A Zinc–Bromine Flow Battery with Improved Design of Cell Structure and Electrodes

The zinc–bromine flow battery (ZBFB) is regarded as one of the most promising candidates for large-scale energy storage owing to its high energy density and low cost. However, because of the large internal resistance and poor electrocatalytic activity of graphite- or carbon-felt electrodes, conventional ZBFBs usually can only be operated at a relatively low current density, which limits their widespread application. Herein, we propose an asymmetrical cell by replacing the conventional thick felt electrode with a thin and electrocatalytically active carbon-paper (CP) electrode interfacing with a flow-field structure. With the enhanced electrocatalytic activity of CP for the Br₂/Br⁻ redox reaction and the reduced internal resistance of the thinner electrode, the ZBFB with this newly proposed structure exhibits an energy efficiency of up to 83.5 % at a current density of 40 mA cm⁻², much higher than that with a graphite-felt electrode of only 73.0 %. Remarkably, the battery can even be operated at a high current density up to 100 mA cm⁻² while maintaining an energy efficiency of more than 70 %, demonstrating an excellent rate capability.