Thermodynamic Overpotentials and Nucleation Rates for Electrodeposition on Metal Anodes.

Abstract

Rechargeable batteries employing metal negative electrodes (i.e., anodes) are attractive next-generation energy storage devices because of their greater theoretical energy densities compared to intercalation-based anodes. An important consideration for a metal's viability as an anode is the efficiency with which it undergoes electrodeposition and electrodissolution. The present study assesses thermodynamic deposition/dissolution efficiencies and associated nucleation rates for seven metals (Li, Na, K, Mg, Ca, Al, and Zn) of relevance for battery applications. First-principles calculations were used to evaluate thermodynamic overpotentials at terraces and steps on several low-energy surfaces of these metals. In general, overpotentials are observed to be the smallest for plating/stripping at steps and largest at terrace sites. The difference in the coordination number for a surface atom from that in the bulk was found to correlate with the overpotential magnitude. Consequently, because of their low bulk coordination, the body-centered alkali metals (Li, Na, and K) are predicted to be among the most thermodynamically efficient for plating/stripping. In contrast, metals with larger bulk coordination such as Al, Zn, and the alkaline earths (Ca and Mg) generally exhibit higher thermodynamic overpotentials. The rate of steady-state nucleation during electrodeposition was estimated using a classical nucleation model informed by the present first-principles calculations. Nucleation rates are predicted to be several orders of magnitude larger on alkali metal surfaces than on the other metals. This multiscale model highlights the sensitivity of the nucleation behavior on the structure and composition of the electrode surface.