Evaluation of solid electrolytes: Development of conventional and interdisciplinary approaches

Solid-state lithium batteries (SSLBs) have received considerable attention due to their advantages in thermal stability, energy density, and safety. Solid electrolyte (SE) is a key component in developing high-performance SSLBs. An in-depth understanding of the intrinsic bulk and interfacial properties is imperative to achieve SEs with competitive performance. This review first introduces the traditional electrochemical approaches to evaluating the fundamental parameters of SEs, including the ionic and electronic conductivities, activation barrier, electrochemical stability, and diffusion coefficient. After that, the characterization techniques to evaluate the structural and chemical stability of SEs are reviewed. Further, emerging interdisciplinary visualization techniques for SEs and interfaces are highlighted, including synchrotron X-ray tomography, ultrasonic scanning imaging, time-of-flight secondary-ion mass spectrometry, and three-dimensional stress mapping, which improve the understanding of electrochemical performance and failure mechanisms. In addition, the application of machine learning to accelerate the screening and development of novel SEs is introduced. This review article aims to provide an overview of advanced characterization from a broad physical chemistry view, inspiring innovative and interdisciplinary studies in solid-state batteries.