Characterization of Solid Electrolyte Interphases on Carbon-Based Negative Electrodes for Lithium-Ion Batteries: Methods, Artifacts, and Correlative Workflows

Solid electrolyte interphase (SEI) characterization is needed to interpret the performance, degradation, and lifetime of graphite and Si-containing carbon-based negative electrodes in lithium-ion batteries. However, SEI claims are often difficult to compare because measured signals, inferred assignments, sample history, and electrode architecture are not always clearly separated. This review presents a claim-bounded framework for SEI characterization that distinguishes direct observables from inferred chemical, molecular, structural, morphological, and functional information. Photoelectron spectroscopy methods provide chemical-state and relative-depth-sensitivity constraints; secondary-ion mass spectrometry methods provide fragment and isotope distributions; vibrational spectroscopies support functional-group and local vibrational evidence; nuclear magnetic resonance and molecular mass spectrometry provide molecular or product-level constraints; and microscopy, tomography, and atomic force microscopy provide morphology, architecture, local thickness, topography, and mechanical response. Across these methods, rinsing, drying, sputtering, beam exposure, extraction, and limited sampling can alter the observable and therefore the defensible claim. The review emphasizes the distinction between native electrode-associated SEI features and extracted, soluble, or electrolyte-phase products, and between morphology-only evidence and chemically assigned morphology. It concludes by proposing claim-driven correlative workflows and reporting guidance for reproducible interpretation on graphite, Si/graphite, Si/C, and carbon-coated Si architectures where directly studied or present.