Advanced methods for characterizing battery interfaces: Towards a comprehensive understanding of interfacial evolution in modern batteries

Batteries are complex systems operating far from equilibrium, relying on intricate reactions at interfaces for
performance. Understanding and optimizing these interfaces is crucial, but challenges arise due to the diverse
factors influencing their development, making comprehensive characterization essential despite experimental
difficulties. Recent advancements in characterization tools offer new opportunities to explore interfacial evolution, particularly in the solid electrolyte interphase (SEI).
In this perspective article, leading experts in physical-chemical characterization techniques for electrochemical systems discuss the current state-of-the-art and emerging approaches to study interfaces and their
evolution in batteries. The focus here is on the capabilities, technical challenges, limitations, and requirements
that these techniques must meet to advance our understanding of battery interfacial evolution. The emphasis is
placed on techniques that enable probing interfaces under realistic conditions, close to commercial battery
systems, and on the integration of multiple approaches within a single measurement (multimodal) to minimise
variable effects.
This article focuses on the most promising techniques for characterizing all phases relevant to interfacial
processes, as well as their integration with correlative analyses and computational modelling. We discuss solid
phase characterization with X-ray spectroscopies and microscopies (XPS, XAS, STXM, X-PEEM & XCT), Raman
spectroscopies (SERS, TERS & SHINERS), solid-state NMR and electron microscopies and spectroscopies (STEM,
EDXS, EELS & 4D-STEM). The liquid phase characterization is discussed in terms of solution NMR spectroscopy,
TEM and optical spectroscopies, while the gas phase can be characterized using OEMS, pressure monitoring and
GCMS. Computational modelling and simulation (DFT, ReaxFF & MLIP) are also discussed