JP7608966B2 - Fluoride ion battery and manufacturing method thereof - Google Patents

Description

This disclosure relates to a fluoride ion battery and a method for manufacturing the same.

For example, Li-ion batteries are known as high-voltage, high-energy density batteries. Li-ion batteries are cation-based batteries that utilize the reaction between Li ions and a positive electrode active material and the reaction between Li ions and a negative electrode active material. On the other hand, fluoride-ion batteries that utilize the reaction of fluoride ions (fluoride anions) are known as anion-based batteries. For example, Patent Document 1 discloses a fluoride-ion battery that uses a positive electrode active material material that contains at least one of Ag, Co, Mn, Cu, W, and V, and a fluoride that coats the active material.

JP 2018-063905 A

Copper (Cu), which is used as the positive electrode active material in fluoride ion batteries, has the advantage that it is easy to improve the energy density because it is capable of two-electron reactions. However, Cu tends to aggregate and become coarse during charging and discharging, so the fluorination reaction does not progress to the inside during charging, and sufficient capacity characteristics may not be obtained.

This disclosure was made in consideration of the above-mentioned circumstances, and its main objective is to provide a fluoride ion battery with good capacity characteristics.

The present disclosure provides a fluoride ion battery including a positive electrode active material layer containing a Cu-based active material and _BiF3 .

According to the present disclosure, since the positive electrode active material layer contains a Cu-based active material and _BiF3 , a fluoride ion battery with good capacity characteristics is obtained.

In the above disclosure, the positive electrode active material layer may contain composite particles in which the Cu-based active material is coated with the _BiF3 .

In the above disclosure, the molar ratio of Cu to Bi (Cu/Bi) in the positive electrode active material layer may be 1 or more and 3 or less.

In the above disclosure, the Cu-based active material may contain Cu as the main component of the metal element.

In the above disclosure, the Cu-based active material may further contain F.

In the above disclosure, the average particle size of the Cu-based active material may be 100 nm or less.

The present disclosure also provides a method for producing a fluoride ion battery, the method including: forming a precursor layer containing a Cu-based active material and Bi; and introducing fluoride ions into the precursor layer to form a cathode active material layer containing a Cu-based active material and _BiF3 .

According to the present disclosure, a positive electrode active material containing a Cu-based active material and _BiF3 is formed, so that a fluoride ion battery with good capacity characteristics can be obtained.

The present disclosure has the effect of providing a fluoride ion battery with good capacity characteristics.

FIG. 1 is a schematic cross-sectional view illustrating a fluoride ion battery according to the present disclosure. FIG. 1 is a schematic cross-sectional view illustrating a fluoride ion battery according to the present disclosure. FIG. 1 is an explanatory diagram for explaining a problem of Cu. FIG. 2 is a schematic cross-sectional view illustrating the relationship between a Cu-based active material and _BiF3 in a positive electrode active material layer. 1A to 1C are schematic cross-sectional views illustrating a method for manufacturing a fluoride ion battery in the present disclosure. 1 shows the results of TEM-EDX measurement of the CuBi nanoparticles (before the first charge) obtained in Example 1. 1 shows the results of TEM-EDX measurement of the CuBi nanoparticles (after the first charge) obtained in Example 1. 4 shows the results of a charge/discharge test on the evaluation cell obtained in Example 1. 1 shows the results of a charge/discharge test on the evaluation cell obtained in Comparative Example 1. 1 shows the results of a charge/discharge test on the evaluation cell obtained in Comparative Example 2.

The fluoride ion battery and its manufacturing method in this disclosure are described in detail below.

A. Fluoride-ion battery Fig. 1 is a schematic cross-sectional view illustrating a fluoride-ion battery in the present disclosure. The fluoride-ion battery 10 shown in Fig. 1 has a positive electrode active material layer 1, a negative electrode active material layer 2, an electrolyte layer 3 arranged between the positive electrode active material layer 1 and the negative electrode active material layer 2, a positive electrode current collector 4 that collects current from the positive electrode active material layer 1, and a negative electrode current collector 5 that collects current from the negative electrode active material layer 2. In the present disclosure, the positive electrode active material layer 1 contains at least a Cu-based active material and _BiF3 .

FIG. 2 is a schematic cross-sectional view illustrating a fluoride ion battery in the present disclosure, showing a battery in which a negative electrode active material layer is self-formed by charging. The fluoride ion battery 10 shown in FIG. 2(a) does not have a negative electrode active material layer between the electrolyte layer 3 and the negative electrode current collector 5, and the electrolyte layer 3 and the negative electrode current collector 5 are in direct contact with each other. The electrolyte layer 3 contains a metal fluoride (e.g., Pb _2-x Sn _x F ₄ ) containing two or more metal elements as a solid electrolyte. In the fluoride ion battery 10 shown in FIG. 2(a), a defluorination reaction of the metal fluoride occurs at the interface between the electrolyte layer 3 and the negative electrode current collector 5 during the initial charge, and a negative electrode active material (e.g., Pb) is generated. As a result, the negative electrode active material layer 2 is self-formed as shown in FIG. 2(b).

According to the present disclosure, the positive electrode active material layer contains Cu-based active material and BiF ₃ , so that the fluoride ion battery has good capacity characteristics. As described above, copper (Cu) used as the positive electrode active material of the fluoride ion battery is capable of two-electron reaction (two electrons react with one Cu), and therefore has the advantage of being easy to improve the energy density. On the other hand, when Cu is fluorinated, CuF ₂ is generated, but CuF ₂ does not have electronic conductivity and has low fluoride ion conductivity. Therefore, as shown in FIG. 3, if the particle size of Cu is large, the fluorination reaction does not proceed to the inside during charging. Therefore, it is preferable that the particle size of Cu is small, and particularly preferably nano-sized.

In addition, Cu is likely to aggregate and become coarse during charging and discharging. Specifically, when Cu becomes _CuF2 , the volume expands to a maximum of 1.5 times, but when the expanded Cu particles come into contact with each other, it is thought that they change into spherical lumps to reduce the surface tension. Therefore, even if nano-sized Cu is used, if coarsening occurs, the fluorination reaction will not progress to the inside during charging. In contrast, in the present disclosure, the presence of _BiF3 around Cu can suppress the coarsening of particles. As a result, a fluoride ion battery with good capacity characteristics is obtained.

The reason why the presence of BiF ₃ can suppress the coarsening of particles is presumed to be because the presence of BiF ₃ can reduce the frequency of contact between Cu particles. Furthermore, since BiF ₃ has a higher fluoride ion conductivity than CuF ₂ , even when the reaction temperature is low, for example, charging and discharging proceeds smoothly and the capacity characteristics are improved. That is, the fluoride ion battery in the present disclosure has the advantage of having good capacity characteristics at relatively low temperatures (for example, 60 ° C.). In addition, since the fluorination/defluorination potential of Bi is lower than the fluorination/defluorination potential of Cu, when Cu functions as an active material, it can always exist as BiF ₃ , and the above effect can be stably exerted. Furthermore, since Bi can exist stably as a single element, it also has the advantage of being easy to synthesize CuBi nanoparticles, which will be described later.

1. Positive electrode active material layer The positive electrode active material layer in the present disclosure is a layer containing a Cu-based active material and _BiF3 . The Cu-based active material contains at least Cu. The Cu-based active material may contain only Cu as a metal element, or may contain other metals in addition to Cu. Examples of other metals include alkali metals, alkaline earth metals, transition metals, and lanthanoid metals. In addition, the Cu-based active material may contain Pb or may not contain Pb.

The Cu-based active material preferably contains Cu as the main metal element. "Containing Cu as the main metal element" means that the molar ratio of Cu is the highest among all metal elements in the Cu-based active material. The ratio of Cu to all metal elements in the Cu-based active material may be, for example, 50 mol% or more, 70 mol% or more, or 90 mol% or more. The ratio of metal elements in the Cu-based active material can be confirmed, for example, by performing high-frequency inductively coupled plasma (ICP) emission spectroscopy.

The Cu-based active material may or may not contain F. The Cu-based active material can be expressed, for example, as CuF _x (0≦x≦2), where x varies depending on the state of charge (SOC) of the fluoride ion battery.

The shape of the Cu-based active material is preferably particulate. The average particle size (D ₅₀ ) of the Cu-based active material is, for example, 100 nm or less, and may be 65 nm or less. If the average particle size of the Cu-based active material is too large, the fluorination reaction does not proceed to the inside during charging, and sufficient capacity characteristics may not be exhibited. On the other hand, the average particle size (D ₅₀ ) of the Cu-based active material is, for example, 10 nm or more, and may be 20 nm or more. If the average particle size of the Cu-based active material is too small, its production may be difficult. The average particle size (D ₅₀ ) can be measured, for example, by observation with a scanning electron microscope (SEM) (for example, n≧100). It can also be calculated from the measured value of the BET specific surface area. Note that when Cu becomes CuF ₂ , the volume expands to a maximum of 1.5 times. In consideration of this point, the average particle size (D ₅₀ ) of the Cu-based active material that does not contain F is preferably, for example, 65 nm or less.

The content of Cu-based active material in the positive electrode active material layer is, for example, 30% by weight or more, or may be 50% by weight or more, or may be 70% by weight or more.

BiF ₃ usually functions as a coarsening inhibitor for the Cu-based active material. For example, as shown in FIG. 4(a), BiF ₃ may cover the Cu-based active material. That is, the positive electrode active material layer may contain composite particles in which the Cu-based active material is covered with BiF _3. The coverage of the surface of the Cu-based active material with BiF ₃ may be, for example, 20% or more, 50% or more, or 70% or more. On the other hand, the coverage of BiF ₃ may be 100%. Examples of methods for measuring the coverage include transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The average thickness of BiF ₃ in the composite particles is, for example, 0.5 nm or more, 1 nm or more, or 10 nm or more. On the other hand, the average thickness of BiF ₃ in the composite particles is, for example, 30 nm or less, or 20 nm or less. Methods for measuring the average thickness of _BiF3 include, for example, a transmission electron microscope (TEM).

On the other hand, for example, as shown in FIG. 4(b), BiF ₃ and Cu-based active material may each be particles. That is, the positive electrode active material layer may contain particles of Cu-based active material and particles of BiF _3. The average particle size (X) of the particles of BiF ₃ is preferably smaller than the average particle size (Y) of the particles of Cu-based active material. This is because the particles of BiF ₃ are easily arranged in the gaps between the particles of Cu-based active material. The ratio of X to Y (X/Y) is, for example, 0.5 or less, may be 0.3 or less, or may be 0.1 or less.

The molar ratio of Cu to Bi in the positive electrode active material layer is Cu/Bi. Cu/Bi is not particularly limited, but may be, for example, 0.1 or more, and may be 1 or more. If Cu/Bi is too small, the proportion of Cu-based active material will be relatively small, and the volumetric energy density may be low. On the other hand, the value of Cu/Bi may be, for example, 10 or less, and may be 3 or less. If Cu/Bi is too large, coarsening of the Cu-based active material may not be sufficiently suppressed. When the positive electrode active material layer contains the above-mentioned composite particles, Cu/Bi is preferably 1 or more and 3 or less.

The positive electrode active material layer may contain a conductive material. The addition of a conductive material improves the electronic conductivity of the positive electrode active material layer. Examples of conductive materials include carbon materials. Examples of carbon materials include carbon black such as acetylene black, ketjen black, furnace black, and thermal black, graphene, fullerene, and carbon nanotubes.

The proportion of conductive material in the positive electrode active material layer is, for example, 1% by weight or more, and may be 5% by weight or more. If the proportion of conductive material is too small, a good electron conduction path may not be formed. On the other hand, the proportion of conductive material in the positive electrode active material layer is, for example, 20% by weight or less, and may be 15% by weight or less. If the proportion of conductive material is too high, the proportion of positive electrode active material will be relatively small, and the energy density may decrease.

The positive electrode active material layer may contain an electrolyte. The addition of an electrolyte improves the ionic conductivity of the positive electrode active material layer. The electrolyte may be a solid electrolyte or a liquid electrolyte (electrolytic solution). The electrolyte is the same as that described in "2. Electrolyte Layer" below. The positive electrode active material layer may contain a binder. Examples of the binder include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). The thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

2. Electrolyte Layer The electrolyte layer in the present disclosure is a layer disposed on the side of the positive electrode active material layer opposite to the positive electrode current collector. The electrolyte contained in the electrolyte layer may be a solid electrolyte or a liquid electrolyte (electrolytic solution).

Examples of solid electrolytes include inorganic solid electrolytes containing a metal element and a fluorine element. The inorganic solid electrolyte may contain only one type of metal element, or may contain two or more types. Examples of inorganic solid electrolytes include fluorides containing lanthanoid elements such as La and Ce, fluorides containing alkali metal elements such as Li, Na, K, Rb, and Cs, and fluorides containing alkaline earth elements such as Ca, Sr, and Ba.

The inorganic solid electrolyte is preferably a fluoride containing at least one of La, Ba, Pb, Sn, Ca and Ce. Specific examples of the inorganic solid electrolyte include La _1-x Ba _x F _3-x (0≦x≦1), Pb _2-x Sn _x F ₄ (0≦x≦2), Ca _2-x Ba _x F ₄ (0≦x≦2), and Ce _1-x Ba _x F _3-x (0≦x≦1). Each of the x may be greater than 0, 0.3 or more, 0.5 or more, or 0.9 or more. Each of the x may be smaller than 1, 0.9 or less, 0.5 or less, or 0.3 or less. The shape of the inorganic solid electrolyte may be, for example, particulate.

The electrolyte contains, for example, a fluoride salt and a solvent. Examples of the fluoride salt include inorganic fluoride salts, organic fluoride salts, and ionic liquids. Examples of the inorganic fluoride salt include XF (X is Li, Na, K, Rb, or Cs). Examples of the cation of the organic fluoride salt include alkyl ammonium cations such as tetramethylammonium cations. The concentration of the fluoride salt in the electrolyte is, for example, 0.1 mol/L or more and 6 mol/L or less.

Examples of the solvent include glymes represented by R ¹ -O(CH ₂ CH ₂ O) _n -R ² (R ¹ and R ² are each independently an alkyl group having 4 or less carbon atoms or a fluoroalkyl group having 4 or less carbon atoms, and 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), and chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The electrolyte may contain an alkali metal amide salt.

The negative electrode active material layer in the present disclosure is a layer containing at least a negative electrode active material. The negative electrode active material layer may further contain at least one of a conductive material, a binder, and an electrolyte.

Examples of negative electrode active materials include simple metals, alloys, metal oxides, and fluorides of these. Examples of metal elements contained in the negative electrode active material include 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.

In addition, carbon materials such as graphite, coke, and carbon nanotubes, and polymer materials such as polyaniline, polypyrrole, polyacetylene, and polythiophene can also be used as the negative electrode active material. The conductive material, electrolyte, and binder can be the same materials as those described in "1. Positive electrode active material layer" above.

As described above, in the present disclosure, the negative electrode active material layer may be self-formed by a defluorination reaction of the solid electrolyte contained in the electrolyte layer. The thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

4. Other Configurations The fluoride ion battery of the present disclosure may have a positive electrode current collector that collects the current of the positive electrode active material layer, and a negative electrode current collector that collects the current of the negative electrode active material layer. The positive electrode current collector and the negative electrode current collector may have, for example, a foil shape, a mesh shape, or a porous shape. The fluoride ion battery may also have a separator between the positive electrode active material layer and the negative electrode active material layer. By providing a separator, a safer battery can be obtained.

5. Fluoride ion battery The fluoride ion battery in the present disclosure may be a primary battery or a secondary battery, but is preferably a secondary battery. This is because the battery can be repeatedly charged and discharged, and is useful, for example, as an in-vehicle battery. In addition, the shape of the fluoride ion battery in the present disclosure may be, for example, a coin type, a laminate type, a cylindrical type, or a square type.

B. Manufacturing method of fluoride ion battery FIG. 5 is a schematic cross-sectional view illustrating a manufacturing method of a fluoride ion battery in the present disclosure. In the manufacturing method of a fluoride ion battery shown in FIG. 5, first, an intermediate structure 11 having a precursor layer 1X containing a Cu-based active material and Bi is prepared (FIG. 5(a)). The precursor layer 1X contains, for example, composite particles in which a Cu-based active material is coated with Bi. In addition, the intermediate structure 11 has a negative electrode active material layer 2, an electrolyte layer 3, a positive electrode current collector 4, and a negative electrode current collector 5 in addition to the precursor layer 1X. Next, the intermediate structure 11 is charged to introduce fluoride ions into the precursor layer 1X, forming a positive electrode active material layer 1 containing a Cu-based active material and BiF ₃ , and a fluoride ion battery 10 is obtained (FIG. 5(b)).

According to the present disclosure, a positive electrode active material containing a Cu-based active material and BiF ₃ is formed, so that a fluoride ion battery with good capacity characteristics can be obtained. In particular, when the precursor layer contains composite particles in which a Cu-based active material is coated with Bi, damage to the BiF ₃ coat can be suppressed by fluorinating Bi after the precursor layer is produced and producing BiF _3. For example, when a composite particle in which a Cu-based active material is previously coated with BiF ₃ is used, the BiF ₃ coat may be damaged by colliding with other materials (e.g., conductive materials) during the production of the positive electrode active material layer. In contrast, damage to the BiF ₃ coat can be suppressed by fluorinating Bi after the precursor layer is produced and producing BiF ₃ .

1. Precursor Layer Forming Step The precursor layer forming step in the present disclosure is a step of forming a precursor layer containing a Cu-based active material and Bi.

The precursor layer contains a Cu-based active material and Bi. The precursor layer may contain composite particles in which the Cu-based active material is coated with Bi. The composite particles in the precursor layer formation process usually do not contain fluorine. For example, a method of synthesizing the composite particles may involve subjecting a mixture of a Cu-based active material and simple Bi to thermal plasma treatment. The precursor layer may also contain particles of a Cu-based active material and Bi particles. The value of Cu/Bi, the average particle size of the Cu-based active material, and other items are the same as those described above in "A. Fluoride ion battery."

The precursor layer may further contain at least one of a conductive material, a binder, and an electrolyte. These points are the same as those described above in "A. Fluoride ion battery."

In addition, the present disclosure can also provide the above-mentioned method for producing composite particles, which includes a thermal plasma treatment step of performing a thermal plasma treatment on a mixture of a Cu-based active material and Bi (Bi alone). In addition, the present disclosure can also provide composite particles in which a Cu-based active material is coated with Bi (Bi alone). The coverage of Bi on the surface of the Cu-based active material is, for example, 20% or more, may be 50% or more, or may be 70% or more. On the other hand, the coverage of Bi may be 100%. The average thickness of Bi in the composite particles is, for example, 0.5 nm or more, may be 1 nm or more, or may be 10 nm or more. On the other hand, the average thickness of Bi in the composite particles is, for example, 30 nm or less, or may be 20 nm or less.

2. Positive electrode active material layer forming step The positive electrode active material layer forming step is a step of introducing fluoride ions into the precursor layer to form a positive electrode active material layer containing a Cu-based active material and _BiF3 .

Comparing Cu and Bi, the fluorination potential of Bi is lower than that of Cu, so during charging, the fluorination reaction of Bi occurs first, and then the fluorination reaction of Cu occurs. On the other hand, during discharging, the defluorination reaction of Cu occurs, but the defluorination reaction of Bi does not occur.

The method of introducing fluoride ions into the precursor layer is not particularly limited, but includes a method of preparing a chargeable intermediate structure and performing a charging process. The intermediate structure may be a fluoride ion battery before the first charge, as shown in FIG. 5(a), for example. The charging conditions are not particularly limited, and are set so that at least a fluorination reaction of Bi occurs. The Cu-based active material in the positive electrode active material layer may or may not contain F. The positive electrode active material layer obtained by this process is the same as that described above in "A. Fluoride ion battery".

This disclosure is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and anything that has substantially the same configuration as the technical ideas described in the claims of this disclosure and has similar effects is included within the technical scope of this disclosure.

[Example 1]
(Synthesis of CuBi nanoparticles)
CuBi nanoparticles were synthesized using a thermal plasma method with Cu powder and Bi powder as raw materials. The molar ratio of Cu/Bi was 2.66. The surfaces of the CuBi nanoparticles were measured by TEM-EDX. The results are shown in Figures 6(a) and 6(b). As shown in Figures 6(a) and 6(b), it was confirmed that the CuBi nanoparticles were composite particles in which Cu and Bi were separated into separate phases and Cu was coated with Bi. The average particle size of Cu in the CuBi nanoparticles was 38 nm.

(Preparation of Positive Electrode Composite)
The above CuBi nanoparticles were used as a positive electrode active material, Pb _1.2 Sn _0.8 F ₄ was used as a solid electrolyte, and carbon powder was used as a conductive material, and these were mixed together to obtain a positive electrode mixture.

(Preparation of Evaluation Cell)
250 mg of Pb _1.2 Sn _0.8 F ₄ was weighed into a 1 cm ² ceramic mold and pressed at 1 ton/cm ² to form a solid electrolyte layer. 10 mg of a positive electrode composite was placed on one side of the obtained solid electrolyte layer and pressed at 1 ton/cm ² to prepare a positive electrode active material layer. A positive electrode current collector (Pt foil) and a negative electrode current collector (Pt foil) were placed on the surfaces of the positive electrode active material layer and the solid electrolyte layer, respectively, and pressed at 4 ton/cm ^2. In this way, a pellet-type evaluation cell of 1 cm ² was prepared. During charging, the CuBi nanoparticles are fluorinated, and CuF _x (0≦x≦2) and BiF ₃ are formed. During charging, a defluorination reaction occurs in the region of the solid electrolyte layer on the negative electrode current collector side, and the negative electrode active material layer is self-formed.

[Comparative Example 1]
A pellet-type evaluation cell was produced in the same manner as in Example 1, except that Cu nanoparticles (average particle size 29 nm) were used as the positive electrode active material.

[Comparative Example 2]
In the same manner as in the example of JP 2018-063905 A, Cu nanoparticles coated with _LaF3 were synthesized by a thermal plasma method. A pellet-type evaluation cell was produced in the same manner as in Example 1, except that these particles were used.

[evaluation]
A charge/discharge test was performed on the evaluation cell obtained in Example 1. The process in which a fluorination reaction occurred on the positive electrode side and a defluorination reaction occurred on the negative electrode side was defined as charging, and the process in which a defluorination reaction occurred on the positive electrode side and a fluorination reaction occurred on the negative electrode side was defined as discharging. The evaluation cell was placed in a sealed container, and was charged and discharged while being evacuated. The charge/discharge conditions were rate: 0.05C, voltage range: 1.3 to 0.3V (counter electrode Pb), and temperature: 60°C.

The results of TEM-EDX measurement of the fluorinated CuBi nanoparticles after the first charge are shown in Figures 7(a) and (b). As shown in Figures 7(a) and (b), it was confirmed that the fluorinated CuBi nanoparticles were composite particles in which CuF _x (0<x≦2) was coated with BiF _3. In addition, the average particle size of CuF _x in the fluorinated CuBi nanoparticles was 50 nm. That is, the average particle size of Cu increased by about 1.3 times due to the first charge. On the other hand, although not particularly shown, the average particle size of Cu used in Comparative Example 1 increased by about 3.1 times due to the first charge. In this way, it was confirmed that the coexistence of the Cu-based active material and BiF ₃ can suppress the coarsening of particles.

The results of the charge/discharge test for the evaluation cell obtained in Example 1 are shown in Figure 8. The evaluation cells obtained in Comparative Examples 1 and 2 were charged and discharged under the same conditions. The results are shown in Figures 9 and 10. The results of the capacity obtained by the charge/discharge test are shown in Table 1.

As shown in FIG. 8 to FIG. 10 and Table 1, it was confirmed that Example 1 had better capacity characteristics than Comparative Examples 1 and 2. At the time of the first charge in FIG. 8, from the start of charging to about 300 mAh/g, a reaction occurs in which Bi in the CuBi nanoparticles becomes BiF _3. On the other hand, from about 300 mAh/g to 950 mAh/g, a reaction occurs in which Cu in the CuBi nanoparticles becomes CuF _x (0<x≦2). The charge capacity (650 mAh/g) associated with the fluorination of Cu was sufficiently large compared to Comparative Examples 1 and 2. On the other hand, it was confirmed that no defluorination reaction of BiF ₃ occurred during the first discharge. In addition, the discharge capacity of Example 1 was also sufficiently large compared to Comparative Examples 1 and 2. In this way, it was confirmed that good capacity characteristics can be obtained by the coexistence of the Cu-based active material and BiF ₃ .

REFERENCE SIGNS LIST 1 ... positive electrode active material layer 2 ... negative electrode active material layer 3 ... electrolyte layer 4 ... positive electrode current collector 5 ... negative electrode current collector 10 ... fluoride ion battery

Claims (6)

A positive electrode active material layer containing a Cu-based active material and _BiF3 ,
The Cu-based active material is a fluoride ion battery represented by CuF _x (0≦x≦2). The fluoride ion battery according to claim 1 , wherein the positive electrode active material layer contains composite particles in which the Cu-based active material is coated with the BiF ₃ . The fluoride ion battery according to claim 2, wherein the molar ratio of Cu to Bi (Cu/Bi) in the positive electrode active material layer is 1 or more and 3 or less. The fluoride ion battery according to any one of claims 1 to 3 , wherein the x satisfies 0<x≦2 . The fluoride ion battery according to any one of claims 1 to 4 , wherein the Cu-based active material has an average particle size of 100 nm or less. a precursor layer forming step of forming a precursor layer containing a Cu-based active material and Bi;
a positive electrode active material layer forming step of introducing fluoride ions into the precursor layer to form a positive electrode active material layer containing a Cu-based active material and _BiF3 ;
having
The method for producing a fluoride ion battery, wherein the Cu-based active material is represented by CuF _x (0≦x≦2).