Modulated Zn Deposition by Glass Fiber Interlayers for Enhanced Cycling Stability of Zn–Br Redox Flow Batteries

The zinc bromine redox flow battery (ZBB) is one of the most promising candidates for next-generation energy storage systems due to its low cost, inflammability, and high power and energy densities. However, dendritic Zn growth, which intensifies at higher current densities and larger deposition capacities, practically hinders the high-current and high-capacity operation of ZBBs. Herein, we demonstrate that a non-conductive, highly porous, and zincophilic glass fiber (GF) layer on top of a carbon felt electrode notably suppresses dendritic Zn growth. The ZBB with the GF layer successfully operates for more than 4000 cycles at 80 mA cm–2 and 20 mA h cm–2, in contrast to the cell failure outcome at the 45th cycle for a GF-free ZBB. Electrochemical analysis and simulations suggest that the surface polar groups of the GF facilitate Zn ion transport and matrix-guided Zn deposition. A GF layer decorated with negatively charged polymer achieves highly superior uniform Zn deposition and remarkable cycling stability at 200 mA cm–2 and 50 mA h cm–2, verifying the validity of this approach