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 of80 m A 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 k Wh based on a10 h system with a power of 9.9 k W. This work provides a new option for next-generation cost-effective flow batteries for long duration large scale energy storage.