Positive electrode composite material for fluoride-ion batteries and method for manufacturing the same, and fluoride-ion battery

Abstract

This disclosure provides a cathode composite material for fluoride-ion batteries that can improve the Coulomb efficiency and cycle characteristics of the battery, a method for manufacturing the same, and a fluoride-ion battery containing such a cathode composite material for fluoride-ion batteries. [Solution] The positive electrode material for fluoride-ion batteries of the present disclosure comprises covellite and a solid electrolyte. In the positive electrode material for fluoride-ion batteries of the present disclosure, the ionic conductivity of the solid electrolyte at 80°C is 5.0 × 10⁻⁶. -6 The ratio is S / cm or higher. 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. The method of manufacturing the positive electrode composite material for fluoride-ion batteries of the present disclosure comprises the following steps: providing raw materials including covelite and a solid electrolyte; and mixing the raw materials while applying mechanical shock to the raw materials.

Description

Technical Field

[0001] The present disclosure relates to a positive electrode composite material for a fluoride ion battery, a method for manufacturing the same, 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 , 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 copper sulfide as a positive electrode active material, there is room for improvement from the viewpoints of Coulomb efficiency and cycle characteristics.

[0007] The present disclosure aims to provide a positive electrode composite material for a fluoride ion battery capable of improving the Coulomb efficiency and cycle characteristics of the battery, a method for manufacturing the same, and a fluoride ion battery including such a positive electrode composite material for a fluoride ion battery.

Means for Solving the Problems

[0008] The Disclosing Party has found that the above-mentioned problems can be solved by the following means. <Aspect 1> Covelite, and solid electrolyte Includes, The ionic conductivity of the aforementioned solid electrolyte at 80°C is 5.0 × 10⁻⁶. -6 It is S / cm or higher. Positive electrode composite material for fluoride-ion batteries. <Aspect 2> The copelite described above has the composition of the following formula (1), wherein the positive electrode material for a fluoride ion battery according to Embodiment 1: Cu x S(0.80≦x≦1.30) … (1). <Aspect 3> The positive electrode composite material for a fluoride ion battery according to embodiment 1 or 2, wherein the solid electrolyte has the composition of the following formula (2): Pb 1-y Zr y F 2+2y (0 <y<1) … (2)。 <Aspect 4> The positive electrode composite material for a fluoride ion battery according to embodiment 3, wherein in formula (2), y is 0.01 or more and 0.3 or less. <Aspect 5> 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 any one of embodiments 1 to 4. Fluoride ion battery. <Aspect 6> A method for producing a positive electrode composite material for a fluoride ion battery according to any one of embodiments 1 to 4, including the following steps: To provide raw materials including the aforementioned covelite and the aforementioned solid electrolyte, and Mixing the raw materials while applying mechanical impact to them. [Effects of the Invention]

[0009] According to this disclosure, a cathode composite material for fluoride-ion batteries and a method for manufacturing the same can be provided, which can improve the Coulomb efficiency and cycle characteristics of the battery, as well as a fluoride-ion battery containing such a cathode composite material for fluoride-ion batteries. [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 XRD pattern of the positive electrode active material layer in Example 1. [Figure 3] Figure 3 shows the XRD pattern of the positive electrode active material layer of Comparative Example 1. [Figure 4] Figure 4 shows the XRD pattern of the positive electrode active material layer of Comparative Example 2. [Figure 5] Figure 5 shows the charge-discharge curve of the fluoride-ion battery of Example 1. [Figure 6] Figure 6 shows the charge-discharge curve of the fluoride-ion battery of Comparative Example 1. [Figure 7] Figure 7 shows the charge-discharge curve of the fluoride-ion battery of Comparative Example 2. [Figure 8] Figure 8 shows the cycle characteristics of the charge capacity, discharge capacity, and Coulomb efficiency of the fluoride-ion battery of Example 1. [Figure 9] Figure 9 shows the cycle characteristics of the charge capacity, discharge capacity, and Coulomb efficiency of the fluoride-ion battery of Comparative Example 1. [Figure 10] Figure 10 shows the cycle characteristics of the charge capacity, discharge capacity, and Coulomb efficiency of the fluoride-ion battery of Comparative Example 2. [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] <<Positive electrode composite material for fluoride-ion batteries>> The cathode composite material for fluoride-ion batteries of this disclosure comprises covellite and a solid electrolyte. In the cathode composite material for fluoride-ion batteries of this disclosure, the ionic conductivity of the solid electrolyte at 80°C is 5.0 × 10⁻⁶. -6 It is S / cm or higher.

[0013] Below, the ionic conductivity at 80°C is 5.0 × 10⁻⁶. -6 Solid electrolytes with a density of S / cm or higher are sometimes referred to as "specific solid electrolytes."

[0014] The disclosing parties believe that one of the reasons for the insufficient Coulomb efficiency and cycle characteristics in conventional fluoride-ion batteries containing copper sulfide other than covelite, such as digenite, as the positive electrode active material lies in the battery's charge-discharge mechanism. In other words, in conventional fluoride-ion batteries containing copper sulfide as the positive electrode active material, charge-discharge is thought to occur through a conversion mechanism that significantly changes the crystal structure and lattice volume of the copper sulfide. As a result, it becomes difficult for particles to come into contact with each other within the positive electrode active material layer, and therefore the above-mentioned problems arise.

[0015] In response to this, the Disclosers have found that a positive electrode composite material for fluoride-ion batteries containing covellite and a specific solid electrolyte improves the Coulomb efficiency and cycle characteristics of the battery. The reason for this is presumed to be as follows, although this is not intended to be bound by any theory: In covellite as a positive electrode active material, the intercalation and deintercalation of fluoride ions during charging and discharging occurs through an insertion mechanism in which the crystal structure and lattice volume do not change significantly, thereby suppressing the difficulty of particles coming into contact with each other within the positive electrode active material layer. Furthermore, in the positive electrode composite material for fluoride-ion batteries disclosed herein, by including a specific solid electrolyte, i.e., a solid electrolyte with high ionic conductivity, in addition to covellite as a positive electrode active material, it is believed that the effect of intercalation and deintercalation of fluoride ions through such an insertion mechanism can be optimized, thereby improving the Coulomb efficiency and cycle characteristics of the battery.

[0016] Whether a positive electrode composite material for a fluoride ion battery or a positive electrode active material layer containing the positive electrode composite material for a fluoride ion battery contains covellite can be confirmed, for example, by X-ray diffraction (XRD). Specifically, in the discharged state before the operation of the battery, the structure of covellite can be confirmed by performing XRD measurement on a sample of the positive electrode active material layer formed from the positive electrode composite material. The XRD measurement can be performed by the convergent beam method of irradiating with CuKα rays under the conditions of a tube voltage of 45 kV and a tube current of 200 mA using SmartLab manufactured by Rigaku Corporation as an X-ray diffractometer. The above measurement can be performed by sealing the sample in an airtight sample stage in an argon atmosphere. As a substrate for mounting the sample, a Si non-reflecting plate can be used.

[0017] Hereinafter, each element constituting the positive electrode composite material for a fluoride ion battery of the present disclosure will be described.

[0018] <Copper sulfide> The positive electrode composite material for a fluoride ion battery of the present disclosure contains covellite. According to the positive electrode composite material containing covellite, charge and discharge of the battery can be performed by a mechanism suitable for improving the Coulomb efficiency and cycle characteristics of the battery.

[0019] Covellite typically has a composition of CuS and is a hexagonal copper sulfide of the space group P63 / mmc. Covellite is also called chalcocite or cobelin.

[0020] Covellite may have the composition of the following formula (1): Cu x S(0.80≦x≦1.30) … (1)

[0021] In the above formula (1), x may be 0.85 or more, 0.90 or more, 0.95 or more, or 1.00 or more, may be 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. When x is within the above range, the Coulomb efficiency and cycle characteristics of the battery can be effectively improved.

[0022] The composition of covellite can be identified, for example, by inductively coupled plasma atomic emission spectroscopy (ICP-AES).

[0023] The cobelite contained in the positive electrode composite material for fluoride-ion batteries of this disclosure may be a commercially available product or may be prepared by a conventional method.

[0024] In the positive electrode composite material for fluoride-ion batteries of this disclosure, Covelite functions as a positive electrode active material.

[0025] 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.

[0026] The positive electrode active material contained in the positive electrode composite material may be covellite alone, or it may be a combination of covellite and other positive electrode active materials. Examples of positive electrode active materials other than covellite 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.

[0027] The proportion of covellite in the total (100% by mass) of positive electrode active material contained in the positive electrode mixture may be, for example, 50% to 100% by mass, 60% to 100% by mass, 70% to 100% by mass, 80% to 100% by mass, 90% to 100% by mass, 95% to 100% by mass, 99% to 100% by mass, or 100% by mass. In other words, all of the positive electrode active material contained in the positive electrode mixture may be covellite.

[0028] 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.

[0029] <Solid electrolyte> The positive electrode composite material for fluoride-ion batteries disclosed herein includes a solid electrolyte. The ionic conductivity of the solid electrolyte at 80°C is 5.0 × 10⁻⁶. -6 The ratio is S / cm or higher. By using such a specific solid electrolyte in combination with covellite as the positive electrode active material, it is possible to charge and discharge the battery in a mechanism suitable for improving the Coulomb efficiency and cycle characteristics of the battery.

[0030] This ionic conductivity is 7.5 × -6 S / cm or more, 1.0× -5 S / cm or more, 2.5× -5 S / cm or more, 5.0× -5 S / cm or more, 7.5× -5 S / cm or more, 1.0× -4 S / cm or more, 2.5× -4 S / cm or more, 5.0× -4 S / cm or larger, or 7.5× -4 It may be S / cm or more, and 1.0 × -2 S / cm or less, 7.5× -3 S / cm or less, 5.0× -3 S / cm or less, 2.5× -3 S / cm or less, or 1.0 × -3 It may be less than or equal to S / cm, and also 9.0 × -4 It may also be S / cm. When this ionic conductivity is within the above range, the Coulomb efficiency and cycle characteristics of the battery can be effectively improved.

[0031] Ionic conductivity can be calculated, for example, by using an electrochemical measurement system equipped with a frequency response analyzer manufactured by Biologic Inc. to measure the AC impedance of a pellet-shaped solid electrolyte obtained by uniaxial molding using a blocking electrode, thereby measuring the total resistance originating from the solid electrolyte, and then normalizing the total resistance value using the thickness of the solid electrolyte pellet and the area of ​​the blocking electrode.

[0032] In the positive electrode composite material for fluoride-ion batteries of this disclosure, the solid electrolyte may have the composition of the following formula (2): Pb 1-y Zr y F 2+2y (0 <y<1) … (2)。

[0033] The Disclosing Party has further discovered that even when covelite is used as a raw material, depending on the type of solid electrolyte, the structure of covelite may change during the manufacturing of the positive electrode composite material. In particular, when the raw materials containing covelite and solid electrolyte are mixed while subjected to mechanical shock to obtain the positive electrode composite material, the structure of covelite changes to that of other copper sulfides such as digenite. While not intending to be bound by any theory, this is thought to be because, depending on the type of solid electrolyte, contact with the solid electrolyte accelerates the alteration of covelite. Such alteration of the structure of covelite prevents the battery from being charged and discharged using the desired insertion mechanism.

[0034] In contrast, a specific solid electrolyte having the composition of formula (2) above is less likely to cause alteration of the covellite structure in the positive electrode composite, thereby effectively improving the Coulomb efficiency and cycle characteristics of the battery.

[0035] In the above formula (2), y may be between 0.01 and 0.3. When y is within the above range, it is possible to further reduce the likelihood of structural alteration of the covellite in the positive electrode composite, and effectively improve the Coulomb efficiency and cycle characteristics of the battery. y may be between 0.03 and 0.05, 0.07 and 0.09, or 0.1, and may also be between 0.25, 0.2, 0.15, 0.12, or 0.1. y may even be 0.1, i.e., Pb 0.9 Zr 0.1 F 2.2 That's fine.

[0036] The specific solid electrolyte contained in the positive electrode composite material for fluoride-ion batteries of this disclosure may be a commercially available product or may be prepared by conventional methods. An example of a method for preparing a specific solid electrolyte is a mechanical milling mixture of fluorides of metal elements constituting the desired specific solid electrolyte.

[0037] The solid electrolyte content 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 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.

[0038] The solid electrolyte contained in the positive electrode composite material may be a specific solid electrolyte alone, or a combination of a specific solid electrolyte and other solid electrolytes. Examples of solid electrolytes other than the specific solid electrolyte include fluorides of lanthanide elements such as La and Ce; fluorides of alkali elements such as Li, Na, K, Rb, and Cs; and fluorides of alkaline earth elements such as Ca, Sr, and Ba.

[0039] The proportion of a specific solid electrolyte in the total amount (100% by mass) of solid electrolytes contained in the positive electrode mixture may be, for example, 30% to 100% by mass, 40% to 100% by mass, 50% to 100% by mass, 60% to 100% by mass, 70% to 100% by mass, 80% to 100% by mass, 90% to 100% by mass, 95% to 100% by mass, 99% to 100% by mass, or 100% by mass. In other words, all solid electrolytes contained in the positive electrode mixture may be the specific solid electrolyte.

[0040] Solid electrolytes assist in the conduction of fluoride ions.

[0041] The shape of the solid electrolyte is not particularly limited. The solid electrolyte may, for example, be particulate. The size of the solid electrolyte is not particularly limited as long as it can function as a solid electrolyte in a fluoride-ion battery.

[0042] (The mass ratio of the covellite content to the content of a specific solid electrolyte) The mass ratio of the covellite content in the positive electrode composite material to the content of a specific solid electrolyte is not particularly limited. This mass ratio may be, for example, 0.1 to 10, 0.2 to 5, or 0.3 to 1.

[0043] <Liquid electrolytes, conductive additives, and binders> The positive electrode composite material for fluoride-ion batteries of this disclosure may optionally include a liquid electrolyte, a conductive additive, and a binder.

[0044] (liquid electrolyte) A liquid electrolyte includes, for example, a solvent and a salt dissolved in the solvent.

[0045] The solvent may be, for example, an organic solvent. The organic solvent should be capable of dissolving the salt. Examples of organic solvents include triethylene glycol dimethyl ether (G3), tetraethylene glycol dimethyl ether (G4), etc. 1 -O(CH2CH2O) n -R2 (R 1 and R 2 Each 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] (Conductive additive) The conductive additive is not particularly limited as long as it has electronic conductivity.

[0050] 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.

[0051] 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.

[0052] The shape of the conductive additive is not particularly limited. The conductive additive may be, for example, particulate or fibrous.

[0053] (Binder) The binder in a fluoride-ion battery only needs to be chemically and electrically stable.

[0054] The binder may be a fluorine-based binder such as polyvinylidene fluoride (PVDF) binder or polytetrafluoroethylene (PTFE) binder, or it may be a rubber-based binder such as styrene-butadiene rubber (SBR).

[0055] The binder content in the cathode composite material is not particularly limited.

[0056] <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.

[0057] <<Manufacturing method for cathode composite material for fluoride-ion batteries>> The method for manufacturing a cathode composite material for fluoride-ion batteries according to this disclosure includes the following steps: To provide raw materials including covelite and a solid electrolyte, and Mixing raw materials while applying mechanical shock to them.

[0058] In order to manufacture the positive electrode composite material for fluoride-ion batteries according to this disclosure, it is necessary to mix the raw materials while applying mechanical shock to them. However, by using covellite and a specific solid electrolyte as raw materials, the desired positive electrode composite material can be obtained without altering the covellite.

[0059] <Raw material provision process> The method disclosed herein includes providing raw materials comprising covelite and a solid electrolyte.

[0060] For cobelite and solid electrolytes, refer to the above description of the cathode composite material for fluoride-ion batteries in this disclosure.

[0061] <Raw material mixing process> The method of this disclosure includes mixing raw materials while applying mechanical impact to them. An example of such a method is mixing by mechanical milling. Specifically, a method of mixing raw materials using a ball mill apparatus is provided. The ball mill apparatus may be operated by any of the following methods: planetary, vibration, or rotation. By using a planetary ball mill apparatus, the sample can be mixed efficiently. This process may be carried out under an inert gas atmosphere.

[0062] 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.

[0063] 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.

[0064] <<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. Because the fluoride-ion battery of the present disclosure contains the positive electrode composite material for fluoride-ion batteries of the present disclosure, it has improved Coulomb efficiency and cycle characteristics.

[0065] 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.

[0066] 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.

[0067] A fluoride-ion battery may be a primary battery or a secondary battery.

[0068] The shape of the fluoride-ion battery may be, for example, coin-type, laminate-type, cylindrical, or prismatic.

[0069] Fluoride-ion batteries can be manufactured by molding each layer using a dry or wet process, among other methods.

[0070] 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).

[0071] The following describes the elements that may constitute the fluoride-ion battery of this disclosure.

[0072] <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.

[0073] Examples of positive electrode current collector layer shapes include foil-like, mesh-like, and porous shapes.

[0074] <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.

[0075] 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.

[0076] 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.

[0077] <Electrolyte layer> The electrolyte layer contains at least an electrolyte. The electrolyte may be a solid electrolyte or a liquid electrolyte.

[0078] 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.

[0079] The solid electrolyte may be appropriately selected from among the examples of materials that may be included in the positive electrode mixture described above. The solid electrolyte that may be included in the positive electrode mixture and the solid electrolyte included in the electrolyte layer may be of the same type or of different types. In other words, the solid electrolyte included in the electrolyte layer does not have to be the specific solid electrolyte described herein.

[0080] For information regarding the binder, please refer to the above description concerning the cathode composite material for fluoride-ion batteries in this disclosure.

[0081] 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.

[0082] For liquid electrolytes, refer to the above description of the positive electrode composite material for fluoride-ion batteries in this disclosure.

[0083] As for the separator, a known separator for fluoride-ion batteries can be used.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] <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.

[0088] 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.

[0089] The negative electrode active material is, for example, Pb 0.9 Zr 0.1 F 2.2 That's fine.

[0090] For the electrolyte, conductive additive, and binder, refer to the above description of the positive electrode mixture for fluoride-ion batteries in this disclosure.

[0091] 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.

[0092] 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.

[0093] <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.

[0094] Examples of negative electrode current collector layer shapes include foil-like, mesh-like, and porous shapes. [Examples]

[0095] <<Example 1>> <Preparation of positive electrode composite material> (Provision of raw materials) The raw materials were provided as follows:

[0096] Copper sulfide (manufacturing by Mitsuwa Chemical Co., Ltd.), which is covellite (composition formula: CuS), was prepared as the positive electrode active material.

[0097] In a glove box under an argon (Ar) atmosphere, lead fluoride (PbF2) and zirconium fluoride (ZrF4) were weighed to obtain a solid electrolyte in the desired composition ratio. These were then mechanically milled and mixed using a planetary ball mill (Fritsch Premium Line PL-7 planetary ball mill) to obtain powdered Pb as a solid electrolyte. 0.9 Zr 0.1 F 2.2 The ionic conductivity obtained was 9.0 × 10 at 80°C. -4 The ionic conductivity was measured using an electrochemical measurement system equipped with a frequency response analyzer manufactured by Biologic, Inc., for pelletized Pb obtained by uniaxial molding. 0.9 Zr 0.1 F 2.2 For this, AC impedance measurements were performed using blocking electrodes, and Pb 0.9 Zr 0.1 F 2.2 The total resistance is measured, and Pb is applied to the total resistance value. 0.9 Zr 0.1 F 2.2 The calculation was performed by normalizing the pellet thickness and the area of ​​the blocking electrode.

[0098] <Mixing of raw materials> 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 2.2The positive electrode mixture was obtained in powder form by mechanical milling the positive electrode active material, solid electrolyte, and conductive additive (acetylene black (AB)) using a planetary ball mill (Fritsch Premium Line PL-7). The mass ratio of the positive electrode active material, solid electrolyte, and conductive additive was 30:66:4. The ball milling was performed in a dry argon atmosphere for 3 hours at a disc rotation speed of 600 rpm.

[0099] <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 (working electrode).

[0100] 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.

[0101] Pb as the negative electrode active material layer (counter electrode) 0.9 Zr 0.1 F 2.2 A compacted powder was formed using 50 mg of a mixture of powder and AB powder as a conductive additive. The AB content in the mixture was 5% by mass of the total mixture. 220 mg of Pb plate was pressed onto one surface of the formed negative electrode active material layer (the side that would later be in contact with the negative electrode current collector layer). It is believed that using this Pb plate suppresses the decrease in cycle characteristics on the counter electrode side when performing charge-discharge tests of the half-cell. As a result, in this embodiment, it is considered that the positive electrode active material layer (working electrode) was more dominant in determining the cycle characteristics of the test half-cell.

[0102] A test half-cell of 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.

[0103] <<Comparative Example 1>> As a solid electrolyte contained in the positive electrode composite material, Pb 0.6 Sn 0.4 An all-solid-state fluoride ion battery was fabricated in the same manner as in Example 1, except that F2 was used.

[0104] Pb 0.6 Sn 0.4 For F2, a sample synthesized by mechanically milling and mixing PbF2 and tin fluoride (SnF2) was used. The ionic conductivity of this solid electrolyte, measured by the above method, was 4.2 × 10⁻⁶ at 80°C. -3 The conductivity was S / cm. In other words, the solid electrolyte of Comparative Example 1 had a higher ionic conductivity than the solid electrolyte of Example 1.

[0105] <<Comparative Example 2>> As a solid electrolyte contained in the positive electrode composite material, La 0.95 Sr 0.05 F 2.95 An all-solid-state fluoride ion battery was fabricated in the same manner as in Example 1, except that a different material was used.

[0106] La 0.95 Sr 0.05 F 2.95 For this purpose, a sample synthesized by solid-phase reaction of lanthanum fluoride (LaF3) and strontium fluoride (SrF2) as raw materials was used by calcination. The ionic conductivity of this solid electrolyte, measured by the above method, was 8.8 × 10⁻⁶ at 80°C. -5 The value was S / cm.

[0107] <<Rating>> <Crystal structure of copper sulfide in the positive electrode active material layer> XRD measurements were performed on samples of the positive electrode active material layer formed from the positive electrode composite material in the discharged state before battery operation. The XRD measurements were performed using a Rigaku SmartLab X-ray diffractometer, under an inert gas atmosphere, with a tube voltage of 45kV and a tube current of 200mA, using a concentrated method with CuKα radiation. The samples were sealed in an airtight sample stage under an argon atmosphere for the measurements. A Si non-reflective plate was used as the substrate for mounting the samples. The obtained XRD patterns for each example are shown in Figures 2 to 4.

[0108] For comparison, the patterns of the covellite (CuS) reagent used and the solid electrolytes contained in the positive electrode active material layer for each example are also shown in the figures. In addition, in Figures 2 and 4, copper sulfide (Cu x To clarify the diffraction lines due to S), the XRD measurement results of the positive electrode active material layer magnified in the vertical axis direction are also shown. Furthermore, in Figures 3 and 4, Digenite (Cu 1.81 The pattern calculated based on the ICDD card data from S) is also shown.

[0109] As shown in Figure 2, in Example 1, the covellite (CuS; hexagonal system, P63 / mmc) used as a raw material for the positive electrode composite maintained its crystal structure even within the positive electrode active material layer.

[0110] In contrast, as shown in Figures 3 and 4, in Comparative Examples 1 and 2, covelite (CuS) is not included in the positive electrode active material layer as copper sulfide, and digenite (Cu 1.81 S and Cu 1.8 S (cubic crystal system, space group Fm-3m) was present in the positive electrode active material layer. This is thought to be because, in the comparative example, the chemical stability of covellite with respect to the solid electrolyte was low, and as a result, the covellite was transformed into digenite during the process of preparing the positive electrode composite material.

[0111] <Evaluation of fluoride-ion batteries> For each example of fluoride-ion batteries, the test was conducted in a sealed container under vacuum at a test temperature of 80°C and a current density of 0.05 mA / cm². 2 The battery was charged and discharged five times. The charging termination condition was set to whichever came first: the upper voltage limit of 1.4V or the charging capacity of 240mAh / g. The reason for adopting the capacity value of 240mAh / g is that prior studies of crystal structure analysis suggested that charging and discharging proceeded up to approximately this capacity range due to the insertion reaction mechanism of covellite (CuS). The discharge termination condition was set to a lower voltage limit of 0.5V. An electrochemical measurement system equipped with a frequency response analyzer (VMP-300 high-performance electrochemical measurement system, Biologic Corporation) was used for the charge and discharge tests. Figures 5 to 7 show the charge and discharge curves obtained in each test. Furthermore, Figures 8 to 10 show the changes in charging capacity, discharge capacity, and Coulomb efficiency for each cycle as a result of the charge and discharge tests in each example. In addition, Table 1 shows the charging capacity and discharge capacity, capacity retention rate (capacity of cycle 5 / capacity of cycle 1 × 100), and Coulomb efficiency in cycle 1 for the first and fifth cycles.

[0112] [Table 1]

[0113] As shown in Figures 5-10 and Table 1, in the fluoride-ion battery of Example 1, in which the positive electrode composite material constituting the positive electrode active material layer was configured according to the present invention, the Coulomb efficiency and cycle characteristics were improved.

[0114] In contrast, the comparative example fluoride-ion battery exhibited inferior Coulomb efficiency and cycle characteristics compared to the fluoride-ion battery of Example 1.

[0115] Generally speaking, for solid electrolytes contained in the positive electrode active material layer of fluoride-ion batteries, the higher the ionic conductivity of the electrolyte, the more efficiently charging and discharging proceeds, which in turn improves various battery characteristics such as capacity, Coulomb efficiency, and cycle characteristics.

[0116] In contrast, the solid electrolyte of Example 1 is Pb 0.9 Zr 0.1 F 2.2 The ionic conductivity of the solid electrolyte Pb in Comparative Example 1 is 0.6 Sn 0.4 Despite having a lower ionic conductivity than F2, the capacity, Coulomb efficiency, and cycle characteristics of the battery in Example 1 were higher than those of the battery in Comparative Example 1. This is because, in the positive electrode composite, a specific copper sulfide, i.e., covelite, as the positive electrode active material, and a specific solid electrolyte, i.e., a solid electrolyte with a predetermined ionic conductivity, particularly Pb 0.9 Zr 0.1 F 2.2 This suggests that the effects of this disclosure will be achieved by using them in combination. [Explanation of symbols]

[0117] 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. Covelite, and solid electrolyte Includes, The ionic conductivity of the aforementioned solid electrolyte at 80°C is 5.0 × 10⁻⁶. －６ It is S / cm or higher. Positive electrode composite material for fluoride-ion batteries.

2. The positive electrode composite material for a fluoride-ion battery according to claim 1, wherein the cobelite has the composition of the following formula (1): Cổ ｘ S(0.80≦x≦1.30) … (1).

3. The positive electrode composite for a fluoride-ion battery according to claim 1, wherein the solid electrolyte has the composition of the following formula (2): Pb １－ｙ Zr ｙ F ２＋２ｙ (0<y<1) … (2)。

4. The positive electrode composite material for a fluoride ion battery according to claim 3, wherein in formula (2), y is 0.01 or more and 0.3 or less.

5. 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 any one of claims 1 to 4. Fluoride ion battery.

6. A method for producing a positive electrode composite material for a fluoride ion battery according to any one of claims 1 to 4, comprising the following steps: To provide raw materials including the aforementioned covelite and the aforementioned solid electrolyte, and Mixing the raw materials while applying mechanical impact to them.

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