Density Functional Theory Study of Ethylene Carbonate Adsorption on the (0001) Surface of Aluminum Oxide α-Al2O3

Surface coating is one of the techniques used to improve the electrochemical performance and enhance the resistance against decomposition of cathode materials in lithium-ion batteries. Despite several experimental studies addressing the surface coating of secondary Li-ion batteries using α-Al2O3, the reactivity of the material toward the electrolyte components is not yet fully understood. Here, we have employed calculations based on the density functional theory to investigate the adsorption of the organic solvent ethylene carbonate (EC) on the major α-Al2O3(0001) surface. During adsorption of a single EC molecule, it was found that it prefers to bind parallel to the surface through its carboxyl oxygen. As the surface coverage (θ) was increased up to a monolayer, we observed larger adsorption energies per EC molecule (Eads/NEC) for parallel interactions and a reduction for perpendicular interactions. We also noted that increasing the surface coverage with both parallel and perpendicularly interacting EC molecules led to a decrease of the surface free energies and hence increased stability of the α-Al2O3(0001) surface. Despite the larger Eads/NEC observed when the molecule was placed parallel to the surface, minimal charge transfer was calculated for single EC interactions and at higher surface coverages. The simulated scanning tunneling microscopy images are also presented for a clean corundum α-Al2O3 surface and after adsorption with different coverages of parallel and perpendicularly placed EC molecules.