Probing Buried Interfaces in Batteries: Toward Operando Visibility and Quantitative Diagnosis

The evolution of buried interfaces, the hidden junctions where distinct phases exchange charge, mass, and mechanical response under nonequilibrium conditions, strongly influences the performance and stability of functional devices such as batteries, but they remain difficult to probe directly. This perspective summarizes the types of buried interfaces that form within battery electrodes and their electrochemical function in the device, and it discusses how advances in operando probes, cell architectures, and multimodal and correlative strategies have enabled dynamic and chemically specific visibility of their evolution. Despite this progress, operando signals remain challenging to interpret because they are affected by, for example, beam damage-induced changes, variations in operando cell geometry, and intrinsic sample-to-sample differences, which together limit quantitative insight. Building on these considerations, the perspective examines how operando visibility can be transformed into quantitative diagnosis by integrating multimodal measurements with physically informed interface models and data-driven analysis. The final section outlines a roadmap for reproducible and quantitative operando analysis, centered on standardized cell architectures, long-term autonomous measurements, and artificial intelligence approaches that incorporate physical constraints. In summary, these developments define a pathway from operando visibility to quantitative diagnosis and provide a foundation for advancing interface characterization and quantitative analysis in batteries and related energy materials.