Clewlike ZnV2O4 Hollow Spheres: Nonaqueous Sol-Gel Synthesis, Formation Mechanism, and Lithium Storage Properties

Hollow ZnV2O4 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 ZnV2O4 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 VO2 particles took place quickly. Then, clewlike ZnV2O4 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 ZnV2O4 nanocrystals. With the reaction proceeding, the interior ZnO would dissolve and then spontaneously diffuse outwards to nucleate as ZnO nanocrystals on the preformed ZnV2O4 nanowires. These renascent ZnO nanocrystals would further react with VO2 and benzyl alcohol, ultimately resulting in the final formation of a hollow spatial structure. The lithium storage ability of clewlike ZnV2O4 hollow microspheres was studied. When cycled at 50 m Ag-1 in the voltage range of 0.0.1-3 V, this peculiarly structured ZnV2O4 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 ZnV2O4 hollow spheres are promising for lithium-ion batteries.