Low-Cost Al₂O₃ Coating Layer As a Preformed SEI on Natural Graphite Powder to Improve Coulombic Efficiency and High-Rate Cycling Stability of Lithium-Ion Batteries

Coulombic efficiency especially in the first cycle, cycling stability, and high-rate performance are crucial factors for commercial Li-ion batteries (LIBs). To improve them, in this work, Al₂O₃-coated natural graphite powder was obtained through a low-cost and facile sol-gel method. Based on a comparison of various coated amounts, 0.5 mol % Al(NO₃)₃ (vs mole of graphite) could bring about a smooth Al₂O₃ coating layer with proper thickness, which could act as a preformed solid electrolyte interface (SEI) to reduce the regeneration of SEI and lithium-ions consumption during subsequent cycling. Furthermore, we examined the advantages of Al₂O₃ coating by relating energy levels in LIBs using density functional theory calculations. Owing to its proper bandgap and lithium-ion conduction ability, the coating layer performs the same function as a SEI does, preventing an electron from getting to the outer electrode surface and allowing lithium-ion transport. Therefore, as a preformed SEI, the Al₂O₃ coating layer reduces extra cathode consumption observed in commercial LIBs.