REDOX FLOW BATTERY

Redox flow battery includes cell stack , first positive-electrode tank , second positive-electrode tank , first negative-electrode tank , and second negative-electrode tank . Cell stack is divided into a plurality of cell groups , each of which consists of a plurality of cells . The plurality of cell groups are connected to first and second positive-electrode tanks such that a positive-electrode fluid containing positive-electrode active material flows in parallel through the plurality of cell groups , and are connected to first and second negative-electrode tanks such that a negative-electrode fluid containing negative-electrode active material flows in parallel through the plurality of cell groups . The plurality of cells in each cell group are connected to each other such that the positive-electrode fluid flows in series through a plurality of positive cells and such that the negative-electrode fluid flows in series through a plurality of negative cells