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

Abstract

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.