Mitigating capacity decay and improving charge-discharge performance of a vanadium redox flow battery with asymmetric operating conditions

Highlights: • A VRFB model with considering vanadium ions crossover was presented. • Capacity decay and charge-discharge behaviors of a VRFB were analyzed. • Effects of asymmetric electrolyte concentrations were examined. • Effects of asymmetric operation pressures were examined. • Overall performance was improved with asymmetric operating conditions. -- Abstract: A two-dimensional transient model with considering vanadium ion crossover was presented to examine the influence of asymmetric electrolyte concentrations and operation pressures strategies on the characteristics of capacity decay, vanadium ions crossover and charge-discharge performance of a vanadium redox flow battery during battery cycling. It was indicated that for asymmetric electrolyte operating concentrations, with increasing the initial concentration of positive electrolyte while keeping initial concentration of negative electrolyte unchanged, the discharge capacity decay behavior during battery cycling can be effectively mitigated due to the reason that the imbalance of vanadium ions crossover is alleviated by the increased diffusion flux of VO²⁺/VO₂⁺ couple from positive to negative side. Also, the overall charge-discharge performance of the battery is greatly improved due to the reduced potential losses of both electrode reactions. Moreover, it was shown that the discharge capacity decay can also be suppressed by increasing the outlet pressure of positive electrode, which is attributed to the reason that the imbalance of vanadium ions crossover can be eliminated with the increased vanadium osmotic convection driven by pressure gradient. However, asymmetric operation pressures showed little impact on batter charge-discharge voltages.