The present application relates to the technical field of
electrochemical energy storage, and particularly relates to a
vanadium flow battery stack of secondary battery, which comprises two or more than two single batteries connected in series, each single battery comprises an
ion exchange membrane, two sides of the
ion exchange membrane are respectively provided with a polar frame, an
electrode is arranged in the polar frame, the
electrode is a gradient thickness
electrode, and the electrode is a porous electric conductor, a liquid inlet and a liquid outlet are arranged in the polar frame, and the thickness of the electrode on the liquid inlet side is less than the thickness of the electrode on the liquid outlet side. The gradient electrode with the thickness increasing from the liquid inlet to the liquid outlet actively matches the natural attenuation gradient of the
electrolyte active substance concentration, the thickness is reduced on the inlet end to reduce the
mass transfer resistance and promote the reaction, and the thickness is increased on the outlet end to prolong the
reaction path and improve the
utilization rate of the low concentration reactant, so that the concentration difference polarization and the electrochemical polarization are synergistically reduced from the root, and the
voltage efficiency and the capacity
utilization rate of the stack are significantly improved.