Relaxation of the Adsorbed Material and Shadowing Effects on the Shape and Size of Electrodeposited Dendrites

Abstract

Materials with dendritic morphologies exhibit large surface areas that improve the catalytic, optical, and wetting properties but have ambiguous effects in batteries, so modeling their growth may help find the best operation conditions in each case. Kinetic Monte Carlo simulations are used here to study a metal electrodeposition model that represents the interplay between diffusive cation flux in the electrolyte and surface diffusion of adsorbed atoms (adatoms) with electrodes perpendicular to the gradient of the electrolyte concentration and different crystallographic orientations. In FCC lattices, dendrites with a pine tree shape are formed for all orientations, with dominant (111) surfaces and with trunks propagating in [001] and equivalent directions. However, with (110) and (111) substrates, secondary branches do not grow because the inclined primary branches block the cation flux (shadowing effect), so the dendrites may have a leaf-like shape. Some morphologies obtained here resemble those of the silver and gold electrodeposits. The extension to electrodeposition of HCP crystals with (0001) substrates shows the formation of leaf-like dendrites with a hexagonal symmetry. In both lattices, hierarchically organized structures appear for model parameters that warrant large diffusion lengths of adsorbed atoms on flat planes (typically coordination numbers n ≤ 4) and their stability at low-energy configurations (n ≥ 7). Average dendrite widths scale approximately with the diffusion length from adsorption to permanent incorporation to the crystal. These results show that dendrite widths are directly related to the relaxation of the electrodeposited material, and their crystallography is controlled by the energetics of the relaxation, but their visual appearance may depend on their angles with the electrode. In the range of model parameters where the coordination number weakly affects the diffusion of adsorbed atoms, the dendrites become rounded and have flower-like shapes. Possible effects of the orientation on the physicochemical properties of thin dendritic films are discussed.