Untapped Potential: The Need and Opportunity for High-Voltage Aqueous Redox Flow Batteries

Redox flow batteries (RFBs) are attractive long-duration energy storage solutions, especially if system costs can be further reduced. One approach to lowering the system cost is to increase the energy and power densities through the use of higher voltage redox chemistries. To date, most techno-economic studies have considered the maximum open-circuit voltage (OCV) of aqueous RFBs to be ≤1.5 V. We provide a simple techno-economic analysis to illustrate the impact of cell voltage on capital cost and note the secondary benefits that arise from the operational flexibility enabled by aqueous RFBs with OCVs >1.5 V. We subsequently discuss potential pathways to achieving higher voltage chemistries. The goal of this Perspective is to inspire the research community to re-examine the perceived upper limits of aqueous RFB voltages and to explore options for achieving high-voltage systems, as well as identify the need for fundamental research on a variety of topics.