SBIR Phase II: A Novel High Voltage All-Iron Flow Battery for Long-Duration Energy Storage

The broader/commercial impact of this SBIR Phase II project is the prototype development of a cost-effective, durable, and efficient all-iron flow battery suitable for long-duration energy storage. Cost-effective storage is a key enabler for power generation from intermittent and weather-dependent sources. For short-duration energy storage, the rapidly improving Lithium-ion batteries are already practical, but flow batteries are needed for long-duration energy storage. The state-of-the-art flow battery technology is the vanadium redox-flow battery, but the high costs and limited supply of vanadium restrict its application also to short-duration energy storage, where Lithium-ion batteries are dominant. The all-iron flow battery is based instead on iron as the active material, offering a potential pathway meeting the cost targets for grid energy transition. This Small Business Innovation Research (SBIR) Phase II project aims to scale up the all-iron flow battery from the laboratory-scale single cell unit to a modular prototype with a multi-cell stack the size of a small residential energy storage unit. Unlike other all-iron batteries that involve solid metal at the negative electrode and are hybrid batteries, this technology uses all-solution iron complexes for both the posolyte and the negolyte, offering a true flow battery technology based on iron. The Phase II project targets a cell voltage exceeding 1.5 V, overcoming the lower voltages typical of traditional iron-based systems, boosting capacity and round-trip efficiency. By utilizing specialized ligands and tailoring electrolyte pH and composition, the design reduces gas evolution and cross-contamination, essential for stable long-term cycling. The planned work includes optimization of electrolyte composition, cell architecture, and operating conditions in a smaller stack to validate performance demonstrating a low area-specific resistance and durability, before building a larger multi-cell stack and balance-of-plant for a complete bidirectional grid-connected prototype to establish the efficacy of the technology in offering a lower cost alternative with secure supply-chain, enhanced efficiency and modular scalability. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.