The development of energy storage systems with increased energy density beyond conventional lithium-ion batteries is crucial for addressing global energy demands. Solid-state batteries are a promising technology as they potentially offer higher energy densities, improved safety, and enhanced stability. Energy densities can be further increased either through “anode-free” architectures or using alloy anodes. Anode-free solid-state batteries eliminate the graphite anode and excess lithium, but they require a detailed understanding of and control over how lithium evolves at the solid-solid interface throughout cycling. Alloy anodes, in contrast, provide high capacities and low lithiation potentials that help mitigate dendritic lithium metal growth; however, they face challenges due to significant volumetric expansion of the alloy active material that alters microstructure and transport pathways. My work utilizes advanced characterization techniques (operando X-ray computed tomography (XCT), cryogenic and plasma focused ion beam (FIB), along with electrochemical techniques) to investigate interfacial dynamics at solid-solid interfaces and probe transport properties. In this seminar, I will first present how lithium deposition and stripping behavior is influenced by the solid-electrolyte microstructure in anode-free systems using operando XCT. I will then discuss the impact of alloy interlayers on lithium behavior, probing the structural and morphological evolution of these interlayers using cryo- and plasma-FIB methods. Finally, I will discuss how the ionic, electronic, and thermal transport properties of silicon-based alloy anodes change with varying particle size and their effects on performance and safety. Altogether, understanding the relationship between material structural evolution and transport properties is critical to engineer next-generation energy storage systems that meet future energy demands.