AbstractWidespread adoption of redox flow batteries (RFBs) for renewable energy storage is inhibited by a relatively high cost of storage. This is due largely to typical RFBs requiring two flows, two external tanks, and expensive ion‐exchange membranes. Here, we propose a potentially inexpensive Zn‐Br2 RFB which is membraneless and requires only a single flow. The flow is an emulsion consisting of a continuous, Br2‐poor aqueous phase and a dispersed, Br2‐rich polybromide phase, pumped through the channel separating anode and cathode. With our prototype cell, we explore the effect of polybromide‐phase volume fraction and Br2 concentration on cell performance and plating efficiencies. We demonstrate high discharge currents of up to 270 mA/cm2, plating efficiencies up to 88 %, and dendriteless plating up to the highest Zn loading investigated of 250 mAh/cm2. We provide mechanistic insights into cell behavior and elucidate paths towards unlocking ultra‐low‐cost single‐flow RFBs with multiphase flow.