On the Mechanism of Mossy Zn Deposition

Electrochemical deposition of Zn metal from a zincate electrolyte can lead to a peculiar mossy morphology comprising numerous slim kinky filaments. Like mossy Li in Li metal batteries, mossy Zn is considered detrimental to the stability of rechargeable Zn batteries. Yet unlike Li, the cleaner interface and the easier characterizations of Zn metal offer us an opportunity to dig deeper into the mechanism of mossy deposition. With well-polished and annealed polycrystalline Zn foil as an electrode, we show that the mossy deposition, occurring at a low overpotential, is localized at the surface intersects of defects such as grain boundaries. Through the measurements of cross-sectional microstructures, stress, and surface composition, we gain insights into the formation sites, the driving force, and the kinetics, drawing a close comparison to both mossy Li and metal whiskers.