Modulation of the Crystal Structure and Ultralong\nLife Span of a Na<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>‑Based Cathode for a High-Performance Sodium-Ion Battery by\nNiobium–Vanadium Substitution

Building\nbetter batteries with low cost, long life, and safety\ncan effectively meet the diverse energy demands. Na₃V₂(PO₄)₃ (NVP) is a potential cathode\nin energy storage systems due to its stable crystal structure, high-voltage\nplatform, and rapid migration rate of Na⁺. Nevertheless,\nits poor conductivity results in inferior electrochemical properties.\nHerein, the high-valence niobium (Nb⁵⁺) as a dopant can\nregulate the crystal structure of NVP and act as an activator to catalyze\nthe formation of the graphitization carbon layer, which shortens the\nelectron/ion diffusion pathway and enhances the electrochemical kinetics.\nDensity functional calculations show that Nb⁵⁺ doping decreases\nthe band gap energy and promotes electron transport. Physical and\nchemical characterizations prove that Nb⁵⁺ doping induces\nthe lattice distortion of NVP. Cyclic voltammetry and electrochemical\nimpedance tests show that Nb⁵⁺ doping promotes Na⁺ diffusion. Finally, the optimal NVP/Nb-0.3 delivers an excellent\nperformance of 103.8 mAh g^–1 with a capacity retention\nof 92.3% at 1 C for 200 cycles, a rate performance of 99.6 mAh g^–1 at 20 C, and cycling stability at 50 C for 6000 cycles\nwith a capacity retention of 72.7%. This modification strategy of\ncathode materials provides an important reference for optimizing battery\nperformance.