In situ visualization of interfacial processes at nanoscale in non-alkaline Zn-air batteries

Zn-air batteries (ZABs) present high energy density and high safety but suffer from low oxygen reaction reversibility and dendrite growth at Zn electrode in alkaline electrolytes. Non-alkaline electrolytes have been considered recently for improving the interfacial processes in ZABs. However, the dynamic evolution and reaction mechanisms regulated by electrolytes at both the positive and Zn negative electrodes remain elusive. Herein, using in situ atomic force microscopy, we disclose that thin ZnO2 nanosheets deposit in non-alkaline electrolyte during discharge, followed by the formation of low-modulus products encircled around them. During recharge, the nanosheets are completely decomposed, revealing the favorable reversibility of the O2/ZnO2 chemistry. The circular outlines with low-modulus, composed of C = C and ZnCO3, are left which play a key role in promoting the oxygen reduction reaction (ORR) during the subsequent cycles. In addition, in situ optical microscopy shows that Zn can be uniformly dissolved and deposited in non-alkaline electrolyte, with the formation of homogeneous solid electrolyte interphase. Our work provides straightforward evidence and in-depth understanding of the interfacial reactions at both electrode interfaces in non-alkaline electrolyte, which can inspire strategies of interfacial engineering and material design of advanced ZABs.