Frame body, cell frame, battery cell, cell stack, and redox flow battery system

Abstract

This plate-like frame body for use in a cell frame of a battery cell has a first main surface and a second main surface, which is the opposite surface to the first main surface, wherein: the first main surface includes a plurality of recessed portions that are open at the first main surface, and liquid grooves constituting a portion of flow passages of an electrolytic solution within the battery cell; and each of the plurality of recessed portions is distributed and arranged in a position different from that of the liquid grooves.

Description

Frame, cell frame, battery cell, cell stack, and redox flow battery system

[0001] The present disclosure relates to a frame, a cell frame, a battery cell, a cell stack, and a redox flow battery system. This application claims priority to Japanese Patent Application No. 2023-117323, filed on July 19, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] Patent Literature 1 discloses a frame used in a cell frame of a battery cell included in a redox flow battery system. The cell frame is composed of a bipolar plate and a frame that supports the outer periphery of the bipolar plate. The redox flow battery system includes a stack in which a cell frame, a positive electrode, a diaphragm, a negative electrode, and another cell frame are stacked in this order. In this configuration, one battery cell is formed between the bipolar plates of two adjacent cell frames.

[0003] International Publication No. 2018 / 066095

[0004] The frame body of the present disclosure is a plate-shaped frame body used in a cell frame of a battery cell, and includes a first main surface and a second main surface opposite the first main surface. The first main surface includes a plurality of recesses opening to the first main surface and a liquid groove that forms part of a flow path for an electrolyte within the battery cell. Each of the plurality of recesses is disposed at a different position from the liquid groove.

[0005] Fig. 1 is a plan view of a cell frame according to an embodiment. Fig. 2 is a cross-sectional view taken along line II-II of Fig. 1. Fig. 3 is a plan view of a cell frame according to Modification 1. Fig. 4 is a plan view of a cell frame according to Modification 2. Fig. 5 is a plan view of a cell frame according to Modification 3. Fig. 6 is a schematic configuration diagram of a redox flow battery system according to an embodiment. Fig. 7 is a schematic configuration diagram of a cell stack according to an embodiment. Fig. 8 is a diagram schematically showing the positional relationship between one region and a corner region of a frame.

[0006] [Problem to be Solved by the Present Disclosure] It is desirable to improve the ease of assembling battery cells, and more specifically, to prevent misalignment between adjacent frame bodies.

[0007] An object of the present disclosure is to provide a frame body that allows for excellent assembly of battery cells.

[0008] [Advantages of the Present Disclosure] The frame body of the present disclosure is excellent in terms of assembly of the battery cell.

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

[0010] (1) A frame according to an embodiment of the present disclosure is a plate-shaped frame used in a cell frame of a battery cell, and includes a first main surface and a second main surface opposite the first main surface. The first main surface includes a plurality of recesses opening into the first main surface and a liquid groove that forms part of a flow path for an electrolyte within the battery cell. Each of the plurality of recesses is disposed at a different position from the liquid groove.

[0011] The multiple recesses provided in the frame body generate an appropriate frictional force between the frame body and the members that come into contact with the frame body when assembling the battery cell. This frictional force can prevent adjacent frame bodies from shifting out of position. When a diaphragm is placed between one frame body and the adjacent frame body, it can also prevent the diaphragm from shifting out of position. Therefore, a frame body with recesses is excellent for assembling battery cells.

[0012] Furthermore, each of the multiple recesses provided in the frame body can store excess electrolyte that may occur within the battery cell. Compared to when protrusions are provided on the first main surface, recesses prevent gaps from forming between the frame bodies or between the frame body and the diaphragm. Therefore, a frame body with recesses is less likely to cause electrolyte to leak between adjacent frame bodies to the outside of the battery cell. A frame body with recesses is less likely to damage components in contact with the frame body than a frame body with protrusions.

[0013] (2) In the frame body of (1) above, the first main surface may further include a sealing groove provided annularly along the entire circumference of the frame body in a plan view of the first main surface so that a sealing member can be disposed therein.

[0014] When a seal member is disposed on the first main surface, it is possible to prevent the electrolyte from leaking out of the battery cell from between the frame body and the adjacent frame body.

[0015] (3) In the frame of (1) or (2) above, at least one of the plurality of recesses may have a depth of 0.1% to 10% of the maximum thickness of the frame.

[0016] If the depth of the recess is 0.1% or more of the maximum thickness of the frame body, a large frictional force can be generated between the opening edge of the recess and the member in contact with the frame body. If the depth of the recess is 10% or less of the maximum thickness of the frame body, the strength of the frame body is sufficiently maintained. If a diaphragm is disposed between an adjacent frame body, if the depth of the recess is 5% or less of the maximum thickness of the frame body, it is easy to prevent the diaphragm from entering the recess.

[0017] (4) In any of the frame bodies described in (1) to (3) above, at least one of the plurality of recesses may have a shape in which the opening edge of the recess is curved when viewed in a plane on the first main surface.

[0018] When the opening edge of the recess has a curved planar shape, the planar shape of the opening edge is rounded and does not have any sharp corners, so that members in contact with the frame are less likely to be damaged by the opening edge.

[0019] (5) In the frame of any one of (1) to (4), the frame includes four half regions and four corner regions, each corner region being located between two of the half regions. Each half region includes an outer peripheral region extending inward from the outer peripheral edge of the first main surface and having a width within 50% of the maximum width of the half region. The maximum width of the half region is the maximum length between the inner peripheral edge and the outer peripheral edge of each half region, and at least one of the plurality of recesses may be provided in the outer peripheral region.

[0020] Providing the recesses in the outer peripheral region of the frame body makes it easier to prevent misalignment between adjacent frame bodies or between the frame body and the diaphragm. Providing the recesses in the outer peripheral region of the frame body makes it possible to collect excess electrolyte that reaches the vicinity of the outer peripheral edge of the frame body. This makes it easier to more reliably prevent electrolyte from leaking out of the battery cell from between the frame body and the adjacent frame body.

[0021] (6) In the frame of (2) above, the frame includes four half regions and four corner regions, and each corner region is located between two of the half regions. Each half region includes an outer peripheral region extending inward from the outer peripheral edge of the first main surface and having a width within 50% of the maximum width of the half region. The maximum width of the half region is the maximum length between the inner peripheral edge and the outer peripheral edge of each half region. The seal groove may be disposed in the outer peripheral region, and at least one of the plurality of recesses may be provided in the vicinity of the seal groove.

[0022] If the recess is provided near the seal groove, the electrolyte can be stored in the recess near the seal groove, which makes it easier to prevent the electrolyte from leaking out of the battery cell from between the frame body and the adjacent frame body.

[0023] (7) In the frame body of any one of (1) to (6), the frame body includes four half regions and four corner regions, and each corner region is located between two of the half regions. Each half region includes an inner peripheral region extending from the inner peripheral edge of the first main surface outwardly, the inner peripheral region being within 50% of the maximum width of the half region. The maximum width of the half region is the maximum length between the inner peripheral edge and the outer peripheral edge of each half region. At least one of the plurality of recesses may be provided in the inner peripheral region.

[0024] When the recess is provided in the inner peripheral region of the frame, misalignment of the frames relative to each other that may occur in the inner peripheral region can be prevented. Even when the outer peripheral edge of the diaphragm is located on or near the inner peripheral edge of the frame, misalignment of the frame and the diaphragm can be prevented. When the recess is provided in the inner peripheral region of the frame, excess electrolyte in the inner peripheral region of the frame can be collected in the recess.

[0025] (8) In any of the frame bodies described in (1) to (7) above, at least two of the plurality of recesses may be provided at positions symmetrical with respect to a through hole provided in the frame body.

[0026] The symmetrical positions across the through hole correspond to positions facing each other across the through hole. Bipolar plates are placed in the through holes provided in the frames. If recesses are provided at positions facing each other across the through hole, it is easy to prevent misalignment of the frames. If a diaphragm is placed between one frame and an adjacent frame, it is also easy to prevent misalignment between the frame and the diaphragm.

[0027] (9) In the frame of any one of (1) to (8) above, at least one of the plurality of recesses may be provided in the vicinity of the liquid groove.

[0028] If the recess is provided near the liquid groove, excess electrolyte from the liquid groove can be collected in the recess.

[0029] (10) In any of the frames described in (1) to (9), a manifold may be further provided that forms part of a flow path for the electrolyte, and at least one of the plurality of recesses may be provided in the vicinity of the manifold.

[0030] If the recess is provided near the manifold, it is possible to prevent the manifolds of adjacent frames from being misaligned with each other.

[0031] (11) In the frame body of any one of (1) to (10), at least one of the plurality of recesses is 7 mm ２ 7855mm or more ２ It may have the following opening area:

[0032] The opening area of ​​the recess is 7 mm ２ If the opening area of ​​the recess is 7855 mm or more, a large friction force can be generated between the member in contact with the frame body. ２ If the opening area of ​​the recess is 7855 mm or less, the strength of the frame body is ensured. ２ If it is equal to or less than this, it is easy to prevent the diaphragm from getting into the recess.

[0033] (12) In the frame body according to any one of (1) to (11) above, the number of opening edges of each recess may be one in a plan view of the first main surface.

[0034] The recess with a single opening edge generates a frictional force between the frame body and the adjacent frame body, making it possible to prevent misalignment between the frame body and the adjacent frame body. When a diaphragm is disposed between the frame body and the adjacent frame body, it is also possible to prevent misalignment between the frame body and the diaphragm.

[0035] (13) A cell frame according to an embodiment of the present disclosure includes a frame body according to any one of (1) to (12) above, and a bipolar plate supported by the frame body.

[0036] The cell frame has the frame body, which allows for excellent assembly of the battery cells.

[0037] (14) A battery cell according to an embodiment of the present disclosure includes the cell frame described above in (13).

[0038] The battery cell is excellent in assembling ability due to the cell frame.

[0039] (15) A cell stack according to an embodiment of the present disclosure includes the battery cell according to (14) above.

[0040] The cell stack is easy to assemble because it includes the battery cells.

[0041] (16) A redox flow battery system according to an embodiment of the present disclosure includes the battery cell of (14) above or the cell stack of (15) above.

[0042] The redox flow battery system includes the battery cell or the cell stack, and thus has excellent assembly properties for the battery cell and the cell stack.

[0043] [Details of the embodiments of the present disclosure] Specific examples of the frame, cell frame, battery cell, cell stack, and redox flow battery system of the present disclosure will be described with reference to the drawings. The same reference numerals in the drawings indicate the same or equivalent parts. In each drawing, for the convenience of explanation, some of the configuration may be exaggerated or simplified. The dimensional ratios of each part in the drawings may also differ from the actual ratios. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. Hereinafter, redox flow batteries may be referred to as "RF batteries."

[0044] <Frame> The frame 2 of the embodiment will be described with reference to Figures 1 and 2. The frame 2 is a component of the cell frame 1. The cell frame 1 is a component of the RF battery system 6, which will be described later with reference to Figures 6 and 7. One of the features of the frame 2 of the embodiment is that it has a plurality of recesses 4 on a first main surface 21 of the frame 2.

[0045] The frame body 2 is a plate-shaped member. A through-hole 20 is provided in the center of the frame body 2, penetrating the frame body 2 in the thickness direction. As shown in FIG. 2 , the frame body 2 has a first main surface 21, a second main surface 22, an outer peripheral surface 23, and an inner peripheral surface 24. The frame body 2 includes four half regions 11 and four corner regions 12. Each corner region is located between two half regions. The shape of the outer peripheral edge of the frame body 2 in a plane is rectangular. The four half regions 11 and the four corner regions 12 are not independent members. The four half regions 11 and the four corner regions 12 form the frame body 2 together. The positional relationship between the half regions 11 and the corner regions 12 in the frame body 2 is shown schematically in FIG. 8 .

[0046] 1 and 2 . The first main surface 21 and the second main surface 22 constitute the front and back of the frame body 2. Each of the first main surface 21 and the second main surface 22 faces another frame body arranged adjacent to the frame body 2. The frame body 2 has a through hole 20. Each of the first main surface 21 and the second main surface 22 has an inner peripheral edge. The inner peripheral edge is the same as the opening edge of the through hole 20. The through hole 20 includes the axis of the frame body 2. A bipolar plate 5, described below, is arranged in the through hole 20. Each of the first main surface 21 and the second main surface 22 includes a flat surface. The first main surface 21 and the second main surface 22 are arranged so that their flat surfaces are parallel to each other. Adjacent frame bodies 2 are stacked so that the flat surfaces of the first main surface 21 and the second main surface 22 face each other.

[0047] The outer peripheral surface 23 is continuous with the first main surface 21 and the second main surface 22, and forms the outer shape of the frame body 2. The inner peripheral surface 24 is continuous with the first main surface 21 and the second main surface 22, and forms the through hole 20. The frame body 2 shown in FIG. 1 has a rectangular outer shape in a plan view, and the shape of the through hole 20 is also rectangular. The outer shape of the frame body 2 and the shape of the through hole 20 can be selected as appropriate.

[0048] The maximum thickness T2 of the frame 2 is, for example, 3 mm or more and 15 mm or less. The maximum thickness T2 refers to the maximum length of the distance between the first main surface 21 and the second main surface 22. If the maximum thickness T2 is 3 mm or more, the mechanical strength of the frame 2 is high. If the maximum thickness T2 is 15 mm or less, it is possible to prevent the battery cell 7 (upper diagrams in FIGS. 6 and 7) including the frame 2 from becoming large, and further, it is possible to prevent the cell stack 9 (lower diagrams in FIGS. 6 and 7) including the battery cell 7 from becoming large. The maximum thickness T2 may be 4 mm or more and 14 mm or less, or 5 mm or more and 13 mm or less.

[0049] The four piece regions 11 include a supply piece region 2s and a discharge piece region 2d. The supply piece region 2s and the discharge piece region 2d are arranged to face each other across the through hole 20 in a plan view. In the frame 2 shown in Figure 2, the supply piece region 2s is located at the bottom and the discharge piece region 2d is located at the top.

[0050] The first main surface 21 has supply and discharge paths for the electrolyte. The supply paths are provided in the supply piece region 2s, and the discharge paths are provided in the discharge piece region 2d. The supply and discharge paths are composed of liquid grooves and manifolds provided in the first main surface 21. In other words, the first main surface 21 has liquid grooves and manifolds that form part of the electrolyte flow path within the battery cell 7 (FIG. 6). The liquid grooves include the liquid supply slits 25s and the liquid drain slits 27s shown in FIG. 1. The manifolds include the liquid supply manifold 25 and the liquid drain manifold 27 shown in FIG. 1.

[0051] The liquid supply manifold 25 and the liquid supply slit 25s form a supply path in the first main surface 21. The liquid supply manifold 25 is a supply port for the electrolyte. The liquid supply manifold 25 penetrates the first main surface 21 and the second main surface 22. The liquid supply slit 25s connects the liquid supply manifold 25 to the through-hole 20. The liquid groove may further include a liquid supply rectification section (not shown). When the liquid supply rectification section is provided in the frame 2, the liquid supply rectification section is provided along the inner periphery of the first main surface 21. When the liquid supply rectification section is provided, the liquid supply slit 25s connects the liquid supply manifold 25 and the liquid supply rectification section. The liquid supply rectification section diffuses the electrolyte flowing from the liquid supply slit 25s along the inner periphery of the first main surface 21. The liquid supply rectification section may be provided in the bipolar plate 5.

[0052] The drainage manifold 27 and the drainage slit 27s form a drainage path in the first main surface 21. The drainage manifold 27 is a drain port for the electrolyte. The drainage manifold 27 penetrates the first main surface 21 and the second main surface 22. The drainage slit 27s connects the drainage manifold 27 to the through-hole 20. The liquid groove may further include a drainage rectification section (not shown). When a drainage rectification section is provided, the drainage rectification section is provided along the inner periphery of the first main surface 21. When a drainage rectification section is provided in the frame 2, the drainage slit 27s connects the drainage manifold 27 and the drainage rectification section. The drainage rectification section collects the electrolyte flowing from the positive electrode 72 or the negative electrode 73 (described later) arranged on the bipolar plate 5 along the inner periphery of the first main surface 21 and distributes it to the drainage slit 27s. The waste liquid rectifying section may be provided on the bipolar plate 5 .

[0053] The first main surface 21 further includes a seal groove 29. The seal groove 29 is provided in an annular shape along the entire periphery of the frame 2 so that a seal member 75 ( FIG. 6 ), which will be described later, can be disposed therein. The seal groove 29 is provided so as to surround the supply path (such as the liquid supply manifold 25 and the liquid supply slit 25s) and the discharge path (such as the liquid discharge manifold 27 and the liquid discharge slit 27s) of the electrolyte.

[0054] The first main surface 21 has a plurality of recesses 4 that open to the first main surface 21. Each recess 4 is not a through hole that penetrates the first main surface 21 and the second main surface 22. Each recess 4 is a blind hole that opens to the first main surface 21 but does not open to the second main surface 22. In a plan view of the first main surface 21, each recess 4 is not integrated along the entire circumference of the frame body 2. In a plan view of the first main surface 21, each recess 4 is not annular along the entire circumference of the frame body 2. Each recess 4 is provided independently of the liquid groove. Each recess 4 is distributed and arranged at a position different from the liquid groove. Each recess 4 is provided at a distance from one another.

[0055] Each recess 4 is provided independently of the liquid groove and the manifold. Each recess 4 is provided with a gap between it and the liquid groove and the manifold. If the first main surface 21 includes a seal groove 29, each recess 4 is also provided independently of the seal groove 29. Each recess 4 is provided with a gap between it and the seal groove 29. The multiple recesses 4 are recesses other than the liquid groove and manifold that form part of the electrolyte flow path within the battery cell 7 ( FIG. 6 ), as well as the seal groove 29. In a plan view of the first main surface 21, each of the multiple recesses 4 has one opening edge. An annular groove such as the seal groove 29 has two opening edges. Therefore, an annular groove is not a recess 4.

[0056] An opening edge 40 of each recess 4 is provided on the first main surface 21. Each recess 4, including the opening edge 40, functions to generate an appropriate frictional force between itself and a member in contact with the frame body 2. For example, when assembling the battery cells 7 described below, a frictional force is generated between adjacent frame bodies 2, which can prevent misalignment of the frame bodies 2. When a diaphragm 71 described below is disposed between the frame body 2 and the adjacent frame body 2, it can also prevent misalignment of the frame body 2 and the diaphragm 71.

[0057] The ratio of the major axis length to the minor axis length of the opening edge 40 of the recess 4 (major axis length / minor axis length) is, for example, 0.5 or more and 2.0 or less. If the opening edge 40 is a perfect circle in a plan view of the first main surface 21, the above ratio is 1. The closer the ratio of the major axis length to the minor axis length of the opening edge 40 is to 1, the closer the shape of the opening edge 40 of the recess 4 is to a perfect circle. Note that the ratio of the major axis length to the minor axis length of the liquid groove and seal groove 29 exceeds 2.0. In the liquid groove and seal groove 29, the minor axis length is the shortest length of the opening edge in a plan view of the first main surface 21. The major axis length is the maximum length along a direction perpendicular to the minor axis length.

[0058] At least one of the recesses 4 may have a depth D4 of 0.1% to 10% of the maximum thickness T2 of the frame 2. The depth D4 is the distance from a line connecting two opposing points on the opening edge 40 of the recess 4 to the deepest point within the range of this reference line. A recess 4 having a depth D4 within the above range is sufficiently shallow compared to the liquid groove and the seal groove 29. If the depth D4 is 0.1% or more of the maximum thickness T2, the opening edge 40 can be provided on the first main surface 21. This allows for a large frictional force to be generated between the frame 2 and a member in contact with the frame 2. If the depth D4 is 10% or less of the maximum thickness T2, the strength of the frame 2 is sufficiently maintained. If a diaphragm 71 is disposed between the frame 2 and an adjacent frame 2, if the depth D4 is 10% or less of the maximum thickness T2, the diaphragm 71 can be easily prevented from entering the recess 4. The depth D4 may be 0.3% or more and 10% or less, or 0.5% or more and 10% or less, of the maximum thickness T2.

[0059] The number of recesses 4 having a depth D4 within the above range is, for example, 50% or more of the total number of recesses 4. The number of recesses 4 having a depth D4 within the above range may be 70% or more, 80% or more, or 90% or more of the total number of recesses 4. All recesses 4 may have a depth D4 within the above range.

[0060] The depth D4 is, for example, 0.05 mm or more and 1.0 mm or less. If the depth D4 is 0.05 mm or more, the first main surface 21 can be provided with an opening edge 40. This allows a large frictional force to be generated between the frame body 2 and a member in contact with the frame body 2. If the depth D4 is 1.0 mm or less, the strength of the frame body 2 is sufficiently maintained. When a diaphragm 71 is disposed between the frame body 2 and an adjacent frame body 2, if the depth D4 is 1.0 mm or less, it is easy to prevent the diaphragm 71 from entering the recess 4. The depth D4 may be 0.08 mm or more and 0.8 mm or less, or 0.1 mm or more and 0.5 mm or less.

[0061] At least one of the multiple recesses 4 may have a curved opening edge 40 when the frame 2 is viewed in plan. When the opening edge 40 has a curved planar shape, the planar shape of the opening edge 40 is rounded and does not have any angular portions. As a result, components in contact with the frame 2 are less likely to be damaged by the opening edge 40. The curved shape may be, for example, circular or elliptical. The number of recesses 4 having a curved opening edge 40 may be, for example, 50% or more of the total number of recesses 4. The number of recesses 4 having a curved opening edge 40 may be 70% or more, 80% or more, or 90% or more of the total number of recesses 4. All recesses 4 may have a curved opening edge 40. In this example, as shown in FIG. 1 , the planar shape of the opening edges 40 of all recesses 4 is circular. At least one of the multiple recesses 4 may include an opening edge 40 having a polygonal planar shape.

[0062] At least one of the plurality of recesses 4 is 7 mm ２ 7855mm or more ２ The opening area is the area of ​​the opening of the recess 4 in a plan view of the first main surface 21. ２ If the opening area of ​​the recess 4 is 7855 mm or more, the opening edge 40 can be provided on the first main surface 21. This allows a large friction force to be generated between the frame body 2 and the member in contact with the frame body 2. ２ If the diaphragm 71 is disposed between the frame 2 and the adjacent frame 2, the opening area of ​​the recess 4 is 7855 mm ２If the opening area is 19 mm or less, it is easy to prevent the diaphragm 71 from entering the recess 4. ２ Over 1963mm ２ or less, or 19 mm ２ 707mm or more ２ or less. In other words, the circle-equivalent diameter of the opening area of ​​the recess 4 may be 3 mm or more and 100 mm or less, 5 mm or more and 50 mm or less, or 5 mm or more and 30 mm or less. The circle-equivalent diameter refers to the diameter of a perfect circle having the opening area of ​​the recess 4. The number of recesses 4 having an opening area in the above range is, for example, 50% or more of the total number of recesses 4. The number of recesses 4 having an opening area in the above range may be 70% or more, 80% or more, or 90% or more of the total number of recesses 4. All recesses 4 may have an opening area in the above range.

[0063] The multiple recesses 4 are, for example, dispersed across the first main surface 21. Dispersed recesses 4 means that the multiple recesses 4 are not unevenly distributed across the first main surface 21, but are uniformly distributed across the entire first main surface 21. Adjacent recesses 4 are spaced apart from one another at a certain distance. Adjacent recesses 4 are spaced apart from one another at a distance of, for example, 5 mm to 50 mm. This distance is the shortest distance between the opening edges 40 of adjacent recesses 4. If the distance is 5 mm or greater, the number of recesses 4 is not too large, and sufficient strength of the frame 2 is ensured. If the distance is 50 mm or less, frictional force is likely to be generated between the frame 2 and a member in contact with it. The distance may be 6 mm to 45 mm, or 10 mm to 40 mm.

[0064] 1, the interval A between adjacent recesses 4 on the left and right sides of the paper is equal, and the interval B between adjacent recesses 4 on the top and bottom sides of the paper is equal. The interval A is larger than the interval B. The intervals A and B may be equal, or the interval A may be smaller than the interval B. The recesses 4 may be arranged randomly over the entire first main surface 21.

[0065] The recesses 4 may be arranged on the first main surface 21 with the same size and shape, or may be arranged with recesses 4 with different sizes and shapes. As shown in FIGS. 1 and 2, the size of the recesses 4 includes the depth D4 and opening area of ​​the recesses 4. FIG. 1 shows an example in which the recesses 4 with the same size and shape are arranged regularly. However, in other embodiments of the present disclosure, the recesses 4 with the same size and shape may be arranged randomly. Recesses 4 with different sizes and shapes may also be included. The multiple recesses 4 may include pairs of recesses 4 with different intervals between adjacent recesses 4.

[0066] The number of recesses 4 is, for example, 10 to 250. If the number of recesses 4 is 10 or more, a large frictional force can be generated between the frame body 2 and a member in contact with the frame body 2. If the number of recesses 4 is 250 or less, the strength of the frame body 2 is sufficiently ensured. The number of recesses 4 may be 15 to 230, 20 to 200, or 30 to 180.

[0067] The maximum width W2 of the four-piece region 11 is the longest distance between the outer peripheral surface 23 and the inner peripheral surface 24 in the piece region 11 (the distance between the outer peripheral edge 23e and the inner peripheral edge 24e). The region extending from the outer peripheral edge 23e of the first main surface 21 to within 50% of the maximum width W2 of each piece region 11 is called the outer peripheral region. The region extending from the inner peripheral edge 24e of the first main surface 21 to within 50% of the maximum width W2 of each piece region 11 is called the inner peripheral region.

[0068] At least one of the plurality of recesses 4 is provided, for example, in the outer peripheral region. Providing the recesses 4 in the outer peripheral region makes it easier to prevent misalignment between adjacent frames 2 or misalignment between the frame 2 and the diaphragm 71. When the recesses 4 are provided in the outer peripheral region, the outer peripheral region includes the vicinity of the outer peripheral edge 23e, so that excess electrolyte extending up to the vicinity of the outer peripheral edge 23e can be stored in the recesses 4. The vicinity of the outer peripheral edge 23e refers to a region within 25% of the maximum width W2 of the frame 2 from the outer peripheral edge 23e. At least one of the plurality of recesses 4 may be provided within 40% of the maximum width W2 from the outer peripheral edge 23e, or may even be provided in a region within 30% of the maximum width W2.

[0069] The number of recesses 4 provided in the outer peripheral region is, for example, 40% to 80% of the total number of recesses 4. When 40% or more of the total number of recesses 4 are provided in the outer peripheral region, it is easier to prevent misalignment between adjacent frames 2 or misalignment between the frame 2 and the diaphragm 71. When 80% or less of the total number of recesses 4 are provided in the outer peripheral region, it is possible to prevent misalignment between frames 2 that may occur in the inner peripheral region of the frame 2. In other words, when more than 20% of the total number of recesses 4 are provided in the inner peripheral region, it is possible to prevent misalignment between frames 2 that may occur in the inner peripheral region of the frame 2. The number of recesses 4 provided in the outer peripheral region may be 45% to 75% or 50% to 70% of the total number of recesses 4. Recesses 4 provided so as to straddle the boundary between the outer peripheral region and the inner peripheral region are recesses 4 provided in both the outer peripheral region and the inner peripheral region.

[0070] At least one of the multiple recesses 4 is provided, for example, in the inner circumferential region. Providing the recess 4 in the inner circumferential region prevents misalignment of the frames 2 relative to each other, which can occur in the inner circumferential region. Even when the outer peripheral edge of the diaphragm 71 is located in the inner circumferential region, misalignment between the frame 2 and the diaphragm 71 can be prevented. Providing the recess 4 in the inner circumferential region includes the vicinity of the inner circumferential edge 24e, so that excess electrolyte near the inner circumferential edge 24e can be stored in the recess 4. The vicinity of the inner circumferential edge 24e refers to a region within 25% of the maximum width W2 of the frame 2 from the inner circumferential edge 24e. At least one of the multiple recesses 4 may be provided within 40% of the maximum width W2 from the inner circumferential edge 24e, or even within 30%.

[0071] The number of recesses 4 provided in the inner peripheral region is, for example, more than 20% and less than 60% of the total number of recesses 4. When more than 20% of the total number of recesses 4 are provided in the inner peripheral region, it is easier to prevent misalignment between the frame bodies 2 that may occur in the inner peripheral region. When less than 60% of the total number of recesses 4 are provided in the inner peripheral region, it is possible to prevent misalignment between the frame bodies 2 in the outer peripheral region. In other words, when 40% or more of the total number of recesses 4 are provided in the outer peripheral region, it is possible to prevent misalignment between the frame bodies 2 in the outer peripheral region. The number of recesses 4 provided in the inner peripheral region may be 25% or more and 55% or less, more than 25% and less than 55%, 30% or more and 50% or less, or more than 30% and less than 50% of the total number of recesses 4.

[0072] At least one of the plurality of recesses 4 is provided, for example, near each of the liquid supply manifolds 25, 26 and the liquid discharge manifolds 27, 28. The vicinity of each of the liquid supply manifolds 25, 26 and the liquid discharge manifolds 27, 28 refers to an area on the first main surface 21 that is a predetermined length from the opening edge of each of the liquid supply manifolds 25, 26 and the liquid discharge manifolds 27, 28. The predetermined length is 50% of the diameter R of each of the manifolds 25, 26, 27, 28. Providing recesses 4 near each of the liquid supply manifolds 25, 26 and the liquid discharge manifolds 27, 28 can prevent misalignment between the liquid supply manifolds 25, 26 and the liquid discharge manifolds 27, 28 of adjacent frames 2. At least one of the plurality of recesses 4 may be provided in an area extending from the opening edge of each of the liquid supply manifolds 25, 26 and the liquid discharge manifolds 27, 28 to a point that is 40% of the diameter R. A plurality of recesses 4 may be provided near each of the liquid supply manifolds 25, 26 and the liquid discharge manifolds 27, 28. As illustrated in Fig. 1, the plurality of recesses 4 may be provided at symmetrical positions with respect to each of the liquid supply manifolds 25, 26 and the liquid discharge manifolds 27, 28.

[0073] At least one of the recesses 4 is provided, for example, near the liquid groove. The vicinity of the liquid groove refers to a region from the opening edge of the liquid groove to a point having a length eight times the minimum width of the liquid groove. At least one of the recesses 4 is provided, for example, near each of the liquid supply slits 25s and the liquid drain slits 27s. The vicinity of each of the liquid supply slits 25s and the liquid drain slits 27s refers to a region from the opening edge of each of the liquid supply slits 25s and the liquid drain slits 27s to a point having a length eight times the minimum width of each of the slits 25s and 27s. In FIG. 1 , the multiple recesses 4 provided near each of the liquid supply slits 25s and the liquid drain slits 27s include recesses 4 provided in the inner peripheral region and recesses 4 provided in the outer peripheral region. When recesses 4 are provided near each of the liquid supply slits 25s and the liquid drain slits 27s, excess electrolyte from the liquid supply slit 25s or the liquid drain slit 27s can be collected in the recesses 4. At least one of the recesses 4 may be provided in a region extending from the opening edge of each of the liquid supply slits 25s and the liquid drainage slits 27s to a point having a length five times the minimum width of each of the slits 25s and 27s. Multiple recesses 4 may be provided near each of the liquid supply slits 25s and the liquid drainage slits 27s. For example, multiple recesses 4 may be provided at predetermined intervals along the length of each of the liquid supply slits 25s and the liquid drainage slits 27s. If the frame 2 includes a liquid supply rectification unit and a liquid drainage rectification unit (not shown), at least one of the recesses 4 may be provided near each of the liquid supply rectification unit and the liquid drainage rectification unit. The vicinity of each of the liquid supply rectification unit and the liquid drainage rectification unit refers to a region extending from the opening edge of each of the liquid supply rectification unit and the liquid drainage rectification unit to a point having a length twice the minimum width of each rectification unit.

[0074] At least one of the multiple recesses 4 is provided, for example, near the seal groove 29. The vicinity of the seal groove 29 refers to the region from the opening edge of the seal groove 29 to a point having a length eight times the maximum width of the seal groove 29. The seal groove 29 is provided, for example, in the outer peripheral region. In FIG. 1 , the recesses 4 provided near the seal groove 29 are also recesses 4 provided in the outer peripheral region. When a recess 4 is provided near the seal groove 29, the electrolyte can be stored in the recess 4 near the seal groove 29, making it easier to prevent the electrolyte from leaking between the frame 2 and the adjacent frame 2 to the outside of the battery cell 7. At least one of the multiple recesses 4 may be provided in the region from the opening edge of the seal groove 29 to a point having a length five times the maximum width of the seal groove 29. Multiple recesses 4 may be provided near the seal groove 29. For example, multiple recesses 4 may be provided at predetermined intervals along the length of the seal groove 29.

[0075] At least two of the plurality of recesses 4 are provided symmetrically with respect to, for example, the through hole 20. Here, "symmetrically" means line symmetry with respect to the symmetry axis C in FIG. 1 , line symmetry with respect to the symmetry axis D, or both. This makes it easy to prevent misalignment of the frame bodies 2 by the recesses 4. When a diaphragm 71 is disposed between the frame body 2 and an adjacent frame body 2, it also makes it easy to prevent misalignment between the frame body 2 and the diaphragm 71. As exemplified in FIG. 1 , a plurality of pairs of recesses 4 may be provided at positions symmetrically with respect to the through hole 20.

[0076] The second main surface 22, like the first main surface 21, has supply and discharge paths for the electrolyte. The supply and discharge paths are configured by liquid grooves and manifolds provided in the second main surface 22. In other words, the second main surface 22 has liquid grooves and manifolds that form part of the electrolyte flow path within the battery cell 7 (FIG. 6). The liquid grooves include the liquid supply slits 26s and the liquid drain slits 28s shown in FIG. 1. The liquid grooves may further include a liquid supply rectification section and a liquid drainage rectification section (not shown). The liquid supply rectification section and the liquid drainage rectification section may be provided in the bipolar plate 5. The manifolds include the liquid supply manifold 26 and the liquid drainage manifold 28 shown in FIG. 1.

[0077] The liquid supply manifold 26 and the liquid supply slit 26s constitute the supply channel of the second main surface 22. The liquid drain manifold 28 and the liquid drain slit 28s constitute the discharge channel of the second main surface 22. In FIG. 1 , the liquid supply slit 26s and the liquid drain slit 28s are indicated by dashed lines. If the electrolyte flowing through the supply channel and discharge channel of the first main surface 21 is a positive electrode electrolyte, the electrolyte flowing through the supply channel and discharge channel of the second main surface 22 is a negative electrode electrolyte. If the electrolyte flowing through the supply channel and discharge channel of the first main surface 21 is a negative electrode electrolyte, the electrolyte flowing through the supply channel and discharge channel of the second main surface 22 is a positive electrode electrolyte. The second main surface 22 may or may not be provided with a seal groove (not shown).

[0078] The second main surface 22 may or may not have a recess, similar to the recess 4 provided in the first main surface 21. The second main surface 22 in this example does not have a recess.

[0079] The frame 2 has a notch 35 provided at a corner defined by the first main surface 21 and the inner peripheral surface 24. The notch 35 has a function of supporting the bipolar plate 5, which will be described later. The notch 35 forms a step into which the bipolar plate 5 is fitted. Fitting the bipolar plate 5 into this step makes it easy to determine the position of the bipolar plate 5 relative to the frame 2. The surface that forms the notch 35 is part of the inner peripheral surface 24.

[0080] The frame 2 is made of an electrically insulating material. The electrically insulating material is, for example, a resin such as a thermoplastic resin. Specific examples of the electrically insulating material include one type of resin selected from the group consisting of vinyl chloride, polypropylene, polyethylene, fluororesin, epoxy, acrylonitrile butadiene styrene, vinylidene chloride, polyamide, polyester, polystyrene, acrylic, polyvinyl alcohol, diacetate, triacetate, and polycarbonate. The frame 2 is an injection-molded product obtained by injection molding.

[0081] <<Variation 1>> As shown in FIG. 3 , all of the recesses 4 may be provided in the inner circumferential region. The recesses 4 provided in the inner circumferential region may be provided at predetermined intervals along the entire circumference of the frame 2. The recesses 4 provided in the inner circumferential region may include pairs of recesses 4 provided at symmetrical positions across the through hole 20. The recesses 4 provided in the inner circumferential region can prevent misalignment of the frames 2 that may occur in the inner circumferential region. When the outer peripheral edge of the diaphragm 71 is located in the inner circumferential region, the recesses 4 provided in the inner circumferential region can prevent misalignment between the frame 2 and the diaphragm 71. Because the inner circumferential region includes the vicinity of the inner circumferential edge 24e, the recesses 4 provided in the inner circumferential region can collect excess electrolyte in the recesses 4 near the inner circumferential edge 24e. In the first modified example, all of the recesses 4 are arranged inside the liquid supply manifold 25 , part of the liquid supply slit 25 s , the liquid discharge manifold 27 , part of the liquid discharge slit 27 s , and the seal groove 29 .

[0082] <<Modification 2>> As shown in FIG. 4 , all of the recesses 4 may be provided in the outer peripheral region. The recesses 4 in the outer peripheral region may be provided at predetermined intervals along the entire circumference of the frame 2. The recesses 4 in the outer peripheral region may include pairs of recesses 4 provided symmetrically across the through-hole 20. The recesses 4 in the outer peripheral region can prevent misalignment of the frames 2 that may occur in the outer peripheral region. When the outer peripheral edge of the diaphragm 71 is located in the outer peripheral region, the recesses 4 in the outer peripheral region can prevent misalignment between the frame 2 and the diaphragm 71. Because the outer peripheral region includes the vicinity of the outer peripheral edge 23e, the recesses 4 in the outer peripheral region can collect excess electrolyte that extends to the vicinity of the outer peripheral edge 23e. In Modification 2, all of the recesses 4 are located outside the liquid supply manifold 25, the liquid supply slit 25s, the liquid discharge manifold 27, the liquid discharge slit 27s, and the seal groove 29.

[0083] <<Variation 3>> As shown in Fig. 5 , all of the multiple recesses 4 may be provided near the seal groove 29. The multiple recesses 4 provided near the seal groove 29 may be provided at predetermined intervals along the length of the seal groove 29. The multiple recesses 4 provided near the seal groove 29 may include pairs of recesses 4 provided at symmetrical positions with the seal groove 29 in between. In other words, the multiple recesses 4 provided near the seal groove 29 may include pairs of recesses 4 provided at symmetrical positions with the seal groove 29 in between. The multiple recesses 4 provided near the seal groove 29 can collect the electrolyte in the recesses 4 near the seal groove 29, making it easier to prevent the electrolyte from leaking between the frame body 2 and the adjacent frame body 2 to the outside of the battery cell 7.

[0084] <Cell Frame> As shown in Figures 1 and 2, the cell frame 1 includes the frame body 2 and the bipolar plate 5 described above. The bipolar plate 5 is disposed in the through-hole 20 of the frame body 2 so that its outer peripheral edge is supported by the frame body 2. The cell frame 1 is formed by fitting the bipolar plate 5 into the through-hole 20 of the frame body 2. The bipolar plate 5 includes a thin-walled portion 51 formed thinner than other portions at the portion supported by the frame body 2. This thin-walled portion 51 is fitted into a recess defined by the notch 35 of the frame body 2. The cell frame 1 may be formed by injection molding the frame body 2 around the outer periphery of the bipolar plate 5.

[0085] As shown in FIG. 2 , the thickness of the bipolar plate 5 is thinner than the thickness of the frame 2. When the bipolar plate 5 is placed in the through-hole 20, a recess is formed between the inner circumferential surface 24 of the frame 2 and the surface of the bipolar plate 5. This recess is provided on both the first and second surfaces of the bipolar plate 5. A positive electrode 72 is placed in the recess formed by the inner circumferential surface 24 of the frame 2, i.e., the inner circumferential surface of the notch 35 in this example, and the first surface of the bipolar plate 5. A negative electrode 73 is placed in the recess formed by the inner circumferential surface 24 of the frame 2 and the second surface of the bipolar plate 5. In FIG. 2 , the positive electrode 72 and the negative electrode 73 are indicated by two-dot chain lines.

[0086] <RF Battery System> An RF battery system 6 according to an embodiment will be described with reference to Figures 6 and 7. The RF battery system 6 is one type of electrolyte circulation type storage battery system. The RF battery system 6 includes battery cells 7 and a circulation mechanism 8 that circulates electrolyte through the battery cells 7. The RF battery system 6 charges and discharges while supplying electrolyte to the battery cells 7. For ease of explanation, the recesses 4 of the frame 2 are not shown in Figures 6 and 7.

[0087] The RF battery system 6 is typically connected to a power generation unit 110 and a load 130 via a substation 120 and an AC / DC converter 100. The RF battery system 6 charges the power generation unit 110 as a power supply source and discharges the power from the load 130. The power generation unit 110 is, for example, a solar power generator, a wind power generator, or other general power plant. The load 130 is, for example, a power grid or a power consumer. The RF battery system 6 is used, for example, for load leveling, voltage sag compensation, emergency power supply, or output smoothing of natural energy power generation.

[0088] <Battery Cell> As shown in Fig. 6 , the battery cell 7 is separated into a positive electrode cell 7P and a negative electrode cell 7N by a diaphragm 71. A positive electrode 72 is built into the positive electrode cell 7P. A positive electrode electrolyte is circulated through the positive electrode cell 7P. The positive electrode 72 is a reaction field where an active material contained in the positive electrode electrolyte undergoes a battery reaction. A negative electrode 73 is built into the negative electrode cell 7N. A negative electrode electrolyte is circulated through the negative electrode cell 7N. The negative electrode 73 is a reaction field where an active material contained in the negative electrode electrolyte undergoes a battery reaction. The diaphragm 71 is, for example, an ion exchange membrane.

[0089] As shown in the upper diagrams of FIGS. 6 and 7 , the battery cell 7 includes a stack of a cell frame 1, a positive electrode 72, a diaphragm 71, a negative electrode 73, and another cell frame 1 stacked in this order. The battery cell 7 further includes a sealing member 75. The sealing member 75 may be annular. In each cell frame 1, the positive electrode 72 is disposed on a first surface of the bipolar plate 5, and the negative electrode 73 is disposed on a second surface of the bipolar plate 5. One battery cell 7 is formed between the bipolar plates 5 of two adjacent cell frames 1. The sealing member 75 is disposed between the frame 2 and the adjacent frame 2. The sealing member 75 is disposed in a sealing groove 29 provided in the first main surface 21. The sealing member 75 is made of a material that is easily elastically deformed, such as rubber. Such a sealing member 75 prevents leakage of electrolyte from the battery cell 7, even if the frame 2 is made of a material, such as resin, that is less elastically deformable than the sealing member 75.

[0090] <Cell Stack> Battery cells 7 are typically arranged inside a structure called a cell stack 9. As shown in the lower diagram of FIG. 7 , the cell stack 9 includes a substack 9S, two end plates 92, and a clamping mechanism 93. The cell stack 9 includes, for example, multiple substacks 9S. Each substack 9S includes a stack and two supply / discharge plates 91. As shown in the upper diagrams of FIGS. 6 and 7 , the stack is formed by stacking multiple cell frames 1, positive electrodes 72, diaphragms 71, negative electrodes 73, and other cell frames 1 in this order. As shown in the lower diagram of FIG. 7 , the supply / discharge plates 91 are arranged on both ends of the stack. A supply pipe 84 and a discharge pipe 86 of a positive electrode circulation mechanism 8P, and a supply pipe 85 and a discharge pipe 87 of a negative electrode circulation mechanism 8N, which will be described later, are connected to the supply / discharge plates 91. The multiple substacks 9S are sandwiched between the two end plates 92. The clamping mechanism 93 clamps the two end plates 92 so that they approach each other.

[0091] 6, the circulation mechanism 8 includes a positive electrode circulation mechanism 8P and a negative electrode circulation mechanism 8N. The positive electrode circulation mechanism 8P circulates the positive electrode electrolyte through the positive electrode cell 7P. The negative electrode circulation mechanism 8N circulates the negative electrode electrolyte through the negative electrode cell 7N.

[0092] The positive electrode circulation mechanism 8P includes a positive electrode electrolyte tank 82, a supply pipe 84, a discharge pipe 86, and a pump 88. The positive electrode electrolyte tank 82 stores positive electrode electrolyte. The supply pipe 84 and the discharge pipe 86 connect the positive electrode electrolyte tank 82 and the positive electrode cell 7P. The pump 88 is provided midway along the supply pipe 84 and pressure-feeds the positive electrode electrolyte in the positive electrode electrolyte tank 82 to the positive electrode cell 7P. The positive electrode electrolyte is supplied from the positive electrode electrolyte tank 82 through the supply pipe 84 to the positive electrode cell 7P and is returned from the positive electrode cell 7P through the discharge pipe 86 to the positive electrode electrolyte tank 82. Specifically, the positive electrode electrolyte that has passed through the supply pipe 84 is supplied to the positive electrode 72 from the liquid supply manifold 25 shown in the upper diagram of FIG. 7 through the liquid supply slit 25s. The positive electrode electrolyte supplied to the positive electrode 72 flows from the bottom to the top of the positive electrode 72, as indicated by the arrows in the upper diagram of FIG. 7. The positive electrode electrolyte that has flowed through the positive electrode 72 passes through the drain slit 27 s and is discharged from the drain manifold 27 to the discharge pipe 86 .

[0093] The anode circulation mechanism 8N includes an anode electrolyte tank 83, a supply pipe 85, a discharge pipe 87, and a pump 89. The anode electrolyte tank 83 stores the anode electrolyte. The supply pipe 85 and the discharge pipe 87 connect the anode electrolyte tank 83 and the anode cell 7N. The pump 89 is provided midway along the supply pipe 85 and pressure-feeds the anode electrolyte in the anode electrolyte tank 83 to the anode cell 7N. The anode electrolyte is supplied from the anode electrolyte tank 83 to the anode cell 7N through the supply pipe 85 and is returned from the anode cell 7N through the discharge pipe 87 to the anode electrolyte tank 83. Specifically, the anode electrolyte that has passed through the supply pipe 85 is supplied to the anode electrode 73 from the liquid supply manifold 26 shown in the upper diagram of FIG. 7 through the liquid supply slit 26s. The anode electrolyte supplied to the anode electrode 73 flows from the bottom to the top of the anode electrode 73, as indicated by the arrows in the upper diagram of FIG. 7. The negative electrode electrolyte that has flowed through the negative electrode 73 passes through the drain slit 28s and is discharged from the drain manifold 28 to the discharge pipe 87.

[0094] By circulating the positive electrode electrolyte to the positive electrode cell 7P and the negative electrode electrolyte to the negative electrode cell 7N, the battery cell 7 is charged and discharged in accordance with the valence change reaction of the active material ions in the electrolyte of each electrode.

[0095] The active material contained in the positive electrode electrolyte, the solvent for the positive electrode electrolyte, the active material contained in the negative electrode electrolyte, and the solvent for the negative electrode electrolyte are not particularly limited. The active material for the positive electrode electrolyte is, for example, one or more selected from the group consisting of vanadium ions, manganese ions, iron ions, polyacids, quinone derivatives, amines, and organometallic complexes. The active material for the negative electrode electrolyte is, for example, one or more selected from the group consisting of vanadium ions, titanium ions, chromium ions, polyacids, quinone derivatives, amines, and organometallic complexes. In this 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.

[0096] DESCRIPTION OF SYMBOLS 1 Cell frame 2 Frame body 2s Supply piece region 2d Discharge piece region 11 Piece region 12 Corner region 20 Through hole 21 First main surface 22 Second main surface 23 Outer peripheral surface 23e Outer peripheral edge 24 Inner peripheral surface 24e Inner peripheral edge 25, 26 Liquid supply manifold 25s, 26s Liquid supply slit (liquid groove) 27, 28 Liquid drain manifold 27s, 28s Liquid drain slit (liquid groove) 29 Seal groove 35 Notch 4 Recess 40 Opening edge 5 Bipolar plate 51 Thin portion 6 RF battery system (redox flow battery system) 7 Battery cell 7P Positive electrode cell, 7N Negative electrode cell 71 Diaphragm 72 Positive electrode, 73 Negative electrode 75 Seal member 8 Circulation mechanism 8P Positive electrode circulation mechanism, 8N Negative electrode circulation mechanism 82 Positive electrode electrolyte tank, 83 Negative electrode electrolyte tank 84, 85 Supply pipe, 86, 87 Discharge pipe 88, 89 Pump 9 Cell stack, 9S Sub-stack 91 Supply and discharge plate, 92 End plate, 93 Fastening mechanism 100 AC / DC converter, 110 Power generation unit, 120 Substation equipment, 130 Load T2 Maximum thickness W2 Maximum width D4 Depth A Spacing B Spacing C Axis of symmetry D Axis of symmetry

Claims

1. A plate-shaped frame body used in a cell frame of a battery cell, the frame body having a first main surface and a second main surface opposite to the first main surface, the first main surface having a plurality of recesses opening into the first main surface and a liquid groove forming part of a flow path for an electrolyte within the battery cell, each of the plurality of recesses being dispersed and arranged at a position different from the liquid groove.

2. A frame as described in claim 1, wherein the first main surface further comprises a seal groove provided annularly along the entire circumference of the frame in a plan view of the first main surface so that a seal member can be disposed therein.

3. A frame body according to claim 1 or 2, wherein at least one of the plurality of recesses has a depth of 0.1% to 10% of the maximum thickness of the frame body.

4. A frame body according to any one of claims 1 to 3, wherein at least one of the plurality of recesses has an opening edge having a curved shape when viewed in a plane on the first main surface.

5. A frame body as described in any one of claims 1 to 4, wherein the frame body includes four piece regions and four corner regions, each of the corner regions being located between two of the piece regions, each of the piece regions including an outer circumferential region extending inward from the outer circumferential edge of the first main surface and within 50% of the maximum width of the piece region, the maximum width of the piece region being the maximum length between the inner circumferential edge and the outer circumferential edge of each of the piece regions, and at least one of the plurality of recesses being provided in the outer circumferential region.

6. A frame body as described in claim 2, wherein the frame body includes four half regions and four corner regions, each of the corner regions being located between two of the half regions, each of the half regions including an outer peripheral region extending inward from the outer peripheral edge of the first main surface and within 50% of the maximum width of the half region, the maximum width of the half region being the maximum length between the inner peripheral edge and the outer peripheral edge of each of the half regions, the seal groove being arranged in the outer peripheral region, and at least one of the plurality of recesses being provided in the vicinity of the seal groove.

7. A frame body as described in any one of claims 1 to 6, wherein the frame body includes four piece regions and four corner regions, each of the corner regions being located between two of the piece regions, each of the piece regions including an inner peripheral region extending from the inner peripheral edge of the first main surface outwardly within 50% of the maximum width of the piece region, the maximum width of the piece region being the maximum length between the inner peripheral edge and the outer peripheral edge of each of the piece regions, and at least one of the plurality of recesses being provided in the inner peripheral region.

8. A frame body according to any one of claims 1 to 7, wherein at least two of the plurality of recesses are provided at positions symmetrical with respect to a through hole provided in the frame body.

9. A frame according to any one of claims 1 to 8, wherein at least one of the plurality of recesses is provided in the vicinity of the liquid groove.

10. A frame as described in any one of claims 1 to 9, further comprising a manifold that forms part of a flow path of the electrolyte, and at least one of the plurality of recesses is provided in the vicinity of the manifold.

11. At least one of the plurality of recesses is 7 mm ２ 7855mm or more ２ The frame according to claim 1 , having an opening area of:

12. A frame body according to any one of claims 1 to 11, wherein the number of opening edges of each recess in a plan view of the first main surface is one.

13. A cell frame comprising: a frame body according to any one of claims 1 to 12; and a bipolar plate supported by the frame body.

14. A battery cell comprising the cell frame according to claim 13.

15. A cell stack comprising the battery cell according to claim 14.

16. A redox flow battery system comprising the battery cell according to claim 14 or the cell stack according to claim 15.

Images