Multifunctional Carbon Felt Electrode with N‐Rich Defects Enables a Long‐Cycle Zinc‐Bromine Flow Battery with Ultrahigh Power Density

Abstract Zinc‐bromine flow batteries (ZBFBs) are regarded as one of the most promising technologies for energy storage owing to high energy density and low cost. However, the sluggish reaction kinetics of Br 2 /Br − couples and zinc dendrite issue lead to low power density and poor cycle stability. Herein, a multifunctional carbon felt‐based electrode (NTCF) with N‐rich defects is fabricated for ZBFBs. The defects with abundant N‐containing groups on carbon fibers of NTCF provide high catalytic activity on Br 2 /Br − reactions. Simultaneously, the lower energy barrier of N‐rich defects to adsorb zinc atoms, and more deposition sites on NTCF induce more uniform zinc deposition. Thus, a ZBFB using NTCF as both the anode and cathode can stably operate at an unprecedentedly high current density of 180 mA cm −2 with a coulombic efficiency of 97.25%. Moreover, a long cycle life of over 140 cycles with a coulombic efficiency of 98.93% for a Zn symmetric flow battery at 80 mA cm −2 is achieved under a high areal capacity of 40 mAh cm −2 . This current density and areal capacity are by far the highest values ever reported for Zn symmetry flow batteries. Therefore, this work provides an available approach to improve the power density and cycle life of ZBFBs.