A Low-Cost Neutral Zinc-Iron Flow Battery with High Energy Density for Stationary Energy Storage.

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 FeCl2 /ZnBr2 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.