Molecular Beam Epitaxy (MBE) Growth of Model Cathode to Study Interfacial Ion Diffusion*

High performance lithium transition metal oxide battery cathodes, such as LiMn₂O_4, remain a highly active research area. Single-crystals provide well-defined orientations, defect concentrations, homogeneity, and surface terminations that allow isolation of specific chemical and structural aspects of intercalation to be examined. These features make single crystals highly desirable for characterization of pristine and cycled cathodes, compared to polycrystals/particles.
Here we present single-crystal LiMn₂O₄ thin films grown using MBE as model cathodes. Pristine and electrochemically cycled films were characterized using X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), transmission electron microscopy (TEM/STEM), and electron energy loss spectroscopy (EELS) to study the effects of surface orientation, Mn dissolution, defects, and solid electrolyte interface (SEI) on the structural changes in the films and interfaces during (de)intercalation.