Lithium-ion storage performances of sunflower-like and nano-sized hollow SnO₂ spheres by spray pyrolysis and the nanoscale Kirkendall effect

Nanostructured metal selenides with a variety of morphologies are crucial for fabricating porous, hollow metal-oxide nanomaterials by nanoscale Kirkendall diffusion. Herein, SnSe-SnO₂ composite powders and SnSe nanospheres were synthesized via one-pot spray pyrolysis by optimizing the concentration of the Se precursor in the spray solution; these were then used to fabricate sunflower-like SnO₂ and hollow SnO₂ nanospheres, respectively, via nanoscale Kirkendall diffusion. Post-treatment of the SnSe-decorated SnO₂ under air produced sunflower-like SnO₂, in which ray and disk florets consisting of hollow nanoplates and dense nanospheres, respectively, were present. The mean diameter of the homogeneous hollow SnO₂ nanospheres was 150 nm. The hollow morphology shortens the diffusion length, increasing the contact area between the electrolyte and voids and buffering large volume changes during repeated cycling. As anode materials for lithium-ion batteries, the hollow SnO₂ nanospheres showed excellent cycling and rate performances. The discharge capacity of the hollow SnO₂ nanospheres, after 500 cycles from 0.001 V to 3.0 V, was 1043 mA h g^-1, at a current density of 3.0 A g^-1. The hollow SnO₂ nanospheres showed a high reversible capacity of 638 mA h g^-1, even at current density as high as 10 A g^-1.