“Fishnet-like” ion-selective nanochannels in advanced membranes for flow batteries

Abstract

“Fishnet-like” ion-selective nanochannels for advanced membranes are designed for the first time to enhance the efficiency and durability of flow batteries. A fishnet-like structure with 10 nm ion-transport channels is achieved by tuning the hydrophobic/hydrophilic nanophase separation structure of the membrane, in which absorbed water molecules are restricted around hydrophilic polyethylenimine (PEI) chains by hydrophobic polybenzimidazole (PBI). Owing to the size-exclusion and high-density protonated amine groups of PEI fishnets, the membrane exhibits ultralow VO²⁺ permeability without sacrificing its ion conductivity, ensuring high energy efficiency of vanadium flow batteries. Furthermore, the demonstrated vanadium flow battery with the fishnet-based membrane steadily run at 120 mA cm⁻² over 2000 cycles (about 120 days). These findings provide a new strategy for the design of high-performance and cost-effective membranes for vanadium flow battery applications.