Surface X-ray Diffraction Observation of Interfaces in Thin-Film Lithium Ion Batteries

Surface x-ray diffraction (SXRD) is a unique method that can analyze atomic structures of buried interfaces non-destructively. Although the SXRD measurements require a very flat and uniform samples, model thin-film batteries which satisfy the requirements allow for the atomic-scale analysis of batteries interfaces. In this chapter, SXRD studies of interface phenomena in thin-film batteries with epitaxial cathode layers are presented: (i) an effect of structural perfection of a LiCoO2 cathode surface to the ionic transport across the electrolyte/cathode interface, (ii) an energy-band alignment between a LiCoO2 cathode and current collector, induced by an interface insertion layer, and (iii) a depth-resolved structural evolution of a Ni-rich cathode during battery operation, observed by a unique time-resolved technique. These results provide insights into atomic-scale interface phenomena occurring during electrode fabrication processes or battery operation and their effects on the battery performance.