Sodium metal batteries are considered one of the most promising low-cost high-energy-density electrochemical energy storage systems. However, the growth of unfavourable Na metal deposition and the limited cell cycle life hamper the application of this battery system at a large scale. Here, we propose the use of polypropylene separator coated with a composite material comprising polydopamine and multilayer graphene to tackle these issues. The oxygen- and nitrogen- containing moieties as well as the nano- and meso- porous network of the coating allow cycling of Na metal electrodes in symmetric cell configuration for over 2000 h with a stable 4 mV overpotential at 1 mA cm-2. When tested in full Na || Na3V2(PO4)3 coin cell, the coated separator enables the delivery of a stable capacity of about 100 mAh g-1 for 500 cycles (90% capacity retention) at a specific current of 235 mA g-1 and satisfactory rate capability performances (i.e., 75 mAh g-1 at 3.5 A g-1).
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