Multi‐Dimensional Insights Into the Surface and Interfaces of Battery Materials by Time‐of‐Flight Secondary Ion Mass Spectrometry

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) has emerged as a pivotal analytical technique for characterizing the complex surface and interfacial chemistry of battery materials. This review article comprehensively discusses the fundamental principles and unique attributes of ToF-SIMS, highlighting its advantages such as ultrahigh surface sensitivity (ppm-ppb), high spatial resolution (< 50 nm laterally, and < 1 nm in depth), and high mass resolution for hydrogen and isotope study. In the field of battery study, these attributes enable precise, multi-dimensional characterization of electrode-electrolyte interphases (EEIs). In the previous works, ToF-SIMS has been employed to resolve the composition and structures at the nanoscale of EEIs, track the dynamic evolution and degradation of electrode surface, differentiate artificial coating interphases from the bulk materials, and detect isotopes for mechanistic studies. The burgeoning field of in situ liquid ToF-SIMS for probing the authentic solvation structures and aging mechanism of electrolytes is also highlighted. Challenges of using ToF-SIMS for battery study, such as the matrix effects, beam-induced damage, and need for higher sensitivity and depth resolution, are also discussed. In summary, ToF-SIMS provides multi-dimensional insights into battery interfaces, which help to establish structure-property correlations and will continuously guide the rational design of the next-generation high-performance energy storage systems.