Growth mechanism and electrochemical properties of hierarchical hollow SnO2 microspheres with a “chestnut” morphology.

Hierarchical hollow microspheres (HHMSs) constitute a very popular class of materials for use as drug-delivery carriers, photocatalysts and electrode materials in batteries, owing to their large, porous surface area and mechanical integrity during intercalation reactions. Here, we used a template- and additive-free hydrothermal route to prepare an unusually shaped SnO₂ material that comprises a hollow spherical morphology with uniform diameters and very thin petal-like nano-sheets grown perpendicularly on the sphere's surface, resembling a “chestnut cupule”. We thoroughly investigated the formation mechanism by ¹¹⁹Sn Mössbauer spectroscopy, powder X-ray diffraction and X-ray photoelectron spectroscopy. Key to this process is the ultrasonic pre-treatment of an aqueous SnCl₂ solution, followed by Ostwald “inside-out” ripening upon hydrothermal processing. This unique morphology has greatly improved the storage capacity and cycling performance of SnO₂ as an anode material for lithium and sodium ion batteries compared with conventional SnO₂ materials. [ABSTRACT FROM AUTHOR]