JP2017143046A - Active material and fluoride ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel active material which can be used for a fluoride ion battery.SOLUTION: In the present invention, the above problem is solved by providing an active material which is to be used for a fluoride ion battery, and comprises crystal phases including an M element (M represents at least one of La, Ce, Pr, Nd, Sm, Ca, Sr and Ba), a F element, a Bi element, and a S element. According to X-ray diffraction measurement with Cu Kα rays, the crystal phases have peaks at particular positions.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a novel active material that can be used in a fluoride ion battery.

  As a battery having a high voltage and a high energy density, for example, a Li ion battery is known. Li-ion batteries are cation-based batteries that use Li ions as carriers. On the other hand, a fluoride ion battery using fluoride ions as a carrier is known as an anion-based battery.

For example, Patent Document 1 discloses an electrolyte solution for a fluoride ion battery using an aromatic material having an aromatic cation and an anion as a solvent. Moreover, metal active materials, such as Cu, are illustrated as an active material. An object of this technique is to provide an electrolyte for a fluoride ion battery capable of increasing the capacity of the battery. Although not related to fluoride ion batteries, Non-Patent Document 1 discloses SrFBiS ₂ and Non-Patent Document 2 discloses Sr _0.5 Ce _0.5 FBiS _{2 as} superconductors. .

Japanese Patent Laid-Open No. 2015-191797

Hechang Lei et al., “New Layered Fluorosulfide SrFBiS2”, Inorg. Chem., 2013, 52 (18), 10685-10689 Lin Li et al., “Coexistence of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2”, Phys. Rev. B91 (2015) 014508

  Currently, there are few materials known as active materials that can be used in fluoride ion batteries. This invention is made | formed in view of the said situation, and it aims at providing the novel active material which can be used for a fluoride ion battery.

  In order to achieve the above object, according to the present invention, an active material used in a fluoride ion battery is an M element (M is at least one of La, Ce, Pr, Nd, Sm, Ca, Sr, and Ba). In the X-ray diffraction measurement using a CuKα ray, the above crystal phase is 2θ = 25.7 ° ± 0. Provided is an active material having a peak at positions of 5 °, 31.2 ° ± 0.5 °, 41.5 ° ± 0.5 °.

  According to this invention, since it has a specific crystal phase, it can be set as the active material which can be used for a fluoride ion battery.

  In the said invention, it is preferable that the said crystal phase has a crystal structure of space group P4 / nmm.

  In the present invention, a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer And the positive electrode active material or the negative electrode active material is the active material described above.

  According to this invention, it can be set as the fluoride ion battery with favorable cycling characteristics by using the active material mentioned above.

  In this invention, there exists an effect that the novel active material which can be used for a fluoride ion battery can be provided.

It is a schematic sectional drawing which shows an example of the fluoride ion battery of this invention. It is a result of the XRD measurement with respect to the active material obtained in the Example. It is a result of the CV measurement with respect to the battery produced using the active material obtained in the Example. It is the result of the charging / discharging test with respect to the battery produced using the active material obtained in the Example.

  Hereinafter, the active material and fluoride ion battery of the present invention will be described in detail.

A. Active Material The active material of the present invention is an active material used for a fluoride ion battery, and is an M element (M is at least one of La, Ce, Pr, Nd, Sm, Ca, Sr, and Ba) A crystal phase containing an F element, a Bi element, and an S element, and the crystal phase is 2θ = 25.7 ° ± 0.5 ° in an X-ray diffraction measurement using CuKα ray, It has a peak at a position of 31.2 ° ± 0.5 °, 41.5 ° ± 0.5 °.

  According to this invention, since it has a specific crystal phase, it can be set as the active material which can be used for a fluoride ion battery. Although this material having a crystal phase is known as a superconductor, it has not been known at all to be useful as an active material of a fluoride ion battery.

In addition, many of the conventionally known active materials for fluoride ion batteries are metal active materials, and their functions as active materials are manifested by the fluorination defluorination reaction of metals.
MeF _x + xe ⁻ ⇔ Me + xF ⁻ (Me is composed of one or more metal elements)
Since the metal fluorination / defluorination reaction involves a large change in crystal structure, resistance tends to increase. Further, since the expansion and contraction when the crystal structure changes is large, the cycle characteristics tend to be low.

  On the other hand, the active material of the present invention is a layered fluorosulfide, and it is presumed that the function as the active material is expressed not by the fluorinated defluorination reaction but by the insertion / elimination reaction (intercalation reaction). Specifically, as described in Examples described later, since high Coulomb efficiency is obtained, it is presumed that fluoride ions are inserted into and desorbed from the crystal structure. Such an intercalating type active material is a material based on a novel concept different from a conventional active material for a fluoride ion battery (fluorinated defluoridation type active material). Since the intercalation reaction is a reaction with little change in crystal structure, there is an advantage that resistance is not easily increased. Further, since the expansion and contraction when the crystal structure changes is small, there is an advantage that the cycle characteristics are high.

  The reason why the intercalation reaction occurs is not completely clear, but the F element layer included in the crystal structure of the crystal phase may function. That is, the crystal phase has a layered structure having a layer of F element in the crystal structure. In the layer of F element, F is continuous, and there is a diffusion path of F ions. It is speculated that the reaction will occur.

  The active material of the present invention contains an M element (M is at least one of La, Ce, Pr, Nd, Sm, Ca, Sr, and Ba), an F element, a Bi element, and an S element. Has a crystalline phase.

  Among the M elements, Ca, Sr and Ba are alkaline earth metals. Similarly, among M elements, La, Ce, Pr, Nd, and Sm are lanthanoids. Since these elements all have an ionic radius, they can form the crystal phase. In the present invention, it is preferable to contain at least Sr as the M element. In this case, the M element may be a combination of Sr and other elements, and the M element may be only Sr. In particular, in the former case, it can be considered that a part of Sr is replaced with another element. The other element may be the alkali metal element or the lanthanoid. The ratio of Sr in the entire M element is, for example, 30 mol% or more, and may be 50 mol% or more.

  The crystal phase may be composed of only M element, F element, Bi element and S element, and may further contain other elements. Examples of other elements include Se element and O element. In addition, each of the M element, the F element, the Bi element, and the S element may be partially substituted with another element. Specifically, a part of the S element may be substituted with the Se element, and a part of the F element may be substituted with the O element. The amount of substitution with other elements is preferably less than 50 mol%, for example.

  In the X-ray diffraction measurement using CuKα ray, the crystal phase was 2θ = 25.7 ° ± 0.5 °, 31.2 ° ± 0.5 °, 41.5 ° ± 0.5 °, 44. It is preferable to have a peak at a position of 6 ° ± 0.5 °, 52.5 ° ± 0.5 °, 64.8 ° ± 0.5 °, 73.5 ° ± 0.5 °. The width of these peak positions may be ± 0.3 ° or ± 0.1 °. The crystal phase preferably has a crystal structure of space group P4 / nmm.

  The active material of the present invention preferably contains the above crystal phase as a main component. Specifically, the proportion of the crystal phase is preferably 50 mol% or more, more preferably 70 mol% or more, and 90 mol% or more with respect to all the crystal phases contained in the active material. Is more preferable.

The composition of the active material of the present invention is not particularly limited as long as the composition can obtain the above crystal phase. Here, the composition of the active material is expressed as _{M a F b Bi c S d} X e. X is an element other than M, F, Bi, and S.

  Each of a to c is, for example, 0.5 or more, 0.7 or more, or 0.9 or more. Further, each of a to c is, for example, 1.5 or less, 1.3 or less, or 1.1 or less.

  For example, d is 1 or more, may be 1.5 or more, and may be 1.7 or more. Moreover, d is 3 or less, for example, may be 2.8 or less, and may be 2.5 or less.

  e may be 0 or may be greater than 0. E is, for example, 2.5 or less, 2 or less, or 1.5 or less.

Although the shape of the active material of this invention is not specifically limited, For example, a particulate form can be mentioned. The average particle diameter (D ₅₀ ) of the active material is, for example, in the range of 0.1 μm to ₅₀ μm, and preferably in the range of 1 μm to 20 μm. The average particle diameter (D ₅₀ ) of the active material can be obtained from the result of particle size distribution measurement by a laser diffraction scattering method, for example.

  The method for producing the active material of the present invention is not particularly limited as long as it can obtain the target active material, and examples thereof include a solid phase reaction method. In the solid phase reaction method, a raw material composition containing an M element, an F element, a Bi element, and an S element is subjected to a heat treatment to cause a solid phase reaction and synthesize an active material.

B. Fluoride ion battery FIG. 1 is a schematic sectional view showing an example of a fluoride ion battery of the present invention. A fluoride ion battery 10 shown in FIG. 1 includes a positive electrode active material layer 1 containing a positive electrode active material, a negative electrode active material layer 2 containing a negative electrode active material, a positive electrode active material layer 1 and a negative electrode active material layer 2. The electrolyte layer 3 formed therebetween, the positive electrode current collector 4 that collects current from the positive electrode active material layer 1, the negative electrode current collector 5 that collects current from the negative electrode active material layer 2, and these members are accommodated. And a battery case 6. In the present invention, the active material described above is used as the positive electrode active material or the negative electrode active material.

According to this invention, it can be set as the fluoride ion battery with favorable cycling characteristics by using the active material mentioned above.
Hereinafter, the fluoride ion battery of the present invention will be described for each configuration.

1. Positive electrode active material layer The positive electrode active material layer in the present invention is a layer containing at least a positive electrode active material. The positive electrode active material layer may further contain at least one of a conductive material and a binder in addition to the positive electrode active material.

  In the present invention, the active material described above can be used as the positive electrode active material. On the other hand, when the active material described above is used as the negative electrode active material, any active material having a higher potential can be used as the positive electrode active material.

  The conductive material is not particularly limited as long as it has desired electronic conductivity, and examples thereof include a carbon material. Examples of the carbon material include carbon black such as acetylene black, ketjen black, furnace black, and thermal black, graphene, fullerene, and carbon nanotube. On the other hand, the binder is not particularly limited as long as it is chemically and electrically stable. For example, a fluorine-based binder such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE). Materials can be mentioned.

  Further, 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. It is more preferable. Further, the thickness of the positive electrode active material layer varies greatly depending on the configuration of the battery, and is not particularly limited.

2. Negative electrode active material layer The negative electrode active material layer in the present invention 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 and a binder in addition to the negative electrode active material.

  In the present invention, the above-described active material can be used as the negative electrode active material. On the other hand, when the active material described above is used as the positive electrode active material, any active material having a lower potential can be used as the negative electrode active material.

  As the conductive material and the binder, the same materials as those described in “1. Positive electrode active material layer” described above can be used. Further, the content of the negative electrode active material in the negative electrode active material layer is preferably higher from the viewpoint of capacity, for example, 30% by weight or more, preferably 50% by weight or more, and 70% by weight or more. It is more preferable. In addition, the thickness of the negative electrode active material layer varies greatly depending on the configuration of the battery, and is not particularly limited.

3. Electrolyte layer The electrolyte layer in this invention is a layer formed between a positive electrode active material layer and a negative electrode active material layer. The electrolyte constituting the electrolyte layer may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

  The electrolytic solution in the present invention contains, for example, a fluoride salt and an organic solvent. Examples of fluoride salts include inorganic fluoride salts, organic fluoride salts, and ionic liquids. As an example of the inorganic fluoride salt, for example, XF (X is Li, Na, K, Rb or Cs) can be exemplified. As an example of the cation of the organic fluoride salt, an alkylammonium cation such as a tetramethylammonium cation can be given. The concentration of the fluoride salt in the electrolytic solution is, for example, in the range of 0.1 mol% to 40 mol%, and preferably in the range of 1 mol% to 10 mol%.

  The organic solvent of the electrolytic solution is usually a solvent that dissolves the fluoride salt. Examples of the organic solvent include glyme such as triethylene glycol dimethyl ether (G3) and tetraethylene glycol dimethyl ether (G4), ethylene carbonate (EC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), and propylene carbonate (PC). ), Cyclic carbonates such as butylene carbonate (BC), and chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). An ionic liquid may be used as the organic solvent.

On the other hand, examples of the solid electrolyte include fluorides of lanthanoid elements such as La and Ce, fluorides of alkali elements such as Li, Na, K, Rb, and Cs, and fluorides of alkaline earth elements such as Ca, Sr, and Ba Etc. Specific examples include fluorides of La and Ba (for example, La _0.9 Ba _0.1 F _2.9 ), fluorides of Pb and Sn, and the like.

  In addition, the thickness of the electrolyte layer in the present invention varies greatly depending on the configuration of the battery, and is not particularly limited.

4). Other Configurations The fluoride ion battery of the present invention has at least the negative electrode active material layer, the positive electrode active material layer, and the electrolyte layer described above. Furthermore, it usually has a positive electrode current collector for collecting current of the positive electrode active material layer and a negative electrode current collector for collecting current of the negative electrode active material layer. Examples of the shape of the current collector include a foil shape, a mesh shape, and a porous shape. Moreover, the fluoride ion battery of the present invention may have a separator between the positive electrode active material layer and the negative electrode active material layer. This is because a battery with higher safety can be obtained.

5. Fluoride ion battery The fluoride ion battery of the present invention may be a primary battery or a secondary battery, and among these, a secondary battery is preferable. This is because it can be repeatedly charged and discharged and is useful, for example, as an in-vehicle battery. Note that the primary battery includes primary battery use (use for the purpose of discharging only once after charging). In addition, examples of the shape of the fluoride ion battery of the present invention include a coin type, a laminate type, a cylindrical type, and a square type.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  Hereinafter, the present invention will be described in more detail with reference to examples.

[Example]
(Synthesis of active material)
2.659 g of SrF ₂ , 3.2454 g of Ce ₂ S ₃ , 7.2067 g of Bi, and 1.3823 g of S were weighed and put into an agate mortar and pulverized and mixed to obtain a mixture. The composition of the mixture corresponds to a molar ratio of SrF ₂ : Ce ₂ S ₃ : Bi: S = 0.50: 0.25: 1: 2. The resulting mixture was pelletized and vacuum sealed in a quartz tube. The quartz tube was placed in an electric furnace and fired at 800 ° C. The firing conditions were such that the temperature was raised to 800 ° C. in 2 hours and 40 minutes and held at 800 ° C. for 10 hours. Then, it cooled naturally and the obtained sample was grind | pulverized and mixed using the agate mortar. In addition, the sample before baking was reddish brown, the sample surface after baking was gray, and the sample after grinding | pulverization mixing was black.

The sample after pulverization and mixing was pelletized again and vacuum-sealed in a quartz tube. The quartz tube was placed in an electric furnace and fired at 800 ° C. The firing conditions were such that the temperature was raised to 800 ° C. in 2 hours and 40 minutes and held at 800 ° C. for 10 hours. Then, it cooled naturally and the obtained sample was grind | pulverized and mixed using the agate mortar. Thus, the active material _{(Sr 0.5} Ce _0.5 FBiS _2, black) was obtained.

[Evaluation]
(XRD measurement)
X-ray diffraction measurement (using CuKα rays) was performed using the active material obtained in the examples. The result is shown in FIG. As shown in FIG. 2, it is characteristic in the vicinity of 2θ = 25.7 °, 31.2 °, 41.5 °, 44.6 °, 52.5 °, 64.8 °, and 73.5 °. A peak was confirmed. These peak positions were the same as those of Sr _0.5 Ce _0.5 FBiS ₂ described in FIG.

(CV measurement and charge / discharge test)
A pellet battery was prepared using the active material obtained in the examples, and cyclic voltammetry (CV) measurement and charge / discharge test were performed. First, the active material obtained in the example, La _0.9 Ba _0.1 F _2.9 which is a fluoride ion conductive material, and VGCF which is an electron conductive material are mixed and pelletized. Thus, an electrode pellet was obtained. A pellet battery including the obtained electrode pellet (working electrode), a solid electrolyte layer using La _0.9 Ba _0.1 F _2.9 , and a Pb foil (counter electrode) was produced by pressing. CV measurement and a charge / discharge test were performed in a cell heated to 150 ° C. The conditions for CV measurement were a potential sweep range: -1.5 V to 2 V, and a sweep speed: 1.0 mV / sec. On the other hand, the conditions of the charge / discharge test were -1.5 V to 2.5 V (vs. Pb / PbF ₂ ), constant current charge / discharge (discharge start) of 5 μA / cm ² .

The results are shown in FIGS. As shown in FIG. 3, it was confirmed that the active materials obtained in the examples exhibited redox behavior. Moreover, as shown in FIG. 4, it was confirmed that the capacity was developed by charging and discharging. Thus, the active material obtained in the example reacted reversibly with fluoride ions. In particular, it can be seen from the charge / discharge curve shown in FIG. 4 that high Coulomb efficiency is obtained. Therefore, it was suggested that a battery having good cycle characteristics can be obtained. In addition, since the high Coulomb efficiency is acquired, it is estimated that the active material obtained in the Example has caused an intercalation reaction, not a fluorination defluorination reaction. In the fluorinated defluorination reaction, the crystal structure changes greatly, but in the intercalation reaction, the change in the crystal structure is suppressed and high coulomb efficiency is obtained. In addition, since it is suggested that an intercalation reaction has occurred, it is assumed that the chargeable / dischargeable property (property as an active material) is caused by the crystal structure of Sr _0.5 Ce _0.5 FBiS _2. Is done.

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 (3)

An active material used in a fluoride ion battery,
A crystal phase containing an M element (M is at least one of La, Ce, Pr, Nd, Sm, Ca, Sr and Ba), an F element, a Bi element, and an S element;
In the X-ray diffraction measurement using CuKα rays, the crystal phase is located at 2θ = 25.7 ° ± 0.5 °, 31.2 ° ± 0.5 °, 41.5 ° ± 0.5 °. An active material characterized by having a peak.   The active material for a fluoride ion battery according to claim 1, wherein the crystal phase has a crystal structure of a space group P4 / nmm. Fluoride ions having a positive electrode active material layer containing a positive electrode active material, a negative electrode active material layer containing a negative electrode active material, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer A battery,
The fluoride ion battery, wherein the positive electrode active material or the negative electrode active material is the active material according to claim 1 or 2.