Advanced Charged Sponge‐Like Membrane with Ultrahigh Stability and Selectivity for Vanadium Flow Batteries

Advanced charged sponge‐like porous membranes with ultrahigh stability and selectivity are designed and fabricated for vanadium flow battery (VFB) applications. The designed porous membranes are fabricated via constructing positively charged cross‐linked networks on the pore walls of polysulfone membranes. The charge density of the pore walls can be tuned by changing the crosslinking time. The positively charged pore walls can effectively retain vanadium ions via Donnan exclusion, hence keeping extremely high selectivity, while the crosslinked network effectively increases the membrane stability. As a result, the designed membranes exhibit an outstanding performance, combining extremely high selectivity and stability. The single cell assembled with the prepared porous membrane shows a columbic efficiency of 99% and an energy efficiency of 86% at a current density of 80 mA cm^?2, which is much higher than Nafion 115 (93.5%; 82.3%). A battery assembled with the prepared membrane shows a stable battery performance over more than 6000 cycles, which is by far the longest record for porous membranes ever reported. These results indicate that advanced, charged, sponge‐like, porous membranes with a crosslinked pore‐wall structure are highly promising for VFB applications.