Influence of the Electron Beam Dose on the Battery Material Characterization Using Cryo-TEM

Title: Electron Beam-Induced Artifacts in SEI Characterization: Evidence from Controlled-Dose Diffraction Studies
Authors: Koh et al.,
Journal: ACS Energy Letters Link

The solid electrolyte interphase (SEI) is a critical component in batteries, acting as a charge transport bridge between the electrode and electrolyte, significantly influencing battery performance. While cryogenic transmission electron microscopy (cryo-TEM) has been widely used to evaluate SEI, many studies simply assume and even claim its ability to protect against any electron beam irradiation damage.

This study disproves that assumption by demonstrating the formation of Li₂O under accumulated electron doses by comparing short and prolonged electron exposure of SEI. High-resolution TEM (HRTEM), used quite often in cryo-conditions in previous studies and also in this study, requires a high dose rate (~1000 e⁻/Ų·s), which can immediately induce artifacts. In contrast, scanning electron nanobeam diffraction with a low probe dose of less than 200 e⁻/Ų and small convergence semi-angle reveals the SEI as amorphous, contradicting HRTEM observation. Selected area electron diffraction and electron energy loss spectroscopy indicate that total electron doses of 450 e⁻/Ų and 600 e⁻/Ų are sufficient to induce Li₂O formation in SEI layers of Li metal deposited in LiFSI+LiTFSI/DME and LiPF₆/EC-DEC electrolytes, respectively.

Nanostructure characterization in batteries can be challenging due to electron beam interactions that can lead to erroneous conclusions. The paper suggests the use of scanning TEM, and even more, 4D-STEM for comprehensive yet artifact-free characterization in the cryogenic environment but note that this can certainly be data-intensive and expensive to be considered for routine work.