Boosting the rate capability and cycle life of Zr-substituted Na3V2(PO4)3/C enwrapped on carbon nanotubes for symmetric Na-ion batteries

Abstract Na3V2(PO4)3 (NVP) has been deemed to be an ideal cathode candidate due to the high capacity but suffers from the intrinsic poor conductivity. Herein, we adopt a dual modification route of Zr substitution and carbon nanotubes (CNTs) enwrapping to improve the kinetic characteristics and stabilize the structural framework. The replacement of V3+ by Zr4+ is favorable to expanding the migration channels for Na+ diffusion and supporting the structure. Furthermore, Zr4+ substitution contributes to restraining the particle agglomeration and facilitating the uniform distribution. The evenly intertwined CNTs construct an efficient network and establish the beneficial connections for the adjacent Zr-doped NVP particles to accelerate the electronic conductivity significantly. Distinctively, the modified Na2.9V1.9Zr0.1(PO4)3/C@CNTs (Zr0.1-NVP/C@CNTs) exhibits a superior electrochemical performance: it delivers a capacity of 102.1 mAh g−1 at 20 C with a retention of 86.3% after 1000 cycles. Notably, it still reveals an outstanding capacity of 74.3 mAh g−1 and remains 62.2 mAh g−1 after 2000 cycles at 200 C, indicating a low capacity loss of 0.0081% per cycle. Moreover, the symmetric full cell constituted by Zr0.1-NVP/C@CNTs presents competitive practical applicability. Furthermore, the improved kinetic characteristics are demonstrated by multiple methods, indicating the significant improvement of conductivities resulted from the synergetic utility.