Analysis and optimization for multi-stack vanadium flow battery module incorporating electrode permeability

The large-scale all-vanadium flow battery module is commonly formed by a number of hydraulically parallel connected stacks. The existence of permeability difference in applicated electrode is supposed to be of great influential on module performance. Hence in this paper, the electrode permeability is firstly measured via a self-designed device, followed by an in-depth analysis of its effects by a zero-dimensional dynamic model for multi-stack flow battery module on the basis of mass balance. The simulation results depicted that the permeability variations can notably influence the flow rate, pump loss and overall efficiency for stacks, as well as the voltage uniformity for electrically series connected modules. Besides, the performance, especially the capacity, of electrically series-parallel hybrid multi-stack module can be significantly increased by arranging the stacks with similar electrode permeability in the same branch. In addition, increasing the flow rate, particularly by individual control mode can further increase the module capacity with an acceptably additional efficiency loss. The present study offers not only a full understanding of cardon felt permeability, but also a cost-effective way to evaluate the module performance.