Fixed‐Linkage Enabled Ultra‐Stable Ion Transport Channels in Membranes for Long‐Life Alkaline Flow Batteries

ABSTRACT Alkaline zinc–iron redox flow batteries (Zn─Fe FBs) are promising candidates for developing high‐voltage and cost‐effective grid‐scale energy storage systems. However, the low ionic conductivity and poor alkaline stability of membranes lead to battery performance degradation and shortened lifespan. Here, we develop fixed ethylene linkage‐based polybenzimidazole (FE‐PBI) membranes to break this dilemma. Introducing fixed ethylene linkages enlarges the ion transport channel and provides inter‐support for polymer chains, thereby preserving highly ordered and flux ion transport channels in the alkaline environment. By this unique channel design, this FE‐PBI membrane enables alkaline Zn‐based asymmetric FBs to deliver excellent rate performance (up to 240 mA cm ⁻² ) with high reversibility of Zn deposition. Furthermore, the Zn─Fe FBs using FE‐PBI membranes deliver a highly stable rate performance across the range of 60–180 mA cm ⁻² and 120 mAh cm ⁻² . At a challenging condition of high current density (100 mA cm ⁻² ) and areal capacity (80 mAh cm ⁻² ), the developed Zn─Fe FBs achieve an impressive energy efficiency of >85.56% and remarkable stability over 800 h (500 cycles), surpassing the lifespan performance of current alkaline Zn─Fe FBs. This work offers a new membrane design approach to combine high energy efficiency with an extended lifespan, realizing long‐lifetime alkaline FBs.