Stabilizing Multi‐Electron NASICON‐Na 1.5 V 0.5 Nb 1.5 (PO 4 ) 3 Anode via Structural Modulation for Long‐Life Sodium‐Ion Batteries

Multi‐electron NAtrium SuperIonic CONductor (NASICON)‐Nb 2 (PO 4 ) 3 (N 0 NbP) is an attractive Na‐ion battery anode, owing to its low intercalation voltage (1.4 V vs Na + /Na 0 ) and high capacity (≈150 mAh g −1 ). However, it suffers from poor capacity retention due to structural degradation. To overcome this issue, extra Na + ions are introduced at the Na(1) sites, via V 3+ substitution, which can act as stabilizing agents to hold lantern units together during cycling, producing NASICON‐Na 1.5 V 0.5 Nb 1.5 (PO 4 ) 3 (N 1.5 VNbP). The N 1.5 VNbP anode exhibits reversible capacities of ≈140 mAh g −1 at 1.4 V versus Na + /Na 0 through Nb 5+ /Nb 4+ /Nb 3+ and V 3+ /V 2+ redox activities. The extra Na + ions in the framework forms a complete solid‐solution during Na (de)intercalation and enhances sodium diffusivity, in agreement with first‐principles calculations. Further, N 1.5 VNbP demonstrates extraordinary cycling (89% capacity retention at 5C after 500 cycles) and rate performances (105 mAh g −1 at 5C). Upon pairing the N 1.5 VNbP anode with the NASICON‐Na 3 V 2 (PO 4 ) 3 cathode, the full Na‐ion cell delivers a remarkable energy density of 98 Wh kg −1 (based on the mass of anode and cathode) and retains 80% of its capacity at 5C rate over 1000 cycles. The study opens new possibilities for enhancing the electrochemical performance of NASICON anodes via chemical and structural modulations.