WO2022153615A1 - Battery cell, cell stack, and redox flow battery system - Google Patents

Abstract

This battery cell comprises a positive electrode, a negative electrode, and a barrier membrane, and includes a first layer that is disposed between the positive electrode and the barrier membrane and/or between the negative electrode and the barrier membrane. The first layer is a first fiber aggregate that includes a plurality of first fibers formed of an insulative material. The average diameter of the plurality of first fibers is 2 μm to 50 μm, and the void ratio of the first fiber aggregate is 20% to 99%.

Description

Battery cell, cell stack, and redox flow battery system

The present disclosure relates to battery cells, cell stacks, and redox flow battery systems.
This application claims priority based on Japanese Patent Application No. 2021-002853 of the Japanese application dated January 12, 2021, and incorporates all the contents described in the Japanese application.

The battery element of the redox flow battery of Patent Document 1 includes a positive electrode, a negative electrode, an ion exchange membrane, and a porous sheet material. The ion exchange membrane is arranged between the positive electrode and the negative electrode. The porous sheet material is provided on each surface of the ion exchange membrane facing the positive electrode and the surface facing the negative electrode. The positive electrode and the negative electrode are made of a non-woven fabric made of carbon fiber. The porous sheet material is composed of an organic material.

Japanese Unexamined Patent Publication No. 2013-65530

The battery cell of the present disclosure is a battery cell including a positive electrode, a negative electrode, and a diaphragm, and is arranged between the positive electrode and the diaphragm and at least one of the negative electrode and the diaphragm. The first layer is a first fiber aggregate having a plurality of first fibers made of an insulating material, and the average diameter of the plurality of first fibers is 2 μm or more and 50 μm or less. The void ratio of the first fiber aggregate is 20% or more and 99% or less.

The cell stack of the present disclosure includes a plurality of battery cells, and at least one of the plurality of battery cells is the battery cell of the present disclosure.

The redox flow battery system of the present disclosure includes the battery cells of the present disclosure or the cell stack of the present disclosure.

FIG. 1 is a schematic configuration diagram of a redox flow battery system according to an embodiment. FIG. 2 is a schematic configuration diagram of a cell stack provided in the redox flow battery system according to the embodiment. FIG. 3 is an enlarged view showing an enlarged surface of the first layer provided in the redox flow battery system according to the embodiment. FIG. 4 is an enlarged view showing an enlarged surface of an electrode provided in the redox flow battery system according to the embodiment. FIG. 5 is an explanatory diagram showing measurement points for measuring the thickness of the first layer provided in the redox flow battery system according to the embodiment.

[Issues to be solved by this disclosure]
The porous sheet material protects the ion exchange membrane by being provided between the electrode and the ion exchange membrane. The protection of the ion exchange membrane prevents damage to the ion exchange membrane due to contact between the electrode and the ion exchange membrane. Specifically, it prevents the fibers of the electrode from sticking into the ion exchange membrane and cracking the ion exchange membrane. By preventing damage to the ion exchange membrane, it is possible to prevent the positive electrode electrolyte and the negative electrode electrolyte from being short-circuited through the damaged portion of the ion exchange membrane. Therefore, the decrease in current efficiency is suppressed. The porous sheet material may inhibit the diffusion of the electrolytic solution. If the diffusion of the electrolytic solution is inhibited, the reaction resistivity of the battery cell may increase.

One of the purposes of the present disclosure is to provide a battery cell, a cell stack, and a redox flow battery system that can easily achieve both improvement in current efficiency and reduction in reaction resistivity.

[Effect of the present disclosure]
The battery cell, cell stack, and redox flow battery system of the present disclosure can easily achieve both improvement in current efficiency and reduction in reaction resistivity.

<< Explanation of Embodiments of the present disclosure >>
First, embodiments of the present disclosure will be listed and described.

(1) The battery cell according to one aspect of the present disclosure is a battery cell including a positive electrode, a negative electrode, and a diaphragm, and is between the positive electrode and the diaphragm and between the negative electrode and the diaphragm. It comprises a first layer arranged between at least one of the first layers, which is a first fiber assembly having a plurality of first fibers made of an insulating material, and is an average of the plurality of first fibers. The diameter is 2 μm or more and 50 μm or less, and the void ratio of the first fiber aggregate is 20% or more and 99% or less.

In a battery cell in which the first layer is not arranged, the diaphragm is easily damaged especially when the battery cell is assembled. The battery cell is usually assembled by stacking the cell frame, the positive electrode, the diaphragm, and the negative electrode in this order. During the flat stacking, the electrodes and the diaphragm may rub against each other when aligning the members. Excessive rubbing between the electrodes and the diaphragm makes the diaphragm more susceptible to damage.

In the battery cell of the present disclosure, the contact between the electrode and the diaphragm is easily suppressed by the first layer arranged between at least one of the positive electrode and the negative electrode and the diaphragm. The first layer, which is composed of the first fiber aggregate having a porosity of 99% or less, contributes to maintaining the distance between the electrode and the diaphragm. In particular, the first layer composed of the first fiber aggregate having a porosity of 99% or less has the second fiber even if the electrode is composed of the second fiber aggregate having a plurality of second fibers. It is easy to suppress the penetration of the diaphragm through the voids of the first layer. Therefore, the battery cell of the present disclosure can easily suppress damage to the diaphragm due to contact between the electrode and the diaphragm.

The first layer is composed of a first fiber aggregate having a plurality of first fibers. The first fiber having an average diameter of 2 μm or more is unlikely to pierce the septum. The first fiber having an average diameter of 50 μm or less is less likely to be caught in the diaphragm. Therefore, the battery cell of the present disclosure can easily suppress damage to the diaphragm due to contact between the first layer and the diaphragm.

By suppressing the damage to the diaphragm, it is possible to prevent the positive electrode electrolyte and the negative electrode electrolyte from being short-circuited through the damaged portion of the diaphragm. Therefore, the battery cell of the present disclosure tends to improve the current efficiency.

The first layer in which the porosity of the first fiber aggregate satisfies 20% or more easily diffuses the electrolytic solution. Therefore, the battery cell of the present disclosure tends to reduce the reaction resistivity.

(2) As one form of the battery cell, the basis weight of the first fiber aggregate is 5 g / m ² or more and 100 g / m ² or less.

The first fiber aggregate having a grain size of 5 g / m ² or more can easily suppress damage to the diaphragm due to contact between at least one of the positive electrode and the negative electrode and the diaphragm. The first fiber aggregate having a basis weight of 100 g / m ² or less can easily suppress damage to the diaphragm due to contact between the first layer and the diaphragm. Moreover, the first fiber aggregate having a basis weight of 100 g / m ² or less easily diffuses the electrolytic solution.

(3) As one form of the battery cell, the thickness of the first fiber aggregate is 5 μm or more and 3000 μm or less.

The first fiber aggregate having a thickness of 5 μm or more can easily suppress damage to the diaphragm due to contact between at least one of the positive electrode and the negative electrode and the diaphragm. The first fiber aggregate having a thickness of 3000 μm or less easily diffuses the electrolytic solution.

(4) As one form of the battery cell, the density of the first fiber aggregate is 0.1 g / cm ³ or more and 1.2 g / cm ³ or less.

The first fiber aggregate having a density of 0.1 g / cm ³ or more easily suppresses contact between at least one of the positive electrode and the negative electrode and the diaphragm. The first fiber aggregate having a density of 1.2 g / cm ³ or less easily diffuses the electrolytic solution.

(5) As one form of the battery cell, the insulating material is a resin or ceramics, and the resin is polyphenylene sulfide, polyethylene, polypropylene, polyamide, polyvinyl chloride, polystyrene, polybutylene succinate, acrylic, poly. It is tetrafluoroethylene, tetrafluoroethylene / ethylene copolymer, polycarbonate, phenol, or epoxy, and the ceramics may be silica, alumina, zirconia, or silicon carbide.

The first fiber aggregate composed of the first fiber made of resin is more susceptible to damage to the diaphragm due to contact between the first layer and the diaphragm than the first fiber aggregate composed of the first fiber made of ceramics. Easy to suppress. This is because, in general, the first fiber made of resin is softer than the first fiber made of ceramics. The first fiber aggregate composed of the first fiber made of ceramics is easier to diffuse the electrolytic solution than the first fiber aggregate composed of the first fiber made of resin. This is because the first fiber made of ceramics is easier to improve the strength of the first fiber aggregate than the first fiber made of resin, so that the number of first fibers can be easily reduced. That is, the first fiber made of ceramics is more likely to increase the porosity of the first fiber aggregate than the first fiber made of resin.

(6) As one form of the battery cell, the average Young's modulus of the plurality of first fibers is 200 GPa or less.

When the average Young's modulus of the plurality of first fibers is 200 GPa or less, the first fiber aggregate can easily suppress the damage to the diaphragm due to the contact between the first layer and the diaphragm.

(7) As one form of the battery cell, the thickness of the diaphragm is 60 μm or less.

Even if the thickness of the diaphragm is 60 μm or less, damage to the diaphragm is easily suppressed by arranging the first layer as described above.

(8) As one form of the battery cell, the electrode adjacent to at least the first layer of the positive electrode and the negative electrode is a second fiber aggregate having a plurality of second fibers made of a conductive material. , The second fiber aggregate may be a non-woven fabric, a woven cloth, or a paper.

Even if the electrode adjacent to the first layer is a second fiber aggregate, damage to the diaphragm is easily suppressed by arranging the first layer as described above.

(9) The cell stack according to one aspect of the present disclosure includes a plurality of battery cells, and at least one of the plurality of battery cells is any one of the above (1) to (8).

Since the cell stack of the present disclosure includes the above battery cells, it is easy to improve the current efficiency and reduce the reaction resistivity at the same time.

(10) The redox flow battery system according to one aspect of the present disclosure includes any one of the battery cells (1) to (8) above, or the cell stack according to (9) above.

Since the redox flow battery system of the present disclosure includes the battery cell or the cell stack, it is easy to improve the current efficiency and reduce the reaction resistivity at the same time.

<< Details of Embodiments of the present disclosure >>
Details of the redox flow battery system according to the embodiment of the present disclosure will be described below. The same reference numerals in the figures indicate the same names. Hereinafter, the redox flow battery system may be referred to as an RF battery system.

<< Embodiment >>
[RF battery system]
The RF battery system 1 of the embodiment will be described with reference to FIGS. 1 to 5. As shown in FIG. 1, the RF battery system 1 includes a battery cell 10 and a circulation mechanism. The battery cell 10 has a positive electrode 14, a negative electrode 15, and a diaphragm 11. The diaphragm 11 is arranged between the positive electrode 14 and the negative electrode 15. The circulation mechanism circulates the electrolytic solution in the battery cell 10. One of the features of the RF battery system 1 of the present embodiment is that a specific first layer 17 is arranged between the positive electrode 14 and the diaphragm 11 and at least one between the negative electrode 15 and the diaphragm 11. There is a point to prepare. FIG. 1 shows a case where the first layer 17 is arranged between the positive electrode 14 and the diaphragm 11. The first layer 17 is not arranged between the negative electrode 15 and the diaphragm 11. The following description will be given in the order of an outline and basic configuration of the RF battery system 1 and details of each configuration of the RF battery system 1 of the present embodiment.

[Overview of RF battery system]
The RF battery system 1 shown in FIG. 1 charges and discharges electric power. The charging power is the power generated by the power generation unit 510. The discharge power is supplied to the load 530. Examples of the power generation unit 510 include a solar power generation device, a wind power generation device, and other general power plants. Examples of the load 530 include electric power consumers. The RF battery system 1 is typically connected to the power generation unit 510 and the load 530 via the AC / DC converter 500 and the substation equipment 520. The solid arrow between the AC / DC converter 500 and the substation equipment 520 in FIG. 1 means charging, and the broken line arrow means discharging. The RF battery system 1 is used, for example, for load leveling applications, applications such as instantaneous low compensation or emergency power supply, and applications for smoothing the output of natural energy such as solar power generation or wind power generation, which are being introduced in large quantities. To. The RF battery system 1 uses a positive electrode electrolytic solution and a negative electrode electrolytic solution. The positive electrode electrolytic solution and the negative electrode electrolytic solution contain metal ions whose valences change due to redox as an active material. The charging / discharging of the RF battery system 1 is performed by utilizing the difference between the redox potential of the metal ions contained in the positive electrode electrolytic solution and the redox potential of the metal ions contained in the negative electrode electrolytic solution.

[Basic configuration of RF battery]
The RF battery system 1 includes a battery cell 10. The battery cell 10 includes a positive electrode cell and a negative electrode cell. The positive electrode cell and the negative electrode cell are separated by a diaphragm 11 described later.

The positive electrode cell has a built-in positive electrode 14 which will be described later. The positive electrode electrolytic solution circulates in the positive electrode cell by the positive electrode circulation mechanism 10P. The positive electrode circulation mechanism 10P includes a positive electrode electrolyte tank 18, a supply pipe 20, a discharge pipe 22, and a pump 24. The positive electrode electrolyte tank 18 stores the positive electrode electrolyte. The positive electrode electrolyte flows through the supply pipe 20 and the discharge pipe 22. The supply pipe 20 connects the positive electrode electrolyte tank 18 and the positive electrode cell. The discharge pipe 22 connects the positive electrode cell and the positive electrode electrolyte tank 18. The pump 24 pumps the positive electrode electrolyte in the positive electrode electrolyte tank 18. The pump 24 is provided in the middle of the supply pipe 20.

The negative electrode cell has a built-in negative electrode 15 which will be described later. The negative electrode electrolytic solution is circulated in the negative electrode cell by the negative electrode circulation mechanism 10N. The negative electrode circulation mechanism 10N includes a negative electrode electrolyte tank 19, a supply pipe 21, a discharge pipe 23, and a pump 25. The negative electrode electrolyte tank 19 stores the negative electrode electrolyte. The negative electrode electrolyte flows through the supply pipe 21 and the discharge pipe 23. The supply pipe 21 connects the negative electrode electrolyte tank 19 and the negative electrode cell. The discharge pipe 23 connects the negative electrode cell and the negative electrode electrolyte tank 19. The pump 25 pumps the negative electrode electrolyte in the negative electrode electrolyte tank 19. The pump 25 is provided in the middle of the supply pipe 21.

During the operation in which charging and discharging are performed, the positive electrode electrolytic solution and the negative electrode electrolytic solution pumped by the pump 24 and the pump 25 circulate as follows. The positive electrode electrolyte flows through the supply pipe 20 and is supplied from the positive electrode electrolyte tank 18 to the positive electrode cell. This positive electrode electrolyte flows through the discharge pipe 22 and is discharged from the positive electrode cell to the positive electrode electrolyte tank 18. The negative electrode electrolytic solution flows through the supply pipe 21 and is supplied from the negative electrode electrolytic solution tank 19 to the negative electrode cell. This negative electrode electrolytic solution flows through the discharge pipe 23 and is discharged from the negative electrode cell to the negative electrode electrolytic solution tank 19. The pump 24 and the pump 25 are stopped during standby when charging / discharging is not performed. That is, the positive electrode electrolyte and the negative electrode electrolyte do not circulate.

[First layer]
The first layer 17 suppresses contact between the electrode 100 and the diaphragm 11, which will be described later. By suppressing the contact between the electrode 100 and the diaphragm 11, damage to the diaphragm 11 due to the contact between the electrode 100 and the diaphragm 11 is suppressed. By suppressing damage to the diaphragm 11, it is possible to prevent the positive electrode electrolyte and the negative electrode electrolyte from being short-circuited through the damaged portion of the diaphragm 11. By suppressing short circuits, current efficiency is improved. The first layer 17 is separate from the electrode 100. The first layer 17 is arranged between the positive electrode 14 and the diaphragm 11 and between at least one of the negative electrode 15 and the diaphragm 11. An example of the planar shape of the first layer 17 is a rectangular shape. The planar shape is the contour shape of the first surface or the second surface when the first surface or the second surface of the first layer 17 is viewed in a plan view. The first surface is the surface facing the electrode 100. The second surface is the surface facing the diaphragm 11. The rectangular shape referred to here includes a rectangle and a square. This point is the same for the planar shape of the electrode 100 and the planar shape of the diaphragm 11, which will be described later. As shown in FIG. 3, the first layer 17 is composed of the first fiber aggregate 171. The first fiber assembly 171 has a plurality of first fibers 171a. Each first fiber 171a is made of an insulating material.

(Fiber diameter)
The average diameter of the plurality of first fibers 171a is 2 μm or more. The first fiber 171a having an average diameter of 2 μm or more tends to improve the strength of the first fiber aggregate 171. The larger the average diameter of the plurality of first fibers 171a, the easier it is to suppress the damage to the diaphragm 11 due to the contact between the first layer 17 and the diaphragm 11. In particular, the average diameter of the first fiber 171a is preferably the same as or larger than the average diameter of the second fiber 111a constituting the electrode 100. When the average diameter of the first fiber 171a is larger than that of the second fiber 111a, damage to the diaphragm 11 due to contact between the first layer 17 and the diaphragm 11 is likely to be suppressed. The average diameter of the plurality of first fibers 171a may be further 5 μm or more, and particularly 8 μm or more.

The average diameter of the plurality of first fibers 171a is 50 μm or less. The first fiber 171a having an average diameter of 50 μm or less has low rigidity, and damage to the diaphragm 11 due to contact between the first layer 17 and the diaphragm 11 is likely to be suppressed. The average diameter of the plurality of first fibers 171a may be further 30 μm or less, and particularly 20 μm or less.

That is, the average diameter of the plurality of first fibers 171a is 2 μm or more and 50 μm or less, further 5 μm or more and 30 μm or less, and particularly 8 μm or more and 20 μm or less.

The average diameter of the plurality of first fibers 171a is obtained as follows. The first layer 17 is cut to expose the cross section of the first fiber 171a. The cutting of the first layer 17 is performed in the thickness direction of the first layer 17. Enlarge the cross section with a microscope. The magnification of the microscope is 1000 times. For five or more first fibers 171a, the diameter of each first fiber 171a is determined. The diameter is the diameter of a circle having the same area as the cross-sectional area of the first fiber 171a. Average the diameters of all the circles found.

(Young's modulus)
The average Young's modulus of the plurality of first fibers 171a is, for example, 200 GPa or less. When the average Young's modulus of the plurality of first fibers 171a is 200 GPa or less, the first fiber aggregate 171 can easily suppress damage to the diaphragm 11 due to contact between the first layer 17 and the diaphragm 11. In particular, the average Young's modulus of the plurality of first fibers 171a is preferably smaller than the Young's modulus of the second fibers 111a constituting the electrode 100. When the average Young's modulus of the plurality of first fibers 171a is smaller than the average Young's modulus of the plurality of second fibers 111a, damage to the diaphragm 11 due to contact between the first layer 17 and the diaphragm 11 is likely to be suppressed. Further, the average Young's modulus of the plurality of first fibers 171a is 150 GPa or less, 100 GPa or less, and particularly 10 GPa or less.

The lower limit of the average Young's modulus of the plurality of first fibers 171a is, for example, 100 MPa. Since the average Young's modulus of the plurality of first fibers 171a is 100 MPa or more, the strength of the first fiber aggregate 171 can be easily improved.

That is, the average Young's modulus of the plurality of first fibers 171a is 100 MPa or more and 200 GPa or less, further 100 MPa or more and 150 GPa or less, 300 MPa or more and 100 GPa or less, and particularly 500 MPa or more and 10 GPa or less.

The average Young's modulus of the plurality of first fibers 171a is a value obtained by averaging the Young's modulus of five or more first fibers 171a.

(Material)
Examples of the insulating material constituting the first fiber 171a include resin and ceramics. Examples of the resin include polyphenylene sulfide, polyethylene, polypropylene, polyamide, polyvinyl chloride, polystyrene, polybutylene succinate, acrylic, polytetrafluoroethylene, tetrafluoroethylene / ethylene copolymer, polycarbonate, phenol, and epoxy. Examples of the resin include polyphenylene sulfide. Examples of the ceramics include silica, alumina, zirconia, and silicon carbide.

The first fiber assembly 171 made of the first fiber 171a made of resin is in contact with the first layer 17 and the diaphragm 11 more than the first fiber assembly 171 made of the first fiber 171a made of ceramics. It is easy to suppress the damage of the diaphragm 11 due to the above. This is because, in general, the first fiber 171a made of resin is softer than the first fiber 171a made of ceramics. The first fiber aggregate 171 made of the first fiber 171a made of ceramics is easier to diffuse the electrolytic solution than the first fiber aggregate 171 made of the first fiber 171a made of resin. This is because the first fiber 171a made of ceramics is easier to improve the strength of the first fiber aggregate 171 than the first fiber 171a made of resin, so that the number of first fibers 171a can be easily reduced. That is, the first fiber 171a made of ceramics is easier to increase the porosity of the first fiber aggregate 171 than the first fiber 171a made of resin.

In particular, the insulating material constituting the first fiber 171a is preferably a material softer than the constituent material of the second fiber 111a constituting the electrode 100. The first fiber 171a made of a soft material can easily suppress damage to the diaphragm 11 due to contact between the first layer 17 and the diaphragm 11.

The material of the first fiber 171a is obtained by X-ray diffraction.

(Porosity)
The porosity P ₁ of the first fiber aggregate 171 is 20% or more and 99% or less. The porosity P1 of the _first fiber aggregate 171 is the porosity of the first fiber aggregate 171 in the compressed state. The compressed state refers to a state after assembling the battery cell 10 or the cell stack 200 described later. The first fiber aggregate 171 having a porosity P ₁ of 20% or more easily diffuses the electrolytic solution. The _first fiber aggregate 171 having a porosity P1 of 99% or less can easily prevent the second fibers 111a constituting the electrode 100 from penetrating the diaphragm 11 through the voids of the first fiber aggregate 171. Therefore, damage to the diaphragm 11 is suppressed. Further, the _first fiber aggregate 171 having a porosity P1 of 99% or less easily retains the shape of the first fiber aggregate 171. The porosity P ₁ of the first fiber aggregate 171 is further referred to as 25% or more and 99% or less, 30% or more and 95% or less, and particularly 35% or more and 90% or less. The porosity P ₁ of the first fiber assembly 171 is preferably larger than the porosity of the electrode 100. The first fiber aggregate 171 having a porosity P ₁ larger than the porosity of the electrode 100 can easily suppress damage to the diaphragm 11 due to contact with the diaphragm 11.

The porosity P ₁ of the first fiber assembly 171 is determined by P ₁ = 100-{(100-P ₀ ) d ₀ / d ₁ }. P ₀ is the porosity of the electrode 100 in the uncompressed state. The porosity _P0 of the electrode 100 in the uncompressed state is determined by the mercury intrusion method. d ₀ is the thickness of the first fiber assembly 171 in the uncompressed state. d ₁ is the thickness of the first fiber assembly 171 in the compressed state. The thickness d ₁ of the first fiber assembly 171 in the compressed state is determined by a compression test. In the compression test, a pressure equivalent to the pressure acting on the first fiber assembly 171 is applied to the first fiber assembly 171 in a state after the battery cell 10 or the cell stack 200 described later is assembled. The thickness d ₀ and the thickness d ₁ are the average values of the thicknesses of five or more places. As shown in FIG. 5, an example of the measurement points of the thickness d ₀ and the thickness d ₁ is at least the first intersection C1 to the fifth intersection C5. FIG. 5 illustrates a case where the planar shape of the first fiber assembly 171 is rectangular. In FIG. 5, the length of the short side of the rectangle is the width Wa, and the length of the long side of the rectangle is the length La.

The first intersection C1 is the intersection of the first virtual line V1 and the third virtual line V3.
The second intersection C2 is the intersection of the first virtual line V1 and the fourth virtual line V4.
The third intersection C3 is the intersection of the second virtual line V2 and the third virtual line V3.
The fourth intersection C4 is the intersection of the second virtual line V2 and the fourth virtual line V4.
The fifth intersection C5 is the intersection of the diagonal lines D1 and D2.

The first virtual line V1 is a straight line along the short side direction of the first fiber assembly 171 and the distance from the first short side of the first fiber assembly 171 to the first virtual line V1 is the length La ×. It is a straight line having a length of 0.1 times or more and La × 0.2 times or less.
The second virtual line V2 is a straight line along the short side direction of the first fiber assembly 171 and the distance from the second short side of the first fiber assembly 171 to the second virtual line V2 is the length La ×. It is a straight line having a length of 0.1 times or more and La × 0.2 times or less.
The distance from the first short side to the first virtual line V1 and the distance from the second short side to the second virtual line V2 are the same.
The third virtual line V3 is a straight line along the long side direction of the first fiber assembly 171 and the distance from the first long side of the first fiber assembly 171 to the third virtual line V3 is width Wa × 0. . It is a straight line having a width of 1 times or more and a width of Wa × 0.2 times or less.
The fourth virtual line V4 is a straight line along the long side direction of the first fiber assembly 171 and the distance from the second long side of the first fiber assembly 171 to the fourth virtual line V4 is width Wa × 0. . It is a straight line having a width of 1 times or more and a width of Wa × 0.2 times or less.
The distance from the first long side to the third virtual line V3 and the distance from the second long side to the fourth virtual line V4 are the same.

When increasing the number of measurement points, it is preferable to satisfy at least one of the following requirements (a) and (b).
(A) The first virtual line V1 and the second virtual line V2 are evenly divided, and one or more additional virtual lines intersecting the third virtual line V3 and the fourth virtual line V4 are taken.
(B) The third virtual line V3 and the fourth virtual line V4 are evenly divided, and one or more additional virtual lines intersecting the first virtual line V1 and the second virtual line V2 are taken.
In the case of the above requirement (a), one or more additional intersections are lined up between the first intersection C1 and the third intersection C3 on the third virtual line V3, and the second intersection C2 on the fourth virtual line V4. One or more additional intersections are lined up with the fourth intersection C4. The number of additional intersections on the third virtual line V3 and the number of additional intersections on the fourth virtual line V4 are the same. The additional intersections on the third virtual line V3, the first intersection C1 and the third intersection C3 are arranged at equal intervals. The additional intersections on the fourth virtual line V4, the second intersection C2, and the fourth intersection C4 are arranged at equal intervals.
In the case of the above requirement (b), one or more additional intersections are arranged between the first intersection C1 and the second intersection C2 on the first virtual line V1 and the third intersection C3 on the second virtual line V2. One or more additional intersections are lined up with the fourth intersection C4. The number of additional intersections on the first virtual line V1 and the number of additional intersections on the second virtual line V2 are the same. The additional intersections on the first virtual line V1, the first intersection C1 and the second intersection C2 are arranged at equal intervals. The additional intersections on the second virtual line V2, the third intersection C3, and the fourth intersection C4 are arranged at equal intervals.

(Metsuke amount)
The basis weight of the first fiber aggregate 171 is, for example, 5 g / m ² or more and 100 g / m ² or less. The first fiber aggregate 171 having a basis weight of 5 g / m ² or more can easily prevent the second fibers 111a constituting the electrode 100 from penetrating the diaphragm 11 through the voids of the first fiber aggregate 171. Moreover, the first fiber aggregate 171 having a basis weight of 5 g / m ² or more easily suppresses the first fiber 171a from sticking to the diaphragm 11. The first fiber aggregate 171 having a basis weight of 100 g / m ² or less easily diffuses the electrolytic solution. The basis weight of the first fiber aggregate 171 is further 8 g / m ² or more and 50 g / m ² or less, and particularly 10 g / m ² or more and 30 g / m ² or less.

(thickness)
The thickness of the first fiber assembly 171 is, for example, 5 μm or more and 3000 μm or less. The thickness of the first fiber assembly 171 is the thickness d ₁ of the first fiber assembly 171 in the compressed state described above. That is, the thickness of the first fiber assembly 171 is determined by the measurement method as described above with reference to FIG. The first fiber assembly 171 having a thickness of 5 μm or more can easily prevent the second fiber 111a of the electrode 100 from penetrating the diaphragm 11 through the voids of the first fiber assembly 171. Even if the thickness of the first fiber aggregate 171 is 5 μm or more, the first fiber aggregate 171 easily diffuses the electrolytic solution by satisfying the above _- mentioned porosity P1. The first fiber aggregate 171 having a thickness of 3000 μm or less easily diffuses the electrolytic solution. The thickness of the first fiber assembly 171 is further 8 μm or more and 200 μm or less, and particularly 10 μm or more and 100 μm or less. The thickness of the first fiber assembly 171 is the average value of the thicknesses of five or more places.

(density)
The density of the first fiber assembly 171 is, for example, 0.1 g / cm ³ or more and 1.2 g / cm ³ or less. The first fiber assembly 171 having a density of 0.1 g / cm ³ or more can easily prevent the second fiber 111a of the electrode 100 from penetrating the diaphragm 11 through the voids of the first fiber assembly 171. The first fiber aggregate 171 having a density of 1.2 g / cm ³ or less easily diffuses the electrolytic solution. The density of the first fiber aggregate 171 is 0.1 g / cm ³ or more and 1.0 g / cm ³ or less, 0.2 g / cm ³ or more and 0.95 g / cm ³ or less, and is particularly 0.3 g / cm. ³ or more and 0.9 g / cm ³ or less can be mentioned. The density of the first fiber aggregate 171 is obtained by dividing the basis weight of the first fiber aggregate 171 by the thickness of the first fiber aggregate 171. As described above, the thickness of the first fiber aggregate 171 referred to here is the thickness d ₁ of the first fiber aggregate 171 in the compressed state.

[Positive electrode / Negative electrode]
The positive electrode 14 and the negative electrode 15 are places where a battery reaction is performed. The positive electrode 14 and the negative electrode 15 may use the same electrodes or different electrodes from each other. Of the positive electrode 14 and the negative electrode 15, the electrode adjacent to the first layer 17 is composed of the electrode 100. Of the positive electrode 14 and the negative electrode 15, the electrodes that are not adjacent to the first layer 17 may be composed of the electrode 100 or may be composed of an electrode different from the electrode 100. As an electrode different from the electrode 100, a known electrode can be used. An example of the planar shape of the electrode 100 is a rectangular shape. The planar shape is a shape when the first surface or the second surface of the electrode 100 is viewed from the thickness direction of the electrode 100. The first surface is a surface facing the bipolar plate 161 described later. The second surface is the surface facing the first layer 17 or the diaphragm 11.

The electrode 100 is made of a porous material. As a specific example of the porous material, as shown in FIG. 4, a second fiber assembly 111 can be mentioned. The second fiber assembly 111 has a plurality of second fibers 111a made of a conductive material. Since the contact between the electrode 100 and the diaphragm 11 is easily suppressed by the first layer 17, even if the electrode 100 is the second fiber aggregate 111, the decrease in current efficiency is easily suppressed. The second fiber assembly 111 tends to increase the number of contacts between the second fibers 111a. Therefore, the electrode 100 composed of the second fiber assembly 111 tends to improve the conductivity. Further, the second fiber assembly 111 can easily secure a gap. Therefore, the electrode 100 composed of the second fiber assembly 111 tends to improve the flowability of the electrolytic solution. Examples of the second fiber assembly 111 include non-woven fabric, woven fabric, and paper. The non-woven fabric is made by entwining independent second fibers 111a. The woven fabric is made by alternately weaving the warp and weft of the second fiber 111a. The paper has a plurality of second fibers 111a and a binder for binding the second fibers 111a. Nonwoven fabrics include felt, spunlace, marifleece and the like.

(Fiber diameter)
The average diameter of the plurality of second fibers 111a is, for example, 1 μm or more and 20 μm or less. The second fiber 111a having an average diameter of 1 μm or more tends to increase the strength of the second fiber assembly 111. Since the second fiber 111a having an average diameter of 20 μm or less has a large surface area of the second fiber 111a per unit weight, it is easy to improve the battery reactivity. Further, the average diameter of the plurality of second fibers 111a is 5 μm or more and 18 μm or less, and particularly 8 μm or more and 15 μm or less. The method of obtaining the average diameter of the plurality of second fibers 111a is the same as the method of obtaining the average diameter of the plurality of first fibers 171a.

(Young's modulus)
The average Young's modulus of the plurality of second fibers 111a is, for example, 200 GPa or more. Even if the average Young's modulus of the plurality of second fibers 111a is 200 GPa or more, the first layer 17 tends to suppress damage to the diaphragm 11 due to contact between the electrode 100 and the diaphragm 11. The average Young's modulus of the plurality of second fibers 111a further includes 250 GPa or more, and particularly 300 GPa or more. The upper limit of the average Young's modulus of the plurality of second fibers 111a is, for example, 500 GPa. Further, the average Young's modulus of the plurality of second fibers 111a is 450 GPa or less, and in particular, 400 GPa or less. That is, the average Young's modulus of the plurality of second fibers 111a is 200 GPa or more and 500 GPa or less, further 250 GPa or more and 450 GPa or less, and particularly 300 GPa or more and 400 GPa or less. The method of obtaining the average Young's modulus of the plurality of second fibers 111a is the same as the method of obtaining the average Young's modulus of the plurality of first fibers 171a.

(Material)
Examples of the second fiber 111a include carbon fibers. Carbon fiber tends to improve battery reactivity. Examples of the carbon fiber include pitch-based carbon fiber and PAN (polyacrylonitrile) -based carbon fiber. Pitch-based carbon fibers are made from petroleum pitch or coal pitch. The PAN-based carbon fiber is made from polyacrylonitrile. The rigidity of these carbon fibers is relatively high. Even in the electrode 100 composed of the second fiber aggregate 111 having a plurality of these carbon fibers, the first layer 17 tends to suppress the damage of the diaphragm 11 due to the contact between the electrode 100 and the diaphragm 11.

(binder)
Although not shown, the electrode 100 may have a binder that binds the second fibers 111a to each other. The Young's modulus of the electrode 100 having a binder tends to be larger than that of the electrode 100 having no binder. Even in the electrode 100 having a binder, the first layer 17 tends to suppress damage to the diaphragm 11 due to contact between the electrode 100 and the diaphragm 11.

The material of the binder includes a material that is difficult to dissolve in the electrolytic solution. The binder contains one or more selected from the group consisting of resins, metals, carbides, and metal oxides. A binder containing these materials can easily firmly fix the second fibers 111a to each other. Examples of the resin include phenol, polytetrafluoroethylene, and polyvinylidene fluoride. Examples of the metal include Ti (titanium) and W (tungsten). Examples of the carbide include titanium carbide, manganese carbide, and tungsten carbide. Examples of the metal oxide include alumina and tin oxide.

(Porosity)
The porosity of the second fiber assembly 111 is, for example, 25% or more and 90% or less. The porosity of the second fiber assembly 111 is the porosity of the second fiber assembly 111 in the compressed state. The second fiber aggregate 111 having a porosity of 25% or more is excellent in the flowability of the electrolytic solution. The second fiber assembly 111 having a porosity of 90% or less is excellent in conductivity. The porosity of the second fiber assembly 111 is further 60% or more and 80% or less, and particularly 70% or more and 80% or less. The method of obtaining the porosity of the second fiber assembly 111 is the same as the method of obtaining the porosity P1 of the _first fiber assembly 171.

(Metsuke amount)
The basis weight of the second fiber assembly 111 is 20 g / m ² or more and 600 g / m ² or less. Since the second fiber aggregate 111 having a basis weight of 20 g / m ² or more tends to have many contacts between the second fibers 111a, it is easy to increase the conductivity. The second fiber aggregate 111 having a basis weight of 600 g / m ² or less is excellent in the flowability of the electrolytic solution because it is easy to secure voids. The basis weight of the second fiber assembly 111 is further 50 g / m ² or more and 550 g / m ² or less, and particularly 100 g / m ² or more and 500 g / m ² or less.

(thickness)
The thickness of the second fiber assembly 111 is, for example, 200 μm or more and 1000 μm or less. The thickness of the second fiber assembly 111 is the thickness of the second fiber assembly 111 in the compressed state. The second fiber aggregate 111 having a thickness of 200 μm or more tends to increase the volume of the reaction field where the battery reaction is carried out. The second fiber assembly 111 having a thickness of 1000 μm or less can construct a thin RF battery system 1. Further, the thickness of the second fiber assembly 111 is 300 μm or more and 800 μm or less, and particularly 400 μm or more and 700 μm or less. The thickness of the second fiber assembly 111 corresponds to the depth of the recess 160 of the cell frame 16 described later. The thickness of the second fiber assembly 111 is the average value of the depths of the recesses 160 at five or more locations. An example of the measurement point of the thickness of the second fiber assembly 111 can be the same as the first intersection C1 to the fifth intersection C5 described with reference to FIG.

(density)
The density of the second fiber assembly 111 is, for example, 0.1 g / cm ³ or more and 1.2 g / cm ³ or less. Since the second fiber assembly 111 having a density of 0.1 g / cm ³ or more tends to have many contacts between the second fibers 111a, it is easy to increase the conductivity. The second fiber assembly 111 having a density of 1.2 g / cm ³ or less is excellent in the flowability of the electrolytic solution. The density of the second fiber aggregate 111 further includes 0.1 g / cm ³ or more and 1.0 g / cm ³ or less, 0.2 g / cm ³ or more and 0.95 g / cm ³ or less, and particularly 0.3 g / cm. ³ or more and 0.9 g / cm ³ or less can be mentioned. The density of the second fiber assembly 111 is obtained by dividing the basis weight by the thickness.

[diaphragm]
The diaphragm 11 is arranged between the positive electrode 14 and the negative electrode 15. The diaphragm 11 partitions the positive electrode cell and the negative electrode cell. The diaphragm 11 allows hydrogen ions to permeate. Examples of the type of diaphragm 11 include an ion exchange membrane. As the diaphragm 11, a known diaphragm can be used. An example of the planar shape of the diaphragm 11 is a rectangular shape. The planar shape is the contour shape of the first surface or the second surface when the first surface or the second surface of the diaphragm 11 is viewed in a plan view. The first surface is a surface facing the positive electrode electrode 14. The second surface is a surface facing the negative electrode electrode 15.

(thickness)
The thickness of the diaphragm 11 is, for example, 60 μm or less. The diaphragm 11 having a thickness of 60 μm or less can easily reduce the cell resistivity. This is because such a diaphragm 11 easily allows hydrogen ions to permeate, so that it is easy to reduce the electrical resistance. Even if the diaphragm 11 has a thickness of 60 μm or less, the first layer 17 suppresses damage to the diaphragm 11 due to contact between the electrode 100 and the diaphragm 11. The thickness of the diaphragm 11 is further 40 μm or less, and particularly 30 μm or less.

The lower limit of the thickness of the diaphragm 11 is, for example, 5 μm. The diaphragm 11 having a thickness of 5 μm or more is not easily damaged. The thickness of the diaphragm 11 is further 8 μm or more, and particularly 10 μm or more.

That is, the thickness of the diaphragm 11 is 5 μm or more and 60 μm or less, further 8 μm or more and 40 μm or less, and particularly 10 μm or more and 30 μm or less.

The thickness of the diaphragm 11 is the average value of the thicknesses of 5 or more places. An example of the measurement point of the thickness of the diaphragm 11 can be the same as the first intersection C1 to the fifth intersection C5 described with reference to FIG.

As shown in FIG. 2, the battery cell 10 is provided between the two cell frames 16.

[Cell frame]
The cell frame 16 includes a bipolar plate 161 and a frame body 162. The cell frame 16 includes a recess 160 in which the positive electrode 14 or the negative electrode 15 is arranged. The recess 160 is formed by the surface of the bipolar plate 161 and the inner peripheral surface of the frame body 162. One battery cell 10 is formed between the bipolar plates 161 of the adjacent cell frames 16. A positive electrode cell and a negative electrode cell of adjacent battery cells 10 are formed on the front and back sides of one bipolar plate 161. The bipolar plate 161 and the frame body 162 may have known configurations.

The frame body 162 surrounds the outer peripheral edge portion of the bipolar plate 161. The region inside the outer peripheral edge of the surface of the bipolar plate 161 is exposed from the frame body 162. The frame body 162 supports the bipolar plate 161. The frame body 162 forms an area to be the battery cell 10 inside. The shape of the frame body 162 is a rectangular frame shape. That is, the opening shape of the recess 160 is rectangular. The frame body 162 includes a liquid supply side piece and a liquid drainage side piece. When the cell frame 16 is viewed in a plan view, the direction in which the liquid supply side piece and the liquid drainage side piece face each other is the vertical direction, and the direction orthogonal to the vertical direction is the horizontal direction. In FIG. 2, the liquid supply side piece is located on the lower side in the vertical direction, and the liquid drain side piece is located on the upper side in the vertical direction. The liquid supply side piece has a liquid supply manifolds 163 and 164 and liquid supply slits 163s and 164s that supply the electrolytic solution to the inside of the battery cell 10. The drainage side piece has a drainage manifold 165, 166 and drainage slits 165s, 166s for draining the electrolytic solution to the outside of the battery cell 10. The direction in which the electrolytic solution flows is from the lower side in the vertical direction to the upper side in the vertical direction of the frame body 162.

A liquid supply rectifying unit may be formed on the inner edge of the liquid supply side piece. The liquid supply rectifying unit diffuses the electrolytic solution supplied from the liquid supply slits 163s and 164s along the inner edge of the liquid supply side piece. A drainage rectifying portion may be formed on the inner edge of the drainage side piece. The effluent rectifying unit collects the electrolytic solution flowing through the positive electrode 14 or the negative electrode 15 from the entire inner edge of the effluent side piece and circulates it through the effluent slits 165s and 166s. The illustration of the liquid supply rectifying unit and the drainage rectifying unit is omitted.

The flow of each electrode electrolyte in the cell frame 16 is as follows. The positive electrode electrolytic solution flows from the liquid supply manifold 163 through the liquid supply slit 163s formed in the liquid supply side piece on the first surface side of the frame body 162 and is supplied to the positive electrode electrode 14. As shown by the arrow in the upper part of FIG. 2, the positive electrode electrolytic solution flows from the lower side to the upper side of the positive electrode electrode 14 and flows through the drainage slit 165s formed in the drainage side piece to drain the drainage manifold 165. Is discharged to. The supply and discharge of the negative electrode electrolytic solution are the same as those of the positive electrode electrolytic solution except that the negative electrode electrolytic solution is supplied and discharged on the second surface side of the frame body 162. The first surface and the second surface of the frame body 162 are surfaces facing each other in the thickness direction of the frame body 162.

Between each frame 162, an annular seal member 167 such as an O-ring or flat packing is arranged in an annular seal groove. The seal member 167 suppresses leakage of the electrolytic solution from the battery cell 10.

[Cell stack]
The battery cell 10 is usually provided inside a structure called a cell stack 200, as shown in FIGS. 1 and 2 below. The cell stack 200 includes a sub-stack 200s, two end plates 220, and a tightening mechanism 230. The cell stack 200 includes a plurality of sub-stacks 200s, for example, as shown in the lower figure of FIG. Each sub-stack 200s includes a laminated body and two supply / discharge plates 210. The laminate shown in FIGS. 1 and 2 is composed of a plurality of cell frames 16, positive electrode 14, first layer 17, diaphragm 11, and negative electrode 15 in this order. As shown in the lower figure of FIG. 2, the supply / discharge plate 210 is arranged at both ends of the laminated body. The two end plates 220 sandwich the plurality of sub-stacks 200s from the outside of the sub-stacks 200s at both ends. The tightening mechanism 230 tightens both end plates 220.

The cell frame 16 provided in the sub-stack 200s and the cell stack 200 includes an intermediate cell frame and an end cell frame. The intermediate cell frame is arranged between the adjacent battery cells 10 of the laminated body. The end cell frames are arranged at both ends of the laminate.
In the intermediate cell frame, the positive electrode 14 of the first battery cell 10 is in contact with the first surface of the bipolar plate 161. In the intermediate cell frame, the negative electrode 15 of the second battery cell 10 is in contact with the second surface of the bipolar plate 161. In the end cell frame, one of the positive electrode 14 and the negative electrode 15 of the battery cell 10 is in contact with the first surface of the bipolar plate 161. The end cell frame has no electrodes on the second surface of the bipolar plate 161. The first surface and the second surface of the bipolar plate 161 are surfaces facing each other in the thickness direction of the bipolar plate 161. The configuration of the cell frame 16 is the same for both the intermediate cell frame and the end cell frame.

[Electrolytic solution]
As described above, the positive electrode electrolytic solution and the negative electrode electrolytic solution are circulated to the positive electrode electrode 14 and the negative electrode electrode 15 by the positive electrode circulation mechanism 10P and the negative electrode circulation mechanism 10N. By this circulation, charging and discharging are performed according to the valence change reaction of ions which are active materials contained in the positive electrode electrolytic solution and the negative electrode electrolytic solution.

The active material of the positive electrode electrolytic solution may contain one or more selected from the group consisting of manganese ion, vanadium ion, iron ion, polyacid, quinone derivative, and amine. The active material of the negative electrode electrolytic solution may contain one or more selected from the group consisting of titanium ion, vanadium ion, chromium ion, polyacid, quinone derivative, and amine. FIG. 1 illustrates a form in which the positive electrode electrolytic solution contains manganese (Mn) ions and the negative electrode electrolytic solution contains titanium (Ti) ions.

The concentration of the positive electrode active material and the concentration of the negative electrode active material can be appropriately selected. For example, at least one of the concentration of the positive electrode active material and the concentration of the negative electrode active material is 0.3 mol / L or more and 5 mol / L or less. When the above concentration is 0.3 mol / L or more, it is possible to have an energy density that can be satisfactorily used as a large-capacity storage battery. The energy density is, for example, about 10 kWh / m ³ . The higher the concentration, the higher the energy density. Further, the above-mentioned concentration is 0.5 mol / L or more and 1.0 mol / L or more, and particularly 1.2 mol / L or more and 1.5 mol / L or more. When the above concentration is 5 mol / L or less, the solubility in a solvent can be easily increased. It is easy to use the above concentration of 2 mol / L or less. An electrolytic solution satisfying this concentration is excellent in manufacturability.

Examples of the solvent of the electrolytic solution include an aqueous solution containing one or more acids or acid salts selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid.

[Action effect]
The RF battery system 1 of this embodiment can easily achieve both improvement in current efficiency and reduction in reaction resistivity. The first layer 17 suppresses damage to the diaphragm 11 due to contact between at least one of the positive electrode 14 and the negative electrode 15 and the diaphragm 11. In addition, damage to the diaphragm 11 due to contact between the plurality of first fibers 171a constituting the first layer 17 and the diaphragm 11 is suppressed. By suppressing the damage to the diaphragm 11, it is possible to prevent the positive electrode electrolytic solution and the negative electrode electrolytic solution from being short-circuited through the damaged portion of the diaphragm 11. Therefore, the RF battery system 1 of the present disclosure tends to improve the current efficiency. The first layer 17 easily diffuses the electrolytic solution. Therefore, the RF battery system 1 of the present disclosure tends to reduce the reaction resistivity.

<< Test example >>
In the test example, the difference in battery characteristics due to the presence or absence of the first layer and the difference in the configuration of the first layer was investigated.

[Sample No. 1]
Sample No. In No. 1, a single cell battery was prepared as the battery cell. The single cell battery was constructed by stacking the first cell frame, the positive electrode, the diaphragm, the negative electrode, and the second cell frame in this order. Sample No. In battery cell 1, the first layer is not arranged between the positive electrode and the diaphragm and between the negative electrode and the diaphragm. “-” In the column of the first layer shown in Table 2 means that the first layer is not arranged.

A cation exchange membrane was used as the diaphragm. The thickness of the diaphragm was 15 μm. The thickness of the diaphragm was determined by averaging the thicknesses of the above-mentioned five or more locations.
A non-woven fabric made of carbon fiber was used for the positive electrode. The specifications of the positive electrode are as shown in Table 1. The method for measuring the average diameter and the average Young's modulus of the carbon fibers constituting the positive electrode and the method for measuring the thickness, the amount of the grain, the density, and the void ratio of the positive electrode are described in Sample No. It will be described later together with the measurement method of the first layer such as 2.
The same non-woven fabric as the positive electrode was used for the negative electrode.
The reaction area of each of the positive electrode and the negative electrode was about 9 cm ² .

[Sample No. From sample No. 2 7]
Sample No. From sample No. 2 In No. 7, the sample No. 7 was prepared except that the first layer was arranged between the positive electrode and the diaphragm. A single cell battery similar to the battery cell of No. 1 was prepared. Sample No. From sample No. 2 In the RF battery system of No. 7, the first layer is not arranged between the negative electrode and the diaphragm. Sample No. From sample No. 2 The first layer of 6 is a first fiber assembly having a plurality of first fibers composed of PPS (polyphenylene sulfide). Sample No. The first layer of No. 7 is a first fiber aggregate having a plurality of first fibers made of PE (polyethylene). Sample No. From sample No. 2 The specifications of the first layer of 7 are as shown in Table 2.

〔Measuring method〕
The average diameter and average Young's modulus of the carbon fibers constituting the positive electrode shown in Table 1, the thickness, the amount of grain, the density, and the void ratio of the positive electrode, and the plurality of orders constituting the first layer shown in Table 2. The average diameter and the average Young's modulus of one fiber and the thickness, the amount of the grain, the density, and the void ratio of the first layer were determined as follows.
The thickness is the thickness of the compressed positive electrode and the first layer.
The porosity is the porosity of the compressed positive electrode and the first layer.

The average diameter of the fibers was determined by averaging the diameters of the five fibers. The diameter of each fiber is the diameter of a circle having the same area as the cross-sectional area of each fiber.
The average Young's modulus of the fibers was determined by averaging the Young's modulus of the five fibers.
The thickness was determined by averaging the thicknesses of the above-mentioned five locations. The thickness of each portion is a thickness measured in a state where a pressure of 0.2 MPa is applied to the positive electrode and the first layer.
The basis weight was determined by measuring the weight per unit area.
The density was determined by dividing the basis weight by the thickness.
The porosity of the first layer was determined in the same manner as the method for determining the porosity P1 of the _first fiber aggregate 171 described above. The porosity of the positive electrode was determined by the same method as the method for determining the porosity of the first layer.

[Measurement of battery characteristics]
The battery cells of each sample were charged and discharged with a constant current having a current density of 256 mA / cm ² . In this test, 5 cycles of charging and discharging were performed. In this test, when a preset predetermined switching voltage was reached, charging was switched to discharging, and when a preset predetermined switching voltage was reached, discharging was switched to charging. The switching voltage from charging to discharging was 1.62V. The switching voltage from discharge to charge was 1.00 V.

After charging and discharging, the current efficiency (%), cell resistivity (Ω · cm ² ), conductivity resistivity (Ω · cm ² ), and reaction resistivity (Ω · cm ² ) of each sample were determined.
The current efficiency was calculated by multiplying each cycle (total discharge time / total charge time) × 100 and used as an average value.
The cell resistivity was calculated by {(difference between average voltage during charging and average voltage during discharging) / (average current / 2)} × effective area of the electrode. The average voltage during charging and the average voltage during discharging were defined as the average voltage in any one cycle among the plurality of cycles.
The conductivity resistivity is the impedance when the measurement frequency is 1 kHz in the AC impedance method.
The reaction resistivity was a value obtained by subtracting the conductivity resistivity from the cell resistivity.
The results are shown in Table 3.

As shown in Table 3, sample No. From sample No. 2 The current efficiency of No. 6 is the sample No. Higher than 1. The reason for this result is considered to be that the first layer was able to suppress the damage to the diaphragm. Sample No. From sample No. 2 The reaction resistivity of No. 6 is the sample No. Less than 1. It is considered that the reason for such a result is that the diffusion of the electrolytic solution was hardly inhibited even though the first layer was provided. As a result, it is considered that the electrodes were able to carry out the battery reaction satisfactorily. Sample No. The current efficiency of No. 7 is the sample No. From sample No. 2 Lower than 6. The reason for this result is the sample No. Although the porosity of the first layer of No. 7 satisfies 20% or more and 99% or less, it is considered that the first fiber damaged the diaphragm due to the increased rigidity of the first fiber having an average diameter of more than 50 μm. Be done.

In addition, when the following first layer is arranged between the positive electrode and the diaphragm, the following results are considered.
Although the porosity satisfies 20% or more and 99% or less, the first layer having an average diameter of less than 2 μm of the first fiber is clogged, so that the flowability of the electrolytic solution deteriorates.
Although the average diameter of the first fiber satisfies 2 μm or more and 50 μm or less, the first layer having a porosity of less than 20% is clogged and the flowability of the electrolytic solution deteriorates.
Although the average diameter of the first fiber satisfies 2 μm or more and 50 μm or less, the first layer having a porosity of more than 99% cannot retain the shape of the first layer in the battery cell.

The present invention is not limited to these examples, but is indicated by the claims and is intended to include all modifications within the meaning and scope equivalent to the claims.

1 RF battery system 10 Battery cell 11 diaphragm, 14 positive electrode, 15 negative electrode 16 cell frame, 160 recess, 161 bipolar plate, 162 frame 163, 164 liquid supply manifold, 163s, 164s liquid supply slit 165, 166 drainage manifold , 165s, 166s Drainage slit 167 Sealing member 17 First layer, 171 First fiber assembly, 171a First fiber Wa width, La length C1 First intersection, C2 Second intersection, C3 Third intersection C4 Fourth Intersection, C5 Fifth intersection V1 First virtual line, V2 Second virtual line V3 Third virtual line, V4 Fourth virtual line D1, D2 Diagonal line 10P Positive electrode circulation mechanism, 10N Negative electrode circulation mechanism 18 Positive electrode electrolyte tank, 19 Negative electrode electrolyte tank 20, 21 Supply pipe, 22, 23 Discharge pipe, 24, 25 Pump 100 Electrode, 111 Second fiber assembly, 111a Second fiber 200 cell stack, 200s Substack 210 Supply / discharge plate, 220 end plate, 230 Tightening mechanism 500 AC / DC converter 510 Power generation unit, 520 Substation equipment, 530 Load

Claims (10)

1. A battery cell including a positive electrode, a negative electrode, and a diaphragm.
   It comprises a first layer disposed between the positive electrode and the diaphragm and between at least one of the negative electrode and the diaphragm.
   The first layer is a first fiber aggregate having a plurality of first fibers made of an insulating material.
   The average diameter of the plurality of first fibers is 2 μm or more and 50 μm or less.
   The porosity of the first fiber aggregate is 20% or more and 99% or less.
   Battery cell.
2. The battery cell according to claim 1, wherein the basis weight of the first fiber aggregate is 5 g / m ² or more and 100 g / m ² or less.
3. The battery cell according to claim 1 or 2, wherein the thickness of the first fiber aggregate is 5 μm or more and 3000 μm or less.
4. The battery cell according to any one of claims 1 to 3, wherein the density of the first fiber aggregate is 0.1 g / cm ³ or more and 1.2 g / cm ³ or less.
5. The insulating material is resin or ceramics.
   The resin is polyphenylene sulfide, polyethylene, polypropylene, polyamide, polyvinyl chloride, polystyrene, polybutylene succinate, acrylic, polytetrafluoroethylene, tetrafluoroethylene / ethylene copolymer, polycarbonate, phenol, or epoxy.
   The battery cell according to any one of claims 1 to 4, wherein the ceramic is silica, alumina, zirconia, or silicon carbide.
6. The battery cell according to any one of claims 1 to 5, wherein the average Young's modulus of the plurality of first fibers is 200 GPa or less.
7. The battery cell according to any one of claims 1 to 6, wherein the thickness of the diaphragm is 60 μm or less.
8. Of the positive electrode and the negative electrode, the electrode adjacent to at least the first layer is a second fiber aggregate having a plurality of second fibers made of a conductive material.
   The battery cell according to any one of claims 1 to 7, wherein the second fiber aggregate is a non-woven fabric, a woven fabric, or paper.
9. Equipped with multiple battery cells
   The battery cell according to any one of claims 1 to 8, at least one of the plurality of battery cells.
   Cell stack.
10. The battery cell according to any one of claims 1 to 8, or the cell stack according to claim 9.
    Redox flow battery system.

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