Crosslinking-induced spontaneous growth: A novel strategy for synthesizing sandwich-type graphene@Fe3O4 dots/amorphous carbon with high lithium storage performance

Graphene/Fe3O4 hybrids have long been regarded as promising anode materials for lithium-ion batteries but remain significant bottlenecks of inhomogeneous/large Fe3O4 particle size and agglomeration during the repeated lithiation/dethiation process. By carefully selecting a metallo-organic molecule of ferrocene as the building block, a novel methodology has been explored herein for the preparation of sandwich-type graphene@Fe3O4 dots/amorphous carbon (G@Fe3O4/C) hybrids via a Friedel-Crafts crosslinking-induced spontaneous growth process. As prepared, ultra-small Fe3O4 dots of 2-3 nm are distributed uniformly in the amorphous carbon matrix coated on the surface of graphene. The ultralow size of Fe3O4 dots is able to minimize the volume change and Li+ migrating distance, while the carbon matrix and graphene framework prevent Fe3O4 dots from aggregation and offer a superior conductive skeleton along with a flexible framework to buffer the volume changes. In addition, the well-developed pore structure can accommodate the large volume change and facilitate the electrolyte diffusion/transfer, thereby increasing the ion accessible surface area, especially at high charge-discharge rates. Consequently, G@Fe3O4/C presents excellent lithium storage performances, including a highly reversible capacity of 1241 mAh g(-1), an outstanding cycling stability after 200 cycles (1055 mAh g(-1)) and a superior high-rate capability (724 mAh g(-1) at 5 A g(-1)).