Understanding Ion-Beam Damage to Air-Sensitive Lithium Metal With Cryogenic Electron and Ion Microscopy

Hyeongjun Koh; Eric Detsi; Eric A Stach

doi:10.1093/micmic/ozad074

Understanding Ion-Beam Damage to Air-Sensitive Lithium Metal With Cryogenic Electron and Ion Microscopy

Microsc Microanal. 2023 Jul 25;29(4):1350-1356. doi: 10.1093/micmic/ozad074.

Authors

Hyeongjun Koh¹, Eric Detsi¹, Eric A Stach^{1

2}

Affiliations

¹ Department of Materials Science and Engineering, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA 19104, USA.
² Laboratory for Research on the Structure of Matter, University of Pennsylvania, 3231 Walnut Street, Philadelphia, PA 19104, USA.

PMID: 37488829
DOI: 10.1093/micmic/ozad074

Abstract

It is essential to understand the nanoscale structure and chemistry of energy storage materials due to their profound impact on battery performance. However, it is often challenging to characterize them at high resolution, as they are often fundamentally altered by sample preparation methods. Here, we use the cryogenic lift-out technique in a plasma-focused ion beam (PFIB)/scanning electron microscope (SEM) to prepare air-sensitive lithium metal to understand ion-beam damage during sample preparation. Through the use of cryogenic transmission electron microscopy, we find that lithium was not damaged by ion-beam milling although lithium oxide shells form in the PFIB/SEM chamber, as evidenced by diffraction information from cryogenic lift-out lithium lamellae prepared at two different thicknesses (130 and 225 nm). Cryogenic energy loss spectroscopy further confirms that lithium was oxidized during the process of sample preparation. The Ellingham diagram suggests that lithium can react with trace oxygen gas in the FIB/SEM chamber at cryogenic temperatures, and we show that liquid oxygen does not contribute to the oxidation of lithium process. Our results suggest the importance of understanding how cryogenic lift-out sample preparation has an impact on the high-resolution characterization of reactive battery materials.

Keywords: cryogenic scanning transmission electron microscopy (cryo-STEM); cryogenic transmission electron microscopy (cryo-TEM); cryogenic-focused ion beam/scanning electron microscope (cryo-FIB/SEM); energy storage devices; lithium metal batteries.