Robust, High‐Temperature‐Resistant Aramid Nanofiber Separator with Hierarchical Structure for High‐Performance Lithium‐Ion Batteries

Abstract Lithium‐ion batteries (LIBs) face significant safety challenges due to the inherent limitations of conventional polyolefin separators, such as poor mechanical strength and inadequate thermal stability, which heighten the risk of thermal runaway episodes. This study presents a robust, high‐temperature‐resistant aramid nanofiber (ANF) separator with a hierarchical lamellar interconnected network structure, synthesized via a bottom‐up low‐temperature polycondensation strategy. The resulting ANF separator exhibits exceptional mechanical strength (192 MPa), outstanding thermal stability (initial degradation temperature of ≈510 °C), and negligible thermal shrinkage even at 300 °C. Electrochemical evaluations reveal superior Li⁺ transference number (0.536) and high temperature cycling stability (94.6% capacity retention after 100 cycles at 100 °C), outperforming commercial polypropylene (PP) separators. Compared with PP, the pouch lithium cell assembled by ANF separator can effectively maintain structural integrity even under harsh thermal conditions (150 °C). This work demonstrates a scalable, efficient method to fabricate advanced separators with a multiscale structure composed of ANF, addressing critical safety concerns and enhancing the performance of high‐energy‐density LIBs.