Oxygen Vacancy Engineered BiOCl Nanosheets Enable Synergistic LiF‐Rich SEI Construction and Polysulfide Shuttle Suppression for Lithium Metal Batteries

ABSTRACT To solve the drawbacks of low lithium‐ion transference number (t Li + ) and poor interface stability of poly(ethylene oxide) (PEO)‐based solid electrolytes, La 3+ ‐doped BiOCl nanosheets were developed as new functional fillers. Via a surfactant‐assisted microemulsion method, the stacking defects of nanosheets were suppressed, and the controllable synthesis of dispersed nanosheets was realized. These nanosheets ensure uniform dispersion in the PEO matrix, construct continuous ion transport channels, and reduce interfacial impedance. It is worth noting that La 3+ doping can accurately control the oxygen vacancy (O v ) concentration, and the optimal doping amount can increase t Li + to 0.47. The assembled Li||Li symmetrical cells deliver a long‐term cycle lifespan of over 2000 h, accompanied by outstanding cycling durability for lithium metal batteries. Theoretical calculations confirm that superior performance originates from lanthanum doping and O v , which facilitate electron delocalization and induced the formation of TFSI − ‐rich interface layer and a LiF‐dominated stable SEI film. Furthermore, the O v remarkably accelerates the redox reaction kinetics of polysulfides and simultaneously boosts the cycling stability of lithium‐sulfur batteries. The universality of the electrolyte design strategy was verified by multi‐scale electrochemical analysis and theoretical calculation, which provided a new idea for the development of high‐performance solid‐state batteries.