Stabilizing Multi‐Electron NASICON‐Na1.5V0.5Nb1.5(PO4)3 Anode via Structural Modulation for Long‐Life Sodium‐Ion Batteries

Abstract

AbstractMulti‐electron NAtrium SuperIonic CONductor (NASICON)‐Nb2(PO4)3 (N0NbP) is an attractive Na‐ion battery anode, owing to its low intercalation voltage (1.4 V vs Na+/Na0) 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 V3+ substitution, which can act as stabilizing agents to hold lantern units together during cycling, producing NASICON‐Na1.5V0.5Nb1.5(PO4)3 (N1.5VNbP). The N1.5VNbP anode exhibits reversible capacities of ≈140 mAh g−1 at 1.4 V versus Na+/Na0 through Nb5+/Nb4+/Nb3+ and V3+/V2+ 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, N1.5VNbP demonstrates extraordinary cycling (89% capacity retention at 5C after 500 cycles) and rate performances (105 mAh g−1 at 5C). Upon pairing the N1.5VNbP anode with the NASICON‐Na3V2(PO4)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.