Sweeping potential regulated structural and chemical evolution of solid-electrolyte interphase on Cu and Li as revealed by cryo-TEM

Abstract

A fundamental understanding of solid-electrolyte interphase (SEI) is paramount importance for controlling the cycling performance of rechargeable lithium metal batteries. The structural and chemical evolution of SEI with respect to electrochemical operating condition remains barely established. Here we develop a unique method for imaging the evolution of SEI formed on the Cu foil under sweeping electrochemical potential. By using cryogenic TEM imaging combined with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy electronic structure analyses, we reveal that, for the vinylene carbonate (VC)-free electrolyte, the SEI formed at 1.0 V is a monolithic amorphous structure, which evolves to amorphous matrix embedded with Li 2 O particles as the voltage decreases to 0 V. In the case of VC-containing electrolyte, the SEI is featured by an amorphous matrix with Li 2 O particles from 1.0 V to 0 V. The thickness of SEI formed on Cu foil increases with decreasing voltage. Associated with the localized charge modulation by the surface topographic feature and defects in the Cu foil, the SEI layer shows direct spatial correlation with these structural defects in the Cu. In addition, upon Li deposition, the SEI formed on the Li metal has similar thickness with, but different composition from the SEI formed on the Cu foil at 0 V. Those results provide insight toward SEI engineering for enhanced cycling stability of Li metal. A fundamental understanding of solid-electrolyte interphase is paramount importance for controlling the cycling performance of rechargeable lithium metal batteries. Here we develop a unique method for imaging the evolution of SEI formed on the Cu foil under sweeping electrochemical potential. By using cryogenic TEM imaging combined with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy electronic structure analyses to directly probe the morphology, atomic structure, and chemical bonding of solid-electrolyte interphase formed on Cu and Li in the electrolyte without/with vinylene carbonate additive. We reveal that the vinylene carbonate additive is shown to significantly affect the solid electrolyte interphase on Cu at different potentials. Solid electrolyte interphases formed on Cu and Li show significantly different in chemical composition. • Developing a unique method for the formation of solid electrolyte interphase on Cu to facilitate cryo-TEM imaging. • Structural and chemical evolution of SEI formed on Cu with sweeping potentials were revealed by Cryo-TEM and XPS. • Vinylene carbonate additive is shown to significantly affect the solid electrolyte interphase on Cu at different potentials. • Solid electrolyte interphases formed on Cu and Li show significance difference in chemical composition.