In-situ induction of porous coral structure by phosphomolybdic acid activating V4+/V5+ redox couple of Na3V2(PO4)3

The wide bandgap characteristics of polyanionic group lead to diminished electronic and ionic conductivities of Na3V2(PO4)3 (NVP). Meanwhile, the low capacity and energy also limit its further application. To tackle these obstacles, a triple modification approach is implemented on phosphomolybdic acid (PMA), encompassing the establishment of a porous coral-like structure, Mo4+ incorporation, and MoO3 encapsulation. Significantly, PMA adeptly mitigates the deficiencies in ionic and electronic conductivity through this triple modification strategy, resulting in enhanced electrochemical performance. The strategic induction of V4+/V5+ serves as a catalyst for the creation of a formidable 3.9 V platform, facilitating the liberation of the third Na+ for active involvement in the electrochemical process, thereby augmenting specific capacity to achieve elevated levels. Consequently, the amalgamation of a high plateau and substantial capacity engenders a heightened energy density, effectively remedying the issue of low energy density. Simultaneously, CO(NH2)2, serving as an supplementary nitrogen-doped carbon reservoir, can supplement the imperfections and active sites to efficiently promote the ionic and electronic transfer, thereby enhancing the electronic and ionic conductivity of the materials. Remarkably, the electrochemical storage mechanism and the V4+/V5+ excitation mechanism are elucidated through in-situ electrochemical XRD and ex-situ XPS techniques, which illustrates that the de-intercalation of 2Na+ at Na2 site is accompanied by the phase transition reaction and the migration of the third Na+ at Na1 site occurs along with the solid-solution transformation. Notably, Na3V2(PO4)3/C@15 %PMA@20 %CO(NH2)2 sample reveals a notable 124.2 mAh g−1 at 0.1C and remains 88.27 % after 2000 cycles even at 60C.