JP7058051B2 - Power storage device - Google Patents

Description

The present application discloses a power storage device.

Patent Document 1 discloses a photoelectric material made of a sintered body of a rare earth metal sulfide (Ln ₂ S ₃ ) as a power storage device material. In Patent Document 2, the chemical formula a (Ba _x Sr _1-x ) TiO ₃ -bBi (M _0.5 Ti _0.5 ) O ₃ -cBi _0.5 (N _y K _1-y ) _0.5 TiO ₃ is used. A dielectric ceramic composition comprising a perovskite-type oxide represented is disclosed.

International Publication No. 2004/085339 Japanese Unexamined Patent Publication No. 2016-160166

Since rare earth metals are rare and expensive, there is a demand for new dielectric materials that can be obtained at low cost. Further, in order to increase the capacitance of the power storage device, a dielectric material having a high relative permittivity is also required. Examples of inexpensive materials include lithium-containing sulfides, but it has been known that lithium-containing sulfides have a small relative permittivity.

Therefore, in the present application, it is an object to improve the capacitance in a power storage device having an inexpensive dielectric material.

As a result of diligent studies, the present inventor has found that a single crystal dielectric having an LGPS-based crystal structure exhibits a very large relative permittivity in a specific orientation, and has completed the present invention.

That is, the present application is a power storage device in which a dielectric is arranged between two electrodes as one means for solving the above-mentioned problems, and the dielectric is Li _4-x M _1-x P _x S _{4-y Oy} . It has a composition represented by (0 <x <1, 0 ≦ y ≦ 2, M is Si, Sn, or Ge), the dielectric has a square crystal structure, and the above crystal structure. Has symmetry belonging to the space group P4 ₂ / nmc (137), and the electrode planes of the two electrodes are arranged at positions where a voltage can be applied in the direction perpendicular to the [001] crystal lattice plane of the dielectric. Disclose the power storage device.

According to the present disclosure, it is possible to provide a power storage device having a high capacitance.

It is a schematic diagram of the power storage device 10. It is a Core-Cole plot in an example.

<Power storage device>
FIG. 1 shows a schematic diagram of the power storage device 10 which is an embodiment of the power storage device of the present disclosure. As shown in FIG. 1, the power storage device 10 arranges the dielectric 2 between the two electrodes 1a and 1b.

(Electrodes 1a, 1b)
The electrodes 1a and 1b can be made of a known material used for a power storage device. A metal plate used as a metal collector may be attached to a dielectric to form an electrode, or a metal powder may be applied to the dielectric 2 to form an electrode. Preferably, a metal powder is applied to the dielectric 2 to form an electrode. Further, as the metal used for the electrodes 1a and 1b, a known metal material can be used. For example, Au, Cu, Al, carbon and the like can be mentioned. Au is preferred.

(Dielectric 2)
Dielectric 2 has a composition represented by Li _4-x M _1-x P _x S _{4-y Oy} (0 <x <1, 0 ≦ y ≦ 2, M is Si, Sn, or Ge). Have. The preferred M is Ge. Further, the dielectric 2 has a tetragonal crystal structure, and the crystal structure has symmetry belonging to the space group P42 / _nmc (137). The crystal system, space group, etc. of the dielectric 2 can be measured by an X-ray diffractometer.

The dielectric 2 is preferably a single crystal that does not contain grain boundaries. Further, the lattice constant of the dielectric 2 at room temperature is preferably 8.5 ≦ a ≦ 8.9 and 12.3 ≦ c ≦ 13.0.

The method for producing the dielectric 2 is not particularly limited, and the dielectric 2 can be produced by a known method. For example, J. Am. Ceram. Soc. , 1-9 (2015).

(Power storage device 10)
The power storage device 10 is manufactured by arranging the dielectric 2 between the two electrodes 1a and 1b. However, the electrode surfaces of the two electrodes 1a and 1b need to be arranged at positions where a voltage can be applied in the direction perpendicular to the [001] crystal lattice surface of the dielectric 2.
The crystal lattice plane of the dielectric 2 can be determined by, for example, a single crystal X-ray diffractometer.

By arranging the two electrodes 1a and 1b and the dielectric 2 as described above in the power storage device 10, the capacitance is improved. This is because the dielectric 2 exhibits a specifically high relative permittivity by applying a voltage to the direction perpendicular to the [001] crystal lattice plane of the dielectric 2.
The reason for this is considered to be that the lithium ions are likely to be displaced specifically in the [001] direction.

Here, the distance between the two electrodes 1a and 1b, that is, the thickness of the dielectric 2 (d in FIG. 1) is not particularly limited, but the upper limit is preferably 500 μm or less, and more preferably 150 μm or less. , 100 μm or less, more preferably 10 μm or less, most preferably 1 μm or less, and the lower limit is preferably 100 nm.

Hereinafter, the power storage device of the present disclosure will be described with reference to examples.

(Making a dielectric)
Li ₂ S (manufactured by Furuuchi Chemical Co., Ltd.), Ge (manufactured by High Purity Chemical Research Institute Co., Ltd.), P (manufactured by High Purity Chemical Research Institute Co., Ltd.), S (manufactured by High Purity Chemical Research Institute Co., Ltd.) Li _3. It was mixed in a glove box to have a composition of ₁₅ Ge _0.15 P _{0.85 S4 ,} pelleted and encapsulated in a quartz tube. The raw material sealed in the quartz tube was heated to 400 ° C. at a heating rate of 50 ° C./h, and heated for 8 hours while maintaining 400 ° C. Next, it was heated to 670 ° C. at a heating rate of 50 ° C./h, and heated for 1 hour while maintaining 670 ° C. Then, it was slowly cooled to 580 ° C. at a temperature lowering rate of 1 ° C./h, and when it reached 580 ° C., it was centrifuged. The centrifugally separated quartz tube was opened in a glove box to obtain a single crystal on the order of mm.

(Identification of dielectric)
The single crystal obtained above was enclosed in a quartz capillary in a glove box, and an X-ray diffraction pattern was measured using a single crystal X-ray diffractometer (Rigaku R-axis rapid). From the obtained X-ray diffraction pattern, it was found that the single crystal had a tetragonal crystal and had a symmetry belonging to the space group P42 / _nmc (137). The lattice constants were a = 8.6640 (2) Å and c = 12.5383 (5) Å. In addition, the crystal orientation of the single crystal was determined.

(Creation of power storage device)
The crystal particles were polished in a glove box so that the single crystal became a rectangular parallelepiped. Then, as shown in Table 1 below, a current collector (electrode) was molded by applying the uniform powder to a surface perpendicular to the direction in which the voltage was to be applied to obtain a power storage device according to Examples and Comparative Examples. The distance between the electrodes (thickness of the dielectric) and the area of the electrode surface (area of the electrode surface of the dielectric) were measured with a caliper.

(Measurement of permittivity)
The relative permittivity _εr of the power storage device according to the examples and comparative examples obtained above was measured by the impedance method. An impedance analyzer (4294A) manufactured by Agilent was used for the measurement, and the measurement was performed in the range of 100 Hz to 100 MHz.

As a result, the complex capacitance C ^* = C'-jωC "of the power storage device can be obtained. Here, C ^* is a complex capacitance, C'(F) is a real part, C'' (F) is an imaginary part, ω (rad / sec) is an angular frequency, and j is the following equation (1). be.

Then, the relative permittivity ε _r was calculated from the relational expression represented by the following equation (2). The dielectric constant ε ₀ of the vacuum was calculated as 8.854 pF / m.

The Core-Cole plot of the relative permittivity _εr calculated by the above method is shown in FIG. Here, the value of the real part ε _r'of the complex permittivity on the horizontal axis when the imaginary part ε _r '' of the complex permittivity on the vertical axis of the Core-Cole plot is maximized is the relative permittivity ε. It was adopted as _r .

As shown in FIG. 2, the relative permittivity ε _r of the electricity storage device according to the example was 2727, whereas the relative permittivity ε _r of the electricity storage device according to the comparative example was 850. Therefore, it was found that the relative permittivity ε _r of the power storage device is improved by applying a voltage in the direction perpendicular to the [001] crystal lattice plane.

Claims (1)

A power storage device in which a dielectric is placed between two electrodes.
The dielectric has a composition represented by Li _4-x M _1-x P _x S _{4-y Oy} (0 <x <1, 0 ≦ y ≦ 2, M is Si, Sn, or Ge). Have and
The dielectric has a tetragonal crystal structure, and the crystal structure has symmetry belonging to the space group P42 / _nmc (137).
The electrode surfaces of the two electrodes are arranged at positions where a voltage can be applied in the direction perpendicular to the [001] crystal lattice surface of the dielectric.
Power storage device.

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