Unveiling zinc anode corrosion

Zinc batteries are promising for grid-scale energy storage due to their safety, low cost, and high capacity. A key part of their appeal lies in the use of metallic zinc at the anode, which is abundant, non-toxic, and water compatible. However, even when the battery is resting — not charging or discharging — the zinc anode gradually corrodes. Now, Yi Yuan, Alex Robertson and colleagues at the University of Warwick, the University of Oxford and Central South University reveal the mechanisms behind this subtle degradation. Using in situ electrochemical liquid cell transmission electron microscopy, they directly visualize the corrosion processes of zinc metal anodes in the most commonly used aqueous electrolytes — those based on mildly acidic zinc sulfate.

Their study shows that corrosion occurs in two stages: first, the zinc metal dissolves into the electrolyte, releasing hydrogen gas and increasing the local pH. This pH change results in the formation of basic, insoluble zinc hydroxysulfate byproducts with porous and loose structures, which gradually deplete zinc and degrade battery performance. Surprisingly, using excess zinc at the anode — previously considered a safe buffer against loss — actually exacerbates the problem by accelerating pH shifts and corrosion. In contrast, a simple electrolyte additive, zinc acetate, helps stabilize the pH and significantly reduces these losses. This work highlights a subtle but important issue: zinc anodes corrode even when the battery is not in use, compromising shelf life, safety, and performance. The findings underscore the importance of carefully balancing zinc content and electrolyte composition to improve battery longevity. As zinc batteries move closer to real-world deployment, understanding and controlling this hidden degradation process may prove key to their long-term success.