Hierarchical vanadium pentoxide spheres as high-performance anode materials for sodium-ion batteries
We report the synthesis of hierarchical vanadium pentoxide (V2O5) spheres as anode materials for sodium-ion batteries (Na-ion batteries). Through field emission scanning electron microscopy, X-ray diffraction, and transmission electron microscopy characterizations, it was found that the as-prepared V2O5 spheres are composed of primary nanoparticles with pores between them. The as-prepared hierarchical V2O5 spheres achieved a discharge capacity of 271 mA h g-1 at a current density of 40 mA g-1, and 177 mA h g-1 discharge capacity after 100 cycles. Even at high current densities, V2O5 spheres still delivered high capacity and superior cyclability (179 and 140 mA h g-1 discharge capacities at 640 and 1280 mA g-1 current densities, respectively). The promising electrochemical performances of V2O5 spheres should be ascribed to the unique architecture of hierarchical spheres and the predominant exposed (110) facets, which provides open interlayers for facile sodium ion intercalation. Each nanoparticle contains predominantly exposed (110) crystal planes. The ex situ FESEM analysis revealed that the pores formed by the primary nanocrystals effectively buffer volume changes in the electrode during cycling, contributing to the excellent cycling performance.