Highly stable surface and structural origin for lithium-rich layered oxide cathode materials

Surface/interfacial engineering is critical for preventing particle degradation of Li-rich layered oxides (LLOs), particularly facet degradation, thereby optimizing their electrochemical performance. Thus, the current study details the investigative analysis of the surface structure of an LLO, followed by its surface engineering. The surface structure was analyzed using scanning transmission electron microscopy (STEM) and soft X-ray absorption spectroscopy (sXAS), and the electrochemical performance was evaluated. The results indicate that an integrated spinel/rock salt (ISR) surface structure formed on the surface in situ. More precisely, the spinel phase originated from the C2/m surface, whereas the rock salt phase originated from the R3m surface, which significantly increased the cycle stability and suppressed voltage decay. After 2000 cycles, the surface-modified LLO cathode retained an extremely high capacity of 69.6% and a low discharge medium voltage with a decay rate of 0.44 mV cycle(-1). Additionally, the structural and morphological changes observed after prolonged cycling confirmed the stability of the surface layer. The outstanding performance was attributed to the ultra-stable ISR surface layer, the presence of multiple ion conductivities (LiPO3 and Li2SO4), and the substantial prevention of electrochemical facet degradation. The findings, therefore, highly suggest that the ISR surface concept and the method for surface modification is highly likely to aid in the rapid commercialization of LLOs for battery applications.