LiNbO$_3$ Coatings on NCM622: Structure and Performance Insights

For enhancing the electrochemical performance of solid-state batteries (SSBs), protective coatings are applied on the cathode active material (CAM) to mitigate the degradation of the cathode/electrolyte interface. A comprehensive understanding of the structural properties of these coatings is crucial for further optimization. This study investigates the effect of LiNbO$_3$-related coatings on LiNi$_{0.6}$Co$_{0.2}$Mn$_{0.2}$O$_2$ (NCM622) CAM, focusing on the relationship between coating structure and electrochemical performance in battery cells. Therefore, three samples calcinated at 550, 350 and, 80 °C temperature are analyzed with scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), and scanning precession electron diffraction (SPED) in combination with a pair distribution function (PDF) analysis. The results reveal that only an amorphous LiNbO$_3$ coating with a calcination temperature of 350 °C significantly improves the electrochemical performance of the CAM. In contrast, at higher calcination temperatures the coating crystallizes, while at lower calcination temperatures the coating becomes a mixed niobium oxide phase, both of which correlate with reduced battery performance.