Vanadium Nitride Quantum‐Dot Bidirectional Catalysis for Accelerated Polysulfide Redox in Room‐Temperature Na–S Batteries

The formation of soluble polysulfide intermediates is crucial for the multistep redox reactions of sulfur‐based batteries; however, their irreversibility and uncontrollable shuttling through the electrolyte lead to suboptimal capacity, self‐discharge, and rapid capacity fading. Here, we report a vanadium nitride quantum dot‐graphene (VNQ‐G) composite bidirectional catalyst that accelerates the reversible conversion of polysulfides during both discharging and charging for room‐temperature sodium–sulfur (Na–S) batteries. The VNQ‐G composite with a quantum‐confined VNQ catalyst and a conductive graphene scaffold enables strong d–p hybridization with sodium polysulfide, accelerating redox kinetics and ensuring effective polysulfide trapping and utilization during discharge, and accelerating Na 2 S oxidation to soluble polysulfides during charging. As a result, the Na‐S battery employing VNQ‐G effectively mitigates the shuttle effect, delivering a maximum capacity of 302 mAh g −1 at 1C, maintaining 70% of its capacity over 400 cycles, and achieving a specific capacity of approximately 30 Ah per dollar of electrolyte. Our study demonstrates that the bidirectional catalyst is a critical factor in the reversibility of Na–S, and establishes that VNQ‐G is a practical interfacial design strategy for realizing high‐performance, cost‐effective Na–S batteries.