g-C3N4 in situ derived ionic-electronic dual-conducting interlayer with N-rich sites for long lifespan sodium metal anodes

Sodium (Na) metal has been considered as promising anode materials for next generation high-energy-density Na-based batteries due to its high theoretical capacity, abundant resources and low cost. However, the unstable electrode/electrolyte interface caused by side reaction and dendrite growth usually results in unsatisfying cycling lifespan of Na metal batteries. Herein, an ionic-electronic dual-conducting interlayer with N-rich sites is constructed upon Na metal anode by an in situ reaction between metallic Na and graphitic carbon nitride (g-C3N4). Benefiting from the strong absorption to Na+, the abundant N-sites in interlayer can form transient Na-N bonds to stabilize the electrode/electrolyte interphase for uniform Na nucleation and growth. Meanwhile, the ionic-electronic dual-conducting interlayer contributes to gradient and uniform Na deposition. As a result, the Na symmetric cells can be cycled stably for an exceptionally prolonged over time of 6000 h with a much lower voltage hysteresis at 1 mA cm−2. Moreover, the full cells paired with the constructed Na anode and Na3V2(PO4)3 cathode show an outstanding capacity retention of 96.2% after 1200 cycles at 3 C (while a sharp decay after 760 cycles for bare Na anodes). It is believed that this work provides a rational interface design that stimulates further large-scale utilization of Na metal batteries.