A Single‐Flow Battery with Multiphase Flow

Widespread 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‐Br 2 RFB which is membraneless and requires only a single flow. The flow is an emulsion consisting of a continuous, Br 2 ‐poor aqueous phase and a dispersed, Br 2 ‐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 Br 2 concentration on cell performance and plating efficiencies. We demonstrate high discharge currents of up to 270 mA/cm 2 , plating efficiencies up to 88 %, and dendriteless plating up to the highest Zn loading investigated of 250 mAh/cm 2 . We provide mechanistic insights into cell behavior and elucidate paths towards unlocking ultra‐low‐cost single‐flow RFBs with multiphase flow.