Focused Ion Beam-Defined Analytical Geometries for Correlative Battery Characterization

Battery reactions and degradation processes frequently originate or evolve at buried interfaces, extend through complex three-dimensional composite architectures, and change with electrochemical state. Analysis of an exposed surface or an arbitrarily selected cross-section can therefore lose the positional, volumetric, or state information required for interpretation. This focused Review organizes FIB-supported correlative battery characterization according to three analytical dimensions established by focused ion beam (FIB)-defined geometries: position, depth/volume, and electrochemical state/time. Four representative workflows—orientation-preserving lift-out, tomography-guided exposure, serial PFIB-EDS-SIMS sectioning, and FIB-prepared operando observation windows—are examined through a common measurement-to-claim chain comprising geometry definition, direct signal acquisition, data transformation, derived quantities, and the highest physical inference supported by the evidence. The comparison identifies workflow-specific uncertainties associated with target relocation, milling depth, matrix effects, slice spacing, cross-modal registration, segmentation, and observation-window perturbation. It further distinguishes local structural or chemical association, cross-depth persistence, and state-resolved morphology from stronger claims concerning transport, kinetics, or degradation mechanisms, which require independent electrochemical, mechanical, spectroscopic, or modelling evidence. This framework provides a basis for selecting FIB-defined analytical geometries, reporting their uncertainty, and matching the resulting evidence to defensible physical claims in battery characterization.