Figure 2

a Schematic presentation of the fabrication of nanographene-constructed hollow carbon nanospheres (NGHCs); b diffusion of lithium ions and electrons during charge/discharge processes of the NGHCs electrode. In the exterior walls of NGHCs, nanochannels arrange perpendicularly to the surface of curved nanospheres, which is favorable for Li⁺ diffusion from different orientations; the interior graphitic solid walls facilitate the collection and transport of electrons during the cycling process [29]