Performance and Cost Characteristics of Multi-Electron Transfer, Common Ion Exchange Non-Aqueous Redox Flow Batteries

Abstract

Non-aqueous redox flow batteries (NAqRFBs) have recently received considerable attention as promising high voltage, low cost grid-level energy storage technologies. Despite these attractive features, NAqRFBs are still at an early stage of development, and innovative design techniques are necessary to improve performance and decrease costs. In this work, we investigate multi-electron transfer, common ion exchange NAqRFBs. Common ion systems decrease the supporting electrolyte required for RFB operation, which subsequently improves active material solubility and decreases electrolyte cost. Voltammetric and electrolytic techniques are used to study the electrochemical performance and chemical compatibility of model redox active materials, Fe(bpy)3(BF4)2 and Fc1N112-BF4. These results help to disentangle complex cycling behavior observed in flow cell experiments. Further, a simple techno-economic model demonstrates the cost benefits of employing a common ion exchange NAqRFB, afforded by decreasing the salt and solvent contributions to the total chemical cost. This study offers the first analysis of the benefits of common ion exchange NAqRFBs and the demonstration of a 2e- flow cell. In addition, the compatibility analysis developed for asymmetric chemistries can apply to other promising active species, including organics, metal coordination complexes (MCCs) and mixed MCC/organic systems, enabling the design of low cost NAqRFBs.