Bifunctional Surface Coating of LiNbO on High-Ni Layered Cathode Materials for Lithium-Ion Batteries.

High-Ni cathode materials with a layered structure generally suffer from structural instability induced by a highly reactive Ni component, especially at the surface. Crystalline LiNbO, with excellent thermal stability and ionic conductivity, has the potential to considerably enhance the interfacial stability of these cathode materials. By optimizing the crystalline coating of bifunctional LiNbO on a high-Ni cathode material, we are able to improve cycle performance and rate capability by minimizing the direct exposure of Ni with electrolytes. Since a LiNbO coating layer directly affects electrochemical performance, we also focus on the correlation of LiNbO crystallinity with electrochemical behaviors of Li in the cathode materials. We show that the Li conducting behaviors are closely related to the crystallinity of LiNbO. Highly crystalline LiNbO effectively suppresses the structural changes of the cathode materials by facilitating strain relaxation induced by repeated Li intercalation and deintercalation into and from the host structure. Moreover, it offers strong enhancement in mechanical and thermal stabilities at elevated temperatures above 60 °C. In this regard, this research provides a practical solution for successfully utilizing high-Ni layered cathode materials in commercial LIBs.