Effect of battery material and operation on dynamic performance of a vanadium redox flow battery under electrolyte imbalance conditions

An electrolyte imbalance in a vanadium redox flow battery (VRFB) is a significant problem that can degrade the performance of VRFB during a long-term operation. The systematic analysis of a VRFB is, therefore, performed to examine the battery performance and capacity degradation caused by an electrolyte imbalance through the use of different electrode materials and membranes, which consider carbon felt structures and their treatment, and cation- and anion-exchange types of membrane. A dynamic model of the VRFB explains the gas evolutions and self-discharge side reactions coupled with the mass balance of the vanadium and proton ions. Investigation of the VRFB performance reveals that the rate of capacity loss resulting from the electrolyte imbalance considerably depends on the material and operating conditions. The variation of the vanadium ions during long-term operation depends on the gassing and self-discharge side reactions. The VRFB using Type 3 electrodes and an AMV membrane provides the highest energy efficiency. The battery operating time is considered a key factor in managing the vanadium variation caused by self-discharge reactions. Current density, temperature, and total vanadium concentration are found to affect the battery capacity degradation rate. A high-capacity degradation rate is observed under low current density, high temperature, and high total vanadium concentration conditions. However, changes in the electrolyte flow rate do not improve the battery capacity during long-term operation because the state of charge of the VRFB decreases due to the electrolyte imbalance.