Integrating Multi-Functionality that enables In-Situ TEM probing of Solid Electrolyte Interphase Characteristics

For better battery performances, solid electrolyte interphase (SEI) layer is expected to possess three ideal characteristics: electrically insulative, ionically conductive, and constant thickness. These three characteristics are interactively correlated, typically, the thickness of SEI layer is controlled by the electrical properties of SEI layer. However, SEI layers do not seem to behave the ideal characteristics, rather the thickness of the SEI continuously increases during charge-discharge cycling and shelf storage, indicating that the SEI does not behave as an electrical insulator. We use in-situ bias transmission electron microscopy to directly measure the electrical properties of SEI. We discover that the current-voltage characteristics of SEIs resemble certain electrical conductance, rather than electrical insulation as conventionally assumed. We further demonstrate by tailoring the solvation sheath of the electrolyte, the electrical properties of the SEIs can be readily tuned, which inherently correlate to electrochemical properties. The work highlights the significance of electrical properties of the SEI layer and their tuning towards the enhanced performance of an electrochemical cell.