A Low‐Cost Neutral Zinc–Iron Flow Battery with High Energy Density for Stationary Energy Storage

Abstract Flow batteries (FBs) are one of the most promising stationary energy‐storage devices for storing renewable energy. However, commercial progress of FBs is limited by their high cost and low energy density. A neutral zinc–iron FB with very low cost and high energy density is presented. By using highly soluble FeCl 2 /ZnBr 2 species, a charge energy density of 56. 30 Wh L −1 can be achieved. DFT calculations demonstrated that glycine can combine with iron to suppress hydrolysis and crossover of Fe 3+ /Fe 2+. The results indicated that an energy efficiency of 86. 66 % can be obtained at 40 mA cm −2 and the battery can run stably for more than 100 cycles. Furthermore, a low‐cost porous membrane was employed to lower the capital cost to less than 50 per kWh, which was the lowest value that has ever been reported. Combining the features of low cost, high energy density and high energy efficiency, the neutral zinc–iron FB is a promising candidate for stationary energy‐storage applications.