Unravelling the regulation mechanism of nanoflower shaped Na3V2(PO4)3 in methanol–water system for high performance sodium ion batteries

Abstract

Researchers are accustomed to utilizing traditional solid-state and sol–gel routes to synthesize Na3V2(PO4)3 (NVP). No regulation mechanism is proposed to illustrate the growth process of NVP in solvothermal environment. In current work, uniform spherical particles with positive charge are synthesized by molecular self-assembly of nanosphere micelles using structural guiding agent polyethylene glycol (PEG) and surfactant Cetyltrimethylammonium bromide (CTAB). Nanoflower-shaped NVP sample is successfully prepared in the 100 % methyl alcohol medium, derived from the plate V2O5 (negative charge) combining with the nuclear nanospheres (positive charge) with the induction of electrostatic attraction. Based on the multi-dimensional tests and molecular dynamic calculation, the protective mechanism of polar solution for NVP system is proposed for the first time, that is, methanol solvent system can better protect the morphological features of NVP than water environment to maintain the original special nanoflower morphology. Due to the distinctive and stabilized nanoflower construction, the optimized NVP60 sample can provide more extra active sites for the efficient de-intercalation of Na+ and possess a large contacting area with electrolyte, resulting in the facilitated kinetic characteristics and superior electrochemical performance. The optimized NVP60 cathode possesses superior sodium storage property in both half cell and full cell. This work proposes a synergetic strategy combining theory and experiment to design and synthesize the modified NVP-based cathode materials from the molecular bonding aspect, further promoting the development of high performance cathode for SIBs.