Dynamic model based membrane permeability estimation for online SOC imbalances monitoring of vanadium redox flow batteries

A model based approach is developed to determine the membrane permeability properties including vanadium ion crossover and water transfer behaviour for the vanadium redox flow battery (VRB) system. The permeability of vanadium ions and water transfer coefficients are estimated through nonlinear optimisation with measured negative and positive half-cell potentials. Experimental studies were conducted to test two different membranes as examples to illustrate the effectiveness of the proposed approach. This method can significantly simplify the conventional approach to characterising the membrane permeability property. The results are useful for online prediction of the battery system capacity decay and for scheduling regular maintenance such as electrolyte rebalancing to restore capacity.