(Invited) Advanced Redox Flow Batteries: Process and Design Innovation Opportunities

Abstract

Large-scale electric-energy-storage (EES) systems have the potential to transform the electric grid, especially long-duration energy storage (LDES) solutions [1]. However, the economic requirements for LDES systems are more challenging than those for EES applications with shorter discharge durations, since the value proposition for most LDES applications tends to be significantly lower on a normalized basis (i.e., $/kWh of EES capacity). EES systems with independent power and energy components, e.g., pumped-storage hydro (PSH), redox flow batteries (RFBs), and reversible fuel cells (RFCs) have a major inherent cost advantage, since one can readily increase the energy/power ratio by selectively adding more energy capacity, without the added cost of excessive power components. RFBs also have other unique attributes that make this battery architecture ideally suited for grid-scale LDES, namely: long cycle life even with deep cycles, inherently superior safety [2], good round-trip energy efficiency (i.e., compared to RFCs), and simplified recyclability due to the separated components. A rigorous techno-economic analysis (TEA) model has shown that RFBs can enable LDES systems with lower capital cost than other types of batteries at comparable production volumes [3]. However, production volumes of RFBs are currently substantially lower than some other types of batteries, especially lithium-ion batteries. This same TEA model also projects that the capital cost of all-vanadium RFBs (VRFBs) at low production volumes is > $500/kWh. Therefore, what is needed to accelerate the commercialization of VRFBs are innovations that can potentially improve capital costs at low production volumes [4]. This invited talk will focus on some potentially near-term possibilities; namely, those that do not necessarily require new materials. This includes: 1) high performance RFB cells [5], 2) a variety of advanced RFB manufacturing processes, including innovative electrolyte-purification [6] and electrolyte-shipping processes [7], 3) alternative state-of-charge (SOC) measurement methods [8], 4) simple RFB performance diagnostics [9], 5) novel RFB system architectures (e.g., [10]), and 6) business-model innovations [11]. References P. Denholm, et.al., “Storage Futures Study, The Four Phases of Storage Deployment” National Renewable Energy Laboratory, NREL/TP-6A20-77480 (2021).R. Wittman, M. L. Perry, et.al, “Perspective: On the Need for Reliability and Safety of Grid-Scale Aqueous Batteries,” JES, 167 (2020). DOI: 10.1149/1945-7111/ab9406R. M. Darling, et.al., “Pathways to Low-Cost Electrochemical Energy Storage,” Energy & Environ. Science (2014). DOI: 10.1039/c4ee02158dM. L. Perry, “The Pathway to Widespread Commercialization of Redox Flow Batteries,” A03-0475 (Invited), 241st ECS Meeting (2022).M. L. Perry, et.al., “High Power Density Redox Flow Battery Cells,” ECS Transactions, 53 (2013). DOI: 10.1149/05307.0007ecstC. Tai-Chieh Wan, K. E. Rodby, M. L. Perry, Y.-M. Chiang, F. R. Brushett, “Hydrogen evolution mitigation in iron-chromium redox flow batteries via electrochemical purification of the electrolyte,” J. of Power Sources, 554 (2023). DOI: 10.1016/j.jpowsour.2022.232248T. V. Nguyen, Y. Li, and M. L. Perry, “Densification, Precipitation, and Dissolution of Vanadium Electrolyte for Vanadium Redox Flow Battery Systems,” Submitted for 2023 ECS Meeting, Symposia A03.E. J. Alexandrescu and M. L. Perry, “Measuring Electrochemical Potentials for Health Monitoring of RFBs,” Submitted for 2023 ECS Meeting, Symposia A03.M. L. Perry, “Development of a Simple and Rapid Diagnostic for Redox Flow-Battery Cells,” Symposium I02, 242nd ECS Meeting, (2022).M. L. Perry, “Flow battery with two-phase storage,” U.S. Patent 9,350,039 (2016).Largo Physical Vanadium, Investor Presentation, lpvanadium.com (2022).