A review of multiscale characterization methods of ion transport in solid-state electrolytes

Solid-state batteries that present lower risk factors and higher energy density are promising for advanced energy storage and applications. In particular, solid-state electrolytes (SSEs) are the critical components that responsible for ionic transport between negative electrodes and positive electrodes. It is crucial to fundamentally understand the ionic transport models and behaviors in the SSEs, with purpose of enhancing ion transport rate and stability of SSEs. To rationally improve the solid-state ion transport behavior of electrolytes, this review summarizes recent progresses on the transport principles and multiscale characterization methods of ion transport in SSEs, including traditional electrochemical methods, frequency-dependent spectroscopy, two-dimensional morphological imaging and three-dimensional morphological imaging. It is emphasized that combination of multiscale and multiple methods would be a developing trend for fundamentally understanding the mechanism of ion transport in SSEs. According to comprehensive transport principle and behaviors, hierarchical fillers are designed for composite electrolytes with fast ionic transport abilities. The remaining challenges for establishing advanced multiscale characterization methods are also discussed.