Moss-like Growth of Metal Electrodes: On the Role of Competing Faradaic Reactions and Fast Charging

Uncontrolled crystal growth during electroreduction of reactive metals in liquid electrolytes produces mossy metal deposits. Here, we use electroanalytical rotating disk electrode (RDE) studies to elucidate the origin of moss-like electrodeposition of metals. Competing Faradaic reactions on the electrode surface are shown to be the source of the phenomenon. A moss-like growth regime can be accessed by subtle shifts in electrolyte chemistry and deposition rate. For Zn─a metal that conventionally is not known to form moss-like electrodeposits─obvious moss-like patterns emerge at low-current densities in strongly alkaline electrolytes. Conversely, under conditions where the electroreduction rate is large relative to competing Faradaic reactions, moss-like Zn growth is eliminated. The same principle holds for Li metal deposition. On that basis, an empirical rule is proposed─an applied current density i that satisfies the relation 10 i s < i < 0.8 i lim is required for achieving favorable metal electrodeposit morphology and fast charging in batteries.