A high-energy and low-cost polysulfide/iodide redox flow battery

Redox flow batteries (RFBs) have been limited by low energy density and high cost. Here, we employ highly soluble, inexpensive and reversible polysulfide and iodide species to demonstrate a high-energy and low-cost all-liquid polysulfide/iodide redox flow battery (PSIB). In contrast to metal-hybrid or semi-solid approaches that are usually adapted for high-energy RFBs, the all-liquid characteristic of the PSIB is crucial to enable practical scale-up development. Combining the achieved energy density (43.1 W h L-catholyteAnolyt(-1)) and the inherent low materials cost of sulfur and iodine compared to vanadium, the PSIB system demonstrates a significantly lower materials cost per kilowatt hour ($85.4 kWh(-1)) compared to the state-of-the-art vanadium based redox flow batteries ($152.0-154.6 kW h(-1)). Operando UV-Visible spectroscopy reveals superior electrochemical reversibility of both electrolytes. With its demonstrated energy density, inherent low material cost and benign chemical natures, the all-liquid PSIB offers a promising solution for high-energy-density and low-cost energy storage applications.