•Chemical cost analyzed for 40 rechargeable couples developed over the past 60 years
•Aqueous sulfur/sodium/air system identified with ultralow chemical cost of ∼US$1/kWh
•Air-breathing flow battery architecture demonstrated at laboratory scale
•Techno-economic analysis shows installed cost is comparable with PHS and CAES

Above – Curves for the present air-breathing aqueous sulfur flow battery approach using Na and Li chemistry are shown in green and gray, respectively. The chemical costs for Na and Li are shown as dashed lines. Curves of constant power cost show that the power stack dominates the system cost at short storage durations, whereas at long duration the cost asymptotically approaches the energy cost due to chemical constituents plus storage tank and related costs. 5 M concentrations of both Na and S are assumed, with cycling of the sulfur over the speciation range S22− to S42− corresponding to 25% of theoretical capacity.