A Trilayer Composite Separator with LiTFSI-Functionalized Silica Aerogel for Safe and Stable Lithium-Ion Batteries

Lithium-ion batteries (LIBs) are extensively used in modern energy storage systems but continue to face safety challenges related to thermal instability and dendritic growth. Conventional polyolefin separators exhibit limited thermal stability and are prone to failure under extreme conditions. In this study, a novel trilayer composite separator—denoted as PVDF-HFP/SiO 2 Li/PVDF-HFP (HFL)—was developed by incorporating lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) into a silica aerogel matrix via solution impregnation, followed by bilateral coating with PVDF-HFP. The resulting HFL separators demonstrated significantly enhanced thermal dimensional stability, flame retardancy, and electrolyte wettability. Electrochemical analyses revealed improved ionic conductivity (up to 2.934 mS cm −1 ) and lithium-ion transference number (up to 0.627), facilitating stable lithium deposition and suppressing dendrite formation. Long-term cycling tests showed exceptional capacity retention (99.1% after 100 cycles at 0.5 C and 82% after 800 cycles at 2 C) and remarkable stability under high current density. These findings underscore the potential of functionalized silica aerogel-based separators for enhancing the safety and performance of next-generation LIBs.