Investigation of failure mechanism of rechargeable zinc–air batteries with poly(acrylic acid) alkaline gel electrolyte during discharge–charge cycles at different current densities

Flexible zinc–air batteries (FZABs) show a promising future for emerging electronic devices, while the short cycle life seriously limits their large-scale applications. Although numerous opinions on the failure reasons for FZABs during discharge–charge cycles have been raised, the bottleneck factors that influence the cycle lifetime of the FZABs remain unclear. Herein, we fabricated a FZAB with poly(acrylic acid) alkaline gel electrolyte and conducted a series of comparative experiments to explore the bottleneck factors of battery failure when cycling under different current densities. Under a low current density of 2 mA cm−2, the content of OH− in the gel polymer electrolyte (GPE) highly determines the cycling life of FZABs. Owing to the formation of ZnO and carbonates as well as the carbon oxidation of the air electrode, the content of OH− is significantly reduced, shortening the battery cycling life. Furthermore, under a high current density of 10 mA cm−2, the deteriorative electrochemical performance of air electrode caused by the carbon oxidation at high charging potential is the key factor leading to the battery failure. Therefore, reducing the charging potential of the battery or optimizing the composition and structure of the air electrode is critical to extend battery life. Besides, under a higher current density of 20 mA cm−2, the passivation of the Zn electrode, increased interface resistance between the Zn electrode and GPE, as well as the reduced electrochemical performance of the air electrode are reasons for the battery failure. This work provides a significant guidance for prolonging the cycle lifespan of next generation batteries.