Montmorillonite-Based Separator Enables a Long-Life Alkaline Zinc–Iron Flow Battery

Alkaline zinc–iron flow batteries (AZIFBs) demonstrate great potential in the field of stationary energy storage. However, the reliability of alkaline zinc–iron flow batteries is limited by dendritic zinc and zinc accumulation, which has been treated as one of the most critical issues for the practical application of alkaline zinc–iron flow batteries. Herein, montmorillonite (MMT) with high mechanical stability and negatively charged property is introduced on the surface of a porous poly(ether sulfone) substrate, which enables an efficient and highly stable alkaline zinc–iron flow battery. The high mechanical strength of MMT can avoid damaging from metallic zinc, while its negatively charged property can effectively equilibrate the distribution of zincate ions at the interface between the membrane and the electrode. The synergistic effects of charge property and mechanical strength enabled by the montmorillonite flake layer can in turn effectively adjust the deposited zinc from "honeycomb-like" to "stick-like" morphology, thus affording the battery with a stable performance for 500 cycles at a current density of 140 mA cm–2, maintaining an energy efficiency of ∼80%. The results of this study are important for the regulation of zinc deposition morphology and the improvement of the operational reliability of zinc-based flow batteries.