Modulated Interphase Chemistry Unlocks Ultra‐Stable Ni‐Rich Single‐Crystal Cathode in Sulfide All‐Solid‐State Batteries

ABSTRACT Single‐crystalline Ni‐rich cathodes with high capacity and operation voltage present the huge potential for sulfide‐based all‐solid‐state lithium batteries (ASSLBs). However, the surface‐bulk structural degradation severely limits their practical application. Herein, a modulated interphase chemistry strategy on single‐crystal LiNi 0.8 Co 0.1 Mn 0.1 O 2 by combining the gradient lattice rivets and an in situ formed super‐ion conductor epitaxial layer with 3D Li + diffusion path is employed to collaboratively enhance the overall framework stability from surface to bulk. A new intermediate energy level appears between the conduction and valence band, which improves material's intrinsic electronic conductivity. The generated robust bond with lattice oxygen creates the local rigid‐flexible structure units, dissipating the localized stress‐strain. Concurrently, the formed conformal layer reduces interfacial interaction energy and mitigates side reactions related to electron leakage, thereby suppressing interfacial degradation and irreversible transformation from layered to spinel/rock‐salt phases. Thus the optimized sample exhibits the remarkably long‐term cycling stability with 95.3% capacity retention after 1000 cycles (1 C, 4.4 V, 30°C). Importantly, it delivers the 168.4 mAh g −1 initial capacity with 83.7% capacity retention after 300 cycles even under harsher conditions (1 C, 4.5 V, 60°C). This study provides a new insight into deep interface design on layered cathode materials for high‐performance ASSLBs.