Electrode Materials for Enhancing the Performance and Cycling Stability of Zinc Iodide Flow Batteries at High Current Densities

Aqueous redox flow battery systems that use a zinc negativeelectrodehave a relatively high energy density. However, high current densitiescan lead to zinc dendrite growth and electrode polarization, whichlimit the battery's high power density and cyclability. Inthis study, a perforated copper foil with a high electrical conductivitywas used on the negative side, combined with an electrocatalyst onthe positive electrode in a zinc iodide flow battery. A significantimprovement in the energy efficiency (ca. 10% vs using graphite felton both sides) and cycling stability at a high current density of40 mA cm(-2) was observed. A long cycling stabilitywith a high areal capacity of 222 mA h cm(-2) is obtainedin this study, which is the highest reported areal capacity for zinc-iodideaqueous flow batteries operating at high current density, in comparisonto previous studies. Additionally, the use of a perforated copperfoil anode in combination with a novel flow mode was discovered toachieve consistent cycling at exceedingly high current densities of>100 mA cm(-2). In situ and ex situ characterizationtechniques, including in situ atomic force microscopy coupled within situ optical microscopy and X-ray diffraction, are applied to clarifythe relationship between zinc deposition morphology on the perforatedcopper foil and battery performance in two different flow field conditions.With a portion of the flow going through the perforations, a significantlymore uniform and compact zinc deposition was observed compared tothe case where all of the flow passed over the surface of the electrode.Results from modeling and simulation support the conclusion that theflow of a fraction of electrolyte through the electrode enhances masstransport, enabling a more compact deposit.