JP2019050119A - Cathode active material - Google Patents

Abstract

To provide a novel cathode active material that is available for a fluoride ion battery.SOLUTION: The present invention relates to a cathode active material to be used for a fluoride ion battery, and the cathode active material contains a manganese oxide represented by MnO(meeting 2y=(x)×(valence of Mn)).SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to novel positive electrode active materials that can be used in fluoride ion batteries.

  For example, a Li-ion battery is known as a high voltage and high energy density battery. The Li-ion battery is a cation-based battery using Li ions as a carrier. On the other hand, as an anion-based battery, a fluoride ion battery using fluoride ion as a carrier is known.

For example, Non-Patent Document 1 discloses a positive electrode active material (LaSrMnO ₄ ) for a fluoride ion battery having a crystal phase of a layered perovskite structure. On the other hand, although not a technology related to a fluoride ion battery, Patent Document 1 discloses a mixture of sodium fluoride (NaF) and a divalent metal oxide (MO) (M is Fe, Mn, Ti, V, Co, Ni A positive electrode active material for a sodium ion secondary battery comprising at least one metal element) is disclosed.

JP, 2014-220203, A

Mohammad Ali Nowroozi et al., “LaSrMnO4: Reversible Electrochemical Intercalation of Fluoride Ions in the Context of Fluoride Ion Batteries”, Chem. Mater. 2017, 29, 3441-3453

  In order to improve the performance of a fluoride ion battery, a novel positive electrode active material is required. This indication is made in view of the said situation, and makes it a main purpose to provide the novel positive electrode active material which can be used for a fluoride ion battery.

In order to achieve the above object, in the present disclosure, a positive electrode active material used for a fluoride ion battery, which is represented by Mn _x O _y (2 y = x x (valence of Mn)) Provided is a positive electrode active material containing an oxide.

According to the present disclosure, it has been found that the manganese oxide represented by Mn _x O _y can be used as a positive electrode active material of a fluoride ion battery.

  The present disclosure has the effect of being able to provide a novel positive electrode active material that can be used for a fluoride ion battery.

It is a schematic sectional drawing which shows an example of the fluoride ion battery of this indication. It is the result of the charging / discharging test with respect to the battery for evaluation obtained in Examples 1-3. It is the result of the charging / discharging test with respect to the battery for evaluation obtained in Example 1 and Comparative Examples 1-4. It is the result of the XRD measurement with respect to the positive electrode active material layer (positive electrode compound material layer) produced in Example 1. It is the result of the XPS measurement with respect to the positive electrode active material layer (positive electrode mixture layer) produced in Example 1.

  Hereinafter, the positive electrode active material of the present disclosure will be described in detail.

The positive electrode active material of the present disclosure is a positive electrode active material used for a fluoride ion battery, and contains a manganese oxide represented by Mn _x O _y (2 y = x x (valence of Mn)). .

According to the present disclosure, it has been found that the manganese oxide represented by Mn _x O _y can be used as a positive electrode active material of a fluoride ion battery. For example, metals such as Cu (metal active materials) are known as conventional fluoride ion battery active materials, but the metal active materials undergo large changes in crystal structure during charge and discharge. Therefore, the resistance tends to be high and the cycle characteristic tends to be low. On the other hand, in the present disclosure, since the manganese oxide represented by Mn _x O _y is used, it is assumed that the crystal structure is less likely to change during charge and discharge compared to the metal active material, and the resistance is reduced and the cycle is reduced. Improvement of the characteristics is expected.

Further, for example, Non-Patent Document 1 discloses a positive electrode active material (LaSrMnO ₄ ) for a fluoride ion battery having a crystal phase of a layered perovskite structure. In an active material having a crystal phase of a layered perovskite structure, it is presumed that the function as an active material is exhibited by an insertion / elimination reaction (intercalation reaction) in which fluoride ions are inserted / eliminated. Since the intercalated type active material has a small expansion and contraction at the time of charge and discharge reaction, the cycle characteristic tends to be high but the capacity tends to be low. On the other hand, for example, as in Example 1 described later, the positive electrode active material using a manganese oxide containing divalent Mn (Mn ²⁺ ) is more effective than the positive electrode active material having a crystal phase of a layered perovskite structure. Also the capacity is large. It is presumed that this is because the crystal structure of the manganese oxide containing divalent Mn (Mn ²⁺ ) is not bulky compared to the crystal structure of the layered perovskite structure. In addition, as in Example 1 described later, the positive electrode active material using a manganese oxide containing divalent Mn (Mn ²⁺ ) has a reaction potential higher than that of a positive electrode active material having a crystal phase of layered perovskite structure. It has the advantage of

The positive electrode active material of the present disclosure contains a manganese oxide represented by Mn _x O _y (2 y = x x (valence of Mn)). Manganese oxides are represented by Mn _x O _y , x and y are both real numbers greater than 0, and usually 2y = x x (valence of Mn) to maintain electrical neutrality. Fulfill. For example, if all Mn in Mn _x O _y are divalent Mn (Mn ²⁺ ), then 2y = x × 2 and the molar ratio of x and y will be the same (MnO). Specific examples of Mn _x O _y include MnO, Mn ₂ O ₃ , and MnO ₂ .

The valence number of Mn in Mn _x O _y is not particularly limited. In general, Mn elements can stably obtain divalent, trivalent, tetravalent, hexavalent, and heptavalent, but the valence number of Mn in Mn _x O _y is bivalent, trivalent and tetravalent. Is preferred. Further, the valence number of Mn in Mn _x O _y may be only one or plural kinds.

In addition, Mn _x O _y preferably has at least bivalent Mn (Mn ²⁺ ). This is because the positive electrode active material has a large capacity. The ratio of divalent Mn (Mn ²⁺ ) to all Mn in Mn _x O _y is not particularly limited, and is, for example, 10 mol% or more, may be 30 mol% or more, and may be 50 mol% or more, 70 mol % Or more, or 90 mol% or more.

The positive electrode active material of the present disclosure contains a manganese oxide represented by Mn _x O _y (2 y = x x (valence of Mn)). The positive electrode active material may be a single phase material containing only the crystalline phase of the manganese oxide, or may be a multiphase material containing the crystalline phase of the manganese oxide and other crystalline phases. In the case of the latter, it is preferable to contain the crystal phase of the said manganese oxide as a main phase.

Although the shape of the positive electrode active material of this indication is not specifically limited, For example, a particulate form can be mentioned. The average particle size (D ₅₀ ) of the positive electrode 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 size (D ₅₀ ) of the positive electrode active material can be determined, for example, from the result of particle size distribution measurement by a laser diffraction scattering method. Moreover, the method of manufacturing the positive electrode active material of the present disclosure is not particularly limited as long as the method can obtain the target positive electrode active material.

  Moreover, in the present disclosure, the positive electrode active material layer containing the above-described positive electrode active material, the negative electrode active material layer containing the negative electrode active material, and the positive electrode active material layer and the negative electrode active material layer It is also possible to provide a fluoride ion battery having an electrolyte layer. FIG. 1 is a schematic cross-sectional view showing an example of a fluoride ion battery. The fluoride ion battery 10 shown in FIG. 1 comprises 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 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 performing current collection of the positive electrode active material layer 1, the negative electrode current collector 5 performing current collection of the negative electrode active material layer 2, and these members are accommodated. And a battery case 6.

  The positive electrode active material layer is a layer containing at least a positive electrode active material. The positive electrode active material is the same as the contents described above. The content of the positive electrode active material in the positive electrode active material layer is, for example, 25% by weight or more, preferably 50% by weight or more, and more preferably 75% by weight or more. Further, the thickness of the positive electrode active material layer is largely different depending on the configuration of the battery, and is not particularly limited. In addition to the positive electrode active material, the positive electrode active material layer may further contain at least one of a solid electrolyte, a conductive material, and a binder.

  The negative electrode active material layer is a layer containing at least a negative electrode active material. As the negative electrode active material, any active material having a potential lower than that of the positive electrode active material can be selected. As a negative electrode active material, a metal single-piece | unit, an alloy, a metal oxide, and these fluorides can be mentioned, for example. Examples of the metal element 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, Pb, etc. can be mentioned.

  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, 25% by weight or more, preferably 50% by weight or more, and 75% by weight or more More preferable. Further, the thickness of the negative electrode active material layer is largely different depending on the configuration of the battery, and is not particularly limited. In addition to the negative electrode active material, the negative electrode active material layer may further contain at least one of a solid electrolyte, a conductive material, and a binder.

  The electrolyte layer is a layer formed between the positive electrode active material layer and the negative electrode active material layer. The electrolyte constituting the electrolyte layer may be a liquid electrolyte (electrolyte solution) or a solid electrolyte. That is, the electrolyte layer may be a liquid electrolyte layer or a solid electrolyte layer.

  The electrolyte contains, for example, a fluoride salt and an organic solvent. As a fluoride salt, an inorganic fluoride salt and an organic fluoride salt can be mentioned, for example. As an example of inorganic fluoride salt, XF (X is Li, Na, K, Rb or Cs) can be mentioned. As an example of the cation of the organic fluoride salt, an alkyl ammonium cation such as tetramethyl ammonium cation can be mentioned.

  As the organic solvent, for example, glyme such as triethylene glycol dimethyl ether (G3), tetraethylene glycol dimethyl ether (G4), ethylene carbonate (EC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), propylene carbonate (PC) And cyclic carbonates such as butylene carbonate (BC) and linear carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC). Moreover, you may use an ionic liquid as an organic solvent.

  On the other hand, as a solid electrolyte, an inorganic solid electrolyte can be mentioned, for example. As the inorganic solid electrolyte, for example, a fluoride containing a lanthanoid element such as La or Ce, a fluoride containing an alkali element such as Li, Na, K, Rb or Cs, an alkaline earth such as Ca, Sr or Ba Mention may be made of element-containing fluorides. The thickness of the electrolyte layer is largely different depending on the configuration of the battery, and is not particularly limited.

  The fluoride ion battery preferably has a positive electrode current collector for collecting current in the positive electrode active material layer and a negative electrode current collector for collecting current in the negative electrode active material layer. The fluoride ion battery may be a primary battery or a secondary battery, and among them, a secondary battery is preferable. This is because the battery can be repeatedly charged and discharged, and it is useful as, for example, an on-vehicle battery. The secondary battery also includes primary battery use of the secondary battery (use for the purpose of discharging only once after charging). Moreover, as a shape of a fluoride ion battery, coin shape, a laminate type, cylindrical shape, and a square shape can be mentioned, for example.

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

  The present disclosure will be described more specifically.

Example 1
MnO: La _0.9 Ba _0.1 F _2.9 : MnO which is a positive electrode active material, La _0.9 Ba _0.1 F _2.9 which is a solid electrolyte, and VGCF which is a conductive material It mixed by the weight ratio of VGCF = 30: 60: 10, and obtained the positive electrode compound material. The obtained positive electrode mixture (working electrode), a solid electrolyte (La _0.9 Ba _0.1 F _2.9 ) forming a solid electrolyte layer, and a negative electrode mixture (Pb _{0. 2} ) forming a negative electrode active material layer _. A mixture of ₆ Sn _0.4 F ₂ and acetylene black) and a Pb foil (counter electrode) were compacted to obtain a battery for evaluation.

Example 2
An evaluation battery was obtained in the same manner as Example 1, except that Mn ₂ O ₃ was used as the positive electrode active material.

[Example 3]
An evaluation battery was obtained in the same manner as Example 1, except that MnO ₂ was used as the positive electrode active material.

Comparative Example 1
A battery for evaluation was obtained in the same manner as in Example 1 except that La _1.2 Sr _1.8 Mn ₂ O ₇ F ₂ was used as the positive electrode active material.

Comparative Example 2
An evaluation battery was obtained in the same manner as Example 1, except that CaMnO ₃ was used as the positive electrode active material.

Comparative Example 3
An evaluation battery was obtained in the same manner as Example 1, except that LaMnO ₃ was used as the positive electrode active material.

Comparative Example 4
An evaluation battery was obtained in the same manner as Example 1, except that SrMnO ₃ was used as the positive electrode active material.

(Charge and discharge test)
The charging / discharging test was implemented in the cell heated at 140 degreeC with respect to the battery for evaluation obtained in Examples 1-3 and Comparative Examples 1-4. The current conditions were 50 μA / cm ² (discharge) and 50 μA / cm ² (charge). The results are shown in FIG. 2 and FIG.

FIGS. 2A to 2C show the results of Examples 1 to 3, respectively, and it was confirmed that any manganese oxide can be charged and discharged as a positive electrode active material. In particular, Example 1 had large charge capacity and discharge capacity. Moreover, as shown in FIG. 3, the discharge capacity was larger in Example 1 than in Comparative Examples 1 to 4. Furthermore, it was confirmed that Example 1 has a higher potential of the discharge reaction than Comparative Examples 1 to 4 and is advantageous in terms of improvement of the energy density and the power density. It is presumed that this is because Example 1 uses MnO containing low valence Mn ²⁺ .

(XRD measurement)
With respect to the positive electrode active material layer (positive electrode mixture layer) in Example 1, X-ray diffraction measurement (XRD measurement) was performed in a state where charge and discharge states are different. Specifically, XRD measurement was performed in a pre-charge state (pristine), 1 V charge state, 2 V charge state, 3 V charge state, and -1.5 V discharge state. The results are shown in FIG. As shown in FIG. 4, in the charged state, the crystal peaks derived from MnO (eg, peaks near 2θ = 40 ° and 60 °) disappear, but after discharge, the crystal peaks derived from MnO are again Appeared. Therefore, it was confirmed that the fluorination reaction and the defluorination reaction occur reversibly.

(XPS measurement)
With respect to the positive electrode active material layer (positive electrode mixture layer) in Example 1, X-ray photoelectron spectroscopy (XPS measurement) was performed in a state in which charge and discharge states are different. Specifically, XPS measurement is performed in the pre-charge state (pristine), 1 V charge state, 2 V charge state, 3 V charge state, 0 V discharge state, −1.5 V discharge state, Mn (2 p), La (3 d), The behavior of F (1s) and Ba (3d) was investigated. The results are shown in FIG. As shown in FIG. 5 (a), it was confirmed that the peak position of Mn shifts with charge and discharge. Specifically, the peak of Mn shifted to the high energy side as charging was performed. This suggests that Mn is changing to a high number with fluorination. On the other hand, the peak of Mn shifted to the low energy side with the discharge. This suggested that Mn was changed to a lower valence number along with the defluorination. From these things, it is inferred that the charge-discharge reaction of MnO is progressing by Redox of Mn. On the other hand, as shown in FIGS. 5 (b) to 5 (d), the peak positions of La, F and Ba did not shift due to charge and discharge.

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 6 ... battery case 10 ... fluoride ion battery

Claims (1)

A positive electrode active material used for a fluoride ion battery,
Mn _x O _y containing manganese oxide represented by (2y = x × (satisfy Mn valence of)), the positive electrode active material.