Mechanism of Capacity Loss of Zinc Anodes during Calendar Aging

Abstract Zinc-based flow batteries (ZBFBs) hold significant promise for low-cost and safe large-scale energy storage; however, there has been a lack of focus on calendar aging and the corresponding strategies to mitigate capacity decay. Herein, we systematically examined the factors affecting the calendar aging of zinc anodes, identifying current density and dissolved oxygen (DO) as key contributors to capacity loss. Low interfacial impedance and deposition overpotential in oxygen-free electrolytes, especially at low current densities, promote the formation of larger zinc particles. This phenomenon reduces the active contact area between the zinc anode and the electrolyte, thereby alleviating corrosion during calendar aging. The Zn∥Zn symmetrical flow battery (ZSFB) operated at 10 mA cm–2 exhibited a much lower Coulombic efficiency (CE) loss of 2.11% after 12 h of aging, compared to the 29.73% CE loss when operated at 60 mA cm–2. Moreover, for oxygen-free electrolytes, the ZSFB operated at 40 mA cm–2 exhibited a CE loss of 6.83% after 24 h of aging. To demonstrate this concept, potassium iodide (KI) was introduced as an oxygen scavenger, which significantly enhanced aging performance and cycling stability. This research provides valuable insights for future studies aimed at improving the understanding of calendar aging and the overall performance of ZBFBs.