Negative electrode active material for fluoride ion batteries and method for producing the same, negative electrode composite material, 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] This disclosure relates to a negative electrode active material for fluoride ion batteries, a method for producing the same, a negative electrode composite material, and fluoride ion batteries. [Background technology]

[0002] Lithium-ion batteries are known as high-voltage, high-energy-density batteries. Lithium-ion batteries are cation-based batteries that use lithium ions as carriers. In contrast, fluoride-ion batteries, which use fluoride ions as carriers, are known as anion-based batteries.

[0003] As disclosed in Patent Documents 1 and 2, and Non-Patent Document 1, the use of magnesium materials such as metallic magnesium or magnesium fluoride as the negative electrode active material for fluoride-ion batteries is being considered. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Special Publication No. 2008-537312 [Patent Document 2] Japanese Patent Publication No. 2022-123264 [Non-patent literature]

[0005] [Non-Patent Document 1] Journal of Materials Chemistry A, 2014, 2, 20861 [Overview of the project] [Problems that the invention aims to solve]

[0006] In fluoride-ion batteries containing magnesium as the 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 fluoride ion batteries capable of improving battery capacity, a method for producing the same, a negative electrode mixture comprising such a negative electrode active material, and a fluoride ion battery containing such a negative electrode mixture. Means for Solving the Problem

[0008] The present disclosers and others 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 formula (1), M III is a trivalent metal, and x is greater than 0 and less than 0.5.). <Aspect 2> The M III is at least one selected from the group consisting of aluminum, scandium, gallium, yttrium, and lanthanoids. The negative electrode active material according to aspect 1. <Aspect 3> A negative electrode mixture comprising the negative electrode active material according to aspect 1 or 2. <Aspect 4> having a negative electrode active material layer, and the negative electrode active material layer contains the negative electrode mixture according to aspect 3, a fluoride ion battery. <Aspect 5> A method for producing the negative electrode active material according to aspect 1, comprising the following steps: providing a raw material containing magnesium fluoride and a fluoride of the trivalent metal, applying mechanical impact to the raw material to cause a reaction. Effect of the Invention

[0009] According to this disclosure, it is possible to provide a negative electrode active material for a fluoride-ion battery that can improve battery capacity, a method for producing 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 explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of a fluoride-ion battery according to this disclosure. [Figure 2(a)] Figure 2(a) shows the XRD pattern of the negative electrode active material in the example. [Figure 2(b)] Figure 2(b) shows the XRD pattern of the negative electrode active material in the example. [Figure 2(c)] Figure 2(c) shows the XRD pattern of the negative electrode active material of the comparative example. [Figure 3(a)] Figure 3(a) shows the charge and discharge curves of the battery in the embodiment. [Figure 3(b)] Figure 3(b) shows the charge and discharge curves of the battery in the embodiment. [Figure 3(c)] Figure 3(c) shows the charge and discharge curves of the battery in the embodiment. [Figure 3(d)] Figure 3(d) shows the charge and discharge curves of the battery in the embodiment. [Figure 3(e)] Figure 3(e) shows the charge and discharge curves of the battery in the embodiment. [Figure 3(f)] Figure 3(f) shows the charge and discharge curves of the battery in the embodiment. [Figure 3(g)] Figure 3(g) shows the charge and discharge curves of the battery in the example. [Figure 3(h)] Figure 3(h) shows the charge and discharge curves of the battery in the embodiment. [Figure 3(i)] Figure 3(i) shows the charge and discharge curves of the battery in the embodiment. [Figure 3(j)] Figure 3(j) shows the charge and discharge curves of the battery in the embodiment. [Figure 3(k)] Figure 3(k) shows the charge and discharge curves of the battery in the embodiment. [Figure 3(l)] Figure 3(l) shows the charge and discharge curves of the battery in the embodiment. [Figure 3(m)]Fig. 3(m) is a charge-discharge curve of a battery of a comparative example. [Figure 3(n)] Fig. 3(n) is a charge-discharge curve of a battery of a comparative example. [Figure 3(o)] Fig. 3(o) is a charge-discharge curve of a battery of a comparative example. Mode for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present disclosure will be described in detail. It should be noted that the present disclosure is not limited to the following embodiments, and can be implemented with various modifications within the scope of the spirit 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 a negative electrode active material, although the theoretical battery capacity is large, it is difficult to sufficiently increase the actually measured value. The present inventors considered that one of the reasons why a sufficient battery capacity cannot be obtained when magnesium fluoride is used as a negative electrode active material is that diffusion of fluoride ions inside magnesium fluoride is slow, and only the vicinity of the surface of the negative electrode active material particles can contribute to the electrode reaction.

[0014] In this regard, the Disclosing Party has found that by introducing a predetermined proportion of cations with a higher number of magnesium ions than magnesium ions into magnesium fluoride to form a composite fluoride, the capacity of a battery containing this composite fluoride as the negative electrode active material can be improved. The reason for this is presumed to be as follows, although this is not intended to be bound by any theory: That is, by introducing the above cations while maintaining the crystal structure of magnesium fluoride, the fluoride ions in the composite fluoride become more abundant than in unsubstituted magnesium fluoride in order to compensate for the charge. These excess fluoride ions are thought to exist between the lattice of the magnesium fluoride crystal. It is thought that a new diffusion pathway is established between these fluoride ions in the lattice and the fluoride ions at the lattice positions, thereby accelerating the diffusion of fluoride ions. As a result, it is thought that the electrode reaction proceeds not only on the surface of the negative electrode active material particles but also inside them, improving the battery capacity.

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

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

[0017] In equation (1), x is greater than 0 and less than 0.5. This results in an appropriate concentration of excess fluoride ions between the lattice, and consequently, the diffusion of fluoride ions becomes faster. Also, when x is less than 0.5, the magnesium fluoride is converted to M while maintaining the crystal structure of magnesium fluoride. III It can be replaced by M. III The metals that can be used as such differ in their valence and atomic size, so x is M III It may vary depending on the type. For example, M IIIIf x is aluminum, gallium, yttrium, and lanthanides, x may be greater than 0, 0.1 or greater, or 0.2 or greater, and may be 0.4 or less, 0.3 or less, 0.2 or less, or 0.1 or less. III If x is scandium, then x may be greater than 0, 0.1 or greater, 0.2 or greater, or 0.3 or greater, and may be 0.4 or less, or 0.3 or less.

[0018] Method for manufacturing negative electrode active material A method for producing a negative electrode active material according to this disclosure comprises the following steps: providing raw materials comprising magnesium fluoride and a fluoride of a trivalent metal; and reacting the raw materials by applying mechanical shock.

[0019] <Raw material provision process> The method of this disclosure includes providing raw materials comprising magnesium fluoride and a trivalent metal fluoride.

[0020] In the method disclosed herein, the trivalent metal is the M described above. III That is the case.

[0021] <Reaction Process> The method disclosed herein includes subjecting raw materials to mechanical impact to induce a reaction.

[0022] One method for applying mechanical impact is mechanical milling, specifically, mixing using a ball mill. This reaction process can also be carried out in an inert atmosphere, such as a dry argon atmosphere.

[0023] 《Negative electrode mixture》 The negative electrode composite material of this disclosure comprises the negative electrode active material of this disclosure and optionally comprises a fluoride ion conductive material, a conductive additive, and a binder.

[0024] In this disclosure, "negative electrode mixture" means a composition that can constitute a negative electrode active material layer, either as is or by further containing other components.

[0025] <Negative electrode active material> For the negative electrode active material of this disclosure, please refer to the above description regarding the negative electrode active material of this disclosure.

[0026] The content of the negative electrode active material in the negative electrode composite material 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 materials> The negative electrode composite material contains a fluoride ion conductive material containing at least one metal element (excluding metallic magnesium) and fluorine. The fluoride ion conductive material has fluoride ion conductivity. Furthermore, part or all of the fluoride ion conductive material may function as a negative electrode active material during charging and discharging.

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

[0029] The content of 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 additive> Examples of conductive additives include carbon materials. Examples of carbon materials include carbon black such as acetylene black, Ketjen black, furnace black, and thermal black, as well as graphene, fullerene, and carbon nanotubes.

[0031] <binder> Examples of binders include fluorine-based binders such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE).

[0032] Fluoride-ion batteries As shown in Figure 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 this disclosure may be a liquid-based battery or a solid-state battery. In this disclosure, "solid-state battery" means a battery that uses at least a solid electrolyte as the electrolyte, and therefore a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as the electrolyte.

[0034] <Negative electrode current collector> Examples of materials for the negative electrode current collector include stainless steel (SUS), copper, nickel, iron, titanium, platinum, and carbon. Examples of shapes for the negative electrode current collector include foil, mesh, and porous forms.

[0035] <Negative electrode active material layer> The negative electrode active material layer contains the negative electrode composite material of this disclosure. For details of the negative electrode composite material of this disclosure, please refer to the above description relating to the negative electrode composite material of this disclosure.

[0036] The thickness of the negative electrode active material layer is not particularly limited and can be adjusted as appropriate depending on the battery configuration.

[0037] <Electrolyte layer> If the fluoride-ion battery of this disclosure is a liquid-type battery, the electrolyte layer may consist of, for example, an electrolyte solution and an optional separator.

[0038] The electrolyte may contain, for example, a fluoride salt and an organic solvent.

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

[0040] If the fluoride-ion battery of this disclosure is a solid-state 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 an example. Examples of inorganic fluorides include Ca 1-x Ba x We can list F2.

[0042] For information regarding the binder, please refer to the above description concerning the negative electrode mixture in this disclosure.

[0043] <Cathode active material layer> The positive electrode active material layer of this disclosure is a layer containing at least a positive electrode active material. The positive electrode active material layer may optionally contain a solid electrolyte, a conductive additive, and a binder.

[0044] The positive electrode active material is typically an active material that defluorinated during discharge. Examples of positive electrode active materials include elemental metals, alloys, metal oxides, and their fluorides. Examples of metallic elements contained in positive electrode active materials include Cu, Ag, Ni, Co, Pb, Mn, Au, Pt, Rh, V, Os, Ru, Fe, Cr, Bi, Nb, Sb, Ti, Sn, and Zn.

[0045] For solid electrolytes, refer to the above description of the electrolyte layer in this disclosure, and for conductive additives and binders, refer to the above description of the negative electrode mixture in this disclosure.

[0046] The thickness of the positive electrode active material layer is not particularly limited and can be adjusted as appropriate depending on the battery configuration.

[0047] <Positive electrode current collector> Examples of materials for the positive electrode current collector include lead, stainless steel (SUS), aluminum, nickel, iron, titanium, platinum, and carbon. Examples of shapes for the positive electrode current collector include foil, mesh, and porous forms. [Examples]

[0048] Example 1 <Preparation of negative electrode active material> A predetermined amount of magnesium fluoride (MgF2) and aluminum fluoride (AlF3) are mixed and reacted using a ball mill (Fritsch Premium Line PL-7 planetary ball mill) by mechanical milling, thereby producing a powdered negative electrode active material Mg 0.9 Al 0.1 F 2.1 A molar ratio of MgF2:AlF3 (9:1) was obtained. The ball milling was performed at 600 rpm for 20 hours in a dry argon atmosphere.

[0049] <Preparation of negative electrode composite material> A predetermined amount of calcium fluoride (CaF2) and barium fluoride (BaF2) are mixed and reacted using a ball mill (Fritsch Premium Line PL-7 planetary ball mill) by mechanical milling to produce a powdered fluoride ion conductive material, Ca. 0.5 Ba 0.5 F2 (50CaF2·50BaF2 (mol%)) was obtained. The ball milling was carried out at 600 rpm for 20 hours in a dry argon atmosphere. The above anode active material, fluoride ion conductive material, and acetylene black (AB) as a conductive additive were weighed in a mass ratio of 45:48:7 and mixed using a ball mill (Fritsch Premium Line PL-7 planetary ball mill) to obtain a powdered anode mixture. The ball milling was carried out at 600 rpm for 3 hours in a dry argon atmosphere.

[0050] <Preparation of solid electrolytes> A predetermined amount of CaF2 and BaF2 are mixed and reacted using a ball mill (Fritsch Premium Line PL-7 planetary ball mill) by mechanical milling, thereby producing a powdered solid electrolyte Ca. 0.6 Ba 0.4 F2 (60CaF2·40BaF2 (mol%)) was obtained. The ball milling was performed at 600 rpm for 20 hours in a dry argon atmosphere.

[0051] <Fabrication of all-solid-state fluoride-ion batteries> A compacted powder was formed using 10 mg of the above-mentioned negative electrode composite powder, thereby obtaining a negative electrode active material layer. A compacted powder was formed using 100 mg of the above-mentioned solid electrolyte powder, thereby obtaining an electrolyte layer. 220 mg of lead (Pb) metal plate, which functions as a positive electrode active material, was used as the positive electrode active material layer. The platinum foil as the negative electrode current collector, the negative electrode active material layer, the electrolyte layer, the positive electrode active material layer, and the aluminum foil as the 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 ceramic with an inner diameter of 11.28 mm, and was fixed by being sandwiched between stainless steel cylinders with a diameter of 11.28 mm on 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 is Mg 0.7 Al 0.3 F 2.3 An all-solid-state fluoride ion battery for Example 2 was fabricated in the same manner as in Example 1, except that the ratio of MgF2 to AlF3 was changed to 7:3 (molar ratio).

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

[0054] Comparative Example 1 As the negative electrode active material, a trivalent metal (M III A comparative example of a solid-state fluoride ion battery was prepared in the same manner as in Example 1, except that unsubstituted MgF2 (i.e., unsubstituted MgF2) was used.

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

[0056] "evaluation" <Verification of elemental substitution> Whether partially element-substituted MgF2 had been prepared was determined by confirming, through X-ray diffraction (XRD) measurements, that the negative electrode active material had a crystalline phase (tetragonal MgF2 phase) with the same crystal system as MgF2, and that the lattice constant and lattice volume of the crystalline phase had changed from those of unsubstituted MgF2. The lattice constant and lattice volume were determined by pattern fitting of the XRD pattern.

[0057] (XRD measurement) XRD measurements were performed on the negative electrode active material for each example. Specifically, measurements were taken using a concentrated method with CuKα irradiation under the conditions of a tube voltage of 45kV and a tube current of 200mA using a Rigaku SmartLab instrument. The results are shown in Figure 2. As shown in Figure 2, peaks attributed to the tetragonal MgF2 phase were observed in all samples.

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

[0059] [Table 1]

[0060] In each sample, the lattice constant and lattice volume changed compared to the unsubstituted MgF2 phase. This confirmed that partially substituted MgF2 was prepared. In some samples, minor peaks attributed to ZrO2 were observed. These are impurities originating from the ball mill media. Peaks not indicated by symbols are due to unreacted components of each starting material (for example, they can be attributed to AlF3 in Example 2, NdF3 in Example 9, and SmF3 in Example 11). The ZrO2 and unreacted components are trace elements and are not considered to have a significant impact on the properties.

[0061] <Evaluation of fluoride-ion batteries> For each example of a fluoride-ion battery, the test was conducted in a sealed container under vacuum at a test temperature of 200°C and a current density of 0.05 mA / cm². 2 The battery was charged and discharged three times each. The charging termination voltage and discharging termination voltage were set to 2.65V and 1.0V, respectively. A frequency response analyzer-equipped electrochemical measurement system (VMP-300 high-performance electrochemical measurement system, Biologic Corporation) was used for the charge-discharge test. The results of the charge-discharge test are shown in Table 2 and Figure 3. Note that the charging capacity and discharging capacity for each example are specific capacities normalized by the mass of the negative electrode active material in the negative electrode composite.

[0062] [Table 2]

[0063] As shown in Table 2 and Figure 3, MgF2(Mg) is partially substituted with a trivalent metal.1-x M III x F 2+x In the example where ) was used as the negative electrode active material, the battery had a large specific capacity. In contrast, unsubstituted MgF2 or MgF2 (Mg) partially substituted with a monovalent metal 1-x M I x F 2+x The comparative battery, which used ) as the negative electrode active material, had a low 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 Cathode active material layer 50 Positive electrode current collector

Claims

1. The negative electrode active material for fluoride ion batteries represented by the following formula (1): Mg １－ｘ M ＩＩＩ ｘ F ２＋ｘ … (1) (In the above formula (1), M ＩＩＩ x is at least one trivalent metal selected from aluminum, scandium, gallium, yttrium, and lanthanides, and x is greater than 0 and less than 0.

5.

2. A negative electrode composite material comprising the negative electrode active material described in claim 1.

3. It has a negative electrode active material layer, and The negative electrode active material layer contains the negative electrode composite material described in claim 2. Fluoride ion battery.

4. A method for producing a negative electrode active material according to claim 1, comprising the following steps: To provide a raw material containing magnesium fluoride and the fluoride of the trivalent metal, The material is subjected to mechanical impact to cause a reaction.

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