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

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 ─CONH₂) 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//Na₃V₂(PO₄)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.