Mg-diamane-modified polypropylene separators achieving dendrite-free sodium metal batteries with a long cycle lifespan

Sodium metal is regarded as a promising anode material for sodium-ion batteries because of its high theoretical specific capacity and low electrochemical potential. However, its practical application is significantly limited by the formation of dendrites. To overcome this challenge, a sodiophilic separator consisting of a Mg nanoparticle-decorated two-dimensional diamond (diamane) on a commercial polypropylene (PP) membrane (Mg-diamane/PP separator) is designed to inhibit dendrite growth. A symmetric Na∥Na cell with the Mg-diamane/PP separator demonstrates a long cycle life of more than 1850 h at 2 mA cm^-2 with 1 mAh cm^-2. The sodiophilicity originates from the limited solid solution formed between Mg and Na, which can homogenize ion distribution and reduce voltage hysteresis. Furthermore, a full cell incorporating a Na₃V₂(PO₄)₃@C (NVP@C) cathode, the Mg-diamane/PP separator, and a sodium metal anode delivers a high reversible capacity of 95.67 mAh g^-1 for more than 400 cycles. This work highlights the potential of the Mg-diamane/PP separator as a practical solution for enabling high-performance, long-life sodium metal batteries.