Recent Advancements in Redox-Flow Cells and Promising Opportunities

Redox-Flow Cells (RFCs) possesses several key advantages that make this technology potentially well suited for large scale energy-storage applications.  This is especially true of applications that require high energy-to-power requirements (i.e., multiple-hour discharge times at rated power), since the energy capacity can be increased by simply adding reactant solution without necessarily requiring (or negatively impacting) the power-delivery components.  Despite this inherent scaling-factor advantage relative to conventional battery systems, the initial capital cost of flow batteries has been the major barrier to commercialization of RFC-based products.  Capital-cost targets for grid-scale energy storage are challenging; battery systems for major grid-scale applications must cost less ($/kWh) than those currently used for most portable or transportation applications.  One attractive path to cost reduction is the development of RFCs with substantially higher power densities than conventional cells.  United Technologies Research Center (UTRC) has recently developed and demonstrated high performance RFCs in stacks operating in complete Prototype RFB Systems.  A summary of these results has been presented previously.  Therefore, a major focus of this talk will be on new materials and concepts that can potentially enable additional RFC cost reductions.  This includes both advanced cell materials (e.g., electrodes, separators/membranes, bipolar plates), as well as advanced reactant solutions.  Key system-performance indices provide the basis for the formulation of key property requirements for these proposed advancements.  A brief review of the state-of-the-art of each these major materials will be included, as well as some proposed advanced technologies.  The major goal of this presentation is to help researchers focus on potential opportunities that have the greatest likelihood of yielding substantial improvements RFC technology that can have significant commercial impact.

 

Acknowledgements

The author would like to thank his multiple colleagues at UTRC who have been an essential part of UTRC’s advanced flow-battery team.