In order to promote the conduction and stability of anion exchange membranes (AEMs) for the vanadium redox flow battery (VRFB), a kind of quaternary ammonium AEMs with flexible side chains (PAES-4N-xx, xx represents the proportion of monomers containing an amino structure) are prepared via aromatic nucleophilic polycondensation and grafting reactions. The ion exchange capacity (IEC) values of PAES-4N-xx are in the range of 1.58−2.10 mmol g −1 , and their water uptake, swelling ratio, SO 4 2− conductivity, and VO 2+ permeability at 30 °C are in the range of 15−52%, 5−17%, 13.5−22.4 mS cm −1 , and 8.6−43.3 cm 2 min −1 , respectively. In addition, PAES-4N-xx display good stability, and their retention ratio of IEC and conductivity reach more than 95% after soaking in a solution of 1.5 mol L −1 VO 2 + /3 mol L −1 H 2 SO 4 at RT for 30 days. The typical battery assembled with PAES-4N-40 shows high efficiency; its Coulomb efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) are in the range of 93.5%−97.8%, 88.6%−70.5%, and 69.0%− 84.9% at the fixed current density which is between 40 mA cm −2 and 200 mA cm −2 , respectively. The battery also has good stability for 100 cycles of charging and discharging at a current density of 40 mA cm −2 , and its retention of EE reaches 96.5%. The introduction of flexible side chains and dense cationic structures can effectively improve the performance of the VRFB.

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