Stabilizing Solid‐state Lithium Metal Batteries through In Situ Generated Janus‐heterarchical LiF‐rich SEI in Ionic Liquid Confined 3D MOF/Polymer Membranes

Abstract Pursuing high power density lithium metal battery with high safety is essential for developing next‐generation energy‐storage devices, but uncontrollable electrolyte degradation and the consequence formed unstable solid‐electrolyte interface (SEI) make the task really challenging. Herein, an ionic liquid (IL) confined MOF/Polymer 3D‐porous membrane was constructed for boosting in situ electrochemical transformations of Janus‐heterarchical LiF/Li 3 N‐rich SEI films on the nanofibers. Such a 3D‐Janus SEI‐incorporated into the separator offers fast Li + transport routes, showing superior room‐temperature ionic conductivity of 8.17×10 −4 S cm −1 and Li + transfer number of 0.82. The cryo‐TEM was employed to visually monitor the in situ formed LiF and Li 3 N nanocrystals in SEI and the deposition of Li dendrites, which is greatly benefit to the theoretical simulation and kinetic analysis of the structural evolution during the battery charge and discharge process. In particular, this membrane with high thermal stability and mechanical strength used in solid‐state Li||LiFePO 4 and Li||NCM‐811 full cells and even in pouch cells showed enhanced rate‐performance and ultra‐long life spans.