Achieving stable Na metal cycling via polydopamine/multilayer graphene coating of a polypropylene separator

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 || Na 3 V 2 (PO 4 ) 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 ). The development of future Na metal batteries relies on the cycling stability of the metallic anode. Here, the authors propose a polypropylene separator functionalized with polydopamine and multilayer graphene to enable stable and prolonged Na metal cell cycling.