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

Characterizing lithium hydride (LiH) in lithium metal batteries is difficult: LiH is extremely air sensitive and composed of light elements that challenge conventional probes, leaving mesoscale morphology, and chemistry underexplored. We introduce a multifunctional cryogenic time-of-flight secondary ion mass spectrometry workflow that integrates top-view and cross-sectional analyses under temperatures below -145∘C. Using commercial LiH standards, the method identifies LiH via characteristic fragments  7Li1H-,  7Li1H2-,  7Li21H-, and  7Li21H+, and uses depth profiling to minimize surface contamination. Applied to lithium deposits electroplated on copper, cross-sectional mapping indicates that LiH is distributed throughout porous electrodes approximately 4μm thick, while top-view depth profiling resolves sub-nanometer composition gradients within the solid-electrolyte interphase. Complementary cryogenic scanning transmission electron microscopy and electron energy loss spectroscopy support the time-of-flight secondary ion mass spectrometry findings by showing LiH as thin surface-localized layers on individual lithium structures. The combined approach delivers chemically specific mapping across nanometer to micrometer length scales while preserving native states of highly reactive materials. This platform supports quantitative comparisons of spatial trends and strengthens multiscale analysis of complex battery interfaces and other air-sensitive systems.