Visualizing the Future: Recent Progress and Challenges on Advanced Imaging Characterization for All-Solid-State Batteries

All-solid-state batteries (ASSBs) offer high safety and energy density, but their degradation and failure mechanisms remain poorly understood due to the buried interfaces within solid-state electrodes and electrolytes. Local probing methods are crucial for addressing key challenges such as interfacial instabilities, dendrite growth, and chemo-mechanical degradation. State-of-the-art imaging techniques provide critical insights into morphological, structural, and compositional evolution of the ubiquitous interfaces in ASSBs. This review highlights recent progress in cutting-edge visualization techniques, including neutron imaging, X-ray tomography, focused ion beam scanning electron microscopy, and cryogenic electron microscopy, which reveal microstructural and chemical changes in ASSBs at scales from the atomic to the macroscopic level. We particularly focus on the elusive failure behaviors at lithium anodes, composite cathodes, solid-state electrolytes, and beyond. Additionally, we discuss the strengths and limitations of each technique, aiming to enhance the understanding of ASSB operation and degradation mechanisms to advance the development of high-energy-density, high-safety ASSBs.