Space‐Confined Guest Synthesis to Fabricate Sn‐Monodispersed N‐Doped Mesoporous Host toward Anode‐Free Na Batteries

Abstract Severe issues including volume change and dendrite growth on sodium metal anodes hinder the pursuit of applicable high‐energy‐density sodium metal batteries. Herein, an in situ reaction approach is developed that takes metal–organic frameworks as nano‐reactor and pore‐former to produce a mesoporous host comprised of nitrogen‐doped carbon fibers embedded with monodispersed Sn clusters (SnNCNFs). The hybrid host shows outstanding sodiophilicity that enables rapid Na infusion and ultralow Na nucleation overpotential of 2 mV. Its porous structure holds a high Na content and guides uniform Na deposition. Such host provides favorable Na plating/stripping with an average Coulombic efficiency of 99.96% over 2000 cycles (at 3 mA cm −2 and 3 mA h cm −2 ). The Na‐infused SnNCNF anode delivers extreme Na utilization of 86% in symmetric cells (at 10 mA cm −2 and 10 mA h cm −2 ), outstanding rate capability and cycle life in Na‐SnNCNF||Na 3 V 2 (PO 4 ) 3 full cells (at 1 A g −1 for over 1000 cycles with capacity retention of 92.1%). Furthermore, high‐energy/power‐density anode‐less and anode‐free Na cells are achieved. This work presents an effective heteroatom‐doping approach for fabricating multifunctional porous carbon materials and developing high‐performance metal batteries.