Solvent‐Induced Rearrangement of Ion‐Transport Channels: A Way to Create Advanced Porous Membranes for Vanadium Flow Batteries

Porous membranes with critically hydrophobic/hydrophilic phase‐separated‐like structures for use in vanadium flow battery application are first realized by solvent‐induced reassembly of a polymer blend system. Porous poly(ether sulfone) (PES)/sufonated poly(ether ether ketone) (SPEEK) blend membranes with tunable pore size are prepared via the phase inversion method. After solidification, isopropanol (IPA) is introduced to induce the reassembly of sulfonated groups and further form ion‐transport channels by using the interaction between IPA and functional groups in SPEEK. As a result, a highly phase separated membrane structure is created, composed of a highly stable hydrophobic porous PES matrix and hydrophilic interconnected small pores. The charged pore walls are highly beneficial to improving proton conductivity, while pores are simultaneously shrunk during the IPA treatment. Therefore, the resultant membranes show an excellent battery performance with a coulombic efficiency exceeding 99%, along with an energy efficiency over 91%, which is among the highest values ever reported. This article supplies an ease‐to‐operate and efficient method to create membranes with controlled ion‐transport channels.