IN-OPERANDO ELECTRON MICROSCOPY AND SPECTROSCOPY OF INTERFACES THROUGH GRAPHENE-BASED MEMBRANES

Abstract

Electron microscopy and spectroscopy (EMS) techniques enable (near-) surface and interfacial characterization of a variety of materials, providing insights into chemical/electrochemical and morphological information with nanoscale spatial resolution. However, the experimental realization of EMS in liquid/gaseous samples becomes problematic due to their incompatibility with high vacuum (HV)

conditions. To perform EMS under elevated pressure conditions, electron transparent membranes made of thin C, SiO2 or/and Si3N4 are implemented to isolate a liquid/gas sample from HV environment. Nevertheless, even a few ten nanometer thick

membrane deteriorates signal quality due to significant electron scattering. The other challenge of EMS consists in inaccessibility to probe solid state interfaces, e.g. solid-state Li-ion batteries, which makes their operando characterization problematic, limiting the analysis to ex situ and postmortem examination.

The first part of my thesis focuses on developing an experimental platform for operando characterization of liquid interfaces through electron transparent membranes made of graphene (Gr)/graphene oxide (GO). The second part is dedicated to probing Li-ion transport at solid-state-battery surfaces and interfaces using ultrathin carbon anodes. I demonstrated the capability of GO to encapsulate samples with different chemical, physical, and biological properties and characterized them using EMS methods. I proposed and tested a new CVD-Gr transfer method using anthracene as a sacrificial layer. Characterization of transferred Gr revealed the advantages of our route with respect to a standard polymer based approach. A novel platform made of an array of Gr-capped liquid filled microcapsules was developed, allowing for a wide eld of view EMS. I showed the capability of conducting EMS analysis of liquid interfaces through Gr membranes using energy-dispersive X-ray spectroscopy, photoemission electron microscopy, and Auger electron spectroscopy. Using operando SEM and AES, I elucidated the role of oxidizing conditions and charging rate on Li plating morphology in all-solid-state Li-ion batteries with thin carbon anodes. Operando EMS characterization of Li-ion transport at battery interfaces with carbon or Gr anodes will provide valuable insights into safe all-solid-state Li-ion battery with enhanced performance.