Dual‐Modified Polyacrylonitrile Fiber Separator: Enhancing Na ⁺ Desolvation and Migration for Long‐Cycle Life Sodium Metal Batteries

ABSTRACT As a pivotal component in sodium‐metal batteries (SMBs), separators play a crucial role in determining battery electrochemical performance and safety. The development of high‐performance functional separators represents a critical step toward advancing SMBs commercialization. Herein, both the surface chemistry of PAN fibers and the porous structure of the separator are engineered to enhance Na ⁺ transport kinetics and optimize Na ⁺ deposition on the anode surface through chemical modification and microfibrillation of PAN. The separator features abundant functional groups (─COO ⁻ and ─CONH ₂ ) and a unique Na ⁺ relay mechanism to enhance Na ⁺ transport kinetics, while the tailored pore architecture stemming from large numbers of crosslinking microfibrils enables the uniform flux and deposition of Na. The synergistic effect enables the Na//Na symmetric cell to operate stably for 2000 h. Furthermore, the Na//Na ₃ V ₂ (PO ₄ ) ₃ cell demonstrates outstanding cycling stability, maintaining 93.7% of its initial capacity after 6000 cycles at 5C. This work establishes a viable pathway for mass‐producing a high‐performance separator for SMBs.