Cryogenic ToF-SIMS: A Multifunctional Chemical Analysis Strategy for Air-Sensitive LiH in Lithium Metal Anodes

Area of Science:

• Materials Science
• Electrochemistry
• Analytical Chemistry

Background:

• Lithium hydride (LiH) characterization in lithium metal batteries is challenging due to its air sensitivity and light elemental composition.
• Conventional probes struggle to explore the mesoscale morphology and chemistry of LiH.
• Understanding LiH distribution is critical for optimizing lithium metal battery performance and safety.

Purpose of the Study:

• To develop and validate a multifunctional cryogenic time-of-flight secondary ion mass spectrometry (cryo-TOF-SIMS) workflow for LiH analysis.
• To investigate the spatial distribution and chemical state of LiH in lithium metal battery electrodes.
• To enable chemically specific mapping of air-sensitive materials at multiple length scales.

Main Methods:

• A novel cryo-TOF-SIMS workflow integrating top-view and cross-sectional analyses at temperatures below -145°C.
• Utilized commercial LiH standards for method validation, identifying LiH via characteristic fragments (7Li1H-, 7Li1H2-, 7Li21H-, 7Li21H+).
• Employed depth profiling to minimize surface contamination and complementary cryogenic scanning transmission electron microscopy (cryo-STEM) and electron energy loss spectroscopy (EELS) for validation.

Main Results:

• LiH was identified in electroplated lithium deposits on copper, showing distribution throughout porous electrodes (approx. 4μm thick).
• Top-view depth profiling revealed sub-nanometer composition gradients within the solid-electrolyte interphase (SEI).
• Cryo-STEM/EELS confirmed LiH as thin, surface-localized layers on individual lithium structures, supporting cryo-TOF-SIMS findings.

Conclusions:

• The developed cryo-TOF-SIMS platform enables chemically specific mapping of LiH across nanometer to micrometer scales.
• The method preserves the native state of highly reactive LiH, overcoming limitations of conventional techniques.
• This approach facilitates quantitative analysis of spatial trends and strengthens multiscale understanding of complex battery interfaces and other air-sensitive systems.