In-situ constructing Co/Mo co-doped Na3V2(PO4)3 with coral cluster porous structure boosting high performance for sodium ion batteries

Abstract

Na3V2(PO4)3 (NVP) is suffered from poor conductivities and terrible structure stability. Herein, Co/Mo co-doped NVP with unique cluster porous structure is prepared. Notably, Co2+ replacing V3+ provides useful p-type effects, manufacturing more acceptor levels and generating equal hole carriers, which facilitates the ionic conductivity. Moreover, the larger ionic radius of Co2+ significantly enlarges the interplanar spacing to broaden ionic migration channel. The doped Co2+ can function as pillar ions to reinforce the crystal structure, further improving structure stability. Meanwhile, Moderate Mo6+ is introduced to keep charge balance, resulting in beneficial n-type doping effects, which can bring more electrons and increase the electronic concentration to speed up electronic conduction. Notably, a unique coral cluster porous structure is formed after controlling the added Co/Mo contents. This distinctive morphology allows active materials expose more contact areas with electrolyte to enhance infiltration effects, increasing the active sites to release more reversible capacity. Moreover, the porous construction withstands the stress resulting from the volume contraction during Na+ de-insertion. Comprehensively, NVCMP0.15 exhibits a value of 90.7 mAh g−1 at 50C and retains 68.5 mAh g−1 after 2000 cycles with retention ratio of 75.52 %. Ex-situ XRD/XPS/SEM after cycling indicate great improvements in crystal stability of NVCMP0.15.