Advanced Membrane-Free Electrochemical Energy Storage Devices (Phase 1)

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Energy storage is required for making renewable electricity generation, such as wind and solar, dispatchable. A variety of energy storage technologies are technically mature and commercially available. Among these, redox flow batteries (RFBs) operating with vanadium electrochemistry (vanadium redox flow battery, VRFB) offer a unique advantage of independently sizing power and energy density, and are therefore a promising candidate for grid and off-grid stationary energy storage applications. However, the current generation of RFBs suffer from operational inefficiency, primarily due the use of Nafion membrane that separates the anolyte and catholyte. Yet it is necessary to allow the movement of protons across the membrane to support the fundamentals of electrochemistry. The membrane is incapable of preventing vanadium ion crossover through it resulting in electrolyte dilution and efficiency loss, and limiting the battery operating temperature range, generally above 40°C. Additionally, the Nafion membrane is costly and approximately represents 40% of the cell stack cost. We are proposing a radically innovative RFB/VRFB design in which the membrane as well as the associated technical issues are eliminated. In our design, the membrane is replaced with auxiliary electrodes (AE's) made of metal oxides (SnO/SnO2), that change their oxidation states (Sn2+/Sn4+) during charging/discharging, balance the charges in the anolyte and catholyte, and provide the necessary electrochemistry for the electrochemical energy storage. AEs eliminate ionic movement between electrolyte compartments and completely prevent electrolyte crossover without negatively impacting cell performance. This novel design also provides an opportunity to use high-energy-dense electrolytes in the RFB system with flexible operating conditions. Five HQPs will be trained in the RFB technology during this project. These HQPs will be skilled in technical and business aspects of energy storage and suitable for high-demand energy storage positions in industry and academia in the near future.