Interfacial Regulation by Polycationic Polymers for Dendrite‐Free Zinc Deposition in Alkaline Zinc‐Iron Flow Batteries

Zinc-based flow batteries (ZFBs) have emerged as promising energy storage systems due to their high theoretical gravimetric capacity, low electrochemical potential, natural abundance of zinc, and cost-effectiveness. However, their widespread adoption is hindered by the persistent issue of zinc dendrite formation. Herein, we report a facile yet effective strategy to suppress dendrite formation by introducing polyquaternium-6 (PQ-6) as a functional electrolyte additive. Spectroscopic and electrochemical analyses reveal that PQ-6 preferentially adsorbs at the electrode-electrolyte interface, forming a dynamic barrier that modulates the zincate ion diffusion from a two-dimensional (2D) to a three-dimensional (3D) mode and promotes homogeneous nucleation. Consequently, the PQ-6 modified alkaline zinc-iron flow battery (AZIFB) exhibits exceptional cycling stability (nearly 400 h, 1200 cycles) while maintaining high energy efficiency (70.37%) at a current density of 80 mA cm^-2. This work not only provides an effective strategy for mitigating zinc dendrite growth but also advances the development of sustainable and high-performance zinc-based flow batteries.