Template-Free Synthesis of Amorphous Double-Shelled Zinc-Cobalt Citrate Hollow Microspheres and Their Transformation to Crystalline ZnCo2O4 Microspheres

A novel and facile approach was developed for the fabrication of amorphous double-shelled zinc-cobalt citrate hollow microspheres and crystalline double-shelled ZnCo2O4 hollow microspheres. In this approach, amorphous double shelled zinc-cobalt citrate hollow microspheres were prepared through a simple route and with an aging process at 70 degrees C. The combining inward and outward Ostwald ripening processes are adopted to account for the formation of these double shelled architectures. The double shelled ZnCo2O4 hollow microspheres can be prepared via the perfect morphology inheritance of the double-shelled zinc-cobalt citrate hollow microspheres, by calcination at 500 degrees C for 2 h. The resultant double shelled ZnCo2O4 hollow microspheres manifest a large reversible capacity, superior cycling stability, and good rate capability.