Surface encapsulation of layered oxide cathode material with NiTiO₃ for enhanced cycling stability of Na-ion batteries

In Na-ion batteries, O3-type layered oxide cathode materials encounter challenges such as particle cracking, oxygen loss, electrolyte side reactions, and multi-phase transitions during the charge/discharge process. This study focuses on surface coating with NiTiO₃ achieved via secondary heat treatment using a coating precursor and the surface material. Through in-situ x-ray diffraction (XRD) and differential electrochemical mass spectrometry (DEMS), along with crystal structure characterizations of post-cycling materials, it was determined that the NiTiO₃ coating layer facilitates the formation of a stable lattice structure, effectively inhibiting lattice oxygen loss and reducing side reaction with the electrolyte. This enhancement in cycling stability was evidenced by a capacity retention of approximately 74% over 300 cycles at 1 C, marking a significant 30% improvement over the initial sample. Furthermore, notable advancements in rate performance were observed. Experimental results indicate that a stable and robust surface structure substantially enhances the overall stability of the bulk phase, presenting a novel approach for designing layered oxide cathodes with higher energy density.