Carbonate formation on carbon electrode in rechargeable zinc-air battery revealed by in-situ Raman measurements

Carbonate formation on a carbon electrode for rechargeable zinc-air batteries can lead to degraded battery performance and limited lifetime for practical use. In this study, the carbonate formation is observed at an unexpected early working state through in-situ Raman measurements. The origin of carbonate formation from carbon corrosion in the alkaline electrolyte is revealed by its distribution near the potassium hydroxide solution via our self-developed multi-point Raman mapping apparatus. More importantly, it is found that during charging, the carbonate formation affects the formation of the zinc oxide byproduct and impedes the oxygen evolution reaction due to its consumption of hydroxyl ions. In comparison, insoluble carbonate precipitation is generated within the porous carbon electrode during discharging, which could block the oxygen throughput and consequently deteriorate the air electrode performance. This in-situ study clarifies the initial state of carbon electrode corrosion in the alkaline electrolyte, providing an insight into the future optimizations towards the air electrode design.