL) was used.

[Example 2]
The beaker cell of this example was produced by the same method as in Example 1 described above except that a commercially available magnesium (Mg) foil was used as the current collector instead of the aluminum (Al) foil.

[Comparative Example 1]
By the same method as in Example 1 described above, the beaker of this comparative example was used except _{that AlF 3} powder not mixed with _{TiF 3} was used as the active material instead of Al _0.97 Ti _0.03 F _3. A cell was prepared.

[Evaluation of reactivity of active material]
The reactivity of the active material in the beaker cells prepared in each of Example 1, Example 2 and Comparative Example 1 described above was evaluated. Specifically, the reduction resistance of the electrolytic solution was evaluated by cyclic voltammetry (CV) measurement and chronopotencyometry (CP) measurement using the beaker cells prepared in each of the above experimental examples.

Cyclic voltammetry (CV) measurement was performed in an argon atmosphere at room temperature, and the sweep rate was 20 mV / sec. Here, for the purpose of confirming the progress of the redox reaction in the electrolytic solution on each surface of the aluminum (Al) foil and the magnesium (Mg) foil which are the current collectors, the aluminum (Al) foil alone and magnesium ( The cyclic voltammograms obtained as a result of CV measurement for each of the Mg) foils are shown in FIGS. 4A and 4B. On the other hand, the cyclic voltammetrys obtained as a result of the cyclic voltammetry (CV) measurement of Example 1, Example 2 and Comparative Example 1 are shown in FIGS. 5A to 5C, respectively. In addition, based on each cyclic voltammogram, the magnitudes of the reduction current peak and the oxidation current peak are compared with the vicinity of the fluorinated defluorination reaction potential of _{Al / AlF 3 of -2.4 V (vs. Ag).} Then, the fluorinated defluorination reaction activity was judged. As a result, those judged to have sufficiently reversible reaction activity were evaluated as 〇 (OK), and those judged not to have sufficient reversible reaction activity were evaluated as × (NG) as follows. It is shown in Table 2. As shown in Table 2, Example 1 and Example 2 were 〇 (OK).

For Example 2, chronopotencyometry (CP) measurement was also performed. Specifically, CP measurement was performed in an argon atmosphere at room temperature, and the current rate of the constant current test was 0.25 mA / cm ² . The chronopotencyogram obtained as a result of the CP measurement of Example 2 is shown in FIG.

Here, as can be seen from the comparison between FIGS. 4 (A) and 5 (A), Al _0.97 Ti _0.03 F ₃ is supported as an active material on the surface of the aluminum (Al) foil which is the current collector. By doing so, a reversible redox reaction is proceeding. Similarly, as can be seen from the comparison between FIGS. 4 (B) and 5 (B), Al _0.97 Ti _0.03 F ₃ is supported as an active material on the surface of the magnesium (Mg) foil which is a current collector. By doing so, the reduction side reaction in the case of the Mg foil alone is strongly suppressed, and the reversible redox reaction is proceeding. This is also supported by the chronopotency gram for Example 2 shown in FIG. From these facts, it can be said that the negative electrode for a fluoride ion battery according to the present invention is a promising candidate capable of improving the battery performance of the fluoride ion battery. In the cyclic voltammogram of Comparative Example 1 shown in FIG. 5 (C), the reversible progress of the redox reaction was not confirmed. _{This is because AlF 3,} which is a highly insulating active material, is supported on the surface of the aluminum (Al) foil, which is a current collector, and thus the progress of the redox reaction on the surface of the Al foil is hindered. it is conceivable that.

[Example 3]
(Synthesis of active material)
_{TiF 3} as an additive is added to a commercially available AlF ₃ powder at a predetermined ratio, and the mixture is mixed with a ball mill in an argon atmosphere to obtain Al _0.97 Ti _0.03 F ₃ , which is the active material of this example. Synthesized.

(Preparation of electrodes)
The active material prepared above and polyvinylidene fluoride (PVdF), which is a binder, were kneaded at a mass ratio of 95: 5, and N-methyl-2-pyrrolidone (NMP) was further added to obtain a slurry having an appropriate viscosity. .. The obtained slurry was filled with aluminum foam (Sumitomo Electric Industries, Ltd., Aluminum Celmet, porosity 96%) which is a conductive porous body, dried and then pressed to prepare an electrode of this example.

(Creation of cell)
Using the electrode prepared above as the working electrode, an electrode sheet (activated carbon: PTFE = 70:30 (mass ratio)) composed of activated carbon and the binder polytetrafluoroethylene (PTFE) was used as the counter electrode, and the Ag wire was used as the reference electrode. Was used to prepare the beaker cell of this example. As the electrolytic solution, one in which LiFSA (0.14 mol / L) and CsF (0.012 mol / L) were dissolved in γ-butyrolactone (GBL) was used.

[Comparative Example 2]
The active material prepared in Example 3 described above, acetylene black (AB), which is a conductive auxiliary agent made of a carbon material, and polyvinylidene fluoride (PVdF), which is a binder, have a mass of 75: 12.5: 12.5. After kneading at a ratio, N-methyl-2-pyrrolidone (NMP) was further added to obtain a slurry having an appropriate viscosity. The obtained slurry was applied to one surface of a copper (Cu) foil (thickness 20 μm) as a current collector, dried, and then pressed to prepare an electrode of this comparative example. Then, a beaker cell of this comparative example was produced by the same method as in Example 3 described above except that this electrode was used.

[Comparative Example 3]
A beaker cell of this Comparative Example was produced by the same method as in Comparative Example 2 described above, except that an aluminum (Al) foil was used as a current collector instead of the copper (Cu) foil.

[Evaluation of charge / discharge characteristics]
The charge / discharge characteristics of the beaker cells produced in each of Example 3, Comparative Example 2 and Comparative Example 3 described above were evaluated. Specifically, using the beaker cells prepared in each of the above experimental examples, the charge / discharge characteristics of each cell were evaluated by chronopotencyometry (CP) measurement.

Chronopotencyometry (CP) measurement was performed in an argon atmosphere at room temperature, and the current rate of the constant current test was equivalent to 0.04 C. The chronopotencygrams obtained as a result of the chronopotencyometry (CP) measurement of Example 3, Comparative Example 2 and Comparative Example 3 are shown in FIGS. 7A to 7C, respectively. In addition, based on each chronopotency gram, it is evaluated whether the reversible charge / discharge reaction by fluoridation and defluorination of the active material is proceeding and whether sufficient cycle characteristics are achieved, which is a practical problem. Table 3 below shows those that do not exist as 〇 (OK) and those that do not as × (NG). As shown in Table 3, only Example 3 was 〇 (OK).

Here, as shown in FIG. 7 (A), in Example 3, the plateau potential of the charge / discharge reaction was confirmed near the fluorinated defluorination reaction potential of _{Al / AlF 3 at 2.4 V (vs. Ag).} From this, it is considered that the reversible charge / discharge reaction by fluoridation and defluorination of the active material is in progress. Further, as shown in FIG. 7A, the cycle characteristics were also good in Example 3.

On the other hand, in Comparative Example 2 shown in FIG. 7B, a reversible charge / discharge capacity could not be obtained. This is because AB, which is a conductive auxiliary agent made of a carbon material, is used, and copper (Cu) foil is used as a current collector, so that the reduction and decomposition reaction of the electrolytic solution proceeds preferentially. It seems to be. Further, in Comparative Example 3 shown in FIG. 7C, the charge / discharge irreversible capacity was large, and the capacity deterioration due to the charge / discharge cycle was also large. This is because, despite the fact that aluminum (Al) foil is used as the current collector, the reduction and decomposition reaction of the electrolytic solution proceeded preferentially because the conductive auxiliary agent (AB), which is also made of carbon material, was used. It seems that this is due to.

[Comparative Example 4]
(Preparation of electrodes)
A conductive auxiliary agent (AB: acetylene black) was added to a commercially available TiF ₃ powder at a mass ratio of 90:10 and mixed with a ball mill in an argon atmosphere to prepare a TiF ₃ / AB mixture. AB and PVdF were further added to the obtained mixture to obtain _{a mass ratio of TiF 3} : AB: PVdF = 75: 12.5: 12.5, and then NMP was added and kneaded to obtain a slurry having an appropriate viscosity. .. The obtained slurry was applied onto an Al foil, vacuum dried at 120 ° C., and then pressed so that the porosity was 40 to 50% to prepare an electrode sheet. The obtained electrode sheet was cut into a size of 5 mm × 10 mm, and the surface of the mixture was partially peeled off so that the surface of the mixture was 5 mm × 5 mm to prepare an electrode of this comparative example.

(Creation of cell)
Using the electrode produced above as the working electrode, an electrode sheet composed of activated carbon and PTFE (activated carbon: PTFE = 70:30 (mass ratio)) is used as the counter electrode, and an Ag wire is used as the reference electrode, and the beaker of this comparative example is used. A cell was prepared. As the electrolytic solution, one in which LiFSA (0.14 mol / L) and CsF (0.012 mol / L) were dissolved in GBL was used.

[Example 4-1]
_{The same active material (TiF 3} ) as in Comparative Example 4 was pressure-bonded to one surface of a current collector made of a commercially available magnesium (Mg) foil to prepare an electrode of this example. Then, the beaker cell of this example was produced by the same method as in Comparative Example 4 described above except that this electrode was used.

[Example 4-2]
The same active material (TiF ₃ ) as in Comparative Example 4 and PVdF were kneaded at a mass ratio of 95: 5, and NMP was further added to prepare a slurry having an appropriate viscosity. The obtained slurry was filled with foamed aluminum (porosity 96%), which is a conductive porous body, dried, and then pressed to prepare an electrode of this example. Then, the beaker cell of this example was produced by the same method as in Comparative Example 4 described above except that this electrode was used.

[Example 4-3]
(Synthesis of active material)
_{AlF 3} as an additive is added to a commercially available TiF ₃ powder at a predetermined ratio, and the mixture is mixed with a ball mill in an argon atmosphere to obtain Ti _0.95 Al _0.05 F ₃ , which is the active material of this example. Synthesized. Then, the electrodes and the beaker cell of this example were produced by the same method as in Example 4-2 described above except that this active material was used.

[Evaluation of charge / discharge characteristics]
The charge / discharge characteristics of the beaker cells produced in Comparative Example 4 and Examples 4-1 to 4-3 described above were evaluated. Specifically, the charge / discharge test of each beaker cell is performed by a constant current test (charge / discharge rate is 0.02C) at room temperature (25 ° C.) using the beaker cells prepared in each of the above experimental examples. The reversible capacitance in the cycle was measured. The results are shown in Table 4 below. In any of the beaker cells produced in Examples 4-1 to 4-3 above, the depolarization reaction potential of the negative electrode active material is the oxide and fluoride formed on the surface of the negative electrode current collector. It was confirmed from the reaction potential and charge / discharge curve of each negative electrode active material that the potential was noble than the reduction / decomposition potential of the inactive film composed of.

Here, the charge / discharge curves for the beaker cells produced in each of the above experimental examples are shown in FIGS. 8A to 8D. As can be seen from these results, in Comparative Example 4 in which the negative electrode active material layer contained AB, a sufficient reversible capacity could not be obtained. On the other hand, in each example, a sufficient reversible capacity could be obtained. Further, in Examples 4-2 and 4-3 in which foamed aluminum was used as the negative electrode current collector, a higher reversible capacity could be obtained, and a TiF ₃ to which a small amount of Al was added was added as the negative electrode active material. In Example 4-3 used, particularly excellent charge / discharge characteristics could be realized.

[Comparative Example 5]
As the negative electrode active material, a commercially available CeF _{3 powder (Sigma-Aldrich) was used instead of the TiF 3} powder, and an Mg foil was used instead of the Al foil as the negative electrode current collector. The electrodes and beaker cells of this comparative example were prepared by the same method.

[Example 5]
The electrode and beaker of this example were carried out by the same method as in Example 4-1 described above, except that _{the same active material (CeF 3} ) as in Comparative Example 5 was used instead of _{TiF 3} powder as the negative electrode active material. A cell was prepared.

[Evaluation of charge / discharge characteristics]
The charge / discharge characteristics of the beaker cells produced in each of Comparative Example 5 and Example 5 described above were evaluated. Specifically, the charge / discharge test of each beaker cell is performed by a constant current test (charge / discharge rate is 0.02C) at room temperature (25 ° C.) using the beaker cells prepared in each of the above experimental examples. The reversible capacitance in the cycle was measured. The results are shown in Table 5 below. In the beaker cell produced in Example 5 above, the depolarization reaction potential of the negative electrode active material is based on the reduction decomposition potential of the non-functional coating composed of oxides and fluorides formed on the surface of the negative electrode current collector. It was confirmed from the reaction potential and charge / discharge curve of the negative electrode active material that the potential was also noble.

Here, the charge / discharge curves for the beaker cells produced in each of the above experimental examples are shown in FIGS. 9A (A) (Comparative Example 5) and (B) (Example 5). As can be seen from these results, in Comparative Example 5 in which the negative electrode active material layer contained AB, only a side reaction proceeded and a sufficient reversible capacity could not be obtained. In contrast, in Example 5, fluoride / defluorinated reaction of CeF ₃ progresses, it was possible to obtain a sufficient reversible capacity.

[Example 6-1]
The beaker cell produced in Example 4-3 described above was used as the beaker cell of this example.

[Example 6-2]
By the same method as in Example 6-1 described above, except that 2,4,6-trimethoxyboroxine (TMBx), which is one of the boroxine compounds, was added to the electrolytic solution at a concentration of 0.05 M. The beaker cell of this example was prepared.

[Example 6-3]
A beaker cell of this example was prepared by the same method as in Example 6-2 described above except that the concentration of TMBx added was 0.1 M.

[Example 6-4]
A beaker cell of this example was prepared by the same method as in Example 6-2 described above except that the concentration of TMBx added was 0.5 M.

[Evaluation of charge / discharge characteristics]
The charge / discharge characteristics of the beaker cells produced in each of Examples 6-1 to 6-4 described above were evaluated. Specifically, the charge / discharge test of each beaker cell is performed by a constant current test (charge / discharge rate is 0.02C) at room temperature (25 ° C.) using the beaker cells produced in each of the above examples. The reversible capacitance in the cycle was measured. The results are shown in Table 6 below.

Here, the charge / discharge curves of the beaker cells produced in Examples 6-2 to 6-4 are shown in FIGS. 10A to 10C. As can be seen from these results, the addition of the boroxine compound improved the charge / discharge characteristics. This is because the addition of the booxine compound forms a fluoride ion conductive film on the surface of the negative electrode active material layer, which suppresses the progress of irreversible reactions such as reduction decomposition of the electrolytic solution on the surface. Conceivable. Further, in Examples 6-2 and 6-3 in which the addition concentration of the booxine compound was in the range of 0.05 to 0.1 M, particularly excellent charge / discharge identification could be realized.

[Example 7-1]
The beaker cell produced in Example 3 described above was used as the beaker cell of this example.

[Example 7-2]
By the same method as in Example 7-1 described above, except that 2,4,6-trimethoxyboroxine (TMBx), which is one of the boroxine compounds, was added to the electrolytic solution at a concentration of 0.1 M. The beaker cell of this example was prepared.

[Evaluation of charge / discharge characteristics]
The charge / discharge characteristics of the beaker cells produced in Examples 7-1 and 7-2 described above were evaluated. Specifically, the charge / discharge test of each beaker cell is performed by a constant current test (charge / discharge rate is 0.04C) at room temperature (25 ° C.) using the beaker cells produced in each of the above examples. The reversible capacitance in the cycle was measured. The results are shown in Table 7 below.

Here, the charge / discharge curves for the beaker cells produced in Examples 7-1 and 7-2 are shown in FIGS. 11A and 11B. As can be seen from these results, even when Al (Ti) F ₃ was used as the negative electrode active material, the charge / discharge characteristics were improved by the addition of the booxine compound.

1 Fluoride ion battery,
10 Positive electrode,
11 Aluminum (Al) foil (positive electrode current collector),
12 Positive electrode active material layer,
13 Positive electrode active material,
20 negative electrode,
21 Negative electrode active material,
22 Aluminum foam (negative electrode current collector),
30 Electrolyte layer,
40 external load,
F ^- fluoride ion.

Claims (10)

A negative electrode active material layer containing a negative electrode active material and
A negative electrode current collector that collects electricity from the negative electrode active material layer and
It is a negative electrode for a fluoride ion battery having
The negative electrode active material contains metal fluoride, and the defluorination reaction potential of the metal fluoride is higher than the reduction decomposition potential of the inert film composed of oxide and fluoride formed on the surface of the negative electrode current collector. It ’s a precious potential,
The constituent material of the negative electrode current collector is aluminum, magnesium, or an alloy thereof.
A negative electrode for a fluoride ion battery, wherein the negative electrode active material layer does not contain a conductive auxiliary agent made of a carbon material.
.. The metal fluorides are Al _1-x (Ti) _x F ₃ (here, 0 <x ≦ 0.5), Ti _1-y (Al) _y F ₃ (here, 0 ≦ y ≦ 0). a .5) and CeF at least one ₃ is selected from the group consisting of negative electrode for fluoride ion battery according to claim 1. The negative electrode for a fluoride ion battery according to claim 2, wherein the metal fluoride _{contains Al 1-x} (Ti) _x F _{3 (here, 0 <x ≦ 0.5).} The fluoride ion battery according to any one of claims 1 to 3, wherein the negative electrode current collector is composed of a conductive porous body having pores, and the negative electrode active material is supported in the pores. Negative electrode. The negative electrode for a fluoride ion battery according to claim 4, wherein the conductive porous body constituting the negative electrode current collector is made of foamed aluminum. With the positive electrode
With the negative electrode
An electrolyte layer containing an electrolyte, which is arranged between the positive electrode and the negative electrode,
It is a fluoride ion battery having
A fluoride ion battery in which the negative electrode is the negative electrode for a fluoride ion battery according to any one of claims 1 to 5. According to claim 6, the electrolyte is an organic electrolytic solution containing an ester-based or lactone-based single or mixed organic solvent having α-hydrogen and an alkali metal fluoride having an alkali metal cation and a fluoride ion. The fluoride ion battery of the description. The fluoride ion battery according to claim 6 or 7, wherein the electrolyte contains a compound containing boron as an additive. The fluoride ion battery according to claim 8, wherein the boron-containing compound contains a compound having one booxine structure. The fluoride ion battery according to claim 8 or 9, wherein the concentration of the boron-containing compound in the electrolyte is 0.5 M or less.

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