Redox flow battery

A redox flow battery that is charged and discharged through a redox reaction of positive-electrode active material and negative-electrode active material in a cell, the redox flow battery comprising:

• a cell stack including a plurality of cells that are stacked, each of the cells including a positive cell that houses a positive electrode and that is supplied with a positive-electrode fluid containing the positive-electrode active material, and a negative cell that houses a negative electrode and that is supplied with a negative-electrode fluid containing the negative-electrode active material;
• a first positive-electrode tank for storing the positive-electrode fluid having a relatively low state of charge;
• a second positive-electrode tank for storing the positive-electrode fluid having a relatively high state of charge;
• a first negative-electrode tank for storing the negative-electrode fluid having a relatively low state of charge;
• and
• a second negative-electrode tank storing the negative-electrode fluid having a relatively high state of charge,
• wherein the cell stack is divided into a plurality of cell groups, each of which consists of the plurality of cells,
• wherein the plurality of cell groups are connected to the first positive-electrode tank and the second positive-electrode tank such that the positive-electrode fluid flows in parallel through the plurality of cell groups between the first positive-electrode tank and the second positive-electrode tank, and the plurality of cell groups are connected to the first negative-electrode tank and the second negative-electrode tank such that the negative-electrode fluid flows in parallel through the plurality of cell groups between the first negative-electrode tank and the second negative-electrode tank, and
• wherein the plurality of cells in each of the cell groups are connected to each other such that the positive-electrode fluid, that has flowed into each of the cell groups, passes in series through the plurality of positive cells and then flows out of each of the cell groups, and such that the negative-electrode fluid, that has flowed into each of the cell groups, passes in series through the plurality of negative cells and then flows out of each of the cell groups.