In-Situ Characterization of Solid Electrolyte Interphase and Lithium Morphology

The solid electrolyte interphase (SEI) on lithium (Li) metal anode dominates the Li morphologies during repeated deposition and stripping processes, then greatly affects the stability of Li metal anode and the electrochemical performance of Li metal batteries. Though SEI was first proposed by Peled in 1979, it still remains mysterious and has not been comprehensively understood because there are many factors that can influence its components, compositions, morphologies, then the properties, stabilities and performance. Due to the limitations in techniques and instruments in the past decades, the characterization of SEI could only be performed ex situ where the sample treatment like washing the residual electrolyte with fresh solvent would wash away certain SEI components especially the soluble or not tightly adhesive species, then the characterization results for the SEI could not reflect the real case and many times lead to misunderstanding of the SEI. In recent years, a lot of advanced in-situ characterization techniques have emerged, which enable the in-situ characterization of SEI. In this talk, two techniques will be discussed for understanding SEI – one is a dynamic, non-invasive, operando reflection interference microscope that enables the real-time imaging of SEI during its formation and evolution with extremely high sensitivity, and another is an in-situ bias transmission electron microscopy approach to directly measure the electrical properties of SEI layers.