Single‐Atom Nb‐N ₄ Sites Regulate Hard Carbon Interface for Ultrastable and Low‐Temperature Sodium‐Ion Batteries

ABSTRACT Enhancing interfacial kinetics of hard carbon anodes while maintaining structural integrity under high rate and low‐temperature conditions remains a challenge for high‐performance sodium‐ion batteries. Herein, this study achieves comprehensive regulation of the interfacial/bulk electrochemical behavior of N‐doped hard carbon through atomic‐level niobium doping (Nb x ‐NC). The Nb‐N 4 coordination configuration optimizes the electron/ion conduction pathways of the hard carbon, thereby promoting rapid Na + transport and fast pseudocapacitive reactions. As expected, the optimized Nb 0.03 ‐NC demonstrates a stable capacity of 238 mAh·g −1 at 10 C after 3000 cycles (25°C) and maintains a considerable reversible capacity of 184 mAh·g −1 at ‐20°C. Theoretical calculations and multiscale characterizations confirm that the Nb‐N 4 coordination structure, as an active center, not only optimizes the electrode‐electrolyte interface, effectively enhancing the desolvation and diffusion rates of Na + , but also catalyzes the controlled decomposition of the electrolyte components NaPF 6 and DME, promoting the formation of a uniform, stable, and inorganic‐rich solid electrolyte interface layer. When assembled with Na 3 (VPO 4 ) 2 F 3 cathode, the full cell achieves an ultrahigh energy density of 230 Wh·kg −1 and a power density of 6.69 kW·kg −1 . This work elucidates the relationship between atomic‐scale interface engineering and electrochemical performance, offering a new strategy for advanced energy storage systems.