Modulation of the Crystal Structure and Ultralong Life 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 Niobium–Vanadium Substitution
Linnan Bi, Xiaoqing Liu, Xiaoyan Li, Bingbing Chen, Qiaoji Zheng, Fengyu Xie, Yu Huo, Dunmin Lin
Abstract
Building better batteries with low cost, long life, and safety can effectively meet the diverse energy demands. Na3V2(PO4)3 (NVP) is a potential cathode in energy storage systems due to its stable crystal structure, high-voltage platform, and rapid migration rate of Na+. Nevertheless, its poor conductivity results in inferior electrochemical properties. Herein, the high-valence niobium (Nb5+) as a dopant can regulate the crystal structure of NVP and act as an activator to catalyze the formation of the graphitization carbon layer, which shortens the electron/ion diffusion pathway and enhances the electrochemical kinetics. Density functional calculations show that Nb5+ doping decreases the band gap energy and promotes electron transport. Physical and chemical characterizations prove that Nb5+ doping induces the lattice distortion of NVP. Cyclic voltammetry and electrochemical impedance tests show that Nb5+ doping promotes Na+ diffusion. Finally, the optimal NVP/Nb-0.3 delivers an excellent performance of 103.8 mAh g–1 with a capacity retention of 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 with a capacity retention of 72.7%. This modification strategy of cathode materials provides an important reference for optimizing battery performance.