Composite material for negative electrode of fluoride ion secondary battery, negative electrode for fluoride ion secondary battery and secondary battery using the composite material, and method for producing the composite material

Abstract

The present invention provides a composite material for a negative electrode of a fluoride ion secondary battery, which can achieve high initial charge and discharge efficiency in a fluoride ion secondary battery and is a fluoride ion secondary battery that starts charging, a negative electrode for a fluoride ion secondary battery and a secondary battery using the composite material, and a method for manufacturing the composite material. Nanoparticle-sized aluminum and metal fluoride are used as negative electrode active materials and form a composite with other components of the negative electrode composite material to suppress coating with aluminum fluoride formed by refluorination reaction after defluorination, and also suppress aggregation of particles of the negative electrode active material.

Description

Technical Field

[0001] The present invention relates to a composite material for a negative electrode of a fluoride ion secondary battery, a negative electrode for a fluoride ion secondary battery and a secondary battery using the composite material, and a method for producing the composite material. Background Art

[0002] Conventionally, lithium ion secondary batteries have been widely used as secondary batteries with high energy density. A lithium ion secondary battery has a structure in which a separator is provided between a positive electrode and a negative electrode and the battery is filled with a liquid electrolyte (electrolyte).

[0003] Since the electrolyte of a lithium ion secondary battery is generally a flammable organic solvent, safety, especially in terms of heat, may be problematic. Therefore, a solid-state battery has been proposed that uses an inorganic solid electrolyte instead of an organic liquid electrolyte (see Patent Document 1).

[0004] As a battery using a solid electrolyte, a secondary battery using fluoride ions is also being studied (see Patent Document 2). It is known that a fluoride ion secondary battery uses fluoride ions (F － ) as a carrier of secondary batteries, has a high theoretical energy. Moreover, its battery characteristics are expected to exceed those of lithium-ion secondary batteries.

[0005] Here, as a negative electrode active material for a fluoride ion secondary battery, for example, MgF 2 , CaF 2 , CeF 3 etc. (See Non-Patent Documents 1-2). However, the charge and discharge efficiency of fluoride ion secondary batteries using these negative electrode active materials is 10-20%, which is a problem of low energy efficiency for secondary batteries. In addition, the charge and discharge capacity is only about 10-20% of the theoretical capacity, which is not as high as the current lithium ion secondary batteries and Ni-MH batteries.

[0006] Examples of the solid electrolyte used in the fluoride ion secondary battery include La 1－x Ba x F 3－X , x = 0.01 to 0.2 (hereinafter referred to as LBF) (see Non-Patent Documents 1 to 4). The reduction side potential window of LBF is as follows Figure 1 As shown, the La / LaF 3 Potential - 2.41V vs. Pb / PbF 2 restrictions.

[0007] In contrast, the potential of the negative electrode active material of the currently reported fluoride ion secondary battery is as follows Figure 1 As shown, MgF 2 -2.35~-2.87V vs.Pb / PbF 2 , CaF 2 -2.85~-2.89V vs.Pb / PbF 2 , CeF 3 -2.18~-2.37V vs.Pb / PbF 2 Therefore, under the limitation of the reduction potential window of LBF at -2.41 V, the defluorination / refluorination reaction of the negative electrode active material cannot be achieved if overvoltage is taken into consideration.

[0008] On the other hand, regarding the cathode reaction, for example, Cu / CuF 2 、Bi / BiF 3 The positive electrode active materials such as NH40 and NH42 exhibit high utilization and reversible reaction in charge and discharge test results (see Patent Documents 3 to 4 and Non-Patent Documents 1 to 3).

[0009] Therefore, in order to achieve a practical full-cell reaction combining positive and negative electrode reactions in a fluoride ion secondary battery, a negative electrode active material that exhibits a reversible negative electrode reaction at a high utilization rate is required.

[0010] In response to this demand, Patent Document 5 focuses on aluminum fluoride (AlF) which undergoes charge-discharge reactions (defluorination / refluorination reactions) within the potential window of -2.41 V of fluoride ion solid electrolyte, LBF. 3 :-1.78V vs.Pb / PbF 2 ), and further proposed a negative electrode active material, the negative electrode active material is aluminum fluoride (AlF 3 ) has a perfect crystal structure of six coordinated octahedrons, so that some fluoride ions (F － ) is pre-detached, and aluminum fluoride (AlF 3 ) is modified.

[0011] According to the negative electrode active material of Patent Document 5, the pores provided at the positions where fluorine atoms previously existed serve as starting points for defluorination / refluorination reactions, thereby enabling the desired negative electrode reactions to be exhibited with high utilization efficiency and reversibility.

[0012] [Prior Technical Literature]

[0013] (Patent Document)

[0014] Patent Document 1: Japanese Patent Application Publication No. 2000-106154

[0015] Patent Document 2: Japanese Patent Application Publication No. 2017-050113

[0016] Patent Document 3: Japanese Patent Application Publication No. 2018-206755

[0017] Patent Document 4: Japanese Patent Application Publication No. 2019-087403

[0018] Patent Document 5: Japanese Patent Application No. 2018-059703

[0019] (Non-patent literature)

[0020] Non-patent literature 1: J. Mater. Chem. A. 2014.2.20861-20872

[0021] Non-patent document 2: J. Solid State Electrochem (2017) 21: 1243-1251

[0022] Non-patent document 3: J. Mater. Chem., 2011, 21, 17059

[0023] Non-patent document 4: Dalton Trans., 2014, 43, 15771-15778 Summary of the invention

[0024] [Problems to be solved by the invention]

[0025] However, in the fluoride ion secondary battery using the negative electrode active material proposed in Patent Document 5, the electrochemical efficiency in the first electrochemical cycle is about 50%, and further improvement is required.

[0026] In addition, the fluoride ion secondary battery using the negative electrode active material proposed in Patent Document 5 is a discharge-start battery because a compound having fluoride ions is selected in the positive electrode as the counter electrode. However, from the perspective of the stability of the active material in the electrode, the manufacture of the secondary battery is ideally carried out in a discharge state with a low energy state. That is, it is preferably a charge-start battery.

[0027] The present invention is made in view of the above-mentioned background technology, and its purpose is to provide a fluoride ion secondary battery negative electrode composite material complex that can achieve high initial charge and discharge efficiency in a fluoride ion secondary battery and serve as a fluoride ion secondary battery for charging initiation, a fluoride ion secondary battery negative electrode and secondary battery using the composite, and a method for manufacturing the composite.

[0028] [Technical means to solve the problem]

[0029] The present inventors have actively studied the cause of the low electrochemical efficiency of the negative electrode active material proposed in Patent Document 5. They considered that the aluminum fluoride formed by the refluorination reaction after defluorination may cover the surface of the negative electrode active material to form an insulating layer, thereby reducing the reactivity.

[0030] In addition, it is considered that since the negative electrode active material is nanoparticles, the particles aggregate during initial charge and discharge, resulting in insufficient formation of electron conduction paths and ion conduction paths.

[0031] Furthermore, it is considered that if a compound capable of releasing fluoride ions as ion carriers during charge can be present as a negative electrode active material, it is possible to construct a battery using a compound having no fluoride ions as a positive electrode.

[0032] Furthermore, the inventors have discovered that if aluminum and metal fluoride of nanoparticle size are used as negative electrode active materials and form a composite together with other components of the negative electrode composite material, it is possible to suppress coating with aluminum fluoride formed by a refluorination reaction after defluorination, and further, it is possible to suppress aggregation of particles of the negative electrode active material. As a result, a fluoride ion secondary battery having a high initial charge and discharge efficiency and capable of charge initiation can be realized, thereby completing the present invention.

[0033] That is, the present invention is a negative electrode composite material for a fluoride ion secondary battery, comprising a negative electrode active material and a fluoride ion conductive fluoride, wherein the negative electrode active material comprises aluminum and a metal fluoride.

[0034] The metal fluoride can also release fluoride ions under battery reaction conditions and is composed of a metal having a voltage of 0 V or higher based on a standard hydrogen electrode (SHE).

[0035] The metal fluoride may be silver fluoride.

[0036] The average particle size of the aluminum may be 10 to 200 nm.

[0037] The negative electrode composite material composite for a fluoride ion secondary battery may further contain carbon black.

[0038] In addition, another aspect of the present invention is a negative electrode for a fluoride ion secondary battery, comprising the negative electrode composite material composite for a fluoride ion secondary battery.

[0039] Another aspect of the present invention is a fluoride ion secondary battery comprising the above-mentioned negative electrode for fluoride ion secondary battery, a solid electrolyte, and a positive electrode.

[0040] In addition, another present invention is a method for manufacturing a negative electrode composite material composite for a fluoride ion secondary battery, which is a method for manufacturing a negative electrode composite material composite for a fluoride ion secondary battery, comprising: a mixing step, mixing a negative electrode active material, a fluoride ion conductive fluoride and carbon black to obtain a negative electrode composite material mixture; and a compounding step, by crushing and mixing the aforementioned negative electrode composite material mixture, thereby compounding the aforementioned negative electrode active material, the aforementioned fluoride ion conductive fluoride and the aforementioned carbon black to obtain a composite; and the aforementioned negative electrode active material contains aluminum and metal fluoride.

[0041] In the method for producing a negative electrode composite material for a fluoride ion secondary battery, the metal fluoride may release fluoride ions under battery reaction conditions and be composed of a metal having a SHE standard of 0 V or higher.

[0042] In the method for producing the negative electrode composite material for a fluoride ion secondary battery, the metal fluoride may be silver fluoride.

[0043] In the method for producing a negative electrode composite material for a fluoride ion secondary battery, the average particle size of the aluminum may be 10 to 200 nm.

[0044] In the method for producing the negative electrode composite material for a fluoride ion secondary battery, the pulverization and mixing treatment may be dry pulverization.

[0045] In the method for producing the negative electrode composite material for a fluoride ion secondary battery, the pulverization and mixing treatment may be performed using a ball mill.

[0046] (Effects of the Invention)

[0047] According to the negative electrode composite material composite for a fluoride ion secondary battery of the present invention, it is possible to realize a fluoride ion secondary battery having high initial charge and discharge efficiency and being capable of starting charging. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a graph showing the potential calculated from the Gibbs energy.

[0049] Figure 2 It is an X-ray diffraction (XRD) chart of various substances and the negative electrode composite material composite for fluoride ion secondary battery of Example 1.

[0050] Figure 3 It is a diagram showing the method of manufacturing the fluoride ion secondary battery in the example and the comparative example.

[0051] Figure 4It is a cross-sectional view of the fluoride ion secondary battery produced in the Example and the Comparative Example.

[0052] Figure 5 These are charge and discharge curves of the fluoride ion secondary batteries produced in Examples and Comparative Examples. DETAILED DESCRIPTION

[0053] Hereinafter, embodiments of the present invention will be described.

[0054] <Negative electrode composite material for fluoride ion secondary battery>

[0055] The negative electrode of a fluoride ion secondary battery needs to be able to accommodate fluoride ions (F － ) and releases fluoride ions (F － ).

[0056] The negative electrode composite material for a fluoride ion secondary battery of the present invention is a composite material containing a negative electrode active material and a fluoride ion conductive fluoride, and containing aluminum and a metal fluoride as the negative electrode active material.

[0057] The negative electrode composite material for fluoride ion secondary battery of the present invention may contain aluminum and metal fluoride as negative electrode active materials and further contain fluoride ion conductive fluoride as constituent components, and may also contain other components as desired.

[0058] In the negative electrode composite material composite for a fluoride ion secondary battery of the present invention, aluminum as the negative electrode active material is an alloy with other components of the composite and does not exist as a single substance of aluminum.

[0059] [Shape of the complex]

[0060] The shape of the composite material for negative electrode of the fluoride ion secondary battery of the present invention is not particularly limited. Among them, it is preferably granulated into a spherical shape. Moreover, it is preferred that aluminum and metal fluoride, fluoride ion conductive fluoride, and any other components as negative electrode active materials are present in each particle.

[0061] When the granules are granulated into a spherical shape, the electrodes can be filled with more gaps during electrode pressing, thereby increasing the volume energy density of the battery.

[0062] In the case of a spherical shape, since the constituent components of the composite exist within each composite particle, an electron conduction path and an ion conduction path for fluorination / defluorination reaction required for an electrochemical reaction can be formed at a nanometer size.

[0063] In addition, in order to improve the electrochemical reaction efficiency of the fluoride ion secondary battery, it is effective to expand the surface area of ​​the material constituting the negative electrode, and if the shape of the negative electrode composite material complex is spherical, the negative electrode for the fluoride ion secondary battery that becomes a collection of spherical objects will become a structure with a high surface area. As a result, the contact area with the solid electrolyte contained in the adjacent solid electrolyte layer can be increased.

[0064] (Average particle size)

[0065] When the shape of the negative electrode composite material for fluoride ion secondary batteries of the present invention is spherical, the average particle size is preferably in the range of 0.5 to 10 μm, and particularly preferably in the range of 1 to 5 μm.

[0066] If the average particle size of the negative electrode composite material composite for fluoride ion secondary battery is within the above range, the particles collide with each other and granulate during the pulverization and mixing process for obtaining the composite particles, thereby firmly bonding and forming an electron conduction path and an ion conduction path for fluorination / defluorination reaction in the micro-sized particles. The particle structure with the electron conduction path and the ion conduction path can follow the volume change caused by the reaction of aluminum as the negative electrode active material, so that the structural collapse of the negative electrode layer can be suppressed, thereby further improving the reversibility of the electrochemical reaction.

[0067] [Negative electrode active material]

[0068] The negative electrode active material of the negative electrode composite material for a fluoride ion secondary battery of the present invention contains aluminum and metal fluoride.

[0069] 〔aluminum〕

[0070] Aluminum fluoride AlF as aluminum fluoride 3 The potential of Figure 1 As shown, it is -1.78V vs.Pb / PbF 2 There are charge and discharge reactions (defluorination / refluorination reactions) within the potential window of -2.41V of the fluoride ion solid electrolyte, namely LBF.

[0071] Therefore, within the reduction potential window of LBF of -2.41 V, even if overvoltage is considered, the defluorination / refluorination reaction of aluminum will proceed sufficiently. In addition, aluminum is an inexpensive material, so it is also economically advantageous.

[0072] In addition, an oxide film may also exist on the surface of aluminum.

[0073] (shape)

[0074] The shape of aluminum as the negative electrode active material is preferably spherical. By being spherical, the electrode can be filled with more gaps during electrode pressing, thereby increasing the volume energy density of the battery.

[0075] (Average particle size)

[0076] The average particle size of aluminum is preferably in the range of 10 to 200 nm, particularly preferably in the range of 40 to 100 nm.

[0077] When the average particle size of aluminum as the negative electrode active material is in the range of 10 to 200 nm, the obtained negative electrode composite material for a fluoride ion secondary battery will be granulated bodies that are close to true spherical shapes.

[0078] 〔Metal fluorides〕

[0079] The metal fluoride as the second component of the negative electrode active material is preferably composed of a metal that releases fluoride ions under battery reaction conditions and has a SHE standard of 0 V or higher.

[0080] If the metal fluoride is composed of a metal having a SHE voltage of 0 V or higher, when it is used as a negative electrode active material, the metal fluoride is reduced to a metal during a reduction reaction at the negative electrode, and can release fluoride ions.

[0081] The potentials of various metals based on the SHE standard are shown below.

[0082] Ag 2+ +e － →Ag + (1.98V SHE )

[0083] Bi 3+ +3e － →Bi(0.32V SHE )

[0084] Cu 2+ +2e － →Cu(0.34V SHE )

[0085] Mn 3+ +e － →Mn 2+ (1.5V SHE )

[0086] Pb 2+ +2e － →Pb(-0.13V SHE )

[0087] Sn 2+ +2e －→Sn(-0.14V SHE )

[0088] Sn 4+ +2e － →Sn 2+ (0.15V SHE ))

[0089] Preferred metal fluorides of the present invention that are composed of metals having a SHE voltage of 0 V or higher include BiF 3 ,CuF 2 、MnF 3 、SnF 4 , AgF 2 wait.

[0090] Furthermore, the metal fluoride as the second component of the negative electrode active material preferably has electronic conductivity and fluoride ion conductivity after releasing fluoride ions by reduction reaction. If it becomes insulating after releasing fluoride ions or has low fluoride ion conductivity, it will hinder the reactivity of the battery.

[0091] In the present invention, silver fluoride (AgF) is most preferred because it satisfies the above-mentioned necessary conditions and has a high SHE standard. 2 ).

[0092] [Fluoride ion conductive fluoride]

[0093] The fluoride ion conductive fluoride which is an essential component of the negative electrode composite material composite for the fluoride ion secondary battery of the present invention is not particularly limited as long as it is a fluoride having fluoride ion conductivity. For example, Ce 0.95 Ba 0.05 F 2.95 , Ba 0.6 La 0.4 F 2.4 wait.

[0094] Among these, Ce is preferably used because of its high ion conductivity. 0.95 Ba 0.05 F 2.95 .

[0095] (Average particle size)

[0096] The average particle size of the fluoride ion conductive fluoride is preferably in the range of 0.1 to 100 μm, particularly preferably in the range of 0.1 to 10 μm.

[0097] When the average particle size of the fluoride ion conductive fluoride is in the range of 0.1 to 100 μm, a thin electrode can be formed while having relatively high ion conductivity.

[0098] [Other ingredients]

[0099] The negative electrode composite material composite for fluoride ion secondary battery of the present invention may also contain other components arbitrarily in addition to the essential components, i.e., aluminum and metal fluoride as negative electrode active materials, and fluoride ion conductive fluoride. Other components include, for example, conductive additives and binders.

[0100] (Conductive additive)

[0101] In the negative electrode composite material composite for fluoride ion secondary battery of the present invention, carbon black is particularly preferably contained as a conductive auxiliary agent. The presence of carbon black in the composite can easily form an electron conduction path and an ion conduction path for fluorination / defluorination reaction required for electrochemical reaction.

[0102] The type of carbon black is not particularly limited, and examples thereof include furnace black, Ketjen black, and acetylene black.

[0103] The average particle size of carbon black is not particularly limited, but is preferably in the range of 20 to 50 nm.

[0104] When the average particle size of carbon black is in the range of 20 to 50 nm, an electrode having a small weight and high electron conductivity can be formed.

[0105] [composition]

[0106] (aluminum)

[0107] The ratio of aluminum in the negative electrode composite material for fluoride ion secondary batteries of the present invention is preferably 1 to 25% by mass, more preferably 1 to 13% by mass, based on the entire negative electrode composite material for fluoride ion secondary batteries.

[0108] In the negative electrode composite material composite for a fluoride ion secondary battery of the present invention, when the ratio of aluminum is within the above range, the capacity per unit weight of the obtained fluoride ion secondary battery becomes large.

[0109] (Metal Fluoride)

[0110] The ratio of the metal fluoride in the negative electrode composite material for fluoride ion secondary batteries of the present invention is preferably 0.4 to 25% by mass, more preferably 0.4 to 13% by mass, based on the entire negative electrode composite material for fluoride ion secondary batteries.

[0111] In the negative electrode composite material composite for a fluoride ion secondary battery of the present invention, when the ratio of the metal fluoride is within the above range, the capacity per unit weight of the obtained fluoride ion secondary battery becomes large.

[0112] (Ratio of aluminum to metal fluoride)

[0113] In the negative electrode composite material composite for a fluoride ion secondary battery of the present invention, the mass ratio of aluminum as the negative electrode active material to the metal fluoride is preferably in the range of 7:3 to 4:6, and more preferably in the range of 7:3 to 5:5.

[0114] (Fluoride ion conductive fluoride)

[0115] The ratio of the fluoride ion conductive fluoride in the negative electrode composite material for fluoride ion secondary batteries of the present invention is preferably 70 to 90 mass %, more preferably 80 to 90 mass % based on the entire negative electrode composite material for fluoride ion secondary batteries.

[0116] In the negative electrode composite material composite for a fluoride ion secondary battery of the present invention, when the ratio of the fluoride ion conductive fluoride is within the above range, an electrode having high ion conductivity can be formed.

[0117] (Conductive additive)

[0118] When the negative electrode composite material for fluoride ion secondary batteries of the present invention contains a conductive additive, the ratio of the conductive additive is preferably 5 to 25% by mass, more preferably 5 to 10% by mass, based on the entire negative electrode composite material for fluoride ion secondary batteries.

[0119] In the negative electrode composite material composite for a fluoride ion secondary battery of the present invention, when the ratio of the conductive auxiliary agent is within the above range, an electrode having high electron conductivity can be formed.

[0120] (Ratio of aluminum, metal fluoride, fluoride ion conductive fluoride and conductive additive)

[0121] In the negative electrode composite material composite for fluoride ion secondary battery of the present invention, the mass ratio of aluminum, metal fluoride, fluoride ion conductive fluoride and conductive auxiliary agent is preferably in the range of 1-25:0.4-25:70-90:5-25, and more preferably in the range of 1-13:0.4-13:80-90:5-10.

[0122] In the negative electrode composite material composite for a fluoride ion secondary battery of the present invention, when the mass ratio of aluminum, metal fluoride, fluoride ion conductive fluoride and conductive auxiliary agent is within the above range, the capacity per unit weight of the obtained fluoride ion secondary battery becomes large.

[0123] <Negative electrode for fluoride ion secondary battery>

[0124] The negative electrode for a fluoride ion secondary battery of the present invention is characterized by comprising the negative electrode composite material composite for a fluoride ion secondary battery of the present invention. As long as the negative electrode composite material composite for a fluoride ion secondary battery of the present invention is included, other configurations are not particularly limited.

[0125] <Fluoride ion secondary battery>

[0126] The fluoride ion secondary battery of the present invention comprises a fluoride ion secondary battery negative electrode comprising the fluoride ion secondary battery negative electrode composite material composite of the present invention, a solid electrolyte and a positive electrode. The fluoride ion secondary battery of the present invention has no particular limitation on other configurations as long as the negative electrode comprising the fluoride ion secondary battery negative electrode composite material composite of the present invention is used.

[0127] In the present invention, by selecting a positive electrode material that provides a sufficiently high standard electrode potential relative to the standard electrode potential of the negative electrode for a fluoride ion secondary battery comprising the negative electrode composite material composite for a fluoride ion secondary battery of the present invention, the characteristics as a fluoride ion secondary battery are high and the desired battery voltage can be achieved.

[0128] In particular, if a material without fluoride ions is selected as the positive electrode, a battery that is charge-initiated can be realized. That is, a battery can be manufactured in a discharge state with a low energy state, thereby improving the stability of the active material in the electrode.

[0129] Preferred positive electrodes for the fluoride ion secondary battery of the present invention include, for example, Cu, Bi, and Ag. Among these, Cu is particularly preferred because it is an inexpensive material.

[0130] <Method for producing negative electrode composite material for fluoride ion secondary battery>

[0131] The method for producing a composite negative electrode composite material for a fluoride ion secondary battery of the present invention includes a mixing step and a composite step.

[0132] [Mixing process]

[0133] The mixing step in the method for producing a negative electrode composite material for a fluoride ion secondary battery of the present invention is a step of mixing a negative electrode active material, a fluoride ion conductive fluoride and carbon black to obtain a negative electrode composite material mixture. In the present invention, the negative electrode active material contains aluminum and metal fluoride.

[0134] The aluminum and metal fluoride as the negative electrode active material, the fluoride ion conductive fluoride, and the carbon black as the conductive auxiliary agent are the same as described above. In addition, as long as aluminum, metal fluoride, fluoride ion conductive fluoride and carbon black are included as essential components, other substances may be arbitrarily blended.

[0135] The mixing method is not particularly limited, and the desired mass of each component can be measured and added into the same space simultaneously or successively to mix. In addition, when adding successively, the order is not particularly limited.

[0136] [Combination process]

[0137] The composite step is a step of pulverizing and mixing the negative electrode composite material mixture obtained in the mixing step to composite the negative electrode active material, fluoride ion conductive fluoride and carbon black to obtain a composite.

[0138] In the composite forming step, the negative electrode active material, the fluoride ion conductive fluoride and the carbon black constituting the negative electrode composite material mixture are alloyed.

[0139] Aluminum as the negative electrode active material is a relatively soft material, so due to the impact during the pulverization and mixing process, it is supported on the hard material fluoride ion conductive fluoride. In addition, it is generally believed that since it is a nanoparticle, it can be thermally diffused inside the composite by the heat during the pulverization and mixing process, resulting in alloying the composite.

[0140] The pulverization and mixing treatment for alloying and granulating the negative electrode composite material mixture is not particularly limited as long as the negative electrode composite material mixture can be pulverized and mixed under an inert atmosphere.

[0141] The pulverization and mixing treatment may be dry pulverization or wet pulverization. However, since the oxide film on the particle surface is peeled off during the pulverization and mixing treatment, an active surface is revealed. Therefore, dry pulverization under an inert atmosphere is preferred.

[0142] In the present invention, it is particularly preferred to use a ball mill to implement the pulverizing and mixing process. If it is a ball mill, since it is a closed type, a stable pulverizing and mixing process can be implemented in which the mixing ratio does not change during the pulverizing and dispersing process. Among them, a planetary ball mill is preferred because it has a large pulverizing power, can be finely pulverized, and can shorten the pulverizing time. There are no particular restrictions on the pulverizing and mixing conditions when using a ball mill, for example, it is set to 10 hours at 400rpm.

[0143] Example

[0144] Next, examples and the like of the present invention will be described, but the present invention is not limited to these examples and the like.

[0145] <Example 1>

[0146] In Example 1, aluminum and silver fluoride (AgF 2), CeBaF as a fluoride ion conductive fluoride 2.95 , acetylene black as a conductive additive, and a negative electrode composite material composite for fluoride ion secondary batteries was produced.

[0147] [Mixing process]

[0148] As shown in Table 1, weigh aluminum, silver fluoride (AgF 2 )、Ce 0.95 Ba 0.05 F 2.95 After weighing, Ce 0.95 Ba 0.05 F 2.95 and acetylene black were placed in a silicon nitride ball mill container (manufactured by Fritsch, Germany, internal volume: 80cc, PL-7 dedicated container), followed by aluminum and silver fluoride (AgF 2 ). Furthermore, 40 g of silicon nitride balls with a diameter of 2 mm were added, and the ball mill container was sealed.

[0149] [Combination process]

[0150] The sealed ball mill container was rotated at a rotation speed of 400 rpm for 10 hours to perform a pulverization and mixing treatment to obtain a negative electrode composite material composite for a fluoride ion secondary battery. After the pulverization and mixing treatment, the treated powder was recovered. The recovery rate is shown in Table 1.

[0151] [Table 1]

[0152]

[0153] <Comparative Example 1>

[0154] In addition to using the modified aluminum fluoride described in Japanese Patent Application No. 2018-059703 as the negative electrode active material to replace aluminum and silver fluoride (AgF 2 ), a negative electrode composite material for a fluoride ion secondary battery was obtained in the same manner as in Example 1.

[0155] The operation for obtaining modified aluminum fluoride is shown below. Table 1 shows the recovery rate of the obtained negative electrode composite material for fluoride ion secondary battery.

[0156] [Modified aluminum fluoride]

[0157] Using lithium (Li) metal, aluminum fluoride (AlF 3 ) to make modified aluminum fluoride.

[0158] (Weighing and premixing of raw materials)

[0159] Weigh aluminum fluoride (AlF 3) and lithium (Li) metal were added so that aluminum fluoride:lithium (molar ratio) was 90:10 and the total amount was 6.0 g. A mortar and pestle made of agate were used for pre-mixing for about 1 hour to obtain a raw material mixed powder.

[0160] In addition, aluminum fluoride (AlF 3 ) and lithium (Li) metal are highly reactive with water, so the weighing and premixing of the raw materials were carried out in a glove box (manufactured by (Stock) Miwa Manufacturing Co., Ltd., model DBO-1.5BNK-SQ1).

[0161] <Comparative Example 2>

[0162] In addition to not using silver fluoride (AgF 2 ), a negative electrode composite material composite for a fluoride ion secondary battery was obtained in the same manner as in Example 1 except that aluminum was used as the negative electrode active material.

[0163] <Evaluation of negative electrode composite material for fluoride ion secondary battery>

[0164] Various observations and evaluations were performed on the negative electrode composite materials for fluoride ion secondary batteries and the negative electrode composite materials for fluoride ion secondary batteries produced in Examples and Comparative Examples.

[0165] [X-ray diffraction pattern]

[0166] XRD (Rigaku, SmartLaB, Cu-Kα source, ), the negative electrode composite material composite for fluoride ion secondary battery prepared in Example 1, aluminum (Al), silver fluoride (AgF 2 )、CeBaF 2.95 (Expressed as CeBaF x ), the modified aluminum fluoride (AlF 3 ) was analyzed. The XRD pattern is shown in Figure 2 .

[0167] like Figure 2 As shown, no single peak of aluminum (Al) was confirmed in the negative electrode composite material composite for fluoride ion secondary batteries prepared in Example 1. Therefore, it is known that in the negative electrode composite material composite for fluoride ion secondary batteries prepared in Example 1, aluminum exists in an alloyed state.

[0168] <Production of fluoride ion secondary battery>

[0169] A fluoride ion secondary battery was produced using the following materials and by the following method.

[0170] [Negative electrode composite material powder]

[0171] The negative electrode composite material composites for fluoride ion secondary batteries or the negative electrode composite materials for fluoride ion secondary batteries prepared in the examples and comparative examples were used.

[0172] [Solid Electrolyte]

[0173] The solid electrolyte of tysonite is La 0.95 Ba 0.05 F 2.95 (LBF) LBF is a known compound (see Non-Patent Documents 5 to 7), and is prepared by the method described in Document 5.

[0174] Non-patent document 5: American Chemical Society - Applied Materials and Interfaces 2014, 6, 2103-2110 (ACS Appl. Mater. Interfaces 2014, 6, 2103-2110)

[0175] Non-patent document 6: Journal of Physical Chemistry C 2013, 117, 4943-4950 (J. Phys. Chem. C 2013, 117, 4943-4950)

[0176] Non-patent document 7: Journal of Physical Chemistry C 2014, 118, 7117-7129 (J. Phys. Chem. C 2014, 118, 7117-7129)

[0177] [Positive electrode composite material powder]

[0178] 63.7 mass % of lead fluoride powder (manufactured by High Purity Chemical Co., Ltd.), 29.6 mass % of tin fluoride (manufactured by High Purity Chemical Co., Ltd.), and 6.7 mass % of acetylene black (manufactured by Denka Co., Ltd.) were mixed in a ball mill and calcined at 400° C. for 1 hour in an argon atmosphere to prepare a positive electrode composite material powder.

[0179] [Method for producing fluoride ion secondary battery]

[0180] exist Figure 3 The method for making a fluoride ion secondary battery is shown in FIG. Figure 3As shown, using tablet forming devices (1a and 1b), battery material 3 is sequentially added into ceramic tube 2, and pressed from top to bottom at a pressure of 40 MPa, thereby producing a pellet-type cell formed by pressed powder. As battery material 3, gold foil (made of (stock) nilaco, 99.9+%, thickness: 10μm) as a negative electrode collector, 10mg of the above-mentioned negative electrode composite material powder, 200mg of solid electrolyte, 30mg of positive electrode composite material powder, and lead foil (made of (stock) nilaco, purity: 99.99%, thickness: 200μm) as a positive electrode collector are sequentially added.

[0181] exist Figure 4 A cross-sectional view of the fabricated fluoride ion secondary battery is shown in FIG. Figure 4 As shown, the manufactured pellet-type fluoride ion secondary battery has a positive electrode composite material layer 4, a solid electrolyte layer 5, and a negative electrode composite material layer 6 laminated in a state of being sandwiched by a tablet forming machine.

[0182] <Evaluation of fluoride ion secondary batteries>

[0183] [Constant current charge and discharge test]

[0184] The particle-type fluoride ion secondary battery obtained above was heated to 140°C in a vacuum environment, and an electrochemical reaction (charge and discharge reaction) was carried out. Specifically, a potentiogalvanostat device (Solartron, SI1287 / 1255B) was used, with a current of 0.02 mA for charging and 0.01 mA for discharging, and a lower limit voltage of -2.35V and an upper limit voltage of -0.1V. The fluoride ion secondary batteries prepared in Example 1 and Comparative Example 1 were applied from the charging current, and the fluoride ion secondary batteries prepared in Comparative Example 2 were applied from the discharging current, and a constant current charge and discharge test was carried out. The charge and discharge curves are shown in Figure 5 .

[0185] like Figure 5 As shown, the fluoride ion secondary battery using the negative electrode composite material composite for fluoride ion secondary batteries of the present invention has a small difference between the capacity during charge and the capacity during discharge even when charge and discharge are performed from the start of charge, and the reversibility of the electrochemical reaction is improved.

[0186] Reference numerals

[0187] 1a, 1b: Tablet former

[0188] 2: Ceramic tube

[0189] 3: Battery Materials

[0190] 4: Positive electrode composite material layer

[0191] 5: Solid electrolyte layer

[0192] 6: Negative electrode composite material layer

Claims

1. A negative electrode composite material for a fluoride ion secondary battery, comprising a negative electrode active material and a fluoride ion conductive fluoride, wherein: The negative electrode active material comprises aluminum and metal fluoride. The metal fluoride releases fluoride ions under battery reaction conditions and is composed of a metal having a voltage of 0 V or higher based on a standard hydrogen electrode.

2. The negative electrode composite material composite for a fluoride ion secondary battery according to claim 1, wherein: The aforementioned metal fluoride is silver fluoride.

3. The negative electrode composite material composite for a fluoride ion secondary battery according to claim 1, wherein: The average particle size of the aluminum is 10 to 200 nm.

4. The negative electrode composite material composite for a fluoride ion secondary battery according to claim 1, wherein: Also contains carbon black. 5 . A negative electrode for a fluoride ion secondary battery, comprising the negative electrode composite material composite for a fluoride ion secondary battery according to claim 1 . 6 . A fluoride ion secondary battery comprising the negative electrode for a fluoride ion secondary battery according to claim 5 , a solid electrolyte, and a positive electrode.

7. A method for producing a negative electrode composite material composite for a fluoride ion secondary battery, comprising: a mixing step of mixing the negative electrode active material, the fluoride ion conductive fluoride and the carbon black to obtain a negative electrode composite material mixture; and The composite step comprises: performing a pulverizing and mixing treatment on the negative electrode composite material mixture to composite the negative electrode active material, the fluoride ion conductive fluoride and the carbon black to obtain a composite; wherein, The negative electrode active material comprises aluminum and metal fluoride. The metal fluoride releases fluoride ions under battery reaction conditions and is composed of a metal having a voltage of 0 V or higher based on a standard hydrogen electrode.

8. The method for producing a negative electrode composite material for a fluoride ion secondary battery according to claim 7, wherein: The aforementioned metal fluoride is silver fluoride.

9. The method for producing a negative electrode composite material for a fluoride ion secondary battery according to claim 7, wherein: The average particle size of the aluminum is 10 to 200 nm.

10. The method for producing a negative electrode composite material for a fluoride ion secondary battery according to claim 7, wherein: The above-mentioned pulverization and mixing process is dry pulverization.

11. The method for producing a negative electrode composite material for a fluoride ion secondary battery according to claim 7, wherein: The pulverization and mixing process is performed using a ball mill.

Images