A flow battery such as a redox flow battery (RF battery) is a large-capacity storage battery that stores power derived from natural energy obtained by solar power generation, wind power generation, or the like. An RF battery performs charging and discharging using the difference in oxidation reduction potential between ions contained in a positive electrode electrolyte and ions contained in a negative electrode electrolyte.
As shown in an operating principle diagram of FIG. 6 for an RF battery, an RF battery 1 includes a cell 100 which is separated into a positive electrode cell 102 and a negative electrode cell 103 by a membrane 101 that permeates hydrogen ions. The positive electrode cell 102 contains a positive electrode 104 and is connected via a supply duct 108 and a discharge duct 110 to a positive electrode electrolyte tank 106 that stores a positive electrode electrolyte. Similarly, the negative electrode cell 103 contains a negative electrode 105 and is connected via a supply duct 109 and a discharge duct 111 to a negative electrode electrolyte tank 107 that stores a negative electrode electrolyte. The electrolytes stored in the tanks 106 and 107 are circulated within the cells 102 and 103 by pumps 112 and 113, respectively.
As shown in FIG. 7, the RF battery 1 usually includes a cell stack 200 in which a plurality of stacked sub-cell stacks 200s are sandwiched between two end plates 210 and 220 and fastened with a fastening mechanism 230. The sub-cell stack 200s includes a stacked body formed by stacking a frame assembly 120 which includes a bipolar plate 121 and a frame piece 122 that holds the bipolar plate 121, a positive electrode 104, a membrane 101, and a negative electrode 105 in this order. In this configuration, a cell 100 is formed between the bipolar plates 121 of the adjacent frame assemblies 120. Integration between the bipolar plate 121 and the frame piece 122 is performed by holding the periphery of the bipolar plate 121 between a pair of divided frames, welding the divided frames together using an organic solvent to form a frame piece 122, and welding the frame piece 122 and the bipolar plate 121 (for example, refer to paragraph 0028 of Patent Literature 1).
Furthermore, the sub-cell stack 200s includes a pair of current collector plates disposed on both sides of the stacked body and a pair of supply/discharge plates 201 disposed on the pair of current collector plates. The current collector plates are electrically connected to the bipolar plates 121 located at both ends in the stacking direction of the stacked body. A terminal portion protrudes outward from the periphery of the current collector plate between the pair of supply/discharge plates 201 (between the supply/discharge plate 201 and the end bipolar plate 121). Input and output of electricity between the cell 100 of the sub-cell stack 200s and an external device are performed through the terminal portion. Each supply/discharge plate 201 is provided with a supply pipe 202i to be connected to the supply duct 108 (109) and a discharge pipe 202o to be connected to the discharge duct 110 (111). The electrolytes are circulated between the sub-cell stack 200s and the tanks 106 and 107 through the pipes 202i and 202o, respectively.
In the sub-cell stack 200s, circulation of the electrolytes is performed by using liquid supply manifolds 123 and 124 and liquid discharge manifolds 125 and 126 which are provided on the frame piece 122. The positive electrode electrolyte is supplied from the liquid supply manifold 123 through a channel formed on one surface side (front side of the sheet) of the frame piece 122 to the positive electrode 104, and is discharged through a channel formed on the upper part of the frame piece 122 to the liquid discharge manifold 125. Similarly, the negative electrode electrolyte is supplied from the liquid supply manifold 124 through a channel formed on the other surface side (back side of the sheet) of the frame piece 122 to the negative electrode 105, and is discharged through a channel formed on the upper part of the frame piece 122 to the liquid discharge manifold 126. Ring-shaped sealing members 127, such as O-rings and flat packings, are disposed between the frame pieces 122 so that leakage of the electrolytes from the sub-cell stack 200s can be prevented.