WO2019234867A1 - Bipolar plate, cell frame, cell stack, and redox flow battery - Google Patents

Abstract

A bipolar plate having an electrode of a redox flow battery positioned thereon and comprising: a facing surface that faces said electrode; and at least one groove that forms, in the facing surface, a flow path through which an electrolytic solution flows, wherein when the bipolar plate is in planar view, at least one of the grooves has a curved section.

Description

Bipolar plate, cell frame, cell stack, and redox flow battery

The present invention relates to a bipolar plate, a cell frame, a cell stack, and a redox flow battery.

As one of large-capacity storage batteries, a redox flow battery (hereinafter sometimes referred to as “RF battery”) is known (see, for example, Patent Documents 1 and 2). In general, an RF battery uses a cell stack in which a plurality of cell frames, positive electrodes, diaphragms, and negative electrodes are stacked. The cell frame includes a bipolar plate disposed between the positive electrode and the negative electrode, and a frame provided on the outer periphery of the bipolar plate. In the cell stack, positive and negative electrodes are arranged between bipolar plates of adjacent cell frames with a diaphragm interposed therebetween to form one cell. The RF battery performs charging / discharging by circulating an electrolyte solution in a cell containing an electrode by a pump.

Patent Documents 1 and 2 describe that a channel is formed by forming a plurality of grooves through which an electrolytic solution flows on the electrode side surface of a bipolar plate.

JP2015-122230A JP 2015-210849 A

The bipolar plate of the present disclosure is
An electrode of a redox flow battery is disposed, and is a bipolar plate provided with a facing surface facing the electrode, and at least one groove constituting a flow path through which an electrolyte flows in the facing surface,
When the bipolar plate is viewed in plan, at least one of the grooves has a curved portion.

The cell frame of the present disclosure is
The bipolar plate of the present disclosure and a frame body provided on the outer periphery of the bipolar plate.

The cell stack of the present disclosure is
The cell frame of the present disclosure is provided.

The redox flow battery of the present disclosure is
The cell stack of the present disclosure is provided.

It is an operation principle figure of the redox flow battery concerning an embodiment. It is a schematic block diagram which shows an example of the redox flow battery which concerns on embodiment. It is a schematic block diagram which shows an example of the cell stack which concerns on embodiment. It is a schematic plan view when a cell frame provided with the bipolar plate which concerns on embodiment is planarly viewed from the one surface side of the bipolar plate. FIG. 5 is an enlarged view showing one of the grooves constituting the flow path of the electrolytic solution shown in FIG. 4. It is a schematic sectional drawing which shows typically the cross-sectional shape of the groove | channel in embodiment. It is a schematic plan view which shows the modification of the bipolar plate which concerns on embodiment. Sample No. used in Test Example 1 It is a top view which shows 1 bipolar plate. Sample No. used in Test Example 1 It is a top view which shows 2 bipolar plates. Sample No. used in Test Example 1 3 is a plan view showing a bipolar plate 3. FIG.

[Problems to be solved by the present disclosure]
Further improvement of the battery performance of the redox flow battery is desired. From the viewpoint of improving the battery performance, it is required to reduce the internal resistance (cell resistance) of the battery. As a factor of the internal resistance, there are a flow state of the electrolytic solution, for example, a flow resistance of the electrolytic solution, a reaction resistance at the electrode, and the like.

The electrode of the redox flow battery functions as a reaction field that promotes the battery reaction of the active material (metal ions) contained in the supplied electrolyte. A porous material such as carbon felt made of carbon fiber is usually used for the electrode, and an electrolytic solution flows in the electrode. When a flow path having a groove through which the electrolytic solution flows is provided on the electrode side surface of the bipolar plate, the flow resistance of the electrolytic solution can be reduced, and the pressure loss due to the flow resistance of the electrolytic solution can be reduced. Further, by using a bipolar plate having a channel having a groove, the flow of the electrolyte solution penetrating into the electrode can be controlled, and the distribution of the electrolyte solution in the electrode can be suppressed from becoming non-uniform. By suppressing variations in the distribution of the electrolyte solution penetrating into the electrode, the reactivity between the electrode and the electrolyte solution can be improved, and the reaction resistance at the electrode can be reduced.

However, in the past, it has not necessarily been fully studied to reduce the internal resistance after sufficiently considering the flow state of the electrolyte solution at the electrode. In the conventional bipolar plate, since the flow path is mainly composed of linear grooves, the degree of freedom in the layout of the grooves is low, and it is difficult to sufficiently improve the uniformity of the distribution of the electrolyte in the electrodes. There is room for improving the reactivity between the electrode and the electrolyte.

Therefore, an object of the present disclosure is to provide a bipolar plate that can improve the reactivity between the electrode and the electrolyte while reducing the flow resistance of the electrolyte. Another object of the present disclosure is to provide a cell frame and a cell stack that can improve battery performance. Furthermore, an object of the present disclosure is to provide a redox flow battery having excellent battery performance.

[Effects of the present disclosure]
According to the present disclosure, it is possible to provide a bipolar plate that can improve the reactivity between the electrode and the electrolytic solution while reducing the flow resistance of the electrolytic solution. Moreover, according to this indication, the cell frame and cell stack which can improve battery performance can be provided. Furthermore, according to the present disclosure, a redox flow battery having excellent battery performance can be provided.

[Description of Embodiment of Present Invention]
First, the contents of the embodiments of the present invention will be listed and described.

(1) The bipolar plate according to the embodiment is
An electrode of a redox flow battery is disposed, and is a bipolar plate provided with a facing surface facing the electrode, and at least one groove constituting a flow path through which an electrolyte flows in the facing surface,
When the bipolar plate is viewed in plan, at least one of the grooves has a curved portion.

According to the bipolar plate, the flow path of the electrolytic solution is formed on the facing surface facing the electrode, so that the flow resistance of the electrolytic solution can be reduced and the distribution of the electrolytic solution penetrating into the electrode can be controlled. Since at least one groove constituting the flow path has a curved portion, the degree of freedom in layout is increased compared to a straight groove, so that the groove can be efficiently formed so that the distribution of the electrolyte in the electrode is uniform. It is possible to arrange. Thereby, the uniformity of the distribution of the electrolytic solution in the electrode can be sufficiently increased, and the reactivity between the electrode and the electrolytic solution can be improved. Therefore, the bipolar plate can improve the reactivity between the electrode and the electrolytic solution while reducing the flow resistance of the electrolytic solution. Therefore, when the bipolar plate is used in a redox flow battery, the reaction resistance at the electrode can be reduced while the pressure loss due to the flow resistance of the electrolyte can be reduced, so the internal resistance of the battery (cell resistance) Can be reduced.

The “curved part” of the groove refers to a curved part in the longitudinal direction of the groove. The curved portion is typically a non-periodic curved shape.

(2) As one form of the bipolar plate,
It is mentioned that the curvature radius of the curved portion is 0.1 mm or more.

When the radius of curvature of the curved portion is 0.1 mm or more, the groove having the curved portion can be easily formed. The upper limit of the curvature radius of the curved portion is not particularly limited, but is, for example, 100 mm or less.

(3) As one form of the bipolar plate,
It is mentioned that the opening width of the groove becomes smaller toward the tip side.

As the opening width of the groove decreases toward the tip, the pressure of the electrolyte increases as it approaches the tip, and the electrolyte can easily penetrate from the groove into the electrode.

(4) As one form of the bipolar plate,
Of the opposing surfaces of the bipolar plate, A / (A + B) is more than 0.5 and less than 0.95, where A is the contact area in contact with the electrode and B is the planar opening area of the groove. Can be mentioned.

Since the ratio [A / (A + B)] of the contact area (A) of the electrode to the area (A + B) of the opposite surface of the bipolar plate is more than 0.5, the contact area between the electrode and the bipolar plate is secured. The contact resistance between the electrode and the bipolar plate can be reduced. Thereby, the internal resistance (cell resistance) of the battery can be reduced. In addition, from the viewpoint of ensuring the groove formation area (electrolyte flow path area) on the opposing surface of the bipolar plate, the ratio [A / (A + B)] of the electrode contact area is preferably less than 0.95. Thereby, the distribution | circulation resistance of electrolyte solution can be reduced effectively.

The “planar opening area” of the groove means the opening area of the groove on the opposite surface when the bipolar plate is viewed in plan.

(5) As one form of the bipolar plate,
In the cross section orthogonal to the flow direction of the electrolytic solution in the groove, the width on the opening side of the groove is equal to or larger than the width on the bottom side.

In the cross section of the groove, when the width on the opening side of the groove is equal to or larger than the width on the bottom side, it is easier to form the groove than when the width on the bottom side is wider than the width on the opening side.

(6) As one form of the bipolar plate described in (5) above,
It is mentioned that the cross-sectional shape of the groove is formed in a tapered shape from the opening side toward the bottom side.

Since the cross section of the groove is formed in a tapered shape from the opening side to the bottom side, the electrolyte can easily penetrate from the groove into the electrode.

(7) As one form of the bipolar plate,
The groove is formed in a dendritic shape, and includes a trunk groove part and at least one branch groove part branched from the trunk groove part,
It is mentioned that at least one of the branch groove portions intersects the trunk groove portion non-orthogonally.

Since the groove is formed in a dendritic shape, it is easy to permeate and diffuse the electrolytic solution from the groove over a wide range in the electrode, and the distribution of the electrolytic solution in the electrode can be made more uniform. Therefore, the reactivity between the electrode and the electrolytic solution can be further improved. Further, the branch groove portion branched from the trunk groove portion intersects the trunk groove portion in a non-orthogonal direction, so that the flow resistance of the electrolytic solution can be reduced as compared with the case where the branch groove portion is orthogonal to the trunk groove portion.

(8) As one form of the bipolar plate described in (7) above,
It is mentioned that at least one of the branch groove portions has the curved portion.

It is possible to arrange the grooves efficiently by having the curved part in the branch groove part.

(9) As one form of the bipolar plate described in (7) or (8) above,
It is mentioned that at least one of the branch groove portions has a branch groove portion that further branches from the branch groove portion.

By having a branch groove part that further branches from the branch groove part, it is easy to effectively permeate and diffuse the electrolyte into the electrode.

(10) As one form of the bipolar plate described in (9) above,
When the branching frequency of the branch groove portion is N (N: natural number), N is 3 or less.

繰 り 返 す By repeating branching from the trunk groove part, the groove width (opening width) of the branched branch groove part is reduced and narrowed. By restricting the number of branches (N) of the branch groove portion to 3 or less, excessive narrowing of the groove width of the branch groove portion due to branching can be avoided.

“The number of branching” means the number of times the branching part branches from the trunk part. When there is a branch groove part (primary branch groove) branched from the trunk groove part, the branching number is set to 1. When there is a branch groove part (secondary branch groove) further branched from the branch groove part, the branching number is set to 2. And count. When there is a branch groove portion (third branch groove) that further branches from the secondary branch groove, the number of branches is counted as three. The “N” is a natural number (1, 2, 3,...).

(11) As one form of the bipolar plate described in (9) or (10) above,
It is mentioned that the opening width of the branch groove part after branching is smaller than the opening width of the branch groove part before branching.

The contact width between the electrode and the bipolar plate can be increased and the contact resistance between the electrode and the bipolar plate can be reduced by decreasing the opening width of the branched branch groove portion step by step each time it branches.

(12) As one form of the bipolar plate,
The flow path is
An inlet and an outlet for the electrolyte;
An introduction path for introducing the electrolyte solution from the introduction port, and a discharge path for discharging the electrolyte solution to the discharge port independently without communicating with the introduction path,
The introduction path and the discharge path each include at least one groove;
It is mentioned that at least one of the introduction path and the discharge path includes a rectification unit that is connected to the introduction port or the discharge port and is formed along an edge of the bipolar plate.

Since the flow path includes the introduction path and the discharge path, the electrolyte flows so as to cross between the introduction path and the discharge path. At that time, the electrolyte penetrates and diffuses into the electrode, and the electrolyte The entire electrode can be evenly distributed. As a result, the distribution of the electrolytic solution in the electrode can be made more effective and uniform, and the reactivity between the electrode and the electrolytic solution can be further improved. Further, by providing the rectifying unit, it is possible to efficiently introduce or discharge the electrolytic solution from the introduction port or the discharge port with respect to at least one of the introduction path and the discharge path.

(13) As one form of the bipolar plate described in (12) above,
The effective electrode region where the bipolar plate and the electrode face each other is rectangular, and the introduction port and the discharge port are provided at diagonal positions of the effective electrode region,
An angle formed by the rectifying unit and a diagonal line of the effective electrode region is 40 ° or more and 50 ° or less.

The pressure loss in the rectification unit can be reduced by the angle between the rectification unit and the diagonal of the effective electrode region being 40 ° or more and 50 ° or less.

(14) As one form of the bipolar plate according to (12) or (13),
In the bipolar plate, when the inlet side is the lower side and the outlet side is the upper side,
It is mentioned that the said flow path is asymmetrical up and down.

It is possible to improve the flow of the electrolyte solution on the discharge side where the pressure of the electrolyte solution is reduced because the flow path is asymmetrical between the introduction side and the discharge side.

(15) As one form of the bipolar plate according to any one of (12) to (14),
It is mentioned that the groove | channel of the said introduction path and the groove | channel of the said discharge path have opposing comb-tooth area | regions which are alternately arranged facing each other.

When the flow path has the opposing comb-tooth region, the amount of the electrolyte flowing through the introduction path and the discharge path increases, and the electrolyte that permeates and diffuses into the electrode increases. Thereby, the reaction efficiency of an electrode and electrolyte solution can be improved.

(16) As one form of the bipolar plate,
It can be mentioned that at least a part of the groove has a wide part having an opening width of 2 mm or more, and a convex part protruding from the bottom part is formed in the wide part.

It is possible to suppress the electrode from being buried in the groove by providing the convex part in the wide part of the groove.

(17) The cell frame according to the embodiment is
The bipolar plate according to any one of (1) to (16) above and a frame body provided on the outer periphery of the bipolar plate.

Since the cell frame includes the bipolar plate according to the above-described embodiment, the reactivity between the electrode and the electrolytic solution can be improved while reducing the flow resistance of the electrolytic solution. While being able to reduce, it is possible to reduce the reaction resistance at the electrode. Therefore, when the cell frame is used for a redox flow battery, the internal resistance (cell resistance) of the battery can be reduced, and the battery performance can be improved.

(18) The cell stack according to the embodiment is
The cell frame according to (17) is provided.

The cell stack includes the cell frame according to the above-described embodiment, so that the reaction resistance at the electrode can be reduced while the pressure loss due to the flow resistance of the electrolytic solution can be reduced. Therefore, when the cell stack is used for a redox flow battery, the internal resistance (cell resistance) of the battery can be reduced, and the battery performance can be improved.

(19) The redox flow battery according to the embodiment is
The cell stack according to (18) is provided.

Since the redox flow battery includes the cell stack according to the above-described embodiment, it is possible to reduce the reaction loss at the electrode while reducing the pressure loss due to the flow resistance of the electrolytic solution. Resistance (cell resistance) can be reduced. Therefore, the redox flow battery is excellent in battery performance.

[Details of the embodiment of the present invention]
Specific examples of a bipolar plate for a redox flow battery, a cell frame and a cell stack, and a redox flow battery (RF battery) according to an embodiment of the present invention will be described below with reference to the drawings. The same reference numerals in the drawings indicate the same or corresponding parts. In addition, this invention is not limited to these illustrations, is shown by the claim, and intends that all the changes within the meaning and range equivalent to a claim are included.

FIG. 4 is a schematic plan view of the cell frame 3 including the bipolar plate 31 according to the embodiment when viewed from the one surface side of the bipolar plate 31. One of the features of the bipolar plate 31 of the embodiment is, as shown in FIG. 4, provided with at least one groove 5 constituting the flow path 4 through which the electrolytic solution flows on the facing surface facing the electrode 14, and the bipolar plate 31. When viewed in plan, at least one of the grooves 5 is at a point having a curved portion.

In the following, referring to FIG. 1 to FIG. 4, the outline of the RF battery 1 according to the embodiment, and the cell 10 (cell stack 2) and the bipolar plate 31 (cell frame 3) included in the RF battery 1 will be described. explain. Thereafter, the flow path 4 and the groove 5 provided in the bipolar plate 31 according to the embodiment will be described in detail mainly with reference to FIGS.

<< RF battery >>
First, an example of the RF battery 1 and the cell 10 (cell stack 2) according to the embodiment will be described with reference to FIGS. The RF battery 1 shown in FIG. 1 and FIG. 2 uses an electrolytic solution containing, as an active material, a metal ion whose valence changes as a result of oxidation and reduction in the positive electrode electrolyte and the negative electrode electrolyte. The battery performs charging / discharging by utilizing the difference between the redox potential and the redox potential of ions contained in the negative electrode electrolyte. Here, as an example of the RF battery 1, a vanadium-based RF battery using a vanadium electrolyte solution containing V ions in the positive electrode electrolyte and the negative electrode electrolyte is shown. A solid line arrow in the cell 10 in FIG. 1 indicates a charging reaction, and a broken line arrow indicates a discharging reaction. The RF battery 1 is connected to the electric power system P via an AC / DC converter C, for example, for load leveling applications, applications such as sag compensation and emergency power supplies, natural energy power generation such as solar power generation and wind power generation. Used for output smoothing.

The RF battery 1 includes a cell 10 for charging / discharging, tanks 106 and 107 for storing an electrolyte, and circulation channels 100P and 100N for circulating the electrolyte between the tanks 106 and 107 and the cell 10. .

"cell"
As shown in FIG. 1, the cell 10 includes a positive electrode 14, a negative electrode 15, and a diaphragm 11 interposed between the electrodes 14 and 15. The structure of the cell 10 is separated into a positive electrode cell 12 and a negative electrode cell 13 with a diaphragm 11 interposed therebetween, and a positive electrode 14 is incorporated in the positive electrode cell 12 and a negative electrode 15 is incorporated in the negative electrode cell 13.

Each electrode of the positive electrode 14 and the negative electrode 15 is formed of a carbon fiber aggregate including carbon fibers. Since the electrode of the carbon fiber aggregate is porous and has voids in the electrode, the electrolytic solution flows through the electrode, and the electrolytic solution can permeate and diffuse. Examples of the carbon fiber aggregate include carbon felt, carbon cloth, and carbon paper. Examples of the carbon fiber include PAN-based carbon fiber using polyacrylonitrile (PAN) fiber as a raw material, pitch-based carbon fiber using pitch fiber as a raw material, and rayon-based carbon fiber using rayon fiber as a raw material. The diaphragm 11 is formed of, for example, an ion exchange membrane that transmits hydrogen ions.

In the cell 10 (the positive electrode cell 12 and the negative electrode cell 13), an electrolytic solution (a positive electrode electrolytic solution and a negative electrode electrolytic solution) circulates through the circulation channels 100P and 100N. A positive electrode electrolyte tank 106 that stores a positive electrode electrolyte is connected to the positive electrode cell 12 via a positive electrode circulation channel 100P. Similarly, a negative electrode electrolyte tank 107 that stores a negative electrode electrolyte is connected to the negative electrode cell 13 via a negative electrode circulation channel 100N. Each circulation flow path 100P, 100N has forward piping 108, 109 for sending the electrolytic solution from each tank 106, 107 to the cell 10 and return piping 110, 111 for returning the electrolytic solution from the cell 10 to each tank 106, 107. Pumps 112 and 113 for pumping the electrolytic solution stored in the tanks 106 and 107 are provided in the outgoing pipes 108 and 109, and the electrolytic solution is circulated to the cell 10 by the pumps 112 and 113.

Cell stack
The cell 10 may be configured as a single cell including a single cell 10 or may be configured as a multi-cell including a plurality of cells 10. The cell 10 is normally used in a form called a cell stack 2 including a plurality of stacked cells 10 as shown in FIG. As shown in the lower diagram of FIG. 3, the cell stack 2 is configured by sandwiching the sub stack 200 from two end plates 220 from both sides and fastening the end plates 220 on both sides by a fastening mechanism 230. FIG. 3 illustrates a cell stack 2 including a plurality of substacks 200. A plurality of sub-stacks 200 are stacked in the order of the cell frame 3, the positive electrode 14, the diaphragm 11, and the negative electrode 15 (see the upper diagram of FIG. 3), and supply / discharge plates 210 (see the lower diagram of FIG. 2 is not shown in FIG. Connected to the supply / discharge plate 210 are the forward pipes 108 and 109 and the return pipes 110 and 111 of the circulation passages 100P and 100N (see FIGS. 1 and 2).

《Cell Frame》
3, the cell frame 3 includes a bipolar plate 31 disposed between the positive electrode 14 and the negative electrode 15 and a frame body 32 provided around the bipolar plate 31 (see FIG. 3). (See also 4). On one surface side of the bipolar plate 31, the positive electrode 14 is disposed so as to face the other surface, and on the other surface side of the bipolar plate 31, the negative electrode 15 is disposed so as to face it. A bipolar plate 31 is provided inside the frame body 32, and a recess 32 o is formed by the bipolar plate 31 and the frame body 32. The recesses 32o are respectively formed on both sides of the bipolar plate 31, and the positive electrode 14 and the negative electrode 15 are accommodated in each recess 32o with the bipolar plate 31 interposed therebetween. Each recessed part 32o forms each cell space of the positive electrode cell 12 and the negative electrode cell 13 (refer FIG. 1). The planar shape of each of the positive electrode 14 and the negative electrode 15 is not particularly limited, but is rectangular in this embodiment. Moreover, the planar opening shape of the recessed part 32o is the same rectangular shape as an electrode, and the size of the recessed part 32o and an electrode is substantially the same. And the area | region (Effective electrode area | region where the bipolar plate 31 and the electrode 14 which are shown in FIG. 4 oppose) each electrode in the bipolar plate 31 overlaps in a lamination direction is a rectangular shape.

The bipolar plate 31 is made of, for example, plastic carbon, and the frame body 32 is made of, for example, plastic such as vinyl chloride resin (PVC), polypropylene, polyethylene, fluorine resin, or epoxy resin. In the cell frame 3, a frame 32 is integrated around the bipolar plate 31 by injection molding or the like.

In the cell stack 2 (sub-stack 200), the one surface side and the other surface side of the frame 32 of each adjacent cell frame 3 face each other and face each other, and between the bipolar plates 31 of each adjacent cell frame 3 respectively. One cell 10 is formed. When the cell 10 is assembled, the electrodes 14 and 15 are accommodated in the recessed portions 32o of the frame body 32 in a compressed state in the thickness direction. An annular seal member 37 such as an O-ring or a flat packing is disposed between the frame bodies 32 of each cell frame 3 in order to suppress leakage of the electrolytic solution. A seal groove 38 (see FIG. 4) for arranging the seal member 37 is formed in the frame body 32.

The electrolyte solution in the cell 10 flows through the supply manifolds 33 and 34 and the drainage manifolds 35 and 36 formed through the frame 32 of the cell frame 3 and the supply slits 33 s formed in the frame 32. , 34s and drainage slits 35s, 36s. In the case of the cell frame 3 (frame body 32) shown in this example, the positive electrode electrolyte is supplied from a liquid supply manifold 33 formed in the lower part of the frame body 32 through a liquid supply slit 33s formed on one surface side of the frame body 32. Are supplied to the positive electrode 14 and discharged to the drainage manifold 35 through the drainage slit 35 s formed in the upper part of the frame 32. Similarly, the negative electrode electrolyte is supplied from the liquid supply manifold 34 formed in the lower part of the frame 32 to the negative electrode 15 through the liquid supply slit 34 s formed on the other surface side of the frame 32, and the frame 32. The liquid is discharged to the drainage manifold 36 through the drainage slit 36s formed in the upper part. The liquid supply manifolds 33 and 34 and the drainage manifolds 35 and 36 constitute a flow path for the electrolytic solution by stacking the cell frames 3. These flow paths communicate with the forward pipes 108 and 109 and the return pipes 110 and 111 of the circulation flow paths 100P and 100N (see FIGS. 1 and 2) via the supply / discharge plate 210 (see the lower figure of FIG. 3), respectively. It is possible to distribute the electrolyte in the cell 10.

In the cell 10 shown in this example, the electrolytic solution is introduced from the lower side of the positive electrode 14 and the negative electrode 15, and the electrolytic solution is discharged from the upper side of the electrodes 14, 15. The electrolyte flows from the lower edge of 15 toward the upper edge. 2 and 3, the arrows in the electrodes 14 and 15 indicate the overall flow direction of the electrolytic solution.

《Dipolar plate》
As shown in FIG. 4, a flow path 4 through which an electrolytic solution flows is formed on the opposing surface of the bipolar plate 31 that faces the electrodes 14 and 15. In the present embodiment, the flow path 4 is constituted by a plurality of grooves 5 (introducing grooves 51a to 51c and discharging grooves 52a to 52c). By forming the flow path 4 (groove 5) in the bipolar plate 31, the flow resistance of the electrolyte can be reduced. In FIG. 4, for easy understanding, a portion where the flow path 4 (groove 5) is not formed is hatched. One side (the front side of the drawing) of the bipolar plate 31 shown in FIG. 4 is a facing surface facing the positive electrode 14, and the other side (the back side of the drawing) is the negative electrode 15 (see FIG. 3, not shown in FIG. 4). It is the opposing surface which opposes. In the bipolar plate 31 shown in FIG. 4, the lower side to which the liquid supply slit 33s is connected is the positive electrode electrolyte introduction side, and the upper side to which the drainage slit 35s is connected is the positive electrode electrolyte discharge side. In FIG. 4, the thick line arrow on the left side of the drawing indicates the overall flow direction of the electrolytic solution.

In FIG. 4, only one surface side of the bipolar plate 31 facing the positive electrode 14 is shown, but the flow path of the electrolytic solution is also provided on the other surface side of the bipolar plate 31 facing the negative electrode 15, similarly to the one surface side. Is formed. Since the structure of the negative electrode electrolyte channel formed on the other surface side of the bipolar plate 31 is the same as that of the positive electrode electrolyte channel 4 shown in FIG.

(Flow path)
<Inlet / outlet>
The flow path 4 is designed so as to control the distribution of the electrolytic solution penetrating into the electrode 14 and make the distribution of the electrolytic solution in the electrode 14 uniform. The flow path 4 includes an inlet 4i and an outlet 4o for electrolyte. The introduction port 4i and the discharge port 4o are portions to which the liquid supply slit 33s and the drainage slit 35s are connected, respectively, and the electrolytic solution is introduced from the introduction port 4i through the liquid supply slit 33s, and the liquid discharge slit 35s from the discharge port 4o. The electrolyte is discharged. In the present embodiment, the introduction port 4i is positioned at the center of the lower side of the effective electrode region, and the discharge port 4o is positioned at the center of the upper side of the effective electrode region.

<Introduction route / Discharge route>
The flow path 4 includes an introduction path 41 for introducing the electrolyte solution from the introduction port 4i and a discharge path 42 for discharging the electrolyte solution to the discharge port 4o. The introduction path 41 and the discharge path 42 are independent without communicating with each other. The introduction path 41 includes introduction grooves 51a to 51c, and the discharge path 42 includes discharge grooves 52a to 52c. When the flow path 4 includes the introduction path 41 and the discharge path 42, the electrolytic solution flows so as to cross between the introduction path 41 and the discharge path 42, and at that time, the electrolytic solution permeates and diffuses into the electrode 14. Thus, the electrolytic solution can be uniformly distributed throughout the electrode 14. As a result, the distribution of the electrolytic solution in the electrode 14 can be made more effective and uniform, and the reactivity between the electrode 14 and the electrolytic solution can be further improved.

<Rectification unit>
Furthermore, the introduction path 41 and the discharge path 42 include rectifying units 510 and 520 connected to the introduction port 4i and the discharge port 4o, respectively. The introduction-side rectifier 510 is formed along the lower edge of the bipolar plate 31, and the discharge-side rectifier 520 is formed along the upper edge of the bipolar plate 31. The introduction path 41 is connected to the rectification unit 510, and the introduction grooves 51a to 51c communicate with the introduction port 4i via the rectification unit 510. The discharge path 42 is connected to the rectification unit 520, and the discharge grooves 52a to 52c communicate with the discharge port 4o via the rectification unit 520. The rectifying unit 510 diffuses the electrolyte introduced from the introduction port 4i along the lower edge of the bipolar plate 31, and introduces the electrolyte evenly into the introduction path 41 (introduction grooves 51a to 51c). The rectifying unit 520 collects the electrolyte discharged from the discharge path 42 (discharge grooves 52a to 52c) along the upper edge of the bipolar plate 31 to the discharge port 4o. The rectifiers 510 and 520 can efficiently introduce and discharge the electrolytic solution from the introduction port 4i and the discharge port 4o to the introduction path 41 and the discharge path 42, respectively.

The flow path 4 shown in FIG. 4 has a line symmetry (left-right symmetry) with a center line (indicated by a one-dot chain line in the figure) connecting the inlet 4i and the outlet 4o as the axis of symmetry. The 4i side (lower side) and the outlet 4o side (upper side) are asymmetric in the vertical direction. Since the flow path 4 is formed asymmetrically between the introduction side and the discharge side, it is possible to improve the flow of the electrolyte solution on the discharge side where the pressure of the electrolyte solution decreases.

(groove)
The introduction grooves 51a to 51c constituting the introduction path 41 are connected to the rectification unit 510 on the introduction side, extend from the introduction side (lower side) to the discharge side (upper side), and the distal end side on the discharge side becomes a closed end. Yes. The discharge grooves 52a to 52c constituting the discharge path 42 are connected to the discharge-side rectifying unit 520 and extend from the discharge side (upper side) toward the introduction side (lower side), and the leading end side of the introduction side becomes a closed end. Yes.

Each groove 5 (introduction grooves 51a to 51c and discharge grooves 52a to 52c) is open on the surface of the bipolar plate 31 facing the electrode 14, and as shown in FIG. It is formed so as to become smaller toward. In the case of the introduction grooves 51a to 51c, the opening width decreases toward the tip side, so that the pressure of the electrolyte increases as it approaches the tip side, and the electrolyte solution easily penetrates into the electrode 14 from the introduction grooves 51a to 51c. . The “opening width” of the groove 5 refers to a groove width orthogonal to the longitudinal direction of the groove 5.

The opening width (groove width) and depth (groove depth) of the groove 5 can be appropriately selected according to the size and thickness of the bipolar plate 31 and are not particularly limited. The groove width is, for example, from 0.2 mm to 10 mm, further from 0.5 mm to 5 mm, and the groove depth is, for example, from 0.5 mm to 5 mm, further from 1 mm to 3 mm.

As a method for forming the groove 5, for example, the surface of the bipolar plate 31 is cut with a cutting tool such as an end mill. Alternatively, it is also possible to provide a projection corresponding to the shape of the groove 5 in the mold for forming the bipolar plate 31 and form the groove 5 by mold forming such as injection molding.

<Percentage of electrode contact area>
Of the surface of the bipolar plate 31 facing the electrode 14 (that is, the effective electrode region), the contact area (the hatched portion area of the bipolar plate 31 shown in FIG. 4) in contact with the electrode 14 is A, and the planar opening area of the groove 5 When B is the area of the white portion of the bipolar plate 31 shown in FIG. 4, A / (A + B) is preferably more than 0.5 and less than 0.95. Since the ratio [A / (A + B)] of the contact area (A) of the electrode 14 to the area (A + B) of the opposite surface of the bipolar plate 31 is more than 0.5, the contact area between the electrode 14 and the bipolar plate 31 And the contact resistance between the electrode 14 and the bipolar plate 31 can be reduced. Thereby, the internal resistance (cell resistance) of the battery can be reduced. Further, from the viewpoint of securing the formation area of the groove 5 (the flow path area of the electrolytic solution) on the facing surface of the bipolar plate 31, the ratio [A / (A + B)] of the contact area of the electrode 14 is less than 0.95. Is preferable, and the flow resistance of the electrolytic solution can be effectively reduced. The ratio [A / (A + B)] of the contact area of the electrode 14 is, for example, 0.6 or more and 0.9 or less, and more preferably 0.7 or more and 0.8 or less. The “planar opening area” of the groove 5 refers to the opening area of the groove 5 on the facing surface when the bipolar plate 31 is viewed in plan.

<Cross-sectional shape>
FIG. 6 shows a cross-sectional shape of the groove 5 in the present embodiment. In the present embodiment, as shown in FIG. 6, the width of the groove 5 on the opening 56 side is equal to or larger than the width on the bottom 57 side in the cross section orthogonal to the flow direction of the electrolyte in the groove 5. The cross-sectional shape is tapered from the opening 56 side toward the bottom 57 side. Therefore, when the width of the groove 56 on the opening 56 side is equal to or larger than the width of the bottom 57 side, the groove 5 is formed compared to the case where the width on the bottom 57 side is wider than the width on the opening 56 side. easy. Further, when the cross-sectional shape of the groove 5 (particularly, the introduction grooves 51a to 51c) is tapered from the opening 56 side toward the bottom 57 side, the electrolytic solution can easily penetrate from the groove 5 into the electrode. Examples of the cross-sectional shape of the groove 5 include a rectangular shape, a triangular shape (V shape), a trapezoidal shape, a semicircular shape, and a semielliptical shape.

<Dendrite groove>
Among the grooves 5 shown in FIG. 4, the introduction grooves 51 a and 51 c and the discharge grooves 52 a and 52 c are dendritic grooves formed in a dendritic shape. 61. Since at least one of the grooves 5 is formed in a dendritic shape, it is easy to permeate and diffuse the electrolytic solution over a wide range in the electrode 14, and the distribution of the electrolytic solution in the electrode 14 can be made more uniform. . Therefore, the reactivity between the electrode 14 and the electrolytic solution can be further improved. Here, the “trunk groove portion” refers to a groove portion that is directly connected to the introduction port 4 i or the discharge port 4 o or indirectly through the rectifying units 510 and 520. The “branch groove portion” refers to a groove portion branched from the trunk groove portion 60 and having a smaller opening width than the trunk groove portion 60.

Further, like the introduction groove 51 c and the discharge groove 52 a, the branch groove part 61 may have a branch groove part 62 that further branches from the branch groove part 61. By having the branch groove portion 62 that further branches from the branch groove portion 61, it is easy to effectively permeate and diffuse the electrolytic solution into the electrode 14. Here, the branch groove portion 61 is called a primary branch groove, and the branch groove portion 62 is called a secondary branch groove. In the present embodiment, the opening width of the branch groove portion 62 (secondary branch groove) after branching is smaller than the opening width of the branch groove portion 61 (primary branch groove) before branching.

FIG. 5 shows a drawing of the introduction groove 51c, and the relationship between the trunk groove part 60 and the branch groove part 61, and the branch groove part 61 and the branch groove part 62 will be described by taking the introduction groove 51c as an example. As shown in FIG. 5, the opening width (W _a1 ) of the branch groove portion 61 is smaller than the opening width (W _a0 ) of the trunk groove portion 60 at a location where the branch groove portion 61 branches from the trunk groove portion 60. Further, at the location where the branch groove portion 62 branches from the branch groove portion 61, the opening width (W _a2 ) of the branch groove portion 62 is smaller than the opening width (W _b1 ) of the branch groove portion 61. As the opening width of the branched branch groove portions 61 and 62 decreases step by step, the contact area between the electrode 14 and the bipolar plate 31 increases, and the contact resistance between the electrode 14 and the bipolar plate 31 can be reduced. .

<Number of branches>
In the dendritic groove, N is preferably 3 or less, where N (N: natural number) is the number of branches in the branch groove portion. The “branching frequency” here means the number of times the branch groove part branches from the trunk groove part. For example, in the introduction groove 51c and the discharge groove 52a, the branching frequency N of the branching groove 61 that branches from the trunk groove 60 is 1, and the branching frequency N of the branching groove 62 that further branches from the branching groove 61 is 2. If there is another branch groove part that further branches from the branch groove part 62, the branching frequency N is three. In the present embodiment, by repeating branching from the trunk groove portion 60, the groove widths (opening widths) of the branched groove portions 61 and 62 are reduced and narrowed. By restricting the branching frequency N to 3 or less as in the present embodiment, excessive narrowing of the groove widths of the branch groove portions 61 and 62 due to branching can be avoided.

Furthermore, in this embodiment, as shown in FIG. 4, for example, in the introduction groove 51 c and the discharge groove 52 a, the branch groove part 61 intersects the trunk groove part 60 non-orthogonally. When the branch groove portion 61 intersects the trunk groove portion 60 non-orthogonally, the flow resistance of the electrolytic solution can be reduced as compared with the case where the branch groove portion 61 is orthogonal to the trunk groove portion 60. “Intersecting non-orthogonally” typically refers to a case where the inclination angle α (see FIG. 5) in the extending direction of the branch groove portion 61 with respect to the extending direction of the trunk groove portion 60 is an acute angle. The inclination angle α is, for example, not less than 10 ° and not more than 80 °.

<Counter comb region>
In the present embodiment, the introduction grooves 51a to 51c of the introduction path 41 and the discharge grooves 52a to 52c of the discharge path 42 have opposing comb tooth regions that are alternately arranged facing each other. Further, in the case of the flow path 4 shown in FIG. 4, for example, the branch groove portions 61 of the introduction groove 51a and the branch groove portions 62 of the discharge groove 52a are alternately arranged facing each other, and these also form an opposing comb tooth region. Has been. Since the flow path 4 has the opposing comb tooth region, the amount of the electrolyte flowing so as to cross between the introduction path 41 (introduction grooves 51a to 51c) and the discharge path 42 (discharge grooves 52a to 52c) increases. The electrolyte solution that permeates and diffuses into the electrode 14 increases. Thereby, the reaction efficiency of the electrode 14 and electrolyte solution can be improved.

<Convex>
When at least a part of the groove 5 has a wide portion with an opening width of 2 mm or more, a convex portion 59 protruding from the bottom portion may be formed in the wide portion. Since the convex portion 59 is provided in the wide portion of the groove 5, it is possible to suppress the electrode 14 from being buried in the groove 5. In the present embodiment, as shown in FIG. 4, the base end sides (sides connected to the rectifying units 510 and 520) of the introduction groove 51a and the discharge groove 52a are partially widened, and the portion Convex part 59 is provided in this. The shape of the convex portion 59 when viewed in plan is not particularly limited, and various shapes such as a polygonal shape such as a triangle and a quadrangle, a circular shape, and an elliptical shape can be employed. Further, the number of the convex portions 59 arranged in the wide portion may be one or plural.

<Curved part>
One of the features of this embodiment is that at least one of the grooves 5 has a curved portion. The “curved portion” refers to a portion that is curved in the longitudinal direction of the groove 5, and is typically a non-periodic curved shape. In the present embodiment, for example, the branch groove portions 61 and 62 of the introduction groove 51c and the branch groove portions 61 and 62 of the discharge groove 52a are formed in a curved shape, and each is constituted by a curved portion. The curvature radius of the curved portion is, for example, 0.1 mm or more, further 1 mm or more, and further 3 mm or more.

[Effect of the embodiment]
In the bipolar plate 31 according to the above-described embodiment, the flow path 4 of the electrolytic solution is formed on the opposing surface facing the electrode 14, so that the flow resistance of the electrolytic solution can be reduced and the electrolysis that penetrates into the electrode 14. The liquid distribution can be controlled. Since at least one groove 5 constituting the flow path 4 has a curved portion, the degree of freedom in layout is increased as compared with a linear groove, so that the distribution of the electrolyte in the electrode 14 is uniform. It is possible to arrange the grooves 5 efficiently. Thereby, the uniformity of the distribution of the electrolytic solution in the electrode 14 can be sufficiently increased, and the reactivity between the electrode 14 and the electrolytic solution can be improved. Accordingly, the bipolar plate 31 can improve the reactivity between the electrode 14 and the electrolytic solution while reducing the flow resistance of the electrolytic solution. Therefore, when the bipolar plate 31 of the embodiment is used for the RF battery 1, it is possible to reduce the reaction resistance at the electrode 14 while reducing the pressure loss due to the flow resistance of the electrolytic solution. (Cell resistance) can be reduced.

When the groove 5 has a curved portion, the direction of the electrolytic solution flowing in the groove 5 can be changed smoothly, and the flow resistance can be easily reduced even when the electrolytic solution flows smoothly compared to the case where the groove 5 is bent at a right angle or an acute angle.

Since the cell frame 3 according to the embodiment includes the bipolar plate 31, the reactivity between the electrode 14 and the electrolytic solution can be improved while reducing the flow resistance of the electrolytic solution. The reaction resistance at the electrode 14 can be reduced.

Since the cell stack 2 according to the embodiment includes the cell frame 3, it is possible to reduce the reaction resistance at the electrode 14 while reducing the pressure loss due to the flow resistance of the electrolytic solution.

Since the RF battery 1 according to the embodiment includes the cell stack 2, the reaction resistance at the electrode 14 can be reduced while the pressure loss due to the flow resistance of the electrolytic solution can be reduced. Resistance (cell resistance) can be reduced.

[Modification]
A modification of the bipolar plate 31 will be described with reference to FIG. The bipolar plate 31 shown in FIG. 7 is different from the bipolar plate 31 of the embodiment shown in FIG. Below, it demonstrates centering on difference with embodiment mentioned above.

The effective electrode area of the bipolar plate 31 shown in FIG. 7 is rectangular. In the modification, as shown in FIG. 7, the inlet 4i is located at the lower right corner of the effective electrode region, the outlet 4o is located at the upper left corner of the effective electrode region, and the inlet 4i and the outlet 4o Are provided at diagonal positions of the effective electrode region. Further, in the modification, the rectification unit 510 formed along the lower edge of the bipolar plate 31 and the right edge of the bipolar plate 31 are formed as the rectification unit on the introduction side connected to the introduction port 4i. A rectifying unit 511 is included. Further, as a discharge side rectification unit connected to the discharge port 4o, a rectification unit 520 formed along the upper edge of the bipolar plate 31 and a rectification unit 521 formed along the left edge of the bipolar plate 31 are provided. Have. The rectification units 510 and 511 on the introduction side and the rectification units 520 and 521 on the discharge side are formed so as not to communicate with each other.

7 includes an introduction path 41 and a discharge path 42. The introduction path 41 includes introduction grooves 51a to 51d connected to the introduction- side rectifying sections 510 and 511, and the discharge path 42 includes discharge grooves 52a to 52d connected to the discharge- side rectification sections 520 and 521. Among these grooves, the introduction grooves 51 c and 51 d and the discharge groove 52 c are dendritic grooves formed in a dendritic shape, and include a trunk groove part 60 and a branch groove part 61 branched from the trunk groove part 60. For example, in the introduction grooves 51 c and 51 d and the discharge groove 52 c, the branch groove part 61 intersects the trunk groove part 60 non-orthogonally. Further, for example, the branch groove portions 61 of the introduction grooves 51c and 51d and the branch groove portion 61 of the discharge groove 52c have curved portions.

The flow path 4 is line-symmetric with respect to a diagonal line (indicated by a one-dot chain line in the figure) connecting the inlet 4i and the outlet 4o. The angle formed by the rectifying units 510 and 520 and the diagonal line of the effective electrode region (the diagonal line connecting the inlet 4i and the outlet 4o) is 40 ° or more and 50 ° or less. The pressure loss in the rectifying units 510 and 520 can be reduced by setting the angle formed by each of the rectifying units 510 and 520 and the diagonal line of the effective electrode region within the above range.

7 has an intermediate groove 54 that is not connected to the introduction path 41 and the discharge path 42, as shown in FIG. The intermediate groove 54 is an independent closed groove that does not communicate with the introduction- side rectifying portions 510 and 511, the discharge- side rectifying portions 520 and 521, and the introduction grooves 51a to 51d and the discharge grooves 52a to 52d. The intermediate groove 54 is a dendritic groove extending along the diagonal line and formed in a dendritic shape from the intermediate portion in the longitudinal direction toward both ends. In detail, the trunk groove part 60 located in the intermediate part of the longitudinal direction of the intermediate groove 54, and the branch groove part 61 branched from each edge part of the introduction side (lower right side) and discharge | emission side (upper left side) of the trunk groove part 60, respectively. The branch groove portions 62 further branch from the respective branch groove portions 61. In the intermediate groove 54, the branch groove portion 61 intersects the trunk groove portion 60 non-orthogonally, and the branch groove portions 61 and 62 have curved portions.

In the flow path 4 shown in FIG. 7, in addition to the opposing comb tooth region formed by the introduction grooves 51c and 51d and the discharge grooves 52c and 52d, the opposed comb tooth region formed by the introduction grooves 51a to 51c or the discharge grooves 52a to 52c and the intermediate groove 54. Have Since the opposing comb-tooth region is formed by the introduction groove 51a to 51d, the discharge groove 52a to 52d, and the intermediate groove 54, the electrolyte solution can be easily diffused over a wide range and the electrolysis in the electrode can be performed. It is easy to make the liquid distribution more uniform.

Furthermore, in the modification, the introduction groove 51a and the trunk groove part 60 of the intermediate groove 54 each have a wide part, and the convex part 59 is arranged in each wide part.

[Test Example 1]
A bipolar plate having an electrolyte flow path corresponding to the embodiment was fabricated, and an RF battery was assembled using the bipolar plate, and the cell resistivity was examined.

In Test Example 1, sample No. 1 in which the flow path shown in FIGS. 1-No. Three grooved bipolar plates were prepared. The material of the bipolar plate is plastic carbon. Sample No. 1-No. The bipolar plate No. 3 has the same shape and size, and only the flow path is different, and the electrode contact area A on the surface facing the electrode and the planar opening area B of the grooves constituting the flow path are different. The area (A + B) of the opposing surface of each bipolar plate is the same at 891 mm ² (27 mm × 33 mm). Table 1 shows the electrode contact area A of the bipolar plate in each sample and the ratio [A / (A + B)] of the electrode contact area (A) to the area (A + B) of the facing surface. In addition, the numerical value of the electrode contact area ratio [A / (A + B)] shown in Table 1 is a value obtained by rounding down the third decimal place.

Sample No. 1-No. A single cell RF battery was assembled using 3 bipolar plates. The single cell was prepared by placing positive and negative electrodes on both sides of the diaphragm and sandwiching the cell frame with bipolar plates from both sides. Carbon felt was used for each positive and negative electrode.

(Measurement of cell resistivity)
A single cell RF battery using the bipolar plate of each sample was subjected to a charge / discharge test under the following test conditions. And the cell resistivity (ohm * cm < ² >) at the time of 3 cycles charging / discharging was calculated | required. Table 1 shows the cell resistivity of each sample. The cell resistivity was calculated by the calculation formula shown below.

<Test conditions>
<Electrolyte>
Vanadium sulfate aqueous solution (V concentration: 1.7 mol / L, sulfuric acid concentration: 3.4 mol / L)
<Electrolyte flow rate>
Inlet flow rate: 0.31 (mL / min)
Outlet flow rate: Free outflow
Charging / discharging method: constant current Current density: 70 (mA / cm ² )
Charging end voltage: 1.55 (V)
Discharge end voltage: 1.00 (V)
Temperature: 25 ° C
<Cell resistivity>
Formula: R = (V2-V1) / 2I
R: Cell resistivity (Ω · cm ² )
I: Current density (A / cm ² )
V1: Voltage (V) at the middle of the charging time
V2: Voltage (V) at the intermediate point of the discharge time

As shown in Table 1, sample no. 1-No. The cell resistivity of No. 3 1> No. 2> No. No. 3 in order, sample No. 2, No. 3 is sample No. Compared with 1, the cell resistivity can be greatly reduced. From this result, it is understood that the ratio [A / (A + B)] of the electrode contact area is preferably more than 0.5.

1 Redox flow battery (RF battery)
2 cell stack 10 cell 11 diaphragm 12 positive electrode cell 13 negative electrode cell 14 positive electrode 15 negative electrode 3 cell frame 31 bipolar plate 32 frame 32o recess 33, 34 liquid supply manifold 35, 36 drainage manifold 33s, 34s liquid supply slit 35s, 36s Drain slit 37 Seal member 38 Seal groove 4 Flow path 4i Inlet port 4o Discharge port 41 Inlet channel 42 Discharge channel 5 Groove 51a, 51b, 51c, 51d Inlet groove 52a, 52b, 52c, 52d Discharge groove 510, 511 Rectifier (Introduction side)
520, 521 Rectifier (discharge side)
54 Intermediate groove 56 Opening portion 57 Bottom portion 59 Protruding portion 60 Trunk groove portion 61 Branch groove portion (primary branch groove)
62 Branch (secondary branch)
100P Cathode circulation channel 100N Cathode circulation channel 106 Cathode electrolyte tank 107 Cathode electrolyte tank 108, 109 Outward piping 110, 111 Return piping 112, 113 Pump 200 Substack 210 Supply / discharge plate 220 End plate 230 Tightening mechanism C AC / DC converter P Power system

Claims (19)

1. An electrode of a redox flow battery is disposed, and is a bipolar plate provided with a facing surface facing the electrode, and at least one groove constituting a flow path through which an electrolyte flows in the facing surface,
   When the bipolar plate is viewed in plan, at least one of the grooves has a curved portion.
2. The bipolar plate according to claim 1, wherein a radius of curvature of the curved portion is 0.1 mm or more.
3. The bipolar plate according to claim 1 or 2, wherein the opening width of the groove decreases toward the tip side.
4. The A / (A + B) is more than 0.5 and less than 0.95, where A is a contact area in contact with the electrode and B is a planar opening area of the groove in the facing surface of the bipolar plate. The bipolar plate according to any one of claims 1 to 3.
5. The bipolar plate according to any one of claims 1 to 4, wherein the width of the groove on the opening side is equal to or larger than the width on the bottom side in a cross section perpendicular to the flow direction of the electrolyte in the groove.
6. The bipolar plate according to claim 5, wherein a cross-sectional shape of the groove is formed in a tapered shape from the opening side toward the bottom side.
7. The groove is formed in a dendritic shape, and includes a trunk groove part and at least one branch groove part branched from the trunk groove part,
   The bipolar plate according to any one of claims 1 to 6, wherein at least one of the branch groove portions intersects the trunk groove portion non-orthogonally.
8. The bipolar plate according to claim 7, wherein the curved portion is provided in at least one of the branch groove portions.
9. The bipolar plate according to claim 7 or 8, wherein at least one of the branch groove portions has a branch groove portion that further branches from the branch groove portion.
10. The bipolar plate according to claim 9, wherein N is 3 or less, where N (N: natural number) is the number of branches of the branch groove portion.
11. The bipolar plate according to claim 9 or 10, wherein an opening width of the branch groove part after branching is smaller than an opening width of the branch groove part before branching.
12. The flow path is
    An inlet and an outlet for the electrolyte;
    An introduction path for introducing the electrolyte solution from the introduction port, and a discharge path for discharging the electrolyte solution to the discharge port independently without communicating with the introduction path,
    The introduction path and the discharge path each include at least one groove;
    12. At least one of the introduction path and the discharge path includes a rectification unit that is connected to the introduction port or the discharge port and is formed along an edge of the bipolar plate. The bipolar plate according to item.
13. The effective electrode region where the bipolar plate and the electrode face each other is rectangular, and the introduction port and the discharge port are provided at diagonal positions of the effective electrode region,
    The bipolar plate according to claim 12, wherein an angle formed by the rectifying unit and a diagonal line of the effective electrode region is 40 ° or more and 50 ° or less.
14. In the bipolar plate, when the inlet side is the lower side and the outlet side is the upper side,
    The bipolar plate according to claim 12 or 13, wherein the flow path is vertically asymmetric.
15. The bipolar plate according to any one of claims 12 to 14, wherein the introduction path grooves and the discharge path grooves have opposed comb-tooth regions in which the grooves are alternately arranged facing each other.
16. The bipolar electrode according to any one of claims 1 to 15, wherein at least a part of the groove has a wide portion having an opening width of 2 mm or more, and a convex portion protruding from a bottom portion is formed in the wide portion. Board.
17. A cell frame comprising the bipolar plate according to any one of claims 1 to 16, and a frame provided on an outer periphery of the bipolar plate.
18. A cell stack comprising the cell frame according to claim 17.
19. A redox flow battery comprising the cell stack according to claim 18.

Images