Functional complexed zincate ions enable dendrite-free long cycle alkaline zinc-based flow batteries

Highly reliable alkaline zinc-based flow batteries are promising options for stationary energy storage and require uniform zinc plating determined by anolyte chemistry. However, the anolyte properties, particularly molecular structure of zincate ion are intricate and yet to be clearly identified. Herein, we report a N, N, N′ N′-Tetra(2-hydroxyethyl) ethylenediamine (THEED) additive to enable uniform zinc plating by altering molecular structure of zincate couple. The THEED can complex with Zn(OH)42- and form Zn(OH)xx−2-THEED-H2O with slow-down deposition kinetics on anode and realizing uniform plating of zinc, and form new hydrogen bond networks with water, favoring trapping water molecules. These in turn enable alkaline zinc-iron flow battery single cell and cell stack with dramatically improved reliability. Additionally, the THEED could suppress the migration of water during charge/discharge process. This work illustrates new ways for realizing uniform zinc plating based on scientific understanding of electrolyte chemistry to promote the development of alkaline zinc-based flow batteries.