In situ fabrication of hierarchical iron oxide spheres@N-doped 3D porous graphene aerogel for superior lithium storage

To improve the electronic conductivity and dramatic volume change of iron oxide as anode for lithium-ion batteries, we finally fabricate a hierarchical aerogel composite of FeOx spheres encapsulated in porous N-doped three-dimensional graphene (FeOx@N-3DG) via a facile in situ electrostatic self-assembly strategy assisted with hydrothermal. In the hierarchical architecture, the distributed FeOx spheres that consist of Fe2O3 and Fe3O4 crystals are intimately wrapped by N-3DG acting as protective elastomer to buffer the volume change during cycling. Moreover, the integrally interconnected porous structure is beneficial for fast electron transfer and penetration of the electrolyte. More importantly, the abundant grain boundaries of Fe2O3 and Fe3O4 crystals inside FeOx spheres provide smooth channels for fast lithium-ion transport and increase lithium storage sites. Therefore, FeOx@N-3DG anode material exhibits high specific capacity (1100 mAh g−1 after 200 cycles at 0.5 A g−1), excellent rate performance (550 mAh g−1 at 5 A g−1) and outstanding long cycling stability (81.6% of capacity retention after 1000 cycles at 1 A g−1), which is attributed to the superior surface capacitance behavior in the hierarchical architecture during charging and discharging. Thus, the hierarchical FeOx@N-3DG aerogel has potential to be an advanced anode material for lithium-ion batteries.