Cell stack and redox flow battery

A cell stack in which a plurality of battery cells are stacked, the cell stack comprising:

• an electrode of a porous body;
• and
• a bipolar plate facing the electrode, wherein
• the bipolar plate includes
• an introduction portion of an electrolyte,
• a discharge portion of the electrolyte, and
• a plurality of first grooves extending from a side at which the introduction portion is disposed toward a side at which the discharge portion is disposed,
• each of the plurality of first grooves allows the electrolyte in each of the plurality of first grooves flow toward the discharge portion,
• R2/R1 is 7×10−11 or more and 2×10−4 or less,
• R1 is a permeation resistance indicating a difficulty of a flow of the electrolyte in the electrode,
• R1=(L1/K1)×μ×(1/S1),
• L1 is a length of the electrode,
• K1 is a permeability of the electrode,
• μ is a viscosity of the electrolyte,
• S1 is a sectional area of the electrode,
• R2 is a permeation resistance indicating the difficulty of the flow of the electrolyte in each of the plurality of first grooves,
• R2=(32×μ×L2)/(de2×S2),
• L2 is a length of each of the plurality of first grooves,
• de is an equivalent diameter of each of the plurality of first grooves, and
• S2 is a sectional area of each of the plurality of first grooves.