Rational design of a hybrid artificial protective layer for a dendrite-free, long-cycling-life Na metal anode

Metallic sodium (Na) serving as anode for sodium-based batteries (SBBs) has caught much attention, owning to its low electrode potential and high theoretical capacity. However, the notorious Na dendrites severely restrict its practical application in Na metal batteries (SMBs). Herein, the hybrid artificial layer (Na/VN-S) composed of sodium sulfide, vanadium nitride and metal vanadium are constructed on Na anode via pretreatment metallic Na with vanadium nitride and vanadium sulfide powders. The obtained Na/VN-S electrode presents superior electrolyte wettability, high sodiophilicity, low activation energy barrier and high Young's modulus, leading to homogeneous distribution of Na ions and even Na deposition, so that the Na dendrite growth can be suppressed. Owing to these virtues, the Na/VN-S symmetrical cells present a long cycle life of 1400 h at 0.5 mA cm−2 with 1 mAh cm−2, and can stably cycle at a higher current density of 4 mA cm−2. Moreover, when the commercial Na3V2(PO4)3 (NVP) cathodes are coupled with the Na/VN-S anodes, the Na/VN-S||NVP full cells display a prolonged life of 1900 cycles at 5 C with an outstanding capacity retention of 84.2%. This work contributes to the advancement of Na metal anode in high performance SBBs.