Cell frame structure, cell stack, and redox flow battery system

Abstract

This cell frame structure comprises a bipolar plate, a frame body provided on an outer periphery of the bipolar plate, and a first member superimposed on the frame body, wherein the frame body and the first member are fixed by a joining portion.

Description

Cell frame structure, cell stack, and redox flow battery system

[0001] The present disclosure relates to a cell frame structure, a cell stack, and a redox flow battery system. This application claims priority to Japanese Patent Application No. 2022-155357, filed on September 28, 2022. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] The redox flow battery of Patent Document 1 includes a cell stack having a laminate in which a cell frame, an electrode, a protective plate, a diaphragm, another protective plate, and an electrode are stacked in this order. The cell frame has a bipolar plate and a frame body provided on the outer periphery of the bipolar plate. The frame body has a manifold and a flow groove. The manifold and the flow groove are flow paths for the electrolyte. The manifold penetrates the frame body. The flow groove connects the manifold and the inner peripheral edge of the frame body. A recess is formed by the inner peripheral surface of the frame body and the surface of the bipolar plate. An electrode is disposed in this recess. A protective plate is disposed between the frame body and the diaphragm. The protective plate is disposed on the surface of the frame body so as to cover the flow groove of the frame body.

[0003] International Publication No. 2017 / 134780

[0004] The cell frame structure of the present disclosure comprises a bipolar plate, a frame body provided on the outer periphery of the bipolar plate, and a first member overlapped on the frame body, and the frame body and the first member are fixed together by a joint.

[0005] FIG. 1 is a schematic plan view of a cell frame structure of Embodiment 1. FIG. 2 is a cross-sectional view taken along II-II in FIG. 1. FIG. 3 is a schematic cross-sectional view of another example of the cell frame structure of Embodiment 1. FIG. 4 is a schematic cross-sectional view of another example of the cell frame structure of Embodiment 1. FIG. 5 is a schematic enlarged view of region A in FIG. 2. FIG. 6 is a schematic configuration diagram of a redox flow battery system and a cell stack of Embodiment 1. FIG. 7 is a schematic plan view of a cell frame structure of Embodiment 2. FIG. 8 is a schematic plan view of a cell frame structure of Embodiment 3. FIG. 9 is a schematic plan view of a cell frame structure of Embodiment 4.

[0006] [Problem to be Solved by the Present Disclosure] The assembly of the stack is typically performed by stacking each component of the stack flat in order. In Patent Document 1, the frame of the cell frame and the first component, which is a protective plate, are not fixed. When stacked flat, even if the components are aligned, there is a risk of the first component being misaligned due to friction between the components. Furthermore, there is a risk of the first component being misaligned due to thermal expansion or contraction of the components caused by current flow through the redox flow battery, or due to the flow of liquid. If the first component is misaligned, there is a risk of the diaphragm coming into contact with the inner peripheral edge of the frame or the opening edge of the flow groove of the frame. This contact may damage the diaphragm.

[0007] An object of the present disclosure is to provide a cell frame structure in which the frame body and the first member are less likely to become misaligned.

[0008] In the cell frame structure of the present disclosure, the frame body and the first member are less likely to become misaligned.

[0009] <Description of Embodiments of the Present Disclosure> First, embodiments of the present disclosure will be listed and described.

[0010] (1) A cell frame structure according to one aspect of the present disclosure includes a bipolar plate, a frame body provided on the outer periphery of the bipolar plate, and a first member overlapped on the frame body, and the frame body and the first member are fixed together by a joint.

[0011] In the above-described cell frame structure, the frame body and the first member are fixed by a joint, so that the frame body and the first member are less likely to become misaligned. Therefore, the above-described cell frame structure can construct a cell stack that is more likely to prevent contact between the edge portion of the frame body (described later) and the diaphragm (described later). Therefore, the above-described cell frame structure can construct a cell stack that is more likely to prevent damage to the diaphragm due to the contact.

[0012] (2) In the cell frame structure of (1) above, the joint may include a welded portion between the frame body and the first member.

[0013] The welded portion can be formed by the constituent material of the frame body and the constituent material of the first member. Therefore, in the above configuration, unlike the adhesive portion and mechanically joined portion described below, the joint can be formed only by the frame body and the first member. Furthermore, in the above configuration, the joint is resistant to the electrolyte.

[0014] (3) In the cell frame structure of (1) or (2), the joint may include an adhesive portion between the frame body and the first member.

[0015] The adhesive portion can be formed by bonding the frame body and the first member with an adhesive. Therefore, unlike a welded portion, the above configuration can form a joint without melting the frame body and the first member.

[0016] (4) In the cell frame structure according to any one of (1) to (3), the joint may include a mechanical joint between the frame body and the first member.

[0017] As will be described in detail later, the mechanically joined portion can be formed by mechanically joining the frame body and the first member mainly using separate members for the frame body and the first member. Therefore, unlike a welded portion, the above configuration can form a joint without melting the frame body and the first member.

[0018] (5) In any one of the cell frame structures (1) to (4) above, the first member may have a ring-shaped shape in a plan view, and the first member may cover the entire inner peripheral edge of the frame body.

[0019] The above configuration makes it possible to construct a cell stack in which contact between the inner peripheral edge and the diaphragm can be easily suppressed over the entire periphery of the frame.

[0020] (6) In the cell frame structure of (5) above, the joint may be provided in an annular shape along the entire periphery of the first member.

[0021] The joint can have a sealing function that suppresses leakage of the electrolyte solution from between the frame body and the first member, and therefore the above configuration can construct a cell stack that is less susceptible to leakage of the electrolyte solution from between the frame body and the first member.

[0022] (7) In any of the cell frame structures (1) to (4) above, the frame body has a rectangular frame shape, and the frame body has long sides facing each other and short sides facing each other, each of the long sides has a manifold penetrating the long side and a groove connecting the manifold to an inner edge of the long side, and the first member may have a first piece covering an opening edge of the groove of each of the long sides.

[0023] The above configuration makes it possible to construct a cell stack that can easily prevent contact between the opening edge and the diaphragm. Furthermore, the above configuration makes it possible to reduce the amount of material used for the first member compared to the annular first member described above.

[0024] (8) In the cell frame structure of (7) above, the first member may further have a second piece covering an inner edge portion of each of the short sides.

[0025] The above configuration makes it possible to construct a cell stack in which contact between the inner edge portion and the diaphragm can be easily suppressed.

[0026] (9) In any of the cell frame structures (1) to (6) above, the frame body has a rectangular frame shape, and the frame body has long sides facing each other and short sides facing each other, each of the long sides has a manifold penetrating the long side and a groove connecting the manifold and an inner edge of the long side, and the joint may be arranged to surround the groove of each of the long sides.

[0027] The above configuration makes it possible to construct a cell stack that is easy to prevent contact between the opening edge and the diaphragm. Furthermore, the above configuration makes it possible to construct a cell stack that is difficult for electrolyte to leak between the frame and the first member.

[0028] (10) In the cell frame structure of (7) or (8), the joint may be provided between the groove and the outer edge of the long side, the groove and the joint may extend along the long side from the first short side toward the second short side, and the joint may be provided from the groove to near the first short side and near the second short side. This configuration makes it possible to construct a cell stack that is less susceptible to electrolyte leakage between the frame and the first member. (11) In any of the cell frame structures of (1) to (10), the thickness of the first member may be 1 / 20 to 1 / 5 times the thickness of the frame.

[0029] A first member having a thickness of 1 / 20 or more times the thickness of the frame has excellent mechanical strength. Therefore, the above configuration can suppress damage to the first member. A first member having a thickness of 1 / 5 or less times the thickness of the frame does not have excessive rigidity. Therefore, the above configuration can suppress damage to the diaphragm due to contact between the first member and the diaphragm. Furthermore, the above configuration can contribute to the miniaturization of the cell stack because the thickness of the first member is 1 / 5 or less times the thickness of the frame.

[0030] (12) In the cell frame structure according to any one of (1) to (11) above, the bonding strength between the frame body and the first member may be 0.2 MPa or more.

[0031] If the joint strength is 0.2 MPa or more, displacement from the frame due to the liquid pressure of the electrolyte is unlikely to occur. Furthermore, if the joint strength is 0.2 MPa or more, the sealing function of the joint for the electrolyte can be easily maintained.

[0032] (13) In the cell frame structure according to any one of (1) to (12) above, the frame body and the first member may be made of a resin.

[0033] The resin has resistance to the electrolyte and electrical insulation properties.

[0034] (14) In any of the cell frame structures (1) to (13) above, the constituent materials of the frame body and the first member may each be one selected from the group consisting of vinyl chloride resin, polypropylene resin, polyethylene resin, fluororesin, epoxy resin, acrylonitrile butadiene styrene resin, vinylidene chloride resin, polyamide resin, polyester resin, polystyrene resin, acrylic resin, polyvinyl alcohol resin, diacetate resin, triacetate resin, and polycarbonate resin.

[0035] The above-mentioned constituent materials have excellent resistance to the electrolyte and electrical insulation properties, and are inexpensive and easily available.

[0036] (15) In any one of the cell frame structures (1) to (14) above, the difference between the solubility parameter of the constituent material of the frame and the solubility parameter of the constituent material of the first member may be 15 or less.

[0037] The above configuration provides excellent compatibility between the frame body and the first member, making it easy to construct a particularly strong joint.

[0038] (16) A cell stack according to one aspect of the present disclosure includes any one of the cell frame structures (1) to (15) above.

[0039] The cell stack has the cell frame structure, which makes it easy to prevent damage to the diaphragm due to contact between the frame and the first member.

[0040] (17) A redox flow battery system according to one aspect of the present disclosure includes the cell stack according to (16).

[0041] The above-described redox flow battery system includes a cell stack that can easily prevent damage to the diaphragm due to contact between the frame and the first member, and therefore can easily prevent mixing of the positive electrode electrolyte and the negative electrode electrolyte, thereby easily preventing a decrease in current efficiency.

[0042] Details of the cell frame structure, cell stack, and redox flow battery system of the present disclosure are described below. The same reference numerals in the drawings indicate the same items. The sizes of components shown in each drawing are expressed for the purpose of clarifying the description and do not necessarily represent the actual dimensional relationships.

[0043] First Embodiment [Cell Frame Structure] A cell frame structure 1 of a first embodiment will be described with reference to FIGS. 1 to 5. For ease of explanation, FIGS. 2 to 4 show an assembly in which a positive electrode 7P is disposed between a first recess 61 of the cell frame structure 1 and a first member 4, and a negative electrode 7N is disposed between a second recess 62 of the cell frame structure 1 and the first member 4. FIGS. 3 and 4 are cross-sectional views showing the cell frame structure 1 cut at the same position as the cross-sectional view shown in FIG. 2. The cell frame structure 1 includes a bipolar plate 2, a frame 3, and a first member 4. The frame 3 is provided on the outer periphery of the bipolar plate 2. The frame 3 has an edge portion 38. The first member 4 is overlapped on the frame 3 so as to cover the edge portion 38. The cell frame structure 1 is a component constituting a cell stack 200 included in a redox flow battery system 100, which will be described later with reference to FIG. 6. For ease of explanation, the first member 4 is omitted from FIG. 6. One of the features of the cell frame structure 1 is that the frame body 3 and the first member 4 are fixed by a joint 5, as shown in FIGS.

[0044] [Bipolar Plate] The bipolar plate 2 shown in FIG. 1 separates adjacent battery cells 7 in the cell stack 200 shown in FIG. 6. The cell stack 200 and the battery cells 7 will be described later. As shown in FIG. 2, the bipolar plate 2 has a first surface 21 facing the positive electrode 7P and a second surface 22 facing the negative electrode 7N. In this embodiment, the bipolar plate 2 has a rectangular shape in a plan view. The plan view refers to viewing an object from a direction along the thickness of the bipolar plate 2, which is the object of interest. The thickness of the bipolar plate 2 is the length between the first surface 21 and the second surface 22. Hereinafter, the meaning of the plan view is the same as that described for the plan view of the bipolar plate 2. A known bipolar plate can be used as the bipolar plate 2.

[0045] [Frame] The frame 3 shown in FIG. 1 forms an area that will become the battery cell 7 inside the cell stack 200 shown in FIG. 6. As shown in FIG. 2, the frame 3 and the bipolar plate 2 are integrated. The frame 3 is formed, for example, by injection molding around the periphery of the bipolar plate 2. The frame 3 has an opening that exposes the bipolar plate 2. As shown in FIG. 2, a first recess 61 is formed by the inner circumferential surface of the frame 3 and the first surface 21 of the bipolar plate 2. A positive electrode 7P is disposed in the first recess 61. A second recess 62 is formed by the inner circumferential surface of the frame 3 and the second surface 22 of the bipolar plate 2. A negative electrode 7N is disposed in the second recess 62.

[0046] The outer peripheral edge 3e and inner peripheral edge 3i of the frame 3 are shaped so as to be able to surround the outer peripheral edge of the bipolar plate 2. The frame 3 of this embodiment has a rectangular frame shape in plan view. The opening shapes of the first recess 61 and the second recess 62 of this embodiment are rectangular. The positive electrode 7P arranged in the first recess 61 and the negative electrode 7N arranged in the second recess 62 are also rectangular in plan view. The frame 3 of this embodiment has two long sides 31 and two short sides 32. The two long sides 31 face each other. The two short sides 32 face each other.

[0047] The frame 3 has a plurality of manifolds 35 and a plurality of grooves 36. Each manifold 35 and each groove 36 is a flow path for the electrolyte. Each manifold 35 penetrates a first surface 33 and a second surface 34 of the frame 3. Each groove 36 is provided in the first surface 33 and the second surface 34 of the frame 3. In FIG. 1 , the first surface 33 is the front surface, and the second surface 34 is the back surface.

[0048] In this embodiment, the manifolds 35 and the grooves 36 are provided on each long side portion 31. The manifolds 35 and the grooves 36 are not provided on each short side portion 32. Each manifold 35 penetrates the first surface 33 and the second surface 34 of the long side portion 31. The number of manifolds 35 provided on each long side portion 31 is not particularly limited and can be selected appropriately. Figure 1 shows an example in which the number of manifolds 35 provided on each long side portion 31 is two.

[0049] Grooves 36 are formed on the first surface 33 and the second surface 34 of each long side portion 31. The grooves 36 on the first surface 33 of each long side portion 31 are connected to the first manifold 35a and the inner edge portion 31i of each long side portion 31, but are not connected to the second manifold 35b. On the long side portion 31 on the lower side in FIG. 1 , the left manifold 35 is the first manifold 35a, and the right manifold 35 is the second manifold 35b. On the long side portion 31 on the upper side in FIG. 1 , the right manifold 35 is the first manifold 35a, and the left manifold 35 is the second manifold 35b. Although not shown, the grooves on the second surface 34 of each long side portion 31 are not connected to the first manifold 35a, but are connected to the second manifold 35b and the inner edge portion 31i of the long side portion 31. The grooves 36 on the first surface 33 of each long side portion 31 have the same configuration as the grooves on the second surface 34. The following description will be given of the grooves 36 on the first surface 33 of each long side portion 31 as a representative.

[0050] Each groove 36 has a guide groove 37. Each guide groove 37 connects the first manifold 35a to the inner peripheral edge 3i of the frame 3. In this embodiment, each guide groove 37 connects the first manifold 35a to the inner edge 31i of each long side 31. Each guide groove 37 guides the electrolyte from the first manifold 35a to the inner edge 31i, or from the inner edge 31i to the first manifold 35a. Each guide groove 37 may be a known guide groove. The guide grooves 37 shown in FIG. 1 are merely exemplary and are not limited to the layout shown in FIG. 1. Each guide groove 37 in FIG. 1 is composed of one first guide groove 37a and six second guide grooves 37b. The first guide groove 37a is a groove that extends linearly from the first manifold 35a toward the second manifold 35b, until it reaches the vicinity of the second manifold 35b. The second guide groove 37b is a groove that extends linearly from the first guide groove 37a toward the inner edge 31i of the long side 31. Each second guide groove 37b connects the first guide groove 37a to the inner edge 31i of the long side 31. Each groove 36 may further have a rectifying portion (not shown). Each rectifying portion diffuses or concentrates the electrolyte. Each rectifying portion is formed over the entire length of the inner edge 31i of the long side 31. Each rectifying portion may be a known rectifying portion. When a rectifying portion is included, each guide groove 37 connects the first manifold 35a and the rectifying portion.

[0051] When the electrolyte flows from the lower long side portion 31 to the upper long side portion 31 in FIG. 1 , the flow of the electrolyte on the first surface 33 of each long side portion 31 is as follows. The electrolyte that has passed through the first manifold 35 a of the lower long side portion 31 flows through the guide groove portion 37 of the lower long side portion 31 to the inner edge portion 31 i of the lower long side portion 31. The electrolyte that has flowed to the inner edge portion 31 i of the lower long side portion 31 flows to the positive electrode 7P shown in FIG. 2. The electrolyte that has flowed through the positive electrode 7P flows sequentially through the inner edge portion 31 i of the upper long side portion 31 in FIG. 1 and the guide groove portion 37 of the upper long side portion 31. The electrolyte that has flowed through the guide groove portion 37 of the upper long side portion 31 flows to the first manifold 35 a of the upper long side portion 31. When a rectifying portion is provided, the electrolyte that flows into the rectifying portion of the lower long side portion 31 diffuses over the entire length of the inner edge portion 31i and flows to the positive electrode 7P. The diffusion of the electrolyte makes it easier for the electrolyte to reach the entire area along the long side of the positive electrode 7P. The electrolyte that flows into the positive electrode 7P is collected by the rectifying portion of the upper long side portion 31 and flows into the guide groove portion 37 of the upper long side portion 31.

[0052] The frame 3 has an edge portion 38. The edge portion 38 includes an inner peripheral edge portion 3i of the frame 3 and an opening edge portion 36i of the groove portion 36. For convenience of explanation, the cross-sectional shape of the inner peripheral edge portion 3i in FIGS. 2 to 4 is shown as a right angle. As shown in FIG. 5, which is an enlarged view of region A in FIG. 2, the cross-sectional shape of the inner peripheral edge portion 3i may be an arc. The bending radius of the edge portion 38 may be, for example, equal to or less than the thickness of the frame 3. The bending radius of the edge portion 38 may be, for example, 1 mm or less, 0.8 mm or less, or 0.5 mm or less.

[0053] The thickness of the frame 3 may be, for example, 2 mm or more and 20 mm or less. The thickness of the frame 3 is the length between the first surface 33 and the second surface 34. A frame 3 having a thickness of 2 mm or more has excellent mechanical strength. A frame 3 having a thickness of 20 mm or less can contribute to the miniaturization of the cell stack 200. The thickness of the frame 3 may further be 3 mm or more and 15 mm or less, particularly 5 mm or more and 10 mm or less.

[0054] The frame 3 is made of a material that has excellent resistance to the electrolyte, electrical insulation, and mechanical properties. The frame 3 may be made of a resin, for example. The frame 3 may be made of a material selected from the group consisting of vinyl chloride resin, polypropylene resin, polyethylene resin, fluororesin, epoxy resin, acrylonitrile-butadiene-styrene resin, vinylidene chloride resin, polyamide resin, polyester resin, polystyrene resin, acrylic resin, polyvinyl alcohol resin, diacetate resin, triacetate resin, and polycarbonate resin. These resins have excellent resistance to the electrolyte and electrical insulation. Furthermore, these resins are inexpensive and readily available.

[0055] [First Member] The first member 4 prevents contact between the edge portion 38 of the frame 3 and the diaphragm 7M shown in FIG. 6 . The diaphragm 7M will be described later. Preventing this contact reduces damage to the diaphragm 7M due to contact between the edge portion 38 and the diaphragm 7M. As shown in FIG. 2 , the first member 4 is overlaid on each of the first surface 33 and the second surface 34 of the frame 3. The frame 3 and each first member 4 are fixed by joints 5, which will be described later. That is, the frame 3 and both first members 4 are integral. The first member 4 overlaid on the first surface 33 of the frame 3 and the first member 4 overlaid on the second surface 34 are the same member. In this embodiment, each first member 4 is a flat plate material with a uniform thickness. Because each first member 4 is a flat plate material, each first member 4 can be stably stacked on the frame 3 when forming the joints 5. Unlike this embodiment, both first members 4 may be plate materials with a non-uniform thickness, such as elliptical or semicircular cross-sectional shapes, or may be rod materials. The following description will be given representatively of the first member 4 placed on the first surface 33 of the frame body 3 .

[0056] The shape of the first member 4 is not particularly limited and can be selected appropriately. The shape of the first member 4 in this embodiment in a plan view is a rectangular frame as shown in FIG. 1 . The length of the long side of the outer peripheral edge 4e of the first member 4 is longer than the length of the long side of the inner peripheral edge 3i and shorter than the length of the long side of the outer peripheral edge 3e. The length of the long side of the inner peripheral edge 4i of the first member 4 is shorter than the length of the long side of the inner peripheral edge 3i. The length of the short side of the outer peripheral edge 4e of the first member 4 is longer than the length of the short side of the inner peripheral edge 3i and shorter than the length of the short side of the outer peripheral edge 3e. The length of the short side of the inner peripheral edge 4i of the first member 4 is shorter than the length of the short side of the inner peripheral edge 3i.

[0057] In this embodiment, the first member 4 is disposed so as to cover the entire inner peripheral edge 3i and groove 36 of the frame 3. The first member 4 is disposed so as to straddle the inner peripheral edge 3i. Because the first member 4 blocks the opening of the groove 36, the first member 4 and the groove 36 form a flow path for the electrolyte. The inner peripheral edge 4i of the first member 4 is located inside the inner peripheral edge 3i of the frame 3. That is, the inner peripheral edge 4i of the first member 4 protrudes from the inner peripheral edge 3i toward the positive electrode 7P. The portion of the first member 4 located inside the inner peripheral edge 3i of the frame 3, i.e., a second portion of the first member 4 described below, presses against the positive electrode 7P as shown in FIG. 2. The outer peripheral edge 4e of the rectangular frame-shaped first member 4 is located inside the outer peripheral edge 3e of the frame 3.

[0058] The first member 4 has a first portion, a second portion, and a third portion. The first portion overlaps the first surface 33 of the frame 3 ( FIGS. 2 to 4 ). The first portion includes a portion overlapping the groove 36 shown in FIG. 1 . Because the first portion covers the opening edge 36i of the groove 36, contact between the opening edge 36i and the diaphragm 7M is suppressed. A portion of the first portion constitutes the joint 5. If the joint 5 is formed by a welded portion 51 (described later with reference to FIG. 2 ) or a connecting portion 53 (described later with reference to FIG. 4 ), the first portion contacts the first surface 33. If the joint 5 is formed by an adhesive portion 52 (described later with reference to FIG. 3 ), the first portion does not contact the first surface 33, and a gap is provided between the first portion and the first surface 33. The second portion overlaps the bipolar plate 2 without overlapping the frame 3 ( FIGS. 2 to 4 ). The second portion does not contact the bipolar plate 2. A space in which the positive electrode 7P is disposed is provided between the second portion, the first surface 21 of the bipolar plate 2, and the inner circumferential surface of the frame 3. The positive electrode 7P is disposed in this space. The third portion is a portion between the first portion and the second portion. The third portion is a portion that overlaps the inner circumferential edge portion 3i of the frame 3, in this case, the inner edge portion 31i (FIGS. 2 to 5). When the inner circumferential edge portion 3i is configured in an arc shape as shown in FIG. 5, the third portion is a region of the first member 4 that faces the arc-shaped inner circumferential edge portion 3i. The third portion prevents contact between the inner circumferential edge portion 3i and the diaphragm 7M.

[0059] A through hole 45 corresponding to the diameter of the manifold 35 is provided in the first portion of the first member 4 at a position corresponding to the manifold 35. In Fig. 1, for convenience of explanation, the through hole 45 of the first member 4 is shown larger than the manifold 35, but in reality they are the same size.

[0060] The constituent material of the first member 4 is a material that has excellent resistance to the electrolyte, electrical insulation, and mechanical properties. The constituent material of the first member 4 may be, for example, a resin. The constituent material of the first member 4 may be, for example, one type selected from the group of resins described in the constituent materials of the frame body 3. The constituent material of the first member 4 may be the same as or different from the constituent material of the frame body 3. The difference in solubility parameter between the constituent material of the first member 4 and the constituent material of the frame body 3 may be, for example, 15 or less. If the difference in solubility parameter is 15 or less, the compatibility between the first member 4 and the frame body 3 is excellent, and a particularly strong welded portion 51 is easily formed.

[0061] The solubility parameter can be determined, for example, using turbidity titration. Turbidity titration is a titration method that utilizes the point at which a resin solution becomes cloudy when a poor solvent is continuously added to the resin solution. Specifically, the solubility parameter can be determined using the following titration procedure and calculation software: 99 g of acetone is added to 1.0 g of a resin sample to prepare a 1.0 mass% acetone solution. 10 g of acetone solution is prepared and stirred. Water is dripped into the stirred acetone solution. If the cloudiness does not disappear after 30 seconds of water dripping, the end point is determined as the point at which 30 seconds have elapsed. 10 g of the above acetone solution is prepared again and stirred. n-hexane is dripped into the stirred acetone solution. If the cloudiness does not disappear after 30 seconds of n-hexane dripping, the end point is determined as the point at which 30 seconds have elapsed. The masses of the resin sample, acetone, and acetone solution, as well as the amounts of water and n-hexane dripped, are entered into the calculation software. The calculation software used is "Resin SP Value Measurement" manufactured by IT-Alia. The value calculated by the calculation software is the solubility parameter of the resin sample. By using the constituent material of the first member 4 and the constituent material of the frame 3 as resin samples, the solubility parameters of the constituent material of the first member 4 and the constituent material of the frame 3 can be determined.

[0062] The thickness of the first member 4 may be, for example, 1 / 20 to 1 / 5 times the thickness of the frame 3. A first member 4 having a thickness of 1 / 20 or more times the thickness of the frame 3 has superior mechanical strength compared to a first member 4 having a thickness less than 1 / 20 times the thickness of the frame 3. Therefore, when the cell stack 200 is constructed, damage to the first member 4 due to the pressure applied to tighten the cell stack 200 is suppressed. Therefore, the first member 4 is likely to suppress contact between the edge portion 38 and the diaphragm 7M. A first member 4 having a thickness of 1 / 5 or less times the thickness of the frame 3 has lower rigidity compared to a first member 4 having a thickness more than 1 / 5 times the thickness of the frame 3. Therefore, damage to the diaphragm 7M due to contact with the diaphragm 7M is likely to be suppressed. Furthermore, a first member 4 having a thickness of 1 / 5 or less times the thickness of the frame 3 can contribute to the miniaturization of the cell stack 200. The thickness of the first member 4 may further be 1 / 15 to 1 / 6 times the thickness of the rim body 3, and particularly 1 / 10 to 1 / 8 times the thickness of the rim body 3. The thickness of the first member 4 is the maximum length between the first surface and the second surface of the first member 4. The first surface of the first member 4 is the surface proximal to the first surface 33 of the rim body 3. The second surface of the first member 4 is the surface distal to the first surface 33.

[0063] The bond strength between the frame body 3 and the first member 4 may be equal to or greater than the hydraulic pressure of the electrolyte, for example. The bond strength is the maximum stress when the first member 4 is peeled off from the frame body 3. When the bond strength is equal to or greater than the hydraulic pressure, displacement of the frame body 3 and the first member 4 due to the hydraulic pressure is unlikely to occur. Furthermore, when the bond strength is equal to or greater than the hydraulic pressure, the sealing function of the joint 5 (described later) for the electrolyte is easily maintained. The hydraulic pressure is, for example, less than 0.2 MPa. That is, the bond strength may be equal to or greater than 0.2 MPa. The bond strength may be equal to or greater than 0.5 MPa, 0.8 MPa, 1 MPa, or 3 MPa. The bond strength may be, for example, 10 MPa or less. That is, the bond strength of the first member 4 may be equal to or greater than 0.2 MPa and 10 MPa or less, further equal to or greater than 1 MPa and 5 MPa, particularly equal to or greater than 1 MPa and 3 MPa, or equal to or greater than 1 MPa and 2 MPa.

[0064] [Joint] The joint 5 fixes the frame body 3 and the first member 4. This fixation integrates the frame body 3 and the first member 4. This integration reduces misalignment between the frame body 3 and the first member 4. Therefore, when fabricating the cell stack 200, the frame body 3 and the first member 4 are less likely to become misaligned. When fabricating the cell stack 200, the above-described assemblies and the diaphragms 7M are stacked in this order in multiple layers. Because the frame body 3 and the first member 4 are less likely to become misaligned, contact between the edge portion 38 of the frame body 3 and the diaphragm 7M is reduced, thereby reducing damage to the diaphragm 7M due to contact between the edge portion 38 and the diaphragm 7M. Furthermore, it is easy to reduce misalignment of the first member 4 due to thermal expansion or contraction of members caused by current flow in the redox flow battery system 100 or due to the flow of liquid.

[0065] The joint portion 5 has at least one of a welded portion 51 between the frame body 3 and the first member 4 as shown in Fig. 2, an adhesive portion 52 between the frame body 3 and the first member 4 as shown in Fig. 3, and a mechanically coupled portion 53 between the frame body 3 and the first member 4 as shown in Fig. 4. The welded portion 51 and the adhesive portion 52 are more likely to fix the frame body 3 and the first member 4 over a wide area than the coupled portion 53. The welded portion 51 and the adhesive portion 52 are more likely to prevent leakage of the electrolyte from between the frame body 3 and the first member 4 than the mechanically coupled portion 53.

[0066] As shown in FIG. 2 , the welded portion 51 is formed by welding the constituent material of the frame body 3 and the constituent material of the first member 4. Welding refers to the mixing or compatibility of the constituent materials of the frame body 3 and the first member 4. Therefore, unlike the adhesive portion 52 and the mechanically bonded portion 53, the welded portion 51 can form a joint 5 using only the frame body 3 and the first member 4. Furthermore, the joint 5 is resistant to electrolytes. The welded portion 51 can be formed by, for example, welding or welding. Examples of welding include ultrasonic welding, high-frequency dielectric welding, induction welding, laser welding, and friction welding. In the case of induction welding, an induction-heated metal wire is placed between the frame body 3 and the first member 4. In this case, when the welded portion 51 is formed, the metal wire remains between the frame body 3 and the first member 4. An example of welding is flat fusion. The welded portion 51 can also be formed by dissolving at least one of a portion of the frame body 3 and a portion of the first member 4 in a solvent. The welded portion 51 can also be formed by blowing hot air onto at least one of the frame body 3 and the first member 4 or by bringing a hot plate into contact with them.

[0067] As shown in Figure 3, the adhesive portion 52 is formed by bonding the frame body 3 and the first member 4 together with an adhesive. That is, the adhesive portion 52 can be formed with an adhesive. Therefore, unlike the welded portion 51, the adhesive portion 52 can form the joint 5 without melting the frame body 3 and the first member 4. There are no particular restrictions on the type of adhesive, as long as it has excellent resistance to the electrolyte. For ease of explanation, Figure 3 exaggerates the thickness of the adhesive portion 52. The thinner the thickness of the adhesive portion 52, the thinner the cell frame structure 1 that is constructed.

[0068] As shown in FIG. 4 , the mechanical joint 53 is formed by mechanically joining the frame body 3 and the first member 4. Therefore, unlike the welded portion 51, the mechanical joint 53 can form the joint 5 without melting the frame body 3 and the first member 4. The mechanical joint 53 can be formed, for example, by a combination of screws, rivets, bolts and nuts, or by a snap fit. The constituent materials of the screws, rivets, bolts, and nuts are not particularly limited as long as they are made of a material that has excellent resistance to the electrolyte. The constituent materials of the screws, rivets, bolts, and nuts may be made of, for example, the same resin as the frame body 3. The snap fit is formed by a part of the frame body 3 or the first member 4. FIG. 4 shows an example in which the joint 53 is formed by a screw.

[0069] The location of the joint 5 is not particularly limited as long as it is a location where the frame 3 and the first member 4 are unlikely to become misaligned when the cell stack 200 is fabricated. In this embodiment, the joint 5 is provided in an annular shape along the entire circumference of the first member 4, as shown in FIG. 1 . Specifically, the joint 5 is provided in a rectangular annular shape along the entire circumference of the first member 4 so as to surround the outer periphery of the first member 4 more than the manifolds 35 and the grooves 36. From another perspective, the annular joint 5 is disposed between the inner peripheral edge 3i of the frame 3 and the outer peripheral edge 3e of the frame 3. The annular joint 5 is disposed closer to the outer peripheral edge 3e of the frame 3 than the grooves 36 of the frame 3. The annular or rectangular annular joint 5 can function as a seal to prevent leakage of the electrolyte from between the frame 3 and the first member 4. FIG. 6 shows a seal member 8 disposed between the frame 3. The seal member 8 has an annular shape. When the joint 5 is provided in a rectangular annular shape as in this embodiment, the seal member 8 may be omitted.

[0070] [Redox Flow Battery System] A redox flow battery system 100 of embodiment 1 will be described with reference to FIG. 6 . The redox flow battery system 100 charges and stores power generated by a power generation unit 310, and discharges the stored power to supply to a load 330. The redox flow battery system 100 is typically connected to an AC / DC converter 300. The AC / DC converter 300 is connected to a substation 320. The substation 320 is connected to the power generation unit 310 and a load 330. An example of the power generation unit 310 is a solar power generation system, a wind power generation system, or other general power plants. An example of the load 330 is a power consumer. A solid arrow extending from the substation 320 to the AC / DC converter 300 indicates charging. A dashed arrow extending from the AC / DC converter 300 to the substation 320 indicates discharging. The redox flow battery system 100 uses a positive electrode electrolyte and a negative electrode electrolyte. The positive electrode electrolyte and the negative electrode electrolyte contain, as active materials, ions whose valence changes due to oxidation-reduction. Charging and discharging of the redox flow battery system 100 are performed by utilizing the difference between the oxidation-reduction potential of the ions contained in the positive electrode electrolyte and the oxidation-reduction potential of the ions contained in the negative electrode electrolyte. Examples of applications of the redox flow battery system 100 include load leveling, voltage sag compensation, emergency power supply, and output smoothing of natural energy. Examples of natural energy include solar power generation and wind power generation.

[0071] [Battery Cell] The redox flow battery system 100 includes a battery cell 7. The battery cell 7 is separated into a positive electrode cell and a negative electrode cell by a diaphragm 7M. A positive electrode 7P is built into the positive electrode cell. A positive electrode circulation mechanism 9P circulates positive electrode electrolyte from a positive electrode electrolyte tank 91 to the positive electrode cell. A negative electrode 7N is built into the negative electrode cell. A negative electrode 7N is built into the negative electrode cell. A negative electrode electrolyte from a negative electrode electrolyte tank 92 is circulated to the negative electrode cell by a negative electrode circulation mechanism 9N. The diaphragm 7M is disposed between the positive electrode 7P and the negative electrode 7N. The battery cell 7 may have a known configuration. The battery cell 7 is usually formed inside a structure called a cell stack 200.

[0072] [Cell Stack] The cell stack 200 includes multiple sub-stacks, two end plates 220, and a clamping mechanism 230. Each sub-stack includes a stack and two supply / discharge plates. The stack is formed by stacking multiple assemblies and diaphragms 7M described above in this order. The assembly is fabricated as follows: A positive electrode 7P is placed in a first recess 61 of the integrated bipolar plate 2 and frame 3. A first member 4 is placed at a predetermined position on the frame 3 and the positive electrode 7P, and the frame 3 and first member 4 are joined. A negative electrode 7N is placed in a second recess 62. A first member 4 is placed at a predetermined position on the frame 3 and the negative electrode 7N, and the frame 3 and first member 4 are joined. After the frame 3 and first member 4 are joined, the positive electrode 7P may be placed in the first recess 61, and the negative electrode 7N may be placed in the second recess 62. Supply / discharge plates are placed at both ends of the stack. The supply and discharge plates are connected to a supply pipe 93 and a discharge pipe 95 of the positive electrode circulation mechanism 9P, and a supply pipe 94 and a discharge pipe 96 of the negative electrode circulation mechanism 9N. The two end plates 220 sandwich the sub-stacks from the outside of the sub-stacks on both ends. The clamping mechanism 230 clamps the end plates 220 together.

[0073] The diaphragm 7M is an ion exchange membrane that does not transmit electrons but transmits, for example, hydrogen ions. The thickness of the diaphragm 7M may be, for example, 60 μm or less. A diaphragm 7M with a thickness of 60 μm or less may be damaged if it comes into contact with the edge portion 38. In this embodiment, the frame 3 and the first member 4 are fixed by the joint 5, thereby preventing the first member 4 from shifting in position. The first member 4 covers the edge portion 38. This prevents contact between the diaphragm 7M and the edge portion 38. Therefore, the diaphragm 7M is less likely to come into contact with the edge portion 38, and therefore, even if the diaphragm 7M has a thickness of 60 μm or less, the diaphragm 7M is not damaged by the contact. The thickness of the diaphragm 7M may be further 40 μm or less, particularly 30 μm or less. The thickness of the diaphragm 7M may be, for example, 5 μm or more. A diaphragm 7M with a thickness of 5 μm or more is less likely to be damaged. The thickness of the diaphragm 7M may be further 8 μm or more, particularly 10 μm or more. That is, the thickness of the diaphragm 7M may be 5 μm or more and 60 μm or less, further 8 μm or more and 40 μm or less, and particularly 10 μm or more and 30 μm or less. The thickness of the diaphragm 7M is the average value of the thicknesses at five or more points.

[0074] [Positive Electrode Circulation Mechanism / Negative Electrode Circulation Mechanism] The positive electrode circulation mechanism 9P includes a positive electrode electrolyte tank 91, a supply pipe 93, a discharge pipe 95, and a pump 97. The positive electrode electrolyte tank 91 stores positive electrode electrolyte. The positive electrode electrolyte is circulated through the supply pipe 93 and the discharge pipe 95. The supply pipe 93 connects the positive electrode electrolyte tank 91 to the positive electrode cell. The discharge pipe 95 connects the positive electrode cell to the positive electrode electrolyte tank 91. The pump 97 pressure-feeds the positive electrode electrolyte in the positive electrode electrolyte tank 91. The pump 97 is provided midway through the supply pipe 93.

[0075] The negative electrode circulation mechanism 9N includes a negative electrode electrolyte tank 92, a supply pipe 94, a discharge pipe 96, and a pump 98. The negative electrode electrolyte tank 92 stores the negative electrode electrolyte. The negative electrode electrolyte is circulated through the supply pipe 94 and the discharge pipe 96. The supply pipe 94 connects the negative electrode electrolyte tank 92 and the negative electrode cell. The discharge pipe 96 connects the negative electrode cell and the negative electrode electrolyte tank 92. The pump 98 pressure-feeds the negative electrode electrolyte in the negative electrode electrolyte tank 92. The pump 98 is provided midway through the supply pipe 94.

[0076] [Electrolyte] The positive electrode active material contained in the positive electrode electrolyte is, for example, one or more selected from the group consisting of manganese ions, vanadium ions, iron ions, polyacids, quinone derivatives, and amines. The negative electrode active material contained in the negative electrode electrolyte is, for example, one or more selected from the group consisting of titanium ions, vanadium ions, chromium ions, polyacids, quinone derivatives, and amines. In a specific example, both the positive electrode electrolyte and the negative electrode electrolyte contain vanadium ions. The solvent for the positive electrode electrolyte and the negative electrode electrolyte is, for example, an aqueous solution containing one or more acids or acid salts selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid.

[0077] [Embodiment 2] A cell frame structure 1 of embodiment 2 will be described with reference to Figure 7. The cell frame structure 1 of this embodiment differs from the cell frame structure 1 of embodiment 1 in the location where the joints 5 are formed. The following description will focus on the differences from embodiment 1. Descriptions of configurations and effects similar to those of embodiment 1 may be omitted.

[0078] The joints 5 are provided in a rectangular frame shape so as to surround the first manifolds 35a and the grooves 36 of each long side portion 31. From another perspective, the joints 5 are disposed on the long side portions 31 between the inner peripheral edge 3i of the frame body 3 and the outer peripheral edge 3e of the frame body 3. The joints 5 include a portion provided closer to the outer peripheral edge 3e of the frame body 3 than the grooves 36 of the frame body 3, and a portion provided closer to the inner peripheral edge 3i of the frame body 3 than the grooves 36 of the frame body 3. The joints 5 are not provided where the first member 4 and the second guide grooves 37b overlap. The joints 5 are also not provided where each short side portion 32 and the first member 4 overlap.

[0079] [Embodiment 3] A cell frame structure 1 of embodiment 3 will be described with reference to Figure 8. The cell frame structure 1 of this embodiment differs from the cell frame structure 1 of embodiment 1 in the configuration of the first member 4 and the location where the joint 5 is formed. The following description will focus on the differences from embodiment 1. Description of the same configuration and effects as embodiment 1 may be omitted.

[0080] The first member 4 has a plurality of first pieces 41. Each first piece 41 is a plate piece. Each first piece 41 has a rectangular shape in a plan view. The length of each long side of the first pieces 41 is longer than the length of the long side of the inner peripheral edge portion 3i and shorter than the length of the long side of the outer peripheral edge portion 3e. Each first piece 41 overlaps each long side portion 31. Each first piece 41 covers the entire inner edge portion 31i and groove portion 36 of each long side portion 31. The inner edge portion 41i of each first piece 41 is located more inward of the frame body 3 than the inner edge portion 31i of each long side portion 31. The outer edge portion 41e of each first piece 41 is located more inward than the outer edge portion 31e of the long side portion 31.

[0081] The joints 5 secure each long side portion 31 to each first piece 41. Each joint 5 is located on each long side portion 31 closer to the outer edge 31e of the long side portion 31 than the first manifold 35a, the second manifold 35b, and the groove 36. Each joint 5 is located parallel to the first guide groove 37a. From another perspective, the joint 5 is located between the groove 36 and the outer edge 31e of the long side portion 31. The guide groove 37a of the groove 36 and the joint 5 extend along the long side portion 31 from the first short side portion 32 to the second short side portion 32 of the two short side portions 32. The joint 5 is located closer to the first short side portion 32 than the groove 36 and closer to the second short side portion 32. Also, although not shown in the figure, unlike this embodiment, the joint 5 may further have portions extending from both ends of the straight portion parallel to each first guide groove portion 37a toward the short side portion 32.

[0082] [Fourth embodiment] A cell frame structure 1 of a fourth embodiment will be described with reference to Fig. 9. The cell frame structure 1 of this embodiment differs from the cell frame structure 1 of the third embodiment in the configuration of the first member 4 and the location of the joint 5. The following description will focus on the differences from the third embodiment. Descriptions of the same configuration and effects as those of the third embodiment may be omitted.

[0083] The first member 4 has a plurality of first pieces 41 and a plurality of second pieces 42. Each first piece 41 is the same as in embodiment 3. Each second piece 42 is a plate piece. Each second piece 42 has a rectangular shape in a plan view. The length of each long side of the second piece 42 is shorter than the length of the short side of the inner peripheral edge portion 3i. Each second piece 42 overlaps each short side portion 32. Each second piece 42 covers the inner edge portion 32i of each short side portion 32. The inner edge portion 42i of each second piece 42 is located more inward of the frame body 3 than the inner edge portion 32i of each short side portion 32. The outer edge portion 42e of each second piece 42 is located more inward than the outer edge portion 32e of each short side portion 32.

[0084] The joints 5 secure each long side portion 31 to each first piece 41, and secure each short side portion 32 to each second piece 42. The joints 5 securing each long side portion 31 to each first piece 41 are the same as those in embodiment 3. The joints 5 securing each short side portion 32 to each second piece 42 are provided along the long sides of the second pieces 42.

[0085] The present invention is not limited to these examples, but is defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0086] For example, the joints may be provided near the grooves and along the grooves. When the grooves 36 have the first guide grooves 37a and the second guide grooves 37b as shown in FIG. 1, the joints 5 may be provided as follows: The joints 5 may be provided near the first guide grooves 37a and along the long sides of the outer peripheral edge 3e. The joints 5 may be provided near the second guide grooves 37b and along the short sides of the outer peripheral edge 3e.

[0087] In each of the above-described embodiments, the first member 4 is fixed to the surface of the frame body 3 by the joint 5. As an alternative to these configurations, for example, a recess may be provided on the surface of the frame body 3, and the first member 4 may be fitted into the recess. The recess is provided in an area of ​​the frame body 3 that overlaps with the first member 4. By making the depth of the recess substantially the same as the thickness of the first member 4, the surface of the frame body 3 that is not covered by the first member 4 can be made flush with the surface of the first member 4. In this case, for example, the bottom surface of the recess and the first member 4 are fixed by the joint 5.

[0088] The joint 5 may be a combination of two or three selected from welding (welded portion 51), adhesion (adhesive portion 52), and mechanical joint (joint portion 53). For example, in the embodiment shown in FIG. 9 , the joint 5 provided on the first piece 41 may be the adhesive portion 51, and the joint 5 provided on the second piece 42 may be the joint portion 53.

[0089] 1 Cell frame structure, 2 Bipolar plate, 21 First surface, 22 Second surface, 3 Frame body, 3i Inner peripheral edge portion, 3e Outer peripheral edge portion, 31 Long side portion, 31i Inner edge portion, 31e Outer edge portion, 32 Short side portion, 32i Inner edge portion, 32e Outer edge portion, 33 First surface, 34 Second surface, 35 Manifold, 35a First manifold, 35b Second manifold, 36 Groove portion, 36i Opening edge portion, 37 Guide groove portion, 37a First guide groove portion, 37b Second guide groove portion, 38 Edge portion, 4 First member, 4i Inner peripheral edge portion, 4e Outer peripheral edge portion, 41 First piece, 41i Inner edge portion, 41e Outer edge portion, 42 Second piece, 42i Inner edge portion, 42e Outer edge portion, 45 Through hole, 5 Joint portion, 51 Welded portion, 52 Adhesive portion, 53 Bonding portion, 61 First recess, 62 Second recess, 100 Redox flow battery system, 7 Battery cell, 7M Diaphragm, 7P Positive electrode, 7N Negative electrode, 8 Sealing member, 9P Positive electrode circulation mechanism, 9N Negative electrode circulation mechanism, 91 Positive electrode electrolyte tank, 92 Negative electrode electrolyte tank, 93, 94 Supply pipe, 95, 96 Discharge pipe, 97, 98 Pump, 200 Cell stack, 220 End plate, 230 Fastening mechanism, 300 AC / DC converter, 310 Power generation unit, 320 Substation equipment, 330 Load.

Claims

1. A bipolar plate; A frame provided on the outer periphery of the bipolar plate; A first member overlapped on the frame body, A cell frame structure in which the frame and the first member are fixed by a joint.

2. The cell frame structure according to claim 1 , wherein the joint portion comprises a welded portion between the frame body and the first member.

3. The cell frame structure according to claim 1 , wherein the joint portion comprises an adhesive portion between the frame body and the first member.

4. The cell frame structure according to claim 1 , wherein the joint portion comprises a mechanical joint portion between the frame body and the first member.

5. The first member has a ring-shaped planar shape, The cell frame structure according to claim 1 , wherein the first member covers an entire inner peripheral edge portion of the frame body.

6. The cell frame structure according to claim 5 , wherein the joint is provided in an annular shape along the entire circumference of the first member.

7. The frame has a rectangular frame shape, The frame body has long sides facing each other and short sides facing each other, Each of the long sides is a manifold penetrating the long side portion; a groove portion connecting the manifold and an inner edge portion of the long side portion, The cell frame structure according to claim 1 , wherein the first member has a first piece covering an open edge of the groove on each of the long sides.

8. The cell frame structure of claim 7 , wherein the first member further comprises a second piece covering an inner edge of each of the short sides.

9. The frame has a rectangular frame shape, The frame body has long sides facing each other and short sides facing each other, Each of the long sides is a manifold penetrating the long side portion; a groove portion connecting the manifold and an inner edge portion of the long side portion, The cell frame structure according to claim 1 , wherein the joints are provided so as to surround the grooves of the respective long sides.

10. The joint portion is provided between the groove portion and an outer edge portion of the long side portion, the groove and the joint extend along the long side from the first short side to the second short side, The cell frame structure according to claim 7 , wherein the joint portion is provided from the groove portion to near the first short side portion and near the second short side portion.

11. The cell frame structure according to claim 1 , wherein the thickness of the first member is 1 / 20 to 1 / 5 times the thickness of the frame.

12. The cell frame structure according to claim 1 , wherein a bonding strength between the frame and the first member is 0.2 MPa or more.

13. The cell frame structure according to claim 1 , wherein the frame and the first member are made of a resin.

14. 2. The cell frame structure according to claim 1, wherein each of the constituent materials of the frame and the first member is one selected from the group consisting of polyvinyl chloride resin, polypropylene resin, polyethylene resin, fluororesin, epoxy resin, acrylonitrile-butadiene-styrene resin, vinylidene chloride resin, polyamide resin, polyester resin, polystyrene resin, acrylic resin, polyvinyl alcohol resin, diacetate resin, triacetate resin, and polycarbonate resin.

15. 2. The cell frame structure according to claim 1, wherein the difference between the solubility parameter of the constituent material of said frame and the solubility parameter of the constituent material of said first member is 15 or less.

16. A cell stack comprising the cell frame structure according to any one of claims 1 to 15.

17. A redox flow battery system comprising the cell stack of claim 16.