The replacement of conventional liquid organic electrolytes by solid-state electrolytes may enable or improve high energy density battery technologies, while simultaneously enhancing cell safety, cycle stability and calendar life. This challenging task typically requires development of novel processing techniques as well as substantial improvements in the conductivity of solid electrolytes and solid electrolyte - electrode interfaces. Our research projects are focused on gaining better fundamental understanding of the impacts of chemistry, microstructure and composition on physical properties, electrochemical stability, metal ion (Li+, Na+, H+, etc.) diffusion and sensitivity to environment in several classes of solid state electrolytes as well as transport properties of the solid electrolyte - electrode interfaces and interphases for a broad range of active anode and cathode materials.