Anchoring oxygen on LiNi_0.94Co_0.05Mn_0.01O₂ surface by coating Ti_xNbB_(1−x)C₂ boosts long-cycle stability of all-solid-state lithium batteries

To satisfy the demands of modern society for high-energy–density sulfide-based all-solid-state lithium batteries (ASSLBs), Ni-rich cathode materials have gained much attention for their high capacity and energy density. However, their practical deployment is hindered by accelerated interface degradation and capacity decay originating from surface oxygen release and lattice oxygen activation during prolonged cycling. In this study, Ti_xNbB_(1−x)C₂ was successfully coated on the surface of LiNi_0.94Co_0.05Mn_0.01O₂. Density functional theory (DFT) calculations first elucidate a “point-to-point” anchoring mechanism where each surface oxygen atom coordinates with single species (Ti/Nb/B) offered by Ti_xNbB_(1−x)C₂, which forms robust O–M bonds and sustain a stable interface structure. The electron energy loss spectroscopy (EELS) reveals the segregation of Ti/Nb toward subsurface layers during cycling, creating an optimized lattice oxygen coordination environment and suppressing oxygen activation. The dual oxygen stabilization mechanism dramatically improves the reversibility of phase transition and the structural stability of the Ni-rich cathode materials. Moreover, Ti_xNbB_(1−x)C₂ as the protective layer decreases mechanical strain and suppresses the parasitic reactions. Consequently, the engineered cathode delivers 91% capacity retention after 1000 cycles at 0.3 C, suggesting excellent cycling stability. The research delivers a new design philosophy for the coating layer that can stabilize surface oxygen. Furthermore, the atomistic understanding of the structure–property relationship of the Ni-rich cathode materials provides valuable guidance for the future design of new cathode materials with superior structural stability in ASSLBs.