Active cathode material for fluoride ion batteries and manufacturing method thereof

Abstract

To provide a positive electrode material that can be used in fluoride-ion batteries, and a manufacturing method thereof.SOLUTION: An active cathode material for fluoride ion batteries contains graphite-like carbon. The graphite-like carbon has a higher proportion of sp2 bonds than sp3 bonds. In the active cathode material for fluoride ion batteries, the graphite-like carbon contains oxygen. The graphite-like carbon contains oxygen, and a proportion of the oxygen with respect to the entire graphite-like carbon can be 0.03 mass% to 30 mass%. A manufacturing method of the active cathode material for fluoride ion batteries includes: oxidizing graphite with acids and oxidizing agents to obtain graphite oxide; and reducing the oxidized graphite by heating the graphite oxide at a temperature of 600°C to 1,100°C in a reducing atmosphere and reducing the same.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode active material for a fluoride ion battery and a method for producing the same. [Background technology]

[0002] Lithium-ion batteries are known as high-voltage, high-energy-density batteries. Lithium-ion batteries are cation-based batteries that utilize the reaction between lithium ions and a positive electrode active material and the reaction between lithium ions and a negative electrode active material. On the other hand, fluoride-ion batteries are known as anion-based batteries that utilize the reaction of fluoride ions (fluoride anions).

[0003] Patent Document 1 discloses an active material for use in a fluoride ion battery, which contains a metal element and has a metal portion capable of reacting with fluoride ions, and in an O1s spectrum obtained by measuring the surface of the active material by X-ray photoelectron spectroscopy, where IA is the intensity at 531.0 eV and IB is the intensity of the peak derived from an oxide of the metal element, IB / IA is 0 or more and 1 or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-47526 Summary of the Invention [Problem to be solved by the invention]

[0005] There is a need for a new positive electrode active material that can be used in a fluoride ion battery. In particular, there is a need for a new positive electrode active material that has excellent discharge capacity as a positive electrode active material for a fluoride ion battery. The present disclosure aims to provide a new positive electrode active material that can be used in a fluoride ion battery and a method for producing the same. [Means for solving the problem]

[0006] The present inventors have found that the above object can be achieved by the following means: <<Aspect 1>> The graphite-like carbon is sp 2 The bond ratio is sp 3 A positive electrode active material for fluoride-ion batteries with a higher bond ratio. <<Aspect 2>> 2. The positive electrode active material for a fluoride ion battery according to embodiment 1, wherein the graphite-like carbon contains oxygen, and the proportion of the oxygen relative to the total amount of the graphite-like carbon is 5% by mass to 25% by mass. Aspect 3 The graphite-like carbon contained in the positive electrode active material for a fluoride ion battery is sp 2 Bonds and sp 3 sp for the sum of bonds and bonds with O (oxygen) 2 3. The positive electrode active material for a fluoride ion battery according to aspect 1 or 2, wherein the bonding ratio is 70% to 99.7%. Aspect 4 A positive electrode mixture for a fluoride ion battery, comprising the positive electrode active material for a fluoride ion battery according to any one of Aspects 1 to 3 and copper. Aspect 5 a positive electrode body, a negative electrode body, and It has an electrolyte, The electrolyte is disposed between the positive electrode body and the negative electrode body, the positive electrode body contains the positive electrode mixture for a fluoride ion battery according to aspect 4; The electrolyte is an electrolytic solution in which CsF is dissolved in a lactone-based non-aqueous solvent. Fluoride-ion battery. Aspect 6 Oxidizing the graphite with an acid and an oxidizing agent to obtain graphite oxide; The graphite oxide is reduced by heating it in a reducing atmosphere at a temperature of 600°C to 1100°C. A method for producing a positive electrode active material for a fluoride ion battery, comprising: [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a novel positive electrode active material that can be used in a fluoride ion battery, and a method for producing the same. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a fluoride-ion battery 1 according to one embodiment of the present disclosure. [Figure 2] 1 is a graph showing X-ray diffraction spectra of samples of Examples 1, 3, and 5. [Figure 3] 1 is a graph showing the relationship between the oxygen content (mass %) and the C-axis length (Å) in the samples of Examples 1 to 5. [Figure 4] 10 is a graph showing the results of a charge / discharge test of the test battery of Example 6. [Figure 5] 1 is a graph showing the results of a charge / discharge test of the test battery of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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 present disclosure.

[0010] 1. Cathode active material for fluoride-ion batteries The positive electrode active material for a fluoride ion battery of the present disclosure contains graphite-like carbon, and the graphite-like carbon is sp 2 The bond ratio is sp 3 The proportion of the bond is greater than the proportion of the bond. Or, the graphite-like carbon is contained, and the graphite-like carbon is sp 2 The bond ratio is sp 3 The ratio of bonds to O (oxygen) is higher.

[0011] In this disclosure, graphite-like carbon refers to a carbon material that has diamond bonds (sp3 Hybrid orbital bonds) and graphite bonds (carbon-carbon sp 2 Among carbons with an amorphous structure in which both bonds (hybrid orbital bonds) are mixed, those in which the proportion of graphite bonds exceeds 50%, that is, those in which the number of graphite bonds is greater than the number of diamond bonds. Note that graphite-like carbon may have a structure in which a crystalline structure partially consisting of a graphite structure and an amorphous structure part are mixed. The sp 3 Bonds and sp 2 The proportion of the bonded state can be analyzed by, for example, X-ray diffraction.

[0012] The graphite-like carbon contained in the positive electrode active material for a fluoride ion battery of the present disclosure is sp 2 Bonds and sp 3 sp for the sum of bonds and bonds with O (oxygen) 2 The binding rate may be 70% to 99.7%. This rate may be 70% or more, 75% or more, 80% or more, or 90% or more, or 99.7% or less, 95% or less, 90% or less, or 85% or less.

[0013] The particle size of the graphite-like carbon may be 10 μm to 100 μm. The particle size of the graphite-like carbon may be 10 μm or more, 20 μm or more, 30 μm or more, or 50 μm or more, and may be 100 μm or less, 90 μm or less, 80 μm or less, or 70 μm or less.

[0014] The C-axis length of the graphite-like carbon may be 6.70 Å to 7.15 Å. The C-axis length of the graphite-like carbon may be 6.70 Å or more, 6.75 Å or more, 6.80 Å or more, 6.85 Å or more, or 6.90 Å or more, and may be 7.15 Å or less, 7.10 Å or less, 7.05 Å or less, 7.00 Å or less, or 6.95 Å or less.

[0015] Graphite-like carbon interplanar spacing d 004 The interplanar spacing d of the graphite-like carbon may be 1.68 Å to 1.78 Å.004 may be 1.68 Å or more, 1.70 Å or more, or 1.72 Å or more, and may be 1.78 Å or less, 1.76 Å or less, or 1.74 Å or less.

[0016] The C-axis length and interplanar spacing d 004 can be analyzed by, for example, X-ray diffraction.

[0017] The graphite-like carbon may contain oxygen. The ratio of oxygen to the entire graphite-like carbon may be 0.03% by mass to 30% by mass, and preferably 5% by mass to 25% by mass. The ratio of oxygen to the entire graphite-like carbon may be 0.03% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more, and may be 30% by mass or less, 25% by mass or less, 20% by mass or less, or 15% by mass or less.

[0018] 2. Cathode mixture for fluoride ion batteries The positive electrode mixture for a fluoride ion battery according to the present disclosure may contain the positive electrode active material for a fluoride ion battery according to the present disclosure and copper. The copper may be, for example, in the form of particles. It is believed that the copper can function as a catalyst for a reaction between the graphite-like carbon serving as the positive electrode active material and fluorine ions, for example, an insertion / desorption reaction of fluorine ions into the graphite-like carbon.

[0019] Specifically, it is believed that the copper surface becomes copper fluoride, and then the fluorine ions react with the graphite-like carbon, as shown in the following formulas (1) and (2): Cu + xF- → CuF x CuF x + C → Cu + CF x

[0020] The positive electrode composite for a fluoride ion battery of the present disclosure may further contain an optional solid electrolyte, a conductive additive, a binder, and the like. Examples of binders include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). Examples of conductive additives include, but are not limited to, carbon materials as long as they have the desired electronic conductivity. Examples of carbon materials include carbon blacks such as acetylene black, ketjen black, furnace black, and thermal black.

[0021] 3. Fluoride-ion batteries The fluoride ion battery of the present disclosure includes a positive electrode assembly, a negative electrode assembly, and an electrolyte. The electrolyte is disposed between the positive electrode assembly and the negative electrode assembly. The positive electrode assembly contains the positive electrode mixture for a fluoride ion battery of the present disclosure. The electrolyte may be an electrolytic solution in which CsF is dissolved in a lactone-based non-aqueous solvent.

[0022] FIG. 1 is a schematic diagram of a fluoride ion battery 1 according to one embodiment of the present disclosure. The fluoride ion battery 1 according to one embodiment of the present disclosure includes a positive electrode body 10, a negative electrode body 20, and an electrolyte layer 30. The positive electrode body 10 includes a positive electrode current collector layer 11 and a positive electrode active material layer 12. The positive electrode active material layer 12 contains a positive electrode composite for a fluoride ion battery. The negative electrode body 20 includes a negative electrode current collector layer 21 and a negative electrode active material layer 22. The electrolyte layer 30 is disposed between the positive electrode body 10 and the negative electrode body 20. The electrolyte layer 30 has a configuration in which, for example, a separator is impregnated with an electrolyte solution. Although not shown, the fluoride ion battery 1 can be housed in a battery case.

[0023] The positive electrode body has, for example, a positive electrode current collector layer and a positive electrode active material layer. The shape of the positive electrode current collector layer may be, for example, foil-like, mesh-like, or porous. The material of the positive electrode current collector layer may be, for example, stainless steel (SUS), aluminum, titanium, iron, nickel, copper, silver, platinum, gold, carbon, or the like. The material of the positive electrode current collector layer is preferably copper. This is because copper is thought to function as a catalyst for the reaction between graphite-like carbon as the positive electrode active material and fluorine ions, for example, the insertion and desorption reaction of fluorine ions into the graphite-like carbon, during charge and discharge.

[0024] The positive electrode active material layer is a layer containing a positive electrode composite. The positive electrode active material layer can be formed, for example, by compacting a powder of the positive electrode composite on the positive electrode current collector. Alternatively, the positive electrode active material layer can be formed by dispersing the positive electrode composite in a dispersion medium to prepare a slurry, applying the slurry to the positive electrode current collector, and drying it.

[0025] The negative electrode body has, for example, a negative electrode current collector layer and a negative electrode active material layer. The shape and material of the negative electrode current collector layer may be the same as those of the positive electrode current collector layer. Aluminum is a preferred material for the negative electrode current collector layer. The negative electrode active material layer is a layer containing a negative electrode mixture. The negative electrode active material layer can be formed on the negative electrode current collector layer by, for example, the same method as that for the positive electrode active material layer.

[0026] The negative electrode mixture can contain a negative electrode active material and an optional binder, a solid electrolyte, a conductive additive, etc. As the negative electrode active material, among general negative electrode active materials used in fluoride ion batteries, for example, elemental metals, alloys, metal oxides, and fluorides thereof, a negative electrode active material having a lower reaction potential than the positive electrode active material for fluoride ion batteries of the present disclosure can be used.

[0027] When the fluoride ion battery of the present disclosure is a liquid battery, the electrolyte may be, for example, an electrolytic solution in which CsF is dissolved in a lactone-based non-aqueous solvent, such as γ-butyl lactone.

[0028] The electrolyte may be impregnated into a separator, which may be made of, for example, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a microporous film of an olefin resin such as polyethylene or polypropylene.

[0029] The fluoride ion battery in the present disclosure may be a primary battery or a secondary battery, but is preferably a secondary battery because it can be repeatedly charged and discharged and is useful, for example, as an in-vehicle battery. Furthermore, the shape of the fluoride ion battery in the present disclosure may be, for example, a coin type, a laminate type, a cylindrical type, or a prismatic type.

[0030] 4. Manufacturing method of positive electrode active material for fluoride ion batteries The manufacturing method disclosed herein is a method for manufacturing a positive electrode active material for a fluoride ion battery, and includes oxidizing graphite with an acid and an oxidizing agent to obtain graphite oxide, and reducing the graphite oxide by heating it in a reducing atmosphere at a temperature of 600°C to 1100°C.

[0031] Examples of graphite that can be used include, but are not limited to, natural flake graphite, spherical natural graphite, and artificial graphite. Graphite can be oxidized using an acid and an optional oxidizing agent. Examples of acids that can be used include fuming nitric acid, nitric acid, fuming sulfuric acid, sulfuric acid, and hydrochloric acid. Examples of oxidizing agents that can be used include potassium permanganate (KMnO4) and potassium chlorate (KClO3).

[0032] The reduction of graphite oxide can be carried out by heating the graphite oxide in a reducing atmosphere at a temperature of 600 to 1100°C. The reducing atmosphere may be any atmosphere that can reduce the graphite oxide within the above temperature range, and may be, for example, a vacuum atmosphere. Alternatively, the reducing atmosphere may contain a gas such as N2, CO, or H2, or may consist of at least one of these.

[0033] The heating temperature in the reduction of graphite oxide may be 600°C or higher, 700°C or higher, 800°C or higher, or 900°C, and may be 1100°C or lower, 1000°C or lower, 900°C or lower, or 800°C or lower. [Example]

[0034] 5. Examples 1 to 5 5-1. Preparation of graphite-like carbon In Examples 1 to 5, graphite was oxidized by adding fuming nitric acid and potassium chlorate (KClO3). The oxidized graphite was then heated in a vacuum atmosphere as a reducing atmosphere to obtain graphite-like carbon. The heating conditions in Examples 1 to 5 were 600°C, 700°C, 800°C, 900°C, and 1000°C, respectively.

[0035] 5-2. X-ray diffraction (XRD) test X-ray diffraction analysis was performed on the samples of Example 1 (heat treatment temperature: 600°C), Example 3 (heat treatment temperature: 800°C), and Example 5 (heat treatment temperature: 1000°C), i.e., graphite-like carbon. The measurement conditions were Cu Kα and an output of 9 kW (45 kV-200 mA).

[0036] The measurement results are shown in Figure 2. Figure 2 is a graph showing the X-ray diffraction spectra of the samples of Example 1 (heat treatment temperature: 600°C), Example 3 (heat treatment temperature: 800°C), and Example 5 (heat treatment temperature: 1000°C). As shown in Figure 2, in the samples of Examples 1, 3, and 5, all of the peaks are assigned to the plane index of Graphite-2H (AB stacking structure), indicating that the structure of graphite is maintained, that is, sp 2 It was shown that the graphite structure was mainly composed of sp bonds. When X-ray diffraction analysis was also performed on Example 2 (heat treatment temperature: 700°C) and Example 4 (heat treatment temperature: 900°C) under the same conditions, similar X-ray diffraction patterns were obtained, indicating that the graphite structure was maintained, i.e., sp 2It was shown that the graphite-like carbon has a structure in which bonds are mainly formed. Furthermore, based on the obtained X-ray diffraction patterns, the C-axis length (Å) of the graphite-like carbon of each example sample was calculated.

[0037] 5-3. Scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX) analysis Next, the samples of each example were analyzed by scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX). The analysis was performed under the condition of an acceleration voltage of 20 kV. The analysis revealed that the graphite-like carbon in each example sample contained 5 mass % to 25 mass % of O (oxygen).

[0038] FIG. 3 shows the relationship between the c-axis length (Å) and the oxygen content (mass %) of the graphite-like carbon of the samples of each example. FIG. 3 is a graph showing the relationship between the oxygen amount (mass %) and the c-axis length (Å) of the samples of Examples 1 to 5. As shown in FIG. 3, a rough correlation was observed between the oxygen amount and the c-axis length of the graphite-like carbon. This result suggests that oxygen in the graphite-like carbon is bonded to C in the graphite structure. Calculations based on this result show that the sp 2 Bonds and sp 3 sp in the bond with O (oxygen) 2 The binding rate is thought to be between 75% and 95%.

[0039] 6. Example 6 and Comparative Example 1 6-1. Example 6 A fluoride ion battery was prepared using the sample of Example 4 (heat treatment temperature: 900° C.) as the positive electrode active material. Specifically, the test battery of Example 6 was prepared as follows.

[0040] The sample of Example 4 (heat treatment temperature: 900°C) and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 90 (sample of Example 4):10 (PVDF), and the mass was 43 mg / 4 cm 2 The mixture was applied to a copper current collector foil and then dried to form a positive electrode body (CF). n, acetylene black (AB), and PVDF, 92 ((CF) n The mixture was applied to an aluminum current collector foil in a mass ratio of 4(AB) / 4(PVDF) and then dried to form a negative electrode body. Silver foil was used as the reference electrode. Polypropylene (PP) nonwoven fabric was used as the separator. γ-Butyl lactone with 0.038 mol / L of CsF dissolved therein was used as the electrolyte. A test battery was prepared using the above positive electrode body, negative electrode body, reference electrode, separator, and electrolyte.

[0041] A charge-discharge test was carried out on the test battery of Example 6. Specifically, the charge-discharge test conditions were an aging treatment of performing six cycles of CC charging (0.5 V vs. Ag) followed by CC discharging (-0.5 V vs. Ag), followed by the following seventh to ninth cycles: 7th cycle: Current density 0.2mA / 4cm 2 CC charging was performed at a current density of 0.2mA / 4cm. 2 CC discharge was performed. 8th cycle: Current density 0.175mA / 4cm 2 CC charging was performed at a current density of 0.2mA / 4cm. 2 CC discharge was performed. 9th cycle: Current density 0.15mA / 4cm 2 CC charging was performed at a current density of 0.2mA / 4cm. 2 CC discharge was performed.

[0042] The results of the charge-discharge test in the 7th to 9th cycles are shown in FIG.

[0043] 6-2. Comparative Example 1 A test battery of Comparative Example 1 was prepared in the same manner as in Example 6, except that only Cu foil was used as the positive electrode body.

[0044] A charge / discharge test was carried out on the test battery of Comparative Example 1. Specifically, the following 1 to 3 cycles were carried out under the conditions of CC charging (0.5 V vs. Ag) followed by CC discharging (-0.5 V vs. Ag): 1st cycle: Current density 0.3mA / 4cm 2 CC charging was performed at a current density of 0.3mA / 4cm. 2 CC discharge was performed. 2nd cycle: Current density 0.25mA / 4cm 2 CC charging was performed at a current density of 0.25mA / 4cm. 2 CC discharge was performed. 3rd cycle: Current density 0.2mA / 4cm 2 CC charging was performed at a current density of 0.2mA / 4cm. 2 CC discharge was performed.

[0045] The results of the charge-discharge test in the first to third cycles are shown in FIG.

[0046] 6-3.Results Referring to FIG. 4 showing the results of the charge-discharge test on the test battery of Example 6 and FIG. 5 below showing the charge-discharge test on the test battery of Comparative Example 1, the test battery of Example 6 had a discharge capacity approximately 300 times that of the test battery of Comparative Example 1. [Explanation of symbols]

[0047] 1. Fluoride-ion battery 10 Positive electrode body 11 Positive electrode current collector layer 12 Cathode active material layer 20 negative electrode body 21 Negative electrode current collector layer 22 Negative electrode active material layer 30 Electrolyte layer

Claims

1. The graphite-like carbon is sp ２ The bond ratio is sp ３ A positive electrode active material for fluoride-ion batteries with a higher bond ratio.

2. 2. The positive electrode active material for a fluoride ion battery according to claim 1, wherein the graphite-like carbon contains oxygen, and a ratio of the oxygen to the entire graphite-like carbon is 0.03% by mass to 30% by mass.

3. The graphite-like carbon contained in the positive electrode active material for a fluoride ion battery is sp ２ Bonding and sp ３ sp to the sum of bonds and O (oxygen) bonds ２ The positive electrode active material for a fluoride ion battery according to claim 1, wherein the bonding ratio is 70% to 99.7%.

4. A positive electrode mixture for a fluoride ion battery, comprising the positive electrode active material for a fluoride ion battery according to any one of claims 1 to 3 and copper.

5. a positive electrode body, a negative electrode body, and It has an electrolyte, The electrolyte is disposed between the positive electrode body and the negative electrode body, The positive electrode body contains the positive electrode mixture for a fluoride ion battery according to claim 4, The electrolyte is an electrolytic solution in which CsF is dissolved in a lactone-based non-aqueous solvent. Fluoride-ion battery.

6. Oxidizing the graphite with an acid and an oxidizing agent to obtain graphite oxide; reducing the graphite oxide by heating it in a reducing atmosphere at a temperature of 600°C to 1100°C; A method for producing a positive electrode active material for a fluoride ion battery, comprising:

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