Negative electrode layer and fluoride ion secondary battery

Abstract

The present invention provides a negative electrode layer, which includes a negative electrode active material, a conductive additive, and a solid electrolyte. The aforementioned negative electrode active material contains a lanthanide fluoride doped with an alkaline earth metal fluoride. The aforementioned conductive additive contains a carbon material. The aforementioned solid electrolyte contains at least one of BaCaF4 and SrCaF4. Moreover, the aforementioned lanthanide fluoride doped with an alkaline earth metal fluoride and the aforementioned carbon material are compounded. The present invention also provides a fluoride ion secondary battery, which includes the negative electrode layer, an electrolyte, and a positive electrode layer.

Description

Technical Field

[0001] The present invention relates to a negative electrode layer and a fluoride ion secondary battery. Background Art

[0002] Conventionally, as a secondary battery having a high energy density, lithium ion secondary batteries have been widely popularized. A lithium ion secondary battery has a separator disposed between a positive electrode and a negative electrode, and is filled with an electrolytic solution.

[0003] Since the electrolytic solution of a lithium ion secondary battery usually contains a flammable organic solvent, there are sometimes safety problems with respect to heat.

[0004] Therefore, as an all-solid-state battery having a solid electrolyte layer disposed between a positive electrode layer and a negative electrode layer, a fluoride ion secondary battery is being studied.

[0005] Since lanthanide fluorides have a relatively low defluorination potential, their application to the negative electrode active material of a fluoride ion secondary battery is being studied.

[0006] For example, as a negative electrode current collector, a fluoride ion secondary battery having a lanthanide metal plate is known (for example, refer to Non-Patent Document 1). At this time, if the fluoride ion secondary battery is discharged, lanthanide fluoride is generated in the lanthanide metal plate, and the lanthanide fluoride functions as a negative electrode active material.

[0007] [Prior Art Documents]

[0008] (Non-Patent Document)

[0009] Patent Document 1: Adv. Funct. Mater. 2017, 27, 1701051 Summary of the Invention

[0010] [Problems to be Solved by the Invention]

[0011] However, there is a problem that the discharge capacity of a fluoride ion secondary battery is insufficient.

[0012] An object of the present invention is to provide a negative electrode layer that can improve the discharge capacity of a fluoride ion secondary battery.

[0013] [Technical Means for Solving the Problems]

[0014] One aspect of the present invention is a negative electrode layer including a negative electrode active material, a conductive assistant, and a solid electrolyte, wherein the negative electrode active material contains a lanthanide fluoride doped with an alkaline earth metal fluoride, the conductive assistant contains a carbon material, the solid electrolyte contains at least one of BaCaF4 and SrCaF4, and the lanthanide fluoride doped with an alkaline earth metal fluoride and the carbon material are compounded.

[0015] The aforementioned lanthanide fluoride may be one or more compounds selected from the group consisting of LaF3, CeF3, SmF3, and NdF3.

[0016] The aforementioned alkaline earth metal fluoride may be one or more compounds selected from the group consisting of CaF2, SrF2, and BaF2.

[0017] The aforementioned lanthanide fluoride doped with an alkaline earth metal fluoride may be selected from the group consisting of La 0.9 Ba 0.1 F 2.9 、Ce 0.95 Ba 0.05 F 2.95 、Ce 0.95 Sr 0.05 F 2.95 and Ce 0.95 Ca 0.05 F 2.95 and one or more compounds selected from the group consisting of.

[0018] The aforementioned solid electrolyte may also contain nanoparticles of at least one of BaCaF4 and SrCaF4.

[0019] Another aspect of the present invention is a fluoride ion secondary battery including the aforementioned negative electrode layer, electrolyte, and positive electrode layer.

[0020] (Effects of the Invention)

[0021] According to the present invention, a negative electrode layer can be provided that can increase the discharge capacity of a fluoride ion secondary battery. Description of the Drawings

[0022] Figure 1 is a graph showing the relationship between the ionic conductivities of Ce 0.95 Ba 0.05 F 2.95 and CeF3 with respect to the reciprocal of the absolute temperature.

[0023] Figure 2 is a graph showing the initial charge-discharge curves of the all-solid-state fluoride ion secondary batteries of Example 1 and Comparative Example 1.

[0024] Figure 3 is a graph showing the cycle characteristics of the all-solid-state fluoride ion secondary battery of Example 1.

[0025] Figure 4 is a graph showing the cycle characteristics of the all-solid-state fluoride ion secondary battery of Comparative Example 1. Detailed Description

[0026] Hereinafter, embodiments of the present invention will be described.

[0027] <Negative electrode layer>

[0028] The negative electrode layer of this embodiment includes a negative electrode active material, a conductive additive, and a solid electrolyte, and is used for a fluoride ion secondary battery. Here, the negative electrode active material contains a lanthanide fluoride doped with an alkaline earth metal fluoride, the conductive additive contains a carbon material, and the solid electrolyte contains at least one of BaCaF4 and SrCaF4. Further, the lanthanide fluoride doped with an alkaline earth metal fluoride and the carbon material are compounded. That is, the negative electrode layer of this embodiment includes a composite of a lanthanide fluoride doped with an alkaline earth metal fluoride and a carbon material (hereinafter, also referred to as a composite of a lanthanide fluoride and a carbon material).

[0029] Since the negative electrode layer of this embodiment contains a lanthanide fluoride doped with an alkaline earth metal fluoride, the ion conductivity is improved. Further, since the negative electrode layer of this embodiment contains a composite of a lanthanide fluoride and a carbon material, the electron conductivity is improved. In addition, since the negative electrode layer of this embodiment contains at least one of BaCaF4 and SrCaF4, the defluorination potential is low. Therefore, the discharge capacity is increased when the negative electrode layer of this embodiment is applied to an all-solid-state fluoride ion secondary battery.

[0030] [Negative electrode active material]

[0031] The negative electrode active material contains a lanthanide fluoride doped with an alkaline earth metal fluoride.

[0032] The lanthanide fluoride is not particularly limited, and examples thereof include LaF3, CeF3, SmF3, NdF3, etc., and two or more thereof may be used in combination.

[0033] The alkaline earth metal fluoride for doping the lanthanide fluoride is not particularly limited as long as it has ion conductivity, and examples thereof include CaF2, SrF2, BaF2, etc., and two or more thereof may be used in combination.

[0034] Examples of the lanthanide fluoride doped with an alkaline earth metal fluoride include La 0.9 Ba 0.1 F 2.9 , Ce 0.95 Ba 0.05 F 2.95 , Ce 0.95 Sr 0.05 F 2.95 , Ce 0.95 Ca 0.05 F 2.95 etc., and two or more thereof may be used in combination.

[0035] The negative electrode active material may further include a negative electrode active material other than the lanthanide fluoride doped with an alkaline earth metal fluoride.

[0036] As the negative electrode active material other than the lanthanide fluoride doped with an alkaline earth metal fluoride, any negative electrode active material that can be used in a fluoride ion secondary battery may be used, and there is no particular limitation.

[0037] [Conductive aid]

[0038] The conductive aid contains a carbon material, and the carbon material may be carbon black.

[0039] Examples of the carbon black include furnace black, Ketjen black, acetylene black, etc., and two or more kinds may be used in combination.

[0040] The conductive aid may further include a conductive aid other than the carbon material.

[0041] As the conductive aid other than the carbon material, any conductive aid that can be used in a fluoride ion secondary battery may be used, and there is no particular limitation.

[0042] [Composite of lanthanide fluoride and carbon material]

[0043] In the composite of lanthanide fluoride and carbon material, for example, at least a part of the surface of the lanthanide fluoride particles is coated with a carbon material.

[0044] The particle size of the composite of lanthanide fluoride and carbon material is preferably 10 μm or less, more preferably 5 μm or less. If the particle size of the composite of lanthanide fluoride and carbon material is 10 μm or less, the ionic conductivity and electronic conductivity are improved.

[0045] From the aspect of the balance between ionic conductivity and electronic conductivity, the mass ratio of the carbon material to the lanthanide fluoride doped with an alkaline earth metal fluoride is preferably 3% by mass or more and 20% by mass or less.

[0046] The content of the composite of lanthanide fluoride and carbon material in the negative electrode layer of the present embodiment is preferably 60% by mass or more and 70% by mass or less. If the content of the composite of lanthanide fluoride and carbon material in the negative electrode layer of the present embodiment is 60% by mass or more and 70% by mass or less, the discharge capacity when the negative electrode layer of the present embodiment is applied to an all-solid-state fluoride ion secondary battery is increased.

[0047] [Method for manufacturing composite of lanthanide fluoride and carbon material]

[0048] A method for manufacturing a composite of a lanthanide fluoride and a carbon material (hereinafter, also referred to as a composite) includes: a first step of obtaining a lanthanide fluoride-alkaline earth metal fluoride mixed powder; a second step of mixing the lanthanide fluoride-alkaline earth metal fluoride mixed powder with a carbon material to obtain a composite precursor; and a third step of calcining the composite precursor to obtain a composite.

[0049] The first step is a step of mixing a lanthanide fluoride and an alkaline earth metal fluoride to obtain a lanthanide fluoride-alkaline earth metal fluoride mixed powder. That is, by mixing a lanthanide fluoride and an alkaline earth metal fluoride, the solid-phase diffusion distance of elements from the lanthanide fluoride and the alkaline earth metal fluoride can be shortened during calcination. And after calcination, a lanthanide fluoride-alkaline earth metal fluoride mixed powder without residual crystal structures of the lanthanide fluoride and the alkaline earth metal fluoride can be obtained.

[0050] As a method for mixing a lanthanide fluoride and an alkaline earth metal fluoride, there is no particular limitation, and either a dry method or a wet method can be used. For example, a method of mixing using a mortar can be cited.

[0051] In addition, conditions such as the temperature and time for mixing the lanthanide fluoride and the alkaline earth metal fluoride can be appropriately set.

[0052] And in the first step, the lanthanide fluoride-alkaline earth metal fluoride mixed powder can also be pulverized.

[0053] As a method for pulverizing the lanthanide fluoride-alkaline earth metal fluoride mixed powder, for example, a method of pulverizing using a ball mill can be cited.

[0054] The second step is a step of mixing the lanthanide fluoride-alkaline earth metal fluoride mixed powder obtained in the first step with a carbon material to obtain a composite precursor.

[0055] The manufacturing method of the composite implements the second step at the stage prior to the third step, and mixes the carbon material in the lanthanide fluoride-alkaline earth metal fluoride mixed powder in advance. Thus, a composite precursor in which the carbon material is disposed on the surface of the lanthanide fluoride-alkaline earth metal fluoride mixed powder is obtained.

[0056] Therefore, in the third step, by calcining the composite precursor, a composite in which at least a part of the surface of the lanthanide fluoride particles doped with the alkaline earth metal fluoride is coated with the carbon material can be obtained.

[0057] In addition, in the second step, by disposing a carbon material on the surface of the lanthanide fluoride-alkaline earth metal fluoride mixed powder, coarsening of the particle diameter caused by particle growth or fusion of particle interfaces of the lanthanide fluoride-alkaline earth metal fluoride mixed powder during the crystallization process in the third step is suppressed, and thus a composite material that substantially maintains the particle diameter of the lanthanide fluoride-alkaline earth metal fluoride mixed powder can be obtained.

[0058] In the second step, as a method for mixing the lanthanide fluoride-alkaline earth metal fluoride mixed powder and the carbon material, there is no particular limitation, and either a dry method or a wet method can be used. Examples thereof include a method of mixing using a mortar.

[0059] In addition, when mixing the lanthanide fluoride-alkaline earth metal fluoride mixed powder and the carbon material, shearing is preferably applied.

[0060] Furthermore, conditions such as the temperature for mixing the lanthanide fluoride-alkaline earth metal fluoride mixed powder and the carbon material can be appropriately set.

[0061] In addition, in the second step, the composite precursor can also be pulverized.

[0062] Examples of the method for pulverizing the composite precursor include a method of pulverizing using a ball mill, a method of pulverizing using a mortar, and the like.

[0063] The third step is a step of calcining the composite precursor obtained in the second step to obtain a composite material.

[0064] In the second step, by obtaining a composite precursor having a carbon material disposed on the surface of the lanthanide fluoride-alkaline earth metal fluoride mixed powder, coarsening of the particle diameter caused by particle growth or fusion of particle interfaces of the lanthanide fluoride-alkaline earth metal fluoride mixed powder during the crystallization process in the third step is suppressed. As a result, a composite material that substantially maintains the particle diameter of the composite precursor can be obtained.

[0065] In addition, the conditions for calcining the composite precursor can be appropriately set.

[0066] In addition, in the third step, the composite material can also be pulverized.

[0067] Examples of the method for pulverizing the composite material include a method of pulverizing using a mortar.

[0068] [Solid electrolyte]

[0069] The solid electrolyte contains at least one of BaCaF4 and SrCaF4, preferably including nanoparticles of at least one of BaCaF4 and SrCaF4. Thus, it is easy to ensure the ion conduction path, thereby increasing the discharge capacity when the negative electrode layer of the present embodiment is applied to an all-solid-state fluoride ion secondary battery.

[0070] The particle size of the nanoparticles of at least one of BaCaF4 and SrCaF4 is, for example, 30 nm or more and 200 nm or less.

[0071] From the aspect of the balance between ion conductivity and defluorination potential, the total amount of BaCaF4 and SrCaF4 relative to the mass ratio of cerium fluoride doped with alkaline earth metal fluoride is preferably 0.36 or more and 0.92 or less.

[0072] The solid electrolyte may also contain a solid electrolyte other than BaCaF4 and SrCaF4.

[0073] As the solid electrolyte other than BaCaF4 and SrCaF4, any solid electrolyte that can be used in a fluoride ion secondary battery may be used, and there is no particular limitation.

[0074] <Fluoride ion secondary battery>

[0075] The fluoride ion secondary battery of the present embodiment includes the negative electrode layer, electrolyte, and positive electrode layer of the present embodiment.

[0076] [Electrolyte]

[0077] The electrolyte may be an electrolytic solution, a solid electrolyte, or a gel-like electrolyte. Moreover, the solid electrolyte or gel-like electrolyte may be organic or inorganic.

[0078] As the solid electrolyte, a well-known solid electrolyte may be used. For example, as the solid electrolyte, the solid electrolyte contained in the negative electrode layer of the present embodiment may be used.

[0079] In addition, when a solid electrolyte is used as the electrolyte, the fluoride ion secondary battery of the present embodiment is an all-solid-state fluoride ion secondary battery. In the all-solid-state fluoride ion secondary battery, for example, a positive electrode current collector, a positive electrode layer, a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector are arranged in sequence.

[0080] [Positive electrode layer]

[0081] The positive electrode layer includes, for example, a positive electrode active material, a solid electrolyte, and a conductive assistant. At this time, it is preferable to use a positive electrode layer that can obtain a standard electrode potential sufficiently high with respect to the standard electrode potential of the negative electrode layer of the present embodiment.

[0082] Examples of the positive electrode active material include, for example, Pb, Cu, Sn, Bi, Ag, etc.

[0083] Examples of the solid electrolyte include, for example, PbSnF4, Ce 1-x Ba x F 3-x etc.

[0084] Examples of the conductive additive include, for example, carbon materials, etc.

[0085] [Positive current collector and negative current collector]

[0086] Examples of the positive current collector include, for example, a lead plate, an aluminum foil, etc. Also, examples of the negative current collector include, for example, a gold foil, etc.

[0087] [Examples]

[0088] Examples of the present invention will be described below, but the present invention is not limited to the examples.

[0089] [Example 1]

[0090] A all-solid-state fluoride ion secondary battery was fabricated using the following method. Additionally, unless otherwise specified, each step was carried out inside a purge type glove box DBO-1.5B (manufactured by Miwa Mfg Co., Ltd.) equipped with an argon circulation purification device.

[0091] [Fabrication of Ce 0.95 Ba 0.05 F 2.95 -AB composite]

[0092] (First step)

[0093] 8.598 g of CeF3 powder (manufactured by Sigma-Aldrich, purity 99.99%) and 0.402 g of BaF2 powder (manufactured by Kojundo Chemical Laboratory Co., Ltd., purity 99.9%) were weighed, and then mixed using an agate mortar and pestle for 5 - 10 minutes to obtain a CeF3-BaF2 mixed powder.

[0094] The CeF3-BaF2 mixed powder and 20 silicon nitride grinding balls with a diameter of 10 mm (manufactured by Fritsch) were put into an 80 cc silicon nitride Premium-Line PL-7 special container (manufactured by Fritsch) used as a ball mill jar, and then sealed.

[0095] After removing the sealed ball mill jar to the outside of the glove box, pulverization treatment is performed using a ball mill. At this time, the pulverization treatment conditions are as described below.

[0096] Rotation speed: 800 rpm

[0097] Pulverization treatment time: 60 minutes

[0098] Number of pulverization treatments: 40 times

[0099] Pause time between pulverization treatments: 5 minutes

[0100] Reverse rotation: ON

[0101] After moving the ball mill jar into the glove box, the CeF3-BaF2 mixed powder is recovered from the inside of the ball mill jar.

[0102] (Second step)

[0103] 500 mg of the CeF3-BaF2 mixed powder is mixed with 36 mg of DENKA BLACK (manufactured by Denka Company Limited), which is acetylene black (AB), using an agate mortar and pestle to obtain a Ce 0.95 Ba 0.05 F 2.95 -AB composite precursor.

[0104] The Ce 0.95 Ba 0.05 F 2.95 -AB composite precursor, 20 zirconia grinding balls with a diameter of 10 mm (manufactured by Fritsch), and 20 silicon nitride grinding balls with a diameter of 10 mm (manufactured by Fritsch) are put into an 80 cc silicon nitride Premium-Line PL-7 special container (manufactured by Fritsch) as the ball mill jar, and then sealed.

[0105] After removing the sealed ball mill jar to the outside of the glove box, pulverization treatment is performed using a ball mill. At this time, the pulverization treatment conditions are as described below.

[0106] Rotation speed: 800 rpm

[0107] Pulverization treatment time: 60 minutes

[0108] Number of pulverization treatments: 40 times

[0109] Pause time between pulverization treatments: 5 minutes

[0110] Reverse rotation: ON

[0111] After moving the ball milling jar into the interior of the glove box, Ce is recovered from the interior of the ball milling jar. 0.95 Ba 0.05 F 2.95 -AB complex precursor. Using an agate mortar and pestle, the recovered Ce 0.95 Ba 0.05 F 2.95 -AB complex precursor is pulverized for 5 to 10 minutes.

[0112] (Third step)

[0113] Transfer the Ce 0.95 Ba 0.05 F 2.95 -AB complex precursor into an alumina crucible, and then calcine it using a small electric furnace KSL-1100X (manufactured by MTI Corporation) to obtain Ce 0.95 Ba 0.05 F 2.95 -AB complex. At this time, the calcination conditions are as described below.

[0114] Flow rate of argon: 300 cc / min

[0115] Heating rate: 184 °C / h

[0116] Highest temperature reached: 1100 °C

[0117] Retention time at the highest temperature reached: 1 hour

[0118] Cooling rate: Uncontrolled

[0119] Cooling method: Natural cooling

[0120] Recover Ce from the interior of the alumina crucible 0.95 Ba 0.05 F 2.95 -AB complex, and then pulverize it using an agate mortar and pestle for 5 to 10 minutes.

[0121] [Production of BaCaF4]

[0122] (Premixing)

[0123] Weigh 690 mg of barium fluoride powder (manufactured by High Purity Chemical Research Institute, purity 99%) and 310 mg of calcium fluoride powder (manufactured by High Purity Chemical Research Institute, purity 99.9%), and then premix them using an agate mortar and pestle for about 1 hour to obtain BaF2-CaF2 mixed powder.

[0124] (Aerosol treatment)

[0125] After removing the sealed powder hopper containing the BaF2-CaF2 mixed powder to the outside of the glove box, it is connected to the high-frequency induction thermal plasma nanoparticle synthesis device TP-40020NPS (manufactured by JEOL Ltd.).

[0126] Argon is supplied to the plasma torch, and the BaF2-CaF2 mixed powder is dissolved into a BaF2-CaF2 melt using thermal plasma. Then, the BaF2-CaF2 melt is spray atomized into the chamber under reduced pressure. The BaF2-CaF2 melt spray atomized into the chamber is cooled and nanoparticulated to form BaCaF4. Next, the BaCaF4 is captured by the exhaust filter downstream of the device. Then, after blocking the upstream and downstream of the exhaust filter with a valve, it is moved into the glove box to recover the BaCaF4.

[0127] [Preparation of the powder composition for the negative electrode layer]

[0128] 536 mg of Ce 0.95 Ba 0.05 F 2.95 -AB complex, 464 mg of BaCaF4, and 40 g of silicon nitride grinding balls with a diameter of 2 mm (manufactured by Fritsch) are put into a 45 cc silicon nitride Premium-Line PL-7 special container (manufactured by Fritsch) as a ball mill jar, and then it is sealed.

[0129] After moving the sealed ball mill jar to the outside of the glove box, a grinding process is performed using a ball mill. The grinding process conditions are as follows.

[0130] Rotation speed: 200 rpm

[0131] Grinding time: 15 minutes

[0132] Number of grinding times: 10 times

[0133] Pause time between grinding processes: 5 minutes

[0134] Reverse rotation: ON

[0135] After moving the ball mill jar into the glove box, the powder composition for the negative electrode layer is recovered from the inside of the ball mill jar.

[0136] [Preparation of the powder for the positive electrode layer (PbSnF4-AB complex)]

[0137] 63.7 mass% of lead fluoride powder (manufactured by the Institute of High Purity Chemistry), 29.6 mass% of tin fluoride powder (manufactured by the Institute of High Purity Chemistry), and 6.7 mass% of acetylene black (manufactured by Denka Co., Ltd.) were mixed using a ball mill and then calcined at 400 °C for 1 hour in an argon atmosphere to produce a PbSnF4-AB composite.

[0138] [Powder for solid electrolyte layer]

[0139] The powder for the solid electrolyte layer is BaCaF4 used when preparing the powder composition for the negative electrode layer.

[0140] [Fabrication of all-solid-state fluoride ion secondary battery]

[0141] Pressing was carried out using a tablet press at a pressure of 40 MPa, thereby fabricating a cylindrical pellet-type battery after powder compaction. Specifically, a 20-μm-thick gold foil (manufactured by Nilaco Co., Ltd., purity 99.99%) as the negative electrode current collector, 10 mg of the powder composition for the negative electrode layer, 40 mg of the powder for the solid electrolyte layer, 20 mg of the powder for the positive electrode layer, a 200-μm-thick lead plate (manufactured by Nilaco Co., Ltd., purity 99.99%) as the positive electrode active material and the positive electrode current collector, and a 20-μm-thick aluminum foil (manufactured by Nilaco Co., Ltd., purity 99+%) as the positive electrode current collector were sequentially inserted into the tablet press to fabricate the pellet-type battery.

[0142] [Comparative Example 1]

[0143] The powder composition for the negative electrode layer was prepared according to the following method, and the all-solid-state fluoride ion secondary battery was fabricated in the same manner as in Example 1 except for this.

[0144] [Fabrication of powder composition for negative electrode layer]

[0145] 500 mg of CeF3 powder (manufactured by Sigma-Aldrich Co., Ltd., purity 99.99%), 36 mg of Denka Black as AB (manufactured by Denka Co., Ltd.), 464 mg of BaCaF4, and 40 g of silicon nitride grinding balls with a diameter of 2 mm (manufactured by Fritsch Co., Ltd.) were put into a 45-cc silicon nitride Premium-Line PL-7 special container (manufactured by Fritsch Co., Ltd.) as a ball mill jar and then sealed.

[0146] After moving the sealed ball mill jar outside the glove box, comminution treatment was carried out using a ball mill. At this time, the comminution treatment conditions are as described below.

[0147] Rotation speed: 200 rpm

[0148] Pulverization processing time: 15 minutes

[0149] Number of pulverization processes: 10 times

[0150] Pause time between pulverization processes: 5 minutes

[0151] Reverse rotation: ON

[0152] After moving the ball mill jar into the glove box, recover the powder composition for the negative electrode layer from the inside of the ball mill jar.

[0153] [Particle size of the powder]

[0154] (Ce 0.95 Ba 0.05 F 2.95 -AB composite particle size)

[0155] After taking pictures of the powder using a scanning electron microscope SU-6600 (manufactured by Hitachi High-Technologies Corporation, Japan), measure the length of the powder in the SEM images of multiple fields of view, and set it as the particle size.

[0156] (Particle size of BaCaF4)

[0157] After measuring the specific surface area of the powder using a fully automatic specific surface area measuring device Macsorb HM Model-1208 (manufactured by Mountech), calculate the particle size based on the specific surface area and true density of the powder.

[0158] As a result, the particle sizes of Ce 0.95 Ba 0.05 F 2.95 -AB composite and BaCaF4 are 50 μm and 110 nm respectively.

[0159] [Ionic conductivities of Ce 0.95 Ba 0.05 F 2.95 and CeF3]

[0160] Use a tablet press to press at a pressure of 40 MPa, thereby producing a cylindrical pellet-shaped battery after powder compaction molding. At this time, use Ce 0.95 Ba 0.05 F 2.95 or CeF3 as the negative electrode active material. Next, use an impedance analyzer 1255B / 1296A (manufactured by Solartron) and use the AC impedance method to measure the ionic conductivities of Ce 0.95 Ba 0.05 F 2.95 and CeF3.

[0161] In addition, in Example 1, Ce 0.95 Ba 0.05 F 2.95 -AB composite was used as the composite of the negative electrode active material and the conductive additive. Therefore, the ionic conductivity of Ce 0.95 Ba 0.05 F 2.95 was compared with the ionic conductivity of CeF3.

[0162] In Figure 1 the relationship between the ionic conductivity of Ce 0.95 Ba 0.05 F 2.95 and CeF3 with respect to the reciprocal of the absolute temperature is shown.

[0163] Moreover, in Table 1, the measurement results of the density and the ionic conductivity at 140 °C of Ce 0.95 Ba 0.05 F 2.95 and CeF3 are shown.

[0164] [Table 1]

[0165] <![CDATA[Ce 0.95 Ba 0.05 F 2.95 > <![CDATA[CeF3]]> Density [g / cc] 5.4 4.7 Ionic conductivity [S / cm] <![CDATA[5.4×10 -4 > <![CDATA[2.4×10 -8 >

[0166] From Figure 1 and Table 1, it can be seen that the ionic conductivity of Ce 0.95 Ba 0.05 F 2.95 is higher than that of CeF3.

[0167] [Charge and Discharge Test]

[0168] A constant current charge and discharge test of the all-solid-state fluoride ion secondary battery was carried out. Specifically, using the potentiostat-galvanostat device SI1287 / 1255B (manufactured by Transpower Co., Ltd.), in a vacuum and at an environment temperature of 140 °C, the current during charge and discharge was set to 0.04 mA, the lower limit voltage was set to -2.7 V, and the upper limit voltage was set to -0.5 V. Starting from charging, the constant current charge and discharge test was carried out.

[0169] In Figure 2 the initial charge and discharge curves of the all-solid-state fluoride ion secondary batteries of Example 1 and Comparative Example 1 are shown.

[0170] From Figure 2 it can be seen that the charge and discharge capacity of the all-solid-state fluoride ion secondary battery of Example 1 is higher than that of the all-solid-state fluoride ion secondary battery of Comparative Example 1.

[0171] [Cycling Test]

[0172] Perform a cycle test on the all-solid-state fluoride ion secondary battery. Specifically, in the same manner as described above, continuously perform a constant current charge-discharge test on the all-solid-state fluoride ion secondary battery for five cycles.

[0173] In Figure 3 and Figure 4 the cycle characteristics of the all-solid-state fluoride ion secondary batteries of Example 1 and Comparative Example 1 are shown, respectively.

[0174] From Figure 3 and Figure 4 it can be seen that the discharge capacity of the all-solid-state fluoride ion secondary battery of Example 1 is higher than that of the all-solid-state fluoride ion secondary battery of Comparative Example 1.

Claims

1. A negative electrode layer, comprising a negative electrode active material, a conductive additive, and a solid electrolyte, The aforementioned negative electrode active material contains a lanthanide fluoride doped with an alkaline earth metal fluoride, The aforementioned conductive additive contains a carbon material, The aforementioned solid electrolyte contains at least one of BaCaF4 and SrCaF4, The aforementioned alkaline earth metal fluoride is CaF2, SrF2, or BaF2, and The aforementioned lanthanide fluoride doped with an alkaline earth metal fluoride and the aforementioned carbon material are compounded.

2. The negative electrode layer according to claim 1, wherein The aforementioned lanthanide fluoride is one or more compounds selected from the group consisting of LaF3, CeF3, SmF3, and NdF3.

3. The negative electrode layer according to claim 1, wherein, The above-mentioned lanthanide fluoride doped with alkaline earth metal fluoride is selected from the group consisting of La 0.9 Ba 0.1 F 2.9 、Ce 0.95 Ba 0.05 F 2.95 、Ce 0.95 Sr 0.05 F 2.95 and Ce 0.95 Ca 0.05 F 2.95 and more than one compound in the group composed of 4. The negative electrode layer according to claim 1, wherein, The aforementioned solid electrolyte contains nanoparticles of at least one of BaCaF4 and SrCaF4.

5. A fluoride ion secondary battery, comprising the negative electrode layer, an electrolyte, and a positive electrode layer according to claim 1.

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