3D vertical ultra-sodiophilic leaf-vein-like MXene/Sn@CNF array of structured sodium enabling high-rate and long-life sodium metal batteries

Abstract

Uncontrolled Na dendrite growth and infinite volume change during cycling have greatly impeded the practical application of Na metal anode for high-energy-density batteries. To address these two issues simultaneously, a 3D vertical ultra-sodiophilic leaf-vein-like MXene/Sn@CNF array (VL-MXene/Sn@CNF) aerogel, integrated by 1D Sn@CNF and 2D MXene, was prepared by an ingenious hydrogen bonding self-assembly and unidirectional ice template method. The low-tortuosity and ultra-sodiophilic vertical array facilitates uniform and rapid Na+ transport along the ordered interspaces, achieving a negligible nucleation overpotential of 1.0 mV. Furthermore, experimental results and theoretical calculations revealed a unique bidirectional growth mode of Na, in which vertical leaf-vein-like lamellae and bridging fibers guided Na to be densely deposited along the vertical and horizontal directions, respectively. Benefitting from the ultra-sodiophilic vertical array of structured Na, the designed material exhibits an endurance of 1000 cycles for asymmetric cell at 3.0 mA cm−2 and 3.0 mAh cm−2, and the symmetrical cell delivers an ultra-long lifespan of 6000 h at 1.0 mA cm−2 and 3.0 mAh cm−2 with a high depth of discharge up to 50 %. Remarkably, at the high current of 15 C, the full cell based on NaTi2(PO4)3 cathode and Na@VL-MXene/Sn@CNF anode can deliver a reversible capacity of 88.94 mAh g−1 after 9200 cycles with an ultralow 0.0016 % capacity decay per cycle, which represents the most impressive full cell performance so far.