JP7147726B2 - Active materials and fluoride ion batteries - Google Patents

Description

The present disclosure relates to active materials and fluoride ion batteries.

Li-ion batteries, for example, are known as high-voltage and high-energy-density batteries. A Li-ion battery is a cation-based battery that utilizes the reaction of Li ions with a positive electrode active material and the reaction of Li ions with a negative electrode active material. On the other hand, as an anion-based battery, a fluoride ion battery using a reaction of fluoride ions (fluoride anions) is known. For example, Non-Patent Document 1 discloses Cu as an active material used in fluoride ion batteries.

Le Zhang et al., “Study of all solid-state rechargeable fluoride ion batteries based on thin-film electrolyte”, J Solid State Electrochem (2017) 21:1243-1251

Active materials with good capacity characteristics are required as active materials used in fluoride ion batteries. The present disclosure has been made in view of the above circumstances, and a main object thereof is to provide an active material with good capacity characteristics.

In order to achieve the above objects, the present disclosure provides an active material used in a fluoride ion battery, which is M ¹ N _x (M ¹ is Cu, Ti, V, Cr, Fe, Mn, Co, Ni , Zn, Nb, In, Sn, Ta, W and Bi, where x satisfies 0.05≦x≦3), or M ² Ln _y N _z (M ² is Cu, Ti, at least one of V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W and Bi; Ln is at least one of Sc, Y and a lanthanoid; y is 0.1 ≤y≤3 and z satisfies 0.15≤z≤6.

According to the present disclosure, by using a specific metal nitride, an active material with good capacity characteristics can be obtained.

In the above disclosure, the active material may have a composition represented by M ¹ N _x above.

In the above disclosure, M1 may include at least ^one of Cu, Ti, Fe and V.

In the above disclosure, the active material may have a composition represented by M ² Ln _y N _z .

In the above disclosure, ^M2 may contain Mn.

In the above disclosure, Ln may contain Ce.

Further, in the present disclosure, a fluoride ion battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer, A fluoride ion battery is provided in which at least one of the positive electrode active material layer and the negative electrode active material layer contains the active material described above.

According to the present disclosure, by using the active material described above, a fluoride ion battery having good capacity characteristics can be obtained.

The present disclosure has the effect of being able to provide an active material with good capacity characteristics.

1 is a schematic cross-sectional view showing an example of a fluoride ion battery in the present disclosure; FIG. 4 shows the result of XRD measurement for the active material obtained in Example 3. FIG. 4 shows the results of a charge/discharge test on the battery for evaluation obtained in Example 1. FIG. 4 shows the results of a charge/discharge test on the battery for evaluation obtained in Example 2. FIG. 4 shows the results of a charge/discharge test on the battery for evaluation obtained in Example 3. FIG. 4 shows the results of a charge/discharge test on the battery for evaluation obtained in Comparative Example 1. FIG. 4 shows the results of a charge/discharge test on the battery for evaluation obtained in Example 4. FIG. 4 shows the results of a charge/discharge test on the battery for evaluation obtained in Example 5. FIG.

The active material and fluoride ion battery in the present disclosure will be described in detail below.

A. Active material The active material in the present disclosure is an active material used in a fluoride ion battery, and M ¹ N _x (M ¹ is Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb , In, Sn, Ta, W and Bi, where x satisfies 0.05≦x≦3), or M ² Ln _y N _z (M ² is Cu, Ti, V, Cr, At least one of Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W and Bi, Ln is at least one of Sc, Y and lanthanoids, and y is 0.1 ≤ y ≤ 3 and z satisfies 0.15≦z≦6).

According to the present disclosure, by using a specific metal nitride, an active material with good capacity characteristics can be obtained. For example, Non-Patent Document 1 discloses Cu as an active material used in fluoride ion batteries. When Cu is used as the positive electrode active material, Cu is fluorinated during charging. Since copper fluoride has high insulating properties, the resistance increases with charging. Specifically, the formation of highly insulating copper fluoride makes it difficult to conduct electrons mainly supplied from the conductive material to the reaction field (the interface between the metal and the metal fluoride). As a result, the charging reaction does not proceed, and sufficient capacity cannot be obtained. In Non-Patent Document 1, the diffusion distance of fluoride ions is reduced by thinning the shape of the electrode, but the resistance is still large and the overvoltage is large. Therefore, sufficient capacity is not obtained as compared with the theoretical capacity.

In contrast, the present disclosure uses a specific metal nitride as the active material. The reaction between the metal nitride and fluoride ions (due to doping with fluorine) introduces holes to form a semiconductor region. Since this semiconductor region has a function of assisting electron conduction, it becomes easier to conduct electrons mainly supplied from the conductive material to the reaction field (the interface between the metal and the metal fluoride). As a result, it is possible to prevent the charging reaction from slowing down, and an active material with good capacity characteristics can be obtained. Furthermore, metal nitrides have higher oxidation resistance and water resistance than simple metals, and therefore have the advantage of being less susceptible to surface oxidation. As a result, deterioration of the active material due to unintended generation of oxides or the like is less likely to occur. Further, for example, when the active material according to the present disclosure is used as the positive electrode active material, the active material according to the present disclosure usually does not contain elemental fluorine, so the initial charge/discharge starts from charging. Therefore, a metal fluoride, which is more stable than a simple metal, can be used as the negative electrode active material.

An active material in the present disclosure has, for example, a composition represented by M ¹ N _x . In M ¹ N _x , M ¹ is at least one of Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W and Bi. ^Nitrides of M1 are known as semiconductors. Moreover, M ¹ may be one kind of the above metal elements, or may be two or more kinds. In M ¹ N _x , x satisfies 0.05≦x≦3. x may be determined according to the ^valence of M1. That is, x may be a value that maintains electrical neutrality.

Among the above metal elements, M1 preferably contains at least ^one of Cu, Ti, V, Mn, Fe, Co, and Ni. Also, the ratio of the specific metal element (M ^1X ) in M ¹ is, for example, 50 mol % or more, may be 70 mol % or more, or may be 90 mol % or more. M ^1X is any one metal element of Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W and Bi.

Active materials having a composition represented by M ¹ N _x include, for example, Cu ₃ N, TiN, Ti ₂ N, VN, MnN, Mn ₂ N, Mn ₃ N ₂ , Mn ₄ N, FeN, Fe ₂ N , Fe ₃ N, Fe ₄ N, Fe ₈ N, CoN, Co ₂ N, Ni ₃ N, Ni ₄ N, and the like.

The active material in the present disclosure has, for example, a composition represented by M ² Ln _y N _z . Since the fluoride of Ln has high fluoride ion conductivity, the diffusion of fluoride ions is improved when the active material is fluorinated. In M ² Ln _y N _z , M ² is at least one of Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W and Bi. Nitrides of ^M2 are known as semiconductors. Further, M2 may be one kind of the above metal elements, or may be ^two or more kinds. Ln is at least one of Sc, Y and lanthanoids. All of Ln are metal elements belonging to Group 3 of the periodic table. In addition, Ln may be one of the above metal elements, or may be two or more. The type of lanthanoid is not particularly limited, but examples include La, Ce, Pr, Nd, Sm, Eu, Gd, and Tb. In M ² Ln _y N _z , y satisfies 0.1≦y≦3, and z satisfies 0.15≦z≦6. z may be determined according to the valence of M1, the valence of ^Ln and the composition (y). That is, z may be a value that maintains electrical neutrality.

Among the above metal elements, ^M2 preferably contains at least one of Cu, Ti, V, Fe, Mn, Co, and Ni. Also, the ratio of the specific metal element (M ^2X ) in M ² is, for example, 50 mol % or more, may be 70 mol % or more, or may be 90 mol % or more. ^M2X is any one metal element of Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W and Bi.

Among the above metal elements, Ln preferably contains at least one of Sc, Y, Ce, La, and Nd. Also, the ratio of the specific metal element (Ln ^X ) in Ln is, for example, 50 mol % or more, may be 70 mol % or more, or may be 90 mol % or more. Ln ^X is any one metal element of Sc, Y and lanthanide.

_Active materials having a _composition represented by _{M2LnyNz include} , for _example , _{MnCe2N3 ,} ^MnSr3N3 _{, Fe17Ce2N3 , Fe17Nd2N3 , and Fe17Y2N2 . .4} , BiLa ₂ N, and the like.

Examples of the shape of the active material include particulate. The average particle size (D ₅₀ ) of the active material is, for example, 1 nm or more, and may be 5 nm or more. On the other hand, the average particle size (D ₅₀ ) of the active material is, for example, 30 μm or less, may be 10 μm or less, or may be 5 μm or less. The average particle size (D ₅₀ ) can be calculated, for example, from measurements using a scanning electron microscope (SEM) or transmission electron microscope (TEM). The number of samples is preferably large, for example 100 or more.

B. Fluoride Ion Battery FIG. 1 is a schematic cross-sectional view showing an example of a fluoride ion battery in the present disclosure. Fluoride ion battery 10 shown in FIG. It has a positive electrode current collector 4 that collects current from the material layer 1, a negative electrode current collector 5 that collects current from the negative electrode active material layer 2, and a battery case 6 that houses these members. In the present disclosure, at least one of the positive electrode active material layer 1 and the negative electrode active material layer 2 contains the active material described above.

According to the present disclosure, by using the active material described above, a fluoride ion battery having good capacity characteristics can be obtained. In addition, in the present disclosure, only the positive electrode active material layer may contain the above-described active material, and only the negative electrode active material layer may contain the above-described active material. Both the positive electrode active material layer and the negative electrode active material layer may contain the active material described above. and an active material with a low reaction potential is used as the negative electrode active material.

1. Positive Electrode Active Material Layer The positive electrode active material layer in the present disclosure is a layer containing at least a positive electrode active material. In the positive electrode active material, a fluorination reaction usually occurs during charging, and a defluorination reaction occurs during discharging. Moreover, the positive electrode active material layer may further contain at least one of a conductive material, a binder and an electrolyte in addition to the positive electrode active material.

The positive electrode active material layer preferably contains the active material described in the above "A. Active material" as the positive electrode active material. In this case, any active material having a reaction potential lower than that of the active material described above can be used as the negative electrode active material. On the other hand, when the active material described in "A. Active Material" above is used as the negative electrode active material, a general positive electrode active material can be used. Common positive electrode active materials include, for example, simple metals, alloys, metal oxides, and fluorides thereof.

The conductive material is not particularly limited as long as it has desired electronic conductivity, and examples thereof include carbon materials. Carbon materials include, for example, carbon blacks such as acetylene black, ketjen black, furnace black, thermal black, graphene, fullerene, and carbon nanotubes. The proportion of the 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 the conductive material is too low, there is a possibility that good electronic conduction paths will not be formed. On the other hand, the ratio of the 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 the conductive material is too high, the proportion of the active material is relatively low, possibly resulting in a decrease in energy density.

The binder is not particularly limited as long as it is chemically and electrically stable, and examples thereof include fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). The electrolyte is the same as described in "3. Electrolyte layer" below.

In addition, the content of the positive electrode active material in the positive electrode active material layer is preferably larger from the viewpoint of capacity, for example, 30% by weight or more, preferably 50% by weight or more, and 70% by weight or more. is more preferable. Moreover, the thickness of the positive electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

2. Negative Electrode Active Material Layer The negative electrode active material layer in the present disclosure is a layer containing at least a negative electrode active material. In the negative electrode active material, a defluorination reaction normally occurs during charging, and a fluorination reaction occurs during discharging. Moreover, the negative electrode active material layer may further contain at least one of a conductive material, a binder and an electrolyte in addition to the negative electrode active material.

The negative electrode active material layer preferably contains the active material described in the above "A. Active material" as the negative electrode active material. In this case, any active material having a reaction potential higher than that of the active material described above can be used as the positive electrode active material. On the other hand, when the active material described in the above "A. Active material" is used as the positive electrode active material, a general negative electrode active material can be used. Common negative electrode active materials include, for example, simple metals, alloys, metal oxides, and fluorides thereof.

As for the conductive material, the binder, and the electrolyte, the same materials as those described in the above "1. Positive electrode active material layer" can be used. In addition, the content of the negative electrode active material in the negative electrode active material layer is preferably larger from the viewpoint of capacity, for example, 30% by weight or more, preferably 50% by weight or more, and 70% by weight or more. is more preferable. Moreover, the thickness of the negative electrode active material layer is, for example, 0.1 μm or more and 1000 μm or less.

3. Electrolyte Layer The electrolyte layer in the present disclosure is a layer formed between the positive electrode active material layer and the negative electrode active material layer. The electrolyte forming the electrolyte layer may be a liquid electrolyte (electrolytic solution), a polymer electrolyte, or an inorganic solid electrolyte.

The electrolyte contains, for example, a fluoride salt and a solvent. Examples of fluoride salts include inorganic fluoride salts, organic fluoride salts, and ionic liquids. Inorganic fluoride salts include, for example, XF, where X is Li, Na, K, Rb or Cs. Examples of cations of organic fluoride salts include alkylammonium cations such as tetramethylammonium cations. The concentration of the fluoride salt in the electrolytic solution is, for example, 0.1 mol/L or more, may be 0.3 mol/L or more, or may be 0.5 mol/L or more. On the other hand, the concentration of the fluoride salt is, for example, 6 mol/L or less, and may be 3 mol/L or less.

Examples of solvents include cyclic carbonates such as ethylene carbonate (EC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), and diethyl carbonate. (DEC), ethyl methyl carbonate (EMC) and other chain carbonates, diethyl ether, 1,2-dimethoxymethane, 1,3-dimethoxypropane and other chain ethers, tetrahydrofuran, 2-methyltetrahydrofuran and other chain ethers, sulfolane cyclic sulfones such as dimethylsulfoxide (DMSO), chain sulfones such as dimethylsulfoxide (DMSO), cyclic esters such as γ-butyrolactone, nitriles such as acetonitrile, and any mixture thereof. A polymer electrolyte can be obtained, for example, by adding a polymer to a liquid electrolyte and gelling it.

On the other hand, inorganic solid electrolytes include, for example, fluorides of lanthanide elements such as La and Ce; fluorides of alkali metal elements such as Li, Na, K, Rb and Cs; and alkaline earth elements such as Ca, Sr and Ba. Fluorides of Moreover, the inorganic solid electrolyte is preferably a fluoride containing at least one metal element selected from La, Ba, Pb, Sn, Ca and Ce. The inorganic solid electrolyte may contain only one type of the above metal element, or may contain two or more types thereof. Specific examples of inorganic solid electrolytes include La _1-x Ba _x F _3-x (0≦x≦2), 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≦2). Each x may be greater than 0, 0.3 or more, 0.5 or more, or 0.9 or more. Moreover, each of the above x may be smaller than 1, may be 0.9 or less, may be 0.5 or less, or may be 0.3 or less. Although the shape of the inorganic solid electrolyte is not particularly limited, for example, a particulate shape can be mentioned.

4. Other Configurations A fluoride ion battery according to the present disclosure has at least the positive electrode active material layer, the negative electrode active material layer, and the electrolyte layer described above. Furthermore, it usually has a positive electrode current collector that collects current for the positive electrode active material layer and a negative electrode current collector that collects current for the negative electrode active material layer. Examples of the shape of the current collector include foil, mesh, and porous. Moreover, the fluoride ion battery may have a separator between the positive electrode active material layer and the negative electrode active material layer. By providing a separator, a battery with higher safety 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 they can be repeatedly charged and discharged, and are useful, for example, as batteries for vehicles. In addition, the shape of the fluoride ion battery in the present disclosure includes, for example, coin type, laminate type, cylindrical type, and rectangular type.

Note that the present disclosure is not limited to the above embodiments. The above embodiment is an example, and any device that has substantially the same configuration as the technical idea described in the claims of the present disclosure and produces the same effect is the present invention. It is included in the technical scope of the disclosure.

[Example 1]
An active material (Cu ₃ N, manufactured by Rare Metallic), a solid electrolyte (PbF ₂ , manufactured by Kojundo Chemical), and a conductive material (acetylene black (AB), HS-100, manufactured by Denka) are combined into Cu ₃ N:PbF. ₂ :AB=30:60:10 weight ratio, and mixed in a ball mill to obtain an electrode mixture. The resulting electrode mixture (working electrode), a solid electrolyte (La _0.9 Ba _0.1 F _2.9 ) for forming a solid electrolyte layer, a solid electrolyte (PbF ₂ , manufactured by Kojundo Chemical Co., Ltd.), and A mixture (counter electrode) obtained by mixing a conductive material (acetylene black (AB), HS-100, manufactured by Denka) at a weight ratio of PbF ₂ :AB = 95:5 and a Pb foil were subjected to powder compaction to form an evaluation battery. got

[Example 2]
An evaluation battery was prepared in the same manner as in Example 1, except that TiN (manufactured by Kojundo Chemical Co., Ltd.) was used as the active material and La _0.9 Ba _0.1 F _2.9 was used as the solid electrolyte in the working electrode. Obtained.

[Example 3]
Manganese metal (Mn) and cerium metal (Ce) were weighed, ground and mixed in a molar ratio of Mn:Ce=1:2 in an Ar glovebox. The resulting mixture was placed in a quartz tube, evacuated, and then fired at 900° C. for 36 hours under a nitrogen gas flow. An active material (MnCe ₂ N ₃ ) was thus obtained. When the obtained active material was subjected to X-ray diffraction measurement using CuKα rays, as shown in FIG. 2, typical MnCe ₂ N ₃ A peak was confirmed, and it was confirmed that MnCe ₂ N ₃ was obtained. A battery for evaluation was obtained in the same manner as in Example 2, except that MnCe ₂ N ₃ was used as the active material in the working electrode.

[Comparative Example 1]
A battery for evaluation was obtained in the same manner as in Example 1, except that Cu was used as the active material in the working electrode.

[evaluation]
The evaluation batteries obtained in Examples 1 to 3 and Comparative Example 1 were subjected to a charge/discharge test. The conditions of the charge-discharge test in Example 1 were a temperature of 140° C., a final potential of the working electrode of 0.3 V (vs Pb/PbF ₂ ) to 1.5 V (vs Pb/PbF ₂ ), and a current of 50 μA/cm ² . In addition, the conditions of the charge-discharge test in Examples 2 and 3 and Comparative Example 1 were a temperature of 140° C., an end potential of the working electrode of −1.5 V (vs Pb/PbF ₂ ) to 3 V (vs Pb/PbF ₂ ), a current It was set to 50 μA/cm ² . The results are shown in FIGS. 3 to 6. FIG.

As shown in FIG. 3, in Example 1 (Cu ₃ N), a discharge reaction plateau was confirmed at about 0.6V, and a charge reaction plateau was confirmed at about 0.8V. Moreover, it was confirmed that the charge/discharge curve and the discharge curve each have two plateaus. Also, a discharge capacity of about 650 mAh/g was obtained, which is close to the theoretical capacity (786 mAh/g). Further, as shown in FIG. 4, in Example 2 (TiN), a discharge reaction plateau was confirmed at about 0.2 V, and a discharge capacity of about 30 mAh/g was obtained.

Further, as shown in FIG. 5, in Example 3 (MnCe ₂ N ₃ ), a discharge reaction plateau was confirmed at about 1.4 V, and a charge reaction plateau was confirmed at about 1.6 V, indicating that the charge-discharge reaction did not occur. occurred at very high potentials. In addition, the potential at which the charging reaction occurs is close to the potential at which the discharging reaction occurs, and the overvoltage is small, suggesting that the battery reaction resistance is low. It is presumed that this is because the active material is a nitride, which has the effect of improving the electron conductivity, and the lanthanide fluoride is generated, which improves the diffusion of fluoride ions. .

On the other hand, as shown in FIG. 6, in Comparative Example 1 (Cu), the discharge capacity did not reach 20 mAh/g, which was significantly lower than the theoretical capacity (843 mAh/g). The reason for this is presumed to be that when charging is started, a structure in which the surface of the active material (Cu) is covered with an insulator (copper fluoride) is formed, and the charging reaction does not progress. As a result, it is presumed that the discharge capacity was significantly lowered. On the other hand, in Examples 1 to 3, it was confirmed that an active material with good capacity characteristics was obtained by using a specific nitride.

[Example 4]
For the evaluation in the same manner as in Example 1, except that Fe ₄ N (manufactured by Kojundo Chemical Co., Ltd.) was used as the active material and La _0.9 Ba _0.1 F _2.9 was used as the solid electrolyte in the working electrode. got a battery.

[Example 5]
An evaluation battery was prepared in the same manner as in Example 1, except that VN (manufactured by Kojundo Chemical Co., Ltd.) was used as the active material and La _0.9 Ba _0.1 F _2.9 was used as the solid electrolyte in the working electrode. Obtained.

[evaluation]
The evaluation batteries obtained in Examples 4 and 5 were subjected to a charge/discharge test. The conditions of the charge/discharge test were a temperature of 140° C., an end potential of the working electrode of −1.5 V (vs Pb/PbF ₂ ) to 3 V (vs Pb/PbF ₂ ), and a current of 50 μA/cm ² . The results are shown in FIGS. 7 and 8. FIG.

As shown in FIG. 7, in Example 4 (Fe ₄ N), a discharge reaction plateau was confirmed at about −0.5 V and about −1.4 V, and a discharge capacity of about 30 mAh/g was obtained. On the other hand, as shown in FIG. 8, in Example 5 (VN), a gentle curve was obtained in the range of about 1.5 V to about -1.1 V in the discharge curve, and the discharge reaction plateaued at about -1.1 V. was confirmed, and a discharge capacity of about 240 mAh/g was obtained.

DESCRIPTION OF SYMBOLS 1... Positive electrode active material layer 2... Negative electrode active material layer 3... Electrolyte layer 4... Positive electrode collector 5... Negative electrode collector 6... Battery case 10... Fluoride ion battery

Claims (7)

An active material used in a fluoride ion battery,
M ¹ N _x (M ¹ is at least one of Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W and Bi, and x is 0.05≦ x≦3), or M ² Ln _y N _z (M ² is Cu, Ti, V, Cr, Fe, Mn, Co, Ni, Zn, Nb, In, Sn, Ta, W and Bi Ln is at least one of Sc, Y and a lanthanoid, y satisfies 0.1 ≤ y ≤ 3, and z satisfies 0.15 ≤ z ≤ 6). , active material. 2. The active material of claim 1, wherein said active material has a composition represented _by said ^M1Nx . 3. The active material of claim 2, wherein said M1 comprises at least ^one of Cu, Ti, Fe and V. 2. The active material according to claim 1, wherein said active material has a _composition represented by _said ^M2LnyNz . 5. The active material of claim 4, wherein said ^M2 comprises Mn. 6. The active material according to claim 4 or 5, wherein said Ln comprises Ce. A fluoride ion battery having a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer,
A fluoride ion battery, wherein at least one of the positive electrode active material layer and the negative electrode active material layer contains the active material according to any one of claims 1 to 6.

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