JP7120190B2 - Active material - Google Patents

Description

The present disclosure relates to novel active materials that can be used in 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 uses Li-ions as carriers. On the other hand, as an anion-based battery, a fluoride ion battery using fluoride ions as carriers is known.

For example, Patent Document 1 discloses a fluoride ion battery using a positive electrode active material and a solid electrolyte represented by PbF ₂ or PbMF _x in a positive electrode active material layer.

JP 2019-029206 A

New active materials are required to improve the performance of fluoride ion batteries. The present disclosure has been made in view of the above circumstances, and a main object thereof is to provide a novel active material that can be used in fluoride ion batteries.

In order to achieve the above object, the present disclosure provides an active material for use in fluoride ion batteries, which has a perovskite crystal phase containing Bi element, transition metal element and O element.

According to the present disclosure, since the active material has a specific crystal phase, it is possible to improve the performance of a fluoride ion battery using the active material.

The present disclosure takes advantage of novel active materials that enable fluoride ion batteries with good performance.

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 of the positive electrode active material used in Example 2. FIG. 4 shows the results of a charge/discharge test of the battery for evaluation obtained in Example 1. FIG. 4 shows the results of a charge/discharge test of the battery for evaluation obtained in Example 2. FIG. 4 shows the results of a charge/discharge test of the battery for evaluation obtained in Example 3. FIG. 4 shows the results of rate evaluation of the battery for evaluation obtained in Example 4. FIG. 4 shows the results of rate evaluation of the battery for evaluation obtained in Example 3. FIG. 1 shows the results of a cycle test of evaluation batteries obtained in Examples 1 to 3 and Comparative Example 1. FIG.

1. Active Material Hereinafter, the active material in the present disclosure will be described in detail.
The active material in the present disclosure is an active material used in fluoride ion batteries and has a perovskite crystal phase containing Bi element, transition metal element and O element.

According to the present disclosure, since the active material has a specific crystal phase, it is possible to improve the performance of a fluoride ion battery using the active material. In addition, good performance of a fluoride ion battery means, for example, excellent performance such as capacity, rate characteristics (low resistance), and cycle characteristics.

The active material in the present disclosure has a perovskite crystal phase containing Bi element, transition metal element and O element. The perovskite crystal phase is commonly denoted by _ABO3 . The above A corresponds to the A site in the perovskite structure, and includes a Bi element in the present disclosure. Moreover, the above B corresponds to the B site in the perovskite structure, and includes a transition metal element in the present disclosure.

The ratio of the Bi element at the A site is, for example, 50% or more, may be 70% or more, may be 90% or more, or may be 100%. Also, the proportion of the transition metal element in the B site is, for example, 50% or more, may be 70% or more, may be 90% or more, or may be 100%. Examples of transition metal elements include Fe, Co, and Mn. The perovskite crystal phase may contain only one type of transition metal element, or may contain two or more types.

Also, the active material in the present disclosure is preferably a so-called multiferroic material containing at least Fe as a transition metal element. A multiferroic material is a material that exhibits ferroelectricity and ferromagnetism. If it is ferroelectric, it has excellent F 2 ⁻ ion conductivity, and if it is ferromagnetic, the effect of suppressing structural collapse is high. Therefore, if the active material in the present disclosure is a multiferroic material, a fluoride ion battery with better cycle characteristics, high capacity, and low resistance can be obtained.

When the active material in the present disclosure is a multiferroic material, the perovskite crystal phase is, for example, Bi(Fe _1-x , M _x )O ₃ (M is at least one transition metal element, x is 0≦x<1). x may be 0 or greater than 0. x may be, for example, 0.3 or more, or 0.7 or more. Examples of M above include Co and Mn. The above M may be either one of Co and Mn, or both. When M is Co and Mn, the perovskite crystal phase in the present disclosure is Bi(Fe _1-yz , Co _y , Mn _z )O ₃ (0<y<1, 0<z<1, satisfies 0<y+z<1). y and z are the same as x above. Moreover, y may be smaller than z, may be the same, or may be larger than z.

Moreover, the active material in the present disclosure preferably has the perovskite crystal phase as a main phase. The proportion of the crystal phase in all crystal phases of the active material is, for example, 50 mol % or more, may be 70 mol % or more, or may be 90 mol % or more. In particular, the active material in the present disclosure preferably has the crystal phase as a single phase.

Whether the active material in the present disclosure has the perovskite crystal phase can be confirmed, for example, by performing X-ray structure analysis measurement (XRD measurement). For example, by collating the obtained XRD data with ICSD (crystal structure database), it is possible to determine whether or not the crystal phase is present.

The composition of the active material in the present disclosure is not particularly limited as long as it contains the crystal phase described above, but for example, it is preferably ABO ₃ (A contains a Bi element and B contains a transition metal element). . Further, when the active material in the present disclosure is a multiferroic material, the composition of the active material is Bi(Fe _1-x , M _x )O ₃ (M is at least one transition metal element, x satisfies 0≦x<1). Furthermore, when the active material in the present disclosure contains Fe element, Co element and Mn element, the composition of the active material is Bi(Fe _1-yz , Co _y , Mn _z )O ₃ (0<y<1 , 0<z<1 and 0<y+z<1). The preferred ranges of x, y, and z in these compositions are the same as those described above.

Examples of the shape of the active material in the present disclosure include particulate. The average primary particle diameter (D ₅₀ ) of the active material is, for example, 10 nm or more and 10 μm or less, and may be 20 nm or more and 1 μm or less. Incidentally, the average primary particle size can be determined, for example, by observation with a scanning electron microscope (SEM). The number of samples is preferably large, for example, 20 or more, may be 50 or more, or may be 100 or more. The average primary particle size of the active material can be appropriately adjusted, for example, by appropriately changing the manufacturing conditions of the active material or performing a classification treatment.

The active material in the present disclosure can be used as at least one of a positive electrode active material and a negative electrode active material in a fluoride ion battery described later.

The active material in the present disclosure can be obtained, for example, by solid phase synthesis. Bi ₂ O ₃ , Fe ₂ O ₃ and oxides such as CoO and MnO as doping materials are pulverized and mixed and pelletized. An active material can be synthesized by sintering the pellets in an electric furnace in an air atmosphere at, for example, a temperature range of 1000° C. to 1500° C. for 12 hours.

2. Fluoride Ion Battery FIG. 1 is a schematic cross-sectional view showing an example of a fluoride ion battery in the present disclosure. 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, and and an electrolyte layer 3 formed therebetween. At least one of the positive electrode active material and the negative electrode active material contains the active material. Furthermore, the fluoride ion battery 10 shown in FIG. It has a battery case 6 that houses the members.

(1) Positive electrode active material layer The positive electrode active material layer is a layer containing at least a positive electrode active material. Moreover, the positive electrode active material layer may further contain at least one of an electrolyte, a conductive material and a binder, if necessary.

In the positive electrode active material layer, the positive electrode active material preferably contains the above active material. The positive electrode active material may contain only the above active material, or may contain other positive electrode active materials. Other positive electrode active materials include conventionally known positive electrode active materials used in fluoride ion batteries. When other positive electrode active materials are contained, the proportion of the above active materials in the total positive electrode active materials is, for example, 50% by weight or more, may be 60% by weight or more, or may be 70% by weight or more, It may be 80% by weight or more, or 90% by weight or more.

From the viewpoint of capacity, the proportion of the positive electrode active material in the positive electrode active material layer is preferably higher. The proportion of the positive electrode active material is, for example, 60% by weight or more, and may be 70% by weight or more. On the other hand, the proportion of the positive electrode active material is, for example, 99% by weight or less, and may be 95% by weight or less.

Examples of conductive materials include carbon materials. Specific examples of carbon materials include acetylene black, ketjen black, VGCF, and graphite. 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. On the other hand, the proportion of the conductive material is, for example, 20% by weight or less, and may be 10% by weight or less. If the proportion of the conductive material is too small, an electron conduction path may not be formed, resulting in increased electrode resistance. If the proportion of the conductive material is too high, the proportion of the positive electrode active material is relatively low, which may lower the energy density.

Examples of binders include rubber-based binders and fluoride-based binders. The ratio of the binder in the positive electrode active material layer is, for example, 1% by weight or more and 30% by weight or less.

The contents of the electrolyte are the same as those of "(3) Electrolyte layer" described later.

The thickness of the positive electrode active material layer is not particularly limited, and can be appropriately adjusted according to the configuration of the battery.

(2) Negative Electrode Active Material Layer The negative electrode active material layer is a layer containing at least a negative electrode active material. Moreover, the negative electrode active material layer may further contain at least one of an electrolyte, a conductive material, and a binder, if necessary.

The negative electrode active material layer preferably contains the active material described above as the negative electrode active material. Although the active materials described above may be used for both the positive electrode active material and the negative electrode active material, an active material having a reaction potential higher than that of the negative electrode active material is used as the positive electrode active material. On the other hand, when only the positive electrode active material is the active material described above, the negative electrode active material layer preferably contains an active material containing the F element. An example of the active material containing the F element is PbF ₂ .

From the viewpoint of capacity, it is preferable that the ratio of the negative electrode active material in the negative electrode active material layer is higher. The ratio of the negative electrode active material is, for example, 60% by weight or more, and may be 70% by weight or more. On the other hand, the ratio of the negative electrode active material is, for example, 99% by weight or less, and may be 95% by weight or less.

The types and proportions of the electrolyte, conductive material, and binder used in the negative electrode active material layer can be the same as those described in "(1) Positive electrode active material layer" above. Description is omitted.

The thickness of the negative electrode active material layer is not particularly limited, and can be appropriately adjusted according to the configuration of the battery.

(3) Electrolyte Layer The electrolyte layer 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) or a solid electrolyte. That is, the electrolyte layer may be a liquid electrolyte layer or a solid electrolyte layer, but the latter is preferred.

The electrolytic solution in the present disclosure contains, for example, fluoride salt and organic solvent. Examples of fluoride salts include inorganic fluoride salts, organic fluoride salts, and ionic liquids. An example of an inorganic fluoride salt is 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 % or more and 40 mol % or less, preferably 1 mol % or more and 10 mol % or less.

The organic solvent of the electrolyte is usually a solvent that dissolves the fluoride salt. Examples of organic solvents include glyme such as triethylene glycol dimethyl ether (G3) and tetraethylene glycol dimethyl ether (G4), ethylene carbonate (EC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), propylene carbonate (PC ), butylene carbonate (BC) and other cyclic carbonates, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC) and other chain carbonates. Moreover, you may use an ionic liquid as an organic solvent.

Examples of solid electrolytes include inorganic solid electrolytes. Examples of inorganic solid electrolytes include fluorides containing lanthanoid elements such as La and Ce; fluorides containing alkali elements such as Li, Na, K, Rb, and Cs; and alkaline earth elements such as Ca, Sr, and Ba. Mention may be made of fluoride containing elements. Specific examples of inorganic solid electrolytes include fluorides containing La and Ba, fluorides containing Pb and Sn, and fluorides containing Bi and Sn. La _0.9 Ba _0.1 F _2.9 can be mentioned as a specific solid electrolyte.

The thickness of the electrolyte layer is not particularly limited, and can be appropriately adjusted according to the configuration of the battery.

(4) Other Configurations A fluoride ion battery according to the present disclosure 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 materials for the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon. Examples of the shape of the positive electrode current collector and the negative electrode current collector include, for example, a foil shape, a mesh shape, and a porous shape. In addition, the fluoride ion battery in the present disclosure may have a battery case that houses battery members. A battery case of a general battery can be used as the battery case.

(5) Fluoride ion battery The fluoride ion battery in the present disclosure may be a primary battery or a secondary battery, and is preferably a secondary battery. This is because they can be repeatedly charged and discharged, and are useful, for example, as batteries for vehicles. The secondary battery also includes use of a secondary battery as a primary battery (use for the purpose of discharging only once after charging). In addition, examples of the shape of the fluoride ion battery in the present disclosure include 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 similar effects is the present invention. It is included in the technical scope of the disclosure.

[Example 1]
A positive electrode active material ( _BiFeO3 , manufactured by Toyoshima Seisakusho), a solid electrolyte ( _{La0.9Ba0.1F2.9} ), and a conductive material (acetylene black) were _mixed at a weight ratio of _30:60:10 . A positive electrode mixture was obtained by mixing using a ball mill (working electrode). A negative electrode active material (PbF ₂ ) and a conductive material (acetylene black) were mixed at a weight ratio of 95:5 to obtain a negative electrode mixture. The obtained positive electrode mixture, the solid electrolyte (La _0.9 Ba _0.1 F _2.9 ) forming the solid electrolyte layer, the negative electrode mixture, and the Pb foil (counter electrode) are laminated and compacted. By doing so, a battery for evaluation was produced.

[Example 2]
(Synthesis of positive electrode active material)
As a positive electrode active material, Bi(Fe _0.5 Co _0.5 )O ₃ was synthesized by a solid phase synthesis method. Specifically, Bi ₂ O ₃ , Fe ₂ O ₃ and CoO were weighed to match the stoichiometric ratio, pulverized and mixed in a mortar, and pelletized. After that, it was sintered at 1200° C. for 12 hours in an electric furnace in an air atmosphere to obtain a positive electrode active material.

(Preparation of battery for evaluation)
A battery for evaluation was produced in the same manner as in Example 1, except that the above active material was used as the positive electrode active material contained in the positive electrode mixture.

[Example 3]
(Synthesis of positive electrode active material)
A positive electrode active material (Bi( _Fe0.7 , _Mn0.3 )O3 was prepared by a solid _- phase synthesis method in the same manner as in Example ₂ , except that _Bi2O3 , _Fe2O3 and MnO _were used. ) was synthesized.

(Preparation of battery for evaluation)
A battery for evaluation was produced in the same manner as in Example 1, except that the above active material was used as the positive electrode active material contained in the positive electrode mixture.

[Comparative Example 1]
A battery for evaluation was produced in the same manner as in Example 1, except that CoO was used as the positive electrode active material contained in the positive electrode mixture.

[evaluation]
(XRD measurement)
The positive electrode active material (Bi(Fe _0.5 , Co _0.5 )O ₃ ) in Example 2 was subjected to XRD measurement (using CuKα rays). The results are shown in FIG. The peaks shown in FIG. 2 agreed with the data of Bi(Fe _0.5 , Co _0.5 )O ₃ in ICSD (Inorganic Crystal Structure Database). From this, it was confirmed that the positive electrode active material of Example 2 had a crystal phase of Bi(Fe _0.5 , Co _0.5 )O ₃ in a substantially single phase. Although not shown, the positive electrode active material of Example 3 also had a crystal phase of Bi(Fe _0.7 , Mn _0.3 )O ₃ in a substantially single phase.

(Charging and discharging test)
A charge/discharge test was performed on the evaluation batteries obtained in Examples 1 to 3. The charge/discharge test was conducted in an environment of 140° C. under conditions of a current of 50 μA/cm ² and a final potential of the working electrode of −1.5 V (vs Pb/PbF ₂ ) to 3.0 V (vs Pb/PbF ₂ ). . The results of Examples 1 to 3 are shown in FIGS. 3 to 5. FIG.

As shown in FIG. 3, in Example 1 (BiFeO ₃ ), two-step potential plateaus were confirmed on both the charge side and the discharge side, and a discharge capacity of about 160 mAh/g was obtained. As shown in FIG. 4 , in Example 2 (Bi(Fe _0.5 , Co _0.5 )O ₃ ), a potential plateau was observed near 0.3 V in both charging and discharging, and a voltage of about 270 mAh/g was observed. A discharge capacity was obtained. As shown in FIG. 5, in Example 3 (Bi(Fe _0.7 , Mn _0.3 )O ₃ ), two-stage potential plateaus were confirmed on both the charge side and the discharge side, and a high potential plateau was observed. It was long. The discharge capacity was about 270mAh/g.

(Rate characteristic evaluation)
For the evaluation batteries obtained in Examples 2 and 3, the same charge/discharge test was performed, except that the current was changed to 30 μA/cm ² , 90 μA/cm ² , 300 μA/cm ² and 3 mA/cm ² . The test was conducted under the conditions of The results are shown in FIGS. 6 and 7. FIG. Note that 1 mAh in the figure corresponds to 333 mAh/g.

As shown in FIGS. 6 and 7, Example 2 with Fe and Co on the B-site of the perovskite shows better capacity even at high rates and better F ⁻ ion conduction. It was confirmed that

(Cycle test)
The evaluation batteries obtained in Examples 1 to 3 and Comparative Example 1 were subjected to a cycle test under the same conditions as the charge/discharge test. The capacity after 3 cycles relative to the capacity at the 1st cycle was obtained and evaluated (capacity retention rate (%)). The results are shown in FIG.

As shown in FIG. 8, the fluoride ion battery of the present disclosure had a capacity retention rate of nearly 100%. On the other hand, the battery for evaluation obtained in Comparative Example 1 had a capacity retention rate of about 40%. Thus, it was confirmed that the fluoride ion battery using the active material according to the present disclosure has good performance.

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 (1)

An active material used in a fluoride ion battery,
An active material having a perovskite crystal phase containing a Bi element, a transition metal element and an O element.

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