A two-dimensional analytical unit cell model for redox flow battery evaluation and optimization

Abstract

Cell performance optimization is important for improving the system efficiency of a redox flow battery. To gain better insights into key controlling factors of system efficiency, this work first proposed a theoretical model for a unit cell by extending a two-dimensional analytic model to a full cell. The model is then used for cell performance optimization after validating it with experimental and numerical modeling data. With the results, the activation, equilibrium, and pump energy losses are identified as the dominant battery energy losses. A guideline for reducing these sources is also proposed. Following the guideline, the mass transport coefficient is shown as a key control factor of equilibrium energy loss and Coulombic efficiency (CE). Approaches are then proposed to improve CE and system efficiency. The mass transport also controls pump rate optimization by reducing equilibrium energy loss. An optimal electrode porosity design can further improve a battery’s system efficiency based on an optimal porosity predicted by our model. The model also demonstrates distinct behaviors and overestimation in system efficiency when reduced to a zero-dimensional model. With the model, the guideline, and new insights, this work provides a reliable and efficient tool for the evaluation and optimization of redox flow batteries.