Solid-solid interfaces involving ion conducting materials represent some of the most critical components in many electrochemical systems. The interfacial mass transport and charge transfer behavior both in a static state and upon electrochemical cycling often dictate the performance of the system. Interfaces of solid electrolytes for solid-state batteries form an important example. Unexpectedly high resistivity is often observed at electrolyte-electrolyte/electrode interfaces, and the underlying mechanism is not yet clear. Continuous ion hopping from one mobile ion site to adjacent vacancy lattice sites forms the basis for ion conduction in solids. Interfacial ion transport essentially is determined by the atomic structure, and the distribution of electrons and ions at the atomic scale. Studying these embedded interfaces with a non-centrosymmetric structure is challenging. Scanning transmission electron microscopy (STEM) represents a unique tool for such studies owning to its unprecedented spatial resolution. During the past few years, atomic-scale imaging and electron energy loss spectroscopy (EELS) in STEM have revealed critical structural and chemical features at solid electrolyte interfaces that are responsible for the degradation or enhancement in battery performance. In situ biasing platforms have been integrated to study the formation and stability of interfaces in batteries. These atomic-scale and in situ studies have provided significant insight and continue to highlight the importance of microscopy for battery research. Recent developments in fast cameras and highly stable electronics have enabled the emergence of functional imaging methods such as ptychography, differential phase contrast imaging, and vibrational spectroscopy. These techniques, once tailored for battery research, will not only allow us to probe the atomic structure and chemical species, but will also facilitate the ability to map, directly or indirectly, functionality associated with local nanofeatures in battery materials and devices. The evolving integration of new and emerging microscopy techniques into battery research, from atomic-resolution to in situ and functional imaging, will be demonstrated by several recent studies on solid-electrolyte materials.
Research sponsored by the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy. Microscopy performed as part of a user project at Oak Ridge National Laboratory’s Center for Nanophase Materials Sciences (CNMS), which is a U.S. DOE User Facility.