Three-dimensional hierarchical porous Na3V2(PO4)(3)/C structure with high rate capability and cycling stability for sodium-ion batteries

Na3V2(PO4)(3)(NVP) with an open NASICON structure has drawn worldwide attention as a potential cathode material for sodium-ion batteries (SIBs) owing to its high theoretical capacity. However, the inherently poor electronic conductivity of NVP severely restricts its electrochemical performance, particularly for rate capability and long cycle performance. Herein, high performance NVP/C cathode (denoted as NVP/C-T) is demonstrated by designing and synthesizing three-dimensional (3D) hierarchical porous NVP architecture via a facile hydrothermal technique. In this hierarchical porous structure, ultrathin NVP nanosheets capped with in-situ carbon layers are interlinked to form hierarchical pores, convenient nanochannels and 3D conductive carbon framework. This delicate structure not only provides adequate void for the intimate contact between electrode/electrolyte, shortens ionic diffusion distances, ensures the ultrafast electron transfer but also strengthens the structural stability of electrode material. The as-prepared NVP/C-T cathode exhibits a high reversible initial capacity (114.8 mAh g(-1) at 1 C approaching the theoretical capacity), excellent rate performance (89.3 mAh g-1 at 60 C and 73.2 mAh g(-1) at 80 C) and long life span (93.3 mAh g(-1) after 8000 cycles at 20 C). In addition, the electrochemical properties of symmetric full cell constructed with NVP/C-T/NVP/C-T are also studied and high initial charge capacity (101.8 mAh g(-1) at 0.25 C) and high stability (70.1 mAh g(-1) at 2 C after 200 cycles) are achieved. Significantly, the design of the 3D hierarchical porous nanocrystal@ C strategy and scalable synthesis method may pave a way to develop high performance SIBs.