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

Abstract Lithium‐ion batteries (LIBs) have been the focus of research for decades owing to their superior energy storage potential and wide range of applications. However, long‐term stability issues still persist in LIB cathodes as the result of the formation of a solid electrolyte interface (SEI), structural transformations, or the loss of active cathode materials. In nanoscale cathodes, it is often impossible to isolate, let alone mitigate the causes of the observed capacity loss. Herein, a novel approach is presented to synthesizing LIB cathode model systems using thin‐film molecular beam epitaxy (MBE). Specifically, 100 nm thick LiMn 2 O 4 (LMO) thin‐film cathodes are grown on SrRuO 3 /SrTiO 3 (100) single‐crystal substrates and characterized in their pristine and cycled states. The pristine thin films exhibit the electro‐chemical cycling behavior and structural evolution previously seen in bulk LMO cathodes. The formation of surface‐layer rocksalt MnO and spinel Mn 3 O 4 along with the mass‐loss associated with the corrosion of active Mn ions is also reported. It is, therefore, demonstrated that these MBE‐grown model systems can be used for detailed studies of their surface structures and the electrode/electrolyte interfacial evolution in LIB cathodes, leading to the development of materials for rechargeable batteries with higher capacity and better stability.