Constructing high-performance fluoropoly(aryl piperidinium) ion exchange membranes via side-chain engineering for efficient vanadium flow batteries

Vanadium flow batteries (VFBs) have demonstrated significant potential for large-scale energy storage technology. However, the lack of a highly ion-selective and stable ion exchange membrane (IEM) is a major dilemma for developing high-performance VFBs. Herein, we present a new insight to prepare high-performance fluoropoly(aryl piperidinium) IEMs by side-chain engineering modifications. Benefiting from the synergistic effect between the fluorine-containing structure and the functional side chains, distinct microphase-separated structures are formed within the membrane and the prepared IEMs exhibit lower area resistance (0.16–0.41 Ω cm2) compared to Nafion115 (0.57 Ω cm2). The repulsive effect generated by the intrinsic alkaline cation groups inhibits the cross-penetration of vanadium ions, contributing to the ultra-low VO2+ permeability (∼8.63 × 10−9 cm2 min−1, 96 times lower than Nafion115) of the resultant IEMs. Moreover, the unique fluorinated structure effectively suppresses membrane swelling while enabling excellent mechanical and chemical stability. Consequently, the assembled AMPFMP battery achieves excellent efficiency (coulombic efficiency = 99.23% and energy efficiency = 82.15% at a high current density of 200 mA cm−2) and outstanding cycling performance (no significant decay in efficiency during 1000 cycles at 120 mA cm−2), outperforming Nafion 115. These results indicate that the side-chain engineering design of fluorinated IEM provides a valuable strategy for developing efficient and durable VFB diaphragms.