Multifunctional Separator Enables High‐Performance Sodium Metal Batteries in Carbonate‐Based Electrolytes

Abstract Sodium metal has become one of the most promising anodes for next‐generation cheap and high‐energy‐density metal batteries; however, challenges caused by the uncontrollable sodium dendrite growth and fragile solid electrolyte interphase (SEI) restrict their large‐scale practical applications in low‐cost and wide‐voltage‐window carbonate electrolytes. Herein, a novel multifunctional separator with lightweight and high thinness is proposed, assembled by the cobalt‐based metal–organic framework nanowires (Co‐NWS), to replace the widely applied thick and heavy glass fiber separator. Benefitting from its abundant sodiophilic functional groups and densely stacked nanowires, Co‐NWS not only exhibits outstanding electrolyte wettability and effectively induces uniform Na⁺ ion flux as a strong ion redistributor but also favors constructing the robust N,F‐rich SEI layer. Satisfactorily, with 10 µL carbonate electrolyte, a Na|Co‐NWS|Cu half‐cell delivers stable cycling (over 260 cycles) with a high average Coulombic efficiency of 98%, and the symmetric cell shows a long cycle life of more than 500 h. Remarkably, the full cell shows a long‐term life span (over 1500 cycles with 92% capacity retention) at high current density in the carbonate electrolyte. This work opens up a strategy for developing dendrite‐free, low‐cost, and long‐life‐span sodium metal batteries in carbonate‐based electrolytes.