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-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.