Current Density Regulated Atomic to Nanoscale Process on Li Deposition and Solid Electrolyte Interphase Revealed by Cryogenic Transmission Electron Microscopy.

Abstract

Current density has been perceived to play a critical rule in controlling Li deposition morphology and solid electrolyte interphase (SEI). However, the atomic level mechanism of the effect of current density on Li deposition and the SEI remains unclear. Here based on cryogenic transmission electron microscopy (TEM) imaging combined with energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) electronic structure analyses, we reveal the atomic level correlation of Li deposition morphology and SEI with current density. We discover that increasing current density leads to increased overpotential for Li nucleation and growth, leading to the transition from growth-limited to nucleation-limited mode for Li dendrites. Independent of current density, the electrochemically deposited Li metal (EDLi) exhibits crystalline whisker-like morphology. The SEI formed at low current density (0.1 mA cm-2) is monolithic amorphous; while, a current density of above 2 mA cm-2 leads to a mosaic structured SEI, featuring an amorphous matrix with Li2O and LiF dispersoids, and the thickness of the SEI increases with the increase of current density. Specifically, the Li2O particles are spatially located at the top surface of the SEI, while LiF is spatially adjacent to the Li-SEI interface. These results offer possible ways of regulating crucial microstructural and chemical features of EDLi and SEI through altering deposit conditions and consequently direct correlation with battery performance.