Recently, we developed a novel approach to synthesize hierarchicalflower-like spheres assembled from SnO2 NSs27. The phase purity ofthe product was confirmed by x-ray diffraction (XRD), and it can beseen from the field-emission scanning electron microscope (FESEM)image that the sample contains uniform spheres of ~2 μm in diameter(Fig. 1a). Under a higher magnification, the spheres are shown to haveNS subunits pointing radially outward (Fig. 1b). It was found that theconcentration of urea in the system has an important effect on theassembly of the NS building blocks into the hierarchical structure. Atthe same time, SnO microplatelets are also formed due to incompleteoxidation, and they can be easily separated by sedimentation. Theas-prepared SnO2 hierarchical spheres exhibit much higher reversiblecapacity as well as better cyclic capacity retention compared to the
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