Bifunctional Surface Coating of LiNbO₃ 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 LiNbO₃, 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 LiNbO₃ 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 LiNbO₃ coating layer directly affects electrochemical performance, we also focus on the correlation of LiNbO₃ crystallinity with electrochemical behaviors of Li⁺ in the cathode materials. We show that the Li⁺ conducting behaviors are closely related to the crystallinity of LiNbO₃. Highly crystalline LiNbO₃ 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.