Charge Transfer-Driven Interfacial Bonding Boosts Cyclability of Al2O3-Coated NCM523 for Lithium-Ion Batteries

LiNi0.5Co0.2Mn0.3O2 (NCM523) is a mainstream lithium-ion battery cathode material with high specific capacity, which is widely applied in energy storage and power batteries. Nevertheless, it suffers from transition-metal dissolution, structural phase transition, and interfacial side reactions during long cycling, causing rapid capacity fading and inferior stability, which restricts its large-scale application. Traditionally, the Al2O3 coating layer can effectively isolate the cathode material from direct contact with the electrolyte, alleviate electrolyte decomposition, and suppress transition-metal dissolution as well as interfacial side reactions. However, the underlying charge-transfer-driven bonding mechanism between the coating layer and cathode substrate remains insufficiently understood. Herein, a sol-gel method was used to prepare Al2O3-coated NCM523 with an optimal 1.0 wt % coating content. Electrochemical tests show that 1.0 Al-NCM delivers an initial discharge capacity of 177.1 mAh g-1 at 0.2 C, retains 80.3% capacity after 200 cycles at 0.5 C (8.4% higher than bare NCM523), and exhibits 138.2 mAh g-1 at 5 C. Beyond the conventional physical protection effect of the Al2O3 coating layer, X-ray photoelectron spectroscopy, synchrotron X-ray absorption spectroscopy, and density functional theory calculations reveal a charge-transfer-driven interfacial bonding mechanism between the Al2O3 coating layer and NCM523 substrate, featuring the formation of strong Al-O-TM bonds. The charge transfer across the interface promotes Al-O-TM bonding and regulates the surface electronic structure, thereby enhancing the structural reversibility and cycling stability of the layered cathode. These findings provide new insights into the active role of the Al2O3 interfacial layer in regulating surface chemistry and enhancing the structural stability of layered oxide cathodes.