Realizing an anolyte utilization rate of 99% in low-cost zinc-based flow batteries by rejuvenating dead zinc

Abstract

Zinc-based flow batteries (ZFBs) are regarded as promising candidates for large-scale energy storage systems. However, the formation of dead zinc and dendrites, especially at high areal capacities and current densities, makes ZFBs commonly operate at a low anolyte utilization rate (AUR), limiting their applications. In this study, we developed an effective strategy for addressing these problems through Zn-Bi<inf>2</inf>O<inf>3</inf> chemistry. We found that the electrochemical oxidation of dead zinc by Bi<inf>2</inf>O<inf>3</inf> can rapidly restore the lost capacity of the battery. We also discovered that the presence of saturated high-valent bismuth salts in the anolyte can aid in forming functional Bi and ZnBi alloy interfaces, thus hindering the growth of zinc dendrites. Consequently, alkaline zinc-iron flow batteries (AZIFBs) with Bi<inf>2</inf>O<inf>3</inf> can maintain an AUR of 99% even at 160 mA cm⁻², which is, to our knowledge, the highest value ever reported for ZFBs at such a high current density. These AZIFBs can also achieve ultrahigh cycling stability for over 800 hours, with an average Coulombic efficiency of 99.6% and a high areal capacity of 99.5 mA h cm⁻². Overall, this study provides valuable insights into high-energy-density and low-cost ZFBs with a high AUR and promotes their development.