In Situ Scanning Electron Microscopy Characterization of the Mechanism for Li Dendrite Growth

The nucleation and growth of Li metal deposits and whiskers were studied using a novel in-situ scanning electron microscopy (SEM) platform. The experiments utilized a thin carbon film as a substrate for Li deposition. Rather than depositing primarily at the carbon-electrolyte interface, much of the Li deposits at the carbon-vacuum interface. This allows the effects of concentration polarization and electric field localization to be eliminated as primary mechanisms for whisker and dendrite growth. Instead, measurements performed as a function of vacuum pressure reveal that whisker growth is sensitive to vacuum level. It is proposed that whisker growth results from diffusional relaxation of compressive stress imposed by a thin surface oxide. Similar mechanisms may be extended to Li dendrite growth in solution where solid electrolyte interphase introduces a compressive stress.