Abstract

Vanadium flow batteries (VFBs) have promising applications for grid-scale energy storage. Unfortunately, the widespread integration of VFBs into large-scale energy storage applications is hindered by the lack of low-cost ion-conducting membranes (ICMs) with high ion selectivity and excellent stability. Herein, we propose an intrinsically stabilized ether-free fluoropoly(aryl pyridine) (PFNP) and provide a high-performance acid-doped membrane via a phosphoric acid pre-swelling strategy for the battery. Effective acid-doping enables the formation of discrete hydrophilic nano-channels within the PFNP matrix, and the extensive internal hydrogen-bonding network synergistically facilitates charge carrier transport. Simultaneously, the close stacking of PFNP chains and the Donnan effect of protonated piperidinium groups within the membrane effectively prevent vanadium ions permeation. Consequently, this innovative strategy allows the acid-doped membrane to achieve nearly perfect ion selectivity (3.64 × 105 S min cm−3), outperforming the Nafion 212 membrane (3.01 × 104 S min cm−3). Moreover, the fluorinated ether-free structure and non-weak-bond pyridine structure impart excellent mechanical and chemical stability to the acid-doped membrane, ensuring long-term membrane operation. As expected, the VFBs assembled with the acid-doped membrane achieve high energy efficiency (83.1 %) at high current density (200 mA cm−2), offer an ultra-low capacity decay rate of 0.08 % per cycle and retain outstanding stability after 1500 cycles at 120 mA cm−2. This study provides a potential material system for commercial VFB membranes by achieving high performance at low cost.