Clewlike ZnV2O4 hollow spheres: nonaqueous sol-gel synthesis, formation mechanism, and lithium storage properties.

Hollow ZnV(2)O(4) microspheres with a clewlike feature were synthesized by reacting zinc nitrate hexahydrate and ammonium metavanadate in benzyl alcohol at 180 degrees C for the first time. GC-MS analysis revealed that the organic reactions that occurred in this study were rather different from those in benzyl alcohol based nonaqueous sol-gel systems with metal alkoxides, acetylacetonates, and acetates as the precursors. Time-dependent experiments revealed that the growth mechanism of the clewlike ZnV(2)O(4) hollow microspheres might involve a unique multistep pathway. First, the generation and self-assembly of ZnO nanosheets into metastable hierarchical microspheres as well as the generation of VO(2) particles took place quickly. Then, clewlike ZnV(2)O(4) hollow spheres were gradually produced by means of a repeating reaction-dissolution (RD) process. In this process, the outside ZnO nanosheets of hierarchical microspheres would first react with neighboring vanadium ions and benzyl alcohol and also serve as the secondary nucleation sites for the subsequently formed ZnV(2)O(4) nanocrystals. With the reaction proceeding, the interior ZnO would dissolve and then spontaneously diffuse outwards to nucleate as ZnO nanocrystals on the preformed ZnV(2)O(4) nanowires. These renascent ZnO nanocrystals would further react with VO(2) and benzyl alcohol, ultimately resulting in the final formation of a hollow spatial structure. The lithium storage ability of clewlike ZnV(2)O(4) hollow microspheres was studied. When cycled at 50 mA g(-1) in the voltage range of 0.01-3 V, this peculiarly structured ZnV(2)O(4) electrode delivered an initial reversible capacity of 548 mAh g(-1) and exhibited almost stable cycling performance to maintain a capacity of 524 mAh g(-1) over 50 cycles. This attractive lithium storage performance suggests that the resulting clewlike ZnV(2)O(4) hollow spheres are promising for lithium-ion batteries.