NaF-rich protective layer on PTFE coating microcrystalline graphite for highly stable Na metal anodes

The practical application of Na metal anode is plagued by the dendrite growth, unstable solid electrolyte interphase (SEI) formation and volume change during the cycling process. Herein, poly(tetrafluoroethylene) (noted as PTFE) coating microcrystalline graphite is designed as the sodium metal anode host by a facile and cost-effective strategy. The isotropous microcrystalline graphite (MG) is conducive to guiding Na⁺ to form a co-intercalation structure into MG. And the PTFE coating layer can form NaF as artificial SEI film for uniform ion transport and deposition. As a result, the gained PTFE coating MG electrode can deliver a long-life span over 1,200 cycles with an average Coulombic efficiency (CE) of 99.88%. To note, almost the CE in each cycle is around 99.8%–100%. When assembled with Na₃V₂(PO₄)₂F₃ cathode as full cells, the full cell paired with PTFE coating MG electrode can operate much stable than that of MG electrode for the existence of PTFE coating layer. Even utilized as sodium-free Na metal anode paired with Na₃V₂(PO₄)₂F₃ cathode, it can also deliver a high initial CE of 76.27% at 0.5 C. After 100 cycles, it still has a high discharge capacity of 83.5 mAh·g⁻¹.