Sintering of the nanofiber membranes results in fine-tuning of the membrane properties without disturbing the core structure of the fibers. Here we have demonstrated the robust method with solvent and nonsolvent mixture to tune the pores of an electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) membrane and its utility in an aqueous zinc‑iodine flow battery (ZIFB). The method effectively altered the membrane's pores while improving the inter-fiber adhesion between nanofibers, which also gave the membrane improved mechanical properties. The sintered membrane exhibited its competence in ZIFB by delivering high Coulombic efficiency (CE) and Energy efficiency (EE) of 96 % and 82 % at 40 mA cm−2 over 200 stable charge/discharge cycles without obvious decay. The nanofiber membrane's pores were precisely adjusted to prevent electrolyte cross-over while promoting the battery's ability to heal itself after developing zinc dendrites. In comparison to the best-reported membranes in the literature, we have obtained the best power density of 201 mW cm−2 at 50 mA cm−2 and a capacity of 71.5 mAh cm−2. Other polymer nanofibers compatible with the investigated solvent/nonsolvent system can be used with the technique, indicating its broad applicability and utility.