Electrolyte-circulating batteries such as redox flow batteries (RF batteries) are one type of high-capacity storage batteries used to store power generated by natural energy such as solar power and wind power. RF batteries are a type of batteries that perform charging and discharging by using the difference in oxidation-reduction potential between ions contained in positive electrode electrolytes and ions contained in negative electrode electrolytes. An example of the RF batteries is described in PTL 1.
As illustrated in an operation principle diagram of art RF battery in FIG. 5, the RF battery of PTL 1 includes a battery cell 100 that includes a positive electrode cell 102 and a negative electrode cell 103 separated from each other with a membrane 101 that allows hydrogen ions to permeate through. The positive electrode cell 102 has a positive electrode 104 inside and is connected to a positive electrode electrolyte tank 106, which stores a positive electrode electrolyte, via a circulation channel having an inflow channel 108 and an outflow channel 110. Likewise, the negative electrode cell 103 has a negative electrode 105 inside and is connected to a negative electrode electrolyte tank 107, which stores a negative electrode electrolyte, via a circulating channel having an inflow channel 109 and an outflow channel 111.
The electrolytes in the tanks 106 and 107 flow into the cells 102 and 103 through the inflow channels 108 and 109, respectively, when pumps 112 and 113 provided in the inflow channels 108 and 109 are driven, flow out of the cells 102 and 103, flow through the outflow channels 110 and 111, and are discharged into the tanks 106 and 107 so that the electrolytes circulate to the cells 102 and 103. Typically, aqueous solutions that contain metal ions, such as vanadium ions, whose valence changes by oxidation-reduction reactions are used as the electrolytes. Since the flow channels 108 to 111 come in direct contact with the electrolytes, they are formed of ducts composed of a material unreactive and highly resistant to the electrolyte, such as polyvinyl chloride (PVC). In FIG. 5, arrows in solid lines indicate charging and arrows in broken lines indicate discharging.
In an RF battery 1, the electrolytes generate heat due to battery reaction. The generated heat can degrade battery efficiency and deterioration such as softening of the resin constituting the flow channels 108 to 111 in contact with the electrolytes may occur. To address this issue, in the RF battery 1, heat exchangers 114 and 115 are installed in the outflow channels 110 and 111. Typically, the heat exchangers 114 and 115 each have a cooling region constituting a part of the circulation channel, and the electrolyte inside the cooling region is cooled with a cooling mechanism (not shown in the drawing). The flow channels of the heat exchangers meander as they extend from its inlet to its outlet. The electrolytes have heat removed therefrom as they travel from the inlet to the outlet of the heat exchanger so as to be cooled. A water cooling method with which heat exchangers are cooled with cooling water or an air cooling method with which air is forcibly blown toward heat exchangers is employed for cooling. The flow channels of the heat exchangers may be formed of a plurality of branching straight lines through a course from the inlet to the outlet instead of meandering channels described above.