JP2019012694A - Collector plate - Google Patents

Abstract

To provide a collector plate provided in a redox flow battery having a low cell resistivity.SOLUTION: In a collector plate of a redox flow battery including an ion exchange membrane, a collector plate, and an electrode disposed between the ion exchange membrane and the collector plate, a plurality of flow path networks through which an electrolyte flows are formed on the electrode side surface. Each of the plurality of flow path networks has a rectangular shape, the length of the short side is 5 mm or more and 70 mm or less, and the effective area ratio is 60% or more. Here, the effective area ratio is (the sum of the effective electrode areas of the plurality of flow path networks)/{(the sum of the areas of the plurality of flow path networks)+(the sum of the areas of portions between the plurality of flow path networks)}.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a current collector plate.

  A redox flow battery is known as a large-capacity storage battery. A redox flow battery generally has an ion exchange membrane that separates an electrolytic solution and electrodes provided on both sides of the ion exchange membrane. Charging / discharging is performed by simultaneously proceeding the oxidation reaction and the reduction reaction with this electrode.

  A redox flow battery is required to reduce internal resistance (cell resistance) and pressure loss when an electrolyte is permeated through an electrode in order to increase the overall energy efficiency.

  For example, Patent Document 1 states that the pressure loss can be reduced by forming a groove serving as a flow path for the electrolytic solution on the current collector plate. FIG. 7 is a diagram schematically showing a part of the redox flow battery based on the description in Patent Document 1, (a) is a plan view, and (b) is cut along the XX plane. It is sectional drawing of the principal part.

  The redox flow battery shown in FIG. 7 has a first comb-shaped groove portion M1 connected to the inflow port and a second comb-shaped groove portion M2 connected to the outflow port as groove portions serving as a flow path for the electrolyte solution. The electrolyte supplied from the inlet flows as shown by reference numeral f1, fills the first comb-shaped groove M1, flows out into the second comb-shaped groove M2, flows as shown by reference f2, and flows into the second comb-shaped groove M2. Are discharged from the outlet. Reference numerals f1 and f2 indicate a part of the flow. The electrolyte flow from the first comb-shaped groove M1 to the second comb-shaped groove M2 flows from the first comb-shaped groove M1 to the inside of the electrode E as shown by reference numeral f3 in FIG. Flows into the second comb-shaped groove M2.

  In the redox flow battery disclosed in Patent Document 1, the electrolyte flows in the electrode in the in-plane direction. On the other hand, Patent Document 2 discloses that the electrolyte flows in the in-plane direction when the electrode flows in the vertical direction. It is stated that the pressure loss can be greatly reduced rather than flowing.

JP2015-122231A Special table 2015-530709 gazette JP 2006-156029 A

D. Aaron et.al., ECS Electrochemistry Letters, 2 (3) A29-A31 (2013)

As in the redox flow battery shown in FIG. 7, in a configuration in which the electrolyte enters from the current collector side of the electrode, passes through the electrode, and similarly exits to the current collector side of the electrode, It is essentially impossible to flow uniformly throughout. Referring to FIG. 7 (b), the flow rate of the electrolyte always flows in the portion D1 directly above the first comb groove portion M1 and the portion D2 between the first comb groove portion M1 and the second comb groove portion M2. Is different. Thus, in the redox flow battery having such a configuration, the electrolyte solution cannot be uniformly supplied to the entire electrode E.
This means that the maximum power density that can be achieved if the electrolyte can be uniformly supplied to the entire electrode cannot be essentially reached, and the reduction in internal resistance (cell resistance) is limited.

Patent Document 2 describes that when the electrolytic solution flows in the vertical direction through the electrode, the pressure loss can be greatly reduced so as to flow in the in-plane direction. However, as a method for the electrolytic solution to flow through the electrode in the vertical direction, Only describes a configuration in which an electrolyte inflow region is provided on the electrode inflow side of the electrode, and a closed end is provided at an end of the electrolyte inflow region opposite to the electrolyte supply unit (paragraph). 0044). That is, the electrolytic solution entering from the electrolytic solution supply unit enters the electrolytic solution inflow region, and there is a closed end at the opposite end of the electrolytic solution supply unit, so that the electrolytic solution can only flow vertically to the electrode. It's just that. In addition, in paragraphs 0049 and 0050, the pressure loss when the electrolyte flows in the in-plane direction and the pressure when the electrode flows in the vertical direction is compared using an equation. The pressure loss is merely compared based on the length and cross-sectional area in the direction in which the electrolyte flows.
As in the redox flow battery of Patent Document 1, a redox flow battery in which an electrolyte flows in an in-plane direction (hereinafter referred to as “in-plane flow type redox flow battery” or “in-plane flow type RFB”). In the case of the present invention, there is a drawback essentially as described above. Therefore, there is a possibility of a breakthrough in the redox flow battery, and a configuration in which the electrolyte flows vertically through the electrodes (hereinafter referred to as “vertical flow type redox”). A specific study for realizing “flow battery” or “vertical flow type RFB” is desired.

  By the way, as an electrode material of a redox flow battery, the larger the surface area, the better the battery reaction (oxidation reaction and reduction reaction). As an electrode material having a large surface area, Patent Document 3 describes that vapor grown carbon fiber (carbon nanotube) having an average fiber diameter of about 0.05 to 0.3 μm is used. Such a carbon nanotube has an average fiber diameter of about 1/100 or less of that of a normal carbon fiber, and when formed into a sheet, the size of pores in the sheet is also about 1/100 or less. Since the electrode material using such carbon nanotubes has a very dense structure, the electrolyte permeability is extremely poor. Therefore, a redox flow battery using a sheet using carbon nanotubes as a carbonaceous member has a high pressure loss.

  In order to show the usefulness of this novel vertical flow type redox flow battery, which is different from the conventional in-plane flow type redox flow battery, the present inventors have used the cell resistivity as an index for the vertical flow type redox flow battery. A specific configuration including the electrode material was examined. Specifically, by examining in detail the relationship between various specific configurations and the cell resistivity in the configuration, a cell resistivity lower than the cell resistivity of a conventional in-plane flow type redox flow battery can be obtained. The present invention has been completed by finding the structure. The cell resistivity is a characteristic directly related to the current density of charge / discharge, and the present invention leads to the promotion of the development of a vertical flow type redox flow battery.

  The present invention has been made in view of the above problems, and an object thereof is to provide a redox flow battery having a low cell resistivity.

  The present invention provides the following means in order to solve the above problems.

(1) A redox flow battery according to an aspect of the present invention is a redox flow battery including an ion exchange membrane, a current collector plate, and an electrode disposed between the ion exchange membrane and the current collector plate. The electrode has a main electrode layer in which an electrolyte flows from the current collector side surface to the ion exchange membrane side surface, and the main electrode layer includes a plurality of main electrode pieces juxtaposed in a plane direction. Consists of.

(2) In the redox flow battery described in (1) above, the cell resistivity may be 0.7 Ω · cm ² or less.

(3) In the redox flow battery according to any one of (1) and (2), an electrolyte discharge path may be provided between the adjacent main electrode pieces.

(4) In the redox flow battery according to any one of the above (1) to (3), the current collector plate is formed on a surface of the electrode side, and includes a plurality of flow channel networks through which the electrolyte solution flows. And the main electrode piece may be disposed on each of the plurality of channel networks.

(5) In the redox flow battery according to any one of (1) to (4), the main electrode piece may include carbon nanotubes having an average fiber diameter of 1 μm or less.

(6) In the redox flow battery according to any one of (1) to (5), the electrode further includes a liquid outflow layer disposed on the ion exchange membrane side of the main electrode piece. Also good.

(7) In the redox flow battery according to (6), the Darcy law transmittance in the in-plane direction within the liquid outflow layer is a normal line of the conductive sheet, with the sheet surface of the main electrode piece as a reference surface. It may be larger than the Darcy law transmittance of the direction.

(8) In the redox flow battery according to any one of (4) to (7), each of the plurality of flow channel networks is surrounded by a peripheral wall, and a first flow formed by an inner wall. A liquid passage hole formed on one end side of the peripheral wall extends from a liquid inflow hole formed on one end side of the peripheral wall, and the second flow path is provided. May be connected to the first flow path and may extend in a direction intersecting the first flow path.

(9) In the redox flow battery according to any one of (6) and (7), the thickness of the liquid outflow layer may be 0.1 mm or more and 0.9 mm or less.

(10) In the redox flow battery according to any one of (1) to (9), each of the plurality of main electrode pieces has a rectangular shape, and a short side has a length of 5 mm to 70 mm. It may be.

(11) In the redox flow battery according to any one of (6), (7), and (9), the thickness of the liquid outflow layer is 1/150 or more of the short side length of the main electrode piece. May be.

(12) In the redox flow battery according to (8), each of the plurality of main electrode pieces may have its end portion placed on the top surface of the peripheral wall.

(13) In the redox flow battery according to any one of (1) to (12), the effective area ratio may be 60% or more. Here, the effective area ratio is (sum of effective electrode areas of the plurality of main electrode pieces) / {(sum of areas of the plurality of main electrode pieces) + (of the portion between the plurality of main electrode pieces) Sum of area)}.

  The redox flow battery of the present invention can provide a redox flow battery having a low cell resistivity.

It is a cross-sectional schematic diagram of the redox flow battery concerning one Embodiment of this invention. It is the plane schematic diagram which planarly viewed the current collecting plate accommodated in the cell frame from the lamination direction. (A) is the cross-sectional schematic diagram cut | disconnected by the XX line of FIG. 2, (b) is the cross-sectional schematic diagram cut | disconnected by the YY line | wire of FIG. It is a cross-sectional schematic diagram of the redox flow battery concerning other embodiment of this invention. FIG. 4 is a schematic cross-sectional view of a redox flow battery according to an embodiment of the present invention in which an electrode is disposed on the current collector shown in FIGS. 2 and 3, and (a) is cut along the line XX in FIG. 2. It is the cross-sectional schematic diagram, (b) is the cross-sectional schematic diagram cut | disconnected by the YY line | wire of FIG. It is a schematic diagram for demonstrating the flow of the electrolyte solution of the redox flow battery of this invention, Comprising: It is the cross-sectional schematic diagram cut | disconnected by the YY line of FIG. It is a figure of the groove part provided in the redox flow battery of patent document 1, (a) is a top view, (b) is sectional drawing of the principal part cut | disconnected by the XX plane.

  Hereinafter, the redox flow battery will be described in detail with reference to the drawings as appropriate. In the drawings used in the following description, in order to make the characteristics of the present invention easier to understand, there are cases where the characteristic parts are enlarged for the sake of convenience, and the dimensional ratios of the respective components are different from actual ones. is there. The materials, dimensions, and the like exemplified in the following description are merely examples, and the present invention is not limited to these, and can be implemented with appropriate modifications within the scope of the effects of the present invention.

(First embodiment)
FIG. 1 is a schematic cross-sectional view of a redox flow battery according to the first embodiment.
A redox flow battery 100 shown in FIG. 1 includes an ion exchange membrane 10, a current collector plate 20, and an electrode 30. The current collector plate 20 and the electrode 30 are surrounded by the cell frame 40. The electrode 30 is provided in an electrode chamber K formed by the ion exchange membrane 10, the current collector plate 20, and the cell frame 40. The cell frame 40 prevents the electrolyte supplied to the electrode chamber K from leaking outside.

  A redox flow battery 100 shown in FIG. 1 has a cell stack structure in which a plurality of cells CE are stacked. The number of stacked cells CE can be changed as appropriate according to the application, and only a single cell may be used. A practical voltage can be obtained by connecting a plurality of cells CE in series. One cell CE includes an ion exchange membrane 10, two electrodes 30 that function as a positive electrode and a negative electrode that sandwich the ion exchange membrane 10, and a current collector plate 20 that sandwiches the two electrodes 30.

  Hereinafter, the stacking direction of the cell stack structure in which the cells CE are stacked is referred to as “stacking direction” or “perpendicular direction” or “vertical direction”, and the surface direction perpendicular to the stacking direction of the cell stack structure is referred to as “in-plane direction”. Sometimes.

"Ion exchange membrane"
As the ion exchange membrane 10, a cation exchange membrane or an anion exchange membrane can be used. Specifically, the cation exchange membrane includes a perfluorocarbon polymer having a sulfonic acid group, a hydrocarbon-based polymer compound having a sulfonic acid group, a polymer compound doped with an inorganic acid such as phosphoric acid, and a part thereof. Examples thereof include organic / inorganic hybrid polymers substituted with proton conductive functional groups, and proton conductors in which a polymer matrix is impregnated with a phosphoric acid solution or a sulfuric acid solution. Among these, a perfluorocarbon polymer having a sulfonic acid group is preferable, and Nafion (registered trademark) is more preferable.
The thickness of the ion exchange membrane is not particularly limited, but for example, it can be suitably used if it is 150 μm or less. The thickness of the ion exchange membrane is more preferably 120 μm or less, and still more preferably 60 μm or less.
Hereinafter, the embodiment will be described in the case of a cation exchange membrane.

"Current collector"
The current collector plate 20 is a current collector having a role of transferring electrons to the electrode 30. The current collector plate 20 is sometimes referred to as a bipolar plate when both sides thereof can be used as a current collector.

  The current collector plate 20 can be made of a conductive material. For example, a conductive material containing carbon can be used. Specifically, a conductive resin composed of graphite and an organic polymer compound, or a conductive resin in which a part of graphite is replaced with at least one of carbon black and diamond-like carbon, and a molding in which carbon and a resin are kneaded and molded Materials. Among these, it is preferable to use a molding material obtained by kneading and molding carbon and a resin.

  FIG. 2 is a schematic plan view of an example of the current collector plate 20 housed in the cell frame 40 as viewed in plan from the stacking direction. 3A is a schematic cross-sectional view taken along the line XX in FIG. 2, and FIG. 3B is a schematic cross-sectional view taken along the line YY in FIG.

In the present invention, the current collector plate may have a channel network that is formed on the electrode-side surface and through which the electrolytic solution flows, or may have a plurality of channel networks. Here, the “flow channel network” is a flow channel pattern configured to regulate the flow of the electrolyte, and the two “flow channel networks” shown in FIGS. The flow of the electrolytic solution is isolated between the two and the outlet, and the peripheral wall is configured so that the flow of the electrolytic solution does not go back and forth between the two “flow channel networks”.
The current collecting plate 20 shown in FIGS. 2 and 3 is formed on the surface on the electrode side, and has two flow path networks A and B through which the electrolytic solution flows. The two channel networks A and B preferably have the same configuration as shown in FIGS. 2 and 3, but are not limited thereto. In the following description, only one of the two channel networks A and B will be described, and the description of the other may be omitted.
As shown in FIGS. 2 and 3, the two flow path networks A and B of the current collector plate 20 are formed in the peripheral walls 21A and 21B, respectively.

  In the recesses 20A and 20B surrounded by the peripheral walls 21A and 21B, the electrolytic solution is supplied from the openings 21Ai and 21Bi of the peripheral walls 21A and 21B.

  Inner walls 22A and 22B are provided in the recesses 20A and 20B surrounded by the peripheral walls 21A and 21B. The inner walls 22A and 22B form a flow path C in which the electrolytic solution flows in the inflow portion. The shape of the flow path C formed by the inner walls 22A and 22B is not particularly limited.

  The inner walls 22A and 22B shown in FIG. 2 and FIG. 3 are connected to the first channel C1 in which the channel C extends in one direction from the openings 21Ai and 21Bi, and from the first channel C1 to the first channel C1. And a second flow path C2 that branches in the intersecting direction. In this configuration, the supplied electrolytic solution flows along the first flow path C1 and flows so as to expand into the second flow path C2. That is, the electrolytic solution tends to spread uniformly in the in-plane direction of the recesses 20A and 20B. In FIG. 2, the arrow indicates the direction in which the electrolyte flows.

  Here, the current collector plate 20 is not limited to the configuration shown in FIG. For example, as illustrated in FIG. 4, the current collector plate 20 may include three flow channel networks.

"Discharge path"
As shown in FIG. 2, the discharge path 23 is disposed between the adjacent main electrode pieces 31A and 31B in a plan view. The electrolytic solution that has passed through the electrode is discharged through the discharge path 23.
When the main electrode piece has a rectangular shape as will be described later, it is preferable to dispose the discharge path 23 between the long sides of the main electrode piece because the distance through which the electrolytic solution passes through the liquid outflow layer can be shortened. By shortening the distance, the pressure required for the electrolyte to pass through the liquid outflow layer can be reduced, or the thickness of the liquid outflow layer can be reduced to suppress an increase in cell resistivity. You can also.

"electrode"
The electrode of the present invention has a main electrode layer in which an electrolyte flows from the current collector side surface to the ion exchange membrane side surface. The electrode of the present invention is provided with an auxiliary layer on the collector plate side or ion exchange membrane side, although the battery reaction is smaller than the battery reaction occurring in the main electrode layer, but for enhancing the battery reaction occurring in the main electrode layer. Also good.
Here, “the electrolyte flows from the current collecting plate side surface to the ion exchange membrane side surface” means an electrode in an in-plane flow type redox flow battery (in-plane flow type RFB) as shown in FIG. The flow of the electrolyte in the layer means the flow of the electrolyte in the electrode layer in the vertical flow type redox flow battery (vertical flow type RFB). Here, “vertical flow” in the vertical flow type RFB does not mean that the electrolyte does not flow in the in-plane direction at all in the electrode layer, nor does the electrolyte flow only in the direction perpendicular to the surface of the electrode layer. The vertical flow type RFB is configured with a concept different from the in-plane flow type RFB by providing a configuration intended to allow the electrolyte to flow in a direction perpendicular to the surface of the electrode layer. Therefore, “the electrolyte flows from the current collector side surface to the ion exchange membrane side surface” only needs to have a configuration intended to allow the electrolyte solution to flow in a direction perpendicular to the surface of the electrode layer.

  FIG. 5 is a schematic cross-sectional view of a redox flow battery according to an embodiment of the present invention in which electrodes are arranged on the current collector shown in FIGS. 2 and 3, and FIG. It is the cross-sectional schematic diagram cut | disconnected by XX line, FIG.5 (b) is the cross-sectional schematic diagram cut | disconnected by the YY line | wire of FIG.

The electrode 30 shown in FIG. 5 includes a main electrode layer 31, a liquid outflow layer 32, and a liquid inflow layer 33.
As will be described later, since the liquid outflow layer and the liquid inflow layer can use a carbonaceous porous material, a battery reaction can occur in this case, but the battery reaction that occurs in the liquid outflow layer due to a difference in surface area is the main. It is very small compared to the battery reaction occurring in the electrode layer. The electrode can be composed of a plurality of layers including the main electrode layer, but the battery reaction occurring in layers other than the main electrode layer is much smaller than the battery reaction occurring in the main electrode layer.

The main electrode piece of the present invention refers to a main electrode layer divided into a plurality of parts, and the main electrode layer is a general term for the main electrode piece. Each divided main electrode layer is referred to as a main electrode piece. Therefore, the main electrode layer is composed of a plurality of main electrode pieces juxtaposed in the plane direction. Each of the plurality of main electrode pieces may be disposed on each of the plurality of channel networks.
The main electrode layer 31 shown in FIG. 5 is composed of two main electrode pieces 31A and 31B arranged on the two flow path networks A and B and juxtaposed in the plane direction.

Conventionally, in a redox flow battery, a cell frame is provided with one channel network, and one electrode is disposed thereon. When the electrode is divided into two or more, the effective electrode area causing the battery reaction is reduced. Therefore, it was not considered effective to divide conventionally (as will be described later, peripheral walls 21A and 21B are formed as shown in FIG. 3 as will be described later. In this case, the main electrode layer through which the electrolytic solution passes is formed. Since the area is reduced, the area that contributes substantially to the battery reaction (hereinafter sometimes referred to as “effective electrode area”) becomes smaller, and the “total effective electrode area when divided” is not divided. The value divided by the “effective electrode area in the case of the case is sometimes referred to as“ effective area ratio ”hereinafter.)
In contrast, as a result of intensive studies, the inventor has found that the cell resistivity may be lower in the configuration in which the electrode is divided into two or more than in the case of a single electrode configuration.
Here, the expression “division” does not indicate the essence of the effect of the cell resistivity reduction, but is an unprecedented new idea. Therefore, from the viewpoint of facilitating explanation and understanding, it is convenient. Use the term “split”. The following description will clarify the essence of the effect of reducing the cell resistivity.

Referring to FIGS. 2, 3 and 5, in the vertical flow type RFB of the present invention, the electrolyte supplied to the channel networks A and B from the openings 21Ai and 21Bi formed in the peripheral walls 21A and 21B is obtained. Then, it passes through the main electrode layer and exits to the ion exchange membrane side. When the flow channel network is divided into a plurality, the width w (see FIG. 2) of the flow channel network is narrowed, so that the distance that the electrolytic solution flows through the main electrode layer when it reaches the discharge path is shortened. This means that the electrolyte solution penetrating the main electrode layer is recovered in the discharge path with a lower flow path resistance. Further, in the liquid outflow layer, the electrolytic solution flows in the surface direction and reaches the discharge path. Therefore, if the thickness of the liquid outflow layer is thin, the flow path resistance is increased. However, if the distance flowing in the surface direction through the liquid outflow layer is shortened, the flow resistance is lowered, so that the liquid outflow layer can be made thinner accordingly. If the thickness of the liquid outflow layer can be reduced, the main electrode layer can be brought closer to the ion exchange membrane, and the movement distance of hydrogen ions can be shortened, leading to a decrease in cell resistivity.
Hereinafter, the effect that the electrolytic solution penetrating the main electrode layer can be collected in the discharge path with a lower flow path resistance and the effect that the main electrode layer can be brought close to the ion exchange membrane may be referred to as “dividing effect”.

FIG. 2, FIG. 3 and FIG. 5 show an example of the present invention. The flow channel network is divided into a plurality of pieces, and main electrode pieces are arranged on each flow channel network (that is, the main electrodes are also divided into the same number). The battery is obtained by dividing the main electrode layer by, for example, a configuration in which an opening for supplying an electrolytic solution to the channel network is formed on the peripheral wall surrounding each channel network. The inventor has found that the cell resistivity can be lowered if the “division effect” can be increased with respect to the effect of reducing the effective electrode area causing the reaction.
A person skilled in the art usually reduces the effective area of the main electrode layer by dividing the main electrode layer into a plurality of parts and providing an electrolyte discharge path between the adjacent main electrode pieces. Therefore, the cell resistivity is considered to increase.
The inventor overturned the conventional common sense and found a structure in which the cell resistivity is lower than that before division when the main electrode layer is divided into a plurality of parts, and completed the present invention.

  Further, the following effects can be obtained by using a plurality of channel networks. That is, if a plurality of channel networks are used, the width w (see FIG. 2) of the channel network is narrowed, so that the electrolyte supplied from the opening to the channel network spreads throughout the channel network. The distance that flows is shortened. This means that the electrolyte supplied from the opening to the channel network spreads faster throughout the channel network.

According to the configuration of the redox flow battery of the present invention, the cell resistivity can be set to 0.7 Ω · cm ² or less, as shown in Examples described later.
In the conventional in-plane flow type RFB, the cell resistivity is about 0.8 to 1.7 Ω · cm ² (for example, see Non-Patent Document 1).
A method for calculating the cell resistivity will be described later.

(Main electrode layer)
As the main electrode layer 31, a conductive sheet containing carbon fiber can be used. The carbon fiber referred to here is fibrous carbon, and examples thereof include carbon fiber and carbon nanotube. When electrode 30 contains carbon fiber, the contact area of electrolyte solution and electrode 30 is increased, and the reactivity of redox flow battery 100 is increased. In particular, when carbon nanotubes having a diameter of 1 μm or less are included, the contact area can be increased because the fiber diameter of the carbon nanotubes is small, which is preferable. Moreover, when a carbon fiber having a diameter of 1 μm or more is included, the conductive sheet is not easily broken, which is preferable. As the conductive sheet containing carbon fibers, for example, carbon felt, carbon paper, carbon nanotube sheet or the like can be used.

When the main electrode layer 31 is made of a conductive sheet containing carbon nanotubes having an average fiber diameter of 1 μm or less, the average fiber diameter of the carbon nanotubes is preferably 1 to 300 nm, more preferably 10 to 200 nm, and still more preferably. 15-150 nm. Therefore, the conductive sheet has a very low liquid permeability of the electrolytic solution as compared with a carbon fiber felt made of carbon fiber or the like that is generally used. Therefore, it is preferable to provide the liquid outflow layer 32 on the ion exchange membrane side. Details of the liquid outflow layer 32 will be described later.
The average fiber diameter of the carbon nanotubes was obtained by measuring the diameters of 100 or more fibers at random for each fiber type with a transmission electron microscope, and calculating the arithmetic mean value of each. The following average fiber diameters were also determined by the same means. In this embodiment, the average fiber diameter of each carbon nanotube fiber is 1 μm or less.

The carbon nanotubes contained in the conductive sheet may have a configuration in which a plurality of types of carbon nanotubes having different average fiber diameters are mixed. In that case, for example, it is preferable to include a first carbon nanotube having an average fiber diameter of 100 to 1000 nm and a second carbon nanotube having an average fiber diameter of 30 nm or less.
In addition, when it is the structure which mixes several types of carbon nanotube from which average fiber diameters differ, the shape | molded electroconductive sheet is observed with a transmission electron microscope, and what has a fiber diameter over 50 nm in the same visual field is 1st Carbon nanotubes having a fiber diameter of less than 50 nm are regarded as second carbon nanotubes, and the average fiber diameter is calculated as described above.
In addition, whether or not it is a configuration in which a plurality of types of carbon nanotubes having different average fiber diameters are mixed is observed with a transmission electron microscope, and the fiber diameter distribution is measured in the same field of view. It can be judged by whether there are two or more fiber diameter peaks in the distribution.

The average fiber diameter of the first carbon nanotube is preferably 100 to 300 nm, more preferably 100 to 200 nm, and still more preferably 100 to 150 nm. The average fiber length is preferably 0.1 to 30 μm, more preferably 0.5 to 25 μm, and still more preferably 0.5 to 20 μm.
The average fiber diameter of the second carbon nanotube is preferably 1 to 30 nm, more preferably 5 to 25 nm, and still more preferably 5 to 20 nm. The average fiber length is preferably 0.1 to 10 μm, more preferably 0.2 to 8 μm, and still more preferably 0.2 to 5 μm.
The average fiber length can be obtained as an arithmetic average value by measuring 100 or more fiber lengths randomly for each fiber type with a transmission electron microscope.

  It is preferable that at least a part of the second carbon nanotube has a structure straddling two or more first carbon nanotubes. The straddling structure can be confirmed, for example, by observation with a transmission electron microscope. When a structure in which at least a part of the second carbon nanotubes intersects with two or more first carbon nanotubes can be confirmed, it is determined as “having a straddling structure”.

The “strand structure” does not have to be arranged on all the carbon nanotubes. For example, it is only necessary that the second carbon nanotubes straddling the first carbon nanotubes can be confirmed when the electrode is photographed at a magnification of 100,000 times that of a transmission electron microscope. The ratio of the second carbon nanotubes having a structure straddling two or more first carbon nanotubes is preferably 10% or more, more preferably 50% or more.
This ratio can be calculated, for example, by taking the electrode at a magnification of 100,000 times that of a transmission electron microscope and taking 100% of the second carbon nanotube entirely contained in the photograph. The second carbon nanotube with the end protruding from the photograph is not used in the calculation.

  When it has a straddling structure, the form of the sheet can be stably maintained without the conductive sheet falling apart during the molding process. Further, with this structure, the second carbon nanotubes can fill the gaps between the first carbon nanotubes, which are mainly conductive, and the conductivity of the electrode can be further increased. Increasing the conductivity of the electrode can lower the cell resistivity of the redox flow battery and increase the electric capacity.

  Further, when the average fiber diameter of the first carbon nanotube and the second carbon nanotube is in the above range, the conductive sheet has a structure capable of maintaining high strength and high conductivity. This is because the first carbon nanotube serves as a trunk, and the second carbon nanotube is suspended in a branch shape between the plurality of first carbon nanotubes. For example, if the average diameter of the first carbon nanotubes is 100 nm or more, the trunk becomes stable and cracks are less likely to occur in the electrode structure, and it becomes easy to maintain sufficient strength. On the other hand, when the average diameter of the second carbon nanotubes is 30 nm or less, the second carbon nanotubes can be sufficiently entangled with the first carbon nanotubes, and the conductivity is improved. That is, by using an electrode having a conductive sheet containing two types of carbon nanotubes having different average fiber diameters, the cell resistivity of the redox flow battery can be lowered and the electric capacity can be increased.

It is more preferable that at least a part of the second carbon nanotube has a structure in which two or more first carbon nanotubes are entangled. The entangled structure can also be confirmed by observation with a transmission electron microscope, for example. When a structure in which at least a part of the second carbon nanotubes has one or more rounds around the two or more first carbon nanotubes can be confirmed, it is determined as “having a tangled structure”.
Note that the same effect can be expected for the entangled structure as when the structure is straddled.

The second carbon nanotube is preferably 0.05 to 30 parts by mass with respect to 100 parts by mass in total of the first carbon nanotube and the second carbon nanotube. More preferably, it is 0.1-20 mass parts, More preferably, it is 1-15 mass parts. If the second carbon nanotube is included in this range, the electrode can have a structure capable of maintaining high strength and high conductivity. This is because the second carbon nanotubes are included in this range, so that the first carbon nanotubes function as a main conductive material, and the second carbon nanotubes pass between the first carbon nanotubes. This is thought to be for electrical connection and efficient support of conduction.
The ratio of the second carbon nanotubes to the total of 100 parts by mass of the first carbon nanotubes and the second carbon nanotubes is determined by observing the molded conductive sheet with a transmission electron microscope, and the fiber diameter is 50 nm in the same field of view. Are considered to be the first carbon nanotubes, and those having a fiber diameter of less than 50 nm are considered to be the second carbon nanotubes. From the number and size to the mass, assuming that the first carbon nanotubes and the second carbon nanotubes have the same density. You may convert.

  Further, when the ratio of the first carbon nanotube and the second carbon nanotube is within the above range, the above-mentioned “stretched structure” and “entangled structure” are likely to be formed. For this reason, as described above, effects such as a decrease in cell resistivity and an increase in electric capacity can be expected.

The conductive sheet may include a conductive material other than carbon nanotubes. Specific examples include conductive polymers, graphite, and conductive carbon fibers. In view of acid resistance, oxidation resistance, and ease of mixing with carbon nanotubes, it is preferable to include conductive carbon fibers. The volume resistivity of the carbon fiber is preferably 10 ⁷ Ω · cm or less, and more preferably 10 ³ Ω · cm or less. The volume resistivity of the carbon fiber can be measured by the method described in Japanese Industrial Standards JIS R7609: 2007. It is preferable that the conductive sheet has a combined content of carbon nanotubes and other conductive materials of 80% by mass or more because the conductivity of the electrode can be further increased.

  The average fiber diameter of the carbon fibers contained in the conductive sheet is preferably larger than 1 μm. When a carbon fiber having an average fiber diameter larger than that of the carbon nanotube is used, a larger gap can be formed in the conductive sheet, and a pressure loss when the electrolytic solution is passed through the electrode can be reduced. In addition, effects such as improvement in sheet conductivity and strength can be expected. The structure of the carbon nanotube and the carbon fiber preferably has a structure in which the carbon nanotube adheres to the surface of the carbon fiber and the carbon nanotube straddles between the plurality of carbon fibers. In this case, it is preferable that the pressure loss when the electrolytic solution is passed through the electrode can be reduced and good conductivity can be provided. The average fiber diameter of the carbon fiber is preferably 2 to 100 μm, more preferably 5 to 30 μm. The average fiber length is preferably 0.01 to 20 mm, more preferably 0.05 to 8 mm, and still more preferably 0.1 to 1 mm.

  The content of the carbon fiber contained in the conductive sheet is preferably 95 parts by mass or less with respect to 100 parts by mass in total of the carbon fibers contained in the carbon nanotube and the conductive sheet. In this case, an electrode of a redox flow battery having a small pressure loss when the electrolytic solution is passed through the electrode can be obtained, which is preferable. The content of the carbon fiber contained in the conductive sheet is more preferably 90 parts by mass or less, and still more preferably 85 parts by mass or less, with respect to 100 parts by mass in total of the carbon fibers contained in the carbon nanotube and the conductive sheet.

  The conductive sheet may contain a water-soluble conductive polymer. The water-soluble conductive polymer is preferable because the surface of the carbon nanotube can be hydrophilized and the pressure loss when the electrolytic solution is passed through the electrode is reduced. The water-soluble conductive polymer is preferably a conductive polymer having a sulfo group, and specific examples include polyisothianaphthenesulfonic acid.

  The addition amount of the water-soluble conductive polymer is preferably 5 parts by mass or less with respect to 100 parts by mass in total of the carbon fibers contained in the carbon nanotube and the conductive sheet. 4 parts by mass or less is more preferable, and 1 part by mass or less is more preferable. When the conductive sheet is obtained by filtering a dispersion containing carbon nanotubes and carbon fibers, the water-soluble conductive polymer is usually not contained in an amount of more than 5 parts by mass.

  The thickness of the conductive sheet before incorporation into the battery is preferably 0.01 mm to 1 mm, more preferably 0.01 mm to 0.8 mm, and still more preferably 0.02 to 0.5 mm. If it is 0.01 mm or more, the conductivity is good, and if it is 1 mm or less, good liquid permeability is obtained, which is preferable.

Each of the plurality of main electrode pieces constituting the main electrode layer has a rectangular shape, and the length (width) of the short side can be 5 mm or more and 70 mm or less.
When the width of the main electrode piece (meaning “the width of the effective electrode area”) is 5 mm or more and 70 mm or less, the flow resistance of the electrolytic solution can be lowered. When the thickness of the liquid outflow layer described later is 0.1 to 0.4 mm, the width of the main electrode piece is more preferably in the range of 10 mm to 50 mm, further preferably in the range of 10 mm to 40 mm, and in the range of 15 mm to 35 mm. Most preferred. Further, when the thickness of the liquid outflow layer exceeds 0.4 mm and is 1 mm or less, the width of the main electrode piece is more preferably in the range of 10 mm to 60 mm, further preferably in the range of 20 mm to 50 mm, and in the range of 20 mm to 40 mm. Is most preferred.
Further, when the thickness of the liquid outflow layer described later is 0.1 to 0.4 mm, the effective area ratio is preferably 60% or more, more preferably 85% or more, and most preferably in the range of 85% to 95%. When the thickness of the liquid outflow layer exceeds 0.4 mm and is 1 mm or less, the effective area ratio is preferably 60% or more, more preferably 85% or more, and most preferably in the range of 85% to 95%.

"Liquid outflow layer"
The liquid outflow layer 32 is a member provided for the electrolytic solution that has passed through the main electrode layer 31 to flow out of the electrode 30.
The liquid outflow layer 32 shown in FIG. 5 has a divided structure (a structure made up of a plurality of elements), but it may be formed of one sheet for the entire cell.
The liquid outflow layer 32 has a configuration in which the electrolytic solution flows more easily than the main electrode layer 31. The ease of flow of the electrolyte can be evaluated by the Darcy law transmittance. Darcy's law is used to express the transmittance of the porous medium, but in the present invention, it is also applied to members other than the porous material for convenience. At that time, for the non-uniform and anisotropic member, the transmittance in the direction of the lowest transmittance is adopted.

The Darcy law transmittance (hereinafter, simply referred to as transmittance) in the liquid outflow layer 32 is preferably 50 times or more, for example, 100 times or more, compared with the transmittance of the main electrode layer 31. More preferably. Here, Darcy's law transmittance k (m ² ) is the cross-sectional area S (m ² ) of the member through which the liquid of viscosity μ (Pa · sec) is passed, the length L (m) of the member, and the flow rate Q ( m ³ / sec) from the differential pressure ΔP (Pa) between the liquid inflow side and the liquid outflow side of the member when the liquid is passed through, and is calculated from the relationship of the liquid permeation flux (m / sec) expressed by the following equation: The In addition, when the inside of a liquid outflow member consists of space, the cross-sectional area perpendicular | vertical with respect to the liquid flow direction of space is prescribed | regulated as "the cross-sectional area S of the member which lets liquid flow" in the state integrated in the electrode 30.

  The transmittance in the liquid outflow layer 32 is a transmittance in an in-plane direction (a direction parallel to the sheet surface) with respect to the sheet surface of the main electrode layer 31, and the transmittance of the main electrode layer 31 is It is a transmittance in a normal direction (a direction orthogonal to the sheet surface) with respect to the sheet surface of the main electrode layer 31.

  When the transmittance in the liquid outflow layer 32 is sufficiently high compared to the transmittance of the main electrode layer 31, the electrolyte that has passed through the main electrode layer 31 does not stay on the outflow side, and quickly passes through the outside of the electrode 30. To be discharged. The fact that the electrolytic solution does not stay in the liquid outflow layer 32 means that the pressure necessary for the electrolytic solution to pass through the liquid outflow layer 32 is sufficiently higher than the pressure necessary for the electrolytic solution to pass through the main electrode layer 31. Means low. That is, if the transmittances of the main electrode layer 31 and the liquid outflow layer 32 are in the above relationship, the flow of the electrolyte passing through the main electrode layer 31 is directed in a direction perpendicular to the surface of the main electrode layer 31. In this case, the liquid can flow out of the electrode 30 through the liquid outflow layer 32 without disturbing the vertical flow in the main electrode layer 31.

The thickness (before incorporation) of the liquid outflow layer 32 can be 0.1 mm or more and 0.9 mm or less. The thickness of the liquid outflow layer greatly affects the cell resistivity. By setting the thickness of the liquid outflow layer to 0.1 mm or more and 0.9 mm or less, a redox flow battery having a cell resistivity lower than that of the conventional one can be easily assembled.
On the other hand, by increasing the thickness after incorporation of the liquid outflow layer 32, the pressure required for the electrolytic solution to pass through the liquid outflow layer 32 can be further reduced.
The thickness after incorporation of the liquid outflow layer 32 is preferably 0.08 mm or more, more preferably 0.1 mm to 0.7 mm, and still more preferably 0.15 to 0.5 mm. If it is 0.08 mm or more, the pressure required to allow the electrolyte to pass can be reduced, which is preferable. Moreover, if it is 0.7 mm or less, since the increase in cell resistivity can be suppressed, it is preferable.

The thickness of the liquid outflow layer 32 can be 1/150 or more of the short side length (width) of the main electrode piece. When the thickness of the liquid outflow layer is reduced, the short side length needs to be shortened. However, this requirement is achieved by setting the thickness of the liquid outflow layer 32 to 1/150 or more of the short side length (width) of the main electrode piece. In response to
On the other hand, the thickness of the liquid outflow layer 32 can be set to 1/20 or less of the short side length (width) of the main electrode piece. By setting the thickness of the liquid outflow layer 32 to 1/20 or less of the short side length (width) of the main electrode piece, it may be easy to assemble a redox flow battery having a cell resistivity lower than that in the past.

Further, the ratio of the electrolytic solution after passing through the main electrode layer 31 to the electrolytic solution after the oxidation reaction or the reduction reaction is high. By quickly flowing out the electrolytic solution in this manner, ions after the valence change can be efficiently removed from the vicinity of the main electrode layer 31, and thus the reactivity can be increased. For example, when an electrolytic solution containing vanadium is used, in the charging process, V ⁴⁺ changes to V ⁵⁺ at the positive electrode and V ³⁺ changes to V ²⁺ at the negative electrode. Therefore, the ions (V ⁴⁺ and V ³⁺ ) before the reaction can be quickly supplied to the conductive sheet by efficiently removing the ions (V ⁵⁺ and V ²⁺ ) after the reaction. Ions can be efficiently substituted to increase the reaction efficiency. In the discharging process, the valence change of the ions is reversed, but the ions before and after the reaction are efficiently replaced and the reaction efficiency can be increased as in the charging process.

  The specific mode of the liquid outflow layer 32 is not particularly limited as long as the transmittance of the liquid outflow layer 32 and the transmittance of the main electrode layer 31 have the above relationship. The liquid outflow layer 32 may be an outer frame disposed between the main electrode layer 31 and the ion exchange membrane 10 and provided with a liquid outlet for discharging the electrolytic solution to the outside of the electrode 30. When the liquid outflow layer 32 is composed of such an outer frame, the electrolytic solution flows in the space surrounded by the main electrode layer 31, the ion exchange membrane 10, and the outer frame. In this case, the “transmittance in the liquid outflow layer 32” does not mean the transmittance of the member itself constituting the outer frame, but the liquid flow formed in the space formed in the outer frame and the outer frame. It means the transmissivity in the in-plane direction of the part constituted by the outlet. The outer frame does not mean a frame formed at the outermost part. Moreover, you may have the enclosure (an enclosure etc.) by another member outside the outer frame.

  The liquid outflow layer 32 is preferably made of a porous sheet (first porous sheet). In this case, the liquid outlet corresponds to a large number of holes existing on the side surface of the first porous sheet. Since the liquid outflow layer 32 is made of the first porous sheet, the liquid outflow layer 32 functions as a buffer material between the main electrode layer 31 and the ion exchange membrane 10. Therefore, it is possible to prevent the ion exchange membrane 10 from being scratched and to support the main electrode layer 31 stably. The “transmittance in the liquid outflow layer 32” in this case means the transmittance in the in-plane direction of the entire first porous sheet.

  The first porous sheet may be a sponge-like member having voids or a member in which fibers are intertwined. For example, a woven fabric in which relatively long fibers are woven, felt in which fibers are entangled without being woven, paper in which relatively short fibers are wound and formed into a sheet shape, or the like can be used. When the first porous sheet is made of fibers, the average fiber diameter is preferably made of fibers larger than 1 μm. If the average fiber diameter of a 1st porous sheet is 1 micrometer or more, the liquid permeability of the electrolyte solution in a 1st porous sheet can fully be ensured.

The first porous sheet is preferably not corroded by the electrolytic solution. Specifically, redox flow batteries often use acidic solutions. Therefore, it is preferable that the first porous sheet has acid resistance. Moreover, since oxidation by reaction is also considered, it is preferable to have oxidation resistance. Having acid resistance or oxidation resistance refers to a state in which the porous sheet after use maintains its shape.
For example, fibers made of polymer or glass having acid resistance are preferable. As the polymer, fibers made of at least one of fluorine resin, fluorine elastomer, polyester, acrylic resin, polyethylene, polypropylene, polyarylate, polyether ether ketone, polyimide, and polyphenylene sulfide are preferably used. From the viewpoint of acid resistance, fluorine resin, fluorine elastomer, polyester, acrylic resin, polyethylene, polypropylene, polyether ether ketone, polyimide, and polyphenylene sulfide are more preferable. From the viewpoint of oxidation resistance, fluororesins, fluoroelastomers, polyethylene, polyetheretherketone, and polyphenylene sulfide are more preferable. From the viewpoint of heat resistance, fluorine resin, fluorine-based elastomer, polyester, polypropylene, polyarylate, polyetheretherketone, polyimide, and polyphenylene sulfide are more preferable.

Moreover, it is preferable that this 1st porous sheet has electroconductivity. Here, the conductivity means that the volume resistivity is preferably 10 ⁷ Ω · cm or less, more preferably about 10 ³ Ω · cm or less. If the first porous sheet has conductivity, the electrical conductivity in the liquid outflow layer 32 can be increased. For example, when forming a 1st porous sheet using the fiber which consists of material which has electroconductivity, the fiber which consists of a metal and an alloy with acid resistance and oxidation resistance, and carbon fiber can be used. Examples of the metal or alloy fiber include titanium, zirconium, platinum, and the like. Among these, it is preferable to use carbon fiber.

"Liquid inflow layer"
A liquid inflow layer 33 may be inserted between the current collector 20 and the main electrode layer 31.
The liquid inflow layer preferably has a Darcy law transmittance higher than that of the main electrode layer. For the liquid inflow layer, for example, the materials described in the liquid outflow layer can be used.

  In the redox flow battery shown in FIG. 5, the end portions of the main electrode layers 31A and 31B are placed on the top surfaces 21a and 21b (see FIG. 3) of the peripheral walls 21A and 21B of the current collector plate. Temporarily, when main electrode layer 31A, 31B is the structure fitted in accommodating part 20a, 20b, electrolyte solution short-circuits between a main electrode layer and a peripheral part inner surface, and does not pass a main electrode layer There is a risk of flowing into the discharge path 23 (see FIG. 3). In this way, the electrolyte solution that has short-circuited and does not pass through the main electrode piece and has flowed into the discharge path 23 (see FIG. 3) is discharged unreacted, leading to an increase in cell resistivity. On the other hand, as in the redox flow battery shown in FIG. 5, the end portions of the main electrode layers 31A and 31B are mounted on the top surfaces 21a and 21b (see FIG. 3) of the peripheral walls 21A and 21B of the current collector plates. In the installed configuration, a short circuit is not formed, and the electrolyte always passes through the main electrode layer to cause a battery reaction. The main electrode layer is a portion where the electrolyte flows from the current collector side surface to the ion exchange membrane side surface, taking into account the electrochemical meaning (the width of the main electrode piece, the effective area ratio, etc.). In this case, the portions placed on the top surfaces 21a and 21b are not included. However, in this paragraph, in order to facilitate the description of the above structure, the main electrode layer including the portions placed on the top surfaces 21a and 21b is referred to.

(Flow of electrolyte)
FIG. 6 is a schematic diagram for explaining the flow of the electrolyte solution of the redox flow battery of the present invention, and is a schematic cross-sectional view taken along the line YY of FIG.
FIG. 6A shows a case where the main electrode layer 31 and the liquid outflow layer 32 are provided between the current collector 20 and the ion exchange membrane (see FIG. 5), and FIG. This is a case where the liquid inflow layer 33, the main electrode layer 31, and the liquid outflow layer 32 are provided between the current collector 20 and the ion exchange membrane (see FIG. 5).
As shown in FIG. 6A, the electrolyte solution that has entered the channel network of the current collector 22 quickly spreads in the in-plane direction, then passes through the main electrode layer 31 in the direction perpendicular to the surface, and then the liquid outflow layer 32. Enters the in-plane direction and is collected in the discharge path.
As shown in FIG. 6B, the electrolyte solution that has entered the flow path network of the current collector 22 quickly spreads in the in-plane direction, then enters the liquid inflow layer 33, and also spreads in the in-plane direction in the liquid inflow layer 33. In this state, it passes through the main electrode layer 31 in the direction perpendicular to the surface, then enters the liquid outflow layer 32, proceeds in the in-plane direction, and is collected in the discharge path.

(Calculation of cell resistivity)
The cell resistivity [Ω · cm ² ] was calculated from the following formula (1) using a midpoint method after charging / discharging to obtain a charging / discharging curve. Charging and discharging are performed with the same current.
ρ _{S, cell} = S × (V ₁ −V ₂ ) / (2 × I) (1)
here,
ρ _{S, cell} : Cell resistivity [Ω · cm ² ]
S: Electrode area [cm ² ]
V ₁ : Middle point voltage [V] of the charging curve
V ₂ : Middle point voltage [V] of the discharge curve
I: Charge / discharge current [A]
It is.
This calculation method will be described in more detail.
In the charge / discharge curve, the charge curve is always on the top and the discharge curve is on the bottom. This is due to the internal resistance of the battery. That is, at the time of discharge, the voltage drop (overvoltage) corresponding to the internal resistance of the battery becomes the discharge voltage with respect to the open-circuit voltage (voltage when no current flows). On the other hand, with respect to charging, a voltage increase (overvoltage) corresponding to the internal resistance of the battery becomes a charging voltage with respect to the open-circuit voltage. If this is an expression:
Charging voltage (V) = open end voltage (V) + overvoltage (V) (1-a)
Discharge voltage (V) = open end voltage (V) −overvoltage (V) (1-b)
Overvoltage (V) = Battery internal resistance (Ω) × Charge / discharge current (I) (1-c)
From (1-a) to (1-c),
Battery internal resistance (Ω) = {charge voltage (V) −discharge voltage (V)} / 2 × charge / discharge current (I). Here, when the charge / discharge current (I) is set to a current density, an equation of cell resistivity [Ω · cm ² ] is obtained.
Here, in the charge / discharge curve (horizontal axis: electric capacity (Ah), vertical axis: battery voltage (V)), the voltage (V ₁ ) at half the charge capacity obtained from the charge curve is defined as the charge voltage. The calculation method of the cell resistivity [Ω · cm ² ] according to the midpoint method is that the voltage (V ₂ ) at half the discharge capacity obtained from the discharge curve is the discharge voltage.
The cell resistivity shown in the examples is obtained by performing charge / discharge under charge / discharge conditions of a charge / discharge current density of 100 mA / cm ² , a charge end voltage of 1.8 V, a discharge end voltage of 0.8 V, and a temperature of 25 ° C. It is a thing.

  Examples of the present invention will be described below. In addition, this invention is not limited only to a following example.

First, in contrast to the case where the main electrode layer having a width of 50 mm × the length of 50 mm is not divided (Comparative Example 1), the case where the main electrode layer is divided (consisting of a plurality of main electrode pieces) (Example 1 to Example 1). The result of 5) is shown.
Example 1
[Sample preparation and transmittance measurement]
First, a conductive sheet used for the main electrode layer was produced. A first carbon nanotube having an average fiber diameter of 150 nm and an average fiber length of 15 μm, and a second carbon nanotube having an average fiber diameter of 15 nm and an average fiber length of 3 μm, and a total of 100 masses of the first carbon nanotube and the second carbon nanotube. 90 parts by weight and 10 parts by weight with respect to parts, respectively, mixed in pure water, and further, polyisothionaphthenesulfonic acid, which is a water-soluble conductive polymer, is added to the total of the first carbon nanotube and the second carbon nanotube. 1 mass part was added with respect to 100 mass parts, and the liquid mixture was produced. The obtained mixed solution was treated with a wet jet mill to obtain a carbon nanotube dispersion. Furthermore, 50 parts by mass of carbon fibers having an average fiber diameter of 7 μm and an average fiber length of 0.13 mm are added to this dispersion and 100 parts by mass of the first and second carbon nanotubes and carbon fibers, and the mixture is stirred by a magnetic stirrer. Distributed. The dispersion was filtered on a filter paper, dehydrated together with the filter paper, and then compressed by a press machine and further dried to produce a conductive sheet containing carbon nanotubes. The average thickness of the conductive sheet before incorporation was 0.4 mm.

The transmittance of the produced conductive sheet was evaluated with a length L different from that of the battery of Example 1 because the differential pressure ΔP and the length L were proportional. 30 sheets of the produced conductive sheets are stacked, and a 60-mesh Ni mesh sheet made of Ni wire with a diameter of 0.10 mm is arranged and compressed on both sides so that the total thickness is 1 cm, and the cross-sectional area is 1.35 cm 2 (width 50 mm, It was measured by installing it in a transmittance measuring cell having a height of 2.7 mm and a length of 1 cm. Water (20 ° C., viscosity = 1.002 mPa · sec) was passed through the permeability measurement cell at a permeation flux of 0.5 cm / sec, and the differential pressure (outlet pressure-inlet pressure) due to the laminated conductive sheet was measured. The transmittance was calculated. The transmittance of the conductive sheet used in Example 1 was 2.7 × 10 ⁻¹³ m ² .

Next, as shown in FIG. 2 and FIG. 3, grooves were formed in the current collector plate made of a carbon plastic molded body, and a channel network having an inner wall was produced in the current collector plate. The shape and arrangement of the formed channel network are the same as those shown in FIGS. The size of the entire channel network including the peripheral wall was 50 mm × 50 mm, and two channel networks having a size of 24.5 mm × 50 mm were arranged in parallel with a width of 1 mm. At this time, the two channel networks have the same shape, the width of the outer frame (peripheral wall) is 1.5 mm, the width of the inner wall is 1 mm, the width of the first channel C1 is 1 mm, and the width of the second channel C2 is It was 3 mm. The thickness of the channel network (height of the peripheral wall) was 1 mm, the height of the inner wall was 1 mm, and the upper surface of the peripheral wall and the inner wall was the same surface.
The depth of the first channel and the second channel is 1 mm. The opening was provided at the position shown in FIG. 2 with a 0.8 mmφ hole formed in the peripheral wall. A flow path network is connected to the opening, and the discharge path is provided between both side surfaces of the peripheral wall and the two flow path networks so as to be in the discharge direction shown in FIG. 2 (see the discharge path 23 in FIG. 2). ). The discharge path between the two channel networks utilizes the 1 mm width space.

The transmittance of the channel network formed on the current collector plate was measured by providing the same internal structure as the channel network in the transmittance measuring cell. Water (20 ° C) is passed in the in-plane direction of the channel network at a permeation flux of 2.0 cm / sec, and the differential pressure (outlet pressure-inlet pressure) due to the same internal structure as the channel network is measured to determine the permeability. Calculated. The transmittance in the first flow path direction was 4.7 × 10 ⁻¹⁰ m ² . In the second flow path direction, the differential pressure at a permeation flux of 2.0 cm / sec was less than 1 kPa, smaller than the differential pressure in the first flow path direction, and the transmittance was greater than 1 × 10 ⁻⁹ m ² . The transmittance ratio between the channel network and the conductive sheet was calculated using a value in the first channel direction where the ratio was small.

Furthermore, the 1st carbon fiber (CF) paper (made by SGL, GDL10AA) which has porosity as a liquid outflow layer was prepared. The average thickness of the first CF paper (CFP1) before incorporation was 0.2 mm.
The transmittance of the first CF paper is 11 layers of 50 mm × 50 mm first CF paper, a cross-sectional area of 1.35 cm ² (width 50 mm, height 2.7 mm), and a 5 cm long transmittance measuring cell in the stacking direction. It was measured by compressing and installing. Water (20 ° C.) was passed through the transmittance measuring cell at a permeation flux of 0.5 cm / sec, the differential pressure (outlet pressure—inlet pressure) with the laminated first CF paper was measured, and the transmittance was calculated. The transmittance of the liquid outflow layer used in Example 1 was 4.1 × 10 ⁻¹¹ m ² .

[Battery assembly]
A battery was assembled using the above-described conductive sheet, a current collector plate with a flow path network having an inner wall, and first CF paper as the liquid outflow layer. Two conductive sheets of 24.5 mm × 50 mm were arranged in parallel at a width of 1 mm on two channel networks (including peripheral walls) formed on the current collector plate.
Two more first CF papers were stacked on each conductive sheet. The size of the first CF paper was 24.5 mm × 50 mm, which was the same as that of the channel network (including the peripheral wall), and two of them were arranged in parallel with a width of 1 mm like the conductive sheet.

Thus, the current collector plate having the flow path network, the conductive sheet, and the first CF paper were sequentially laminated to produce a redox flow battery electrode.
Further, Nafion N212 (registered trademark, manufactured by DuPont) is used as an ion exchange membrane, and the two electrodes having the above-described configuration are used as a positive electrode and a negative electrode, respectively, and a redox through a frame, a gasket, a current collector plate, and a push plate (not shown). A flow battery was assembled. The assembled conductive sheet and first CF paper had thicknesses of 0.31 mm and 0.12 mm, respectively.

(Examples 2 to 4, Comparative Example 1)
Examples 2 to 4 and Comparative Examples 1 and 2 differ from Example 1 in the following points.
In Example 2, three 16.0 mm × 50 mm channel networks having a width of 1 mm were arranged in parallel. Three electrically conductive sheets of 16.0 mm × 50 mm were arranged in parallel at a width of 1 mm on three flow channel networks (including the peripheral wall) formed on the current collector plate.
In Example 3, four flow channel networks having a size of 11.8 mm × 50 mm were arranged in parallel with a width of 1 mm. Four conductive sheets of 11.8 mm × 50 mm were arranged in parallel at a width of 1 mm on four channel networks (including the peripheral wall) formed on the current collector plate.
In Example 4, five channel networks having a size of 9.2 mm × 50 mm were arranged in parallel with a width of 1 mm. Five conductive sheets of 9.2 mm × 50 mm were arranged in parallel at a width of 1 mm on five flow channel networks (including the peripheral wall) formed on the current collector plate.
Comparative Example 1 is different from the Example in that there is one channel network having a size of 50 mm × 50 mm, and one conductive sheet having a size of 47.0 mm × 50 mm is disposed on the channel network (including the peripheral wall).

Table 1 shows the cell resistivity of Examples 1 to 5 and Comparative Example 1.
In Table 1 and the following description, “the width of the main electrode piece” means the width of the portion (effective electrode area) that is not placed on the peripheral wall in each main electrode piece. Further, the “effective area ratio” means a value obtained by dividing the sum of the effective electrode areas of the main electrode pieces when divided, by the effective electrode area when not divided. These contents are the same in Tables 2 to 6 described later.
Although the effective electrode area (sum of the effective electrode area of the main electrode piece) that causes the battery reaction of Examples 1 to 4 is smaller than that of Comparative Example 1, the cell resistivity of Examples 1 to 4 is the same as that of Comparative Example 1. Low compared to cell resistivity. This result can be considered that the cell resistivity could be reduced by the “division effect”.
In all cases of Examples 1 to 4, that is, the cell resistivity is 0.7 Ω · cm ² or less in the range where the width of the main electrode piece is 6.2 mm to 21.5 mm.
The cell resistivity is particularly low in Examples 1 to 3, that is, when the width of the main electrode piece is 8.8 mm to 24.5 mm.

  Next, when the main electrode layer is divided (consisting of a plurality of main electrode pieces), compared to the case where the main electrode layer having a width of 100 mm × the length of 50 mm is not divided (Comparative Examples 2 to 7) (implementation) The result of Examples 6-41) is shown. The configuration other than the size is the same as that of the first embodiment.

(Examples 6 to 11 and Comparative Example 2)
Examples 6-11 and the comparative example 2 differ from Example 1 as follows.
In Example 6, two 49.5 mm × 50 mm channel networks having a width of 1 mm were arranged in parallel. Two conductive sheets of 49.5 mm × 50 mm were arranged in parallel at a width of 1 mm on two flow path networks (including the peripheral wall) formed on the current collector plate.
In Example 7, three 32.7 mm × 50 mm channel networks having a width of 1 mm were arranged in parallel. Three conductive sheets of 32.7 mm × 50 mm were arranged in parallel at a width of 1 mm on three flow channel networks (including the peripheral wall) formed on the current collector plate.
In Example 8, four channel networks having a size of 24.3 mm × 50 mm were arranged in parallel with a width of 1 mm. Four conductive sheets having a size of 24.3 mm × 50 mm were arranged in parallel at a width of 1 mm on four flow channel networks (including the peripheral wall) formed on the current collector plate.
In Example 9, five 19.2 mm × 50 mm channel networks having a width of 1 mm were arranged in parallel. Five conductive sheets of 19.2 mm × 50 mm were arranged in parallel at a width of 1 mm on five flow channel networks (including the peripheral wall) formed on the current collector plate.
In Example 10, six 15.8 mm × 50 mm channel networks having a width of 1 mm were arranged in parallel. Six 15.8 mm × 50 mm conductive sheets were arranged in parallel with a width of 1 mm on six channel networks (including the peripheral wall) formed on the current collector plate.
In Example 11, seven channel networks having a size of 9.1 mm × 50 mm were arranged in parallel with a width of 1 mm. Seven conductive sheets of 9.1 mm × 50 mm were arranged in parallel with a width of 1 mm on seven flow channel networks (including the peripheral wall) formed on the current collector plate.
The comparative example 2 is different from the example in that there is one channel network having a size of 100 mm × 50 mm, and one conductive sheet having a size of 100 mm × 50 mm is disposed on the channel network (including the peripheral wall).

Table 2 shows the cell resistivity of Examples 6 to 11 and Comparative Example 2.
Although the effective electrode area (sum of the effective electrode area of the main electrode piece) that causes the battery reaction of Examples 6 to 11 is smaller than that of Comparative Example 2, the cell resistivity of Examples 6 to 11 is the same as that of Comparative Example 2. Low compared to cell resistivity. This result can be considered that the cell resistivity can be reduced by the “division effect” as in the first to fourth embodiments.
In the case of Examples 7 to 11, that is, the cell resistivity was 0.7 Ω · cm ² or less in the range of the width of the main electrode piece from 6.1 mm to 29.7 mm.
The cell resistivity is particularly low in Examples 8 and 9, that is, when the width of the main electrode piece is 21.3 mm and 16.2 mm.
In the case described above (Examples 1 to 4) in which the main electrode layer having a width of 50 mm and a length of 50 mm is divided, the cell resistivity is 0.7 Ω · cm ² in the case where the main electrode layer is divided into five (Example 4). It was. In contrast, in Examples 6 to 11 in which the main electrode layer having a width of 100 mm and a length of 50 mm was divided, the cell resistivity was 0.65Ω even when the main electrode layer was divided into six (Example 10). · cm ^2, the cell resistivity became 0.7Omu · cm ² in the case of dividing the main electrode layer into one 10 (example 11). In Example 11, the width of the main electrode piece is 6.1 mm, and the width of the main electrode piece of Example 4 is almost the same as 6.2 mm. This indicates that the essence of the effect of lowering the cell resistivity is not “division itself”, and that one of the main factors is the distance through which the electrolyte flows.

(Examples 12 to 17, Comparative Example 3)
Examples 12 to 17 and Comparative Example 3 differ from Example 6 in that the average thickness of the first CF paper (CFP1), which is the liquid outflow layer, before assembly is 0.3 mm, and the thickness after assembly is 0.18 mm. It was that. In other configurations, Examples 12 to 17 and Comparative Example 3 are the same as Examples 6 to 11 and Comparative Example 2, respectively.

Table 3 shows the cell resistivity of Examples 12 to 17 and Comparative Example 3.
Although the effective electrode area (sum of the effective electrode area of the main electrode piece) that causes the battery reaction of Examples 12 to 17 is smaller than that of Comparative Example 3, the cell resistivity of Examples 12 to 17 is the same as that of Comparative Example 4. Low compared to cell resistivity. This result can be considered that the cell resistivity could be reduced by the “division effect” as in the above example.
Each of Examples 12 to 17 has a higher cell resistivity than Examples 6 to 11 in which the configuration other than the thickness of the liquid outflow layer is the same. This result shows that the thickness of the liquid outflow layer greatly affects the cell resistivity.
However, in the case of Example 14, that is, when the width of the main electrode piece is 21.3 mm, a cell resistivity of 0.7 Ω · cm ² or less can be realized.

(Examples 18 to 22, Comparative Example 4)
Examples 18 to 22 and Comparative Example 4 differ from Example 6 in that the average thickness before assembly of the first CF paper (CFP1), which is the liquid outflow layer, is 0.5 mm, and the thickness after assembly is 0.30 mm. It was that. In other configurations, each of Examples 18 to 22 is the same as each of Examples 6 to 10, and Comparative Example 4 is the same as Comparative Example 2.

Table 4 shows the cell resistivity of Examples 18 to 22 and Comparative Example 4.
Although the effective electrode area (sum of the effective electrode areas of the main electrode pieces) that causes the battery reaction of Examples 18 to 22 is smaller than that of Comparative Example 4, the cell resistivity of Examples 18 to 22 is the same as that of Comparative Example 4. Low compared to cell resistivity. This result can be considered that the cell resistivity could be reduced by the “division effect” as in the above example.
Each of Examples 18 to 22 has a higher cell resistivity than Examples 6 to 11 and Examples 12 to 17 having the same configuration except the thickness of the liquid outflow layer. This result shows that the thickness of the liquid outflow layer greatly affects the cell resistivity.
In any case of Examples 18 to 22, the cell resistivity is 0.7 Ω · cm ² or more. In the configuration shown in the examples, the liquid outflow layer needs to be 0.3 mm or less. However, this can be said in the configuration shown in the embodiment, and it is needless to say that the cell resistivity cannot be reduced to 0.7 Ω · cm ² or less unless the liquid outflow layer is 0.3 mm or less. .
The cell resistivity is particularly low in Examples 18 to 20, that is, when the width of the main electrode piece is 21.3 mm to 46.5 mm.

  Based on the results of Examples 6 to 22 above, the width of the main electrode piece is preferably in the range of 10 mm to 45 mm, more preferably in the range of 15 mm to 40 mm, and still more preferably in the range of 20 mm to 35 mm.

(Examples 23 to 27, Comparative Example 5)
First, Examples 23 to 27 and Comparative Example 5 are different from Example 6 in that the average thickness of the first CF paper (CFP1), which is the liquid outflow layer, before assembly is 0.7 mm, and the thickness after assembly is 0. .42 mm. In other configurations, Examples 23 to 27 are the same as Examples 6 to 10, and Comparative Example 5 is the same as Comparative Example 3.

Table 5 shows the cell resistivity of Examples 23 to 27 and Comparative Example 5.
Although the effective electrode area (sum of the effective electrode areas of the main electrode pieces) that causes the battery reaction of Examples 23 to 27 is smaller than that of Comparative Example 7, the cell resistivity of Examples 23 to 27 is all that of Comparative Example 7. Low compared to cell resistivity. This result can be considered that the cell resistivity could be reduced by the “division effect” as in the above example.
Each of Examples 23 to 27 has a higher cell resistivity than Examples 6 to 11, Examples 12 to 17, and Examples 18 to 22 that have the same configuration except the thickness of the liquid outflow layer. This result shows that the thickness of the liquid outflow layer greatly affects the cell resistivity.
The cell resistivity is particularly low in Examples 23 to 25, that is, when the width of the main electrode piece is 21.3 mm to 46.5 mm.

(Examples 28 to 32, Comparative Example 6)
Examples 28 to 32 and Comparative Example 6 differ from Example 6 in that the average thickness before assembly of the first CF paper (CFP1), which is the liquid outflow layer, is 1.0 mm, and the thickness after assembly is 0.6 mm. It was that. In other configurations, each of Examples 28 to 32 is the same as each of Examples 6 to 10, and Comparative Example 6 is the same as Comparative Example 3.

Table 6 shows the cell resistivity of Examples 28 to 32 and Comparative Example 6.
Although the effective electrode area (sum of the effective electrode areas of the main electrode pieces) that causes the battery reaction of Examples 28 to 32 is smaller than that of Comparative Example 6, the cell resistivity of Examples 28 to 32 is the same as that of Comparative Example 6. Low compared to cell resistivity. This result can be considered that the cell resistivity could be reduced by the “division effect” as in the above example.
In any of Examples 28 to 32, the cell resistivity was compared with Examples 6 to 11, Examples 12 to 17, Examples 18 to 22, and Examples 23 to 27 having the same configuration except the thickness of the liquid outflow layer. Is big. This result shows that the thickness of the liquid outflow layer greatly affects the cell resistivity.
The cell resistivity is particularly low in Examples 28 to 29, that is, the case where the width of the main electrode piece is 29.7 mm to 46.5 mm.

DESCRIPTION OF SYMBOLS 10 Ion exchange membrane 20 Current collector 20a, 20b Housing part 21, 21A, 21B Peripheral wall 22, 22A, 21B Inner wall 23 Discharge path 30 Electrode 31 Main electrode layer 31A, 31B Main electrode piece 32 Liquid outflow layer 100 Redox flow battery A, B Main electrode piece

Claims (8)

A redox flow battery current collector comprising an ion exchange membrane, a current collector, and an electrode disposed between the ion exchange membrane and the current collector,
A current collector plate in which a plurality of channel networks through which an electrolyte flows is formed on a surface of the current collector plate on the electrode side.   The current collector plate according to claim 1, wherein each of the plurality of channel networks is surrounded by a peripheral wall.   The plurality of flow channel networks have a first flow channel and a second flow channel formed by an inner wall, and the first flow channel is located on the other end side from a liquid inflow hole formed on one end side of the peripheral wall. The current collector plate according to claim 2, wherein the second flow path is connected to the first flow path and extends in a direction intersecting the first flow path.   The current collector plate according to claim 2, wherein an electrolyte discharge path is provided between peripheral walls of the adjacent channel networks.   5. The current collector plate according to claim 1, wherein each of the plurality of channel networks has a rectangular shape, and a length of a short side is 5 mm or more and 70 mm or less. The current collector plate according to any one of claims 1 to 5, wherein the effective area ratio is 60% or more;
Here, the effective area ratio is (sum of effective electrode areas of the plurality of flow channel networks) / {(sum of area of the plurality of flow channel networks) + (part of the portion between the plurality of flow channel networks) Sum of areas)}. The electrode has a main electrode layer having a region in which an electrolyte flows from the current collector side surface to the ion exchange membrane side surface;
The region is composed of a plurality of main electrode pieces juxtaposed in the plane direction,
The current collector plate according to claim 1, wherein the main electrode piece is provided on each of the plurality of channel networks.   The current collector plate according to claim 7, wherein an end of each of the plurality of main electrode pieces is placed on a top surface of a peripheral wall surrounding the channel network.

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