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

Rechargeable batteries, the standard bearer for electrochemical energy storage technologies, are facing increasing demands for large-volume production of highly efficient and stable devices for future applications. Battery cathodes are generally studied in polycrystalline or nano-sized powders form, making detailed study of surfaces and interfaces difficult. To better understand surface chemistry, single-crystal cathodes with defined orientation are highly preferential. A novel method for single-crystal epitaxial growth of cathodes is molecular beam epitaxy (MBE).The unique features of MBE grown thin films allow for precise control of compositional homogeneity, surface terminations, defect concentrations, crystal orientation, and stoichiometry which are fundamental while studying surface reactions. In my thesis, I examine the epitaxial single-crystal LiMn2O4 thin films grown on SrTiO3 substrates using MBE that will function as model cathodes for Li-ion batteries as well as characterization of those films in both pristine and cycled states. This thesis, for the first time, demonstrates the growth of lithium thin films using MBE system. By laying the foundation of lithium incorporation into oxide MBE, this thesis aims to introduce aforementioned unique benefits of MBE to the battery community. In addition, I examine the potential of multivalent batteries as natural successors to Li-ion batteries in search of higher energy density materials, specifically, MgMn2O4 thin films cathodes.