Low-cost all-iron flow battery with high performance towards long-duration energy storage

Long duration energy storage (LDES) technologies are vital for wide utilization of renewable energy sources and increasing the penetration of these technologies within energy infrastructures. Herein, we propose a low-cost alkaline all-iron flow battery by coupling ferri/ferro-cyanide redox couple with ferric/ferrous-gluconate complexes redox couple. The designed all-iron flow battery demonstrates a coulombic efficiency of above 99% and an energy efficiency of ∼83% at a current density of 80 mA cm−2, which can continuously run for more than 950 cycles. Most importantly, the battery demonstrates a coulombic efficiency of more than 99.0% and an energy efficiency of ∼83% for a long duration (∼12, 16 and 20 h per cycle) charge/discharge process. Benefiting from the low cost of iron electrolytes, the overall cost of the all-iron flow battery system can be reached as low as $76.11 per kWh based on a 10 h system with a power of 9.9 kW. This work provides a new option for next-generation cost-effective flow batteries for long duration large scale energy storage.