Performance improvement of a vanadium redox flow battery with asymmetric electrode designs

A two-dimensional transient model with considering vanadium ions crossover and incorporating the impact of electrode compression was presented for a vanadium redox flow battery (VRFB). Emphasis is located on examining the effects of the proposed asymmetric electrode structure designs on capacity degradation, vanadium ions crossover, the charge-discharge voltages and efficiency of the VRFB during long-time cycling. It was indicated that for asymmetric electrode compression with same original thickness, the capacity decay can be effectively alleviated with increasing the positive compression ratio, due to the fact that the electrolyte crossover is balanced by adjusting the convection flux during a charge-discharge cycle. The charge-discharge performance and energy efficiency of the VRFB can also be simultaneously boosted resulting from the reduced contact resistance and increased electrolyte flow velocity in the compressed positive electrode. Also, it was found that with appropriate design of asymmetric original thickness of uncompressed electrode, the capacity decay can be avoided and battery charge-discharge performance can be improved. This study will provide fundamental information for optimizing the asymmetric electrode structures such that the overall battery performance during long-time cycling can be enhanced.