Negative electrode active material for fluoride ion battery and manufacturing method thereof, negative electrode mixture, and fluoride ion battery

Abstract

To provide a negative electrode active material for a fluoride ion battery that can improve a battery capacity, a method for manufacturing the same, a negative electrode composite including such a negative electrode active material, and a fluoride ion battery containing such a negative electrode composite.SOLUTION: A negative electrode active material for a fluoride ion battery according to the present disclosure is represented by the following formula (1): Mg1-xMIIIxF2+x (1) (In the formula (1), MIII is a trivalent metal, and x is greater than 0 and less than 0.5.) The method according to the present disclosure for manufacturing the negative electrode active material includes the following steps: providing a raw material containing magnesium fluoride and a fluoride of a trivalent metal, and applying a mechanical impact to the raw material to cause a reaction. The negative electrode composite according to the present disclosure includes the negative electrode active material according to the present disclosure. The fluoride ion battery 1 according to the present disclosure has a negative electrode active material layer 20, and the negative electrode active material layer contains the negative electrode composite of the present disclosure.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a negative electrode active material for a fluoride ion battery, a method for manufacturing the same, a negative electrode composite material, and a fluoride ion battery.

Background Art

[0002] As a high-voltage and high-energy density battery, for example, a lithium-ion battery is known. A lithium-ion battery is a cation-based battery that uses lithium ions as carriers. On the other hand, as an anion-based battery, a fluoride ion battery that uses fluoride ions as carriers is known.

[0003] As disclosed in Patent Documents 1 and 2 and Non-Patent Document 1, it has been considered to use a magnesium material such as metallic magnesium or magnesium fluoride as a negative electrode active material for a fluoride ion battery.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] In a fluoride ion battery containing a magnesium material as a negative electrode active material, there is room for improvement in battery capacity.

[0007] The present disclosure aims to provide a negative electrode active material for a fluoride ion battery capable of improving battery capacity, a method for manufacturing the same, a negative electrode composite material containing such a negative electrode active material, and a fluoride ion battery containing such a negative electrode composite material.

Means for Solving the Problems

[0008] The present inventors have found that the above problems can be solved by the following means. 〈Aspect 1〉 A negative electrode active material for a fluoride ion battery represented by the following formula (1): Mg 1-x M III x F 2+x … (1) (In the above formula (1), M III is a trivalent metal, and x is greater than 0 and less than 0.5.). 〈Aspect 2〉 The negative electrode active material according to Aspect 1, wherein the M III is at least one selected from aluminum, scandium, gallium, yttrium, and lanthanoids. 〈Aspect 3〉 A negative electrode composite material containing the negative electrode active material according to Aspect 1 or 2. 〈Aspect 4〉 A fluoride ion battery having a negative electrode active material layer, and the negative electrode active material layer contains the negative electrode composite material according to Aspect 3. Fluoride ion battery. 〈Aspect 5〉 A method for manufacturing the negative electrode active material according to Aspect 1, including the following steps: Providing a raw material containing magnesium fluoride and a fluoride of the trivalent metal, Subjecting the raw material to mechanical impact to cause a reaction.

Advantages of the Invention

[0009] According to the present disclosure, it is possible to provide a negative electrode active material for a fluoride ion battery capable of improving battery capacity, a method for manufacturing the same, a negative electrode composite material containing such a negative electrode active material, and a fluoride ion battery containing such a negative electrode composite material.

Brief Description of the Drawings

[0010]

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MODE FOR CARRYING OUT THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described in detail. Note that the present disclosure is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the disclosure.

[0012] 《Negative Electrode Active Material for Fluoride Ion Battery》 The negative electrode active material for a fluoride ion battery of the present disclosure is represented by the following formula (1): Mg 1-x M III x F 2+x … (1) (In formula (1), M III is a trivalent metal, and x is less than 0.5.).

[0013] The present inventors have found that when magnesium fluoride is used as the negative electrode active material, although the theoretical value of the battery capacity is large, it is difficult to sufficiently increase the measured value. The present inventors consider that one of the reasons why sufficient battery capacity cannot be obtained when magnesium fluoride is used as the negative electrode active material is that the diffusion of fluoride ions inside magnesium fluoride is slow, and the electrode reaction can only contribute near the surface of the negative electrode active material particles.

[0014] In this regard, the present inventors have found that by introducing cations having a higher valence than magnesium ions into magnesium fluoride at a predetermined ratio to form a composite fluoride, the capacity of a battery containing this composite fluoride as a negative electrode active material is improved. Although not intending to be bound by any theory, the reason is presumed as follows. That is, while maintaining the crystal structure of magnesium fluoride, when the above cations are introduced, fluoride ions in the above composite fluoride become excessive compared to unsubstituted magnesium fluoride for charge compensation. It is considered that this excessive fluoride ion exists between the crystal lattices of magnesium fluoride. By constructing a new diffusion path between the fluoride ions existing between the lattices and the fluoride ions at the lattice positions, it is considered that the diffusion of fluoride ions is accelerated. As a result, it is considered that the electrode reaction proceeds not only on the surface of the negative electrode active material particles but also inside thereof, and the battery capacity is improved.

[0015] In formula (1), Mg is metallic magnesium and F is fluorine.

[0016] In formula (1), M III may be at least one selected from aluminum, scandium, gallium, yttrium, and lanthanoids. Examples of lanthanoids include samarium, neodymium, and europium.

[0017] In formula (1), x is greater than 0 and less than 0.5. As a result, excessive fluoride ions existing between the lattices have an appropriate concentration, and the diffusion of fluoride ions is accelerated. Further, when x is less than 0.5, magnesium can be substituted by M III while maintaining the crystal structure of magnesium fluoride. Since the metals that can be used as M III differ in the type of valence and the size of atoms, etc., x may differ depending on the type of M III . For example, M IIIWhen M is aluminum, gallium, yttrium, or a lanthanoid, x may be greater than 0, 0.1 or more, or 0.2 or more, and may be 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. M III When M is scandium, x may be greater than 0, 0.1 or more, 0.2 or more, or 0.3 or more, and may be 0.4 or less or 0.3 or less.

[0018] 《Method for Manufacturing Negative Electrode Active Material》 The method of the present disclosure for manufacturing a negative electrode active material includes the following steps: providing a raw material containing magnesium fluoride and a fluoride of a trivalent metal, and subjecting the raw material to mechanical impact to cause a reaction.

[0019] 〈Raw Material Provision Step〉 The method of the present disclosure includes providing a raw material containing magnesium fluoride and a fluoride of a trivalent metal.

[0020] In the method of the present disclosure, the trivalent metal is the above-mentioned M III as described above.

[0021] 〈Reaction Step〉 The method of the present disclosure includes subjecting the raw material to mechanical impact to cause a reaction.

[0022] Examples of the method of applying mechanical impact include, for example, the mechanical milling method, specifically, the method of mixing by a ball mill. Further, this reaction step can be carried out in an inert atmosphere, for example, a dry argon atmosphere.

[0023] 《Negative Electrode Composite Material》 The negative electrode composite material of the present disclosure contains the negative electrode active material of the present disclosure, and optionally contains a fluoride ion conductive material, a conductive assistant, and a binder.

[0024] Regarding the present disclosure, the "negative electrode composite material" means a composition that can form a negative electrode active material layer as it is or by further containing other components.

[0025] 〈Negative electrode active material〉 Regarding the negative electrode active material of the present disclosure, reference can be made to the above description regarding the negative electrode active material of the present disclosure.

[0026] The content of the negative electrode active material in the negative electrode composite may be 10% by mass or more, 20% by mass or more, 30% by mass or more, or 40% by mass or more, and may be 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, or 50% by mass or less.

[0027] 〈Fluoride ion conductive material〉 The negative electrode composite contains a fluoride ion conductive material containing at least one metal element (excluding magnesium metal) and fluorine. The fluoride ion conductive material has fluoride ion conductivity. Further, a part or all of the fluoride ion conductive material may function as a negative electrode active material during charge and discharge.

[0028] Examples of the fluoride ion conductive material include calcium barium fluoride (Ca 1-x Ba x F2). x may be 0.30 or more, 0.35 or more, 0.40 or more, or 0.45 or more, and may be 0.70 or less, 0.65 or less, 0.60 or less, or 0.65 or less.

[0029] The content of the fluoride ion conductive material in the negative electrode composite may be 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, or 45% by mass, and may be 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, or 55% by mass or less.

[0030] 〈Conductive aid〉 Examples of the conductive aid include carbon materials. Examples of the carbon materials include carbon blacks such as acetylene black, ketjen black, furnace black, and thermal black, graphene, fullerene, and carbon nanotubes.

[0031] 〈Binder〉 Examples of the binder include fluorine-based binders such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE).

[0032] 《Fluoride Ion Battery》 As shown in FIG. 1, the fluoride ion battery 1 of the present disclosure has a negative electrode active material layer 20, and the negative electrode active material layer contains the negative electrode composite material of the present disclosure. The fluoride ion battery 1 of the present disclosure may have a negative electrode current collector 10, a negative electrode active material layer 20, an electrolyte layer 30, a positive electrode current collector 40, and a positive electrode active material layer 50 in this order.

[0033] The fluoride ion battery of the present disclosure may be a liquid battery or a solid battery. Regarding the present disclosure, the “solid battery” means a battery using at least a solid electrolyte as an electrolyte. Therefore, the solid battery may use a combination of a solid electrolyte and a liquid electrolyte as an electrolyte.

[0034] 〈Negative Electrode Current Collector〉 Examples of the material of the negative electrode current collector include stainless steel (SUS), copper, nickel, iron, titanium, platinum, and carbon. Examples of the shape of the negative electrode current collector include foil shape, mesh shape, and porous shape.

[0035] 〈Negative Electrode Active Material Layer〉 The negative electrode active material layer contains the negative electrode composite material of the present disclosure. Regarding the negative electrode composite material of the present disclosure, reference can be made to the above description regarding the negative electrode composite material of the present disclosure.

[0036] 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.

[0037] 〈Electrolyte Layer〉 When the fluoride ion battery of the present disclosure is a liquid battery, the electrolyte layer may be composed of, for example, an electrolytic solution and an optional separator.

[0038] The electrolytic solution can contain, for example, a fluoride salt and an organic solvent.

[0039] The separator is not particularly limited as long as it has a composition that can withstand the usage range of the fluoride ion battery.

[0040] When the fluoride ion battery of the present disclosure is a solid battery, the electrolyte layer may be, for example, a layer containing a solid electrolyte. In this case, the electrolyte layer may optionally contain a binder.

[0041] The solid electrolyte is not particularly limited as long as it is a material that can be used in a fluoride ion battery, but inorganic fluorides are exemplified. Examples of the inorganic fluoride include Ca 1-x Ba x F2 can be mentioned.

[0042] Regarding the binder, reference can be made to the above description regarding the negative electrode composite material of the present disclosure.

[0043] 〈Positive electrode active material layer〉 The positive electrode active material layer of the present disclosure is a layer containing at least a positive electrode active material. Further, the positive electrode active material layer may optionally contain a solid electrolyte, a conductive aid, and a binder.

[0044] The positive electrode active material is usually an active material that undergoes defluorination during discharge. Examples of the positive electrode active material include a simple metal, an alloy, a metal oxide, and fluorides thereof. Examples of the metal element contained in the positive electrode active material include Cu, Ag, Ni, Co, Pb, Mn, Au, Pt, Rh, V, Os, Ru, Fe, Cr, Bi, Nb, Sb, Ti, Sn, Zn, etc.

[0045] Regarding the solid electrolyte, reference can be made to the above description regarding the electrolyte layer of the present disclosure, and regarding the conductive aid and the binder, reference can be made to the above description regarding the negative electrode composite material of the present disclosure.

[0046] 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.

[0047] 〈Positive electrode current collector〉 Examples of the material of the positive current collector include lead, stainless steel (SUS), aluminum, nickel, iron, titanium, platinum, and carbon. Examples of the shape of the positive current collector include foil, mesh, and porous.

Examples

[0048] 《Example 1》 〈Preparation of negative electrode active material〉 A predetermined amount of magnesium fluoride (MgF2) and aluminum fluoride (AlF3) were mixed by mechanical milling using a ball mill apparatus (manufactured by Fritsch, planetary ball mill premium line PL-7) and reacted to obtain a powdery negative electrode active material Mg 0.9 Al 0.1 F 2.1 (MgF2:AlF3 = 9:1 (molar ratio)). The mixing by the ball mill was carried out at 600 rpm for 20 hours in a dry argon atmosphere.

[0049] 〈Preparation of negative electrode composite〉 A predetermined amount of calcium fluoride (CaF2) and barium fluoride (BaF2) were mixed by mechanical milling using a ball mill apparatus (manufactured by Fritsch, planetary ball mill premium line PL-7) and reacted to obtain a powdery fluoride ion conductive material Ca 0.5 Ba 0.5 F2 (50CaF2·50BaF2 (mol%)). The mixing by the ball mill was carried out at 600 rpm for 20 hours in a dry argon atmosphere. The above negative electrode active material, fluoride ion conductive material, and acetylene black (AB) as a conductive assistant were weighed at a mass ratio of 45:48:7 and mixed by ball milling using a ball mill apparatus (manufactured by Fritsch, planetary ball mill premium line PL-7) to obtain a powdery negative electrode composite. The mixing by the ball mill was carried out at 600 rpm for 3 hours in a dry argon atmosphere.

[0050] 〈Preparation of solid electrolyte〉 A predetermined amount of CaF2 and BaF2 was mixed and reacted by mechanical milling using a ball mill apparatus (manufactured by Fritsch, planetary ball mill premium line PL-7), thereby obtaining a powdery solid electrolyte Ca 0.6 Ba 0.4 F2 (60CaF2·40BaF2 (mol%)). The mixing by the ball mill was carried out in a dry argon atmosphere at 600 rpm for 20 hours.

[0051] 〈Fabrication of All-Solid-State Fluoride Ion Battery〉 Using 10 mg of the powder of the above negative electrode composite material, a compressed powder body was formed, and thereby a negative electrode active material layer was obtained. Using 100 mg of the powder of the above solid electrolyte, a compressed powder body was formed, and thereby an electrolyte layer was obtained. A 220 mg lead (Pb) metal plate that functions as a positive electrode active material was used as the positive electrode active material layer. A platinum foil as a negative electrode current collector, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and an aluminum foil as a positive electrode current collector were laminated in this order to fabricate the all-solid-state fluoride ion battery of Example 1. The diameter of the all-solid-state fluoride ion battery was 11.28 mm. This all-solid-state fluoride ion battery was placed in a cylindrical container made of ceramics with an inner diameter of 11.28 mm and was sandwiched and fixed by stainless steel cylinders with a diameter of 11.28 mm from both sides of the negative electrode current collector and the positive electrode current collector.

[0052] 《Example 2》 The composition of the negative electrode active material was changed to Mg 0.7 Al 0.3 F 2.3 (MgF2:AlF3 = 7:3 (molar ratio)), and the all-solid-state fluoride ion battery of Example 2 was fabricated in the same manner as in Example 1 except for this change.

[0053] 《Examples 3 to 12》 As a reagent used for preparing the negative electrode active material, except that gallium fluoride (GaF3), scandium fluoride (ScF3), yttrium fluoride (YF3), neodymium fluoride (NdF3), samarium fluoride (SmF3), or europium fluoride (EuF3) was used instead of AlF3, and the composition of the negative electrode active material was changed as described in Table 1, all-solid-state fluoride ion batteries of Examples 3 to 12 were fabricated in the same manner as in Example 1.

[0054] 《Comparative Example 1》 MgF2 not substituted with trivalent metal (M III ) was used, that is, unsubstituted MgF2 was used, and the all-solid-state fluoride ion battery of Comparative Example 1 was fabricated in the same manner as in Example 1.

[0055] 《Comparative Examples 2 and 3》 As a reagent used for preparing the negative electrode active material, except that sodium fluoride (NaF) or potassium fluoride (KF) was used instead of AlF3, and the composition of the negative electrode active material was changed as described in Table 1, all-solid-state fluoride ion batteries of Comparative Examples 2 and 3 were fabricated in the same manner as in Example 1.

[0056] 《Evaluation》 〈Confirmation of Element Substitution〉 Whether partially element-substituted MgF2 could be prepared was determined by confirming that the negative electrode active material had a crystal phase (tetragonal MgF2 phase) of the same crystal system as MgF2 and that the lattice constants and lattice volume of the crystal phase had changed from those of unsubstituted MgF2 as a result of X-ray diffraction (XRD) measurement. The lattice constants and lattice volume were determined by pattern fitting of the XRD pattern.

[0057] (XRD Measurement) XRD measurement was performed on the negative electrode active materials of each example. Specifically, using a Rigaku SmartLab apparatus, measurement was carried out by the focusing method of irradiating CuKα rays under the conditions of a tube voltage of 45 kV and a tube current of 200 mA. The results are shown in Figure 2. As shown in Figure 2, peaks attributable to the tetragonal MgF2 phase were observed in all samples.

[0058] For each of the obtained XRD patterns, pattern fitting analysis was performed using the analysis software PDXL manufactured by Rigaku Corporation to calculate the lattice constant and lattice volume of the MgF₂ phase. The results are shown in Table 1.

[0059]

Table 1

[0060] In the samples of each example, the lattice constant and lattice volume changed with respect to the unsubstituted MgF₂ phase. From the above, it was confirmed that MgF₂ partially substituted with elements was prepared. In addition, minor peaks attributed to ZrO₂ were observed in some samples. This is an impurity derived from the media of the ball mill. Also, the peaks not indicated by symbols of attribution are peaks derived from the unreacted portions of the respective raw materials (for example, in Example 2, it can be attributed to AlF₃, in Example 9, to NdF₃, and in Example 11, to SmF₃, respectively). The above ZrO₂ and the unreacted portions of the raw materials are trace components and are considered to have no significant influence on the properties.

[0061] 〈Evaluation of Fluoride Ion Batteries〉 For each fluoride ion battery of each example, while evacuating in a sealed container, charging and discharging were performed three times each at a test temperature of 200 °C and a current density of 0.05 mA / cm 2 ². The charging cut-off voltage and the discharging cut-off voltage were set to 2.65 V and 1.0 V, respectively. For the charge-discharge test, an electrochemical measurement system equipped with a frequency response analyzer (manufactured by BioLogic, VMP-300 high-performance electrochemical measurement system) was used. The results of the charge-discharge test are shown in Table 2 and Figure 3. Note that the charge capacity and the discharge capacity of each example are specific capacities normalized by the mass of the negative electrode active material in the negative electrode composite material.

[0062]

Table 2

[0063] As shown in Table 2 and Figure 3, MgF₂ (Mg1-x M III x F 2+x ) The battery of the example using [as the negative electrode active material] had a large specific capacity. In contrast, the battery of the comparative example using unsubstituted MgF2 or MgF2 partially substituted with a monovalent metal (Mg 1-x M I x F 2+x ) as the negative electrode active material had a small specific capacity.

Explanation of symbols

[0064] 1 Fluoride ion battery 10 Negative electrode current collector 20 Negative electrode active material layer 30 Electrolyte layer 40 Positive electrode active material layer 50 Positive electrode current collector

Claims

Claim 1 A negative electrode active material for a fluoride ion battery represented by the following formula (1): Mg １－ｘ M ＩＩＩ ｘ F ２＋ｘ … (1) (In the formula (1), M ＩＩＩ is a trivalent metal, and x is greater than 0 and less than 0.5.). Claim 2 The aforementioned M ＩＩＩ The negative electrode active material according to claim 1, wherein M is at least one selected from aluminum, scandium, gallium, yttrium, and lanthanoids. Claim 3 A negative electrode composite material containing the negative electrode active material according to Claim 1 or 2. Claim 4 Having a negative electrode active material layer, and the negative electrode active material layer contains the negative electrode composite material according to Claim 3, A fluoride ion battery. Claim 5 A method for producing the negative electrode active material according to Claim 1, comprising the following steps: Providing a raw material containing magnesium fluoride and a fluoride of the trivalent metal; Subjecting the raw material to mechanical impact to cause a reaction.

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