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–Bi₂O₃ chemistry. We found that the electrochemical oxidation of dead zinc by Bi₂O₃ 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 Bi₂O₃ 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.