Coupling in situ atomic force microscopy (AFM) and ultra-small-angle X-ray scattering (USAXS) to study the evolution of zinc morphology during electrodeposition within an imidazolium based ionic liquid electrolyte

Zinc (Zn) is a low-cost material that is widely used in plating and is under consideration as a reversible deposit for a range of energy storage applications. In recent years, researchers have demonstrated that the Zn morphology can be tuned by electrodepositing from an ionic liquid often leading to morphologies that improve cyclability. However, the underlying mechanisms that control deposition and morphology are not well understood. In this work, we evaluate the evolution of zinc morphology as a function of the deposition thickness using in situ atomic force microscopy (AFM), in situ ultra-small angle X-ray scattering (USAXS) and ex situ electron microscopy. Imaging reveals two dominant features: a hexagonal plate-like morphology associated with individual Zn crystals and larger domains in which the individual crystals appear co-aligned. Analysis of the key features observed by USAXS indicates that the growth of the domain size is non-linear with the charge passed and that at least some of this non-linearity can be attributed to increased coalescence of the individual plates as the deposit thickens. A more detailed analysis suggests that there is little change in the aspect ratio of the individual Zn crystals – this is consistent with a growth mechanism in which previously deposited plates grow in diameter as new plates nucleate on their surface and then coalesce into one crystal.