Bottom-up assembly of strongly-coupled Na3V2(PO4)3/C into hierarchically porous hollow nanospheres for high-rate and -stable Na-ion storage

Herein, a three-dimensional (3D) Na3V2(PO4)(3)-based hollow nanosphere with hierarchical pores (3DHP-NVP@C) has been firstly reported. Detailed studies reveal that this novel architecture is made up from the bottom-up assembly of carbon-coating NVP nanoparticles. The hierarchically porous structure offers ample space for the intimate contact between electrode/electrolyte and eliminates the disadvantageous reducing of effective surface areas in manufacturing the electrodes, as well as stabilizes the structure upon repeated sodium ions insertion/extraction, resulting to the barrier-free sodium ion diffusions and long-term cycling life. On the other hand, the graphitic carbon shells construct into a highly-conductive framework that can ensure the ultrafast electrons transfer. Consequently, extraordinary high-rate and ultralong-cycle capabilities that are superior to any other NVP-based material are obtained: the outstanding high-rate capacity retention (over 80% of the 1 C capacity is retained at 400 C), ultralong life span (90.9% and 92.5% capacity retention after 10,000 cycles at 1 C and 5 C), and extremely high-rate stability (80% capacity retention after 30,000 cycles at 50 C), demonstrating its promising application in sodium ion battery.