Induction of brand new Na3 sites constructing high performance Na3V2(PO4)3 with low strain property and high thermal safety

[Display omitted] •Mg2+ occupies Na1 site to increase the intercellular space to accelerate ionic migration.•Mg2+ at Na1 site causes the slight lattice distortions to induce more active sites for Na+ storage.•NVP/C@Mg-2% possesses a honeycomb morphological structure with homogeneous pores.•After-cycled XRD/SEM/XPS verify the stable crystal structure for NVP/C@Mg-2%.•ARC test further manifests NVP/C@Mg-2% behaves excellent thermal safety and stability. The inert Na1 site of Na3V2(PO4)3 (NVP) leads to poor capacities, which seriously hinders its further application. Herein, Na site regulation is initiatively explored by introducing Mg2+ into Na+ site in NVP bulk. Rietveld XRD refinement with low R values demonstrates the successful occupancy of Na1 (16b) site by Mg2+. Furthermore, Na-NMR testing of the modified Na2.96Mg0.02V2(PO4)3@5%CNTs (NVP/C@Mg-2 %) indicates that additional active Na+ sites at 12c rather than 16b and 18e for traditional Na1 and Na2 sites is generated in the crystal structure after introducing Mg2+. The newly induced Na3 site can provide extra space for the reversible de-intercalation of Na+, which results in the effectively improved electrochemical capacity and kinetic characteristics. In addition, the doping of Mg2+ with a smaller radius is favourable to reduce the lattice strain because of the enlarged internal interspace, constructing a solid structural framework to maintain excellent cyclic stability, which has been demonstrated by ex-situ XRD measurement. Moreover, NVP/C@Mg-2 % possesses a honeycomb morphological structure with homogeneous pores, providing enough room for the volume shrinkage of electrode and benefiting for the infiltration of electrolyte. Accordingly, NVP/C@Mg-2 % delivers 98.3 mAh/g at 30C and maintains a value of 81.5 mAh/g after 2000 cycles, indicating superior rate performance and cyclic stability. Besides, after-cycled XRD/SEM/XPS verify the stable crystal structure for NVP/C@Mg-2 %. ARC test further manifests NVP/C@Mg-2 % behaves excellent thermal safety and stability with higher self-exothermic temperature.