Component and Performance Analysis of Vanadium Redox Flow Batteries: Experimental and Modeling Studies

One major issue limiting the implementation of renewable energy sources is the lack of efficient, cost-effective, and reliable energy storage technologies. The vanadium redox flow battery (VRFB) is a flow-assisted electrochemical system which shows great promise for grid-scale energy storage due to its high energy efficiency (up to 85%), long lifetime (>12,000 cycles) and low maintenance. Despite these many advantages, the current state of VRFB technology possesses several unresolved issues which affect the efficiency, power density, and power output of the system. To address these limitations, a macroscopic 2-D, transient performance model of a VRFB has been developed to understand the role of components, operating conditions and electrolyte flow strategies.

This model is constructed on five main domains to simulate the physical phenomena in components of a vanadium flow cell, namely: the current collectors, the positive and negative porous electrodes, and the membrane. The unique feature of the present model is the incorporation of species crossover through the membrane and utilization of a more complete description of the Nernst equation to accurately predict the open circuit voltage and electrode potentials. Input parameters for the various domains are obtained by direct measurement of the properties of actual cell components. For instance, the microstructure of the graphite felt electrodes is quantified using x-ray microcomputed tomography, and the resulting properties (i.e. porosity, specific surface area, etc.) are incorporated into the model. The 2D temporal distributions of local reaction current density, overpotential, species concentrations and cell potential are predicted. Simulations are performed using experimental data for a variety of components and their impact on cell performance is evaluated to provide guidance for component and cell design efforts.