Dendrite suppression enabled longevous sodium metal batteries by sodiophilic Zein/MXene nanofiber modulated polypropylene separator

Sodium metal batteries with low-cost and high-energy density are considered as the most promising candidate for large-scale energy storage systems. However, dendritic growth of sodium metal anode (SMA) severely hampered their viability. Here, we propose the use of polypropylene separators coated by electrospinning nanofibers containing corn protein (Zein) molecules and MXene (V2CTx) sheets on polyacrylonitrile (PAN) skeletons (denoted as PZM) to tackle these issues. The abundant sodiophilic functional groups on Zein and V2CTx as well as the porous network of electrospinning nanofibers can facilitate homogeneous Na metal deposition and achieve dendrite-free SMA. Additionally, the oxygen- and nitrogen-containing functional moieties on the nanofibers benefit the electrolyte up take (395 %), ion-conductivity (1.43 mS cm-1), Na+transference number (0.77) and inorganic-rich SEI. The PZM separator enables Na metal electrodes in symmetric cells to cycle over 3500 h with a stable overpotential of 10 mV at 1 mA cm-2/1 mAh cm-2 and over 1200 h at 5 mA cm-2/10 mAh cm-2. When tested in Na3V2(PO4)3@C||Na full cells, the PZM separator enables a high capacity of 86.2 mAh g-1 over 1000 cycles with an excellent capacity retention of 87.8 %. The proposed biomaterial-based separator modification strategy can spur the development of feasible sodium metal batteries.