The high freezing point of polybromides, charging products, is a significant obstacle to the rapid development of zinc-bromine flow batteries (Zn-Br2 FBs). Here, a choline-based complexing agent (CCA) is constructed to liquefy the polybromides at low temperatures. Depending on quaternary ammonium group, choline can effectively complex with polybromide anions and form dense oil-phase that has excellent antifreezing property. Benefiting from indispensable strong ion-ion interaction, the highly selectively compatible CCA, consisting of choline and N-methyl-N-ethyl-morpholinium salts (CCA-M), can be achieved to further enhance bromine fixing ability. Interestingly, the formed polybromides with CCA-M are able to keep liquid even at -40°C. The CCA-M endows Zn-Br2 FBs at 40mAcm-2 with unprecedented long cycle life (over 150cycles) and high Coulombic efficiency (CE, average ≈98.8%) at -20°C, but also at room temperature (over 1200cycles, average CE: ≈94.7%). The CCA shows a promising prospect of application and should be extended to other antifreezing bromine-based energy storage systems.