A microscopic view of solid-state lithium batteries

The demand for safe energy storage with high energy density is growing, and as conventional lithium-ion batteries with liquid electrolytes are nearing their performance limits, solid-state Li batteries have emerged as promising successors. Solid-state batteries offer higher energy density, enhanced safety, and faster charge rates. However, their commercialization remains constrained by solid/solid interface processes, including dendrite formation, chemically or mechanically unstable electrolyte/electrode interfaces, and inhomogeneous cathodic reactions. Advanced micro- and nanoscale characterization techniques are essential for unveiling the mechanistic origins of solid-state battery degradation and performing real-time monitoring of local changes within battery materials, which reveal critical insights into dynamic interfacial processes during operation. Such knowledge may unlock the full potential of solid-state batteries by guiding the development of new materials, battery architectures, and microstructures for achieving improved performance and durability. This review surveys research on solid-state battery materials and examines how various micro- and nanoscale characterization techniques can be used to diagnose degradation phenomena and develop strategies to mitigate degradation. We review recent studies with a particular focus on (i) grain and phase boundaries in solid-state electrolytes, (ii) dendrite formation, (iii) the structure and evolution of solid electrolyte interphases, (iv) lithiation-induced heterogeneities in the anode active materials, (v) cathode electrolyte interfacial phenomena, and (vi) contact loss within cathode composites and the resulting spatial heterogeneities revealed through state-of-charge mapping. Finally, we discuss how future developments in characterization methods can enable gaining a deeper insight into the operation and degradation of solid-state batteries.