Hierarchical orthorhombic V2O5 hollow nanospheres as high performance cathode materials for sodium-ion batteries

Vanadyl ethylene glycolate hollow hierarchical nanospheres were synthesized via a template-free polyol-induced solvothermal process. After sintering, vanadium pentoxide (V2O5) with well-preserved spherical structures was obtained. Refined X-ray diffraction and transmission electron microscopy analyses identified that the V2O5 hollow nanospheres were constructed from hierarchical nanocrystals with predominantly exposed {110} crystal planes. When applied as cathode materials for sodium-ion batteries (Na-ion batteries), the V2O5 hollow nanospheres delivered a specific discharge capacity of ∼150 mA h g−1, which is equal to one Na+ ion insertion per V2O5 formula unit. Theoretical modelling on the volume expansion and stress evolution on Na+ ion insertion revealed that the prolonged cycling stability could be ascribed to the porous hollow spherical architecture. Furthermore, the exposed {110} facets of V2O5 nanocrystals with two-dimensional diffusion paths for Na+ ion intercalation also contribute to high rate capacity and excellent cycling performance.