Tank and redox flow battery system

Abstract

A tank for retaining an electrolytic liquid in a redox flow battery system, wherein: the tank comprises a tank body that has an interior space partitioned from the exterior, and a cover member of which at least the surface is solid; the cover member is capable of floating on a liquid surface of the electrolytic liquid retained in the internal space so as to cover the liquid surface; and the area of the liquid surface that is covered by the cover member is 0.90-0.99 times inclusive the total area of the liquid surface.

Description

Tank and redox flow battery system

[0001] The present disclosure relates to a tank and a redox flow battery system. This application claims priority to Japanese Patent Application No. 2022-097117, filed on June 16, 2022. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] Patent Document 1 discloses an electrolyte tank that stores an electrolyte to be circulated and supplied to battery cells of a redox flow battery. The electrolyte tank is open to the atmosphere. An air barrier member is disposed above the electrolyte.

[0003] Japanese Patent Application Laid-Open No. 2000-012065

[0004] The tank of the present disclosure is a tank for storing an electrolyte for a redox flow battery system, and includes a tank body having an internal space isolated from the outside, and a cover member having at least a solid surface, wherein the cover member is floated on the liquid surface of the electrolyte stored in the internal space so as to cover the liquid surface, and the area covered by the cover member on the liquid surface is 0.90 to 0.99 times the total area of ​​the liquid surface.

[0005] The redox flow battery system of the present disclosure includes the tank of the present disclosure.

[0006] FIG. 1 is a schematic configuration diagram of a tank according to an embodiment. FIG. 2 is an explanatory diagram showing an example of a cover member provided on the tank according to an embodiment. FIG. 3 is an explanatory diagram showing another example of a cover member provided on the tank according to an embodiment. FIG. 4 is an explanatory diagram showing another example of a cover member provided on the tank according to an embodiment. FIG. 5 is a schematic configuration diagram of a redox flow battery system according to an embodiment. FIG. 6 is a schematic configuration diagram of a cell stack provided on the redox flow battery system according to an embodiment.

[0007] [Problem to be Solved by the Present Disclosure] It is desirable to suppress the oxidation of the electrolyte in the tank. The oxidation of the electrolyte refers to the oxidation of the active material ions in the electrolyte. When the electrolyte is oxidized, the amount of active material ions available for the battery reaction in the battery cell decreases. As a result, the energy density of the redox flow battery system can decrease.

[0008] An object of the present disclosure is to provide a tank capable of suppressing oxidation of an electrolyte stored therein. Another object of the present disclosure is to provide a redox flow battery system having a high energy density. [Advantages of the present disclosure]

[0009] The tank of the present disclosure can suppress oxidation of the electrolyte stored therein. The redox flow battery system of the present disclosure has high energy density.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0011] (1) A tank according to an embodiment of the present disclosure is a tank for storing an electrolyte solution of a redox flow battery system, and includes a tank body having an internal space isolated from the outside, and a cover member having at least a solid surface, wherein the cover member is floated on the liquid surface of the electrolyte solution stored in the internal space so as to cover the liquid surface, and the area of ​​the cover member covering the liquid surface is 0.90 to 0.99 times the total area of ​​the liquid surface.

[0012] The tank of the present disclosure has two configurations that can effectively suppress oxidation of the electrolyte solution inside the tank. The first configuration is that the internal space of the tank body is separated from the outside. Due to the first configuration, the electrolyte solution stored in the internal space is not substantially in contact with external air. Therefore, oxidation of the electrolyte solution stored in the internal space due to contact with external oxygen is significantly suppressed. The second configuration is that the tank is provided with a cover member that floats on the surface of the electrolyte solution. The cover member prevents contact between the electrolyte solution and oxygen that may be contained in the internal space. Due to the second configuration, oxidation of the electrolyte solution is suppressed even if a trace amount of oxygen is contained in the internal space. If the surface of the cover member is solid, the contact surface of the cover member with the electrolyte solution is well secured, making it easier to suppress oxidation of the electrolyte solution.

[0013] (2) In the tank of (1) above, the maximum horizontal length of the tank body may be longer than the height of the tank body.

[0014] If a cover member is not placed on the electrolyte surface, the electrolyte surface is exposed to the gas in the internal space. The flow resistance of the electrolyte surface exposed to the gas and its vicinity is smaller than the flow resistance inside the electrolyte. The interior of the electrolyte includes the contact surface of the electrolyte with the inner surface of the tank body and its vicinity. Due to the difference in flow resistance, the flow rate is fast at the electrolyte surface and its vicinity and slow inside the electrolyte, resulting in uneven flow of the electrolyte. If the maximum horizontal length of the tank body is longer than the height of the tank body, if a cover member is not placed on the electrolyte surface, the area of ​​the electrolyte surface exposed to the gas in the internal space is relatively large, making the flow of the electrolyte more likely to be uneven. If a cover member is floating on the electrolyte surface, the flow resistance of the electrolyte surface and its vicinity increases, making the flow of the electrolyte more likely to be uniform, even if the maximum horizontal length of the tank body is longer than the height of the tank body. When the flow of the electrolyte becomes uniform, the electrolyte stored in the internal space is utilized efficiently.

[0015] (3) In the tank of (1) or (2) above, the cover member may include a plurality of divided pieces.

[0016] In the configuration (3) above, the size of each divided piece is adjustable. This allows for easier preparation of the cover member compared to a single cover member, and provides greater flexibility in packaging the cover member during transportation and storage. Multiple divided pieces make it easier to position the cover member above the surface of the electrolyte.

[0017] (4) In the tank of (3) above, the area covered by each of the plurality of divided pieces may be 0.002 times or more and less than 0.99 times the total area of ​​the liquid surface.

[0018] If the segments are too small, they may be displaced from their predetermined positions due to the flow of the electrolyte. If the segments are too large, it is difficult to position them above the surface of the electrolyte. In the configuration (4) above, the segments are easily positioned above the surface of the electrolyte, and the segments placed above the surface of the electrolyte are less likely to be displaced from their predetermined positions.

[0019] (5) In the tank of (3) or (4) above, each of the plurality of divided pieces may be a plate material.

[0020] The divided pieces made of plate material can easily ensure a large contact area with the electrolyte. In the configuration (5) above, all the divided pieces are made of plate material, which can easily suppress oxidation of the electrolyte.

[0021] (6) In the tank of (5) above, the shape of the plate may be rectangular or hexagonal.

[0022] In the case of rectangular or hexagonal plates, it is easy to arrange the plates without gaps between them. In the configuration (6), it is easy to arrange the plates without gaps between them, and oxidation of the electrolyte is easily suppressed.

[0023] (7) In the tank of (3) or (4) above, each of the plurality of divided pieces may be a plate material, and the shape of the plate material may be hexagonal.

[0024] The divided pieces made of plate material can easily ensure a large contact area with the electrolyte. The hexagonal plate material makes it easy to arrange multiple plate materials without gaps and to stably maintain the arranged state of multiple plate materials. In the configuration (7) above, multiple plate materials can easily be arranged in predetermined positions without gaps, and oxidation of the electrolyte can easily be suppressed.

[0025] (8) In the tank of (1) or (2) above, the cover member may be a single plate material.

[0026] In the above configuration (8), a large contact area between the cover member and the electrolyte is easily ensured, and oxidation of the electrolyte is easily suppressed.

[0027] (9) In the tank of any one of (1) to (8) above, the tank body may be provided with an intake port and an exhaust port for circulating a non-oxidizing gas in the internal space.

[0028] In the above configuration (9), a non-oxidizing gas can be circulated in the internal space, and oxidation of the electrolyte stored in the internal space is easily suppressed.

[0029] (10) A redox flow battery system according to an embodiment of the present disclosure includes the tank according to any one of (1) to (9) above.

[0030] The redox flow battery system of the present disclosure includes the tank of the present disclosure, which can suppress oxidation of the electrolyte in the tank and suppress a decrease in the amount of active material ions available for the battery reaction in the battery cell, resulting in a high energy density.

[0031] (11) In the redox flow battery system of (10) above, the electrolyte may be stored in the internal space, and the tank body may have a gas phase space in the internal space above the cover member in which a non-oxidizing gas is circulated.

[0032] In the above configuration (11), oxidation of the electrolyte stored in the internal space is easily suppressed.

[0033] [Details of the embodiments of the present disclosure] Specific examples of the tank 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, the redox flow battery system may be referred to as an "RF battery system."

[0034] <Tank> A tank 1 according to an embodiment will be described with reference to Fig. 1 to Fig. 4. The tank 1 according to the embodiment is a positive electrode tank 104 for storing a positive electrode electrolyte 106 or a negative electrode tank 105 for storing a negative electrode electrolyte 107 of an RF battery system 100 (Fig. 5) described below. In the following description of the tank 1, the positive electrode electrolyte 106 and the negative electrode electrolyte 107 shown in Fig. 5 will not be distinguished from each other, and will simply be referred to as "electrolyte 10." Fig. 1 shows a state in which the electrolyte 10 is stored.

[0035] As shown in Fig. 1, the tank 1 comprises a tank body 2 and a cover member 3. One of the features of the tank 1 is that the tank body 2 comprises an internal space 20 separated from the outside, and the cover member 3 floats on the surface of the electrolyte solution 10 stored in the internal space 20. The tank body 2 and the cover member 3 will be described in detail below. The tank 1 shown in Fig. 1 is shown in a cross section taken along a plane along the height direction of the tank body 2. The tank 1 shown in Figs. 2 to 4 is shown in a cross section taken along the A-A section in Fig. 1.

[0036] <Tank Body> As shown in FIG. 1 , the tank body 2 is a container having an internal space 20 in which the electrolyte solution 10 is stored. The tank body 2 is a columnar body. The columnar body is, for example, a prismatic body or a cylindrical body. The prismatic body is, for example, a quadrangular prism. The quadrangular prism includes a rectangular parallelepiped and a cube. The planar shape of the two opposing faces of the quadrangular prism may be a quadrangle other than a square or a rectangle, such as a rhombus or a trapezoid. The tank body 2 has, for example, a uniform cross-sectional shape in the first direction D1 of the tank body 2. The tank body 2 having a uniform cross-sectional shape in the first direction D1 is, for example, a rectangular parallelepiped, a cube, or a cylindrical body. The shape of the tank body 2 in this example is a rectangular parallelepiped. In this example, the internal space 20 of the tank body 2 is also a rectangular parallelepiped.

[0037] The tank body 2 has a first direction D1, a second direction D2, and a third direction D3 represented by a three-dimensional Cartesian coordinate system. In this example, the first direction D1 is the longest direction of the tank body 2. In this example, the first direction D1 is also the longest direction of the internal space 20 of the tank body 2. In this example, the first direction D1 is the horizontal direction. In this example, the second direction D2 is the width direction of the tank body 2. In this example, the second direction D2 is also the width direction of the internal space 20 of the tank body 2. In FIG. 1 , the second direction D2 is a direction perpendicular to the plane of the paper. In this example, the third direction D3 is the height direction of the tank body 2. In this example, the third direction D3 is also the height direction of the internal space 20 of the tank body 2. In this example, the tank body 2 is disposed horizontally. That is, in this example, the maximum horizontal length of the tank body 2 is longer than the height of the tank body 2. In this example, the second direction D2 and the third direction D3 are perpendicular to the first direction D1. In this example, the second direction D2 and the third direction D3 are perpendicular to each other.

[0038] As shown in FIGS. 1 and 2 , the tank body 2 of this embodiment includes a first end wall 21, a second end wall 22, an upper wall 23, a lower wall 24, and two side walls 25, 25. The first end wall 21 and the second end wall 22 face each other in a first direction D1 as shown in FIGS. 1 and 2 . The upper wall 23 and the lower wall 24 face each other in a third direction D3 as shown in FIG. 1 . The two side walls 25, 25 face each other in a second direction D2 as shown in FIG. 2 . The thicknesses of the first end wall 21, the second end wall 22, the upper wall 23, the lower wall 24, and the two side walls 25, 25 can be selected as appropriate. The internal space 20 is a space surrounded by the first end wall 21, the second end wall 22, the upper wall 23, the lower wall 24, and the two side walls 25, 25. The internal space 20 is isolated from the outside, preventing air from entering the internal space 20 from the outside. The first end wall 21, the second end wall 22, the upper wall 23, the lower wall 24, and the two side walls 25, 25 each prevent the electrolyte 10 stored in the internal space 20 from coming into contact with the outside air.

[0039] The first length of the tank body 2 in the first direction D1 is, for example, 4.5 m or more and 13 m or less. The first length is the length between the outer surfaces of the first end wall 21 and the second end wall 22 shown in FIGS. 1 and 2 . When the first length is 4.5 m or more, a large internal space 20 is ensured, and a large capacity of the electrolyte 10 is ensured. When the first length is 13 m or less, excessive enlargement of the tank body 2 is suppressed. The first length may further be 4.5 m or more and 12 m or less, 5 m or more and 11.5 m or less, or 6 m or more and 10 m or less.

[0040] The second length of the tank body 2 in the second direction D2 is, for example, 1 m or more and 3 m or less. The second length is the length between the outer surfaces of the two side walls 25, 25 facing each other in the second direction D2 shown in FIG. 2. When the second length is 1 m or more, a large internal space 20 is ensured, and a large capacity of the electrolyte 10 is ensured. When the second length is 3 m or less, excessive enlargement of the tank body 2 is suppressed. The second length may further be 1.5 m or more and 2.5 m or less.

[0041] The third length of the tank body 2 in the third direction D3 is, for example, 1 m or more and 3 m or less. The third length is the length between the outer surfaces of the two upper walls 23 and the lower wall 24 facing each other in the third direction D3 shown in FIG. 1 . When the third length is 1 m or more, a large internal space 20 is ensured, and a large capacity of the electrolyte 10 is ensured. When the third length is 3 m or less, excessive enlargement of the tank body 2 is suppressed. The third length may further be 1.5 m or more and 2.5 m or less.

[0042] The tank body 2 having a rectangular parallelepiped shape may be, for example, a 20-foot container-type or 40-foot container-type tank conforming to ISO standards. In the 40-foot container-type tank body 2, the first length is 12,192 mm, the second length is 2,438 mm, and the third length is 2,591 mm. In the 40-foot high-cube container-type tank body 2, the first length is 12,192 mm, the second length is 2,438 mm, and the third length is 2,896 mm. The container-type tank body 2 is easy to install and transport.

[0043] The inner surface of the tank body 2 is made of resin or rubber that is resistant to the electrolyte 10. The resin is, for example, polyvinyl chloride, polypropylene, polyethylene, polytetrafluoroethylene, or a vinyl fluoride compound. The rubber is, for example, natural rubber, chloroprene rubber, butyl rubber, ethylene propylene rubber, silicone rubber, or fluororubber.

[0044] 1, the tank body 2 has an inlet 26 for the electrolyte 10 and an outlet 27 for the electrolyte 10. The inlet 26 and the outlet 27 are provided apart from each other in a first direction D1. The flow of the electrolyte 10 will be described later.

[0045] The inlet 26 is an open end 5A of a first pipe 5, which will be described later. The first pipe 5 penetrates the upper wall 23 and extends from the outside of the tank body 2 into the internal space 20. The inlet 26 is provided within the internal space 20. The opening direction of the inlet 26 is the third direction D3. The shape of the inlet 26 can be selected as appropriate.

[0046] The outlet 27 is an open end 6B of a second pipe 6, which will be described later. The second pipe 6 penetrates the upper wall 23 and extends from the outside of the tank body 2 into the internal space 20. The outlet 27 is provided within the internal space 20. The opening direction of the outlet 27 is the third direction D3. The shape of the outlet 27 can be selected as appropriate.

[0047] The length between the inlet 26 and the outlet 27 is, for example, 4 m or more and 11.5 m or less. The length between the inlet 26 and the outlet 27 is the shortest length connecting the central axis of the inlet 26 and the central axis of the outlet 27. When the length is 4 m or more, the inlet 26 and the outlet 27 are far apart, which makes it easier to efficiently use the electrolyte 10 in the tank body 2. When the length is 11.5 m or less, excessive enlargement of the tank body 2 is suppressed. The length may further be 4 m or more and 11 m or less, 4.5 m or more and 11 m or less, or particularly 5.5 m or more and 9.5 m or less.

[0048] 1, the tank body 2 has an intake port 28 and an exhaust port 29 for circulating a non-oxidizing gas in the internal space 20. The intake port 28 and the exhaust port 29 are provided apart from each other in the first direction D1. The circulation of the non-oxidizing gas will be described later.

[0049] The intake port 28 is an open end 8A of a third pipe 8, which will be described later. In this example, the third pipe 8 penetrates the upper wall 23 and extends from the outside of the tank body 2 into the internal space 20. The intake port 28 is provided in the internal space 20. In this example, the opening direction of the intake port 28 is the third direction D3. The shape of the intake port 28 can be selected as appropriate.

[0050] The exhaust port 29 is an open end 9B of the fourth pipe 9, which will be described later. In this example, the fourth pipe 9 penetrates the upper wall 23 and extends from the outside of the tank body 2 into the internal space 20. The exhaust port 29 is provided in the internal space 20. In this example, the opening direction of the exhaust port 29 is the third direction D3. The shape of the exhaust port 29 can be selected as appropriate.

[0051] <Cover Member> As shown in FIG. 1 , the cover member 3 is floated on the surface of the electrolyte solution 10 stored in the internal space 20 of the tank body 2 so as to cover the liquid surface of the electrolyte solution 10. The specific gravity of the cover member 3 is smaller than that of the electrolyte solution 10. The specific gravity of the cover member 3 is, for example, 0.3 to 0.99, where the specific gravity of the electrolyte solution 10 is 1. The specific gravity of the cover member 3 is larger than the specific gravity of the non-oxidizing gas circulated in the gas phase space 20G described below. The cover member 3 is a member independent of the tank body 2. The cover member 3 is not fixed to the tank body 2. The liquid level of the electrolyte solution 10 can fluctuate up and down within the internal space 20. The cover member 3 can follow the fluctuations in the liquid level of the electrolyte solution 10.

[0052] The cover member 3 is a member that prevents oxidation of the electrolyte solution 10 stored in the internal space 20, and in particular prevents contact between the electrolyte solution 10 and oxygen that may be contained in the internal space 20. At least the surface of the cover member 3 is solid. The entire cover member 3 may be solid, or only the surface may be solid so as to surround the gas. If the surface of the cover member 3 is solid, the contact surface of the cover member 3 with the electrolyte solution 10 is well ensured, and oxidation of the electrolyte solution 10 is easily suppressed.

[0053] The area of ​​the cover member 3 covering the liquid surface of the electrolyte solution 10 is 0.90 to 0.99 times the total area of ​​the liquid surface of the electrolyte solution 10. Hereinafter, the area of ​​the cover member 3 covering the liquid surface of the electrolyte solution 10 may be referred to as the "area of ​​the cover member 3." The total area of ​​the liquid surface of the electrolyte solution 10 depends on the size of the internal space 20. The total area of ​​the liquid surface of the electrolyte solution 10 is equal to the planar area of ​​the inner surface of the upper wall 23 or the lower wall 24. The total area of ​​the liquid surface of the electrolyte solution 10 is equal to the planar area of ​​the region enclosed by the inner surfaces of the first end wall 21, the second end wall 22, and the two side walls 25, 25. The electrolyte solution 10 is introduced into the internal space 20 via a first pipe 5 (described later) and discharged from the internal space 20 via a second pipe 6 (described later). The cover member 3 has an opening 36 corresponding to the first pipe 5 and an opening 37 corresponding to the second pipe 6. When the area of ​​the cover member 3 is 0.99 times or less the total area of ​​the liquid surface of the electrolyte solution 10, it is easy to arrange the openings 36 and 37. When the area of ​​the cover member 3 is 0.90 times or more the total area of ​​the liquid surface of the electrolyte solution 10, the cover member 3 covers a wide area of ​​the liquid surface of the electrolyte solution 10, thereby suppressing oxidation of the electrolyte solution 10. The area of ​​the cover member 3 may be 0.95 times or more and 0.98 times or less the total area of ​​the liquid surface of the electrolyte solution 10.

[0054] In this example, the open end 5A of the first pipe 5 is disposed above the liquid surface of the electrolyte 10 with a gap therebetween. The opening 36 is located at the location of the open end 5A projected onto the liquid surface of the electrolyte 10. When the cover member 3 is composed of multiple segments 30 as shown in FIGS. 2 and 3 , the opening 36 is formed by a gap between the multiple segments 30. This gap should be equal to or larger than the size of the open end 5A. The multiple segments 30 forming this gap should be positioned so as not to obstruct the flow of the electrolyte 10 flowing out from the open end 5A. The opening 36 is not shown in FIGS. 2 and 3 . When the cover member 3 is composed of a single plate as shown in FIG. 4 , the opening 36 is formed by a through-hole formed in the plate. The electrolyte 10 is exposed from the opening 36.

[0055] A guide portion 5w may be arranged to connect the opening end 5A and the opening 36. The guide portion 5w is illustrated with a dotted line in the drawings for clarity. The guide portion 5w is composed of, for example, multiple wall portions fixed to the first pipe 5. The multiple wall portions are arranged at equal intervals around the circumferential direction of the first pipe 5. Each wall portion extends from the opening end 5A to the opening 36. A gap is provided between adjacent wall portions. This gap is provided to release the pressure of the electrolyte 10 from the first pipe 5. The guide portion 5w also serves to prevent the cover member 3, or each divided piece 30 in FIGS. 2 and 3, from entering the opening 36. The cover member 3 is arranged to surround the guide portion 5w. The guide portion 5w guides the electrolyte 10 introduced from the first pipe 5 to the opening 36 without affecting the main body of the cover member 3.

[0056] In this example, the open end 6B of the second pipe 6 is placed in the electrolytic solution 10. The second pipe 6 passes through the opening 37. The cover member 3 is placed so as to surround the second pipe 6.

[0057] As shown in FIGS. 2 and 3 , the cover member 3 may include multiple segments 30. In other words, the cover member 3 may be composed of an assembly of multiple segments 30. In FIGS. 2 and 3 , a portion of each segment 30 is illustrated. When the tank body 2 is large, such as a 20-ft container, it is difficult to position a single large cover member 3 that can cover almost the entire surface of the electrolyte 10 above the liquid surface of the electrolyte 10. When the cover member 3 includes multiple segments 30, the size of each segment 30 can be adjusted. Adjusting the size of each segment 30 makes it easy to prepare the cover member 3. When the cover member 3 includes multiple segments 30, the cover member 3 can be easily positioned above the liquid surface of the electrolyte 10. When the cover member 3 includes multiple segments 30, each segment 30 can individually follow fluctuations in the liquid surface of the electrolyte 10, making the movement of the cover member 3 smoother.

[0058] The area covered by each segment 30 on the surface of the electrolyte solution 10 is, for example, 0.002 to 0.01 times the total area of ​​the surface of the electrolyte solution 10. Hereinafter, the area covered by each segment 30 on the surface of the electrolyte solution 10 may be referred to as the "area of ​​each segment 30." The area of ​​each segment 30 is the area covered by one segment 30 on the surface of the electrolyte solution 10. If each segment 30 is too small, the segment 30 may be significantly displaced from its predetermined position due to the flow of the electrolyte solution 10. If the area of ​​each segment 30 is 0.002 or more times the total area of ​​the surface of the electrolyte solution 10, the segment 30 is less likely to be affected by the flow of the electrolyte solution 10 and less likely to be displaced from its predetermined position. If the area of ​​each segment 30 is 0.01 or less times the total area of ​​the surface of the electrolyte solution 10, the segment 30 is easily prepared and easily positioned on the surface of the electrolyte solution 10. The area of ​​each segment 30 may be 0.004 to 0.008 times the total area of ​​the liquid surface of the electrolyte solution 10. The multiple segments 30 may be combined with only small segments 30 having areas within the above-mentioned range. The multiple segments 30 may be combined with segments 30 having the same area, or may include segments 30 having different areas.

[0059] The multiple segments 30 may be a combination of small segments 30 and large segments 30 having areas within the above-mentioned range. The area of ​​the large segments 30 is, for example, more than 0.01 times and less than 0.99 times the total area of ​​the liquid surface of the electrolyte 10. The large segments 30 are easy to place on the liquid surface of the electrolyte 10 if they are flexible enough to be rolled up or folded. The area of ​​the large segments 30 may be 0.8 times or less, 0.75 times or less, or 0.5 times or less the total area of ​​the liquid surface of the electrolyte 10. The small segments 30 are preferably placed so as to cover the liquid surface of the electrolyte 10 that is not covered by the large segments 30.

[0060] The area of ​​each divided piece 30 covering the liquid surface of the electrolyte 10 is 2000 mm ２ More than 1200000mm ２ Below that, another 20,000 mm ２ More than 100,000 mm ２ Below, 40000mm ２ More than 60,000 mm ２The number of the divided pieces 30 depends on the size of the tank body 2, but is preferably 20 to 500, and more preferably 50 to 200.

[0061] The divided pieces 30 are arranged so that openings 36, 37 (FIG. 1) are formed in the cover member 3. For the sake of convenience, the openings 36, 37 are not shown in FIGS.

[0062] Each of the divided pieces 30 is, for example, a plate material. Dividers 30 made of a plate material can easily ensure a large contact area with the electrolyte 10. A large contact area between the divided pieces 30 and the electrolyte 10 can easily suppress oxidation of the electrolyte 10. The number of divided pieces 30 made of a plate material is, for example, 50% or more of the total number of divided pieces 30, and further 70% or more, or 90% or more. Dividers 30 other than a plate material are, for example, spheres. Dividers 30 made of spheres will be described later. In this example, all of the divided pieces 30 are made of a plate material.

[0063] When the divided pieces 30 are plates, the shape of the plates can be selected appropriately. The shape of the plates is planar. The shape of the plates also corresponds to the shape of the contact surface of the plates with the electrolyte solution 10. The shape of the plates may be rectangular as shown in FIG. 2 or hexagonal as shown in FIG. 3. A shape including straight lines, such as a rectangular or hexagonal shape, makes it easier to arrange multiple plates without gaps. Note that a relatively small gap 35a may be formed between the plates due to the flow of the electrolyte solution 10. Even if gap 35a is formed, the area of ​​the cover member 3 covering the liquid surface of the electrolyte solution 10 satisfies 0.90 to 0.99 times the total area of ​​the liquid surface of the electrolyte solution 10.

[0064] In particular, when the plate members are hexagonal, as shown in Fig. 3, the plate members can be easily arranged without gaps, and the state in which the plate members are arranged can be easily maintained stably. However, depending on the shape of the tank body 2, a relatively large gap 35b may be formed between the hexagonal divided piece 30 and the wall surface of the tank body 2. Even if gap 35b is formed, the area of ​​the cover member 3 covering the liquid surface of the electrolyte solution 10 satisfies 0.90 to 0.99 times the total area of ​​the liquid surface of the electrolyte solution 10. When gap 35b is large, plate members having a shape other than a hexagon, such as a trapezoid or a triangle, may be arranged in gap 35b.

[0065] The multiple segment pieces 30 may include multiple plate materials with different shapes. For example, as described above, hexagonal, trapezoidal, and triangular plate materials may be mixed. The multiple segment pieces 30 may include multiple plate materials with different areas, regardless of shape. For example, segment pieces 30 with a relatively large area may be arranged near the projected location of the open end 5A of the first pipe 5 on the liquid surface of the electrolyte solution 10. Near the projected location of the open end 5A of the first pipe 5 on the liquid surface of the electrolyte solution 10, the liquid surface tends to ripple due to the electrolyte solution 10 flowing out from the open end 5A. By arranging segment pieces 30 with a relatively large area in a location where the liquid surface of the electrolyte solution 10 is likely to ripple, each segment piece 30 is less affected by the flow of the electrolyte solution 10 and is less likely to shift from its predetermined position. The vicinity of the wall surface of the tank body 2 is less affected by the flow of the electrolyte solution 10. Therefore, segment pieces 30 with a relatively small area may be arranged near the wall surface of the tank body 2. As described above, depending on the shape of the tank body 2 and the shape of the divider 30, a gap 35b (FIG. 3) may be formed between the divider 30 and the wall surface of the tank body 2. A divider 30 having a relatively small area may be arranged to fill this gap 35b.

[0066] When the segment 30 is a plate, the plate has a first surface 31 and a second surface 32 ( FIG. 1 ). The first surface 31 is a surface that contacts the electrolyte solution 10. The first surface 31 is, for example, a flat surface. A flat surface makes it easier to ensure a large contact area with the electrolyte solution 10. The second surface 32 is a surface facing the first surface 31 and is exposed to the gas phase space 20G described below. The second surface 32 may be a flat surface or a curved surface. The second surface 32 may have a slope that slopes downward from the center toward the periphery. If the second surface 32 has such a slope, even if the electrolyte solution 10 splashes on the second surface 32, the electrolyte solution 10 flows down the slope toward the liquid surface, making it less likely to accumulate on the second surface 32. The segment 30 having such a slope on the second surface 32 is preferably positioned near the point where the open end 5A of the first pipe 5 is projected onto the liquid surface of the electrolyte solution 10. Both the first surface 31 and the second surface 32 may have the inclined surface. When both the first surface 31 and the second surface 32 have an inclined surface, even if the flow of the electrolyte solution 10 turns the divided piece 30 upside down, the inclined surface is always positioned on the upper side.

[0067] For example, each segment 30 is arranged independently of the other. The segments 30 may be connected to each other by a connecting member. The connecting member is, for example, a string. It is preferable that multiple segments 30 arranged in locations that are susceptible to the flow of the electrolyte solution 10 are connected to each other by a connecting member.

[0068] Each segment 30 may be a sphere. The sphere may be a solid sphere or a hollow sphere containing gas inside. In a sphere containing gas inside, only the surface is solid. The multiple segmented pieces 30 made of spheres may be arranged in multiple layers on the liquid surface of the electrolyte solution 10. The multiple segmented pieces 30 made of spheres may be placed in, for example, a net-like bag. All the segmented pieces 30 may be placed in one bag, or they may be divided into multiple bags with multiple segmented pieces 30 placed in each bag.

[0069] The cover member 3 may be a single plate material, as shown in FIG. 4 . A single plate material makes it easier to ensure a large contact area between the cover member 3 and the electrolyte solution 10, and makes it easier to suppress oxidation of the electrolyte solution 10. The single plate material may be, for example, a soft sheet. Openings 36 and 37 are formed in the cover member, which is a single plate material. A plurality of small through holes (not shown) may be formed in the cover member 3, which is a single plate material. The plurality of small through holes may be formed, for example, near the opening 36. Even if the electrolyte solution 10 splashes on the upper surface of the cover member 3, the electrolyte solution 10 flows down through the through holes and is less likely to accumulate on the cover member 3.

[0070] The cover member 3 is made of a resin or rubber that is resistant to the electrolyte 10. The cover member 3 may be made of the same material as the inner surface of the tank body 2, for example.

[0071] <Tank Structure> Tank structures 1P and 1N including the above-described tank 1 will be described with reference to Fig. 5. The tank 1 shown in Fig. 5 is shown in cross section cut along a plane along the height direction of the tank body 2. The direction shown in the upper left of Fig. 5 indicates the arrangement direction of the tank 1. The tank structure 1P circulates the positive electrode electrolyte 106. The tank structure 1N circulates the negative electrode electrolyte 107.

[0072] The tank structure 1P includes the tank 1, first pipe 5P, second pipe 6P, and pump 7P described above. Positive electrode electrolyte 106 is stored in the tank 1. A cover member 3 floats on the liquid surface of the positive electrode electrolyte 106. Hereinafter, the tank 1 in which the positive electrode electrolyte 106 is stored will be referred to as a positive electrode tank 104. The first pipe 5P shown in FIG. 5 is the same as the first pipe 5 shown in FIG. 1. The second pipe 6P shown in FIG. 5 is the same as the second pipe 6 shown in FIG. 1. The black arrows shown in the first pipe 5P and the second pipe 6P indicate the flow direction of the electrolyte 10.

[0073] The first pipe 5P is a pipe for returning the positive electrode electrolyte 106 from the battery cell 100C to the positive electrode tank 104. The first pipe 5P in this example is connected to the tank body 2 so that an open end 5A of the first pipe 5P is located inside the tank body 2. The inlet 26 for the positive electrode electrolyte 106 into the positive electrode tank 104 is the open end 5A of the first pipe 5P. The inlet 26 in this example is located above the center of the tank body 2 in the third direction D3. The inlet 26 in this example is located so as not to be immersed in the positive electrode electrolyte 106.

[0074] The second pipe 6P is a pipe for sending the positive electrode electrolyte 106 from the positive electrode tank 104 to the battery cell 100C. The second pipe 6P in this example is connected to the tank body 2 such that an open end 6B of the second pipe 6P is disposed inside the tank body 2. An outlet 27 for the positive electrode electrolyte 106 from inside the positive electrode tank 104 is the open end 6B of the second pipe 6P. The outlet 27 in this example is disposed below the center of the tank body 2 in the third direction D3. The outlet 27 in this example is disposed so as to be immersed in the positive electrode electrolyte 106.

[0075] The pump 7P is provided midway along the second pipe 6P. The pump 7P pressure-feeds the positive electrode electrolyte 106 in the positive electrode tank 104 to the battery cell 100C.

[0076] The tank structure 1P of this example further includes a third pipe 8 and a fourth pipe 9. The third pipe 8 is a pipe for introducing a non-oxidizing gas into the internal space 20 of the tank body 2. The third pipe 8 of this example is connected to the tank body 2 so that an open end 8A of the third pipe 8 is located inside the tank body 2. The inlet 28 for the non-oxidizing gas to the internal space 20 is the open end 8A of the third pipe 8. The fourth pipe 9 is a pipe for discharging the non-oxidizing gas from the internal space 20 of the tank body 2. The fourth pipe 9 of this example is connected to the tank body 2 so that an open end 9B of the fourth pipe 9 is located inside the tank body 2. The outlet 29 for the non-oxidizing gas from the internal space 20 is the open end 9B of the fourth pipe 9. Although not shown in FIG. 5 , the third pipe 8 and the fourth pipe 9 are each connected to a tank outside the tank body 2 in which a non-oxidizing gas is stored. The outline arrows shown in the third pipe 8 and the fourth pipe 9 indicate the flow direction of the non-oxidizing gas. When the non-oxidizing gas is circulated in the internal space 20 by the third piping 8 and the fourth piping 9, a gas phase space 20G of the non-oxidizing gas is formed in the internal space 20 above the cover member 3 in the tank body 2. The gas phase space 20G will be described later.

[0077] The tank structure 1N includes the tank 1, first piping 5N, second piping 6N, and pump 7N described above. The tank structure 1N has the same configuration as the tank structure 1P, except for the electrolyte that flows through it. The first piping 5N, second piping 6N, and pump 7N in the tank structure 1N have the same configurations as the first piping 5P, second piping 6P, and pump 7P in the tank structure 1P. The tank 1 in the tank structure 1N stores anode electrolyte 107. A cover member 3 floats on the liquid surface of the anode electrolyte 107. Hereinafter, the tank 1 in which the anode electrolyte 107 is stored will be referred to as anode tank 105.

[0078] The tank structure 1N of this example further includes a third pipe 8 and a fourth pipe 9. The third pipe 8 and the fourth pipe 9 in the tank structure 1N have the same configuration as the third pipe 8 and the fourth pipe 9 in the tank structure 1P.

[0079] The basic configurations of the first pipes 5P and 5N, the second pipes 6P and 6N, the pumps 7P and 7N, the third pipe 8, and the fourth pipe 9 can be appropriately selected from known configurations.

[0080] <RF Battery System> An RF battery system 100 according to an embodiment will be described with reference to Figures 5 and 6. As shown in Figure 5, the RF battery system 100 includes a battery cell 100C, the tank structure 1P described above, and the tank structure 1N described above. In Figure 5, the battery cell 100C is simplified, with the positive electrode side of the battery cell 100C indicated by "+" and the negative electrode side by "-". The specific configuration of the battery cell 100C is shown in Figure 6. The basic configuration of the RF battery system 100 can be any known configuration as appropriate.

[0081] The RF battery system 100 charges and stores power generated by a power generation unit, and discharges the stored power to supply it to a load. The RF battery system 100 is typically connected to the power generation unit and the load via a power conversion device and a substation. Examples of the power generation unit include a solar power generation system, a wind power generation system, or other general power plants. Examples of the load include power consumers. Examples of applications of the RF battery system 100 include load leveling, instantaneous voltage drop compensation, emergency power supply, and output smoothing of natural energy such as solar power generation or wind power generation.

[0082] As shown in FIG. 6 , the battery cell 100C is separated into a positive electrode cell 100P and a negative electrode cell 100N by a diaphragm 101. The positive electrode cell 100P contains a positive electrode 102. A positive electrode electrolyte 106 ( FIG. 5 ) is supplied to the positive electrode cell 100P. The negative electrode cell 100N contains a negative electrode 103. A negative electrode electrolyte 107 ( FIG. 5 ) is supplied to the negative electrode cell 100N. The battery cell 100C is sandwiched between a pair of cell frames 110. The cell frame 110 includes a bipolar plate 112 and a frame 111. The positive electrode 102 is disposed on a first surface of the bipolar plate 112, and the negative electrode 103 is disposed on a second surface of the bipolar plate 112. The frame 111 is provided around the outer periphery of the bipolar plate 112. The frame 111 supports the bipolar plate 112. A seal member 113 is disposed between the frame 111 to prevent leakage of the positive electrode electrolyte 106 and the negative electrode electrolyte 107 from the battery cell 100C.

[0083] The RF battery system 100 is typically used in a configuration called a cell stack 120, in which multiple battery cells 100C are stacked. The cell stack 120 includes a stack in which a certain cell frame 110, a positive electrode 102, a diaphragm 101, a negative electrode 103, and another cell frame 110 are repeatedly stacked, two end plates 121 sandwiching the stack, and fastening members (not shown). The fastening members are, for example, long bolts and nuts. The two end plates 121 are fastened together by the fastening members. This fastening maintains the stacked state of the stack. The cell stack 120 is typically used in a configuration in which a predetermined number of battery cells 100C are defined as sub-stacks (not shown), and multiple sub-stacks are stacked. Supply and discharge plates (not shown) are arranged on the outside of the cell frames 110 located at both ends of the stacking direction of the battery cells 100C in the sub-stack or cell stack 120.

[0084] As shown in Fig. 5, a tank structure 1P circulates a cathode electrolyte 106 through the cathode cell 100P. The cathode electrolyte 106 is supplied to the cathode electrode 102 (Fig. 6) in the cathode cell 100P from the cathode tank 104 through a second pipe 6P by pressure feeding from a pump 7P. After flowing through the cathode electrode 102, the cathode electrolyte 106 is returned to the cathode tank 104 through a first pipe 5P. When the pump 7P is stopped, the cathode electrolyte 106 is not circulated.

[0085] As shown in Fig. 5, the anode electrolyte 107 is circulated through the anode cell 100N by a tank structure 1N. The anode electrolyte 107 is supplied to the anode electrode 103 (Fig. 6) in the anode cell 100N from the anode tank 105 through second piping 6N by pressure feeding from a pump 7N. The anode electrolyte 107 that has circulated through the anode electrode 103 is returned to the anode tank 105 through first piping 5N. When the pump 7N is stopped, the anode electrolyte 107 is not circulated.

[0086] The RF battery system 100 circulates a positive electrode electrolyte 106 to the positive electrode 102 and a negative electrode electrolyte 107 to the negative electrode 103, thereby performing charging and discharging in accordance with a valence change reaction of the active material ions in the electrolytes of each electrode.

[0087] The positive electrode electrolyte 106 contains, as a positive electrode active material, one or more selected from the group consisting of, for example, manganese ions, vanadium ions, iron ions, polyacids, quinone derivatives, and amines. The negative electrode electrolyte 107 contains, as a negative electrode active material, one or more selected from the group consisting of, for example, titanium ions, vanadium ions, chromium ions, polyacids, quinone derivatives, and amines. The solvents for the positive electrode electrolyte 106 and the negative electrode electrolyte 107 are aqueous solutions containing, for example, one or more acids or acid salts selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, and hydrochloric acid. As a specific example, both the positive electrode electrolyte and the negative electrode electrolyte contain vanadium ions. As another example, the positive electrode electrolyte contains manganese ions, and the negative electrode electrolyte contains titanium ions. The concentrations of the positive electrode active material and the negative electrode active material can be selected as appropriate.

[0088] In the RF battery system 100 of this example, each of the positive electrode tank 104 and the negative electrode tank 105 has a gas phase space 20G in the tank body 2, as shown in FIG. 5 . The gas phase space 20G is provided above the cover member 3 in the internal space 20 of the tank body 2. A non-oxidizing gas is circulated in the gas phase space 20G by a third pipe 8 and a fourth pipe 9. The non-oxidizing gas is constantly circulated during operation of the RF battery system 100. The non-oxidizing gas is, for example, nitrogen. The non-oxidizing gas significantly suppresses oxidation of the electrolyte solution 10 stored in the internal space 20. The non-oxidizing gas may contain unavoidable oxygen. Even if unavoidable oxygen is contained in the gas phase space 20G, the oxidation of the electrolyte solution 10 is suppressed by disposing the cover member 3 above the liquid surface of the electrolyte solution 10. Even if the amount of oxygen in the gas phase space 20G is minute, in the long term, the oxidation of the electrolyte solution 10 can significantly reduce the energy density of the RF battery system 100. Even if the amount of oxygen is minute, if the oxidation of the electrolyte solution 10 is suppressed by the cover member 3, the oxidation of the electrolyte solution 10 is also suppressed in the long term, and a long-term reduction in the energy density of the RF battery system 100 is suppressed.

[0089] The battery reaction in the battery cell 100C may generate hydrogen gas in the electrolyte. This hydrogen gas flows through the openings 36, 37 or the gaps 35a, 35b in the cover member 3 into the gas phase space 20G and is released to the outside of the internal space 20 from the fourth pipe 9 together with the non-oxidizing gas.

[0090] When a non-oxidizing gas is circulated in the gas phase space 20G, the water content of the electrolyte solution may evaporate. When the cover member 3 is placed on the liquid surface of the electrolyte solution 10, the water content of the electrolyte solution is less likely to evaporate. When the evaporation of water is suppressed, the temperature rise and the precipitation of active material ions in the electrolyte solution 10 are suppressed.

[0091] If the cover member 3 is not placed on the liquid surface of the electrolyte solution 10 stored in the internal space 20, the liquid surface of the electrolyte solution 10 is exposed to the gas phase space 20G. The flow resistance of the liquid surface of the electrolyte solution 10 exposed to the gas phase space 20G and its vicinity is smaller than the flow resistance inside the electrolyte solution 10. Due to the difference in flow resistance, the flow rate of the electrolyte solution 10 is fast at the liquid surface of the electrolyte solution 10 and its vicinity, and slows down inside the electrolyte solution 10, resulting in an uneven flow of the electrolyte solution 10. In particular, in a tank body 2 that is horizontally elongated, such as a container-type tank, if the cover member 3 is not placed on the liquid surface of the electrolyte solution 10, the area of ​​the liquid surface of the electrolyte solution 10 exposed to the gas phase space 20G is relatively large, making the flow of the electrolyte solution 10 prone to be uneven. If the cover member 3 is placed on the liquid surface of the electrolyte solution 10, the flow resistance of the liquid surface of the electrolyte solution 10 and its vicinity increases, making the flow of the electrolyte solution 10 prone to be uniform, even in a tank body 2 that is horizontally elongated, such as a container-type tank. When the flow of the electrolyte 10 becomes uniform, the electrolyte 10 stored in the internal space 20 is efficiently utilized.

[0092] 1 Tank, 1P, 1N Tank structure, 10 Electrolyte, 2 Tank body, 20 Internal space, 20G Vapor space, 21 First end wall, 22 Second end wall, 23 Upper wall, 24 Lower wall, 25 Side wall, 26 Inlet, 27 Outlet, 28 Intake port, 29 Exhaust port, D1 First direction, D2 Second direction, D3 Third direction, 3 Cover member, 30 Divided piece, 31 First surface, 32 Second surface, 35a, 35b Gap, 36, 37 Opening, 5, 5P, 5N First pipe, 5A Open end, 5w Guide portion, 6, 6P, 6N Second pipe, 6B Open end, 7P, 7N Pump, 8 Third pipe, 8A Open end, 9 Fourth pipe, 9B Open end, 100 Redox flow battery system (RF battery system), 100C battery cell, 101 diaphragm, 100P positive electrode cell, 100N negative electrode cell, 102 positive electrode, 103 negative electrode, 104 positive electrode tank, 105 negative electrode tank, 106 positive electrode electrolyte, 107 negative electrode electrolyte, 110 cell frame, 111 frame, 112 bipolar plate, 113 sealing member, 120 cell stack, 121 end plate.

Claims

1. A tank for storing an electrolyte in a redox flow battery system, A tank body having an internal space separated from the outside; A cover member having at least a solid surface, The cover member is floated on the liquid surface of the electrolyte stored in the internal space so as to cover the liquid surface of the electrolyte, The area of ​​the cover member covering the liquid surface is 0.90 times or more and 0.99 times or less of the total area of ​​the liquid surface. tank.

2. The tank according to claim 1 , wherein the maximum horizontal length of the tank body is longer than the height of the tank body.

3. The tank according to claim 1 or 2, wherein the cover member comprises a plurality of segments.

4. The tank according to claim 3 , wherein an area of ​​the liquid surface covered by each of the plurality of divided pieces is equal to or greater than 0.002 times and less than 0.99 times a total area of ​​the liquid surface.

5. The tank according to claim 3 , wherein each of the plurality of segments is a plate material.

6. The tank according to claim 5 , wherein the plate has a shape of a rectangle or a hexagon.

7. Each of the plurality of divided pieces is a plate material, The tank according to claim 3 , wherein the plate has a hexagonal shape.

8. The tank according to claim 1 or 2, wherein the cover member is a single plate material.

9. The tank according to claim 1 or 2, wherein the tank body is provided with an intake port and an exhaust port for circulating a non-oxidizing gas in the internal space.

10. A tank according to claim 1, Redox flow battery system.

11. The electrolyte is stored in the internal space, The redox flow battery system according to claim 10 , wherein the tank body has a gas phase space in the internal space above the cover member, in which a non-oxidizing gas is circulated.