Air-Breathing Aqueous Sulfur Flow Battery for Ultralow-Cost Long-Duration Electrical Storage

Summary The intermittency of renewable electricity generation has created a pressing global need for low-cost, highly scalable energy storage. Although pumped hydroelectric storage (PHS) and underground compressed air energy storage (CAES) have the lowest costs today (∼US$100/kWh installed cost), each faces geographical and environmental constraints that may limit further deployment. Here, we demonstrate an ambient-temperature aqueous rechargeable flow battery that uses low-cost polysulfide anolytes in conjunction with lithium or sodium counter-ions, and an air- or oxygen-breathing cathode. The solution energy density, at 30–145 Wh/L depending on concentration and sulfur speciation range, exceeds current solution-based flow batteries, and the cost of active materials per stored energy is exceptionally low, ∼US$1/kWh when using sodium polysulfide. The projected storage economics parallel those for PHS and CAES but can be realized at higher energy density and with minimal locational constraints.