Co-Engineering of In Situ Lithium Compensation and Oxygen-Anchoring Modulation Enables Thermochemically Stabilized NCM811-LATP Composite Cathodes for Ultra-Long Cyclability

The development of high-energy all-solid-state lithium-ion batteries (ASSLIBs) is hindered by interfacial incompatibility between Ni-rich layered oxides (LiNi 0.8 Co 0.1 Mn 0.1 O 2 , NCM811) and solid electrolytes (Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 , LATP), where co-sintering-induced Li + depletion and the subsequent oxygen release synergistically degrade electrochemical performance. Here, a dual-functional interface engineering strategy is developed through thermochemical coordination of dynamic lithium compensation and oxygen-anchoring modulation. Incorporation of 10 wt.% LiOH effectively suppresses cation interdiffusion during 700 °C co-sintering, while La 4 NiLiO 8 lithium–oxygen conductor stabilizes lattice oxygen via vacancy passivation, thus eventually protecting NCM811 from thermal decomposition (post-sintering XRD, XPS, and TEM). The optimized NCM811-LATP composite cathode achieves a high initial capacity of 217.1 mAh g −1 at 0.1 C with 80% capacity retention over 248 cycles a 143% lifespan improvement compared to baseline systems, while maintaining charge-transfer impedance below 97.8 Ω (EIS) and suppressing layered-to-spinel phase transitions (post-cycling TEM). This work establishes a universal paradigm for oxygen-interface co-stabilization in ASSLIBs, balancing thermochemical stability with interfacial ion transport to unlock ultra-stable cycling in high-energy-density solid-state systems.