Positive electrode active material for fluoride-ion batteries and method for producing the same, positive electrode composite material for fluoride-ion batteries, and fluoride-ion batteries

Abstract

This disclosure provides a positive electrode active material for a fluoride-ion battery that can improve the discharge energy of the battery, a method for producing the same, a positive electrode composite material for a fluoride-ion battery containing such a positive electrode active material, and a fluoride-ion battery containing such a positive electrode composite material. [Solution] The positive electrode active material for a fluoride-ion battery according to this disclosure contains copper and sulfur and is amorphous. The method of manufacturing the positive electrode active material for a fluoride-ion battery according to this disclosure comprises the following steps: providing a fluoride-ion battery having a positive electrode active material layer containing covellite, and charging the fluoride-ion battery at a rate of 500 mAh or more and 800 mAh or less per gram of covellite.

Description

Technical Field

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

Background Art

[0002] As a positive electrode active material for a fluoride ion battery, a compound of a Group 16 element and copper is known.

[0003] For example, Patent Document 1 discloses a fluoride ion battery in which a positive electrode active material layer contains a positive electrode active material having a composition represented by Cu x S (1 ≤ x ≤ 2, particularly 1.8 ≤ x ≤ 2).

[0004] Patent Document 2 discloses a positive electrode active material for a fluoride ion battery, which is copper selenide.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] In a fluoride ion battery containing a positive electrode active material containing copper and sulfur, there is room for improvement from the viewpoint of discharge energy.

[0007] An object of the present disclosure is to provide a positive electrode active material for a fluoride ion battery capable of improving the discharge energy of the battery, a method for manufacturing the same, a positive electrode composite material for a fluoride ion battery containing such a positive electrode active material, and a fluoride ion battery containing such a positive electrode composite material for a fluoride ion battery.

Means for Solving the Problem

[0008] The present inventors have found that the above problems can be solved by the following means. <Aspect 1> A positive electrode active material for a fluoride ion battery, which contains copper and sulfur and is amorphous. <Aspect 2> The positive electrode active material for a fluoride ion battery according to Aspect 1, which is produced by charging a fluoride ion battery having a positive electrode active material layer containing covellite at 500 mAh or more and 800 mAh or less per gram of the covellite. <Aspect 3> The positive electrode active material for a fluoride ion battery according to Aspect 1 or 2, wherein the molar ratio of the copper to the sulfur is 0.70 or more and 1.70 or less. <Aspect 4> The positive electrode active material for a fluoride ion battery according to Aspect 3, wherein the molar ratio is 0.85 or more and 1.25 or less. <Aspect 5> The positive electrode active material layer further contains a solid electrolyte, and the solid electrolyte is Pb 1-x Zr x F 2+2x (0 < x < 1), and is the positive electrode active material for a fluoride ion battery according to any one of Aspects 2 to 4. <Aspect 6> The positive electrode active material for a fluoride ion battery according to Aspect 5, wherein x is 0.01 or more and 0.3 or less. <Aspect 7> A positive electrode composite material for a fluoride ion battery, which contains the positive electrode active material for a fluoride ion battery according to any one of Aspects 1 to 6. <Aspect 8> A fluoride ion battery having a positive electrode active material layer, and the positive electrode active material layer contains the positive electrode composite material for a fluoride ion battery according to Aspect 7. <Aspect 9> ​​A method for producing a positive electrode active material for a fluoride ion battery according to any one of embodiments 1 to 6, including the following steps: To provide a fluoride ion battery having a positive electrode active material layer containing covellite, and The fluoride-ion battery is charged with a capacity of 500mAh or more and 800mAh or less per gram of the aforementioned cobelite. <Aspect 10> A method for producing a positive electrode active material for a fluoride-ion battery according to embodiment 9, wherein the fluoride-ion battery is charged at a temperature of 130°C or lower. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide a positive electrode active material for a fluoride-ion battery that can improve the discharge energy of the battery, a method for producing the same, a positive electrode composite material for a fluoride-ion battery containing such a positive electrode active material, and a fluoride-ion battery containing such a positive 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] Figure 2 shows the charging curves of the batteries in the example and comparative example. [Figure 3] Figure 3 shows the discharge curves of the batteries in the example and comparative example. [Figure 4] Figure 4 shows the XRD pattern of the positive electrode active material layer of Example 1 after charging under predetermined conditions. [Figure 5] Figure 5 shows the XRD patterns of the positive electrode active material layer of Example 1, as well as the XRD patterns of CuS, Pb0.9Zr0.1F2.2 (solid electrolyte of the positive electrode active material layer), and La0.95Sr0.05F2.95 (solid electrolyte of the solid electrolyte layer), in the initial state (before charging), after charging under predetermined conditions, and after discharging. [Figure 6] Figure 6 shows the XRD pattern of the positive electrode active material layer of Comparative Example 1 after charging under predetermined conditions. [Figure 7]Figure 7 shows the XRD pattern of the positive electrode active material layer of Comparative Example 2 after charging under predetermined conditions. [Figure 8] Figure 8 shows the XRD pattern of the positive electrode active material layer of Comparative Example 3 after charging under predetermined conditions. [Figure 9] Figure 9 shows the XRD pattern of the positive electrode active material layer of Comparative Example 4 after charging under predetermined conditions. [Figure 10] Figure 10 shows the XRD patterns of the positive electrode active material layer of Comparative Example 4, both initially (before charging) and after charging under predetermined conditions, as well as the XRD patterns of CuS, Pb0.9Zr0.1F2.2 (solid electrolyte of the positive electrode active material layer) and La0.95Sr0.05F2.95 (solid electrolyte of the solid electrolyte layer). [Modes for carrying out the invention]

[0011] The embodiments of this disclosure will be described in detail below. However, this disclosure is not limited to the embodiments described below, and can be implemented in various modified forms within the scope of the essence of the disclosure.

[0012] 《Active material for positive electrode in fluoride-ion batteries》 The positive electrode active material for fluoride-ion batteries of this disclosure contains copper and sulfur and is amorphous.

[0013] The disclosing parties have unexpectedly discovered a novel cathode active material for fluoride-ion batteries that contains copper and sulfur and is amorphous.

[0014] Furthermore, the Disclosers have found that discharge energy is improved in fluoride-ion batteries containing such positive electrode active materials. The reason for this is presumed to be as follows, although this is not intended to be constrained by any theory: It is thought that the generation of active materials (such as copper fluoride (CuF2)) that have high resistance at low temperatures such as room temperature can be suppressed during charging. In addition, the positive electrode active material of this disclosure is thought to have lower resistance and a higher reaction potential compared to CuF2. As a result, it is thought that the electrode reaction proceeds smoothly even at low temperatures such as room temperature, and therefore a large amount of discharge energy can be extracted.

[0015] The amorphous nature of the positive electrode active material for fluoride-ion batteries disclosed herein can be confirmed by X-ray diffraction (XRD) measurement, where no diffraction peaks originating from copper sulfides such as copper fluoride (CuF2) or covellite (CuS) are observed. XRD measurement can be performed, for example, using a Rigaku SmartLab X-ray diffractometer, irradiated with CuKα rays under conditions of tube voltage of 45kV and tube current of 200mA, using a concentrated method. The above measurement can be performed with the sample sealed in an airtight sample stage in an argon atmosphere. A Si non-reflective plate can be used as the substrate for mounting the sample. Here, the absence of diffraction peaks originating from copper fluoride (CuF2) means that, when using CuKα rays, for example, the peak around 31.5° due to the (100) plane, the peak around 33.5° due to the (-111) plane, the peak around 35.3° due to the (-102) plane, and the peak around 37.4° due to the (110) plane of CuF2 are all not observed. Similarly, the absence of diffraction peaks originating from covellite (CuS) means that, for example, the peak around 29.2° due to the (102) plane, the peak around 31.7° due to the (103) plane, the peak around 32.8° due to the (006) plane, and the peak around 47.9° due to the (110) plane of CuS are all not observed. In addition to CuKα rays, XRD measurements can also use, for example, MoKα rays or synchrotron X-rays of any wavelength. In this case, by using the wavelength of the irradiated X-rays to calculate the diffraction angle that satisfies Bragg's equation for each of the above surfaces and confirming that there is no peak at that angle, it is possible to confirm that no diffraction peaks originating from copper sulfides such as copper fluoride (CuF2) or covellite (CuS) are observed.

[0016] The positive electrode active material for fluoride-ion batteries of this disclosure is manufactured by charging a fluoride-ion battery having a positive electrode active material layer containing covellite (CuS) at a rate of 500 mAh or more and 800 mAh or less per gram of covellite.

[0017] The Disclosing Party found that the novel positive electrode active material for fluoride-ion batteries manufactured in this manner contains copper and sulfur and is amorphous. The presence of copper and sulfur in the positive electrode active material for fluoride-ion batteries can be determined from any of the following: • Uses covellite as a raw material. Identification will be performed using inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0018] Covellite is typically a hexagonal copper sulfide with a CuS composition and a space group P63 / mmc. Covellite is also known as copper azure or covelline.

[0019] Covellite may be a commercially available product or may be prepared by conventional methods.

[0020] In the positive electrode active material for fluoride-ion batteries of this disclosure, the molar ratio of copper to sulfur may be 0.70 or more and 1.70 or less. This molar ratio may be 0.75 or more, 0.80 or more, 0.85 or more, 0.90 or more, 0.95 or more, or 1.00 or more, and may be 1.65 or less, 1.60 or less, 1.50 or less, 1.40 or less, 1.30 or less, 1.25 or less, 1.20 or less, 1.15 or less, 1.10 or less, 1.05 or less, or 1.00 or less, and may also be 1.00. Although the typical composition of covellite is x=1, due to the difficulty of quantitative analysis of sulfur, the composition may be detected as having a sulfur deficit (larger x) or excess (smaller x) than it actually does. In particular, in analytical methods involving acid dissolution steps such as ICP-AES, the analysis results may show a sulfur-deficient composition (larger x) than the actual sulfur content due to volatilization loss of sulfur components. This is also considered to be the case when measuring the composition of the positive electrode active material for fluoride-ion batteries of this disclosure, which can be manufactured using covellite as a raw material. Therefore, x is defined as the above range. Furthermore, when analyzing chalcosite (Cu2S), for example, using the same analytical method, the molar ratio of copper to sulfur is expected to be greater than 2. Therefore, it is considered possible to distinguish between the positive electrode active material of this disclosure, which can be manufactured using covellite as a raw material, and positive electrode active materials made from copper sulfide other than covellite (e.g., chalcosite) as a raw material.

[0021] The composition of the positive electrode active material for fluoride-ion batteries disclosed herein can be identified, for example, by ICP-AES. The test solution used in ICP-AES can be prepared by weighing 10-20 mg of positive electrode powder into a microwave decomposition vessel, adding nitric acid for microwave decomposition, and then diluting it with ultrapure water to the final volume. The ICP-AES apparatus can be an Avio 550 Max from PerkinElmer Japan LLC.

[0022] The positive electrode active material for fluoride-ion batteries of this disclosure may further contain fluorine. This fluorine may be introduced, for example, by charging the battery.

[0023] In the positive electrode active material for a fluoride ion battery of the present disclosure produced by charging a battery under predetermined conditions, the positive electrode active material layer may further contain a solid electrolyte. The solid electrolyte is Pb 1-x Zr x F 2+2x (0 < x < 1). x may be 0.01 or more and 0.3 or less. x may be 0.03 or more, 0.05 or more, 0.07 or more, 0.09 or more, or 0.1 or more, and may also be 0.25 or less, 0.2 or less, 0.15 or less, 0.12 or less, or 0.1 or less. x may be 0.1, that is, Pb 0.9 Zr 0.1 F 2.2 . When the battery is charged with the positive electrode active material layer further containing the solid electrolyte, covellite may be transformed into other copper sulfides. On the other hand, even if the above solid electrolyte is further contained, in the charging process of the battery, the transformation of covellite is difficult to occur, and thus, a decrease in the charging capacity is difficult to occur.

[0024] The solid electrolyte may be a commercially available product or may be prepared by a conventional method. As a method for preparing the solid electrolyte, a method of mechanically milling and mixing fluorides of metal elements constituting the desired solid electrolyte is exemplified.

[0025] <<Method for Manufacturing Positive Electrode Active Material for Fluoride Ion Battery>> The method of the present disclosure for manufacturing a positive electrode active material for a fluoride ion battery includes the following steps: Providing a fluoride ion battery having a positive electrode active material layer containing covellite, and Charging the fluoride ion battery at 500 mAh or more and 800 mAh or less per gram of covellite.

[0026] The present inventors have found that such a manufacturing method can produce a novel positive electrode active material for a fluoride ion battery that contains copper and sulfur and is amorphous.

[0027] <Fluoride-ion battery supply process> There are no particular limitations on the method for providing a fluoride-ion battery having a positive electrode active material layer containing covellite. For example, first, a positive electrode composite material containing covellite may be provided, and the positive electrode active material layer may be formed by compacting the positive electrode composite material. Then, the obtained positive electrode active material layer, a separately provided electrolyte layer, and a negative electrode active material layer may be stacked in this order to provide a fluoride-ion battery.

[0028] In relation to this disclosure, "positive electrode mixture" means a composition that can constitute a positive electrode active material layer, either in itself or by further containing other components.

[0029] <Charging process> The charging capacity in the process of charging the fluoride-ion battery may be 550 mAh or more, or 600 mAh or more per gram of covellite, and may also be 750 mAh or less, 700 mAh or less, or 650 mAh or less. This charging capacity being within the above range facilitates the production of a positive electrode active material for fluoride-ion batteries that contains copper and sulfur and is amorphous.

[0030] In the charging process, the fluoride-ion battery may be charged at a temperature of 130°C or lower. This temperature may be 20°C or higher, 25°C or higher, 30°C or higher, 40°C or higher, 50°C or higher, 60°C or higher, 70°C or higher, or 80°C or higher, and may also be 130°C or lower, 120°C or lower, 110°C or lower, 100°C or lower, 90°C or lower, or 80°C or lower, or even 80°C. Having this temperature within the above range facilitates the production of a positive electrode active material for fluoride-ion batteries that contains copper and sulfur and is amorphous.

[0031] The charging process may be performed from a state where the battery is completely discharged. "A state where the battery is completely discharged" may refer to a state in which a fluoride-ion battery having a positive electrode active material layer containing covellite has never been charged.

[0032] In this case, the standard weight of covellite can be determined based on the amount of raw material used.

[0033] Furthermore, the "completely discharged battery state" may be the following state when a fluoride-ion battery having a positive electrode active material layer containing covellite is provided in a charged state: The battery is disassembled to extract the positive electrode composite material containing covellite, and a fluoride-ion battery having a positive electrode active material layer containing this positive electrode composite material is provided again, and a constant current (0.05 mA / cm²) is generated at 80°C. 2 This shows the state after discharge to a termination voltage of 0.05V.

[0034] In this case, the weight of the reference covellite can be determined by measuring the weights of the contained copper and sulfur and calculating their sum. The weights of copper and sulfur are obtained by multiplying the respective concentrations of these elements by the amount of positive electrode composite material used in the battery, which will be provided separately. The concentrations of copper and sulfur can be measured by elemental analysis, for example, ICP-AES.

[0035] Note that the battery may be discharged within the specified limits before disassembly. Also, the amount of positive electrode composite material used in the fluoride-ion battery provided may be reduced as appropriate.

[0036] <<Positive electrode composite material>> The positive electrode composite material for fluoride-ion batteries of this disclosure comprises the positive electrode active material for fluoride-ion batteries of this disclosure and may optionally include a solid electrolyte, a liquid electrolyte, a conductive additive, and a binder.

[0037] <Positive electrode active material for fluoride-ion batteries> For positive electrode active materials for fluoride-ion batteries, refer to the above description of positive electrode active materials for fluoride-ion batteries in this disclosure.

[0038] The content of the positive electrode active material in the positive electrode composite material may be, for example, 1% by mass or more, 5% by mass or more, 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, or 30% by mass or more, and may also be 100% by mass or less, 80% by mass or less, 60% by mass or less, 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, or 30% by mass or less. This content may also be 10% by mass or more and 50% by mass or less, 15% by mass or more and 45% by mass or less, or 20% by mass or more and 40% by mass or less.

[0039] The positive electrode active material contained in the positive electrode composite material may be only the positive electrode active material for fluoride-ion batteries of this disclosure, or it may be a combination of the positive electrode active material for fluoride-ion batteries of this disclosure and other positive electrode active materials. Examples of positive electrode active materials other than the positive electrode active material for fluoride-ion batteries of this disclosure include copper sulfide (Cu) disclosed in Patent Document 1. x S(1≦x≦2, especially 1.8≦x≦2), and known positive electrode active materials for fluoride-ion batteries such as copper selenide and elemental copper can be used.

[0040] The proportion of the fluoride-ion battery positive electrode active material of this disclosure to the total (100% by mass) of positive electrode active materials contained in the positive electrode mixture may be, for example, 50% by mass or more and 100% by mass or less, 60% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, 90% by mass or more and 100% by mass or less, 95% by mass or more and 100% by mass or less, 99% by mass or more and 100% by mass or less, or 100% by mass. In other words, all of the positive electrode active material contained in the positive electrode mixture may be the fluoride-ion battery positive electrode active material of this disclosure.

[0041] The shape of the positive electrode active material is not particularly limited, as long as it is a shape that can function as the positive electrode active material of a fluoride ion battery. The positive electrode active material may be, for example, particulate. The average particle size of the positive electrode active material particles may be, for example, 1 nm to 500 μm, 10 nm to 100 μm, or 20 nm to 50 μm.

[0042] <Solid electrolyte> The positive electrode composite material for a fluoride ion battery of the present disclosure may contain a solid electrolyte. Regarding the solid electrolyte, reference can be made to the above description regarding the positive electrode active material for a fluoride ion battery of the present disclosure. The solid electrolyte assists fluoride ion conduction.

[0043] The content of the solid electrolyte in the positive electrode composite material may be, for example, 1% by mass or more, 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, or 60% by mass or more, and may also be 99% by mass or less, 95% by mass or less, 90% by mass or less, 80% by mass or less, or 70% by mass or less. This content may also be 40% by mass or more and 90% by mass or less, 50% by mass or more and 80% by mass or less, or 60% by mass or more and 70% by mass or less.

[0044] The solid electrolyte contained in the positive electrode composite material is the above-mentioned Pb [[ID=> 1-x Zr x F 2+2x (0 < x < 1) may be the only solid electrolyte, or may be a combination of the solid electrolyte represented by Pb 1-x Zr x F 2+2x (0 < x < 1) and other solid electrolytes. Examples of solid electrolytes other than the solid electrolyte represented by Pb 1-x Zr x F 2+2x (0 < x < 1) may include fluorides of lanthanoid elements such as La and Ce; fluorides of alkali elements such as Li, Na, K, Rb, and Cs; fluorides of alkaline earth elements such as Ca, Sr, and Ba, etc.

[0045] The total of the solid electrolytes contained in the positive electrode composite material (100% by mass) accounts for Pb 1-x Zr x F 2+2xThe proportion of the solid electrolyte represented by (0 < x < 1) may be, for example, 30% by mass or more and 100% by mass or less, 40% by mass or more and 100% by mass or less, 50% by mass or more and 100% by mass or less, 60% by mass or more and 100% by mass or less, 70% by mass or more and 100% by mass or less, 80% by mass or more and 100% by mass or less, 90% by mass or more and 100% by mass or less, 95% by mass or more and 100% by mass or less, 99% by mass or more and 100% by mass or less, or 100% by mass. That is, all of the solid electrolyte contained in the positive electrode composite material is Pb 1-x Zr x F 2+2x It may be a solid electrolyte represented by (0 < x < 1).

[0046] The shape of the solid electrolyte is not particularly limited. The solid electrolyte may be, for example, in the form of particles. The size of the solid electrolyte is not particularly limited as long as it can function as the solid electrolyte of the fluoride ion battery.

[0047] (Mass ratio of the content of the positive electrode active material to the content of the solid electrolyte) The mass ratio of the content of the positive electrode active material in the positive electrode composite material to the content of the solid electrolyte is not particularly limited. This mass ratio may be, for example, 0.1 or more and 10 or less, 0.2 or more and 5 or less, or 0.3 or more and 1 or less.

[0048] <Liquid electrolyte> The liquid electrolyte contains, for example, a solvent and a salt dissolved in the solvent.

[0049] The solvent may be, for example, an organic solvent. The organic solvent may be any one that can dissolve the salt. The organic solvent is, for example, R such as triethylene glycol dimethyl ether (G3), tetraethylene glycol dimethyl ether (G4), etc. 1 -O(CH2CH2O) n -R 2 (R 1 and R 2Each of these can be independently a glyme (represented by an alkyl group having 4 or fewer carbon atoms, or a fluoroalkyl group having 4 or fewer carbon atoms, where n is in the range of 2 to 10); cyclic carbonates such as ethylene carbonate (EC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), propylene carbonate (PC), and butylene carbonate (BC); or linear carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The organic solvent may be an ionic liquid.

[0050] The salt dissolved in the above solvent may be, for example, a fluoride salt. The fluoride salt may be at least one selected from, for example, inorganic fluoride salts, organic fluoride salts, and ionic liquids. The inorganic fluoride salt may be, for example, XF (where X is at least one selected from Li, Na, K, Rb, and Cs). The organic fluoride salt may have an ammonium cation, such as a tetramethylammonium cation, and a fluorine-containing anion.

[0051] The liquid electrolyte may, for example, include the solvent and the salt dissolved in 1 L of the solvent at a concentration of 0.1 mol to 40 mol, or 1 mol to 10 mol.

[0052] The proportion of liquid electrolyte in the total electrolytes (100% by mass) contained in the positive electrode mixture may be, for example, 0% to 50% by mass, 0% to 30% by mass, 0% to 10% by mass, 0% to 5% by mass, 0% to 3% by mass, 0% to 1% by mass, or 0% by mass. In other words, liquid electrolyte does not need to be included in the positive electrode mixture.

[0053] <Conductive additive> The conductive additive is not particularly limited as long as it has electronic conductivity.

[0054] The conductive additive may be, for example, made of a carbon material. The carbon material used as the conductive additive may be at least one selected from, for example, carbon black such as acetylene black, furnace black, or thermal black, graphene, fullerene, or carbon nanotubes.

[0055] The content of the conductive additive in the positive electrode composite material is not particularly limited and may be, for example, 1% by mass or more, 5% by mass or more, or 10% by mass or more, or 30% by mass or less, 20% by mass or less, or 10% by mass or less.

[0056] The shape of the conductive additive is not particularly limited. The conductive additive may be, for example, particulate or fibrous.

[0057] <Binder> The binder in a fluoride-ion battery only needs to be chemically and electrically stable.

[0058] The binder may be at least one selected from, for example, polyvinylidene fluoride (PVDF) binders, fluorine-based binders such as polytetrafluoroethylene (PTFE) binders, and rubber-based binders such as styrene-butadiene rubber (SBR).

[0059] The binder content in the cathode composite material is not particularly limited.

[0060] <Other ingredients> The positive electrode composite material may or may not contain various additives other than the components listed above. The types and amounts of other substances used as components can be set as appropriate.

[0061] <<Manufacturing method for cathode composite material for fluoride-ion batteries>> The positive electrode composite material for a fluoride ion battery can be manufactured by a method similar to the method of the present disclosure for manufacturing the positive electrode active material for a fluoride ion battery. That is, for example, a fluoride ion battery having a positive electrode active material layer containing cobaltite, and optionally a solid electrolyte, a conductive aid, etc. is provided, and the positive electrode composite material for a fluoride ion battery can be manufactured by charging the fluoride ion battery at 500 mAh or more and 800 mAh or less per gram of cobaltite.

[0062] In addition, when manufacturing the positive electrode composite material for a fluoride ion battery of the present disclosure, a preliminary positive electrode composite material may be manufactured. In the present disclosure, the "preliminary positive electrode composite material" means the positive electrode composite material in a state before charging a fluoride ion battery at 500 mAh or more and 800 mAh or less per gram of cobaltite.

[0063] The method for manufacturing the preliminary positive electrode composite material may include the following steps: Providing a raw material containing cobaltite, and optionally a solid electrolyte, a conductive aid, etc., and Mixing the raw materials while applying mechanical shock to the raw materials.

[0064] In order to manufacture the preliminary positive electrode composite material, it is preferable to mix the raw materials while applying mechanical shock to the raw materials. However, when the solid electrolyte optionally used is a solid electrolyte represented by Pb 1-x Zr x F 2+2x (0 < x < 1), the preliminary positive electrode composite material can be obtained without altering the cobaltite.

[0065] As a method of mixing the raw materials while applying mechanical shock to the raw materials, mixing by a mechanical milling method is exemplified. Specifically, a method of mixing the raw materials using a ball mill device is mentioned. As the operation method of the ball mill device, any method such as planetary, vibration, rotation, etc. may be used. By using a planetary ball mill device, the sample can be efficiently mixed. This step may be performed in an inert gas atmosphere.

[0066] When mixing raw materials using a planetary ball mill apparatus, the rotation speed of the base plate is not particularly limited, but may be, for example, 300 rpm or more, 400 rpm or more, 500 rpm or more, or 600 rpm or more, and may also be 1000 rpm or less, 900 rpm or less, 800 rpm or less, 700 rpm or less, or 600 rpm or less. The rotation speed of the base plate may be 600 rpm.

[0067] When mixing raw materials using a planetary ball mill apparatus, the mixing time is not particularly limited, but may be 0.5 hours or more, 1 hour or more, 2 hours or more, or 3 hours or more, and may also be 10 hours or less, 8 hours or less, 6 hours or less, 4 hours or less, or 3 hours or less. The mixing time may be 3 hours.

[0068] <<Fluoride-ion battery>> As illustrated in Figure 1, the fluoride-ion battery 1 of the present disclosure has a positive electrode active material layer 20, and the positive electrode active material layer contains the positive electrode composite material for fluoride-ion batteries of the present disclosure.

[0069] As illustrated in Figure 1, the fluoride ion battery 1 of this disclosure may have a positive electrode current collector layer 10, a positive electrode active material layer 20, an electrolyte layer 30, a negative electrode active material layer 40, and a negative electrode current collector layer 50 in this order.

[0070] The fluoride-ion battery of this disclosure may be a liquid-type battery containing an electrolyte as an electrolyte layer, or it may be a solid-state battery having a solid electrolyte layer as an electrolyte layer. In this disclosure, "solid-state battery" means a battery using at least a solid electrolyte as an electrolyte, and therefore a solid-state battery may use a combination of a solid electrolyte and a liquid electrolyte as its electrolyte. Furthermore, the solid-state battery of this disclosure may be an all-solid-state battery, i.e., a battery using only a solid electrolyte as its electrolyte.

[0071] A fluoride-ion battery may be a primary battery or a secondary battery.

[0072] The shape of the fluoride-ion battery may be, for example, coin-type, laminate-type (pouch-type), cylindrical, or prismatic.

[0073] The fluoride-ion battery of this disclosure can be suitably used in, for example, at least one type of vehicle selected from hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs).

[0074] The following describes the elements that may constitute the fluoride-ion battery of this disclosure.

[0075] <Positive electrode current collector layer> Examples of materials for the positive electrode current collector layer include lead, stainless steel (SUS), aluminum, nickel, iron, titanium, platinum, and carbon.

[0076] Examples of positive electrode current collector layer shapes include foil-like, mesh-like, and porous shapes.

[0077] <Cathode active material layer> The positive electrode active material layer contains the positive electrode composite material for fluoride-ion batteries of this disclosure. For details regarding the positive electrode composite material for fluoride-ion batteries of this disclosure, please refer to the above description relating to the positive electrode composite material for fluoride-ion batteries of this disclosure.

[0078] The positive electrode active material layer may be, for example, a compacted powder of the positive electrode composite material for fluoride-ion batteries of the present disclosure itself.

[0079] The shape of the positive electrode active material layer is not particularly limited and may be, for example, a sheet with a substantially flat surface.

[0080] The thickness of the positive electrode active material layer is not particularly limited and can be any appropriate thickness depending on the configuration of the fluoride ion battery. For example, the thickness of the positive electrode active material layer may be between 100 nm and 1 mm.

[0081] <Electrolyte layer> The electrolyte layer contains at least an electrolyte. The electrolyte may be a solid electrolyte or a liquid electrolyte.

[0082] If the fluoride-ion battery of this disclosure is a solid-state battery, the electrolyte layer includes a solid electrolyte and may optionally include a binder.

[0083] The solid electrolyte may be appropriately selected from among the examples given above of what can be included in the positive electrode composite material. The solid electrolyte that can be included in the positive electrode composite material and the solid electrolyte that can be included in the electrolyte layer may be of the same type or of different types.

[0084] For information regarding the binder, please refer to the above description concerning the cathode composite material for fluoride-ion batteries in this disclosure.

[0085] The electrolyte layer may include a liquid electrolyte and a separator for holding the liquid electrolyte. In particular, these may be included when the fluoride ion battery of this disclosure is a liquid battery.

[0086] For liquid electrolytes, refer to the above description of the positive electrode composite material for fluoride-ion batteries in this disclosure.

[0087] As for the separator, a known separator for fluoride-ion batteries can be used.

[0088] The electrolyte layer may, for example, partially become a negative electrode active material layer upon charging. Specifically, the electrolyte layer may, during charging of a fluoride-ion battery, cause a defluorination reaction of the metal fluoride as a solid electrolyte at the interface between the electrolyte layer and the negative electrode current collector layer, thereby generating a metal layer (e.g., a Pb layer) as a negative electrode active material layer at that interface.

[0089] The shape of the electrolyte layer is not particularly limited and may, for example, be in the form of a sheet with a substantially flat surface.

[0090] The thickness of the electrolyte layer is not particularly limited and can be any appropriate thickness depending on the configuration of the fluoride ion battery. For example, the thickness of the electrolyte layer may be between 100 nm and 1 mm.

[0091] <Negative electrode active material layer> The negative electrode active material layer contains a negative electrode active material and may optionally contain an electrolyte, a conductive additive, and a binder.

[0092] The negative electrode active material may be at least one selected from, for example, elemental metals, alloys, metal oxides, metal fluorides, carbon materials, and polymer materials. The metal element constituting the negative electrode active material may be at least one selected from, for example, La, Ca, Al, Eu, Li, Si, Ge, Sn, In, V, Cd, Cr, Fe, Zn, Ga, Ti, Nb, Mn, Yb, Zr, Sm, Ce, Mg, and Pb. The carbon material constituting the negative electrode active material may be at least one selected from, for example, graphite, coke, and carbon nanotubes. The polymer material constituting the negative electrode active material may be at least one selected from polyaniline, polypyrrole, polyacetylene, and polythiophene.

[0093] The negative electrode active material is, for example, Pb 0.9 Zr 0.1 F 2.2 That's fine.

[0094] For the electrolyte, conductive additive, and binder, refer to the above description of the positive electrode mixture for fluoride-ion batteries in this disclosure.

[0095] The shape of the negative electrode active material layer is not particularly limited and may be, for example, a sheet with a substantially flat surface.

[0096] The thickness of the negative electrode active material layer is not particularly limited and can be any appropriate thickness depending on the configuration of the fluoride ion battery. For example, the thickness of the negative electrode active material layer may be between 100 nm and 1 mm.

[0097] <Negative electrode current collector layer> Examples of materials for the negative electrode current collector layer include stainless steel (SUS), copper, nickel, iron, titanium, platinum, and carbon.

[0098] Examples of negative electrode current collector layer shapes include foil-like, mesh-like, and porous shapes.

[0099] <<Manufacturing method for fluoride-ion batteries>> A method for manufacturing a fluoride-ion battery includes manufacturing a positive electrode active material for a fluoride-ion battery by the method of this disclosure. For a method of manufacturing a positive electrode active material for a fluoride-ion battery, refer to the above description of the method of manufacturing a positive electrode active material for a fluoride-ion battery as described in this disclosure.

[0100] A method for manufacturing a fluoride-ion battery may more specifically include, for example, providing a positive electrode active material layer containing covellite, and charging it at a rate of 500 mAh or more and 800 mAh or less per gram of covellite. [Examples]

[0101] <<Example 1>> <Preparation of spare positive electrode composite material> Copper sulfide (composition formula: CuS), which is covellite (manufacturing by Mitsuwa Chemical Co., Ltd.), as the positive electrode active material, and Pb as the solid electrolyte. 0.9 Zr 0.1 F 2.2 The cathode active material and acetylene black (AB) as a conductive additive were mechanically milled and mixed using a planetary ball mill (Fritsch Premium Line PL-7 planetary ball mill) to obtain a powdered cathode composite material. The mass ratio of the cathode active material, solid electrolyte, and conductive additive was 30:66:4. The ball mill mixing was performed in a dry argon atmosphere for 3 hours at a disc rotation speed of 600 rpm.

[0102] <Fabrication of all-solid-state fluoride-ion batteries> A compacted powder was formed using 12 mg of the obtained positive electrode mixture powder as the positive electrode active material layer.

[0103] As an electrolyte layer, La as a solid electrolyte 0.95 Sr 0.05 F 2.95 A compacted powder was formed using 150 mg of the powder.

[0104] Pb as the negative electrode active material layer 0.9 Zr 0.1 F 2.2 A compacted powder was formed using a mixture of 50 mg of powder and AB powder as a conductive additive. The AB content in the mixture was 5% by mass relative to the total mixture. 220 mg of Pb plate was pressed onto one surface of the formed negative electrode active material layer (the side where the negative electrode current collector layer would later be placed). This Pb plate was placed to standardize the cell voltage.

[0105] An all-solid-state fluoride ion battery was fabricated by laminating platinum foil as the positive electrode current collector layer, a positive electrode active material layer, an electrolyte layer, a negative electrode active material layer, and aluminum foil as the negative electrode current collector layer in this order. 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 fixed in place by being sandwiched between stainless steel cylinders with a diameter of 11.28 mm on both sides of the negative electrode current collector layer and the positive electrode current collector layer.

[0106] The obtained all-solid-state fluoride-ion battery was tested in a sealed container under vacuum at a test temperature of 80°C and a current density of 0.05 mA / cm². 2 Charging was performed under the condition of a cutoff upper voltage of 1.6V. This resulted in the fabrication of an all-solid-state fluoride-ion battery charged under predetermined conditions. In the obtained battery, it was confirmed by evaluation described later that the positive electrode active material contained copper and sulfur and was amorphous.

[0107] <<Comparative Example 1>> An all-solid-state fluoride-ion battery was fabricated under predetermined conditions, in the same manner as in Example 1, except that the test temperature during charging was changed from 80°C to 140°C and the charging capacity was increased.

[0108] <<Comparative Example 2>> An all-solid-state fluoride-ion battery was prepared in the same manner as in Example 1, except that chalcosite (Cu2S) was used instead of covellite (CuS) as the raw material for preparing the spare cathode composite, and was charged under predetermined conditions.

[0109] <<Comparative Example 3>> An all-solid-state fluoride-ion battery was fabricated in the same manner as in Example 1, except that copper (Cu) was used instead of covellite (CuS) as the raw material for preparing the spare cathode composite, and was charged under predetermined conditions.

[0110] <<Comparative Example 4>> An all-solid-state fluoride-ion battery was fabricated under the same conditions as in Example 1, except that a capacity limit (240mAh / 1g of Covellite) was imposed as the starting and ending conditions for the charging test.

[0111] <<Rating>> <Evaluation of fluoride-ion batteries> For each example of fluoride-ion batteries charged under specified conditions, a discharge test was performed after changing the test temperature to room temperature (24±3℃). Furthermore, after the temperature change, the batteries were held for at least 12 hours before discharge to allow the components heated during charging to cool sufficiently. The current density during discharge was 0.05 mA / cm². 2 The cutoff lower voltage was set to 0.05V. A frequency response analyzer-equipped electrochemical measurement system (VMP-300 high-performance electrochemical measurement system, Biologic Corporation) was used for the charge-discharge test. Discharge testing was not performed on the battery of Comparative Example 4. The charge curve is shown in Figure 2, and the discharge curve is shown in Figure 3. The results of the charge-discharge test are shown in Table 1. In Table 1, "voltage at DOD50" refers to the voltage at a depth of discharge of 50%, i.e., the voltage when the discharge capacity is half of the total capacity. "Discharge energy" was calculated as the energy density per unit mass of the positive electrode active material by performing a definite integral calculation of the area enclosed by the discharge curve and the x-axis using analysis software (EC-Lab, Biologic Corporation).

[0112] <Composition analysis> The composition ratio of Cu to sulfur (S) in the preliminary cathode composite material of each example was analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). The test solution used for ICP-AES was prepared by weighing 10 to 20 mg of the powder of the cathode composite material into a microwave decomposition vessel, adding nitric acid, decomposing it by microwave, and then making up the volume with ultrapure water. The ICP-AES apparatus used was Avio 550 Max of PerkinElmer Japan Co., Ltd. The results are shown in Table 1 as the value of x in Cu x S (mol).

[0113] <XRD analysis> In order to examine the presence or absence of the crystal phase derived from the cathode active material contained in the cathode active material layer in the charged state, X-ray diffraction (XRD) measurement was carried out. The charge tests of each example were reproduced to fabricate batteries in the charged state, and measurements were performed on their cathode active material layers. The batteries after charging were disassembled in a glove box under a dry argon atmosphere, and powder samples were obtained by scratching the cathode active material layer. The measurement was carried out by the focusing method of irradiating with CuKα rays under the conditions of a tube voltage of 45 kV and a tube current of 200 mA using a SmartLab apparatus manufactured by Rigaku Corporation. The sample was sealed in an airtight sample stage under an argon atmosphere and measured without exposure to the atmosphere. A Si non-reflecting plate was used as the substrate for mounting the sample. The XRD patterns of the samples of each example obtained are shown in Figs. 4 to 10. Also, the crystal phases detected by XRD analysis are shown in Table 1.

[0114] In Figs. 4 and Figs. 6 to 9, in order to distinguish the diffraction lines due to the solid electrolyte Pb 0.9 Zr 0.1 F 2.2 and La mixed from the solid electrolyte layer 0.95 Sr 0.05 F 2.95 and clarify the diffraction lines due to the crystal phase derived from the cathode active material, the patterns enlarged in the vertical axis direction are shown together.

[0115] Furthermore, Figure 5 shows the XRD patterns of the positive electrode active material layer of Example 1 in the initial state (before charging), after charging under predetermined conditions, and after discharge, while Figure 10 shows the XRD patterns of the positive electrode active material layer of Comparative Example 4 in the initial state (before charging) and after charging under predetermined conditions. For comparison, CuS and Pb are included in these XRD patterns. 0.9 Zr 0.1 F 2.2 (Solid electrolyte of the positive electrode active material layer), and La 0.95 Sr 0.05 F 2.95 The XRD pattern of the solid electrolyte (in the solid electrolyte layer) is also shown.

[0116] [Table 1]

[0117] As shown in Figures 4 and 5, no crystalline phase originating from the positive electrode active material was observed in the sample obtained from the positive electrode active material layer of Example 1 after charging under predetermined conditions. More specifically, as shown in Figure 5, in the sample obtained from the initial (pre-charging) positive electrode active material layer of Example 1, i.e., the sample corresponding to the preliminary positive electrode composite, a peak of CuS used as a raw material was confirmed around 48°, as indicated by the arrow. In contrast, in the sample obtained from the positive electrode active material layer of Example 1 after charging, i.e., the sample corresponding to the positive electrode composite of this disclosure, no peak around 48°, nor any other diffraction peaks originating from CuS, were observed. This is thought to be because the fluorinated CuS became amorphous due to charging. In other words, it is thought that an amorphous positive electrode active material containing copper and sulfur was formed in Example 1. It is also thought that the positive electrode active material contains fluorine inserted by charging.

[0118] As shown in Figure 5, in Example 1, no peaks around 48° based on CuS, nor any other diffraction peaks originating from CuS, were observed after discharge. This indicates that the positive electrode active material remained amorphous even after discharge, without returning to its original covellite crystal state.

[0119] As shown in Table 1, the battery of Example 1, which contains copper and sulfur and includes an amorphous positive electrode active material, exhibited high discharge energy at room temperature. While not intended to be bound by any theory, the reason for this is presumed to be as follows: During charging, the formation of active materials with high resistance at low temperatures such as room temperature (such as copper fluoride (CuF2)) can be suppressed. Furthermore, the positive electrode active material of the present disclosure in Example 1 is thought to have lower resistance and a higher reaction potential compared to CuF2. As a result, the electrode reaction proceeds smoothly even at low temperatures such as room temperature, and therefore a large discharge energy can be extracted.

[0120] On the other hand, as shown in Figures 6-8, in Comparative Examples 1-3, copper fluoride (CuF2) and copper sulfide (CuS) were observed as crystalline phases derived from the positive electrode active material after charging. In Comparative Example 1, it is thought that a side reaction occurred during charging at high temperature (140°C), resulting in a sulfur deficiency and the formation of CuF2 as a fluoride. Furthermore, in Comparative Example 2, since CuS was observed in the XRD pattern shown in Figure 7, it is thought that the reaction shown in the following equation mainly proceeded during charging, and that a reaction in which amorphous positive electrode active material was formed from CuS also proceeded partially: Cu2S+2F - →CuS+CuF2

[0121] Furthermore, the observation of CuS in the XRD pattern of Comparative Example 2 shown in Figure 7 suggests that the reaction shown in the above equation proceeded and CuF2 was also produced. Nevertheless, the absence of a CuF2 peak is thought to be because the CuS peak is relatively stronger than the CuF2 peak, and the CuS peak is located close to the CuF2 peak, or because the produced CuF2 is in a nanocrystalline state with very weak diffraction intensity.

[0122] In the XRD pattern of Comparative Example 3 shown in Figure 8, CuF2, a charge product of Cu, was clearly observed.

[0123] In other words, in Comparative Examples 1 to 3, because all contained CuF2, which has high resistance, the electrode reaction was inhibited during discharge at low temperatures, resulting in a small amount of energy being extracted. Furthermore, in Comparative Example 1, the charge-discharge efficiency was significantly low due to the aforementioned side reactions occurring during charging.

[0124] In Comparative Example 4, the charging capacity was smaller than that of Example 1. In the XRD patterns of Comparative Example 4 shown in Figures 9 and 10, as indicated by the arrows, a peak around 48° based on CuS was observed in the charged state, similar to the initial (pre-charging) state. This suggests that in Comparative Example 4, although fluoride ions were inserted into the crystal structure of covelite during charging, the formation of amorphous positive electrode active material did not occur, and the crystal structure was maintained. In other words, Comparative Example 4 suggests that charging above a certain capacity is necessary to obtain amorphous positive electrode active material. [Explanation of Symbols]

[0125] 1. Fluoride-ion battery 10 Positive electrode current collector layer 20 Cathode active material layer 30 Electrolyte layer 40 Negative electrode active material layer 50 Negative electrode current collector layer

Claims

1. It contains copper and sulfur, and It is amorphous. Positive electrode active material for fluoride-ion batteries.

2. The positive electrode active material for a fluoride-ion battery according to claim 1, which is manufactured by charging a fluoride-ion battery having a positive electrode active material layer containing covellite at a rate of 500 mAh or more and 800 mAh or less per gram of covellite.

3. The positive electrode active material for a fluoride ion battery according to claim 1, wherein the molar ratio of copper to sulfur is 0.70 or more and 1.70 or less.

4. The positive electrode active material for a fluoride ion battery according to claim 3, wherein the molar ratio is 0.85 or more and 1.25 or less.

5. The positive electrode active material layer further contains a solid electrolyte, and The solid electrolyte is Pb １－ｘ Zr ｘ F ２＋２ｘ A positive electrode active material for a fluoride-ion battery according to claim 2, having a composition of (0 < x < 1).

6. The positive electrode active material for a fluoride ion battery according to claim 5, wherein x is 0.01 or more and 0.3 or less.

7. A positive electrode composite material for a fluoride-ion battery, comprising the positive electrode active material for a fluoride-ion battery described in any one of claims 1 to 6.

8. It has a positive electrode active material layer, and The positive electrode active material layer contains the positive electrode composite material for fluoride ion batteries described in claim 7. Fluoride ion battery.

9. A method for producing a positive electrode active material for a fluoride-ion battery according to any one of claims 1 to 6, comprising the following steps: To provide a fluoride ion battery having a positive electrode active material layer containing covellite, and The fluoride ion battery is charged with a capacity of 500 mAh or more and 800 mAh or less per gram of the aforementioned cobelite.

10. A method for producing a positive electrode active material for a fluoride-ion battery according to claim 9, wherein the fluoride-ion battery is charged at a temperature of 130°C or lower.

Images