Li dendrite growth is a critical safety issue for batteries with lithium metal anodes. Mg metal electrodes offer a promising way to overcome this safety limitation. Yao et.al. has observed that Li and Mg plating show different morphology, where Li plating is more dendritic but Mg plating is more faceted [ ACS Appl. Mater. Interfaces 7 (2015) 7001]. The difference of the morphology evolution of the plated Li and Mg is related to the interfacial reactions kinetics at the electrode and electrolyte interface. One major difference is that an electrical insulating but ionic conducting solid electrolyte interphase (SEI) always covers Li anode, but Mg electrode surface is believed to be SEI free. Here, atomistic simulations are combined with phase-filed model to evaluate the effect of interfacial reaction kinetics on the plated Li/Mg structural morphology. Using both static first-principles calculations and ab initio molecular dynamics, the interfacial structures, de-solvation processes and Li+/Mg2+ ion energy landscapes at Li/SEI/ethylene carbonate (EC)-electrolyte and Mg/ tetrahydrofuran(THF)-electrolyte, and the effects of electric field on them were investigated. Coupling with atomistic calculations, phase-field simulations were performed to investigate the Li/Mg plating morphological evolution from mesoscale. With thermodynamic and kinetic parametric inputs from first-principles calculation (i.e. interfacial energy and anisotropy of Li/SEI (Li2CO3), surface energy and anisotropy of Mg, diffusion coefficient of Li+ in SEI (Li2CO3), and relative difference in charge-transfer energy barrier of Li/Mg plating), our non-linear phase-field model captures the notable morphological evolution difference between dendritic Li plating and faceted Mg plating. Furthermore, the simulation results indicate that, among all possible parameters for Li/Mg electrodeposition processes, the plating charge-transfer energy barrier difference is the major contributing factor that accounts for the morphological discrepancy.

Comparison of the interfacial reaction kinetics and plating morphology of lithium and magnesium anodes

256th National Meeting (2018)

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