JP2017041418A - Bipolar plate, cell frame, cell stack and redox flow cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bipolar plate capable of making flow rate distribution of an electrolyte uniform while reducing a pressure loss of the electrolyte within a cell, a cell frame, a cell stack and a redox flow cell.SOLUTION: The present invention relates to a bipolar plate in which a positive electrode is disposed on one side and a negative electrode is disposed on the other side. On at least one surface at a positive electrode side and a negative electrode side, a plurality of grooves are provided which are formed in a circulation direction of an electrolyte. The plurality of grooves include two or more grooves with different lengths. In the bipolar plate, the grooves are formed in such a manner that a difference of a pressure loss between a region with a longer length of the groove and a region with a shorter length of the groove is reduced.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a bipolar plate, a cell frame and a cell stack, which are components of a redox flow battery, and a redox flow battery. In particular, the present invention relates to a bipolar plate that can make the flow rate distribution of the electrolyte uniform while reducing the pressure loss of the electrolyte in the cell.

  As one of large-capacity storage batteries, redox flow batteries (hereinafter sometimes referred to as “RF batteries”) are known (see Patent Documents 1 to 3). Applications of redox flow batteries include load leveling applications, applications such as instantaneous voltage drop compensation and emergency power supplies, and smoothing of natural energy output such as solar power generation and wind power generation that are being introduced in large quantities. Can be mentioned.

  An RF battery is a battery that performs charge and discharge using an electrolytic solution containing a metal ion (active material) whose valence is changed by oxidation and reduction in a positive electrode electrolyte and a negative electrode electrolyte. FIG. 6 shows an operation principle diagram of a vanadium RF battery 300 using a vanadium electrolyte containing V ions as an active material of the positive electrode electrolyte and the negative electrode electrolyte. The solid line arrow in the battery cell 100 in FIG. 6 indicates a charging reaction, and the broken line arrow indicates a discharging reaction.

  The RF battery 300 includes a cell 100 separated into a positive electrode cell 102 and a negative electrode cell 103 by an ion exchange membrane 101 that transmits hydrogen ions. A positive electrode 104 is built in the positive electrode cell 102, and a positive electrode electrolyte solution tank 106 for storing the positive electrode electrolyte is connected via conduits 108 and 110. Similarly, a negative electrode 105 is built in the negative electrode cell 103, and a negative electrode electrolyte solution tank 107 for storing a negative electrode electrolyte is connected via conduits 109 and 111. Then, the electrolytes stored in the tanks 106 and 107 are circulated and circulated to the cell 100 (the positive electrode cell 102 and the negative electrode cell 103) by the pumps 112 and 113 to perform charging and discharging.

  The RF battery 300 normally uses a configuration including a cell stack in which a plurality of cells 100 are stacked. FIG. 7 is a schematic configuration diagram of a cell stack. A cell stack 10S illustrated in FIG. 7 is formed by laminating a plurality of cell frames 20, a positive electrode 104, an ion exchange membrane 101, and a negative electrode 105, each having a frame 22 provided on the outer periphery of a bipolar plate 21, and the laminated body. Is sandwiched between two end plates 250 and 250 and tightened.

  In the cell stack 10 </ b> S, the positive electrode 104 is disposed on one surface side of the bipolar plate 21 and the negative electrode 105 is disposed on the other surface side, and one cell is formed between the adjacent cell frames 20. The electrolyte solution in the cell stack 10S flows through the manifold 200 provided through the frame body 22 and the slit 210 provided between the manifold 200 and the bipolar plate 21 formed on the surface of the frame body 22. Is called. In the cell stack 10 </ b> S, the positive electrode electrolyte is supplied from the liquid supply manifold 201 to the positive electrode 104 side of the bipolar plate 21 through the slit 211 formed on one surface side (paper surface side) of the frame body 22. The liquid is discharged to the drainage manifold 203 through the slit 213 formed in the upper part. Similarly, the negative electrode electrolyte is supplied from the liquid supply manifold 202 to the negative electrode 105 side of the bipolar plate 21 through the slit 212 formed on the other surface side (the back side of the paper) of the frame body 22, and the upper portion of the frame body 22. Then, the liquid is discharged to the drainage manifold 204 through the slit 214 formed in the above. In addition, a plastic protective plate 30 that protects the ion exchange membrane 101 is disposed at a portion of the frame 22 where the slits 211 to 214 are formed. Each protection plate 30 has a through hole formed at a position corresponding to each of the manifolds 201 to 204 and covers each of the slits 211 to 214. Since the slits 211 to 214 are covered with the protective plate 30, the slits 211 to 214 do not come into contact with the ion exchange membrane 101, and the ion exchange membrane can be prevented from being damaged by the unevenness of the slits.

  The cell frame 20 includes a bipolar plate 21 and a frame body 22 provided on the outer periphery of the bipolar plate 21. The frame 22 is formed so as to sandwich the outer peripheral portion of the bipolar plate 21 from the front and back sides, and is integrated with the bipolar plate 21 by, for example, injection molding. The region of the bipolar plate 21 in the cell frame 20 is a concave portion, and the shape of the concave portion corresponds to the shape of the bipolar plate 21. An electrode having substantially the same shape (positive electrode 104 or negative electrode 105) is accommodated in the recess, and a space surrounded by the bipolar plate 21, the ion exchange membrane 101, and the frame 22 constitutes a cell (positive electrode or negative electrode cell). .

One end of the slit 210 formed in the frame body 22 is connected to the manifold 200,
The other end is connected to the inner edge portion of the frame body 22, and the manifold 200 and the concave portion communicate with each other through a slit 210. In the case of the cell frame 20 illustrated in FIG. 7, slits 211 and 212 extending from the liquid supply manifolds 201 and 202 are connected to the lower inner edge of the frame 22 (concave portion), and slits extending from the drainage manifolds 203 and 204. 213 and 214 are connected to the inner edge on the upper side of the frame 22 (concave portion). That is, the electrolytic solution is supplied into the cell from the lower side of the bipolar plate 21 (electrode), and the electrolytic solution is discharged from the upper side of the bipolar plate 21 (electrode). Usually, a rectification part (not shown) is formed at the inner edge of the frame 22, and the other end of the slit 210 is connected to the rectification part. The rectifying unit has a function of diffusing the supplied electrolytic solution along the edge portion of the electrode accommodated in the recess, and collecting the electrolytic solution discharged from the electrode into the slit 210. By this rectifying portion, the electrolyte flows in the cell from one edge portion (lower edge portion in FIG. 7) of the bipolar plate 21 (electrode) toward the other edge portion (upper edge portion in FIG. 7). It is like that.

JP 2013-80613 A JP 2002-246061 A JP 2007-305339 A

  Further improvement of the battery performance of the redox flow battery is desired, and as one of them, it is required to reduce the internal resistance of the battery. One of the factors that increase the internal resistance is pressure loss due to the flow resistance of the electrolyte. However, in the past, it has not been said that sufficient studies have been made to make the flow rate distribution of the electrolyte uniform while reducing the pressure loss of the electrolyte in the cell.

  The present invention has been made in view of the above circumstances, and one of the objects of the present invention is to provide a bipolar plate capable of reducing the pressure loss of the electrolytic solution in the cell while making the flow rate distribution of the electrolytic solution uniform. There is to do. Another object of the present invention is to provide a cell frame including the bipolar plate, a cell stack including the cell frame, and a redox flow battery including the cell stack.

  In the bipolar plate according to one embodiment of the present invention, the positive electrode is disposed on one side and the negative electrode is disposed on the other side. The bipolar plate includes a plurality of grooves formed along the flow direction of the electrolyte on at least one surface of the positive electrode side and the negative electrode side, and the plurality of grooves include two or more grooves having different lengths. Have And the said groove | channel is formed so that the difference of the pressure loss of the area | region where the length of a groove | channel is long and the area | region where a groove | channel length is short may become small.

  The cell frame which concerns on 1 aspect of this invention is equipped with the bipolar plate which concerns on the said 1 aspect of this invention, and the frame provided in the outer periphery of the said bipolar plate.

  A cell stack according to one embodiment of the present invention is formed by stacking a plurality of cell frames according to one embodiment of the present invention, a positive electrode, an ion exchange membrane, and a negative electrode.

  A redox flow battery according to one embodiment of the present invention includes the cell stack according to one embodiment of the present invention.

  The bipolar plate can reduce the pressure loss of the electrolytic solution in the cell and make the flow rate distribution of the electrolytic solution uniform. The cell frame, the cell stack, and the redox flow battery can reduce the pressure loss of the electrolytic solution in the cell and can make the flow rate distribution of the electrolytic solution uniform.

1 is a schematic plan view showing a bipolar plate according to Embodiment 1. FIG. It is a schematic sectional drawing in alignment with the II-II line of FIG. 6 is a schematic cross-sectional view showing a modification of the bipolar plate according to Embodiment 1. FIG. 6 is a schematic plan view showing a bipolar plate according to Embodiment 2. FIG. It is a schematic sectional drawing in alignment with the VV line of FIG. It is an operation | movement principle figure of a redox flow battery. It is a schematic block diagram of a cell stack. It is a schematic plan view which shows an example of the conventional cell frame. It is a schematic plan view which shows another example of the conventional cell frame.

[Description of Embodiment of the Present Invention]
In the redox flow battery, the inventors have formed a plurality of grooves along the flow direction of the electrolytic solution on the surface on which the electrode of the bipolar plate is arranged, thereby constituting a flow path, thereby allowing electrolysis in the cell. We studied to reduce the pressure loss of the liquid.

  Many conventional bipolar plates are rectangular. In the case of a conventional cell frame having a rectangular bipolar plate, the electrolyte flows through the cell from the lower edge of the bipolar plate 21 toward the upper edge as shown by the arrows in FIG. In the rectangular bipolar plate 21 shown in FIG. 8, the distance from the lower edge to the upper edge is constant in the width direction, and the flowing length of the electrolyte in the cell extends in the width direction of the bipolar plate 21. It is substantially the same. Therefore, when a plurality of grooves having the same cross-sectional shape and the same size (same groove width and groove depth) are formed at equal intervals on the surface of the rectangular bipolar plate 21, The length will be the same. Here, the pressure loss (ΔP) of the electrolytic solution in each groove is expressed by the following formula 1, and is proportional to the length (L) of the groove. The groove pressure loss is also equal, and the flow rate of each groove is also equal. Therefore, in the case of a rectangular bipolar plate, the flow rate of the electrolytic solution flowing in each groove is uniform, so that the flow rate distribution of the electrolytic solution in the cell can be easily made uniform.

(Expression 1) ΔP = 128 × μ × (Q × L) / (π × D _e ⁴ )
μ: electrolyte viscosity Q: electrolyte flow rate L: groove length _De : equivalent groove diameter (D _e = 4 S / l, S: groove cross-sectional area, l = groove circumference)
Here, the length L of the groove is a length measured along the groove from one end to the other end of the groove when the bipolar plate is viewed in plan. The circumferential length l of the groove means the circumferential length in the cross section of the groove perpendicular to the flowing direction of the electrolyte, and in the cross section, the circumferential length of the wall surface constituting the groove and the width of the opening of the groove are totaled. Length. For example, when the cross-sectional shape of the groove is rectangular, the groove width w is 1 mm, and the groove depth h is 1 mm, the circumferential length l of the groove is 4 mm. In this case, the sectional area S of the groove is 1 mm ^2, the equivalent diameter _{D e} of the groove becomes 1 mm.

  On the other hand, in the case of a cell frame having a trapezoidal bipolar plate as shown in Patent Document 3, the electrolyte flows in the cell as shown by the arrows in FIG. In the trapezoidal bipolar plate 21 shown in FIG. 9, the distance from the lower edge to the upper edge is different in the width direction, and the distance between the upper and lower edges at both ends in the width direction is longer than that in the center. . That is, in the region at both end portions in the width direction, the flowing length of the electrolytic solution is longer than that in the central portion. Therefore, when a plurality of grooves having the same cross-sectional shape and the same size (same groove width and groove depth) are formed on the surface of the trapezoidal bipolar plate 21 along the flow direction of the electrolytic solution at equal intervals, the length Thus, different grooves are formed. Specifically, in the regions at both ends, the length of the groove is longer than that in the central portion. As described above, the pressure loss (ΔP) of the electrolyte solution in each groove is proportional to the length of the groove, so that the pressure loss of the groove on both ends is higher than that on the center, and the groove on both ends The flow rate is less than in the center. Therefore, when grooves with different lengths are formed, such as a trapezoidal bipolar plate, the flow rate of the electrolyte flowing in each groove is non-uniform, so the flow rate distribution of the electrolyte in the cell is also non-uniform. Become. If the electrolyte flow distribution is uneven in the cell, there is a risk of cell member damage (electrodes, bipolar plates, etc.) and battery performance degradation due to insufficient supply of electrolyte in the low electrolyte flow area. There is.

  The present inventors paid attention to the above points, and proceeded further studies on uniformizing the flow rate distribution of the electrolyte in the cell even when a plurality of grooves having different lengths are formed in the bipolar plate. The invention has been completed. Hereinafter, embodiments of the present invention will be listed and described.

  (1) In the bipolar plate according to one aspect of the present invention, the positive electrode is disposed on one side and the negative electrode is disposed on the other side. The bipolar plate includes a plurality of grooves formed along the flow direction of the electrolyte on at least one surface of the positive electrode side and the negative electrode side, and the plurality of grooves include two or more grooves having different lengths. Have And the said groove | channel is formed so that the difference of the pressure loss of the area | region where the length of a groove | channel is long and the area | region where a groove | channel length is short may become small.

  According to the bipolar plate, by providing the plurality of grooves along the flow direction of the electrolytic solution, the flow resistance of the electrolytic solution in the cell can be reduced, and the pressure loss of the electrolytic solution in the cell can be reduced. Therefore, the internal resistance of the battery can be reduced. In addition, the groove is formed so that the difference in pressure loss is small between the region where the groove length is long (ie, the region where the flow path is long) and the region where the groove length is short (ie the region where the flow path is short). Therefore, the difference in the electrolyte flow rate between the regions can be reduced. That is, even when the grooves have different lengths, the flow rate distribution of the electrolyte solution in the cell can be made uniform by increasing the flow rate to the long region of the groove (flow path). Therefore, it is difficult for the electrolyte to be insufficiently supplied in the cell, and damage to the cell member and deterioration of the battery performance can be suppressed.

  The smaller the difference in pressure loss between the regions, the better. Specifically, when the bipolar plate is equally divided into at least two regions in the width direction according to the length of the groove (channel), the pressure between the longest and shortest regions of the groove The difference in loss is preferably 20% or less, more preferably 10% or less, with respect to the region having the shortest groove length. The pressure loss in each region can be obtained by calculating the pressure loss of the grooves provided in each region and summing them. Most preferably, the difference in pressure loss between the regions is substantially zero (that is, the pressure loss in the long and short regions of the groove is the same).

(2) As one form of the bipolar plate, the plurality of grooves include a long groove and a short groove that satisfy the following requirements.
The equivalent diameter of the long groove is larger than the equivalent diameter of the short groove.

The groove pressure loss decreases as the groove cross-sectional area increases. Strictly speaking, the pressure loss of the groove is influenced not only by the cross-sectional area of the groove but also by the circumferential length of the groove, and becomes lower as the circumferential length of the groove is smaller. Therefore, the pressure loss of the groove has an equivalent diameter (D _e ) represented by the ratio (S / l) of the cross-sectional area (S) of the groove to the circumferential length (l), as shown in the above formula (1). The larger it is, the lower it is.

  Increasing the groove equivalent diameter by increasing the groove cross-sectional area, such as increasing the groove width or depth, or by reducing the groove circumference, such as changing the groove shape even if the groove cross-sectional area is the same. Thus, the pressure loss of the groove can be reduced. Therefore, by including a long groove and a short groove that satisfy the requirement that the equivalent diameter of the long length groove is larger than the equivalent diameter of the short length groove, the difference in pressure loss between the different length grooves can be reduced. The difference in the flow rate of the electrolyte flowing through each groove can be reduced. That is, by increasing the flow rate to the long groove, the flow rate of each groove can be made uniform, and the flow rate distribution of the electrolyte in the cell can be made uniform. More preferably, the groove is formed so that the equivalent diameter of the groove is increased according to the length of the groove.

  In the said form, when the some groove | channel is formed at equal intervals, it forms so that the pressure loss difference between each groove | channel may become small. Specifically, the difference in pressure loss between the longest groove and the shortest groove is preferably 20% or less, more preferably 10% or less, with respect to the pressure loss of the shortest groove. In particular, it is most preferable that the pressure loss difference between the grooves is substantially 0 (that is, the pressure loss of each groove is the same).

(3) As one form of the bipolar plate, the plurality of grooves include a long groove and a short groove that satisfy the following requirements.
The distance between the long groove and the adjacent groove is smaller than the distance between the short groove and the adjacent groove.

  By reducing the interval between adjacent grooves, a region in which the grooves are densely formed is formed, and the number of grooves in the region increases, so that pressure loss in the region can be reduced. Therefore, by including a long groove and a short groove that satisfy the requirement that the distance between the long groove and the adjacent groove is smaller than the distance between the short groove and the adjacent groove, the groove (flow The difference in pressure loss between regions having different path lengths can be reduced, and the difference in the flow rate of the electrolyte flowing in each region can be reduced. In other words, the flow rate distribution to the long region of the groove (flow path) can be increased, and the flow rate distribution of the electrolytic solution in the cell can be made uniform. More preferably, according to the length of a groove | channel, forming a groove | channel so that the space | interval of an adjacent groove | channel may become small is mentioned.

  (4) As one form of the bipolar plate, the difference in pressure loss between the region with the longest groove and the region with the shortest groove is less than the pressure loss in the region with the shortest groove. 20% or less.

  According to the above aspect, when the electrolyte flows, the difference between the pressure loss of the portion having the longest groove and the pressure loss of the portion having the shortest groove is determined with respect to the pressure loss of the portion having the shortest groove. It can be 20% or less. Thereby, the flow distribution of the electrolyte solution in the cell can be made sufficiently uniform, and the effect of suppressing the damage of the cell member due to the insufficient supply of the electrolyte solution and the deterioration of the battery performance is high. A more preferable difference in pressure loss is 10% or less.

  (5) The cell frame which concerns on 1 aspect of this invention is equipped with the bipolar plate as described in any one of said (1)-(4), and the frame provided in the outer periphery of the said bipolar plate.

  According to the cell frame, since the bipolar plate according to one aspect of the present invention is provided, the flow rate distribution of the electrolytic solution can be made uniform while reducing the pressure loss of the electrolytic solution in the cell. Since the flow distribution of the electrolytic solution in the cell can be made uniform, damage to the cell member due to insufficient supply of the electrolytic solution and a decrease in battery performance can be suppressed.

  (6) A cell stack according to one embodiment of the present invention is formed by laminating a plurality of cell frames, positive electrode electrodes, ion exchange membranes, and negative electrode electrodes described in (5) above.

  According to the cell stack, since the cell frame according to one aspect of the present invention is provided, the flow rate distribution of the electrolytic solution can be made uniform while reducing the pressure loss of the electrolytic solution in the cell. Since the flow distribution of the electrolytic solution in the cell can be made uniform, damage to the cell member due to insufficient supply of the electrolytic solution and a decrease in battery performance can be suppressed.

  (7) The redox flow battery which concerns on 1 aspect of this invention is equipped with the cell stack as described in said (6).

  According to the redox flow battery, since the cell stack according to one aspect of the present invention is provided, the flow rate distribution of the electrolytic solution can be made uniform while reducing the pressure loss of the electrolytic solution in the cell. Since the flow distribution of the electrolytic solution in the cell can be made uniform, damage to the cell member due to insufficient supply of the electrolytic solution and a decrease in battery performance can be suppressed.

[Details of the embodiment of the present invention]
Specific examples of the bipolar plate according to the embodiment of the present invention will be described below with reference to the drawings. The cell frame, the cell stack, and the redox flow battery according to the embodiment of the present invention are characterized by using the bipolar plate according to the embodiment of the present invention. For other configurations, refer to FIG. 6 and FIG. A configuration similar to the conventional one described above can be employed. Therefore, in the following, detailed descriptions of the cell frame, the cell stack, and the redox flow battery are omitted. 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.

[Embodiment 1]
A bipolar plate 21A according to the first embodiment will be described with reference to FIGS. As shown in FIG. 1, the bipolar plate 21 </ b> A has a substantially hexagonal planar shape, and one edge portion (a lower edge portion in FIG. 1) composed of two sides and a corner sandwiched between the two sides. ) Is an electrolyte solution supply side, and the other edge portion (the upper edge portion in FIG. 1) facing the electrolyte solution discharge side is an electrolyte solution discharge side. In the bipolar plate 21A, as indicated by the arrows in the figure, the electrolyte flows from the lower edge toward the upper edge. The bipolar plate 21A includes a plurality of grooves 40 formed on the surface on which the electrode 50 (see FIG. 2) is disposed along the flowing direction of the electrolytic solution (vertical direction in FIG. 1). Has at least two or more grooves 40 having different lengths. In FIG. 1, for easy understanding, a portion where the groove 40 is not formed is hatched (the same applies to FIG. 4 described later). The bipolar plate 21A can be made of plastic carbon.

(Bipolar plate)
The bipolar plate 21A has a hexagonal shape, and the distance from the lower edge to the upper edge is different in the width direction. Specifically, the distance between the upper and lower edges is longer at the center in the width direction and shorter at both ends, and in the region of the center, the length (flow path length) in which the electrolyte flows compared to both ends Becomes longer. Therefore, when a plurality of grooves 40 are formed along the flow direction of the electrolytic solution, the grooves 40 having different lengths are formed in the width direction of the bipolar plate 21A (a direction perpendicular to the flow direction of the electrolytic solution, left and right in FIG. 1). The grooves 40 are formed in parallel and the length of the groove 40 is longer than that of both end portions in the central region.

  The shape of the bipolar plate 21A is such that the plurality of grooves 40 having different lengths are formed when the plurality of grooves 40 are formed along the flow direction of the electrolyte, such as a shape in which the distance between the upper and lower edges differs in the width direction. It is mentioned that it is a shape. Therefore, the shape of the bipolar plate 21A may be a hexagonal shape, a triangular shape, a trapezoidal shape, a rhombus shape, an octagonal shape, or the like.

(groove)
The bipolar plate 21A includes a plurality of grooves 40 having different lengths formed along the flowing direction of the electrolytic solution. In the bipolar plate 21A of the first embodiment, a plurality of grooves 40 are formed at equal intervals along the flow direction of the electrolytic solution, and the cross-sectional shape of each groove 40 is substantially rectangular (see FIG. 2). Further, in this example, each groove 40 is formed such that one end communicates with the lower edge or upper edge of the bipolar plate 21A, and the other end leaves a certain length to the opposite edge. Grooves 40 that communicate with the lower edge of 21A and grooves 40 that communicate with the upper edge of bipolar plate 21A are alternately formed. The groove 40 is formed so that the difference in pressure loss between the central region where the length of the groove 40 is long and the regions at both ends where the length of the groove 40 is short becomes small. Specifically, the groove 40 is formed so that the difference in pressure loss between the central region and both end regions is 20% or less and further 10% or less with respect to the pressure loss in both end regions. ing.

  The width and depth of the groove 40 and the interval between adjacent grooves can be appropriately selected according to the size and thickness of the bipolar plate 21A, and are not particularly limited. For example, the width of the groove 40 is 0.1 mm or more and 10 mm or less, further 5 mm or less, the depth of the groove 40 is 0.1 mm or more and 10 mm or less, further 5 mm or less, and the interval between adjacent grooves is 0.2 mm or more and 10 mm or less. Is mentioned. The cross-sectional shape of the groove 40 is not particularly limited, and may be a triangular shape, a trapezoidal shape, a semicircular shape, a semielliptical shape, or the like in addition to a rectangular shape.

The plurality of grooves 40 constituting the flow path have a long length so that the difference in pressure loss between the central area where the length of the groove 40 is long and the areas at both ends where the length of the groove 40 is short becomes small. The equivalent diameter of the groove 40 is formed to be larger than the equivalent diameter of the groove 40 having a short length. Specifically, the equivalent diameter is formed so as to increase according to the length of the groove 40. In this example, as shown in FIG. 2, the longer the central groove 40 is, the larger the equivalent diameter of the groove 40 is by increasing the depth of the groove 40 and increasing the cross-sectional area. Thereby, the pressure loss of the long groove | channel 40 can be reduced. Specifically, the equivalent diameter of each groove 40 is set so that the difference in pressure loss between the longest groove and the shortest groove is 20% or less and further 10% or less with respect to the pressure loss of the shortest groove. ing. In particular, it is preferable that the equivalent diameter of each groove 40 is set so that the pressure loss of each groove 40 is substantially equal and the pressure loss difference between the grooves 40 is substantially zero. When equalizing the pressure loss of each groove 40, the equivalent diameter of n times the length of the groove for the shortest groove, from the equation (1), is set to ⁴ √n times the equivalent diameter of the shortest groove That's fine.

{Function and effect}
According to the bipolar plate 21A of the first embodiment, by providing the plurality of grooves 40 on the surface on which the electrode 50 is disposed, the flow resistance of the electrolytic solution in the cell is reduced, and the pressure loss of the electrolytic solution in the cell is reduced. Can be reduced. In addition, since the equivalent diameter of the long groove 40 is formed to be larger than the equivalent diameter of the short length groove 40, the difference in pressure loss between the grooves 40 can be reduced. The difference in the flow rate of the electrolytic solution flowing through can be reduced. Therefore, the difference in pressure loss between the central region where the length of the groove 40 is long and the regions at both ends where the length of the groove 40 is short can be reduced, and the difference in flow rate between the regions can be reduced. Therefore, the flow distribution of the electrolyte solution in the cell can be made uniform, and damage to cell members (electrodes, bipolar plates, etc.) due to insufficient supply of the electrolyte solution and battery performance degradation can be suppressed.

<Modification>
In the first embodiment described with reference to FIGS. 1 and 2, the case where the equivalent diameter is increased by increasing the depth of the groove 40 according to the length of the groove 40 is illustrated in FIG. 3. As described above, the equivalent diameter can be increased by increasing the cross-sectional area of the groove 40 by increasing the width of the groove 40. When the width is increased according to the length of the groove 40 (see FIG. 3), the interval between the adjacent grooves 40 is narrower than when the depth is increased (see FIG. 2). The width of the ridge between and becomes narrower. Therefore, when the width of the groove 40 is changed as a means for increasing the equivalent diameter of the groove 40, the contact area between the bipolar plate 21A and the electrode 50 is reduced as compared with the case where the depth is changed. Therefore, it is preferable to change the depth of the groove 40 from the viewpoint of securing the contact area between the bipolar plate 21A and the electrode 50 and reducing the contact resistance.

  Moreover, although Embodiment 1 demonstrated the case where the cross-sectional shape of all the grooves 40 was the same substantially rectangular shape, it is also possible to make the cross-sectional shape of a part of groove | channel 40 different. Since the equivalent diameter of the groove 40 can be increased by reducing the circumferential length of the groove 40, it is conceivable to reduce the circumferential length of the groove 40 according to the length of the groove 40. For example, in the bipolar plate 21A of the first embodiment, the equivalent diameter is increased by reducing the circumferential length of the groove 40, such as by making the cross-sectional shape of the groove 40 a semicircular shape in the central region where the length of the groove 40 is long. To do.

[Embodiment 2]
In the bipolar plate 21A of the first embodiment described above, the configuration in which the equivalent diameter of the long groove 40 is larger than the equivalent diameter of the short length groove 40 has been described. In the second embodiment, an embodiment in which the distance between the long groove 40 and the adjacent groove 40 is smaller than the distance between the short groove 40 and the adjacent groove 40 will be described. Hereinafter, with reference to FIGS. 4 and 5, the bipolar plate 21 </ b> B according to the second embodiment will be described focusing on differences from the bipolar plate 21 </ b> A of the first embodiment.

  In the bipolar plate 21B of Embodiment 2, the cross-sectional shapes of all the grooves 40 are the same rectangular shape, and the cross-sectional area such as width and depth and the equivalent diameter are the same. Further, the long groove 40 and the groove 40 adjacent thereto are reduced so that the difference in pressure loss between the central region where the length of the groove 40 is long and the regions at both ends where the length of the groove 40 is short is small. Is formed to be smaller than the distance between the groove 40 having a short length and the groove 40 adjacent thereto. Specifically, the interval between adjacent grooves 40 is reduced according to the length of the groove 40. That is, the longer the groove 40 on the central side, the narrower the distance between adjacent grooves 40, and the width of the ridge between the groove 40 and the groove 40 is narrower in the central region than in the regions on both ends. It has become. Therefore, the central region is a region where the grooves 40 are densely formed, and the pressure loss in the central region can be reduced. Accordingly, since the gap between the long groove 40 and the adjacent groove 40 is smaller than the distance between the short length groove 40 and the adjacent groove 40, the length of the groove 40 is increased. Thus, the difference in pressure loss between the regions having different sizes can be reduced, and the difference in the flow rate of the electrolyte flowing in each region can be reduced. Therefore, the flow distribution of the electrolytic solution in the cell can be made uniform.

  Further, according to the length of the groove 40, the equivalent diameter of the groove 40 may be increased, and the interval between the adjacent 40 may be decreased, whereby the difference in pressure loss between the regions where the lengths of the grooves 40 are different. Can be reduced.

  The bipolar plate of the present invention can be suitably used for a redox flow battery.

DESCRIPTION OF SYMBOLS 100 cell 101 ion-exchange membrane 102 positive electrode cell 104 positive electrode 103 negative electrode 105 negative electrode 106 positive electrode electrolyte tank 108,110 conduit 112 pump 107 negative electrode electrolyte tank 109,111 conduit 113 pump 20 cell frame 21, 21A, 21B Bipolar plate 22 Frame 200, 201-204 Manifold 210, 211-214 Slit 30 Protection plate 40 Groove 50 Electrode 10S Cell stack 250 End plate 300 Redox flow battery (RF battery)

Claims (7)

A bipolar plate in which a positive electrode is arranged on one side and a negative electrode is arranged on the other side,
Provided with a plurality of grooves formed along the flow direction of the electrolyte on at least one surface of the positive electrode side and the negative electrode side,
The plurality of grooves have two or more grooves having different lengths,
A bipolar plate in which the groove is formed so that a difference in pressure loss between a region having a long groove length and a region having a short groove length is reduced. The bipolar plate according to claim 1, wherein the plurality of grooves include a long groove and a short groove that satisfy the following requirements.
The equivalent diameter of the long groove is larger than the equivalent diameter of the short groove. The bipolar plate according to claim 1, wherein the plurality of grooves include a long groove and a short groove that satisfy the following requirements.
The distance between the long groove and the adjacent groove is smaller than the distance between the short groove and the adjacent groove.   The difference in pressure loss between the region with the longest groove and the region with the shortest groove is 20% or less with respect to the pressure loss in the region with the shortest groove. 4. The bipolar plate according to any one of items 3.   A cell frame provided with the bipolar plate as described in any one of Claims 1-4, and the frame provided in the outer periphery of the said bipolar plate.   A cell stack formed by laminating a plurality of cell frames according to claim 5, a positive electrode, an ion exchange membrane, and a negative electrode.   A redox flow battery comprising the cell stack according to claim 6.

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